N3096
working draft — April 1, 2023
INTERNATIONAL STANDARD
©ISO/IEC
ISO/IEC 9899:2023 (E)
ISO/IEC 9899:2023
Programming languages — C Reply To: JeanHeyd Meneide <[email protected]> Freek Wiedijk <[email protected]> Abstract (This cover sheet to be replaced by ISO.) This document specifies the form and establishes the interpretation of programs expressed in the programming language C. Its purpose is to promote portability, reliability, maintainability, and efficient execution of C language programs on a variety of computing systems. Clauses are included that detail the C language itself and the contents of the C language execution library. Annexes summarize aspects of both of them, and enumerate factors that influence the portability of C programs. Although this document is intended to guide knowledgeable C language programmers as well as implementors of C language translation systems, the document itself is not designed to serve as a tutorial. Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to provide supporting documentation. The following documents, for all intents and purposes, have been applied to this draft from before and during the October 2019 Meeting: DR 476
volatile semantics for lvalues
DR 488
c16rtomb() on wide characters encoded as multiple char16_t
DR 494
Part 1: Alignment specifier expression evaluation
DR 496
offsetof and subobjects (with editorial modification)
DR 497
"white-space character" defined in two places
DR 499
Anonymous structure in union behavior
DR 500
Ambiguous specification for FLT_EVAL_METHOD
DR 501
make DECIMAL_DIG obsolescent
FP DR 13
totalorder parameters
FP DR 20
changes for obsolescing DECIMAL_DIG
FP DR 21
printf of one-digit character string
FP DR 22
changes for obsolescing DECIMAL_DIG, Part 2
FP DR 23
llquantexp invalid case
FP DR 24
remainder NaN case
FP DR 25
totalorder parameters
N2124 and N2319 rounding direction macro FE_TONEARESTFROMZERO N2186
Alternative to N2166
N2212
type generic cbrt (with editorial changes)
Abstract
i
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N2260
Clarifying the restrict Keyword v2
N2265
Harmonizing static_assert with C++
N2267
nodiscard attribute
N2270
maybe_unused attribute
N2271
CR for pow divide-by-zero case
N2293
Alignment requirements for memory management functions
N2314
TS 18661-1 plus CR/DRs for C2X
N2322
preprocessor line numbers unspecified
N2325
DBL_NORM_MAX etc
N2326
floating-point zero and other normalization
N2334
deprecated attribute
N2335
attributes
N3096
N2337
strftime, with ’b’ and ’B’ swapped
N2338
error indicator for encoding errors in fgetwc
N2341
TS 18661-2 plus CR/DRs for C2X
N2345
editors, resolve ambiguity of a semicolon
N2349
the memccpy function
N2350
defining new types in offsetof
N2353
the strdup and strndup functions
N2356
update for payload functions
N2358
no internal state for mblen
N2359
part 2 (remove WANT macros from numbered clauses) and part 3 (version macros for changed library clauses)
N2401
TS 18661-4a for C2X
N2408
The fallthrough attribute
N2412
Two’s complement sign representation for C2x
N2417
Section 6: Add time conversion functions that are relatively thread-safe
N2418
Adding the u8 character prefix
N2432
Remove support for function definitions with identifier lists
N2508
Free Positioning of Labels Inside Compound Statements
N2554
Minor attribute wording cleanups
The following documents have been applied to this draft from the October 2019 Meeting: N2379
*_IS_IEC_60559 Feature Test Macros.
N2416
Floating Point Negation and Conversion.
N2384
Annex F.8 Update for Implementation Extensions and Rounding.
N2424
Why logp1 as a Function Name.
N2406
Signaling NaN Initializers.
N2393
_Bool Definitions For true and false.
The following documents have been applied to this draft from the March/April 2020 Virtual Meeting:
ii
N2444
More optionally per-thread state for the library.
N2446
printf of NAN().
N2448
[[Nodiscard("should have a reason")]].
N2459
Add an interface to query resolution of time bases, v3.
N2464
Zero-size Reallocations are Undefined Behavior.
Abstract
N3096
working draft — April 1, 2023
N2476
Names and Locations of Floating Point Entities.
N2480
Allowing unnamed parameters in function definitions.
N2490
Why no wide string strfrom functions.
ISO/IEC 9899:2023 (E)
The following documents have been applied to this draft from the August 2020 Virtual Meeting: N2491
powr justification
N2492
Note About Math Function Properties.
N2506
Range Errors in Math Functions.
N2508
Free Positioning of Labels.
N2517
Clarification Request for C17 Example of Undefined Behavior.
N2532
Min-max Functions.
N2553
Querying Attribute Support.
N2554
Minor Attribute Wording Cleanup.
The following documents have been applied to this draft from the October and November 2020 Virtual Meetings: N2546
Missing DEC_EVAL_METHOD
N2547
Missing const in decimal getpayload functions
N2548
intmax_t removal from FP functions
N2549
Binary Literals
N2552
Editorial cleanup for rounding macros
N2557
Allow Duplicate Attributes
N2560
FP hex formatting precision
N2562
Unclear type relationship between a format specifier and its argument
N2563
Character encoding of diagnostic text
N2564
Range errors and math functions (updated previous version, N2506)
N2570
Feature and WANT macros for Annex F functions
N2571
snprintf nonnegative clarification
N2572
What We Think We Reserve
N2580
Decimal Floating Point Triples
N2586
Sufficient Formatting Precision
N2594
Remove Mixed Wide String Literal Concatenation
N2559
Update to IEC 60559:2020
N2600
Update to IEC 60559:2020 (updates previous version, N2559)
N2602
Infinity/NAN Macros, Editorial Fixes
N2607
Compatibility of Pointers to Arrays with Qualifiers
The following documents have been applied to this draft from the March/April 2021 Virtual Meeting: N2524
String Functions for Freestanding Implementations
N2626
Digit Separators
N2630
Formatting Input/Output of Binary Integer Numbers
N2640
Missing DEC_EVAL_METHOD, Take 2
N2641
Missing +(x) in Table
N2643
Negative vs. Less Than Zero
N2645
Add Support for Preprocessing Directives #elifdef and #elifndef
N2680
Specific Width Length Modifier for Formatting
Abstract
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ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
The following documents have been applied to this draft from the June 2021 Virtual Meeting: N2651
fabs and copysign Cleanup
N2662
[[maybe_unused]] for Labels
N2665
Zero-size Reallocations Are No Longer an Obsolescent Feature
N2670
Zeros Compare Equal
N2671
Negative Values
N2672
§5.2.4.2.2 Cleanup
N2683
Towards Integer Safety
N2751
signbit Cleanup
N2763
Adding a Fundamental Type for N-bit Integers
The following documents have been applied to this draft from the August/September 2021 Virtual Meeting: N2686
#warning Directive
N2688
Sterile Characters
N2710
SNAN Fixes
N2711
fmin, fmax
N2713
Integer Constant Expressions
N2714
hypot Changes
N2715
cr_ Prefix Potentially Reserved for Identifiers
N2716
Fix "numerically"/"numerically equal" Usage
N2726
_Imaginary_I and _Complex_I Qualifiers
N2728
char16_t & char32_t String Literals Shall be UTF-16 & UTF-32
N2745
Range Error Definition
N2748
Effects of fenv Exception Functions
N2749
IEC 60559 Bindings
N2755
Static Initialization of Decimal Floating Point
N2776
ckd_* Identifiers Should be Potentially Reserved Identifiers
N2799
__has_include for C
The following documents have been applied to this draft from the November/December 2021 Virtual Meeting:
iv
N2747
Annex F Overflow and Underflow
N2770
Remove UB from Incomplete Types in Function Parameters
N2778
Require Variably-Modified Types
N2781
Types do not have Types (with meeting-agreed changes plus some editorial changes)
N2790
"remquo" Changes
N2805
Overflow and Underflow Definitions
N2806
§5.2.4.2.2 Cleanup, Again
N2808
Allow 16-bit ptrdiff_t
N2823
Freestanding CFP Functions
N2838
Types and Sizes
N2837
Clarifying Integer Terms (also, delete Annex H and replace with the Floating Point TS / Annex merge)
N2842
Normal and Subnormal Classification
N2843
Clarification of Max Exponent Macros
N2845
feraiseexcept Update
Abstract
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
N2846
Clarification about Expression Transformations
N2848
INFINITY Macro Contradictions (Wording 1 only!)
N2872
Require Exact-Width Integer Type Interfaces, Part I (Change from proposal’s §3.1 only)
The following documents have been applied to this draft from the January/February 2022 Virtual Meeting, Parts 1 and 2: N2653
char8_t: A type for UTF-8 characters and strings
N2701
@, $, and ` in the source/execution character set
N2754
Decimal Floating Point: Quantum Exponent of NaN
N2762
Fixes for Potentially Reserved Identifiers
N2764
The _Noreturn Attribute
N2775
Literal Suffixes for Bit-Precise Integers
N2797
*_HAS_SUBNORM == 0 Implies What?
N2810
calloc Overflow Handling
N2819
Disambiguate the Storage Class of Some Compound Literals
N2826
unreachable()
N2828
Unicode Sequences More Than 21 Bits are a Constraint Violation
N2829
Make assert() user friendly in C
N2836
Unicode Syntax Identifiers for C
N2840
Make call_once() Mandatory
N2841
No Function Declarators without Prototypes
N2844
Remove default promotions for _FloatN Types
N2847
Revised Suggestions of Change for Numerically Equal / Equivalent
N2879
5.2.4.2.2 Cleanup, Again Again
N2880
Overflow and Underflow Definitions Update
N2881
Normal and Subnormal Classification Update
N2882
Clarification for the Max Exponent Macros
N2900
Consistent, Warningless, and Intuitive Initialization with {}
N2927
Not-So-Magic: typeof(...)
N2931
Macros and Macro Spellings from C Floating Point Integration
N2934
Revised Spelling of Keywords
N2935
Make false and true Language Features
N2937
Properly Define Blocks in the Grammar
The following documents have been applied to this draft from the May 2022 Virtual Meeting: N2601
Annex X (replacing Annex H) for IEC 60599 Interchange (ratified early 2021 but integrated over a long period of time).
N2861
Indeterminate Values and Trap Representations
N2867
Checked N-Bit Integers? (Not Now)
N2886
Remove ATOMIC_VAR_INIT
N2888
Require Exact-width Integer Type Interfaces, Part II
N2897
memset_explicit
N2992
Wording Clarification for Variably-Modified Types
The following documents have been applied to this draft from the July 2022 Virtual Meeting: N2930
Change remove_quals to typeof_unqual
N2939
Identifier Syntax Fixes
Abstract
v
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
N2940
Remove Trigraphs??!
N2969
Bit-Precise Bit Fields
N2974
Queryable Pointer Alignment
N3029
Improved Normal Enumerations
N2975
Relax requirements for va_start
N2993
Make *_HAS_SUBNORM Obsolete
N3011
Oops, Empty Initializers in Compound Literals
N3030
Enhanced Enumerations
N2951
Freestanding C and IEC 60559 Conformance Scope Reduction
N2956
Unsequenced Functions
N3033
Comma Ommission and Deletion (__VA_OPT__ and Preprocessor Wording Improvements)
N3035
_BitInt(...) Fixes
N3006
Underspecified Object Declarations
N3007
Type Inference for Object Declarations
N3018
constexpr for Object Definitions
N3038
Introduce Storage Class Specifiers for Compound Literals
N3034
Identifier Primary Expressions
N3042
Introduce the nullptr_t constant, nullptr
N2929
Memory Layout of union s
N3037
Improved Tag Compatibility
N3020
Qualifier-preserving Standard Functions
N3022
Modern Bit Utilities - without Rotate Left/Right, Memory Reversal ("byteswap"), or Endian-Aware Load/Store
N3017
#embed
N2957
New Optional Time Bases
In addition to these, the document has undergone some editorial changes, including the following. — The synopsis lists in Annex B are now generated automatically and classified according to the feature test or WANT macros that are required to make them available. — A new non-normative clause J.6 added to Annex J categorizes identifiers used by this document. — Renaming of the syntax term "struct declaration", "struct declaration list" "struct declarator", and "struct declarator list" to the more appropriate "member declaration", "member declaration list", "member declarator" and "member declarator list", respectively. — Misspelling of "invokation" fixed to "invocation". — A positional reference to a table was changed to be a more direct reference due to unfortunate page breaks. — Missing macros were added to <float.h> and <limits.h>. — A footnote added for simple atomic assignment (6.5.16). — An issue with "modifying object" being removed from an earlier draft was fixed. This was a mistake: side effects do include modifying an object. — The Decimal Floating Point Initialization text was not well-worded. It was fixed after the paper adding the wording was integrated. — Examples using poor phrasing for objects and their types were fixed to say "object(s) of type int" and similar. — The terms "floating-point type" and "floating-point constant" were changed to just be "floating type" and "floating constant", as are defined in the standard, respectively.
vi
Abstract
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
— The wording "thread-local storage" was normalized to be "thread storage" everywhere, as intended (this is the word defined by the standard, the other just fell naturally out of casual usage and thought). — A footnote clarifying the role for valid pointers with zero size was added to the library frontmatter, specifically concerning functions like memcpy and memset. — Various duplicate spellings (e.g. "function functions" and similar) were removed and typos were fixed (e.g., "stirng" and similar). — The pp-number production was incorrect for digit separators. Adjusted and fixed. — The wording for freestanding headers for <string.h> were very poorly done. It was changed to have better wording. — The introductory sentence for the implementation limits was very wordy and deeply confusing to normal users. The sentence was adjusted to read much better and more clearly. — In a sentence using "respectively" for fmin and fmax descriptions, the order of the respective items was swapped. This gave the wrong definitions to each item. They were put in the proper order. — A missing closing parenthesis in Annex J was fixed. — The term "floating-point multiply add" was changed to "fused multiply add", matching naming conventions in reality.
Abstract
vii
ISO/IEC 9899:2023 (E)
viii
working draft — April 1, 2023
Abstract
N3096
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Contents Foreword
xviii
Introduction
xix
1
Scope
1
2
Normative references
2
3
Terms, definitions, and symbols
3
4
Conformance
8
5
Environment
10
5.1
Conceptual models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
5.1.1
Translation environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
5.1.2
Execution environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
5.2.1
Character sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
5.2.2
Character display semantics . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
5.2.3
Signals and interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
5.2.4
Environmental limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
5.2
6
Language
34
6.1
Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
6.2
Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
6.2.1
Scopes of identifiers, type names, and compound literals . . . . . . . . . . . .
34
6.2.2
Linkages of identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
6.2.3
Name spaces of identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
6.2.4
Storage durations of objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
6.2.5
Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
6.2.6
Representations of types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
6.2.7
Compatible type and composite type . . . . . . . . . . . . . . . . . . . . . . .
42
6.2.8
Alignment of objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
6.2.9
Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
6.3.1
Arithmetic operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
6.3.2
Other operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
Lexical elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
51
6.4.1
53
6.3
6.4
Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contents
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ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
6.4.2
Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
6.4.3
Universal character names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
6.4.4
Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
57
6.4.5
String literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
6.4.6
Punctuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
68
6.4.7
Header names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69
6.4.8
Preprocessing numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
70
6.4.9
Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
70
Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
71
6.5.1
Primary expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
72
6.5.2
Postfix operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
6.5.3
Unary operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
80
6.5.4
Cast operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
82
6.5.5
Multiplicative operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
6.5.6
Additive operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
6.5.7
Bitwise shift operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
85
6.5.8
Relational operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
85
6.5.9
Equality operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
6.5.10 Bitwise AND operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
87
6.5.11 Bitwise exclusive OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . .
87
6.5.12 Bitwise inclusive OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . .
88
6.5.13 Logical AND operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
88
6.5.14 Logical OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
88
6.5.15 Conditional operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
6.5.16 Assignment operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
90
6.5.17 Comma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
93
6.6
Constant expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
94
6.7
Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
96
6.7.1
Storage-class specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
6.7.2
Type specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.7.3
Type qualifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
6.7.4
Function specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
6.7.5
Alignment specifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6.7.6
Declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
6.7.7
Type names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
6.7.8
Type definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
6.7.9
Type inference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
6.5
6.7.10 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 6.7.11 Static assertions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.7.12 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 x
Contents
N3096
6.8
6.9
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Statements and blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 6.8.1
Labeled statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
6.8.2
Compound statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
6.8.3
Expression and null statements . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
6.8.4
Selection statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
6.8.5
Iteration statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
6.8.6
Jump statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
External definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 6.9.1
Function definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
6.9.2
External object definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
6.10 Preprocessing directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 6.10.1 Conditional inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 6.10.2 Source file inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 6.10.3 Binary resource inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 6.10.4 Macro replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 6.10.5 Line control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 6.10.6 Diagnostic directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 6.10.7 Pragma directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 6.10.8 Null directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 6.10.9 Predefined macro names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 6.10.10 Pragma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 6.11 Future language directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.1 Floating types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.2 Linkages of identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.3 External names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.4 Character escape sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.5 Storage-class specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.6 Pragma directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 6.11.7 Predefined macro names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 7
Library 7.1
7.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 7.1.1
Definitions of terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
7.1.2
Standard headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
7.1.3
Reserved identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
7.1.4
Use of library functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 7.2.1
7.3
190
Program diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
Complex arithmetic <complex.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 7.3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Contents
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7.3.2
Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
7.3.3
Branch cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
7.3.4
The CX_LIMITED_RANGE pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 196
7.3.5
Trigonometric functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
7.3.6
Hyperbolic functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
7.3.7
Exponential and logarithmic functions . . . . . . . . . . . . . . . . . . . . . . 199
7.3.8
Power and absolute-value functions . . . . . . . . . . . . . . . . . . . . . . . . 200
7.3.9
Manipulation functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Character handling <ctype.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 7.4.1
Character classification functions . . . . . . . . . . . . . . . . . . . . . . . . . . 204
7.4.2
Character case mapping functions . . . . . . . . . . . . . . . . . . . . . . . . . 206
7.5
Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
7.6
Floating-point environment <fenv.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 7.6.1
The FENV_ACCESS pragma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
7.6.2
The FENV_ROUND pragma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.6.3
The FENV_DEC_ROUND pragma . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
7.6.4
Floating-point exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
7.6.5
Rounding and other control modes . . . . . . . . . . . . . . . . . . . . . . . . 217
7.6.6
Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
7.7
Characteristics of floating types <float.h> . . . . . . . . . . . . . . . . . . . . . . . . 221
7.8
Format conversion of integer types <inttypes.h> . . . . . . . . . . . . . . . . . . . . 222
7.9
7.8.1
Macros for format specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
7.8.2
Functions for greatest-width integer types . . . . . . . . . . . . . . . . . . . . 223
Alternative spellings <iso646.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
7.10 Characteristics of integer types <limits.h> . . . . . . . . . . . . . . . . . . . . . . . . 226 7.11 Localization <locale.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 7.11.1 Locale control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 7.11.2 Numeric formatting convention inquiry . . . . . . . . . . . . . . . . . . . . . . 228 7.12 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 7.12.1 Treatment of error conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 7.12.2 The FP_CONTRACT pragma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 7.12.3 Classification macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 7.12.4 Trigonometric functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 7.12.5 Hyperbolic functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 7.12.6 Exponential and logarithmic functions . . . . . . . . . . . . . . . . . . . . . . 247 7.12.7 Power and absolute-value functions . . . . . . . . . . . . . . . . . . . . . . . . 255 7.12.8 Error and gamma functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 7.12.9 Nearest integer functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 7.12.10 Remainder functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 7.12.11 Manipulation functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 xii
Contents
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ISO/IEC 9899:2023 (E)
7.12.12 Maximum, minimum, and positive difference functions . . . . . . . . . . . . 268 7.12.13 Fused multiply-add . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 7.12.14 Functions that round result to narrower type . . . . . . . . . . . . . . . . . . . 273 7.12.15 Quantum and quantum exponent functions . . . . . . . . . . . . . . . . . . . 275 7.12.16 Decimal re-encoding functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 7.12.17 Comparison macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 7.13 Non-local jumps <setjmp.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 7.13.1 Save calling environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 7.13.2 Restore calling environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 7.14 Signal handling <signal.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 7.14.1 Specify signal handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 7.14.2 Send signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 7.15 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 7.16 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 7.16.1 Variable argument list access macros . . . . . . . . . . . . . . . . . . . . . . . . 288 7.17 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 7.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 7.17.2 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 7.17.3 Order and consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 7.17.4 Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 7.17.5 Lock-free property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 7.17.6 Atomic integer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 7.17.7 Operations on atomic types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 7.17.8 Atomic flag type and operations . . . . . . . . . . . . . . . . . . . . . . . . . . 300 7.18 Bit and byte utilities <stdbit.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 7.18.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 7.18.2 Endian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 7.18.3 Count Leading Zeros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 7.18.4 Count Leading Ones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 7.18.5 Count Trailing Zeros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 7.18.6 Count Trailing Ones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 7.18.7 First Leading Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 7.18.8 First Leading One . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 7.18.9 First Trailing Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 7.18.10 First Trailing One . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 7.18.11 Count Zeros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 7.18.12 Count Ones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 7.18.13 Single-bit Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 7.18.14 Bit Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 7.18.15 Bit Floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Contents
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7.18.16 Bit Ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 7.19 Boolean type and values <stdbool.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 7.20 Checked Integer Arithmetic <stdckdint.h> . . . . . . . . . . . . . . . . . . . . . . . 311 7.20.1 The ckd_ Checked Integer Operation Macros . . . . . . . . . . . . . . . . . . . 311 7.21 Common definitions <stddef.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 7.21.1 The unreachable macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 7.21.2 The nullptr_t type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 7.22 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 7.22.1 Integer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 7.22.2 Widths of specified-width integer types . . . . . . . . . . . . . . . . . . . . . . 317 7.22.3 Width of other integer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 7.22.4 Macros for integer constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 7.22.5 Maximal and minimal values of integer types . . . . . . . . . . . . . . . . . . 318 7.23 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 7.23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 7.23.2 Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 7.23.3 Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322 7.23.4 Operations on files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 7.23.5 File access functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 7.23.6 Formatted input/output functions . . . . . . . . . . . . . . . . . . . . . . . . . 328 7.23.7 Character input/output functions . . . . . . . . . . . . . . . . . . . . . . . . . 346 7.23.8 Direct input/output functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 7.23.9 File positioning functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350 7.23.10 Error-handling functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 7.24 General utilities <stdlib.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 7.24.1 Numeric conversion functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 7.24.2 Pseudo-random sequence generation functions . . . . . . . . . . . . . . . . . 361 7.24.3 Memory management functions . . . . . . . . . . . . . . . . . . . . . . . . . . 362 7.24.4 Communication with the environment . . . . . . . . . . . . . . . . . . . . . . 364 7.24.5 Searching and sorting utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 7.24.6 Integer arithmetic functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 7.24.7 Multibyte/wide character conversion functions . . . . . . . . . . . . . . . . . 369 7.24.8 Multibyte/wide string conversion functions . . . . . . . . . . . . . . . . . . . 371 7.24.9 Alignment of memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 7.25 _Noreturn <stdnoreturn.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 7.26 String handling <string.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 7.26.1 String function conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 7.26.2 Copying functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 7.26.3 Concatenation functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 7.26.4 Comparison functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 xiv
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ISO/IEC 9899:2023 (E)
7.26.5 Search functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 7.26.6 Miscellaneous functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381 7.27 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 7.28 Threads <threads.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 7.28.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 7.28.2 Initialization functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 7.28.3 Condition variable functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 7.28.4 Mutex functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 7.28.5 Thread functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 7.28.6 Thread-specific storage functions . . . . . . . . . . . . . . . . . . . . . . . . . . 395 7.29 Date and time <time.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 7.29.1 Components of time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 7.29.2 Time manipulation functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 7.29.3 Time conversion functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 7.30 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407 7.30.1 Restartable multibyte/wide character conversion functions . . . . . . . . . . 407 7.31 Extended multibyte and wide character utilities <wchar.h> . . . . . . . . . . . . . . . 412 7.31.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 7.31.2 Formatted wide character input/output functions . . . . . . . . . . . . . . . . 413 7.31.3 Wide character input/output functions . . . . . . . . . . . . . . . . . . . . . . 426 7.31.4 General wide string utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 7.31.4.1 Wide string numeric conversion functions . . . . . . . . . . . . . . . 430 7.31.4.2 Wide string copying functions . . . . . . . . . . . . . . . . . . . . . . 434 7.31.4.3 Wide string concatenation functions . . . . . . . . . . . . . . . . . . 436 7.31.4.4 Wide string comparison functions . . . . . . . . . . . . . . . . . . . . 436 7.31.4.5 Wide string search functions . . . . . . . . . . . . . . . . . . . . . . . 438 7.31.4.6 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 7.31.4.7 Miscellaneous functions . . . . . . . . . . . . . . . . . . . . . . . . . 441 7.31.5 Wide character time conversion functions . . . . . . . . . . . . . . . . . . . . . 441 7.31.6 Extended multibyte/wide character conversion utilities . . . . . . . . . . . . 442 7.31.6.1 Single-byte/wide character conversion functions . . . . . . . . . . . 442 7.31.6.2 Conversion state functions . . . . . . . . . . . . . . . . . . . . . . . . 442 7.31.6.3 Restartable multibyte/wide character conversion functions . . . . . 443 7.31.6.4 Restartable multibyte/wide string conversion functions . . . . . . . 444 7.32 Wide character classification and mapping utilities <wctype.h> . . . . . . . . . . . . 447 7.32.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 7.32.2 Wide character classification utilities . . . . . . . . . . . . . . . . . . . . . . . . 447 7.32.2.1 Wide character classification functions . . . . . . . . . . . . . . . . . 447 7.32.2.2 Extensible wide character classification functions . . . . . . . . . . . 450 7.32.3 Wide character case mapping utilities . . . . . . . . . . . . . . . . . . . . . . . 451 Contents
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7.32.3.1 Wide character case mapping functions . . . . . . . . . . . . . . . . . 451 7.32.3.2 Extensible wide character case mapping functions . . . . . . . . . . 451 7.33 Future library directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.1 Complex arithmetic <complex.h> . . . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.2 Character handling <ctype.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.3 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.4 Floating-point environment <fenv.h> . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.5 Characteristics of floating types <float.h> . . . . . . . . . . . . . . . . . . . . 453 7.33.6 Format conversion of integer types <inttypes.h> . . . . . . . . . . . . . . . . 453 7.33.7 Localization <locale.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.8 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 7.33.9 Signal handling <signal.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 7.33.10 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 7.33.11 Boolean type and values <stdbool.h> . . . . . . . . . . . . . . . . . . . . . . 454 7.33.12 Bit and byte utilities <stdbit.h> . . . . . . . . . . . . . . . . . . . . . . . . . . 454 7.33.13 Checked Arithmetic Functions <stdckdint.h> . . . . . . . . . . . . . . . . . 454 7.33.14 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 7.33.15 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 7.33.16 General utilities <stdlib.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 7.33.17 String handling <string.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 7.33.18 Date and time <time.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 7.33.19 Threads <threads.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 7.33.20 Extended multibyte and wide character utilities <wchar.h> . . . . . . . . . . 455 7.33.21 Wide character classification and mapping utilities <wctype.h> . . . . . . . . 455 Annex A (informative) Language syntax summary
456
Annex B (informative) Library summary
471
Annex C (informative) Sequence points
500
Annex D (informative) Universal character names for identifiers
501
Annex E (informative) Implementation limits
503
Annex F (normative) IEC 60559 floating-point arithmetic
506
Annex G (normative) IEC 60559-compatible complex arithmetic
536
Annex H (normative) IEC 60559 interchange and extended types
547
Annex I (informative) Common warnings
580
Annex J (informative) Portability issues
581
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Annex K (normative) Bounds-checking interfaces
619
Annex L (normative) Analyzability
667
Annex M (informative) Change History
669
Bibliography
675
Index
676
Contents
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Foreword 1
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are member of ISO or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
2
The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of document should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
3
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).
4
Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.
5
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see the following URL: www.iso.org/iso/foreword.html.
6
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 22, Programming languages, their environments and system software interfaces.
7
This fifth edition cancels and replaces the fourth edition, ISO/IEC 9899:2018. A complete change history can be found in Annex M.
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Introduction 1
With the introduction of new devices and extended character sets, new features could be added to this document. Subclauses in the language and library clauses warn implementors and programmers of usages which, though valid in themselves, could conflict with future additions.
2
Certain features are obsolescent, which means that they could be considered for withdrawal in future revisions of this document. They are retained because of their widespread use, but their use in new implementations (for implementation features) or new programs (for language [6.11] or library features [7.33]) is discouraged.
3
This document is divided into four major subdivisions: — preliminary elements (Clauses 1–4); — the characteristics of environments that translate and execute C programs (Clause 5); — the language syntax, constraints, and semantics (Clause 6); — the library facilities (Clause 7).
4
Examples are provided to illustrate possible forms of the constructions described. Footnotes are provided to emphasize consequences of the rules described in that subclause or elsewhere in this document. References are used to refer to other related subclauses. Recommendations are provided to give advice or guidance to implementers. Annexes define optional features, provide additional information and summarize the information contained in this document. A bibliography lists documents that were referred to during the preparation of this document.
5
The language clause (Clause 6) is derived from "The C Reference Manual".
6
The library clause (Clause 7) is based on the 1984 /usr/group Standard.
7
The Working Group responsible for this document (WG 14) maintains a site on the World Wide Web at https://www.open-std.org/JTC1/SC22/WG14/ containing ancillary information that may be of interest to some readers.
Introduction
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INTERNATIONAL STANDARD
ISO/IEC 9899:2023 (E)
©ISO/IEC
ISO/IEC 9899:2023
Programming languages — C
1. Scope 1
This document specifies the form and establishes the interpretation of programs written in the C programming language.1) It specifies — the representation of C programs; — the syntax and constraints of the C language; — the semantic rules for interpreting C programs; — the representation of input data to be processed by C programs; — the representation of output data produced by C programs; — the restrictions and limits imposed by a conforming implementation of C.
2
This document does not specify — the mechanism by which C programs are transformed for use by a data-processing system; — the mechanism by which C programs are invoked for use by a data-processing system; — the mechanism by which input data are transformed for use by a C program; — the mechanism by which output data are transformed after being produced by a C program; — the size or complexity of a program and its data that will exceed the capacity of any specific data-processing system or the capacity of a particular processor; — all minimal requirements of a data-processing system that is capable of supporting a conforming implementation.
1) This document is designed to promote the portability of C programs among a variety of data-processing systems. It is intended for use by implementors and programmers. Annex J gives an overview of portability issues that a C program might encounter.
§1
General
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2. Normative references 1
The following documents are referred to in the text in such a way that some or all their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
2
ISO/IEC 2382:2015, Information technology — Vocabulary. Available from the ISO online browsing platform at http://www.iso.org/obp.
3
ISO 4217, Codes for the representation of currencies and funds.
4
ISO 8601, Data elements and interchange formats — Information interchange — Representation of dates and times.
5
ISO/IEC 10646, Information technology —Universal Coded Character Set (UCS). Available from the ISO/IEC Information Technology Task Force (ITTF) web site at https://standards.iso.org/ ittf/PubliclyAvailableStandards/.
6
ISO/IEC 60559:2020, Floating-point arithmetic.
7
ISO 80000–2, Quantities and units — Part 2: Mathematical signs and symbols to be used in the natural sciences and technology.
8
ISO 80000–3, Quantities and units — Part 3: Space and time.
9
The Unicode Consortium. Unicode Standard Annex, UAX #44, Unicode Character Database [online]. Edited by Ken Whistler and Laurentiu Iancu. Available at https://www.unicode.org/reports/ tr44.
10
The Unicode Consortium. Unicode Standard Annex, UAX #31, Unicode Character Database [online]. Edited by Ken Whistler and Laurentiu Iancu. Available at https://www.unicode.org/reports/ tr31.
11
The Unicode Consortium. The Unicode Standard, Derived Core Properties. Available at https: //www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt.
2
General
§2
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3. Terms, definitions, and symbols 1
For the purposes of this document, the terms and definitions given in ISO/IEC 2382, ISO 80000–2, and the following apply.
2
ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https://www.iso.org/obp — IEC Electropedia: available at https://www.electropedia.org/
3
Additional terms are defined where they appear in italic type or on the left side of a syntax rule. Terms explicitly defined in this document are not to be presumed to refer implicitly to similar terms defined elsewhere.
3.1 1
access (verb) ⟨execution-time action⟩ to read or modify the value of an object
2
Note 1 to entry: Where only one of these two actions is meant, "read" or "modify" is used.
3
Note 2 to entry: "Modify" includes the case where the new value being stored is the same as the previous value.
4
Note 3 to entry: Expressions that are not evaluated do not access objects.
3.2 1
alignment requirement that objects of a particular type be located on storage boundaries with addresses that are particular multiples of a byte address
3.3 1
argument actual argument (DEPRECATED: actual parameter) expression in the comma-separated list bounded by the parentheses in a function call expression, or a sequence of preprocessing tokens in the comma-separated list bounded by the parentheses in a function-like macro invocation
3.4 1
behavior external appearance or action
3.4.1 1
implementation-defined behavior unspecified behavior where each implementation documents how the choice is made
2
Note 1 to entry: J.3 gives an overview over properties of C programs that lead to implementation-defined behavior.
3
EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit when a signed integer is shifted right.
3.4.2 1
locale-specific behavior behavior that depends on local conventions of nationality, culture, and language that each implementation documents
2
Note 1 to entry: J.4 gives an overview over properties of C programs that lead to locale-specific behavior.
§ 3.4.2
General
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EXAMPLE An example of locale-specific behavior is whether the islower function returns true for characters other than the 26 lowercase Latin letters.
3.4.3 1
undefined behavior behavior, upon use of a nonportable or erroneous program construct or of erroneous data, for which this document imposes no requirements
2
Note 1 to entry: Possible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message).
3
Note 2 to entry: J.2 gives an overview over properties of C programs that lead to undefined behavior.
4
EXAMPLE An example of undefined behavior is the behavior on dereferencing a null pointer.
3.4.4 1
unspecified behavior behavior, that results from the use of an unspecified value, or other behavior upon which this document provides two or more possibilities and imposes no further requirements on which is chosen in any instance
2
Note 1 to entry: J.1 gives an overview over properties of C programs that lead to unspecified behavior.
3
EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are evaluated.
3.5 1
bit unit of data storage in the execution environment large enough to hold an object that can have one of two values
2
Note 1 to entry: It need not be possible to express the address of each individual bit of an object.
3.6 1
byte addressable unit of data storage large enough to hold any member of the basic character set of the execution environment
2
Note 1 to entry: It is possible to express the address of each individual byte of an object uniquely.
3
Note 2 to entry: A byte is composed of a contiguous sequence of bits, the number of which is implementation-defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order bit.
3.7 1
character ⟨abstract⟩ member of a set of elements used for the organization, control, or representation of data
3.7.1 1
character single-byte character ⟨C⟩ bit representation that fits in a byte
3.7.2 1
multibyte character sequence of one or more bytes representing a member of the extended character set of either the source or the execution environment
2
Note 1 to entry: The extended character set is a superset of the basic character set.
4
General
§ 3.7.2
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3.7.3 1
wide character value representable by an object of type wchar_t, capable of representing any character in the current locale
3.8 1
constraint restriction, either syntactic or semantic, by which the exposition of language elements is to be interpreted
3.9 1
correctly rounded result representation in the result format that is nearest in value, subject to the current rounding mode, to what the result would be given unlimited range and precision
2
Note 1 to entry: In this document, when the words "correctly rounded" are not immediately followed by "result", this is the intended usage.
3
Note 2 to entry: IEC 60559 or implementation-defined rules apply for extreme magnitude results if the result format contains infinity.
3.10 1
diagnostic message message belonging to an implementation-defined subset of the implementation’s message output
3.11 1
forward reference reference to a later subclause of this document that contains additional information relevant to this subclause
3.12 1
implementation particular set of software, running in a particular translation environment under particular control options, that performs translation of programs for, and supports execution of functions in, a particular execution environment
3.13 1
implementation limit restriction imposed upon programs by the implementation
3.14 1
memory location either an object of scalar type, or a maximal sequence of adjacent bit-fields all having nonzero width
2
Note 1 to entry: Two threads of execution can update and access separate memory locations without interfering with each other.
3
Note 2 to entry: A bit-field and an adjacent non-bit-field member are in separate memory locations. The same applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all members declared between them are also (nonzero-length) bit-fields, no matter what the sizes of those intervening bit-fields happen to be.
4
EXAMPLE A structure declared as struct { char a; int b:5, c:11,:0, d:8;
§ 3.14
General
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struct { int ee:8; } e; }
contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate memory locations, and can be modified concurrently without interfering with each other. The bit-fields b and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently modified, but b and a, for example, can be.
3.15 1
object region of data storage in the execution environment, the contents of which can represent values
2
Note 1 to entry: When referenced, an object can be interpreted as having a particular type; see 6.3.2.1.
3.16 1
parameter formal parameter DEPRECATED: formal argument object declared as part of a function declaration or definition that acquires a value on entry to the function, or an identifier from the comma-separated list bounded by the parentheses immediately following the macro name in a function-like macro definition
3.17 1
recommended practice specification that is strongly recommended as being in keeping with the intent of the standard, but that might be impractical for some implementations
3.18 1
runtime-constraint requirement on a program when calling a library function
2
Note 1 to entry: Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and need not be diagnosed at translation time.
3
Note 2 to entry: Implementations that support the extensions in Annex K are required to verify that the runtime-constraints for a library function are not violated by the program; see K.3.1.4.
4
Note 3 to entry: Implementations that support Annex L are permitted to invoke a runtime-constraint handler when they perform a trap.
3.19 1
value precise meaning of the contents of an object when interpreted as having a specific type
3.19.1 1
implementation-defined value unspecified value where each implementation documents how the choice is made
3.19.2 1
indeterminate representation object representation that either represents an unspecified value or is a non-value representation
3.19.3 1
unspecified value valid value of the relevant type where this document imposes no requirements on which value is 6
General
§ 3.19.3
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chosen in any instance
3.19.4 1
non-value representation an object representation that does not represent a value of the object type
3.19.5 1
perform a trap interrupt execution of the program such that no further operations are performed2)
2
Note 1 to entry: Implementations that support Annex L are permitted to invoke a runtime-constraint handler when they perform a trap.
3.20 1
⌈x⌉ ceiling of x the least integer greater than or equal to x
2
EXAMPLE ⌈2.4⌉ is 3, ⌈−2.4⌉ is −2.
3.21 1
⌊x⌋ floor of x the greatest integer less than or equal to x
2
EXAMPLE ⌊2.4⌋ is 2, ⌊−2.4⌋ is −3.
3.22 1
wraparound the process by which a value is reduced modulo 2N , where N is the width of the resulting type
2) Note that fetching a non-value representation might perform a trap but is not required to (see 6.2.6.1).
§ 3.22
General
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4. Conformance 1
In this document, "shall" is to be interpreted as a requirement on an implementation or on a program; conversely, "shall not" is to be interpreted as a prohibition.
2
If a "shall" or "shall not" requirement that appears outside of a constraint or runtime-constraint is violated, the behavior is undefined. Undefined behavior is otherwise indicated in this document by the words "undefined behavior" or by the omission of any explicit definition of behavior. There is no difference in emphasis among these three; they all describe "behavior that is undefined".
3
A program that is correct in all other aspects, operating on correct data, containing unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
4
The implementation shall not successfully translate a preprocessing translation unit containing a #error preprocessing directive unless it is part of a group skipped by conditional inclusion.
5
A strictly conforming program shall use only those features of the language and library specified in this document.3) It shall not produce output dependent on any unspecified, undefined, or implementation-defined behavior, and shall not exceed any minimum implementation limit.
6
The two forms of conforming implementation are hosted and freestanding. A conforming hosted implementation shall accept any strictly conforming program. A conforming freestanding implementation shall accept any strictly conforming program in which the use of the features specified in the library clause (Clause 7) is confined to the contents of the standard headers <float.h>, <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbit.h>, <stdbool.h>, <stddef.h>, <stdint.h>, and <stdnoreturn.h>. Additionally, a conforming freestanding implementation shall accept any strictly conforming program where: — the features specified in the header <string.h> are used, except the following functions: strdup, strndup, strcoll, strxfrm, strerror; and/or, — the selected function memalignment from <stdlib.h> is used. A conforming implementation may have extensions (including additional library functions), provided they do not alter the behavior of any strictly conforming program.4)
7
The strictly conforming programs that shall be accepted by a conforming freestanding implementation that defines __STDC_IEC_60559_BFP__ or __STDC_IEC_60559_DFP__ may also use features in the contents of the standard headers <fenv.h>, <math.h>, and the strto* floating-point numeric conversion functions (7.24.1) of the standard header <stdlib.h>, provided the program does not set the state of the FENV_ACCESS pragma to "ON". All identifiers that are reserved when <stdlib.h> is included in a hosted implementation are reserved when it is included in a freestanding implementation.
8
A conforming program is one that is acceptable to a conforming implementation. 5) 3) A strictly conforming program can use conditional features (see 6.10.9.3) provided the use is guarded by an appropriate
conditional inclusion preprocessing directive using the related macro. For example:
#ifdef __STDC_IEC_60559_BFP__ /* FE_UPWARD defined */ /* ... */ fesetround(FE_UPWARD); /* ... */ #endif
4) This implies that a conforming implementation reserves no identifiers other than those explicitly reserved in this document. 5) Strictly conforming programs are intended to be maximally portable among conforming implementations. Conforming programs can depend upon nonportable features of a conforming implementation.
8
General
§4
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An implementation shall be accompanied by a document that defines all implementation-defined and locale-specific characteristics and all extensions. Forward references: conditional inclusion (6.10.1), error directive (6.10.6), characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h> (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15), variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h> (7.19), common definitions <stddef.h> (7.21), integer types <stdint.h> (7.22), <stdnoreturn.h> (7.25).
§4
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5. Environment 1
An implementation translates C source files and executes C programs in two data-processing-system environments, which will be called the translation environment and the execution environment in this document. Their characteristics define and constrain the results of executing conforming C programs constructed according to the syntactic and semantic rules for conforming implementations. Forward references: In this clause, only a few of many possible forward references have been noted.
5.1 Conceptual models 5.1.1 Translation environment 1
5.1.1.1 Program structure A C program need not all be translated at the same time. The text of the program is kept in units called source files, (or preprocessing files) in this document. A source file together with all the headers and source files included via the preprocessing directive #include is known as a preprocessing translation unit. After preprocessing, a preprocessing translation unit is called a translation unit. Previously translated translation units may be preserved individually or in libraries. The separate translation units of a program communicate by (for example) calls to functions whose identifiers have external linkage, manipulation of objects whose identifiers have external linkage, or manipulation of data files. Translation units may be separately translated and then later linked to produce an executable program. Forward references: linkages of identifiers (6.2.2), external definitions (6.9), preprocessing directives (6.10). 5.1.1.2
1
Translation phases
The precedence among the syntax rules of translation is specified by the following phases.6) 1. Physical source file multibyte characters are mapped, in an implementation-defined manner, to the source character set (introducing new-line characters for end-of-line indicators) if necessary. 2. Each instance of a backslash character (\) immediately followed by a new-line character is deleted, splicing physical source lines to form logical source lines. Only the last backslash on any physical source line shall be eligible for being part of such a splice. A source file that is not empty shall end in a new-line character, which shall not be immediately preceded by a backslash character before any such splicing takes place. 3. The source file is decomposed into preprocessing tokens7) and sequences of white-space characters (including comments). A source file shall not end in a partial preprocessing token or in a partial comment. Each comment is replaced by one space character. New-line characters are retained. Whether each nonempty sequence of white-space characters other than new-line is retained or replaced by one space character is implementation-defined. 4. Preprocessing directives are executed, macro invocations are expanded, and _Pragma unary operator expressions are executed. If a character sequence that matches the syntax of a universal character name is produced by token concatenation (6.10.4.3), the behavior is undefined. A #include preprocessing directive causes the named header or source file to be processed from phase 1 through phase 4, recursively. All preprocessing directives are then deleted. 6) This requires implementations to behave as if these separate phases occur, even though many are typically folded together in practice. Source files, translation units, and translated translation units need not necessarily be stored as files, nor need there be any one-to-one correspondence between these entities and any external representation. The description is conceptual only, and does not specify any particular implementation. 7) As described in 6.4, the process of dividing a source file’s characters into preprocessing tokens is context-dependent. For example, see the handling of < within a #include preprocessing directive.
10
Environment
§ 5.1.1.2
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5. Each source character set member and escape sequence in character constants and string literals is converted to the corresponding member of the execution character set. Each instance of a source character or escape sequence for which there is no corresponding member is converted in an implementation-defined manner to some member of the execution character set other than the null (wide) character.8) 6. Adjacent string literal tokens are concatenated. 7. White-space characters separating tokens are no longer significant. Each preprocessing token is converted into a token. The resulting tokens are syntactically and semantically analyzed and translated as a translation unit. 8. All external object and function references are resolved. Library components are linked to satisfy external references to functions and objects not defined in the current translation. All such translator output is collected into a program image which contains information needed for execution in its execution environment. Forward references: universal character names (6.4.3), lexical elements (6.4), preprocessing directives (6.10), external definitions (6.9).
1
2
5.1.1.3 Diagnostics A conforming implementation shall produce at least one diagnostic message (identified in an implementation-defined manner) if a preprocessing translation unit or translation unit contains a violation of any syntax rule or constraint, even if the behavior is also explicitly specified as undefined or implementation-defined. Diagnostic messages need not be produced in other circumstances.9) EXAMPLE An implementation is required to issue a diagnostic for the translation unit: char i; int i;
because in those cases where wording in this document describes the behavior for a construct as being both a constraint error and resulting in undefined behavior, the constraint error is still required to be diagnosed.
5.1.2 1
Execution environments
Two execution environments are defined: freestanding and hosted. In both cases, program startup occurs when a designated C function is called by the execution environment. All objects with static storage duration shall be initialized (set to their initial values) before program startup. The manner and timing of such initialization are otherwise unspecified. Program termination returns control to the execution environment. Forward references: storage durations of objects (6.2.4), initialization (6.7.10).
1
5.1.2.1 Freestanding environment In a freestanding environment (in which C program execution may take place without any benefit of an operating system), the name and type of the function called at program startup are implementation-defined. Any library facilities available to a freestanding program, other than the minimal set required by Clause 4, are implementation-defined.
2
The effect of program termination in a freestanding environment is implementation-defined.
1
5.1.2.2 Hosted environment A hosted environment need not be provided, but shall conform to the following specifications if present. 8) An implementation may convert each instance of the same non-corresponding source character to a different member of the execution character set. 9) An implementation is encouraged to identify the nature of, and where possible localize, each violation. Of course, an implementation is free to produce any number of diagnostic messages, often referred to as warnings, as long as a valid program is still correctly translated. It can also successfully translate an invalid program. Annex I lists a few of the more common warnings.
§ 5.1.2.2
Environment
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5.1.2.2.1 Program startup The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters: int main(void) { /* ... */ }
or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared): int main(int argc, char *argv[]) { /* ... */ }
or equivalent10) ; or in some other implementation-defined manner. 2
If they are declared, the parameters to the main function shall obey the following constraints: — The value of argc shall be nonnegative. — argv[argc] shall be a null pointer. — If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host environment prior to program startup. The intent is to supply to the program information determined prior to program startup from elsewhere in the hosted environment. If the host environment is not capable of supplying strings with letters in both uppercase and lowercase, the implementation shall ensure that the strings are received in lowercase. — If the value of argc is greater than zero, the string pointed to by argv[0] represents the program name; argv[0][0] shall be the null character if the program name is not available from the host environment. If the value of argc is greater than one, the strings pointed to by argv[1] through argv[argc-1] represent the program parameters. — The parameters argc and argv and the strings pointed to by the argv array shall be modifiable by the program, and retain their last-stored values between program startup and program termination.
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5.1.2.2.2 Program execution In a hosted environment, a program may use all the functions, macros, type definitions, and objects described in the library clause (Clause 7). 5.1.2.2.3 Program termination If the return type of the main function is a type compatible with int, a return from the initial call to the main function is equivalent to calling the exit function with the value returned by the main function as its argument;11) reaching the } that terminates the main function returns a value of 0. If the return type is not compatible with int, the termination status returned to the host environment is unspecified. Forward references: definition of terms (7.1.1), the exit function (7.24.4.4).
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5.1.2.3 Program execution The semantic descriptions in this document describe the behavior of an abstract machine in which issues of optimization are irrelevant. An access to an object through the use of an lvalue of volatile-qualified type is a volatile access. A volatile access to an object, modifying an object, modifying a file, or calling a function that does any 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as char ** argv, or the return type may be specified by typeof(1), and so on. 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main will have ended in the former case, even where they would not have in the latter.
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of those operations are all side effects12) , which are changes in the state of the execution environment. Evaluation of an expression in general includes both value computations and initiation of side effects. Value computation for an lvalue expression includes determining the identity of the designated object. 3
Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations executed by a single thread, which induces a partial order among those evaluations. Given any two evaluations A and B, if A is sequenced before B, then the execution of A shall precede the execution of B. (Conversely, if A is sequenced before B, then B is sequenced after A.) If A is not sequenced before or after B, then A and B are unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced either before or after B, but it is unspecified which.13) The presence of a sequence point between the evaluation of expressions A and B implies that every value computation and side effect associated with A is sequenced before every value computation and side effect associated with B. (A summary of the sequence points is given in Annex C.)
4
In the abstract machine, all expressions are evaluated as specified by the semantics. An actual implementation need not evaluate part of an expression if it can deduce that its value is not used and that no needed side effects are produced (including any caused by calling a function or through volatile access to an object).
5
When the processing of the abstract machine is interrupted by receipt of a signal, the values of objects that are neither lock-free atomic objects nor of type volatile sig_atomic_t are unspecified, as is the state of the dynamic floating-point environment. The representation of any object modified by the handler that is neither a lock-free atomic object nor of type volatile sig_atomic_t becomes indeterminate when the handler exits, as does the state of the dynamic floating-point environment if it is modified by the handler and not restored to its original state.
6
The least requirements on a conforming implementation are: — Volatile accesses to objects are evaluated strictly according to the rules of the abstract machine. — At program termination, all data written into files shall be identical to the result that execution of the program according to the abstract semantics would have produced. — The input and output dynamics of interactive devices shall take place as specified in 7.23.3. The intent of these requirements is that unbuffered or line-buffered output appear as soon as possible, to ensure that prompting messages appear prior to a program waiting for input. This is the observable behavior of the program.
7
What constitutes an interactive device is implementation-defined.
8
More stringent correspondences between abstract and actual semantics may be defined by each implementation.
9
EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual semantics: at every sequence point, the values of the actual objects would agree with those specified by the abstract semantics. The keyword volatile would then be redundant.
10
Alternatively, an implementation might perform various optimizations within each translation unit, such that the actual semantics would agree with the abstract semantics only when making function calls across translation unit boundaries. In such an implementation, at the time of each function entry and function return where the calling function and the called function are in different translation units, the values of all externally linked objects and of all objects accessible via pointers therein would agree with the abstract semantics. Furthermore, at the time of each such function 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status flags and control modes. Floating-point operations implicitly set the status flags; modes affect result values of floating-point operations. Implementations that support such floating-point state are required to regard changes to it as side effects — see Annex F for details. The floating-point environment library <fenv.h> provides a programming facility for indicating when these side effects matter, freeing the implementations in other cases. 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations cannot interleave, but can be executed in any order.
§ 5.1.2.3
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entry the values of the parameters of the called function and of all objects accessible via pointers therein would agree with the abstract semantics. In this type of implementation, objects referred to by interrupt service routines activated by the signal function would require explicit specification of volatile storage, as well as other implementation-defined restrictions. 11
EXAMPLE 2 In executing the fragment char c1, c2; /* ... */ c1 = c1 + c2;
the "integer promotions" require that the abstract machine promote the value of each variable to int size and then add the two ints and truncate the sum. Provided the addition of two chars can be done without integer overflow, or with integer overflow wrapping silently to produce the correct result, the actual execution need only produce the same result, possibly omitting the promotions. 12
EXAMPLE 3 Similarly, in the fragment float f1, f2; double d; /* ... */ f1 = f2 * d;
the multiplication can be executed using single-precision arithmetic if the implementation can ascertain that the result would be the same as if it were executed using double-precision arithmetic (for example, if d were replaced by the constant 2.0, which has type double). 13
EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate semantics. Values are independent of whether they are represented in a register or in memory. For example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load is required to round to the precision of the storage type. In particular, casts and assignments are required to perform their specified conversion. For the fragment double d1, d2; float f; d1 = f = expression; d2 = (float) expression;
the values assigned to d1 and d2 are required to have been converted to float. 14
EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in precision as well as range. The implementation cannot generally apply the mathematical associative rules for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of overflow and underflow. Likewise, implementations cannot generally replace decimal constants to rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real numbers are often not valid (see F.9). double x, y, z; /* ... */ x = (x * y) * z; z = (x - y) + y; z = x + x * y; y = x / 5.0;
15
// not equivalent to x *= y * z; // not equivalent to z = x; // not equivalent to z = x * (1.0 + y); // not equivalent to y = x * 0.2;
EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment int a, b; /* ... */ a = a + 32760 + b + 5;
the expression statement behaves exactly the same as 14
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a = (((a + 32760) + b) + 5);
due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in which integer overflows produce an explicit trap and in which the range of values representable by an int is [−32768, +32767], the implementation cannot rewrite this expression as a = ((a + b) + 32765);
since if the values for a and b were, respectively, −32754 and −15, the sum a + b would produce a trap while the original expression would not; nor can the expression be rewritten either as a = ((a + 32765) + b);
or a = (a + (b + 32765));
since the values for a and b might have been, respectively, 4 and −8 or −17 and 12. However, on a machine in which integer overflow silently generates some value and where positive and negative integer overflows cancel, the above expression statement can be rewritten by the implementation in any of the above ways because the same result will occur. 16
EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the following fragment #include <stdio.h> int sum; char *p; /* ... */ sum = sum * 10 - ’0’ + (*p++ = getchar());
the expression statement is grouped as if it were written as sum = (((sum * 10) - ’0’) + ((*(p++)) = (getchar())));
but the actual increment of p can occur at any time between the previous sequence point and the next sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned value. Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), floating-point environment <fenv.h> (7.6), the signal function (7.14), files (7.23.3).
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5.1.2.4 Multi-threaded executions and data races Under a hosted implementation that does not define __STDC_NO_THREADS__, a program can have more than one thread of execution (or thread) running concurrently. The execution of each thread proceeds as defined by the remainder of this document. The execution of the entire program consists of an execution of all its threads.14) Under a freestanding implementation, it is implementationdefined whether a program can have more than one thread of execution.
2
The value of an object visible to a thread T at a particular point is the initial value of the object, a value stored in the object by T , or a value stored in the object by another thread, according to the rules below.
3
NOTE 1 In some cases, there could instead be undefined behavior. Much of this section is motivated by the desire to support atomic operations with explicit and detailed visibility constraints. However, it also implicitly supports a simpler view for more restricted programs. 14) The execution can usually be viewed as an interleaving of all the threads. However, some kinds of atomic operations, for example, allow executions inconsistent with a simple interleaving as described below.
§ 5.1.2.4
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Two expression evaluations conflict if one of them modifies a memory location and the other one reads or modifies the same memory location.
5
The library defines atomic operations (7.17) and operations on mutexes (7.28.4) that are specially identified as synchronization operations. These operations play a special role in making assignments in one thread visible to another. A synchronization operation on one or more memory locations is one of an acquire operation, a release operation, both an acquire and release operation, or a consume operation. A synchronization operation without an associated memory location is a fence and can be either an acquire fence, a release fence, or both an acquire and release fence. In addition, there are relaxed atomic operations, which are not synchronization operations, and atomic read-modify-write operations, which have special characteristics.
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NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations composing the mutex. Correspondingly, a call that releases the same mutex will perform a release operation on those same locations. Informally, performing a release operation on A forces prior side effects on other memory locations to become visible to other threads that later perform an acquire or consume operation on A. Relaxed atomic operations are not included as synchronization operations although, like synchronization operations, they cannot contribute to data races.
7
All modifications to a particular atomic object M occur in some particular total order, called the modification order of M . If A and B are modifications of an atomic object M , and A happens before B, then A shall precede B in the modification order of M , which is defined below.
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NOTE 3 This states that the modification orders are expected to respect the "happens before" relation.
9
NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be combined into a single total order for all objects. In general this will be impossible since different threads can observe modifications to different variables in inconsistent orders.
10
A release sequence headed by a release operation A on an atomic object M is a maximal contiguous sub-sequence of side effects in the modification order of M , where the first operation is A and every subsequent operation either is performed by the same thread that performed the release or is an atomic read-modify-write operation.
11
Certain library calls synchronize with other library calls performed by another thread. In particular, an atomic operation A that performs a release operation on an object M synchronizes with an atomic operation B that performs an acquire operation on M and reads a value written by any side effect in the release sequence headed by A.
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NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as described below. Such a requirement would sometimes interfere with efficient implementation.
13
NOTE 6 The specifications of the synchronization operations define when one reads the value written by another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total order. Each mutex acquisition "reads the value written" by the last mutex release.
14
An evaluation A carries a dependency15) to an evaluation B if: — the value of A is used as an operand of B, unless: • B is an invocation of the kill_dependency macro, • A is the left operand of a && or || operator, • A is the left operand of a ?: operator, or • A is the left operand of a , operator; or — A writes a scalar object or bit-field M , B reads from M the value written by A, and A is sequenced before B, or — for some evaluation X, A carries a dependency to X and X carries a dependency to B.
15
An evaluation A is dependency-ordered before16) an evaluation B if: 15) The "carries a dependency" relation is a subset of the "sequenced before" relation, and is similarly strictly intra-thread. 16) The "dependency-ordered before" relation is analogous to the "synchronizes with" relation, but uses release/consume in place of release/acquire.
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— A performs a release operation on an atomic object M , and, in another thread, B performs a consume operation on M and reads a value written by any side effect in the release sequence headed by A, or — for some evaluation X, A is dependency-ordered before X and X carries a dependency to B. 16
An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A is dependency-ordered before B, or, for some evaluation X: — A synchronizes with X and X is sequenced before B, — A is sequenced before X and X inter-thread happens before B, or — A inter-thread happens before X and X inter-thread happens before B.
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NOTE 7 The "inter-thread happens before" relation describes arbitrary concatenations of "sequenced before", "synchronizes with", and "dependency-ordered before" relationships, with two exceptions. The first exception is that a concatenation is not permitted to end with "dependency-ordered before" followed by "sequenced before". The reason for this limitation is that a consume operation participating in a "dependency-ordered before" relationship provides ordering only with respect to operations to which this consume operation carries a dependency. The reason that this limitation applies only to the end of such a concatenation is that any subsequent release operation will provide the required ordering for a prior consume operation. The second exception is that a concatenation is not permitted to consist entirely of "sequenced before". The reasons for this limitation are (1) to permit "inter-thread happens before" to be transitively closed and (2) the "happens before" relation, defined below, provides for relationships consisting entirely of "sequenced before".
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An evaluation A happens before an evaluation B if A is sequenced before B or A inter-thread happens before B. The implementation shall ensure that no program execution demonstrates a cycle in the "happens before" relation.
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NOTE 8 This cycle would otherwise be possible only through the use of consume operations.
20
A visible side effect A on an object M with respect to a value computation B of M satisfies the conditions: — A happens before B, and — there is no other side effect X to M such that A happens before X and X happens before B. The value of a non-atomic scalar object M , as determined by evaluation B, shall be the value stored by the visible side effect A.
21
NOTE 9 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data race and the behavior is undefined.
22
NOTE 10 This states that operations on ordinary variables are not visibly reordered. This is not detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent) execution.
23
The value of an atomic object M , as determined by evaluation B, shall be the value stored by some side effect A that modifies M , where B does not happen before A.
24
NOTE 11 The set of side effects from which a given evaluation might take its value is also restricted by the rest of the rules described here, and in particular, by the coherence requirements below.
25
If an operation A that modifies an atomic object M happens before an operation B that modifies M , then A shall be earlier than B in the modification order of M .
26
NOTE 12 The requirement above is known as "write-write coherence".
27
If a value computation A of an atomic object M happens before a value computation B of M , and A takes its value from a side effect X on M , then the value computed by B shall either be the value stored by X or the value stored by a side effect Y on M , where Y follows X in the modification order of M .
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NOTE 13 The requirement above is known as "read-read coherence".
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If a value computation A of an atomic object M happens before an operation B on M , then A shall take its value from a side effect X on M , where X precedes B in the modification order of M .
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NOTE 14 The requirement above is known as "read-write coherence".
§ 5.1.2.4
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If a side effect X on an atomic object M happens before a value computation B of M , then the evaluation B shall take its value from X or from a side effect Y that follows X in the modification order of M .
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NOTE 15 The requirement above is known as "write-read coherence".
33
NOTE 16 This effectively disallows compiler reordering of atomic operations to a single object, even if both operations are "relaxed" loads. By doing so, it effectively makes the "cache coherence" guarantee provided by most hardware available to C atomic operations.
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NOTE 17 The value observed by a load of an atomic object depends on the "happens before" relation, which in turn depends on the values observed by loads of atomic objects. The intended reading is that there exists an association of atomic loads with modifications they observe that, together with suitably chosen modification orders and the "happens before" relation derived as described above, satisfy the resulting constraints as imposed here.
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The execution of a program contains a data race if it contains two conflicting actions in different threads, at least one of which is not atomic, and neither happens before the other. Any such data race results in undefined behavior.
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NOTE 18 It can be shown that programs that correctly use simple mutexes and memory_order_seq_cst operations to prevent all data races, and use no other synchronization operations, behave as though the operations executed by their constituent threads were simply interleaved, with each value computation of an object being the last value stored in that interleaving. This is normally referred to as "sequential consistency". However, this applies only to data-race-free programs, and data-race-free programs cannot observe most program transformations that do not change single-threaded program semantics. In fact, most single-threaded program transformations continue to be allowed, since any program that behaves differently as a result necessarily has undefined behavior even before such a transformation is applied.
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NOTE 19 Compiler transformations that introduce assignments to a potentially shared memory location that would not be modified by the abstract machine are generally precluded by this document, since such an assignment might overwrite another assignment by a different thread in cases in which an abstract machine execution would not have encountered a data race. This includes implementations of data member assignment that overwrite adjacent members in separate memory locations. Reordering of atomic loads in cases in which the atomics in question might alias is also generally precluded, since this could violate the coherence requirements.
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NOTE 20 Transformations that introduce a speculative read of a potentially shared memory location might not preserve the semantics of the program as defined in this document, since they potentially introduce a data race. However, they are typically valid in the context of an optimizing compiler that targets a specific machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that is not tolerant of races or provides hardware race detection.
5.2 Environmental considerations 5.2.1 Character sets 1
Two sets of characters and their associated collating sequences shall be defined: the set in which source files are written (the source character set), and the set interpreted in the execution environment (the execution character set). Each set is further divided into a basic character set, whose contents are given by this subclause, and a set of three or more17) locale-specific members (which are not members of the basic character set) called extended characters. The combined set is also called the extended character set. The values of the members of the execution character set are implementation-defined.
2
In a character constant or string literal, members of the execution character set shall be represented by corresponding members of the source character set or by escape sequences consisting of the backslash \ followed by one or more characters. A byte with all bits set to 0, called the null character, shall exist in the basic execution character set; it is used to terminate a character string. Both the basic source and basic execution character sets shall have the following members: the 26 uppercase letters of the Latin alphabet
3
A N
B O
C P
D Q
E R
F S
G T
H U
I V
J W
K X
L Y
M Z
l y
m z
the 26 lowercase letters of the Latin alphabet a n
b o
c p
d q
e r
f s
g t
h u
i v
j w
k x
17) The extended characters include at least @ (U+0040 Commercial At), $ (U+0024 Dollar Sign), and ‘ (U+0060 Grave Accent, "Backtick").
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the 10 decimal digits 0
1
2
3
4
5
6
7
8
9
* ^
+ _
the following 29 graphic characters ! ;
" <
# =
% >
& ?
’ [
( \
) ]
, {
|
. }
/ ~
:
the space character, and control characters representing horizontal tab, vertical tab, and form feed. The representation of each member of the source and execution basic character sets shall fit in a byte. In both the source and execution basic character sets, the value of each character after 0 in the above list of decimal digits shall be one greater than the value of the previous. In source files, there shall be some way of indicating the end of each line of text; this document treats such an end-of-line indicator as if it were a single new-line character. In the basic execution character set, there shall be control characters representing alert, backspace, carriage return, and new line. If any other characters are encountered in a source file (except in an identifier, a character constant, a string literal, a header name, a comment, or a preprocessing token that is never converted to a token), the behavior is undefined. 4
A letter is an uppercase letter or a lowercase letter as defined above; in this document the term does not include other characters that are letters in other alphabets.
5
The universal character name construct provides a way to name other characters. Forward references: universal character names (6.4.3), character constants (6.4.4.4), preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).
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5.2.1.1 Multibyte characters The source character set may contain multibyte characters, used to represent members of the extended character set. The execution character set may also contain multibyte characters, which need not have the same encoding as for the source character set. For both character sets, the following shall hold: — The basic character set, @ (U+0040 Commercial At), $ (U+0024 Dollar Sign), and ‘ (U+0060 Grave Accent, "Backtick") shall be present and each character shall be encoded as a single byte. — The presence, meaning, and representation of any additional members is locale-specific. — A multibyte character set may have a state-dependent encoding, wherein each sequence of multibyte characters begins in an initial shift state and enters other locale-specific shift states when specific multibyte characters are encountered in the sequence. While in the initial shift state, all single-byte characters retain their usual interpretation and do not alter the shift state. The interpretation for subsequent bytes in the sequence is a function of the current shift state. — A byte with all bits zero shall be interpreted as a null character independent of shift state. Such a byte shall not occur as part of any other multibyte character.
2
For source files, the following shall hold: — An identifier, comment, string literal, character constant, or header name shall begin and end in the initial shift state. — An identifier, comment, string literal, character constant, or header name shall consist of a sequence of valid multibyte characters.
5.2.2 1
Character display semantics
The active position is that location on a display device where the next character output by the fputc function would appear. The intent of writing a printing character (as defined by the isprint function) to a display device is to display a graphic representation of that character at the active § 5.2.2
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position and then advance the active position to the next position on the current line. The direction of writing is locale-specific. If the active position is at the final position of a line (if there is one), the behavior of the display device is unspecified. 2
Alphabetic escape sequences representing non-graphic characters in the execution character set are intended to produce actions on display devices as follows: \a (alert) Produces an audible or visible alert without changing the active position. \b (backspace) Moves the active position to the previous position on the current line. If the active
position is at the initial position of a line, the behavior of the display device is unspecified. \f (form feed) Moves the active position to the initial position at the start of the next logical page. \n (new line) Moves the active position to the initial position of the next line. \r (carriage return) Moves the active position to the initial position of the current line. \t (horizontal tab) Moves the active position to the next horizontal tabulation position on the current
line. If the active position is at or past the last defined horizontal tabulation position, the behavior of the display device is unspecified. \v (vertical tab) Moves the active position to the initial position of the next vertical tabulation
position. If the active position is at or past the last defined vertical tabulation position, the behavior of the display device is unspecified. 3
Each of these escape sequences shall produce a unique implementation-defined value which can be stored in a single char object. The external representations in a text file need not be identical to the internal representations, and are outside the scope of this document. Forward references: the isprint function (7.4.1.8), the fputc function (7.23.7.3).
5.2.3 1
5.2.4 1
1
Signals and interrupts
Functions shall be implemented such that they may be interrupted at any time by a signal, or may be called by a signal handler, or both, with no alteration to earlier, but still active, invocations’ control flow (after the interruption), function return values, or objects with automatic storage duration. All such objects shall be maintained outside the function image (the instructions that compose the executable representation of a function) on a per-invocation basis.
Environmental limits
Both the translation and execution environments constrain the implementation of language translators and libraries. The following summarizes the language-related environmental limits on a conforming implementation; the library-related limits are discussed in Clause 7. 5.2.4.1 Translation limits The implementation shall be able to translate and execute a program that uses but does not exceed the following limitations for these constructs and entities18) : — 127 nesting levels of blocks — 63 nesting levels of conditional inclusion — 12 pointer, array, and function declarators (in any combinations) modifying an arithmetic, structure, union, or void type in a declaration — 63 nesting levels of parenthesized declarators within a full declarator — 63 nesting levels of parenthesized expressions within a full expression 18) Implementations are encouraged to avoid imposing fixed translation limits whenever possible.
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— 63 significant initial characters in an internal identifier or a macro name(each universal character name or extended source character is considered a single character) — 31 significant initial characters in an external identifier (each universal character name specifying a short identifier of 0000FFFF or less is considered 6 characters, each universal character name specifying a short identifier of 00010000 or more is considered 10 characters, and each extended source character is considered the same number of characters as the corresponding universal character name, if any)19) — 4095 external identifiers in one translation unit — 511 identifiers with block scope declared in one block — 4095 macro identifiers simultaneously defined in one preprocessing translation unit — 127 parameters in one function definition — 127 arguments in one function call — 127 parameters in one macro definition — 127 arguments in one macro invocation — 4095 characters in a logical source line — 4095 characters in a string literal (after concatenation) — 32767 bytes in an object (in a hosted environment only) — 15 nesting levels for #included files — 1023 case labels for a switch statement (excluding those for any nested switch statements) — 1023 members in a single structure or union — 1023 enumeration constants in a single enumeration — 63 levels of nested structure or union definitions in a single member declaration list
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5.2.4.2 Numerical limits An implementation is required to document all the limits specified in this subclause, which are specified in the headers <limits.h> and <float.h>. Additional limits are specified in <stdint.h>. Forward references: integer types <stdint.h> (7.22).
1
5.2.4.2.1 Characteristics of integer types <limits.h> The values given below shall be replaced by constant expressions suitable for use in conditional expression inclusion preprocessing directives. Their implementation-defined values shall be equal or greater to those shown. — width for an object of type bool20) BOOL_WIDTH
1
— number of bits for smallest object that is not a bit-field (byte) CHAR_BIT
8
The macros CHAR_WIDTH, SCHAR_WIDTH, and UCHAR_WIDTH that represent the width of the types char, signed char and unsigned char shall expand to the same value as CHAR_BIT. 19) See "future language directions" (6.11.3). 20) This value is exact.
§ 5.2.4.2.1
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— width for an object of type unsigned short int USHRT_WIDTH
16
The macro SHRT_WIDTH represents the width of the type short int and shall expand to the same value as USHRT_WIDTH. — width for an object of type unsigned int UINT_WIDTH
16
The macro INT_WIDTH represents the width of the type int and shall expand to the same value as UINT_WIDTH. — width for an object of type unsigned long int ULONG_WIDTH
32
The macro LONG_WIDTH represents the width of the type long int and shall expand to the same value as ULONG_WIDTH. — width for an object of type unsigned long long int ULLONG_WIDTH
64
The macro LLONG_WIDTH represents the width of the type long long int and shall expand to the same value as ULLONG_WIDTH. — maximum width of a bit-precise integer type BITINT_MAXWIDTH
/* see below */
The macro BITINT_MAXWIDTH represents the maximum width N supported by the declaration of a bit-precise integer (6.2.5) in the type specifier _BitInt( N). The value BITINT_MAXWIDTH shall expand to a value that is greater than or equal to the value of ULLONG_WIDTH. — maximum number of bytes in a multibyte character, for any supported locale MB_LEN_MAX
2
1
For all unsigned integer types for which <limits.h> or <stdint.h> define a macro with suffix _WIDTH holding its width N , there is a macro with suffix _MAX holding the maximal value 2N − 1 that is representable by the type and that has the same type as would an expression that is an object of the corresponding type converted according to the integer promotions. If the value is in the range of the type uintmax_t (7.22.1.5) the macro is suitable for use in conditional expression inclusion preprocessing directives.
3
For all signed integer types for which <limits.h> or <stdint.h> define a macro with suffix _WIDTH holding its width N , there are macros with suffix _MIN and _MAX holding the minimal and maximal values −2N −1 and 2N −1 − 1 that are representable by the type and that have the same type as would an expression that is an object of the corresponding type converted according to the integer promotions. If the values are in the range of the type intmax_t (7.22.1.5) the macros are suitable for use in conditional expression inclusion preprocessing directives.
4
If an object of type char can hold negative values, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of UCHAR_MAX.21) Forward references: representations of types (6.2.6), conditional inclusion (6.10.1), integer types <stdint.h> (7.22). 21) See 6.2.5.
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§ 5.2.4.2.1
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5.2.4.2.2 Characteristics of floating types <float.h> The characteristics of floating types are defined in terms of a model that describes a representation of floating-point numbers and allows other values. The characteristics provide information about an implementation’s floating-point arithmetic.22) An implementation that defines __STDC_IEC_60559_BFP__ or __STDC_IEC_559__ shall implement floating types and arithmetic conforming to IEC 60559 as specified in Annex F. An implementation that defines __STDC_IEC_60559_COMPLEX__ or __STDC_IEC_559_COMPLEX__ shall implement complex types and arithmetic conforming to IEC 60559 as specified in Annex G. The following parameters are used to define the model for each floating type: s b e p fk
sign (±1) base or radix of exponent representation (an integer > 1) exponent (an integer between a minimum emin and a maximum emax ) precision (the number of base-b digits in the significand) nonnegative integers less than b (the significand digits)
For each floating type, the parameters b, p, emin , and emax are fixed constants. 3
For each floating type, a floating-point number (x) is defined by the following model: x = sbe
p P
fk b−k ,
emin ≤ e ≤ emax
k=1
4
Model floating-point numbers x with f1 > 0 are called normalized floating-point numbers.
5
Model floating-point numbers x ̸= 0 with f1 = 0 and e = emin are called subnormal floating-point numbers.
6
Model floating-point numbers x ̸= 0 with f1 = 0 and e > emin are called unnormalized floating-point numbers.
7
Model floating-point numbers x with all fk = 0 are zeros.
8
Floating types shall be able to represent signed zeros or an unsigned zero and all normalized floatingpoint numbers. In addition, floating types may be able to contain other kinds of floating-point numbers23) , such as subnormal floating-point numbers and unnormalized floating-point numbers, and values that are not floating-point numbers, such as NaNs and (signed and unsigned) infinities. A NaN is a value signifying Not-a-Number. A quiet NaN propagates through almost every arithmetic operation without raising a floating-point exception; a signaling NaN generally raises a floating-point exception when occurring as an arithmetic operand24) .
9
Wherever values are unsigned, any requirement in this document to get the sign shall produce an unspecified sign, and any requirement to set the sign shall be ignored, unless otherwise specified.25)
10
Whether and in what cases subnormal numbers are treated as zeros is implementation-defined. Subnormal numbers that in some cases are treated by arithmetic operations as zeros are properly classified as subnormal. However, object representations that could represent subnormal numbers but that are always treated by arithmetic operations as zeros are non-canonical zeros, and the values are properly classified as zero, not subnormal. IEC 60559 arithmetic (with default exception handling) always treats subnormal numbers as nonzero.
11
A value is negative if and only if it compares less than 0. Thus, negative zeros and NaNs are not negative values.
12
An implementation may prefer particular representations of values that have multiple representa-
22) The floating-point model is intended to clarify the description of each floating-point characteristic and does not require the floating-point arithmetic of the implementation to be identical. 23) Some implementations have types that include finite numbers with range and/or precision that are not covered by the model. 24) IEC 60559 specifies quiet and signaling NaNs. For implementations that do not support IEC 60559, the terms quiet NaN and signaling NaN are intended to apply to values with similar behavior. 25) Bit representations of floating-point values might include a sign bit, even if the values can be regarded as unsigned. IEC 60559 NaNs are such values.
§ 5.2.4.2.2
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tions in a floating type, 6.2.6.1 not withstanding.26) The preferred representations of a floating type, including unique representations of values in the type, are called canonical. A floating type may also contain non-canonical representations, for example, redundant representations of some or all its values, or representations that are extraneous to the floating-point model.27) Typically, floating-point operations deliver results with canonical representations. IEC 60559 operations deliver results with canonical representations, unless specified otherwise. 13
The minimum range of representable values for a floating type is the most negative finite floatingpoint number representable in that type through the most positive finite floating-point number representable in that type. In addition, if negative infinity is representable in a type, the range of that type is extended to all negative real numbers; likewise, if positive infinity is representable in a type, the range of that type is extended to all positive real numbers.
14
The accuracy of the floating-point operations (+, -, *, /) and of most of the library functions in <math.h> and <complex.h> that return floating-point results is implementation-defined, as is the accuracy of the conversion between floating-point internal representations and string representations performed by the library functions in <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the accuracy is unknown. Decimal floating-point operations have stricter requirements.
15
All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant expressions suitable for use in conditional expression inclusion preprocessing directives; all floating values shall be arithmetic constant expressions. All except CR_DECIMAL_DIG (F.5), DECIMAL_DIG, DEC_EVAL_METHOD , FLT_EVAL_METHOD, FLT_RADIX, and FLT_ROUNDS have separate names for all floating types. The floating-point model representation is provided for all values except DEC_EVAL_METHOD, FLT_EVAL_METHOD and FLT_ROUNDS.
16
The remainder of this subclause specifies characteristics of standard floating types.
17
The rounding mode for floating-point addition for standard floating types is characterized by the implementation-defined value of FLT_ROUNDS. Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through the function fesetround in <fenv.h>. −1
indeterminable
0
toward zero
1
to nearest, ties to even
2
toward positive infinity
3
toward negative infinity
4
to nearest, ties away from zero
All other values for FLT_ROUNDS characterize implementation-defined rounding behavior. 18
Whether a type has the same precision (p) and exponent range (emin ≤ e ≤ emax ) as an IEC 60559 format is characterized by the implementation-defined values of FLT_IS_IEC_60559 , DBL_IS_IEC_60559 and LDBL_IS_IEC_60559 (this does not imply conformance to Annex F): 0 type does not have the precision and exponent range of an IEC 60559 format 1 type has the precision and exponent range of an IEC 60559 format
19
The values of floating type yielded by operators subject to the usual arithmetic conversions, including the values yielded by the implicit conversion of operands, and the values of floating constants are 26) The library operations iscanonical and canonicalize distinguish canonical (preferred) representations, but this distinction alone does not imply that canonical and non-canonical representations are of different values. 27) Some of the values in the IEC 60559 decimal formats have non-canonical representations (as well as a canonical representation).
24
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§ 5.2.4.2.2
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evaluated to a format whose range and precision may be greater than required by the type. Such a format is called an evaluation format. In all cases, assignment and cast operators yield values in the format of the type. The extent to which evaluation formats are used is characterized by the value of FLT_EVAL_METHOD:28) −1
indeterminable;
0
evaluate all operations and constants just to the range and precision of the type;
1
evaluate operations and constants of type float and double to the range and precision of the double type, evaluate long double operations and constants to the range and precision of the long double type;
2
evaluate all operations and constants to the range and precision of the long double type.
All other negative values for FLT_EVAL_METHOD characterize implementation-defined behavior. The value of FLT_EVAL_METHOD does not characterize values returned by function calls (see 6.8.6.4, F.6). 20
The presence or absence of subnormal numbers is characterized by the implementation-defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and LDBL_HAS_SUBNORM: −1
indeterminable
0
absent (type does not support subnormal numbers)
1
present (type does support subnormal numbers)
The use of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and LDBL_HAS_SUBNORM macros is an obsolescent feature. 21
Each of the signaling NaN macros FLT_SNAN DBL_SNAN LDBL_SNAN
is defined if and only if the respective type contains signaling NaNs. They expand to a constant expression of the respective type representing a signaling NaN.If an optional unary + or - operator followed by a signaling NaN macro is used as an initializer that must be evaluated at translation time, the object is initialized with a signaling NaN value. 22
The macro INFINITY
is defined if and only if the implementation supports an infinity for the type float. It expands to a constant expression of type float representing positive or unsigned infinity. 23
The macro NAN
is defined if and only if the implementation supports quiet NaNs for the float type. It expands to a constant expression of type float representing a quiet NaN. 24
The values given in the following list shall be replaced by constant expressions with implementationdefined values that are greater or equal in magnitude (absolute value) to those shown, with the same sign: 28) The evaluation method determines evaluation formats of expressions involving all floating types, not just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float _Complex operands is represented in the double _Complex format, and its parts are evaluated to double.
§ 5.2.4.2.2
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— radix of exponent representation, b FLT_RADIX
2
— number of base-FLT_RADIX digits in the floating-point significand, p FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG
— number of decimal digits, n, such that any floating-point number with p radix b digits can be rounded to a floating-point number with n decimal digits and back again without change to the value, ( p log10 b if b is a power of 10 ⌈1 + p log10 b⌉ otherwise FLT_DECIMAL_DIG DBL_DECIMAL_DIG LDBL_DECIMAL_DIG
6 10 10
— number of decimal digits, n, such that any floating-point number in the widest of the supported floating types and the supported IEC 60559 encodings with pmax radix b digits can be rounded to a floating-point number with n decimal digits and back again without change to the value, ( pmax log10 b if b is a power of 10 ⌈1 + pmax log10 b⌉ otherwise DECIMAL_DIG
10
This is an obsolescent feature, see 7.33.8. — number of decimal digits, q, such that any floating-point number with q decimal digits can be rounded into a floating-point number with p radix b digits and back again without change to the q decimal digits, ( p log10 b if b is a power of 10 ⌊(p − 1) log10 b⌋ otherwise FLT_DIG DBL_DIG LDBL_DIG
6 10 10
— minimum negative integer such that FLT_RADIX raised to one less than that power is a normalized floating-point number, emin FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP
— minimum negative integer such that10 raised to that power is in the range of normalized floating-point numbers, log 10 bemin −1 FLT_MIN_10_EXP DBL_MIN_10_EXP LDBL_MIN_10_EXP
26
-37 -37 -37
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— maximum integer such that FLT_RADIX raised to one less than that power is a representable finite floating-point number; if that representable finite floating-point number is normalized, the value of the macro is emax FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP
— maximum integer such that 10 raised to that power is in the range of representable finite floating-point numbers, ⌊log 10 ((1 − b−p )bemax )⌋ FLT_MAX_10_EXP DBL_MAX_10_EXP LDBL_MAX_10_EXP
25
+37 +37 +37
The values given in the following list shall be replaced by constant expressions with implementationdefined values that are greater than or equal to those shown: — maximum representable finite floating-point number; if that number is normalized, its value is (1 − b−p )bemax FLT_MAX DBL_MAX LDBL_MAX
1E+37 1E+37 1E+37
— maximum normalized floating-point number, (1 − b−p )bemax FLT_NORM_MAX DBL_NORM_MAX LDBL_NORM_MAX
26
1E+37 1E+37 1E+37
The values given in the following list shall be replaced by constant expressions with implementationdefined (positive) values that are less than or equal to those shown: — the difference between 1 and the least normalized value greater than 1 that is representable in the given floating type, b1−p FLT_EPSILON DBL_EPSILON LDBL_EPSILON
1E-5 1E-9 1E-9
— minimum normalized positive floating-point number, bemin −1 FLT_MIN DBL_MIN LDBL_MIN
1E-37 1E-37 1E-37
— minimum positive floating-point number FLT_TRUE_MIN DBL_TRUE_MIN LDBL_TRUE_MIN
§ 5.2.4.2.2
1E-37 1E-37 1E-37
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Recommended practice Conversion between real floating type and decimal character sequence with at most T_DECIMAL_DIG digits should be correctly rounded, where T is the macro prefix for the type. This assures conversion from real floating type to decimal character sequence with T_DECIMAL_DIG digits and back, using to-nearest rounding, is the identity function. EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum requirements of this document, and the appropriate values in a <float.h> header for type float: x = s16e
6 P
fk 16−k ,
−31 ≤ e ≤ +32
k=1
FLT_RADIX FLT_MANT_DIG FLT_EPSILON FLT_DECIMAL_DIG FLT_DIG FLT_MIN_EXP FLT_MIN FLT_MIN_10_EXP FLT_MAX_EXP FLT_MAX FLT_MAX_10_EXP 29
16 6 9.53674316E-07F 9 6 -31 2.93873588E-39F -38 +32 3.40282347E+38F +38
EXAMPLE 2 The following describes floating-point representations that also meet the requirements for single-precision and double-precision numbers in IEC 60559,29) and the appropriate values in a <float.h> header for types float and double: xf = s2e
24 P
fk 2−k ,
−125 ≤ e ≤ +128
fk 2−k ,
−1021 ≤ e ≤ +1024
k=1
xd = s2e
53 P k=1
FLT_IS_IEC_60559 1 FLT_RADIX 2 FLT_MANT_DIG 24 FLT_EPSILON 1.19209290E-07F // decimal constant FLT_EPSILON 0X1P-23F // hex constant FLT_DECIMAL_DIG 9 FLT_DIG 6 FLT_MIN_EXP -125 FLT_MIN 1.17549435E-38F // decimal constant FLT_MIN 0X1P-126F // hex constant FLT_TRUE_MIN 1.40129846E-45F // decimal constant FLT_TRUE_MIN 0X1P-149F // hex constant FLT_HAS_SUBNORM 1 FLT_MIN_10_EXP -37 FLT_MAX_EXP +128 FLT_MAX 3.40282347E+38F // decimal constant FLT_MAX 0X1.fffffeP127F // hex constant FLT_MAX_10_EXP +38 DBL_MANT_DIG 53 DBL_IS_IEC_60559 1 DBL_EPSILON 2.2204460492503131E-16 // decimal constant DBL_EPSILON 0X1P-52 // hex constant 29) The floating-point model in that standard sums powers of b from zero, so the values of the exponent limits are one less than shown here.
28
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DBL_DECIMAL_DIG 17 DBL_DIG 15 DBL_MIN_EXP -1021 DBL_MIN 2.2250738585072014E-308 // decimal constant DBL_MIN 0X1P-1022 // hex constant DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant DBL_TRUE_MIN 0X1P-1074 // hex constant DBL_HAS_SUBNORM 1 DBL_MIN_10_EXP -307 DBL_MAX_EXP +1024 DBL_MAX 1.7976931348623157E+308 // decimal constant DBL_MAX 0X1.fffffffffffffP1023 // hex constant DBL_MAX_10_EXP +308
Forward references: conditional inclusion (6.10.1), predefined macro names (6.10.9), complex arithmetic <complex.h> (7.3), extended multibyte and wide character utilities <wchar.h> (7.31), floatingpoint environment <fenv.h> (7.6), general utilities <stdlib.h> (7.24), input/output <stdio.h> (7.23), mathematics <math.h> (7.12), IEC 60559 floating-point arithmetic (Annex F), IEC 60559compatible complex arithmetic (Annex G).
1
2
3
5.2.4.2.3 Characteristics of decimal floating types in <float.h> This subclause specifies macros in <float.h> that provide characteristics of decimal floating types (an optional feature) in terms of the model presented in 5.2.4.2.2. An implementation shall provide these macros if and only if it defines __STDC_IEC_60559_DFP__. The prefixes DEC32_, DEC64_, and DEC128_ denote the types _Decimal32, _Decimal64, and _Decimal128 respectively. DEC_EVAL_METHOD is the decimal floating-point analog of FLT_EVAL_METHOD (5.2.4.2.2).
Its implementation-defined value characterizes the use of evaluation formats for decimal floating types: −1
indeterminable;
0
evaluate all operations and constants just to the range and precision of the type;
1
evaluate operations and constants of type _Decimal32 and _Decimal64 to the range and precision of the _Decimal64 type, evaluate _Decimal128 operations and constants to the range and precision of the _Decimal128 type;
2
evaluate all operations and constants to the range and precision of the _Decimal128 type.
Each of the decimal signaling NaN macros DEC32_SNAN DEC64_SNAN DEC128_SNAN
expands to a constant expression of the respective decimal floating type representing a signaling NaN. If an optional unary + or - operator followed by a signaling NaN macro is used for initializing an object of the same type that has static or thread storage duration, the object is initialized with a signaling NaN value. 4
The macro DEC_INFINITY
expands to a constant expression of type _Decimal32 representing positive infinity. 5
The macro DEC_NAN
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expands to a constant expression of type _Decimal32 representing a quiet NaN. 6
The integer values given in the following lists shall be replaced by constant expressions suitable for use in conditional expression inclusion preprocessing directives: — radix of exponent representation, b(=10) For the standard floating types, this value is implementation-defined and is specified by the macro FLT_RADIX. For the decimal floating types there is no corresponding macro, since the value 10 is an inherent property of the types. Wherever FLT_RADIX appears in a description of a function that has versions that operate on decimal floating types, it is noted that for the decimal floating-point versions the value used is implicitly 10, rather than FLT_RADIX. — number of digits in the coefficient DEC32_MANT_DIG DEC64_MANT_DIG DEC128_MANT_DIG
7 16 34
— minimum exponent DEC32_MIN_EXP DEC64_MIN_EXP DEC128_MIN_EXP
-94 -382 -6142
— maximum exponent DEC32_MAX_EXP DEC64_MAX_EXP DEC128_MAX_EXP
97 385 6145
— maximum representable finite decimal floating-point number (there are 6, 15 and 33 9’s after the decimal points respectively) DEC32_MAX DEC64_MAX DEC128_MAX
9.999999E96DF 9.999999999999999E384DD 9.999999999999999999999999999999999E6144DL
— the difference between 1 and the least value greater than 1 that is representable in the given floating type DEC32_EPSILON DEC64_EPSILON DEC128_EPSILON
1E-6DF 1E-15DD 1E-33DL
— minimum normalized positive decimal floating-point number DEC32_MIN DEC64_MIN DEC128_MIN
1E-95DF 1E-383DD 1E-6143DL
— minimum positive subnormal decimal floating-point number DEC32_TRUE_MIN DEC64_TRUE_MIN DEC128_TRUE_MIN
30
0.000001E-95DF 0.000000000000001E-383DD 0.000000000000000000000000000000001E-6143DL
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§ 5.2.4.2.3
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For decimal floating-point arithmetic, it is often convenient to consider an alternate equivalent model where the significand is represented with integer rather than fraction digits. With s, b, e, p, and fk as defined in 5.2.4.2.2, a floating-point number x is defined by the model: x = s · b(e−p)
p X
fk · b(p−k)
k=1
8
With b fixed to 10, a decimal floating-point number x is thus: x = s · 10
(e−p)
p X
fk · 10(p−k)
k=1
The quantum exponent is q = e − p and the coefficient is c = f1 f2 · · · fp , which is an integer between 0 and 10p − 1, inclusive. Thus, x = s · c · 10q is represented by the triple of integers (s, c, q). The quantum of x is 10q , which is the value of a unit in the last place of the coefficient. Quantum exponent ranges Type Maximum Quantum Exponent (qmax ) Minimum Quantum Exponent (qmin )
_Decimal32
_Decimal64
_Decimal128
90 −101
369 −398
6111 −6176
9
For binary floating-point arithmetic following IEC 60559, representations in the model described in 5.2.4.2.2 that have the same numerical value are indistinguishable in the arithmetic. However, for decimal floating-point arithmetic, representations that have the same numerical value but different quantum exponents, e.g., (+1, 10, −1) representing 1.0 and (+1, 100, −2) representing 1.00, are distinguishable. To facilitate exact fixed-point calculation, operation results that are of decimal floating type have a preferred quantum exponent, as specified in IEC 60559, which is determined by the quantum exponents of the operands if they have decimal floating types (or by specific rules for conversions from other types). The table below gives rules for determining preferred quantum exponents for results of IEC 60559 operations, and for other operations specified in this document. When exact, these operations produce a result with their preferred quantum exponent, or as close to it as possible within the limitations of the type. When inexact, these operations produce a result with the least possible quantum exponent. For example, the preferred quantum exponent for addition is the minimum of the quantum exponents of the operands. Hence (+1, 123, −2) + (+1, 4000, −3) = (+1, 5230, −3) or 1.23 + 4.000 = 5.230.
10
The following table shows, for each operation delivering a result in decimal floating-point format, how the preferred quantum exponents of the operands, Q(x), Q(y), etc., determine the preferred quantum exponent of the operation result, provided the table formula is defined for the arguments. For the cases where the formula is undefined and the function result is ±∞, the preferred quantum exponent is immaterial because the quantum exponent of ±∞ is defined to be infinity. For the other cases where the formula is undefined and the function result is finite, the preferred quantum exponent is unspecified.30) Preferred quantum exponents Operation roundeven, round, trunc, ceil, floor, rint, nearbyint nextup, nextdown, nextafter, nexttoward remainder
Preferred quantum exponent of result max(Q(x), 0) least possible min(Q(x), Q(y))
30) Although unspecified in IEC 60559, a preferred quantum exponent of 0 for these cases would be a reasonable implementation choice.
§ 5.2.4.2.3
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fmin, fmax, fminimum, fmaximum, fminimum_mag, fmaximum_mag, fminimum_num, fmaximum_num, fminimum_mag_num, fmaximum_mag_num scalbn, scalbln ldexp logb postfix ++ operator, postfix -- operator, prefix ++ operator, prefix -- operator +, d32add, d64add -, d32sub, d64sub *, d32mul, d64mul /, d32div, d64div sqrt, d32sqrt, d64sqrt fma, d32fma, d64fma
conversion from integer type exact conversion from non-decimal floating type inexact conversion from non-decimal floating type conversion between decimal floating types *cx returned by canonicalize strto, wcsto, scanf, floating constants of decimal floating type −(x), +(x) fabs copysign quantize quantum *encptr returned by encodedec, encodebin *xptr returned by decodedec, decodebin fmod fdim cbrt hypot pow modf *iptr returned by modf frexp *res returned by setpayload, setpayloadsig getpayload compoundn pown powr rootn rsqrt
transcendental functions
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Q(x) if x gives the result, Q(y) if y gives the result
Q(x) + n Q(x) + p 0 min(Q(x), 0) min(Q(x), Q(y)) min(Q(x), Q(y)) Q(x) + Q(y) Q(x) − Q(y) ⌊Q(x)/2⌋ min(Q(x) + Q(y), Q(z)) 0 0 least possible Q(x) Q(*x ) see 7.24.1.6 Q(x) Q(x) Q(x) Q(y) Q(x) Q(*xptr ) Q(*encptr ) min(Q(x), Q(y)) min((Q(x), Q(y)) if x > y, 0 if x ≤ y ⌊Q(x)/3⌋ min(Q(x), Q(y)) ⌊y × Q(x)⌋ Q(value) max(Q(value), 0) Q(value) if value = 0, –(length of coefficient of value) otherwise 0 if pl does not represent a valid payload, not applicable otherwise (NaN returned) 0 if *x is a NaN, unspecified otherwise ⌊n × min(0, Q(x))⌋ ⌊n × Q(x)⌋ ⌊y × Q(x)⌋ ⌊Q(x)/n⌋ −⌊Q(x)/2⌋ 0
A function family listed in the table above indicates the functions for all decimal floating types, where the function family is represented by the name of the functions without a suffix. For example, ceil indicates the functions ceild32, ceild64, and ceild128. 32
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§ 5.2.4.2.3
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Forward references: extended multibyte and wide character utilities <wchar.h> (7.31), floatingpoint environment <fenv.h> (7.6), general utilities <stdlib.h> (7.24), input/output <stdio.h> (7.23), mathematics <math.h> (7.12), type-generic mathematics <tgmath.h> (7.27), IEC 60559 floating-point arithmetic (Annex F).
§ 5.2.4.2.3
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6. Language 6.1 1
Notation
In the syntax notation used in this clause, syntactic categories (nonterminals) are indicated by italic type, and literal words and character set members (terminals) by bold type. A colon (:) following a nonterminal introduces its definition. Alternative definitions are listed on separate lines, except when prefaced by the words "one of". An optional symbol is indicated by the subscript "opt", so that { expressionopt }
indicates an optional expression enclosed in braces. 2
When syntactic categories are referred to in the main text, they are not italicized and words are separated by spaces instead of hyphens.
3
A summary of the language syntax is given in Annex A.
6.2 Concepts 6.2.1 Scopes of identifiers, type names, and compound literals 1
An identifier can denote: — a standard attribute, an attribute prefix, or an attribute name; — an object; a function; — a tag or a member of a structure, union, or enumeration; — a typedef name; — a label name; — a macro name; — or, a macro parameter. The same identifier can denote different entities at different points in the program. A member of an enumeration is called an enumeration constant. Macro names and macro parameters are not considered further here, because prior to the semantic phase of program translation any occurrences of macro names in the source file are replaced by the preprocessing token sequences that constitute their macro definitions.
2
For each different entity that an identifier designates, the identifier is visible (i.e., can be used) only within a region of program text called its scope. Different entities designated by the same identifier either have different scopes, or are in different name spaces. There are four kinds of scopes: function, file, block, and function prototype. (A function prototype is a declaration of a function.)
3
A label name is the only kind of identifier that has function scope. It can be used (in a goto statement) anywhere in the function in which it appears, and is declared implicitly by its syntactic appearance (followed by a : and a statement).
4
Every other identifier has scope determined by the placement of its declaration (in a declarator or type specifier). If the declarator or type specifier that declares the identifier appears outside of any block or list of parameters, the identifier has file scope, which terminates at the end of the translation unit. If the declarator or type specifier that declares the identifier appears inside a block or within the list of parameter declarations in a function definition, the identifier has block scope, which terminates at the end of the associated block. If the declarator or type specifier that declares the identifier appears within the list of parameter declarations in a function prototype (not part of a function definition), the identifier has function prototype scope, which terminates at the end of the function 34
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declarator. If an identifier designates two different entities in the same name space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end strictly before the scope of the other entity (the outer scope). Within the inner scope, the identifier designates the entity declared in the inner scope; the entity declared in the outer scope is hidden (and not visible) within the inner scope. 5
Unless explicitly stated otherwise, where this document uses the term "identifier" to refer to some entity (as opposed to the syntactic construct), it refers to the entity in the relevant name space whose declaration is visible at the point the identifier occurs.
6
Two identifiers have the same scope if and only if their scopes terminate at the same point.
7
Structure, union, and enumeration tags have scope that begins just after the appearance of the tag in a type specifier that declares the tag. Each enumeration constant has scope that begins just after the appearance of its defining enumerator in an enumerator list. An ordinary identifier that has an underspecified definition has scope that starts when the definition is completed; if the same ordinary identifier declares another entity with a scope that encloses the current block, that declaration is hidden as soon as the inner declarator is completed.31) Any other identifier has scope that begins just after the completion of its declarator.
8
As a special case, a type name (which is not a declaration of an identifier) is considered to have a scope that begins just after the place within the type name where the omitted identifier would appear were it not omitted. A compound literal (which is an expression that provides access to an anonymous object) is associated with the enclosing scope that corresponds to the placement of the compound literal in the program; that scope is either file scope, function prototype scope, or block scope. Forward references: declarations (6.7), function calls (6.5.2.2), function calls (6.5.2.5), function definitions (6.9.1), identifiers (6.4.2), macro replacement (6.10.4), name spaces of identifiers (6.2.3), source file inclusion (6.10.2), statements and blocks (6.8).
6.2.2
Linkages of identifiers
1
An identifier declared in different scopes or in the same scope more than once can be made to refer to the same object or function by a process called linkage32) . There are three kinds of linkage: external, internal, and none.
2
In the set of translation units and libraries that constitutes an entire program, each declaration of a particular identifier with external linkage denotes the same object or function. Within one translation unit, each declaration of an identifier with internal linkage denotes the same object or function. Each declaration of an identifier with no linkage denotes a unique entity.
3
If the declaration of a file scope identifier for: — an object contains any of the storage-class specifiers static or constexpr; — or, a function contains the storage-class specifier static, then the identifier has internal linkage.33)
4
For an identifier declared with the storage-class specifier extern in a scope in which a prior declaration of that identifier is visible34) , if the prior declaration specifies internal or external linkage, the linkage of the identifier at the later declaration is the same as the linkage specified at the prior declaration. If no prior declaration is visible, or if the prior declaration specifies no linkage, then the identifier has external linkage.
5
If the declaration of an identifier for a function has no storage-class specifier, its linkage is determined exactly as if it were declared with the storage-class specifier extern. If the declaration of an identifier for an object has file scope and does not contain the storage-class specifier static or constexpr, its linkage is external. 31) That means, that the outer declaration is not visible for the initializer. 32) There is no linkage between different identifiers. 33) A function declaration can contain the storage-class specifier static only if it is at file scope; see 6.7.1. 34) As specified in 6.2.1, the later declaration might hide the prior declaration.
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The following identifiers have no linkage: an identifier declared to be anything other than an object or a function; an identifier declared to be a function parameter; a block scope identifier for an object declared without the storage-class specifier extern.
7
If, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined. Forward references: declarations (6.7), expressions (6.5), external definitions (6.9), statements (6.8).
6.2.3 1
Name spaces of identifiers
If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate name spaces for various categories of identifiers, as follows: — label names (disambiguated by the syntax of the label declaration and use); — the tags of structures, unions, and enumerations (disambiguated by following any35) of the keywords struct, union, or enum); — the members of structures or unions; each structure or union has a separate name space for its members (disambiguated by the type of the expression used to access the member via the . or -> operator); — standard attributes and attribute prefixes (disambiguated by the syntax of the attribute specifier and name of the attribute token) (6.7.12); — the trailing identifier in an attribute prefixed token; each attribute prefix has a separate name space for the implementation-defined attributes that it introduces (disambiguated by the attribute prefix and the trailing identifier token); — all other identifiers, called ordinary identifiers (declared in ordinary declarators or as enumeration constants). Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1), structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags (6.7.2.3), the goto statement (6.8.6.1).
6.2.4
Storage durations of objects
1
An object has a storage duration that determines its lifetime. There are four storage durations: static, thread, automatic, and allocated. Allocated storage is described in 7.24.3.
2
The lifetime of an object is the portion of program execution during which storage is guaranteed to be reserved for it. An object exists, has a constant address36) , and retains its last-stored value throughout its lifetime37) If an object is referred to outside of its lifetime, the behavior is undefined. If a pointer value is used in an evaluation after the object the pointer points to (or just past) reaches the end of its lifetime, the behavior is undefined. The representation of a pointer object becomes indeterminate when the object the pointer points to (or just past) reaches the end of its lifetime.
3
An object whose identifier is declared without the storage-class specifier thread_local, and either with external or internal linkage or with the storage-class specifier static, has static storage duration. Its lifetime is the entire execution of the program and its stored value is initialized only once, prior to program startup.
4
An object whose identifier is declared with the storage-class specifier thread_local has thread storage duration. Its explicit or implicit initializer is evaluated prior to program execution, its lifetime is the entire execution of the thread for which it is created, and its stored value is initialized with the previously determined value when the thread is started. There is a distinct object per thread, and use of the declared name in an expression refers to the object associated with the thread evaluating 35) There is only one name space for tags even though three are possible. 36) The term "constant address" means that two pointers to the object constructed at possibly different times will compare
equal. The address can be different during two different executions of the same program. 37) In the case of a volatile object, the last store need not be explicit in the program.
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the expression. The result of attempting to indirectly access an object with thread storage duration from a thread other than the one with which the object is associated is implementation-defined. 5
An object whose identifier is declared with no linkage and without the storage-class specifier static has automatic storage duration, as do some compound literals. The result of attempting to indirectly access an object with automatic storage duration from a thread other than the one with which the object is associated is implementation-defined.
6
For such an object that does not have a variable length array type, its lifetime extends from entry into the block with which it is associated until execution of that block ends in any way. (Entering an enclosed block or calling a function suspends, but does not end, execution of the current block.) If the block is entered recursively, a new instance of the object is created each time. The initial representation of the object is indeterminate. If an initialization is specified for the object and it is not specified with constexpr, it is performed each time the declaration or compound literal is reached in the execution of the block; if it is specified with constexpr the initializer is evaluated once at translation time and the new instance of the object is initialized to that fixed value each time the specification is reached; otherwise, the representation of the object becomes indeterminate each time the declaration is reached.
7
For such an object that does have a variable length array type, its lifetime extends from the declaration of the object until execution of the program leaves the scope of the declaration.38) If the scope is entered recursively, a new instance of the object is created each time. The initial representation of the object is indeterminate.
8
A non-lvalue expression with structure or union type, where the structure or union contains a member with array type (including, recursively, members of all contained structures and unions) refers to an object with automatic storage duration and temporary lifetime.39) Its lifetime begins when the expression is evaluated and its initial value is the value of the expression. Its lifetime ends when the evaluation of the containing full expression ends. Any attempt to modify an object with temporary lifetime results in undefined behavior. An object with temporary lifetime behaves as if it were declared with the type of its value for the purposes of effective type. Such an object need not have a unique address. Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators (6.7.6), function calls (6.5.2.2), initialization (6.7.10), statements (6.8), effective type (6.5).
6.2.5
Types
1
The meaning of a value stored in an object or returned by a function is determined by the type of the expression used to access it. (An identifier declared to be an object is the simplest such expression; the type is specified in the declaration of the identifier.) Types are partitioned into object types (types that describe objects) and function types (types that describe functions). At various points within a translation unit an object type may be incomplete40) (lacking sufficient information to determine the size of objects of that type) or complete (having sufficient information)41) .
2
An object declared as type bool is large enough to store the values false and true.
3
An object declared as type char is large enough to store any member of the basic execution character set. If a member of the basic execution character set is stored in a char object, its value is guaranteed to be nonnegative. If any other character is stored in a char object, the resulting value is implementation-defined but shall be within the range of values that can be represented in that type.
4
There are five standard signed integer types, designated as signed char, short int, int, long int, and long long int. (These and other types may be designated in several additional ways, as described in 6.7.2.) 38) Leaving the innermost block containing the declaration, or jumping to a point in that block or an embedded block prior to the declaration, leaves the scope of the declaration. 39) The address of such an object is taken implicitly when an array member is accessed. 40) An incomplete type can only be used when the size of an object of that type is not needed. It is not needed, for example, when a typedef name is declared to be a specifier for a structure or union, or when a pointer to or a function returning a structure or union is being declared. The specification has to be complete before such a function is called or defined. 41) A type can be incomplete or complete throughout an entire translation unit, or it can change states at different points within a translation unit.
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A bit-precise signed integer type is designated as _BitInt( N) where N is an integer constant expression that specifies the number of bits that are used to represent the type, including the sign bit. Each value of N designates a distinct type.42) .
6
There may also be implementation-defined extended signed integer types 43) . The standard signed integer types, bit-precise signed integer types, and extended signed integer types are collectively called signed integer types 44) .
7
An object declared as type signed char occupies the same amount of storage as a "plain" char object. A "plain" int object has the natural size suggested by the architecture of the execution environment (large enough to contain any value in the range INT_MIN to INT_MAX as defined in the header <limits.h>).
8
For each of the signed integer types, there is a corresponding (but different) unsigned integer type (designated with the keyword unsigned) that uses the same amount of storage (including sign information) and has the same alignment requirements. The type bool and the unsigned integer types that correspond to the standard signed integer types are the standard unsigned integer types. The unsigned integer types that correspond to the extended signed integer types are the extended unsigned integer types. In addition to the unsigned integer types that correspond to the bit-precise signed integer types there is the type unsigned _BitInt(1), which uses one bit to represent the type. Collectively, unsigned _BitInt(1) and the unsigned integer types that correspond to the bitprecise signed integer types are the bit-precise unsigned integer types. The standard unsigned integer types, bit-precise unsigned integer types, and extended unsigned integer types are collectively called unsigned integer types.45)
9
The standard signed integer types and standard unsigned integer types are collectively called the standard integer types; the bit-precise signed integer types and bit-precise unsigned integer types are collectively called the bit-precise integer types; the extended signed integer types and extended unsigned integer types are collectively called the extended integer types.
10
For any two integer types with the same signedness and different integer conversion rank (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a subrange of the values of the other type.
11
The range of nonnegative values of a signed integer type is a subrange of the corresponding unsigned integer type, and the representation of the same value in each type is the same.46) The range of representable values for the unsigned type is 0 to 2N − 1 (inclusive). A computation involving unsigned operands can never produce an overflow, because arithmetic for the unsigned type is performed modulo 2N .
12
There are three standard floating types, designated as float, double, and long double. 47) The set of values of the type float is a subset of the set of values of the type double; the set of values of the type double is a subset of the set of values of the type long double.
13
There are three decimal floating types, designated as _Decimal32, _Decimal64, and _Decimal128. Respectively, they have the IEC 60559 formats: decimal3248) , decimal64, and decimal128. (Decimal floating types are a conditional feature that implementations need not support; see 6.10.9.3.)
14
The standard floating types and the decimal floating types are collectively called the real floating types.
15
There are three complex types, designated as float _Complex, double _Complex, and long double 42) Thus, _BitInt(3) is not the same type as _BitInt(4). 43) Implementation-defined keywords have the form of an identifier reserved for any use as described in 7.1.3. 44) Any statement in this document about signed integer types also applies to the bit-precise signed integer types and the extended signed integer types, unless otherwise noted. 45) Any statement in this document about unsigned integer types also applies to the bit-precise unsigned integer types and the extended unsigned integer types, unless otherwise specified. 46) The same representation and alignment requirements are meant to imply interchangeability as arguments to functions, return values from functions, and members of unions. 47) See "future language directions" (6.11.1). 48) IEC 60559 specifies decimal32 as a data-interchange format that does not require arithmetic support; however, _Decimal32 is a fully supported arithmetic type.
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_Complex.49) (Complex types are a conditional feature that implementations need not support; see
6.10.9.3.) The real floating and complex types are collectively called the floating types. 16
For each floating type there is a corresponding real type, which is always a real floating type. For real floating types, it is the same type. For complex types, it is the type given by deleting the keyword _Complex from the type name.
17
Each complex type has the same representation and alignment requirements as an array type containing exactly two elements of the corresponding real type; the first element is equal to the real part, and the second element to the imaginary part, of the complex number.
18
The type char, the signed and unsigned integer types, and the floating types are collectively called the basic types. The basic types are complete object types. Even if the implementation defines two or more basic types to have the same representation, they are nevertheless different types.
19
NOTE 1 An implementation can define new keywords that provide alternative ways to designate a basic (or any other) type; this does not violate the requirement that all basic types be different. Implementation-defined keywords have the form of an identifier reserved for any use as described in 7.1.3.
20
The three types char, signed char, and unsigned char are collectively called the character types. The implementation shall define char to have the same range, representation, and behavior as either signed char or unsigned char.50)
21
An enumeration comprises a set of named integer constant values. Each distinct enumeration constitutes a different enumerated type.
22
The type char, the signed and unsigned integer types, and the enumerated types are collectively called integer types. The integer and real floating types are collectively called real types.
23
Integer and floating types are collectively called arithmetic types. Each arithmetic type belongs to one type domain: the real type domain comprises the real types, the complex type domain comprises the complex types.
24
The void type comprises an empty set of values; it is an incomplete object type that cannot be completed.
25
Any number of derived types can be constructed from the object and function types, as follows: — An array type describes a contiguously allocated nonempty set of objects with a particular member object type, called the element type. The element type shall be complete whenever the array type is specified. Array types are characterized by their element type and by the number of elements in the array. An array type is said to be derived from its element type, and if its element type is T, the array type is sometimes called "array of T". The construction of an array type from an element type is called "array type derivation". — A structure type describes a sequentially allocated nonempty set of member objects (and, in certain circumstances, an incomplete array), each of which has an optionally specified name and possibly distinct type. — A union type describes an overlapping nonempty set of member objects, each of which has an optionally specified name and possibly distinct type. — A function type describes a function with specified return type. A function type is characterized by its return type and the number and types of its parameters. A function type is said to be derived from its return type, and if its return type is T, the function type is sometimes called "function returning T". The construction of a function type from a return type is called "function type derivation". — A pointer type may be derived from a function type or an object type, called the referenced type. A pointer type describes an object whose value provides a reference to an entity of the referenced type. A pointer type derived from the referenced type T is sometimes called "pointer to T". 49) A specification for imaginary types is in Annex G. 50) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be used to distinguish the two options. Irrespective of the choice made, char is a separate type from the other two and is not compatible with either.
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The construction of a pointer type from a referenced type is called "pointer type derivation". A pointer type is a complete object type. — An atomic type describes the type designated by the construct _Atomic (type-name). (Atomic types are a conditional feature that implementations need not support; see 6.10.9.3.) These methods of constructing derived types can be applied recursively. 26
Arithmetic types, pointer types, and the nullptr_t type are collectively called scalar types. Array and structure types are collectively called aggregate types51) .
27
An array type of unknown size is an incomplete type. It is completed, for an identifier of that type, by specifying the size in a later declaration (with internal or external linkage). A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete type. It is completed, for all declarations of that type, by declaring the same structure or union tag with its defining content later in the same scope.
28
A complete type shall have a size that is less than or equal to SIZE_MAX. A type has known constant size if it is complete and is not a variable length array type.
29
Array, function, and pointer types are collectively called derived declarator types. A declarator type derivation from a type T is the construction of a derived declarator type from T by the application of an array-type, a function-type, or a pointer-type derivation to T.
30
A type is characterized by its type category, which is either the outermost derivation of a derived type (as noted above in the construction of derived types), or the type itself if the type consists of no derived types.
31
Any type so far mentioned is an unqualified type. Each unqualified type has several qualified versions of its type52) , corresponding to the combinations of one, two, or all three of the const, volatile, and restrict qualifiers. The qualified or unqualified versions of a type are distinct types that belong to the same type category and have the same representation and alignment requirements.53) An array and its element type are always considered to be identically qualified.54) Any other derived type is not qualified by the qualifiers (if any) of the type from which it is derived.
32
Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier designates an atomic type. The size, representation, and alignment of an atomic type need not be the same as those of the corresponding unqualified type. Therefore, this document explicitly uses the phrase "atomic, qualified, or unqualified type" whenever the atomic version of a type is permitted along with the other qualified versions of a type. The phrase "qualified or unqualified type", without specific mention of atomic, does not include the atomic types.
33
A pointer to void shall have the same representation and alignment requirements as a pointer to a character type.53) Similarly, pointers to qualified or unqualified versions of compatible types shall have the same representation and alignment requirements. All pointers to structure types shall have the same representation and alignment requirements as each other. All pointers to union types shall have the same representation and alignment requirements as each other. Pointers to other types need not have the same representation or alignment requirements.
34
EXAMPLE 1 The type designated as "float *" has type "pointer to float". Its type category is pointer, not a floating type. The const-qualified version of this type is designated as "float * const" whereas the type designated as "const float *" is not a qualified type — its type is "pointer to const-qualified float" and is a pointer to a qualified type.
35
EXAMPLE 2 The type designated as "struct tag (*[5])(float)" has type "array of pointer to function returning struct tag". The array has length five and the function has a single parameter of type float. Its type category is array. 51) Note that aggregate type does not include union type because an object with union type can only contain one member at a time. 52) See 6.7.3 regarding qualified array and function types. 53) The same representation and alignment requirements are meant to imply interchangeability as arguments to functions, return values from functions, and members of unions. 54) This does not apply to the _Atomic qualifier. Note that qualifiers do not have any direct effect on the array type itself, but affect conversion rules for pointer types that reference an array type.
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Forward references: compatible type and composite type (6.2.7), declarations (6.7).
6.2.6 1
Representations of types
6.2.6.1 General The representations of all types are unspecified except as stated in this subclause.
2
Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, the number, order, and encoding of which are either explicitly specified or implementation-defined.
3
Values stored in unsigned bit-fields and objects of type unsigned char shall be represented using a pure binary notation.
4
Values stored in non-bit-field objects of any other object type are represented using n× CHAR_BIT bits, where n is the size of an object of that type, in bytes. An object that has the value may be copied into an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is called the object representation of the value. Values stored in bit-fields consist of m bits, where m is the size specified for the bit-field. The object representation is the set of m bits the bit-field comprises in the addressable storage unit holding it. Two values (other than NaNs) with the same object representation compare equal, but values that compare equal may have different object representations.
5
Certain object representations need not represent a value of the object type. If such a representation is read by an lvalue expression that does not have character type, the behavior is undefined. If such a representation is produced by a side effect that modifies all or any part of the object by an lvalue expression that does not have character type, the behavior is undefined.55) Such a representation is called a non-value representation.
6
When a value is stored in an object of structure or union type, including in a member object, the bytes of the object representation that correspond to any padding bytes take unspecified values.56) The object representation of a structure or union object is never a non-value representation, even though the byte range corresponding to a member of the structure or union object may be a non-value representation for that member.
7
When a value is stored in a member of an object of union type, the bytes of the object representation that do not correspond to that member but do correspond to other members take unspecified values.
8
Where an operator is applied to a value that has more than one object representation, which object representation is used shall not affect the value of the result.57) Where a value is stored in an object using a type that has more than one object representation for that value, it is unspecified which representation is used, but a non-value representation shall not be generated.
9
Loads and stores of objects with atomic types are done with memory_order_seq_cst semantics. Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function designators (6.3.2.1), order and consistency (7.17.3).
1
2
6.2.6.2 Integer types For unsigned integer types the bits of the object representation shall be divided into two groups: value bits and padding bits. If there are N value bits, each bit shall represent a different power of 2 between 1 and 2N −1 , so that objects of that type shall be capable of representing values from 0 to 2N − 1 using a pure binary representation; this shall be known as the value representation. The values of any padding bits are unspecified. The number of value bits N is called the width of the unsigned integer type. The type bool shall have one value bit and (sizeof(bool)*CHAR_BIT)- 1 padding bits. Otherwise, there need not be any padding bits; unsigned char shall not have any padding bits. For signed integer types, the bits of the object representation shall be divided into three groups: 55) Thus, an automatic variable can be initialized to a non-value representation without causing undefined behavior, but the value of the variable cannot be used until a proper value is stored in it. 56) Thus, for example, structure assignment need not copy any padding bits. 57) It is possible for objects x and y with the same effective type T to have the same value when they are accessed as objects of type T, but to have different values in other contexts. In particular, if == is defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof(T))== 0. Furthermore, x == y does not necessarily imply that x and y have the same value; other operations on values of type T might distinguish between them.
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value bits, padding bits, and the sign bit. If the corresponding unsigned type has width N , the signed type uses the same number of N bits, its width, as value bits and sign bit. N − 1 are value bits and the remaining bit is the sign bit. Each bit that is a value bit shall have the same value as the same bit in the object representation of the corresponding unsigned type. If the sign bit is zero, it shall not affect the resulting value. If the sign bit is one, it has value −(2N −1 ). There need not be any padding bits; signed char shall not have any padding bits. 3
The values of any padding bits are unspecified. A valid object representation of a signed integer type where the sign bit is zero is a valid object representation of the corresponding unsigned type, and shall represent the same value. For any integer type, the object representation where all the bits are zero shall be a representation of the value zero in that type.
4
The precision of an integer type is the number of value bits.
5
NOTE 1 Some combinations of padding bits might generate non-value representations, for example, if one padding bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a non-value representation other than as part of an exceptional condition such as an integer overflow. All other combinations of padding bits are alternative object representations of the value specified by the value bits.
6
NOTE 2 The sign representation defined in this document is called two’s complement. Previous revisions of this document additionally allowed other sign representations.
7
NOTE 3 For unsigned integer types the width and precision are the same, while for signed integer types the width is one greater than the precision.
6.2.7 1
Compatible type and composite type
Two types are compatible types if they are the same. Additional rules for determining whether two types are compatible are described in 6.7.2 for type specifiers, in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.58) Moreover, two complete structure, union, or enumerated types declared with the same tag are compatible if members satisfy the following requirements: — there shall be a one-to-one correspondence between their members such that each pair of corresponding members are declared with compatible types; — if one member of the pair is declared with an alignment specifier, the other is declared with an equivalent alignment specifier; — and, if one member of the pair is declared with a name, the other is declared with the same name. For two structures, corresponding members shall be declared in the same order. For two unions declared in the same translation unit, corresponding members shall be declared in the same order. For two structures or unions, corresponding bit-fields shall have the same widths. For two enumerations, corresponding members shall have the same values; if one has a fixed underlying type, then the other shall have a compatible fixed underlying type. For determining type compatibility, anonymous structures and unions are considered a regular member of the containing structure or union type, and the type of an anonymous structure or union is considered compatible to the type of another anonymous structure or union, respectively, if their members fulfill the above requirements. Furthermore, two structure, union, or enumerated types declared in separate translation units are compatible in the following cases: — both are declared without tags and they fulfill the requirements above; — both have the same tag and are completed somewhere in their respective translation units and they fulfill the requirements above; — both have the same tag and at least one of the two types is not completed in its translation unit. Otherwise, the structure, union, or enumerated types are incompatible.59) 58) Two types need not be identical to be compatible. 59) A structure, union, or enumerated type without a tag or an incomplete structure, union or enumerated type is not compatible with any other structure, union or enum type declared in the same translation unit.
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§ 6.2.7
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All declarations that refer to the same object or function shall have compatible type; otherwise, the behavior is undefined.
3
A composite type can be constructed from two types that are compatible; it is a type that is compatible with both of the two types and satisfies the following conditions: — If both types are array types, the following rules are applied: • If one type is an array of known constant size, the composite type is an array of that size. • Otherwise, if one type is a variable length array whose size is specified by an expression that is not evaluated, the behavior is undefined. • Otherwise, if one type is a variable length array whose size is specified, the composite type is a variable length array of that size. • Otherwise, if one type is a variable length array of unspecified size, the composite type is a variable length array of unspecified size. • Otherwise, both types are arrays of unknown size and the composite type is an array of unknown size. The element type of the composite type is the composite type of the two element types. — If both types are function types, the type of each parameter in the composite parameter type list is the composite type of the corresponding parameters. — If one of the types has a standard attribute, the composite type also has that attribute. These rules apply recursively to the types from which the two types are derived.
4
For an identifier with internal or external linkage declared in a scope in which a prior declaration of that identifier is visible60) , if the prior declaration specifies internal or external linkage, the type of the identifier at the later declaration becomes the composite type.
5
EXAMPLE Given the following two file scope declarations: int f(int (*)(char *), double (*)[3]); int f(int (*)(char *), double (*)[]);
The resulting composite type for the function is: int f(int (*)(char *), double (*)[3]);
Forward references: array declarators (6.7.6.2).
6.2.8
Alignment of objects
1
Complete object types have alignment requirements which place restrictions on the addresses at which objects of that type may be allocated. An alignment is an implementation-defined integer value representing the number of bytes between successive addresses at which a given object can be allocated. An object type imposes an alignment requirement on every object of that type: stricter alignment can be requested using the alignas keyword.
2
A fundamental alignment is a valid alignment less than or equal to alignof(max_align_t). Fundamental alignments shall be supported by the implementation for objects of all storage durations. The alignment requirements of the following types shall be fundamental alignments: — all atomic, qualified, or unqualified basic types; — all atomic, qualified, or unqualified enumerated types; — all atomic, qualified, or unqualified pointer types; 60) As specified in 6.2.1, the later declaration might hide the prior declaration.
§ 6.2.8
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— all array types whose element type has a fundamental alignment requirement; — all types specified in Clause 7 as complete object types; — all structure or union types whose elements have types with fundamental alignment requirements and none of whose elements have an alignment specifier specifying an alignment that is not a fundamental alignment. 3
An extended alignment is represented by an alignment greater than alignof(max_align_t). It is implementation-defined whether any extended alignments are supported and the storage durations for which they are supported. A type having an extended alignment requirement is an over-aligned type.61)
4
Alignments are represented as values of the type size_t. Valid alignments include only fundamental alignments, plus an additional implementation-defined set of values, which may be empty. Every valid alignment value shall be a nonnegative integral power of two.
5
Alignments have an order from weaker to stronger or stricter alignments. Stricter alignments have larger alignment values. An address that satisfies an alignment requirement also satisfies any weaker valid alignment requirement.
6
The alignment requirement of a complete type can be queried using an alignof expression. The types char, signed char, and unsigned char shall have the weakest alignment requirement.
7
Comparing alignments is meaningful and provides the obvious results: — Two alignments are equal when their numeric values are equal. — Two alignments are different when their numeric values are not equal. — When an alignment is larger than another it represents a stricter alignment.
6.2.9
Encodings
1
The literal encoding is an implementation-defined mapping of the characters of the execution character set to the values in a character constant (6.4.4.4) or string literal (6.4.5). It shall support a mapping from all the basic execution character set values into the implementation-defined encoding. It may contain multibyte character sequences (5.2.1.1).
2
The wide literal encoding is an implementation-defined mapping of the characters of the execution character set to the values in a wchar_t character constant (6.4.4.4) or a wchar_t string literal (6.4.5). It shall support a mapping from all the basic execution character set values into the implementationdefined encoding. The mapping shall produce values identical to the literal encoding for all the basic execution character set values if an implementation does not define __STDC_MB_MIGHT_NEQ_WC__. One or more values may map to one or more values of the extended execution character set.
6.3
Conversions
1
Several operators convert operand values from one type to another automatically. This subclause specifies the result required from such an implicit conversion, as well as those that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes the conversions performed by most ordinary operators; it is supplemented as required by the discussion of each operator in 6.5.
2
Unless explicitly stated otherwise, conversion of an operand value to a compatible type causes no change to the value or the representation. Forward references: cast operators (6.5.4).
6.3.1 1
Arithmetic operands
6.3.1.1 Boolean, characters, and integers Every integer type has an integer conversion rank defined as follows: 61) Every over-aligned type is, or contains, a structure or union type with a member to which an extended alignment has been applied.
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§ 6.3.1.1
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— No two signed integer types shall have the same rank, even if they have the same representation. — The rank of a signed integer type shall be greater than the rank of any signed integer type with less precision. — The rank of long long int shall be greater than the rank of long int, which shall be greater than the rank of int, which shall be greater than the rank of short int, which shall be greater than the rank of signed char. — The rank of a bit-precise signed integer type shall be greater than the rank of any standard integer type with less width or any bit-precise integer type with less width. — The rank of any unsigned integer type shall equal the rank of the corresponding signed integer type, if any. — The rank of any standard integer type shall be greater than the rank of any extended integer type with the same width or bit-precise integer type with the same width. — The rank of any bit-precise integer type relative to an extended integer type of the same width is implementation-defined. — The rank of char shall equal the rank of signed char and unsigned char. — The rank of bool shall be less than the rank of all other standard integer types. — The rank of any enumerated type shall equal the rank of the compatible integer type (see 6.7.2.2). — The rank of any extended signed integer type relative to another extended signed integer type with the same precision is implementation-defined, but still subject to the other rules for determining the integer conversion rank. — For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has greater rank than T3, then T1 has greater rank than T3. 2
The following may be used in an expression wherever an int or unsigned int may be used: — An object or expression with an integer type (other than int or unsigned int) whose integer conversion rank is less than or equal to the rank of int and unsigned int. — A bit-field of type bool, int, signed int, or unsigned int. The value from a bit-field of a bit-precise integer type is converted to the corresponding bit-precise integer type. If the original type is not a bit-precise integer type (6.2.5): if an int can represent all values of the original type (as restricted by the width, for a bit-field), the value is converted to an int62) ; otherwise, it is converted to an unsigned int. These are called the integer promotions63) . All other types are unchanged by the integer promotions.
3
The integer promotions preserve value including sign. As discussed earlier, whether a "plain" char can hold negative values is implementation-defined. Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers (6.7.2.1).
1
6.3.1.2 Boolean type When any scalar value is converted to bool, the result is false if the value is a zero (for arithmetic types), null (for pointer types), or the scalar has type nullptr_t; otherwise, the result is true. 62) E.g., unsigned _BitInt(7): 2 is a bit-field that can hold the values 0, 1, 2, 3, and converts to unsigned _BitInt(7). 63) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain argument expressions, to
the operands of the unary +, -, and ~ operators, and to both operands of the shift operators, as specified by their respective subclauses.
§ 6.3.1.2
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6.3.1.3 Signed and unsigned integers When a value with integer type is converted to another integer type other than bool, if the value can be represented by the new type, it is unchanged.
2
Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or subtracting one more than the maximum value that can be represented in the new type until the value is in the range of the new type.64)
3
Otherwise, the new type is signed and the value cannot be represented in it; either the result is implementation-defined or an implementation-defined signal is raised.
1
6.3.1.4 Real floating and integer When a finite value of standard floating type is converted to an integer type other than bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the behavior is undefined.65)
2
When a finite value of decimal floating type is converted to an integer type other than bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the "invalid" floating-point exception shall be raised and the result of the conversion is unspecified.
3
When a value of integer type is converted to a standard floating type, if the value being converted can be represented exactly in the new type, it is unchanged. If the value being converted is in the range of values that can be represented but cannot be represented exactly, the result is either the nearest higher or nearest lower representable value, chosen in an implementation-defined manner. If the value being converted is outside the range of values that can be represented, the behavior is undefined. Results of some implicit conversions may be represented in greater range and precision than that required by the new type (see 6.3.1.8 and 6.8.6.4).
4
When a value of integer type is converted to a decimal floating type, if the value being converted can be represented exactly in the new type, it is unchanged. If the value being converted cannot be represented exactly, the result shall be correctly rounded with exceptions raised as specified in IEC 60559.
1
6.3.1.5 Real floating types When a value of real floating type is converted to a real floating type, if the value being converted can be represented exactly in the new type, it is unchanged.
2
When a value of real floating type is converted to a standard floating type, if the value being converted is in the range of values that can be represented but cannot be represented exactly, the result is either the nearest higher or nearest lower representable value, chosen in an implementationdefined manner. If the value being converted is outside the range of values that can be represented, the behavior is undefined.
3
When a value of real floating type is converted to a decimal floating type, if the value being converted cannot be represented exactly, the result is correctly rounded with exceptions raised as specified in IEC 60559.
4
Results of some implicit conversions may be represented in greater range and precision than that required by the new type (see 6.3.1.8 and 6.8.6.4).
1
6.3.1.6 Complex types When a value of complex type is converted to another complex type, both the real and imaginary parts follow the conversion rules for the corresponding real types.
64) The rules describe arithmetic on the mathematical value, not the value of a given type of expression. 65) The remaindering operation performed when a value of integer type is converted to unsigned type need not be performed when a value of real floating type is converted to unsigned type. Thus, the range of portable real floating values is (−1, Utype_MAX + 1).
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§ 6.3.1.6
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1
2
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6.3.1.7 Real and complex When a value of real type is converted to a complex type, the real part of the complex result value is determined by the rules of conversion to the corresponding real type and the imaginary part of the complex result value is a positive zero or an unsigned zero. When a value of complex type is converted to a real type other than bool,66) the imaginary part of the complex value is discarded and the value of the real part is converted according to the conversion rules for the corresponding real type. 6.3.1.8 Usual arithmetic conversions Many operators that expect operands of arithmetic type cause conversions and yield result types in a similar way. The purpose is to determine a common real type for the operands and result. For the specified operands, each operand is converted, without change of type domain, to a type whose corresponding real type is the common real type. Unless explicitly stated otherwise, the common real type is also the corresponding real type of the result, whose type domain is the type domain of the operands if they are the same, and complex otherwise. This pattern is called the usual arithmetic conversions: If one operand has decimal floating type, the other operand shall not have standard floating, complex, or imaginary type. First, if the type of either operand is _Decimal128, the other operand is converted to _Decimal128.
Otherwise, if the type of either operand is _Decimal64, the other operand is converted to _Decimal64.
Otherwise, if the type of either operand is _Decimal32, the other operand is converted to _Decimal32.
Otherwise, if the corresponding real type of either operand is long double, the other operand is converted, without change of type domain, to a type whose corresponding real type is long double. Otherwise, if the corresponding real type of either operand is double, the other operand is converted, without change of type domain, to a type whose corresponding real type is double. Otherwise, if the corresponding real type of either operand is float, the other operand is converted, without change of type domain, to a type whose corresponding real type is float.67) Otherwise, the integer promotions are performed on both operands. Then the following rules are applied to the promoted operands: If both operands have the same type, then no further conversion is needed. Otherwise, if both operands have signed integer types or both have unsigned integer types, the operand with the type of lesser integer conversion rank is converted to the type of the operand with greater rank. Otherwise, if the operand that has unsigned integer type has rank greater or equal to the rank of the type of the other operand, then the operand with signed integer type is converted to the type of the operand with unsigned integer type. Otherwise, if the type of the operand with signed integer type can represent all the values of the type of the operand with unsigned integer type, then the operand with unsigned integer type is converted to the type of the operand with signed integer type. Otherwise, both operands are converted to the unsigned integer type corresponding to the type of the operand with signed integer type. 66) See 6.3.1.2. 67) For example, addition of a double _Complex and a float entails just the conversion of the float operand to double (and yields a double _Complex result).
§ 6.3.1.8
Language
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2
The values of floating operands and of the results of floating expressions may be represented in greater range and precision than that required by the type; the types are not changed thereby. See 5.2.4.2.2 regarding evaluation formats.
3
EXAMPLE 1 One consequence of _BitInt being exempt from the integer promotion rules (6.3.1) is that a _BitInt operand of a binary operator is not always promoted to an int or unsigned int as part of the usual arithmetic conversions. Instead, a lower-ranked operand is converted to the higher-rank operand type and the result of the operation is the higher-ranked type. _BitInt(2) a2 = 1; _BitInt(3) a3 = 2; _BitInt(33) a33 = 1; char c = 3; a2 * a3 /* As part of the multiplication, a2 is converted to _BitInt(3) and the result type is _BitInt(3). */ a2 * c /* As part of the multiplication, c is promoted to int, a2 is converted to int and the result type is int. */ a33 * c /* As part of the multiplication, c is promoted to int, then converted to _BitInt(33) and the result type is _BitInt(33), provided int has a width of at most 32 */ void func(_BitInt(8) a1, _BitInt(24) a2) { /* Cast one of the operands to 32-bits to guarantee the result of the multiplication can contain all possible values. */ _BitInt(32) a3 = a1 * (_BitInt(32))a2; }
6.3.2 1
Other operands
6.3.2.1 Lvalues, arrays, and function designators An lvalue is an expression (with an object type other than void) that potentially designates an object;68) if an lvalue does not designate an object when it is evaluated, the behavior is undefined. When an object is said to have a particular type, the type is specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that does not have array type, does not have an incomplete type, does not have a const-qualified type, and if it is a structure or union, does not have any member (including, recursively, any member or element of all contained aggregates or unions) with a const-qualified type.
2
Except when it is the operand of the sizeof operator, or the typeof operators, the unary & operator, the ++ operator, the -- operator, or the left operand of the . operator or an assignment operator, an lvalue that does not have array type is converted to the value stored in the designated object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has qualified type, the value has the unqualified version of the type of the lvalue; additionally, if the lvalue has atomic type, the value has the non-atomic version of the type of the lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete type and does not have array type, the behavior is undefined. If the lvalue designates an object of automatic storage duration that could have been declared with the register storage class (never had its address taken), and that object is uninitialized (not declared with an initializer and no assignment to it has been performed prior to use), the behavior is undefined.
3
Except when it is the operand of the sizeof operator, or typeof operators, or the unary & operator, or is a string literal used to initialize an array, an expression that has type "array of type" is converted to an expression with type "pointer to type" that points to the initial element of the array object and 68) The name "lvalue" comes originally from the assignment expression E1 = E2, in which the left operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an object "locator value". What is sometimes called "rvalue" is in this document described as the "value of an expression". An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
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§ 6.3.2.1
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is not an lvalue. If the array object has register storage class, the behavior is undefined. 4
A function designator is an expression that has function type. Except when it is the operand of the sizeof operator69) , a typeof operator, or the unary & operator, a function designator with type "function returning type" is converted to an expression that has type "pointer to function returning type". Forward references: address and indirection operators (6.5.3.2), assignment operators (6.5.16), common definitions <stddef.h> (7.21), initialization (6.7.10), postfix increment and decrement operators (6.5.2.4), prefix increment and decrement operators (6.5.3.1), the sizeof and alignof operators (6.5.3.4), structure and union members (6.5.2.3).
1
1
6.3.2.2 void The (nonexistent) value of a void expression (an expression that has type void) shall not be used in any way, and implicit or explicit conversions (except to void) shall not be applied to such an expression. If an expression of any other type is evaluated as a void expression, its value or designator is discarded. (A void expression is evaluated for its side effects.) 6.3.2.3 Pointers A pointer to void may be converted to or from a pointer to any object type. A pointer to any object type may be converted to a pointer to void and back again; the result shall compare equal to the original pointer.
2
For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to the q-qualified version of the type; the values stored in the original and converted pointers shall compare equal.
3
An integer constant expression with the value 0, such an expression cast to type void *, or the predefined constant nullptr is called a null pointer constant70) . If a null pointer constant or a value of the type nullptr_t (which is necessarily the value nullptr) is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.
4
Conversion of a null pointer to another pointer type yields a null pointer of that type. Any two null pointers shall compare equal.
5
An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might produce an indeterminate representation when stored into an object.71)
6
Any pointer type may be converted to an integer type. Except as previously specified, the result is implementation-defined. If the result cannot be represented in the integer type, the behavior is undefined. The result need not be in the range of values of any integer type.
7
A pointer to an object type may be converted to a pointer to a different object type. If the resulting pointer is not correctly aligned72) for the referenced type, the behavior is undefined. Otherwise, when converted back again, the result shall compare equal to the original pointer. When a pointer to an object is converted to a pointer to a character type, the result points to the lowest addressed byte of the object. Successive increments of the result, up to the size of the object, yield pointers to the remaining bytes of the object.
8
A pointer to a function of one type may be converted to a pointer to a function of another type and back again; the result shall compare equal to the original pointer. If a converted pointer is used to call a function whose type is not compatible with the referenced type, the behavior is undefined.
69) Because this conversion does not occur, the operand of the sizeof operator remains a function designator and violates the constraints in 6.5.3.4 70) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.21. 71) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to be consistent with the addressing structure of the execution environment. 72) In general, the concept "correctly aligned" is transitive: if a pointer to type A is correctly aligned for a pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is correctly aligned for a pointer to type C.
§ 6.3.2.3
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6.3.2.4 nullptr_t The type nullptr_t may be converted to void, bool or to a pointer type; The result is a void expression, false, or a null pointer value, respectively.
2
A null pointer constant or value of type nullptr_t may be converted to nullptr_t. Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types capable of holding object pointers (7.22.1.4), simple assignment (6.5.16.1), the nullptr_t type (7.21.2).
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§ 6.3.2.4
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Lexical elements
Syntax token: keyword identifier constant string-literal punctuator preprocessing-token: header-name identifier pp-number character-constant string-literal punctuator each universal-character-name that cannot be one of the above each non-white-space character that cannot be one of the above
2
3
Constraints Each preprocessing token that is converted to a token shall have the lexical form of a keyword, an identifier, a constant, a string literal, or a punctuator. A single universal character name shall match one of the other preprocessing token categories. Semantics A token is the minimal lexical element of the language in translation phases 7 and 8. The categories of tokens are: keywords, identifiers, constants, string literals, and punctuators. A preprocessing token is the minimal lexical element of the language in translation phases 3 through 6. The categories of preprocessing tokens are: header names, identifiers, preprocessing numbers, character constants, string literals, punctuators, and both single universal character names as well as single non-whitespace characters that do not lexically match the other preprocessing token categories.73) If a ’ or a " character matches the last category, the behavior is undefined. Preprocessing tokens can be separated by white space; this consists of comments (described later), or white-space characters (space, horizontal tab, new-line, vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances during translation phase 4, white space (or the absence thereof) serves as more than preprocessing token separation. White space may appear within a preprocessing token only as part of a header name or between the quotation characters in a character constant or string literal.
4
If the input stream has been parsed into preprocessing tokens up to a given character, the next preprocessing token is the longest sequence of characters that could constitute a preprocessing token. There is one exception to this rule: header name preprocessing tokens are recognized only within # include and #embed preprocessing directives, in __has_include and __has_embed expressions, as well as in implementation-defined locations within #pragma directives. In such contexts, a sequence of characters that could be either a header name or a string literal is recognized as the former.
5
EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or not E is a macro name.
6
EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on increment operators, even though the parse x ++ + ++ y might yield a correct expression. 73) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.4.3); it cannot occur in source files.
§ 6.4
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Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5), floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.4), postfix increment and decrement operators (6.5.2.4), prefix increment and decrement operators (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals (6.4.5).
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§ 6.4
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Keywords
Syntax keyword: one of alignas alignof auto bool break case char const constexpr continue default do double else
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enum extern false float for goto if inline int long nullptr register restrict return
short signed sizeof static static_assert struct switch thread_local true typedef typeof typeof_unqual union unsigned
void volatile while _Atomic _BitInt _Complex _Decimal128 _Decimal32 _Decimal64 _Generic _Imaginary _Noreturn
Semantics The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as keywords except in an attribute token, and shall not be used otherwise. The keyword _Imaginary is reserved for specifying imaginary types.74) The following table provides alternate spellings for certain keywords. These can be used wherever the keyword can.75) Keyword
Alternative Spelling
alignas alignof bool static_assert thread_local
_Alignas _Alignof _Bool _Static_assert _Thread_local
The spelling of these keywords, their alternate forms, and of false and true inside expressions that are subject to the # and ## preprocessing operators is unspecified.76)
6.4.2
1
Identifiers
6.4.2.1 General Syntax identifier: identifier-start identifier identifier-continue
identifier-start: nondigit XID_Start character universal-character-name of class XID_Start
74) One possible specification for imaginary types appears in Annex G. 75) These alternative keywords are obsolescent features and should not be used for new code and development. 76) The intent of this specification is to allow but not force the implementation of the corresponding feature by means of a predefined macro.
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identifier-continue: digit nondigit XID_Continue character universal-character-name of class XID_Continue
nondigit: one of _ a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
digit: one of 0 1 2 3 4 5 6 7 8 9
2
Semantics An XID_Start character is an implementation-defined character whose corresponding code point in ISO/IEC 10646 has the XID_Start property. An XID_Continue character is an implementationdefined character whose corresponding code point in ISO/IEC 10646 has the XID_Continue property. An identifier is a sequence of one identifier start character followed by 0 or more identifier continue characters, which designates one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct. There is no specific limit on the maximum length of an identifier.
3
The character classes XID_Start and XID_Continue are Derived Core Properties as described by UAX #4477) . Each character and universal character name in an identifier shall designate a character whose encoding in ISO/IEC 10646 has the XID_Continue property. The initial character (which may be a universal character name) shall designate a character whose encoding in ISO/IEC 10646 has the XID_Start property. An identifier shall conform to Normalization Form C as specified in ISO/IEC 10646. Annex D provides an overview of the conforming identifiers.
4
NOTE 1 Uppercase and lowercase letters are considered different for all identifiers.
5
NOTE 2 In translation phase 4 (4), the term identifier also includes those preprocessing tokens (6.4.8) differentiated as keywords (6.4.1) in the later translation phase 7 (7).
6
When preprocessing tokens are converted to tokens during translation phase 7, if a preprocessing token could be converted to either a keyword or an identifier, it is converted to a keyword except in an attribute token.
7
Some identifiers are reserved. — All identifiers that begin with a double underscore (__) or begin with an underscore (_) followed by an uppercase letter are reserved for any use, except those identifiers which are lexically identical to keywords.78) — All identifiers that begin with an underscore are reserved for use as identifiers with file scope in both the ordinary and tag name spaces. Other identifiers may be reserved, see 7.1.3.
8
If the program declares or defines an identifier in a context in which it is reserved (other than as allowed by 7.1.4), the behavior is undefined. 77) On systems that cannot accept extended characters in external identifiers, an encoding of the universal-character-name may be used in forming such identifiers. For example, some otherwise unused character or sequence of characters may be used to encode the u in a universal character name. 78) This allows a reserved identifier that matches the spelling of a keyword to be used as a macro name by the program.
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9
If the program defines a reserved identifier or standard attribute token described in 6.7.12.1 as a macro name, or removes (with #undef) any macro definition of an identifier in the first group listed above or standard attribute token described in 6.7.12.1, the behavior is undefined.
10
Some identifiers may be potentially reserved. A potentially reserved identifier is an identifier which is not reserved unless made so by an implementation providing the identifier (7.1.3) but is anticipated to become reserved by an implementation or a future version of this document. An identifier that this document describes as optional: — If it is defined as a macro it is reserved. — Otherwise, if the definition is given in clauses 1 to 6 it is reserved. — Otherwise, it is potentially reserved.
11
12
13
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Recommended Practice Implementations are encouraged to issue a diagnostic message when a potentially reserved identifier is declared or defined for any use that is not implementation-compatible (see below) in a context where the potentially reserved identifier may be reserved under a conforming implementation. This brings attention to a potential conflict when porting a program to a future revision of this document. An implementation-compatible use of a potentially reserved identifier is a declaration of an external name where the name is provided by the implementation as an external name and where the declaration declares an object or function with a type that is compatible with the type of the object or function provided by the implementation under that name. Implementation limits As discussed in 5.2.4.1, an implementation may limit the number of significant initial characters in an identifier; the limit for an external name (an identifier that has external linkage) may be more restrictive than that for an internal name (a macro name or an identifier that does not have external linkage). The number of significant characters in an identifier is implementation-defined. Any identifiers that differ in a significant character are different identifiers. If two identifiers differ only in nonsignificant characters, the behavior is undefined. Forward references: universal character names (6.4.3), macro replacement (6.10.4), reserved library identifiers (7.1.3), use of library functions (7.1.4), attributes (6.7.12.1).
1
6.4.2.2 Predefined identifiers Semantics The identifier __func__ shall be implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically-enclosing function.79) 2
This name is encoded as if the implicit declaration had been written in the source character set and then translated into the execution character set as indicated in translation phase 5.
3
EXAMPLE Consider the code fragment: #include <stdio.h> void myfunc(void) { printf("%s\n", __func__); /* ... */ } 79) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other identifier is explicitly declared using the name __func__, the behavior is undefined.
§ 6.4.2.2
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Each time the function is called, it will print to the standard output stream: myfunc
Forward references: function definitions (6.9.1).
6.4.3 1
Universal character names
Syntax universal-character-name: \u hex-quad \U hex-quad hex-quad hex-quad: hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
2
Constraints A universal character name shall not designate a code point where the hexadecimal value is: — less than 00A0 other than 0024 ($), 0040 (@), or 0060 (` ); — in the range D800 through DFFF inclusive; or — greater than 10FFFF80) .
3
4
Description Universal character names may be used in identifiers, character constants, and string literals to designate characters that are not in the basic character set. Semantics The universal character name \U nnnnnnnn designates the character whose eight-digit short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.81) Similarly, the universal character name \u nnnn designates the character whose four-digit short identifier is nnnn (and whose eight-digit short identifier is 0000nnnn).
80) The disallowed characters are the characters in the basic character set and the code positions reserved by ISO/IEC 10646 for control characters, the character DELETE, the S-zone (reserved for use by UTF-16), and characters too large to be encoded by ISO/IEC 10646. Disallowed universal character escape sequences can still be specified with hexadecimal and octal escape sequences (6.4.4.4). 81) Short identifiers for characters were first specified in ISO/IEC 10646–1:1993/Amd 9:1997.
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Constants
Syntax constant: integer-constant floating-constant enumeration-constant character-constant predefined-constant
2
3
1
Constraints Each constant shall have a type and the value of a constant shall be in the range of representable values for its type. Semantics Each constant has a type, determined by its form and value, as detailed later. 6.4.4.1 Integer constants Syntax integer-constant: decimal-constant integer-suffixopt octal-constant integer-suffixopt hexadecimal-constant integer-suffixopt binary-constant integer-suffixopt
decimal-constant: nonzero-digit decimal-constant ’opt digit
octal-constant: 0
octal-constant ’opt octal-digit
hexadecimal-constant: hexadecimal-prefix hexadecimal-digit-sequence binary-constant: binary-prefix binary-digit binary-constant ’opt binary-digit
hexadecimal-prefix: one of 0x 0X
binary-prefix: one of 0b 0B
§ 6.4.4.1
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nonzero-digit: one of 1 2 3 4 5 6 7 8 9
octal-digit: one of 0 1 2 3 4 5 6 7
hexadecimal-digit-sequence: hexadecimal-digit hexadecimal-digit-sequence ’opt hexadecimal-digit hexadecimal-digit: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
binary-digit: one of 0 1
integer-suffix: unsigned-suffix long-suffixopt unsigned-suffix long-long-suffix unsigned-suffix bit-precise-int-suffix long-suffix unsigned-suffixopt long-long-suffix unsigned-suffixopt bit-precise-int-suffix unsigned-suffixopt
bit-precise-int-suffix: one of wb WB
unsigned-suffix: one of u U
long-suffix: one of l L
long-long-suffix: one of ll LL
2
Description An integer constant begins with a digit, but has no period or exponent part. It may have a prefix that specifies its base and a suffix that specifies its type. An optional separating single quote character (’) in an integer or floating constant is called a digit separator. Digit separators are ignored when determining the value of the constant. 58
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§ 6.4.4.1
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EXAMPLE The following integer constants use digit separators; the comment associated with each constant shows the equivalent constant without digit separators. 0b11’10’11’01 /* 0b11101101 */ ’1’2 /* character constant ’1’ followed by integer constant 2, not the integer constant 12 */ 11’22 /* 1122 */ 0x’FFFF’FFFF /* invalid hexadecimal constant (’ cannot appear after 0x) */ 0x1’2’3’4AB’C’D /* 0x1234ABCD */
4
5
6
A decimal constant begins with a nonzero digit and consists of a sequence of decimal digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed by a sequence of the decimal digits and the letters a (or A) through f (or F) with values 10 through 15 respectively. A binary constant consists of the prefix 0b or 0B followed by a sequence of the digits 0 or 1. Semantics The value of a decimal constant is computed base 10; that of an octal constant, base 8; that of a hexadecimal constant, base 16; that of a binary constant, base 2. The lexically first digit is the most significant. The type of an integer constant is the first of the corresponding list in which its value can be represented. Decimal Constant
u or U
unsigned int unsigned long int unsigned long long int long int long long int
Both u or U and l or L ll or LL
unsigned long int unsigned long long int long long int
Both u or U and ll or LL wb or WB
unsigned long long int
int unsigned int long int unsigned long int long long int unsigned long long int unsigned int unsigned long int unsigned long long int long int unsigned long int long long int unsigned long long int unsigned long int unsigned long long int long long int unsigned long long int unsigned long long int
_BitInt(N) where the width N
_BitInt(N) where the width N
is the smallest N greater than 1 which can accommodate the value and the sign bit. unsigned _BitInt(N) where the width N is the smallest N greater than 0 which can accommodate the value.
is the smallest N greater than 1 which can accommodate the value and the sign bit. unsigned _BitInt(N) where the width N is the smallest N greater than 0 which can accommodate the value.
l or L
Both u or U and wb or WB
7
Octal, Hexadecimal or Binary Constant
Suffix none
int long int long long int
If an integer constant that does not have suffixes wb, WB, uwb, or UWB cannot be represented by any type in its list, it may have an extended integer type, if the extended integer type can represent its value. If all the types in the list for the constant are signed, the extended integer type shall be signed. If all the types in the list for the constant are unsigned, the extended integer type shall be unsigned. § 6.4.4.1
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If the list contains both signed and unsigned types, the extended integer type may be signed or unsigned. If an integer constant cannot be represented by any type in its list and has no extended integer type, then the integer constant has no type. 8
EXAMPLE 1 The wb suffix results in an _BitInt that includes space for the sign bit even if the value of the constant is positive or was specified in hexadecimal or octal notation. -3wb /* Yields an _BitInt(3) that is then negated; two value bits, one sign bit */ -0x3wb /* Yields an _BitInt(3) that is then negated; two value bits, one sign bit */ 3wb /* Yields an _BitInt(3); two value bits, one sign bit */ 3uwb /* Yields an unsigned _BitInt(2) */ -3uwb /* Yields an unsigned _BitInt(2) that is then negated, resulting in wraparound */
Forward references: preprocessing numbers (6.4.8), numeric conversion functions (7.24.1).
1
6.4.4.2 Floating constants Syntax floating-constant: decimal-floating-constant hexadecimal-floating-constant
decimal-floating-constant: fractional-constant exponent-partopt floating-suffixopt digit-sequence exponent-part floating-suffixopt
hexadecimal-floating-constant: hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-part floating-suffixopt hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-suffixopt
fractional-constant: digit-sequenceopt . digit-sequence digit-sequence .
exponent-part: e signopt digit-sequence E signopt digit-sequence
sign: one of + -
digit-sequence: digit digit-sequence ’opt digit
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hexadecimal-fractional-constant: hexadecimal-digit-sequenceopt . hexadecimal-digit-sequence hexadecimal-digit-sequence .
binary-exponent-part: p signopt digit-sequence P signopt digit-sequence
floating-suffix: one of f l F L df dd dl DF DD DL
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3
4
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Constraints A floating suffix df, dd, dl, DF, DD, or DL shall not be used in a hexadecimal floating constant. Description A floating constant has a significand part that may be followed by an exponent part and a suffix that specifies its type. The components of the significand part may include a digit sequence representing the whole-number part, followed by a period ( .), followed by a digit sequence representing the fraction part. Digit separators (6.4.4.1) are ignored when determining the value of the constant. The components of the exponent part are an e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence. Either the whole-number part or the fraction part has to be present; for decimal floating constants, either the period or the exponent part has to be present. Semantics The significand part is interpreted as a (decimal or hexadecimal) rational number; the digit sequence in the exponent part is interpreted as a decimal integer. For decimal floating constants, the exponent indicates the power of 10 by which the significand part is to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2 by which the significand part is to be scaled. For decimal floating constants, and also for hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either the nearest representable value, or the larger or smaller representable value immediately adjacent to the nearest representable value, chosen in an implementation-defined manner. For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is correctly rounded. An unsuffixed floating constant has type double. If suffixed by a floating suffix it has a type according to the following table: Suffixes for floating constants Suffix f, F l, L df, DF dd, DD dl, DL
6
Type float long double _Decimal32 _Decimal64 _Decimal128
The values of floating constants may be represented in greater range and precision than that required by the type (determined by the suffix); the types are not changed thereby. See 5.2.4.2.2 regarding evaluation formats. 82) 82) Hexadecimal floating constants can be used to obtain exact values in the semantic type that are independent of the
§ 6.4.4.2
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Floating constants of decimal floating type that have the same numerical value but different quantum exponents have distinguishable internal representations. The value shall be correctly rounded as specified in IEC 60559. The coefficient c and the quantum exponent q of a finite converted decimal floating-point number (see 5.2.4.2.3) are determined as follows: — q is set to the value of signopt digit-sequence in the exponent part, if any, or to 0, otherwise. — If there is a fractional constant, q is decreased by the number of digits to the right of the period and the period is removed to form a digit sequence. — c is set to the value of the digit sequence (after any period has been removed). — Rounding required because of insufficient precision or range in the type of the result will round c to the full precision available in the type, and will adjust q accordingly within the limits of the type, provided the rounding does not yield an infinity (in which case the result is an appropriately signed internal representation of infinity). If the full precision of the type would require q to be smaller than the minimum for the type, then q is pinned at the minimum and c is adjusted through the subnormal range accordingly, perhaps to zero.
8
Floating constants are converted to internal format as if at translation-time. The conversion of a floating constant shall not raise an exceptional condition or a floating-point exception at execution time. All floating constants of the same source form 83) shall convert to the same internal format with the same value.
9
EXAMPLE Following are floating constants of type _Decimal64 and their values as triples (s, c, q). Note that for _Decimal64, the precision (maximum coefficient length) is 16 and the quantum exponent range is −398 ≤ q ≤ 369. 0.dd 0.00dd 123.dd 1.23E3dd 1.23E+3dd 12.3E+7dd 12.0dd 12.3dd 0.00123dd 1.23E-12dd 1234.5E-4dd 0E+7dd 12345678901234567890.dd 1234E-400dd 1234E-402dd 1000.dd .0001dd 1000.e0dd .0001e0dd 1000.0dd 0.0001dd 1000.00dd 00.0001dd
(+1, 0, 0) (+1, 0, −2) (+1, 123, 0) (+1, 123, 1) (+1, 123, 1) (+1, 123, 6) (+1, 120, −1) (+1, 123, −1) (+1, 123, −5) (+1, 123, −14) (+1, 12345, −5) (+1, 0, 7) (+1, 1234567890123457, 4) assuming default rounding and DEC_EVAL_METHOD is 0 or 184) (+1, 12, −398) assuming default rounding and DEC_EVAL_METHOD is 0 or 1 (+1, 0, −398) assuming default rounding and DEC_EVAL_METHOD is 0 or 1 (+1, 1000, 0) (+1, 1, −4) (+1, 1000, 0) (+1, 1, −4) (+1, 10000, −1) (+1, 1, −4) (+1, 100000, −2) (+1, 1, −4)
evaluation format. Casts produce values in the semantic type, though depend on the rounding mode and may raise the inexact floating-point exception. 83) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not convert to the same internal format and value.
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001000.dd 001000.0dd 001000.00dd 00.00dd 00.dd .00dd 00.00e-5dd 00.e-5dd .00e-5dd
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(+1, 1000, 0) (+1, 10000, −1) (+1, 100000, −2) (+1, 0, −2) (+1, 0, 0) (+1, 0, −2) (+1, 0, −7) (+1, 0, −5) (+1, 0, −7)
Recommended practice The implementation should produce a diagnostic message if a hexadecimal constant cannot be represented exactly in its evaluation format; the implementation should then proceed with the translation of the program.
11
The translation-time conversion of floating constants should match the execution-time conversion of character strings by library functions, such as strtod, given matching inputs suitable for both conversions, the same result format, and default execution-time rounding. 85)
12
NOTE 1 Floating constants do not include a sign and are negated by the unary - operator (6.5.3.3) which negates the rounded value of the constant. In contrast, the numeric conversion functions in the strto family (7.24.1.5, 7.24.1.6) may include the sign as part of the input value and convert and round the negated input; Annex F requires this behavior. Negating before rounding and negating after rounding might yield different results, depending on the rounding direction and whether the results are correctly rounded. For example, the results are the same when both are correctly rounded using rounding to nearest or rounding toward zero, but the results are different when they are inexact and correctly rounded using rounding toward positive infinity or rounding toward negative infinity. Conversions yielding exact results require no rounding, so are not affected by the order of negating and rounding. For types with radix 10, decimal floating constants expressed within the precision and range of the evaluation format convert exactly. For types whose radix is a power of 2, hexadecimal floating constants expressed within the precision and range of the evaluation format convert exactly.
Forward references: preprocessing numbers (6.4.8), numeric conversion functions (7.24.1), the strto function family (7.24.1.5, 7.24.1.6).
1
2
3
6.4.4.3 Enumeration constants Syntax enumeration-constant: identifier Semantics An identifier declared as an enumeration constant for an enumeration without a fixed underlying type has either type int or the enumerated type, as defined in 6.7.2.2. An identifier declared as an enumeration constant for an enumeration with a fixed underlying type has the associated enumerated type. An enumeration constant may be used in an expression (or constant expression) wherever a value of an integer type may be used. Forward references: enumeration specifiers (6.7.2.2).
1
6.4.4.4 Character constants Syntax character-constant: encoding-prefixopt ’ c-char-sequence ’ 84) That is, assuming the default translation rounding-direction mode is not changed by an FENV_DEC_ROUND pragma (7.6.3). 85) The specification for the library functions recommends more accurate conversion than required for floating constants (see 7.24.1.5).
§ 6.4.4.4
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encoding-prefix: one of u8
u
U
L
c-char-sequence: c-char c-char-sequence c-char c-char: any member of the source character set except the single-quote ’, backslash \, or new-line character escape-sequence
escape-sequence: simple-escape-sequence octal-escape-sequence hexadecimal-escape-sequence universal-character-name
simple-escape-sequence: one of \’ \" \? \\ \a \b \f \n \r \t \v
octal-escape-sequence: \ octal-digit \ octal-digit octal-digit \ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence: \x hexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit
2
3
Description An integer character constant is a sequence of one or more multibyte characters enclosed in singlequotes, as in ’x’. A UTF-8 character constant is the same, except prefixed by u8. A wchar_t character constant is prefixed by the letter L. A UTF-16 character constant is prefixed by the letter u. A UTF-32 character constant is prefixed by the letter U. Collectively, wchar_t, UTF-16, and UTF-32 character constants are called wide character constants. With a few exceptions detailed later, the elements of the sequence are any members of the source character set; they are mapped in an implementationdefined manner to members of the execution character set. The single-quote ’, the double-quote ", the question-mark ?, the backslash \, and arbitrary integer values are representable according to the following table of escape sequences: single quote ’ double quote " question mark ? backslash \ octal character hexadecimal character 64
\’ \" \? \\ \ octal digits \x hexadecimal digits
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4
The double-quote " and question-mark ? are representable either by themselves or by the escape sequences \" and \?, respectively, but the single-quote ’ and the backslash \ shall be represented, respectively, by the escape sequences \’ and \\.
5
The octal digits that follow the backslash in an octal escape sequence are taken to be part of the construction of a single character for an integer character constant or of a single wide character for a wide character constant. The numerical value of the octal integer so formed specifies the value of the desired character or wide character.
6
The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape sequence are taken to be part of the construction of a single character for an integer character constant or of a single wide character for a wide character constant. The numerical value of the hexadecimal integer so formed specifies the value of the desired character or wide character.
7
Each octal or hexadecimal escape sequence is the longest sequence of characters that can constitute the escape sequence.
8
In addition, characters not in the basic character set are representable by universal character names and certain non-graphic characters are representable by escape sequences consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t, and \v.86)
9
Constraints The value of an octal or hexadecimal escape sequence shall be in the range of representable values for the corresponding type: Prefix none u8 L u U
10
11
Corresponding Type unsigned char char8_t
the unsigned type corresponding to wchar_t char16_t char32_t
A UTF-8, UTF-16, or UTF-32 character constant shall not contain more than one character.87) The value shall be representable with a single UTF-8, UTF-16, or UTF-32 code unit, respectively. Semantics An integer character constant has type int. The value of an integer character constant containing a single character that maps to a single value in the literal encoding (6.2.9) is the numerical value of the representation of the mapped character in the literal encoding interpreted as an integer. The value of an integer character constant containing more than one character (e.g., ’ab’), or containing a character or escape sequence that does not map to a single value in the literal encoding, is implementation-defined. If an integer character constant contains a single character or escape sequence, its value is the one that results when an object with type char whose value is that of the single character or escape sequence is converted to type int.
12
A UTF-8 character constant has type char8_t. If the UTF-8 character constant is not produced through a hexadecimal or octal escape sequence, the value of a UTF-8 character constant is equal to its ISO/IEC 10646 code point value, provided that the code point value can be encoded as a single UTF-8 code unit. Otherwise, the value of the UTF-8 character constant is the numeric value specified in the hexadecimal or octal escape sequence.
13
A UTF-16 character constant has type char16_t which is an unsigned integer type defined in the <uchar.h> header. If the UTF-16 character constant is not produced through a hexadecimal or octal escape sequence, the value of a UTF-16 character constant is equal to its ISO/IEC 10646 code point value, provided that the code point value can be encoded as a single UTF-16 code unit. Otherwise, the value of the UTF-16 character constant is the numeric value specified in the hexadecimal or octal escape sequence.
14
A UTF-32 character constant has type char32_t which is an unsigned integer type defined in the 86) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash, the result is not a
token and a diagnostic is required. See "future language directions" (6.11.4). 87) For example u8’ab’ violates this constraint.
§ 6.4.4.4
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<uchar.h> header. If the UTF-32 character constant is not produced through a hexadecimal or octal
escape sequence, the value of a UTF-32 character constant is equal to its ISO/IEC 10646 code point value, provided that the code point value can be encoded as a single UTF-32 code unit. Otherwise, the value of the UTF-32 character constant is the numeric value specified in the hexadecimal or octal escape sequence. 15
A wchar_t character constant prefixed by the letter L has type wchar_t, an integer type defined in the <stddef.h> header. The value of a wchar_t character constant containing a single multibyte character that maps to a single member of the extended execution character set is the wide character corresponding to that multibyte character in the implementation-defined wide literal encoding (6.2.9). The value of a wchar_t character constant containing more than one multibyte character or a single multibyte character that maps to multiple members of the extended execution character set, or containing a multibyte character or escape sequence not represented in the extended execution character set, is implementation-defined.
16
EXAMPLE 1 The construction ’\0’ is commonly used to represent the null character.
17
EXAMPLE 2 Consider implementations that use eight bits for objects that have type char. In an implementation in which type char has the same range of values as signed char, the integer character constant ’\xFF’ has the value −1; if type char has the same range of values as unsigned char, the character constant ’\xFF’ has the value +255.
18
EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction ’\x123’ specifies an integer character constant containing only one character, since a hexadecimal escape sequence is terminated only by a non-hexadecimal character. To specify an integer character constant containing the two characters whose values are ’\x12’ and ’3’, the construction ’\0223’ can be used, since an octal escape sequence is terminated after three octal digits. (The value of this twocharacter integer character constant is implementation-defined.)
19
EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction L’\1234’ specifies the implementation-defined value that results from the combination of the values 0123 and ’4’. Forward references: common definitions <stddef.h> (7.21), the mbtowc function (7.24.7.2), Unicode utilities <uchar.h> (7.30).
1
6.4.4.5 Predefined constants Syntax predefined-constant: false true nullptr
2
Description Some keywords represent constants of a specific value and type.
3
The keywords false and true are constants of type bool with a value of 0 for false and 1 for true88) .
4
The keyword nullptr represents a null pointer constant. Details of its type are described in 7.21.2.
6.4.5 1
String literals
Syntax string-literal: encoding-prefixopt " s-char-sequenceopt "
88) The constants false and true promote to type int, see 6.3.1.1. When used for arithmetic, in translation phase 4, they are signed values and the result of such arithmetic is consistent with the results of later translation phases.
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s-char-sequence: s-char s-char-sequence s-char
s-char: any member of the source character set except the double-quote ", backslash \, or new-line character escape-sequence
2
3
4
5
Constraints If a sequence of adjacent string literal tokens includes prefixed string literal tokens, the prefixed tokens shall all have the same prefix. Description A character string literal is a sequence of zero or more multibyte characters enclosed in double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8. A wchar_t string literal is the same, except prefixed by L. A UTF-16 string literal is the same, except prefixed by u. A UTF-32 string literal is the same, except prefixed by U. Collectively, wchar_t, UTF-16, and UTF-32 string literals are called wide string literals. The same considerations apply to each element of the sequence in a string literal as if it were in an integer character constant (for a character or UTF-8 string literal) or a wide character constant (for a wide string literal), except that the single-quote ’ is representable either by itself or by the escape sequence \’, but the double-quote " shall be represented by the escape sequence \". Semantics In translation phase 6, the multibyte character sequences specified by any sequence of adjacent character and identically-prefixed string literal tokens are concatenated into a single multibyte character sequence. If any of the tokens has an encoding prefix, the resulting multibyte character sequence is treated as having the same prefix; otherwise, it is treated as a character string literal.
6
In translation phase 7, a byte or code of value zero is appended to each multibyte character sequence that results from a string literal or literals. 89) The multibyte character sequence is then used to initialize an array of static storage duration and length just sufficient to contain the sequence. For character string literals, the array elements have type char, and are initialized with the individual bytes of the multibyte character sequence corresponding to the literal encoding (6.2.9). For UTF-8 string literals, the array elements have type char8_t, and are initialized with the characters of the multibyte character sequence, as encoded in UTF-8. For wide string literals prefixed by the letter L, the array elements have type wchar_t and are initialized with the sequence of wide characters corresponding to the wide literal encoding. For wide string literals prefixed by the letter u or U, the array elements have type char16_t or char32_t, respectively, and are initialized sequence of wide characters corresponding to UTF-16 and UTF-32 encoded text, respectively. The value of a string literal containing a multibyte character or escape sequence not represented in the execution character set is implementation-defined. Any hexadecimal escape sequence or octal escape sequence specified in a u8, u, or U string specifies a single char8_t, char16_t, or char32_t value and may result in the full character sequence not being valid UTF-8, UTF-16, or UTF-32.
7
It is unspecified whether these arrays are distinct provided their elements have the appropriate values. If the program attempts to modify such an array, the behavior is undefined.
8
EXAMPLE 1 This pair of adjacent character string literals "\x12" "3"
89) A string literal might not be a string (see 7.1.1), because a null character can be embedded in it by a \0 escape sequence.
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produces a single character string literal containing the two characters whose values are ’\x12’ and ’3’, because escape sequences are converted into single members of the execution character set just prior to adjacent string literal concatenation. 9
EXAMPLE 2 Each of the sequences of adjacent string literal tokens "a" "b" L"c" "a" L"b" "c" L"a" "b" L"c" L"a" L"b" L"c"
is equivalent to the string literal L"abc"
Likewise, each of the sequences "a" "b" u"c" "a" u"b" "c" u"a" "b" u"c" u"a" u"b" u"c"
is equivalent to u"abc"
Forward references: common definitions <stddef.h> (7.21), the mbstowcs function (7.24.8.1), Unicode utilities <uchar.h> (7.30).
6.4.6 1
Punctuators
Syntax punctuator: one of [ ] ( ) { } . -> ++ -- & * + - ~ ! / % << >> < > <= >= ? : :: ; ... = *= /= %= += -= <<= , # ## <: :> <% %> %: %:%:
2
3
==
!=
>>=
&=
^
|
&&
^=
|=
||
Semantics A punctuator is a symbol that has independent syntactic and semantic significance. Depending on context, it may specify an operation to be performed (which in turn may yield a value or a function designator, produce a side effect, or some combination thereof) in which case it is known as an operator (other forms of operator also exist in some contexts). An operand is an entity on which an operator acts. In all aspects of the language, the six tokens90) <:
:>
<%
%>
%:
%:%:
behave, respectively, the same as the six tokens [
]
{
}
#
##
except for their spelling.91) 90) These tokens are sometimes called "digraphs". 91) Thus [ and <: behave differently when "stringized" (see 6.10.4.2), but can otherwise be freely interchanged.
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Forward references: expressions (6.5), declarations (6.7), preprocessing directives (6.10), statements (6.8).
6.4.7 1
Header names
Syntax header-name: < h-char-sequence > " q-char-sequence "
h-char-sequence: h-char h-char-sequence h-char
h-char: any member of the source character set except the new-line character and >
q-char-sequence: q-char q-char-sequence q-char
q-char: any member of the source character set except the new-line character and "
2
3
Semantics The sequences in both forms of header names are mapped in an implementation-defined manner to headers or external source file names as specified in 6.10.2. If the characters ’, \, ", //, or /* occur in the sequence between the < and > delimiters, the behavior is undefined. Similarly, if the characters ’, \, //, or /* occur in the sequence between the " delimiters, the behavior is undefined.92) Header name preprocessing tokens are recognized only within #include and #embed preprocessing directives, in __has_include and __has_embed expressions, as well as in implementation-defined locations within #pragma directives.93)
4
EXAMPLE The following sequence of characters: 0x3<1/a.h>1e2 #include <1/a.h> #define const.member@$
forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited by a { on the left and a } on the right). {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2} {#}{include} {<1/a.h>} {#}{define} {const}{.}{member}{@}{$} 92) Thus, sequences of characters that resemble escape sequences cause undefined behavior. 93) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.10.
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Forward references: source file inclusion (6.10.2).
6.4.8 1
Preprocessing numbers
Syntax pp-number: digit . digit pp-number identifier-continue pp-number ’ digit pp-number ’ nondigit pp-number e sign pp-number E sign pp-number p sign pp-number P sign pp-number .
2
Description A preprocessing number begins with a digit optionally preceded by a period (.) and may be followed by valid identifier characters and the character sequences e+, e-, E+, E-, p+, p-, P+, or P-.
3
Preprocessing number tokens lexically include all floating and integer constant tokens.
4
Semantics A preprocessing number does not have type or a value; it acquires both after a successful conversion (as part of translation phase 7) to a floating constant token or an integer constant token.
6.4.9
Comments
1
Except within a character constant, a string literal, or a comment, the characters /* introduce a comment. The contents of such a comment are examined only to identify multibyte characters and to find the characters */ that terminate it.94)
2
Except within a character constant, a string literal, or a comment, the characters // introduce a comment that includes all multibyte characters up to, but not including, the next new-line character. The contents of such a comment are examined only to identify multibyte characters and to find the terminating new-line character.
3
EXAMPLE "a//b" #include "//e" // */ f = g/**//h; //\ i(); /\ / j(); #define glue(x,y) x##y glue(/,/) k(); /*//*/ l(); m = n//**/o + p;
94) Thus, /
70
// four-character string literal // undefined behavior // comment, not syntax error // equivalent to f = g / h; // part of a two-line comment // part of a two-line comment // syntax error, not comment // equivalent to l(); // equivalent to m = n + p;
* . . . */ comments do not nest.
Language
§ 6.4.9
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Expressions
1
An expression is a sequence of operators and operands that specifies computation of a value, or that designates an object or a function, or that generates side effects, or that performs a combination thereof. The value computations of the operands of an operator are sequenced before the value computation of the result of the operator.
2
If a side effect on a scalar object is unsequenced relative to either a different side effect on the same scalar object or a value computation using the value of the same scalar object, the behavior is undefined. If there are multiple allowable orderings of the subexpressions of an expression, the behavior is undefined if such an unsequenced side effect occurs in any of the orderings.95)
3
The grouping of operators and operands is indicated by the syntax.96) Except as specified later, side effects and value computations of subexpressions are unsequenced.97)
4
Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, collectively described as bitwise operators) are required to have operands that have integer type. These operators yield values that depend on the internal representations of integers, and have implementationdefined and undefined aspects for signed types.
5
If an exceptional condition occurs during the evaluation of an expression (that is, if the result is not mathematically defined or not in the range of representable values for its type), the behavior is undefined.
6
The effective type of an object for an access to its stored value is the declared type of the object, if any.98) If a value is stored into an object having no declared type through an lvalue having a type that is not a non-atomic character type, then the type of the lvalue becomes the effective type of the object for that access and for subsequent accesses that do not modify the stored value. If a value is copied into an object having no declared type using memcpy or memmove, or is copied as an array of character type, then the effective type of the modified object for that access and for subsequent accesses that do not modify the value is the effective type of the object from which the value is copied, if it has one. For all other accesses to an object having no declared type, the effective type of the object is simply the type of the lvalue used for the access.
7
An object shall have its stored value accessed only by an lvalue expression that has one of the following types:99) — a type compatible with the effective type of the object, — a qualified version of a type compatible with the effective type of the object, — a type that is the signed or unsigned type corresponding to the effective type of the object, 95) This paragraph renders undefined statement expressions such as
i = ++i + 1; a[i++] = i; while allowing
i = i + 1; a[i] = i; 96) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators (6.5.3), and an operand contained between any of the following pairs of operators: grouping parentheses () (6.5.1), generic selection parentheses () (6.5.1.1), subscripting brackets code[] (6.5.2.1), function-call parentheses () (6.5.2.2), and the conditional operator ?: (6.5.15). Within each major subclause, the operators have the same precedence. Left- or right-associativity is indicated in each subclause by the syntax for the expressions discussed therein. 97) In an expression that is evaluated more than once during the execution of a program, unsequenced and indeterminately sequenced evaluations of its subexpressions need not be performed consistently in different evaluations. 98) Allocated objects have no declared type. 99) The intent of this list is to specify those circumstances in which an object can or cannot be aliased.
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— a type that is the signed or unsigned type corresponding to a qualified version of the effective type of the object, — an aggregate or union type that includes one of the aforementioned types among its members (including, recursively, a member of a subaggregate or contained union), or — a character type. 8
A floating expression may be contracted, that is, evaluated as though it were a single operation, thereby omitting rounding errors implied by the source code and the expression evaluation method.100) The FP_CONTRACT pragma in <math.h> provides a way to disallow contracted expressions. Otherwise, whether and how expressions are contracted is implementation-defined.101)
9
Operators involving decimal floating types are evaluated according to the semantics of IEC 60559, including production of results with the preferred quantum exponent as specified in IEC 60559. Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.26.2).
6.5.1 1
Primary expressions
Syntax primary-expression: identifier constant string-literal ( expression ) generic-selection
2
Constraints The identifier in an identifier primary expression shall have a visible declaration as an ordinary identifier that declares an object or a function.102)
3
Semantics An identifier primary expression designating an object is an lvalue. An identifier primary expression designating a function is a function designator.
4
A constant is a primary expression. Its type depends on its form and value, as detailed in 6.4.4.
5
A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
6
A parenthesized expression is a primary expression. Its type, value, and semantics are identical to those of the unparenthesized expression.
7
A generic selection is a primary expression. Its type, value, and semantics depend on the selected generic association, as detailed in the following subclause. Forward references: declarations (6.7).
1
6.5.1.1 Generic selection Syntax generic-selection: _Generic ( assignment-expression , generic-assoc-list )
generic-assoc-list: generic-association 100) The intermediate operations in the contracted expression are evaluated as if to infinite range and precision, while the final operation is rounded to the format determined by the expression evaluation method. A contracted expression might also omit the raising of floating-point exceptions. 101) This license is specifically intended to allow implementations to exploit fast machine instructions that combine multiple C operators. As contractions potentially undermine predictability, and can even decrease accuracy for containing expressions, their use needs to be well-defined and clearly documented. 102) An identifier designating an enumeration constant is a primary expression through the constant production, not the identifier production.
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generic-assoc-list , generic-association generic-association: type-name : assignment-expression default : assignment-expression
2
3
Constraints A generic selection shall have no more than one default generic association. The type name in a generic association shall specify a complete object type other than a variably modified type. No two generic associations in the same generic selection shall specify compatible types. The type of the controlling expression is the type of the expression as if it had undergone an lvalue conversion,103) array to pointer conversion, or function to pointer conversion. That type shall be compatible with at most one of the types named in the generic association list. If a generic selection has no default generic association, its controlling expression shall have type compatible with exactly one of the types named in its generic association list. Semantics The controlling expression of a generic selection is not evaluated. If a generic selection has a generic association with a type name that is compatible with the type of the controlling expression, then the result expression of the generic selection is the expression in that generic association. Otherwise, the result expression of the generic selection is the expression in the default generic association. None of the expressions from any other generic association of the generic selection is evaluated.
4
The type and value of a generic selection are identical to those of its result expression. It is an lvalue, a function designator, or a void expression if its result expression is, respectively, an lvalue, a function designator, or a void expression.
5
EXAMPLE A cbrt type-generic macro could be implemented as follows: #define cbrt(X) _Generic((X), long double: cbrtl, default: cbrt, float: cbrtf )(X)
\ \ \ \
7.27 shows how such a macro could be implemented with the required rounding properties.
6.5.2 1
Postfix operators
Syntax postfix-expression: primary-expression postfix-expression [ expression ] postfix-expression ( argument-expression-listopt ) postfix-expression . identifier postfix-expression -> identifier postfix-expression ++ postfix-expression -compound-literal argument-expression-list: assignment-expression argument-expression-list , assignment-expression
103) An lvalue conversion drops type qualifiers.
§ 6.5.2
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6.5.2.1 Array subscripting Constraints One of the expressions shall have type "pointer to complete object type", the other expression shall have integer type, and the result has type "type". Semantics A postfix expression followed by an expression in square brackets [] is a subscripted designation of an element of an array object. The definition of the subscript operator [] is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th element of E1 (counting from zero).
3
Successive subscript operators designate an element of a multidimensional array object. If E is an n-dimensional array (n ≥ 2) with dimensions i × j × · · · × k, then E (used as other than an lvalue) is converted to a pointer to an (n − 1)-dimensional array with dimensions j × · · · × k. If the unary * operator is applied to this pointer explicitly, or implicitly as a result of subscripting, the result is the referenced (n − 1)-dimensional array, which itself is converted into a pointer if used as other than an lvalue. It follows from this that arrays are stored in row-major order (last subscript varies fastest).
4
EXAMPLE Consider the array object defined by the declaration int x[3][5];
Here x is a 3 × 5 array of objects of type int; more precisely, x is an array of three element objects, each of which is an array of five objects of type int. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to a pointer to the initial array of five objects of type int. Then i is adjusted according to the type of x, which conceptually entails multiplying i by the size of the object to which the pointer points, namely an array of five int objects. The results are added and indirection is applied to yield an array of five objects of type int. When used in the expression x[i][j], that array is in turn converted to a pointer to the first of the objects of type int, so x[i][j] yields an int. Forward references: additive operators (6.5.6), address and indirection operators (6.5.3.2), array declarators (6.7.6.2). 6.5.2.2 Function calls Constraints 1
The expression that denotes the called function104) shall have type pointer to function returning void or returning a complete object type other than an array type.
2
The number of arguments shall agree with the number of parameters. Each argument shall have a type such that its value may be assigned to an object with the unqualified version of the type of its corresponding parameter
3
Semantics A postfix expression followed by parentheses () containing a possibly empty, comma-separated list of expressions is a function call. The postfix expression denotes the called function. The list of expressions specifies the arguments to the function.
4
An argument may be an expression of any complete object type. In preparing for the call to a function, the arguments are evaluated, and each parameter is assigned the value of the corresponding argument.105)
5
If the expression that denotes the called function has type pointer to function returning an object type, the function call expression has the same type as that object type, and has the value determined as specified in 6.8.6.4. Otherwise, the function call has type void. 104) Most often, this is the result of converting an identifier that is a function designator. 105) A function can change the values of its parameters, but these changes cannot affect the values of the arguments. On the other hand, it is possible to pass a pointer to an object, and the function can then change the value of the object pointed to. A parameter declared to have array or function type is adjusted to have a pointer type as described in 6.7.6.3.
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6
The arguments are implicitly converted, as if by assignment, to the types of the corresponding parameters, taking the type of each parameter to be the unqualified version of its declared type. The ellipsis notation in a function prototype declarator causes argument type conversion to stop after the last declared parameter, if present. The integer promotions are performed on each trailing argument, and trailing arguments that have type float are promoted to double. These are called the default argument promotions. No other conversions are performed implicitly.
7
If the function is defined with a type that is not compatible with the type (of the expression) pointed to by the expression that denotes the called function, the behavior is undefined.
8
There is a sequence point after the evaluations of the function designator and the actual arguments but before the actual call. Every evaluation in the calling function (including other function calls) that is not otherwise specifically sequenced before or after the execution of the body of the called function is indeterminately sequenced with respect to the execution of the called function.106)
9
Recursive function calls shall be permitted, both directly and indirectly through any chain of other functions.
10
EXAMPLE In the function call (*pf[f1()]) (f2(), f3() + f4())
the functions f1, f2, f3, and f4 can be called in any order. All side effects have to be completed before the function pointed to by pf[f1()] is called. Forward references: function declarators (6.7.6.3), function definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).
1
2
3
6.5.2.3 Structure and union members Constraints The first operand of the . operator shall have an atomic, qualified, or unqualified structure or union type, and the second operand shall name a member of that type. The first operand of the -> operator shall have type "pointer to atomic, qualified, or unqualified structure" or "pointer to atomic, qualified, or unqualified union", and the second operand shall name a member of the type pointed to. Semantics A postfix expression followed by the . operator and an identifier designates a member of a structure or union object. The value is that of the named member,107) and is an lvalue if the first expression is an lvalue. If the first expression has qualified type, the result has the so-qualified version of the type of the designated member.
4
A postfix expression followed by the -> operator and an identifier designates a member of a structure or union object. The value is that of the named member of the object to which the first expression points, and is an lvalue.108) If the first expression is a pointer to a qualified type, the result has the so-qualified version of the type of the designated member.
5
Accessing a member of an atomic structure or union object results in undefined behavior.109)
6
One special guarantee is made to simplify the use of unions: if a union contains several structures that share a common initial sequence (see below), and if the union object currently contains one of these structures, it is permitted to inspect the common initial part of any of them anywhere that a declaration of the completed type of the union is visible. Two structures share a common initial 106) In other words, function executions do not interleave with each other. 107) If the member used to read the contents of a union object is not the same as the member last used to store a value in the object the appropriate part of the object representation of the value is reinterpreted as an object representation in the new type as described in 6.2.6 (a process sometimes called type punning). This might be a non-value representation. 108) If &E is a valid pointer expression (where & is the address of operator, which generates a pointer to its operand), the expression (&E)->MOS is the same as E.MOS. 109) For example, a data race would occur if access to the entire structure or union in one thread conflicts with access to a member from another thread, where at least one access is a modification. Members can be safely accessed using a non-atomic object which is assigned to or from the atomic object.
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sequence if corresponding members have compatible types (and, for bit-fields, the same widths) for a sequence of one or more initial members. 7
EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or union, f().x is a valid postfix expression but is not an lvalue.
8
EXAMPLE 2 In: struct s { int i; const int ci; }; struct s s; const struct s cs; volatile struct s vs;
the various members have the types: s.i s.ci cs.i cs.ci vs.i vs.ci 9
int const int const int const int volatile int volatile const int
EXAMPLE 3 The following is a valid fragment: union { struct { int alltypes; } n; struct { int type; int intnode; } ni; struct { int type; double doublenode; } nf; } u; u.nf.type = 1; u.nf.doublenode = 3.14; /* ... */ if (u.n.alltypes == 1) if (sin(u.nf.doublenode) == 0.0) /* ... */
The following is not a valid fragment (because the union type is not visible within function f): struct t1 { int m; }; struct t2 { int m; }; int f(struct t1 *p1, struct t2 *p2) { if (p1->m < 0) p2->m = -p2->m; return p1->m; } int g() { union { struct t1 s1; struct t2 s2; } u; /* ... */ return f(&u.s1, &u.s2);
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}
Forward references: address and indirection operators (6.5.3.2), structure and union specifiers (6.7.2.1).
1
2
3
6.5.2.4 Postfix increment and decrement operators Constraints The operand of the postfix increment or decrement operator shall have atomic, qualified, or unqualified real or pointer type, and shall be a modifiable lvalue. Semantics The result of the postfix ++ operator is the value of the operand. As a side effect, the value of the operand object is incremented (that is, the value 1 of the appropriate type is added to it). See the discussions of additive operators and compound assignment for information on constraints, types, and conversions and the effects of operations on pointers. The value computation of the result is sequenced before the side effect of updating the stored value of the operand. With respect to an indeterminately sequenced function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object with atomic type is a read-modify-write operation with memory_order_seq_cst memory order semantics.110) The postfix -- operator is analogous to the postfix ++ operator, except that the value of the operand is decremented (that is, the value 1 of the appropriate type is subtracted from it). Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
1
6.5.2.5 Compound literals Syntax compound-literal: ( storage-class-specifiersopt type-name ) braced-initializer storage-class-specifiers: storage-class-specifier storage-class-specifiers storage-class-specifier
2
Constraints The type name shall specify a complete object type or an array of unknown size, but not a variable length array type.
3
All the constraints for initializer lists in 6.7.10 also apply to compound literals.
4
If the compound literal is associated with file scope or block scope (see ??) the storage-class specifiers SC (possibly empty)111) , type name T, and initializer list, if any, shall be such that they are valid specifiers for an object definition in file scope or block scope, respectively, of the following form, SC typeof(T) ID = { IL }; 110) Where a pointer to an atomic object can be formed and E has integer type, E++ is equivalent to the following code sequence where T is the type of E:
T *addr = &E; T old = *addr; T new; do { new = old + 1; } while (!atomic_compare_exchange_strong(addr, &old, new)); with old being the result of the operation. Special care is necessary if E has floating type; see 6.5.16.2. 111) If the storage-class specifiers contain the same storage-class specifier more than once, the following constraint is violated.
§ 6.5.2.5
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where ID is an identifier that is unique for the whole program and where IL is a (possibly empty) initializer list with nested structure, designators, values and types as the initializer list of the compound literal. All the constraints for storage class specifiers in 6.7.1 also apply correspondingly to compound literals. If the compound literal is associated with function prototype scope, constraints as if in block scope apply.
5
Semantics For acompound literal associated with function prototype scope, the type is determined as if in block scope and no object is created; if it is a compound literal constant it is evaluated at translation time; if it is not a compound literal constant, neither the compound literal as a whole nor any of the initializers are evaluated. Otherwise, a compound literal provides an unnamed object whose value, type, storage duration and other properties are as if given by the definition syntax in the constraints; if the storage duration is automatic, the lifetime of the instance of the unnamed object is the current execution of the enclosing block.112) If the storage-class specifiers are absent or contain constexpr, static, register, or thread_local the behavior is as if the object were declared and initialized in the corresponding scope with these storage-class specifiers; if another storage-class specifier is present, the behavior is undefined. If the storage-class specifier constexpr is present, the initializer is evaluated at translation time. Otherwise, if the storage duration is automatic, the initializer is evaluated at each evaluation of the compound literal; if the storage duration is static or thread the initializer is (as if) evaluated once prior to program startup.
6
The value of the compound literal is that of an lvalue corresponding to the unnamed object.
7
All the semantic rules for initializer lists in 6.7.10 also apply to compound literals.113)
8
String literals, and compound literals with const-qualified types, including those specified with constexpr, need not designate distinct objects.114)
9
EXAMPLE 1 Consider the following 2 functions: int f(int*); int g(char * para[f((int[27]){ 0, })]) { /* ... */ return 0; }
Here, each call to g creates an unnamed object of type int[27] to determine the variably-modified type of para for the duration of the call. During that determination, a pointer to the object is passed into a call to the function f. If a pointer to the object is kept by f, access to that object is possible during the whole execution of the call to g. The lifetime of the object ends with the end of the call to g; for any access after that, the behavior is undefined. 10
EXAMPLE 2 The file scope definition int *p = (int []){2, 4};
initializes p to point to the first element of an array of two ints, the first having the value two and the second, four. The expressions in this compound literal are required to be constant. The unnamed object has static storage duration. 11
EXAMPLE 3 In contrast, in void f(void) { 112) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types or void only, and the result of a cast expression is not an lvalue. 113) For example, subobjects without explicit initializers are initialized to zero. 114) This allows implementations to share storage for string literals and constant compound literals with the same or overlapping representations.
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int *p; /*...*/ p = (int [2]){*p}; /*...*/ }
p is assigned the address of the first element of an array of two ints, the first having the value previously pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The unnamed object has automatic storage duration. 12
EXAMPLE 4 Initializers with designations can be combined with compound literals. Structure objects created using compound literals can be passed to functions without depending on member order: drawline((struct point){.x=1, .y=1}, (struct point){.x=3, .y=4});
Or, if drawline instead expected pointers to struct point: drawline(&(struct point){.x=1, .y=1}, &(struct point){.x=3, .y=4}); 13
EXAMPLE 5 A read-only compound literal can be specified through constructions like: (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
14
EXAMPLE 6 The following three expressions have different meanings: "/tmp/fileXXXXXX" (char []){"/tmp/fileXXXXXX"} (const char []){"/tmp/fileXXXXXX"}
The first always has static storage duration and has type array of char, but need not be modifiable; the last two have automatic storage duration when they occur within the body of a function, and the first of these two is modifiable. 15
EXAMPLE 7 Like string literals, const-qualified compound literals can be placed into read-only memory and can even be shared. For example, (const char []){"abc"} == "abc"
might yield 1 if the literals’ storage is shared. 16
EXAMPLE 8 Since compound literals are unnamed, a single compound literal cannot specify a circularly linked object. For example, there is no way to write a self-referential compound literal that could be used as the function argument in place of the named object endless_zeros below: struct int_list { int car; struct int_list *cdr; }; struct int_list endless_zeros = {0, &endless_zeros}; eval(endless_zeros);
17
EXAMPLE 9 Each compound literal creates only a single object in a given scope: struct s { int i; }; int f (void) { struct s *p = 0, *q; int j = 0;
§ 6.5.2.5
Language
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again: q = p, p = &((struct s){ j++ }); if (j < 2) goto again; return p == q && q->i == 1; }
The function f() always returns the value 1. 18
Note that if an iteration statement were used instead of an explicit goto and a label, the lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would have indeterminate representation, which would result in undefined behavior. Forward references: type names (6.7.7), initialization (6.7.10).
6.5.3 1
Unary operators
Syntax unary-expression: postfix-expression ++ unary-expression -- unary-expression unary-operator cast-expression sizeof unary-expression sizeof ( type-name ) alignof ( type-name ) unary-operator: one of &
1
2
3
*
+
-
~
!
6.5.3.1 Prefix increment and decrement operators Constraints The operand of the prefix increment or decrement operator shall have atomic, qualified, or unqualified real or pointer type, and shall be a modifiable lvalue. Semantics The value of the operand of the prefix ++ operator is incremented. The result is the new value of the operand after incrementation. The expression ++E is equivalent to (E+=1), where the value 1 is of the appropriate type. See the discussions of additive operators and compound assignment for information on constraints, types, side effects, and conversions and the effects of operations on pointers. The prefix -- operator is analogous to the prefix ++ operator, except that the value of the operand is decremented. Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
1
6.5.3.2 Address and indirection operators Constraints The operand of the unary & operator shall be either a function designator, the result of a [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is not declared with the register storage-class specifier.
2
The operand of the unary * operator shall have pointer type.
3
Semantics The unary & operator yields the address of its operand. If the operand has type "type", the result has type "pointer to type". If the operand is the result of a unary * operator, neither that operator nor 80
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the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator. Otherwise, the result is a pointer to the object or function designated by its operand. 4
The unary * operator denotes indirection. If the operand points to a function, the result is a function designator; if it points to an object, the result is an lvalue designating the object. If the operand has type "pointer to type", the result has type "type". If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115) Forward references: storage-class specifiers (6.7.1), structure and union specifiers (6.7.2.1).
1
2
6.5.3.3 Unary arithmetic operators Constraints The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, integer type; of the ! operator, scalar type. Semantics The result of the unary + operator is the value of its (promoted) operand. The integer promotions are performed on the operand, and the result has the promoted type.
3
The result of the unary - operator is the negative of its (promoted) operand. The integer promotions are performed on the operand, and the result has the promoted type.
4
The result of the ~ operator is the bitwise complement of its (promoted) operand (that is, each bit in the result is set if and only if the corresponding bit in the converted operand is not set). The integer promotions are performed on the operand, and the result has the promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent to the maximum value representable in that type minus E.
5
The result of the logical negation operator ! is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. The expression !E is equivalent to (0==E).
1
2
6.5.3.4 The sizeof and alignof operators Constraints The sizeof operator shall not be applied to an expression that has function type or an incomplete type, to the parenthesized name of such a type, or to an expression that designates a bit-field member. The alignof operator shall not be applied to a function type or an incomplete type. Semantics The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand. The result is an integer. If the type of the operand is a variable length array type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an integer constant.
3
The alignof operator yields the alignment requirement of its operand type. The operand is not evaluated and the result is an integer constant expression. When applied to an array type, the result is the alignment requirement of the element type.
4
When sizeof is applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1. When applied to an operand that has array type, the result is the total number of bytes in the array.116) When applied to an operand that has structure or 115) Thus, & E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is always true that if E is a * function designator or an lvalue that is a valid operand of the unary & operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an address inappropriately aligned for the type of object pointed to, and the address of an object after the end of its lifetime. 116) When applied to a parameter declared to have array or function type, the sizeof operator yields the size of the adjusted
§ 6.5.3.4
Language
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union type, the result is the total number of bytes in such an object, including internal and trailing padding. 5
The value of the result of both operators is implementation-defined, and its type (an unsigned integer type) is size_t, defined in <stddef.h> (and other headers).
6
EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to allocate and return a pointer to void. For example: extern void *alloc(size_t); double *dp = alloc(sizeof *dp);
The implementation of the alloc function presumably ensures that its return value is aligned suitably for conversion to a pointer to double. 7
EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array: sizeof array / sizeof array[0]
8
EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a function: #include <stddef.h> size_t fsize3(int n) { char b[n+3]; return sizeof b; }
// variable length array // execution time sizeof
int main(void) { size_t size; size = fsize3(10); // fsize3 returns 13 return 0; }
Forward references: common definitions <stddef.h> (7.21), declarations (6.7), structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2).
6.5.4 1
Cast operators
Syntax cast-expression: unary-expression ( type-name ) cast-expression
2
Constraints Unless the type name specifies a void type, the type name shall specify atomic, qualified, or unqualified scalar type, and the operand shall have scalar type.
3
Conversions that involve pointers, other than where permitted by the constraints of 6.5.16.1, shall be specified by means of an explicit cast.
4
A pointer type shall not be converted to any floating type. A floating type shall not be converted to any pointer type. The type nullptr_t shall not be converted to any type other than void, bool or a (pointer) type (see 6.9.1).
82
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pointer type. If the target type is nullptr_t, the cast expression shall be a null pointer constant or have type nullptr_t.
5
Semantics Size expressions and typeof operators contained in a type name used with a cast operator are evaluated whenever the cast expression is evaluated.
6
Preceding an expression by a parenthesized type name converts the value of the expression to the unqualified, non-atomic version of the named type. This construction is called a cast.117) A cast that specifies no conversion has no effect on the type or value of an expression.
7
If the value of the expression is represented with greater range or precision than required by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the type of the expression is the same as the named type and removes any extra range and precision. Forward references: equality operators (6.5.9), function declarators (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).
6.5.5 1
2
3
Multiplicative operators
Syntax multiplicative-expression: cast-expression multiplicative-expression * cast-expression multiplicative-expression / cast-expression multiplicative-expression % cast-expression
Constraints Each of the operands shall have arithmetic type. The operands of the % operator shall have integer type. If either operand has decimal floating type, the other operand shall not have standard floating type, complex type, or imaginary type.
4
Semantics The usual arithmetic conversions are performed on the operands.
5
The result of the binary * operator is the product of the operands.
6
The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined.
7
When integers are divided, the result of the / operator is the algebraic quotient with any fractional part discarded.118) If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is undefined.
6.5.6 1
Additive operators
Syntax additive-expression: multiplicative-expression additive-expression + multiplicative-expression additive-expression - multiplicative-expression
117) A cast does not yield an lvalue. 118) This is often called "truncation toward zero".
§ 6.5.6
Language
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working draft — April 1, 2023
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2
Constraints For addition, either both operands shall have arithmetic type, or one operand shall be a pointer to a complete object type and the other shall have integer type. (Incrementing is equivalent to adding 1.)
3
For subtraction, one of the following shall hold: — both operands have arithmetic type; — both operands are pointers to qualified or unqualified versions of compatible complete object types; or — the left operand is a pointer to a complete object type and the right operand has integer type. (Decrementing is equivalent to subtracting 1.)
4
If either operand has decimal floating type, the other operand shall not have standard floating type, complex type, or imaginary type.
5
Semantics If both operands have arithmetic type, the usual arithmetic conversions are performed on them.
6
The result of the binary + operator is the sum of the operands.
7
The result of the binary - operator is the difference resulting from the subtraction of the second operand from the first.
8
For the purposes of these operators, a pointer to an object that is not an element of an array behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.
9
When an expression that has integer type is added to or subtracted from a pointer, the result has the type of the pointer operand. If the pointer operand points to an element of an array object, and the array is large enough, the result points to an element offset from the original element such that the difference of the subscripts of the resulting and original array elements equals the integer expression. In other words, if the expression P points to the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and (P)-N (where N has the value n) point to, respectively, the i + n-th and i − n-th elements of the array object, provided they exist. Moreover, if the expression P points to the last element of an array object, the expression (P)+1 points one past the last element of the array object, and if the expression Q points one past the last element of an array object, the expression (Q)-1 points to the last element of the array object. If the pointer operand and the result do not point to elements of the same array object or one past the last element of the array object, the behavior is undefined. If the addition or subtraction produces an overflow, the behavior is undefined. If the result points one past the last element of the array object, it shall not be used as the operand of a unary * operator that is evaluated.
10
When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. If the result is not representable in an object of that type, the behavior is undefined. In other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of an array object, the expression (P)-(Q) has the value i − j provided the value fits in an object of type ptrdiff_t. Moreover, if the expression P points either to an element of an array object or one past the last element of an array object, and the expression Q points to the last element of the same array object, the expression ((Q)+1)-(P) has the same value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the expression P points one past the last element of the array object, even though the expression (Q)+1 does not point to an element of the array object.119) 119) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In this scheme the integer expression added to or subtracted from the converted pointer is first multiplied by the size of the object originally pointed to, and the resulting pointer is converted back to the original type. For pointer subtraction, the result of the difference between the character pointers is similarly divided by the size of the object originally pointed to.
84
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EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types. { int n = 4, m = 3; int a[n][m]; int (*p)[m] = a; // p == &a[0] p += 1; // p == &a[1] (*p)[2] = 99; // a[1][2] == 99 n = p - a; // n == 1 }
12
If array a in the above example were declared to be an array of known constant size, and pointer p were declared to be a pointer to an array of the same known constant size (pointing to a), the results would be the same. Forward references: array declarators (6.7.6.2), common definitions <stddef.h> (7.21).
6.5.7 1
Bitwise shift operators
Syntax shift-expression: additive-expression shift-expression << additive-expression shift-expression >> additive-expression
2
3
Constraints Each of the operands shall have integer type. Semantics The integer promotions are performed on each of the operands. The type of the result is that of the promoted left operand. If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined.
4
The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with zeros. If E1 has an unsigned type, the value of the result is E1 × 2E2 , wrapped around. If E1 has a signed type and nonnegative value, and E1 × 2E2 is representable in the result type, then that is the resulting value; otherwise, the behavior is undefined.
5
The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type or if E1 has a signed type and a nonnegative value, the value of the result is the integral part of the quotient of E1/2E2 . If E1 has a signed type and a negative value, the resulting value is implementation-defined.
6.5.8 1
2
Relational operators
Syntax relational-expression: shift-expression relational-expression < shift-expression relational-expression > shift-expression relational-expression <= shift-expression relational-expression >= shift-expression Constraints One of the following shall hold: — both operands have real type; or When viewed in this way, an implementation need only provide one extra byte (which can overlap another object in the program) just after the end of the object to satisfy the "one past the last element" requirements.
§ 6.5.8
Language
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— both operands are pointers to qualified or unqualified versions of compatible object types. 3
If either operand has decimal floating type, the other operand shall not have standard floating type.
4
Semantics If both of the operands have arithmetic type, the usual arithmetic conversions are performed. Positive zeros compare equal to negative zeros.
5
For the purposes of these operators, a pointer to an object that is not an element of an array behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.
6
When two pointers are compared, the result depends on the relative locations in the address space of the objects pointed to. If two pointers to object types both point to the same object, or both point one past the last element of the same array object, they compare equal. If the objects pointed to are members of the same aggregate object, pointers to structure members declared later compare greater than pointers to members declared earlier in the structure, and pointers to array elements with larger subscript values compare greater than pointers to elements of the same array with lower subscript values. All pointers to members of the same union object compare equal. If the expression P points to an element of an array object and the expression Q points to the last element of the same array object, the pointer expression Q+1 compares greater than P. In all other cases, the behavior is undefined.
7
Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.120) The result has type int.
6.5.9 1
2
Equality operators
Syntax equality-expression: relational-expression equality-expression == relational-expression equality-expression != relational-expression
Constraints One of the following shall hold: — both operands have arithmetic type; — both operands are pointers to qualified or unqualified versions of compatible types; — one operand is a pointer to an object type and the other is a pointer to a qualified or unqualified version of void; — both operands have type nullptr_t; — one operand has type nullptr_t and the other is a null pointer constant; or, — one operand is a pointer and the other is a null pointer constant or has type nullptr_t.
3
If either operand has decimal floating type, the other operand shall not have standard floating type, complex type, or imaginary type. 120) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it means (a<b)<c; in other words, "if a is less than b, compare 1 to c; otherwise, compare 0 to c".
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Semantics The == (equal to) and != (not equal to) operators are analogous to the relational operators except for their lower precedence121) Each of the operators yields 1 if the specified relation is true and 0 if it is false. The result has type int. For any pair of operands, exactly one of the relations is true.
5
If both of the operands have arithmetic type, the usual arithmetic conversions are performed. Positive zeros compare equal to negative zeros. Values of complex types are equal if and only if both their real parts are equal and also their imaginary parts are equal. Any two values of arithmetic types from different type domains are equal if and only if the results of their conversions to the (complex) result type determined by the usual arithmetic conversions are equal. If both operands have type nullptr_t or one operand has type nullptr_t and the other is a null pointer constant, they compare equal.
6
Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a null pointer constant or has type nullptr_t, they compare equal if the former is a null pointer. If one operand is a pointer to an object type and the other is a pointer to a qualified or unqualified version of void, the former is converted to the type of the latter.
7
Two pointers compare equal if and only if both are null pointers, both are pointers to the same object (including a pointer to an object and a subobject at its beginning) or function, both are pointers to one past the last element of the same array object, or one is a pointer to one past the end of one array object and the other is a pointer to the start of a different array object that happens to immediately follow the first array object in the address space.122)
8
For the purposes of these operators, a pointer to an object that is not an element of an array behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.
6.5.10 1
Bitwise AND operator
Syntax AND-expression: equality-expression AND-expression & equality-expression
2
Constraints Each of the operands shall have integer type.
3
Semantics The usual arithmetic conversions are performed on the operands.
4
The result of the binary & operator is the bitwise AND of the operands (that is, each bit in the result is set if and only if each of the corresponding bits in the converted operands is set).
6.5.11 1
2
Bitwise exclusive OR operator
Syntax exclusive-OR-expression: AND-expression exclusive-OR-expression ^ AND-expression Constraints Each of the operands shall have integer type. 121) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value. 122) Two objects can be adjacent in memory because they are adjacent elements of a larger array or adjacent members
of a structure with no padding between them, or because the implementation chose to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined behavior.
§ 6.5.11
Language
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ISO/IEC 9899:2023 (E)
3 4
The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit in the result is set if and only if exactly one of the corresponding bits in the converted operands is set).
Bitwise inclusive OR operator
Syntax inclusive-OR-expression: exclusive-OR-expression inclusive-OR-expression | exclusive-OR-expression
2
Constraints Each of the operands shall have integer type.
3
Semantics The usual arithmetic conversions are performed on the operands.
4
The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in the result is set if and only if at least one of the corresponding bits in the converted operands is set).
6.5.13 1
2
3
4
2
3
4
Logical AND operator
Syntax logical-AND-expression: inclusive-OR-expression logical-AND-expression && inclusive-OR-expression Constraints Each of the operands shall have scalar type. Semantics The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it yields 0. The result has type int. Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation; if the second operand is evaluated, there is a sequence point between the evaluations of the first and second operands. If the first operand compares equal to 0, the second operand is not evaluated.
6.5.14 1
N3096
Semantics The usual arithmetic conversions are performed on the operands.
6.5.12 1
working draft — April 1, 2023
Logical OR operator
Syntax logical-OR-expression: logical-AND-expression logical-OR-expression || logical-AND-expression Constraints Each of the operands shall have scalar type. Semantics The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it yields 0. The result has type int. Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the second operand is evaluated, there is a sequence point between the evaluations of the first and second operands. If the first operand compares unequal to 0, the second operand is not evaluated. 88
Language
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Conditional operator
Syntax conditional-expression: logical-OR-expression logical-OR-expression ? expression : conditional-expression
2
Constraints The first operand shall have scalar type.
3
One of the following shall hold for the second and third operands123) : — both operands have arithmetic type; — both operands have compatible structure or union type; — both operands have void type; — both operands are pointers to qualified or unqualified versions of compatible types; — both operands have nullptr_t type; — one operand is a pointer and the other is a null pointer constant or has type nullptr_t; or — one operand is a pointer to an object type and the other is a pointer to a qualified or unqualified version of void.
4
5
If either of the second or third operands has decimal floating type, the other operand shall not have standard floating type, complex type, or imaginary type. Semantics The first operand is evaluated; there is a sequence point between its evaluation and the evaluation of the second or third operand (whichever is evaluated). The second operand is evaluated only if the first compares unequal to 0; the third operand is evaluated only if the first compares equal to 0; the result is the value of the second or third operand (whichever is evaluated), converted to the type described below.124)
6
If both the second and third operands have arithmetic type, the result type that would be determined by the usual arithmetic conversions, were they applied to those two operands, is the type of the result. If both the operands have structure or union type, the result has the type of one operand. If both operands have void type, the result has void type.
7
If both the second and third operands are pointers, the result type is a pointer to a type qualified with all the type qualifiers of the types referenced by both operands; if one is a null pointer constant (other than a pointer) or has type nullptr_t and the other is a pointer, the result type is the pointer type; if both the second and third operands have nullptr_t type, the result also has that type. Furthermore, if both operands are pointers to compatible types or to differently qualified versions of compatible types, the result type is a pointer to an appropriately qualified version of the composite type; if one operand is a null pointer constant, the result has the type of the other operand; otherwise, one operand is a pointer to void or a qualified version of void, in which case the result type is a pointer to an appropriately qualified version of void.
8
EXAMPLE The common type that results when the second and third operands are pointers is determined in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two pointers have compatible types.
9
Given the declarations 123) If a second or third operand of type nullptr_t is used and the other operand is not a pointer and does not have type
nullptr_t itself, a constraint is violated even if that other operand is a null pointer constant such as 0. 124) A conditional expression does not yield an lvalue.
§ 6.5.15
Language
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const void *c_vp; void *vp; const int *c_ip; volatile int *v_ip; int *ip; const char *c_cp;
the third column in the following table is the common type that is the result of a conditional expression in which the first two columns are the second and third operands (in either order): c_vp v_ip c_ip vp ip vp
6.5.16 1
c_ip 0 v_ip c_cp c_ip ip
const void * volatile int * const volatile int * const void * const int * void *
Assignment operators
Syntax assignment-expression: conditional-expression unary-expression assignment-operator assignment-expression assignment-operator: one of =
2
3
*=
/=
%=
+=
-=
<<=
>>=
&=
^=
|=
Constraints An assignment operator shall have a modifiable lvalue as its left operand. Semantics An assignment operator stores a value in the object designated by the left operand. An assignment expression has the value of the left operand after the assignment,125) but is not an lvalue. The type of an assignment expression is the type the left operand would have after lvalue conversion. The side effect of updating the stored value of the left operand is sequenced after the value computations of the left and right operands. The evaluations of the operands are unsequenced. 6.5.16.1 Simple assignment Constraints
1
One of the following shall hold126) : — the left operand has atomic, qualified, or unqualified arithmetic type, and the right operand has arithmetic type; — the left operand has an atomic, qualified, or unqualified version of a structure or union type compatible with the type of the right operand; — the left operand has atomic, qualified, or unqualified pointer type, and (considering the type the left operand would have after lvalue conversion) both operands are pointers to qualified or unqualified versions of compatible types, and the type pointed to by the left operand has all the qualifiers of the type pointed to by the right operand; 125) The implementation is permitted to read the object to determine the value but is not required to, even when the object has volatile-qualified type. 126) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion (specified in 6.3.2.1) that changes lvalues to "the value of the expression" and thus removes any type qualifiers that were applied to the type category of the expression (for example, it removes const but not volatile from the type int volatile * const).
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— the left operand has atomic, qualified, or unqualified pointer type, and (considering the type the left operand would have after lvalue conversion) one operand is a pointer to an object type, and the other is a pointer to a qualified or unqualified version of void, and the type pointed to by the left operand has all the qualifiers of the type pointed to by the right operand; — the left operand has an atomic, qualified, or unqualified version of the nullptr_t type and the right operand is a null pointer constant or its type is nullptr_t127) ; — the left operand is an atomic, qualified, or unqualified pointer, and the right operand is a null pointer constant or its type is nullptr_t; or — the left operand has type atomic, qualified, or unqualified bool, and the right operand is a pointer or its type is nullptr_t.
2
Semantics In simple assignment (=), the value of the right operand is converted to the type of the assignment expression and replaces the value stored in the object designated by the left operand. 128)
3
If the value being stored in an object is read from another object that overlaps in any way the storage of the first object, then the two objects shall occupy exactly the same storage and shall have qualified or unqualified versions of a compatible type; otherwise, the behavior is undefined.
4
EXAMPLE 1 In the program fragment int f(void); char c; /* ... */ if ((c = f()) == -1) /* ... */
the int value returned by the function could be truncated when stored in the char, and then converted back to int width prior to the comparison. In an implementation in which "plain" char has the same range of values as unsigned char (and char is narrower than int), the result of the conversion cannot be negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the variable c would be declared as int. 5
EXAMPLE 2 In the fragment: char c; int i; long l; l = (c = i);
the value of i is converted to the type of the assignment expression c = i, that is, char type. The value of the expression enclosed in parentheses is then converted to the type of the outer assignment expression, that is, long int type. 6
EXAMPLE 3 Consider the fragment: const char **cpp; char *p; const char c = ’A’; cpp = &p; *cpp = &c; *p = 0;
// constraint violation // valid // valid
127) The assignment of an object of type nullptr_t with a value of another type, even if the value is a null pointer constant,
is a constraint violation. 128) As described in 6.2.6.1, a store to an object with atomic type is done with memory_order_seq_cst semantics.
§ 6.5.16.1
Language
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The first assignment is unsafe because it would allow the following valid code to attempt to change the value of the const object c.
1
6.5.16.2 Compound assignment Constraints For the operators += and -= only, either the left operand shall be an atomic, qualified, or unqualified pointer to a complete object type, and the right shall have integer type; or the left operand shall have atomic, qualified, or unqualified arithmetic type, and the right shall have arithmetic type.
2
For the other operators, the left operand shall have atomic, qualified, or unqualified arithmetic type, and (considering the type the left operand would have after lvalue conversion) each operand shall have arithmetic type consistent with those allowed by the corresponding binary operator.
3
If either operand has decimal floating type, the other operand shall not have standard floating type, complex type, or imaginary type.
4
5
Semantics A compound assignment of the form E1 op= E2 is equivalent to the simple assignment expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with respect to an indeterminately sequenced function call, the operation of a compound assignment is a single evaluation. If E1 has an atomic type, compound assignment is a read-modify-write operation with memory_order_seq_cst memory order semantics. NOTE 1 Where a pointer to an atomic object can be formed and E1 and E2 have integer type, this is equivalent to the following code sequence where T1 is the type of E1 and T2 is the type of E2:
T1 *addr = &E1; T2 val = (E2); T1 old = *addr; T1 new; do { new = old op val; } while (!atomic_compare_exchange_strong(addr, &old, new));
with new being the result of the operation. If E1 or E2 has floating type, then exceptional conditions or floating-point exceptions encountered during discarded evaluations of new would also be discarded to satisfy the equivalence of E1 op= E2 and E1 = E1 op (E2). For example, if Annex F is in effect, the floating types involved have IEC 60559 binary formats, and FLT_EVAL_METHOD is 0, the equivalent code would be:
#include <fenv.h> #pragma STDC FENV_ACCESS ON /* ... */ fenv_t fenv; T1 *addr = &E1; T2 val = E2; T1 old = *addr; T1 new; feholdexcept(&fenv); for (;;) { new = old op val; if (atomic_compare_exchange_strong(addr, &old, new)) break; feclearexcept(FE_ALL_EXCEPT); } feupdateenv(&fenv);
If FLT_EVAL_METHOD is not 0, then T2 is expected to be a type with the range and precision to which E2 is evaluated to satisfy the equivalence.
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6.5.17 1
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Comma operator
Syntax expression: assignment-expression expression , assignment-expression
2
3
Semantics The left operand of a comma operator is evaluated as a void expression; there is a sequence point between its evaluation and that of the right operand. Then the right operand is evaluated; the result has its type and value.129) EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists of initializers). On the other hand, it can be used within a parenthesized expression or within the second expression of a conditional operator in such contexts. In the function call f(a, (t=3, t+2), c)
the function has three arguments, the second of which has the value 5. Forward references: initialization (6.7.10).
129) A comma operator does not yield an lvalue.
§ 6.5.17
Language
93
ISO/IEC 9899:2023 (E)
6.6
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Constant expressions
1
Syntax constant-expression: conditional-expression
2
Description A constant expression can be evaluated during translation rather than runtime, and accordingly may be used in any place that a constant may be.
3
Constraints Constant expressions shall not contain assignment, increment, decrement, function-call, or comma operators, except when they are contained within a subexpression that is not evaluated.130)
4
5
Each constant expression shall evaluate to a constant that is in the range of representable values for its type. Semantics An expression that evaluates to a constant is required in several contexts. If a floating expression is evaluated in the translation environment, the arithmetic range and precision shall be at least as great as if the expression were being evaluated in the execution environment. 131)
6
A compound literal with storage-class specifier constexpr is a compound literal constant, as is a postfix expression that applies the . member access operator to a compound literal constant of structure or union type, even recursively. A compound literal constant is a constant expression with the type and value of the unnamed object.
7
An identifier that is: — an enumeration constant, — a predefined constant, or — declared with storage-class specifier constexpr and has an object type, is a named constant, as is a postfix expression that applies the . member access operator to a named constant of structure or union type, even recursively. For enumeration and predefined constants, their value and type are defined in the respective clauses; for constexpr objects, such a named constant is a constant expression with the type and value of the declared object.
8
An integer constant expression132) shall have integer type and shall only have operands that are integer constants, named and compound literal constants of integer type, character constants, sizeof expressions whose results are integer constants, alignof expressions, and floating, named, or compound literal constants of arithmetic type that are the immediate operands of casts. Cast operators in an integer constant expression shall only convert arithmetic types to integer types, except as part of an operand to the typeof operators, sizeof operator, or alignof operator.
9
More latitude is permitted for constant expressions in initializers. Such a constant expression shall be, or evaluate to, one of the following: — a named constant, — a compound literal constant, 130) The operand of a typeof (6.7.2.5), sizeof, or alignof operator is usually not evaluated (6.5.3.4). 131) The use of evaluation formats as characterized by FLT_EVAL_METHOD and DEC_EVAL_METHOD also applies to evaluation in the translation environment. 132) An integer constant expression is required in contexts such as the size of a bit-field member of a structure, the value of an enumeration constant, and the size of a non-variable length array. Further constraints that apply to the integer constant expressions used in conditional-inclusion preprocessing directives are discussed in 6.10.1.
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— an arithmetic constant expression, — a null pointer constant, — an address constant, or — an address constant for a complete object type plus or minus an integer constant expression. 10
An arithmetic constant expression shall have arithmetic type and shall only have operands that are integer constants, floating constants, named or compound literal constants of arithmetic type, character constants, sizeof expressions whose results are integer constants, and alignof expressions. Cast operators in an arithmetic constant expression shall only convert arithmetic types to arithmetic types, except as part of an operand to the typeof operators, sizeof operator, or alignof operator.
11
An address constant is a null pointer133) , a pointer to an lvalue designating an object of static storage duration, or a pointer to a function designator; it shall be created explicitly using the unary & operator or an integer constant cast to pointer type, or implicitly using an expression of array or function type.
12
The array-subscript [] and member-access -> operator, the address & and indirection * unary operators, and pointer casts may be used in the creation of an address constant, but the value of an object shall not be accessed by use of these operators.134)
13
A structure or union constant is a named constant or compound literal constant with structure or union type, respectively.
14
An implementation may accept other forms of constant expressions; however, they are not an integer constant expression.135)
15
Starting from a structure or union constant, the member-access . operator may be used to form a named constant or compound literal constant as described above.
16
If the member-access operator . accesses a member of a union constant, the accessed member shall be the same as the member that is initialized by the union constant’s initializer.
17
The semantic rules for the evaluation of a constant expression are the same as for nonconstant expressions136) . Forward references: array declarators (6.7.6.2), initialization (6.7.10).
133) A named constant or compound literal constant of integer type and value zero is a null pointer constant. A named constant or compound literal constant with a pointer type and a value null is a null pointer but not a null pointer constant; it may only be used to initialize a pointer object if its type implicitly converts to the target type. 134) Named constants or compound literal constants with arithmetic type, including names of constexpr objects, are valid in offset computations such as array subscripts or in pointer casts, as long as the expressions in which they occur form integer constant expressions. In contrast, names of other objects, even if const-qualified and with static storage duration, are not valid. 135) For example, in the statement int arr_or_vla[(int)+1.0];, while possible to be computed by some implementations as an array with a size of one, still results in a variable length array declaration of automatic storage duration. 136) Thus, in the following initialization,
static int i = 2 || 1 / 0; the expression is a valid integer constant expression with value one.
§ 6.6
Language
95
ISO/IEC 9899:2023 (E)
6.7 1
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Declarations
Syntax declaration: declaration-specifiers init-declarator-listopt ; attribute-specifier-sequence declaration-specifiers init-declarator-list ; static_assert-declaration attribute-declaration declaration-specifiers: declaration-specifier attribute-specifier-sequenceopt declaration-specifier declaration-specifiers declaration-specifier: storage-class-specifier type-specifier-qualifier function-specifier init-declarator-list: init-declarator init-declarator-list , init-declarator init-declarator: declarator declarator = initializer attribute-declaration: attribute-specifier-sequence ;
2
3
Constraints A declaration other than a static_assert or attribute declaration shall declare at least a declarator (other than the parameters of a function or the members of a structure or union), a tag, or the members of an enumeration. If an identifier has no linkage, there shall be no more than one declaration of the identifier (in a declarator or type specifier) with the same scope and in the same name space, except that: — a typedef name may be redefined to denote the same type as it currently does, provided that type is not a variably modified type; — enumeration constants and tags may be redeclared as specified in 6.7.2.2 and 6.7.2.3, respectively.
4
All declarations in the same scope that refer to the same object or function shall specify compatible types.
5
In an underspecified declaration all declared identifiers that do not have a prior declaration shall be ordinary identifiers.
6
Semantics A declaration specifies the interpretation and properties of a set of identifiers. A definition of an identifier is a declaration for that identifier that for: — an object, causes storage to be reserved for that object, — a function, includes the function body137) , — an enumeration constant, is the first (or only) declaration of the identifier, or — a typedef name, is the first (or only) declaration of the identifier. 137) Function definitions have a different syntax, described in 6.9.1.
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7
The declaration specifiers consist of a sequence of specifiers, followed by an optional attribute specifier sequence. The declaration specifiers indicate the linkage, storage duration, and part of the type of the entities that the declarators denote. The init declarator list is a comma-separated sequence of declarators, each of which may have additional type information, or an initializer, or both. The declarators contain the identifiers (if any) being declared. The optional attribute specifier sequence in a declaration appertains to each of the entities declared by the declarators of the init declarator list.
8
If an identifier for an object is declared with no linkage, the type for the object shall be complete by the end of its declarator, or by the end of its init-declarator if it has an initializer. In the case of function parameters, it is the adjusted type (see 6.7.6.3) that is required to be complete.
9
The optional attribute specifier sequence terminating a sequence of declaration specifiers appertains to the type determined by the preceding sequence of declaration specifiers. The attribute specifier sequence affects the type only for the declaration it appears in, not other declarations involving the same type.
10
Except where specified otherwise, the meaning of an attribute declaration is implementation-defined.
11
EXAMPLE In the declaration for an entity, attributes appertaining to that entity may appear at the start of the declaration and after the identifier for that declaration. [[deprecated]] void f [[deprecated]] (void); // valid
12
A declaration such that the declaration specifiers contain no type specifier or that is declared with constexpr is said to be underspecified. If such a declaration is not a definition, if it declares no or more than one ordinary identifier, if the declared identifier already has a declaration in the same scope, or if the declared entity is not an object, the behavior is undefined. Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization (6.7.10), storage class specifiers (6.7.1), type inference (6.7.9), type names (6.7.7), type qualifiers (6.7.3).
6.7.1 1
Storage-class specifiers
Syntax storage-class-specifier: auto constexpr extern register static thread_local typedef
2
Constraints At most, one storage-class specifier may be given in the declaration specifiers in a declaration, except that: — thread_local may appear with static or extern, — auto may appear with all the others except typedef138) , and — constexpr may appear with auto, register, or static.
3
In the declaration of an object with block scope, if the declaration specifiers include thread_local, they shall also include either static or extern. If thread_local appears in any declaration of an object, it shall be present in every declaration of that object. 138) See "future language directions" (6.11.5).
§ 6.7.1
Language
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4
thread_local shall not appear in the declaration specifiers of a function declaration. auto shall only appear in the declaration specifiers of an identifier with file scope or along with other storage class specifiers if the type is to be inferred from an initializer.
5
An object declared with storage-class specifier constexpr or any of its members, even recursively, shall not have an atomic type, or a variably modified type, or a type that is volatile or restrict qualified. An initializer of floating type shall be evaluated with the translation-time floating-point environment. The declaration shall be a definition and shall have an initializer.139) The value of any constant expressions or of any character in a string literal of the initializer shall be exactly representable in the corresponding target type; no change of value shall be applied140) .
6
If an object or subobject declared with storage-class specifier constexpr has pointer, integer, or arithmetic type, any explicit initializer value for it shall be null141) , an integer constant expression, or an arithmetic constant expression, respectively. If the object declared has real floating type, the initializer shall have integer or real floating type. If the object declared has imaginary type, the initializer shall have imaginary type. If the initializer has decimal floating type, the object declared shall have decimal floating type and the conversion shall preserve the quantum of the initializer. If the initializer has real type and a signaling NaN value, the unqualified versions of the type of the initializer and the corresponding real type of the object declared shall be compatible.
7
EXAMPLE 1 struct s { void *p; }; constexpr struct s A = { nullptr }; constexpr struct s B = A; /* Although the expression A.p is not a null pointer constant, only a null pointer, the only explicit initializer in the initialization of B is A, not A.p, so no constraint is violated by that initialization. */
8
EXAMPLE 2 void f (void) { constexpr float f = 1.0f; constexpr float g = 3.0f; fesetround(FE_TOWARDSZERO); // does not affect // initialization of "h", below constexpr float h = f / g; // ... }
9
Semantics Storage-class specifiers specify various properties of identifiers and declared features: — storage duration (static in block scope, thread_local, auto, register), — linkage (extern, static and constexpr in file scope, typedef), — value (constexpr), and — type (typedef).
10
The meanings of the various linkages and storage durations were discussed in 6.2.2 and 6.2.4, typedef is discussed in 6.7.8, and type inference using auto is discussed in 6.7.9. 139) All assignment expressions of such an initializer, if any, are constant expressions or string literals, see 6.7.10. 140) In the context of arithmetic conversions, 6.3.1 describes the details of changes of value that occur if values of arithmetic expressions are stored in the objects that for example have a different signedness, excess precision or quantum exponent. Whenever such a change of value is necessary, the constraint is violated. 141) The named constant or compound literal constant corresponding to an object declared with storage-class specifier constexpr and pointer type is a constant expression with a value null, and thus a null pointer and an address constant. Thus, such a named constant is a valid initializer for other constexpr declarations, provided the pointer types match accordingly. However, even if it has type void* it is not a null pointer constant.
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11
A declaration of an identifier for an object with storage-class specifier register suggests that access to the object be as fast as possible. The extent to which such suggestions are effective is implementation-defined142) .
12
The declaration of an identifier for a function that has block scope shall have no explicit storage-class specifier other than extern.
13
If an aggregate or union object is declared with a storage-class specifier other than typedef, the properties resulting from the storage-class specifier, except with respect to linkage, also apply to the members of the object, including recursively for any aggregate or union member objects.
14
If auto appears with another storage-class specifier, or if it appears in a declaration at file scope, it is ignored for the purposes of determining a storage duration or linkage. In this case, it indicates only that the declared type may be inferred.
15
An object declared with a storage-class specifier constexpr has its value permanently fixed at translation-time; if not yet present, a const-qualification is implicitly added to the object’s type. The declared identifier is considered a constant expression of the respective kind, see 6.6.
16
NOTE 1 An object declared in block scope with a storage-class specifier constexpr and without static has automatic storage duration, the identifier has no linkage, and each instance of the object has a unique address obtainable with & (if it is not declared with the register specifier), if any. Such an object in file scope has static storage duration, the corresponding identifier has internal linkage, and each translation unit that sees the same textual definition implements a separate object with a distinct address.
17
NOTE 2 The constraints for constexpr objects are intended to enforce checks for portability at translation time.
constexpr unsigned int minusOne = -1; // constraint violation constexpr unsigned int uint_max = -1U; // ok constexpr double onethird = 1.0/3.0; // possible constraint violation constexpr double onethirdtrunc = (double)(1.0/3.0); // ok constexpr _Decimal32 small = DEC64_TRUE_MIN * 0; // constraint violation If a truncation of excess precision changes the value in the initializer of onethird, a constraint is violated and a diagnostic is required. In contrast to that, the explicit conversion in the initializer for onethirdtrunc ensures that the definition is valid. Similarly, the initializer of small has a quantum exponent that is larger than the largest possible quantum exponent for _Decimal32. 18
NOTE 3 Similarly, implementation-defined behavior related to the char type of the elements of the string literal "\xFF" may cause constraint violations at translation time:
constexpr char string[] = { "\xFF", }; // ok constexpr char8_t u8string[] = { u8"\xFF", }; // ok constexpr unsigned char ucstring[] = { "\xFF", }; // possible constraint // violation In both the string and ucstring initializers, the initializer is a (brace-enclosed) string literal of type char. If the type char is capable of representing negative values and its width is 8, then the code above is equivalent to:
constexpr char string[] = { -1, 0, }; // ok constexpr char8_t u8string[] = { 255, 0, }; // ok constexpr unsigned char ucstring[] = { -1, 0, }; // constraint violation The hexadecimal escape sequence results in a value of 255. For an initializer of type char, it is converted to a signed 8-bit integer, making a value of -1. A negative value does not fit within the range of values for unsigned char, and therefore the initialization of ucstring is a constraint violation under the previously stated implementation conditions. In the case where char is not capable of representing negative values, the original snippet is equivalent to the following and there is no constraint violation.
constexpr char string[] = { 255, 0, }; // ok constexpr char8_t u8string[] = { 255, 0, }; // ok constexpr unsigned char ucstring[] = { 255, 0, }; // ok 142) The implementation can treat any register declaration simply as an auto declaration. However, whether or not addressable storage is used, the address of any part of an object declared with storage-class specifier register cannot be computed, either explicitly (by use of the unary & operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier register is sizeof and the typeof operators.
§ 6.7.1
Language
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ISO/IEC 9899:2023 (E)
19
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EXAMPLE 3 An identifier declared with the constexpr specifier may have its value used in constant expressions: constexpr int K = 47; enum { A = K, // valid, constant initialization }; constexpr int L = K; // valid, constexpr initialization static int b = K + 1; // valid, static initialization int array[K]; // not a VLA
20
EXAMPLE 4 An object declared with the constexpr specifier stores the exact value of its initializer, no implicit value change is applied: #include <float.h> constexpr int A = 42LL; constexpr signed short B = ULLONG_MAX; constexpr float C
= 47u;
#if FLT_MANT_DIG > 24 constexpr float D = 536900000;
// valid, 42 always fits in an int // constraint violation, value never // fits // valid, exactly representable // in float
// constraint violation if float is // IEC 60559 binary32
#endif #if (FLT_MANT_DIG == DBL_MANT_DIG) \ && (0 <= FLT_EVAL_METHOD) \ && (FLT_EVAL_METHOD <= 1) constexpr float E = 1.0 / 3.0;
// only valid if double expressions // and float objects have the same // precision
#endif #if FLT_EVAL_METHOD == 0 constexpr float F = 1.0f / 3.0f; #else constexpr float F = (float)(1.0f / 3.0f);
// valid, same type and precision // needs cast to truncate the // excess precision
#endif
21
EXAMPLE 5 This recursively applies to initializers for all elements of an aggregate object declared with the constexpr specifier: constexpr static unsigned short array[] = { 3000, // valid, fits in unsigned short range 300000, // constraint violation if short is 16-bit -1 // constraint violation, target type is unsigned }; struct S { int x, y; }; constexpr struct S s = { .x = INT_MAX, .y = UINT_MAX, };
// valid // constraint violation
Forward references: type definitions (6.7.8), type definitions (6.7.9). 100
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6.7.2 1
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Type specifiers
Syntax type-specifier: void char short int long float double signed unsigned _BitInt ( constant-expression ) bool _Complex _Decimal32 _Decimal64 _Decimal128
atomic-type-specifier struct-or-union-specifier enum-specifier typedef-name typeof-specifier
2
Constraints Except where the type is inferred (6.7.9), at least one type specifier shall be given in the declaration specifiers in each declaration, and in the specifier-qualifier list in each member declaration and type name. Each list of type specifiers shall be one of the following multisets (delimited by commas, when there is more than one multiset per item); the type specifiers may occur in any order, possibly intermixed with the other declaration specifiers. — void — char — signed char — unsigned char — short, signed short, short int, or signed short int — unsigned short, or unsigned short int — int, signed, or signed int — unsigned, or unsigned int — long, signed long, long int, or signed long int — unsigned long, or unsigned long int — long long, signed long long, long long int, or signed long long int — unsigned long long, or unsigned long long int — _BitInt( constant-expression), or signed _BitInt( constant-expression) — unsigned _BitInt( constant-expression) — float — double — long double § 6.7.2
Language
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N3096
— _Decimal32 — _Decimal64 — _Decimal128 — bool — float _Complex — double _Complex — long double _Complex — atomic type specifier — struct or union specifier — enum specifier — typedef name — typeof specifier 3
The type specifier _Complex shall not be used if the implementation does not support complex types, and the type specifiers _Decimal32, _Decimal64, and _Decimal128 shall not be used if the implementation does not support decimal floating types (see 6.10.9.3).
4
The parenthesized constant expression that follows the _BitInt keyword shall be an integer constant expression N that specifies the width (6.2.6.2) of the type. The value of N for unsigned _BitInt shall be greater than or equal to 1. The value of N for _BitInt shall be greater than or equal to 2. The value of N shall be less than or equal to the value of BITINT_MAXWIDTH (see 5.2.4.2.1).
5
Semantics Specifiers for structures, unions, enumerations, atomic types, and typeof specifiers are discussed in 6.7.2.1 through 6.7.2.5. Declarations of typedef names are discussed in 6.7.8. The characteristics of the other types are discussed in 6.2.5.
6
For a declaration such that the declaration specifiers contain no type specifier a mechanism to infer the type from an initializer is discussed in 6.7.9. In such a declaration, optional elements, if any, of a sequence of declaration specifiers appertain to the inferred type (for qualifiers and attribute specifiers) or to the declared objects (for alignment specifiers).
7
Each of the comma-separated multisets designates the same type, except that for bit-fields, it is implementation-defined whether the specifier int designates the same type as signed int or the same type as unsigned int. Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2), structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).
1
6.7.2.1 Structure and union specifiers Syntax struct-or-union-specifier: struct-or-union attribute-specifier-sequenceopt identifieropt { member-declaration-list } struct-or-union attribute-specifier-sequenceopt identifier struct-or-union: struct union
member-declaration-list: member-declaration member-declaration-list member-declaration
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§ 6.7.2.1
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member-declaration: attribute-specifier-sequenceopt specifier-qualifier-list member-declarator-listopt ; static_assert-declaration specifier-qualifier-list: type-specifier-qualifier attribute-specifier-sequenceopt type-specifier-qualifier specifier-qualifier-list type-specifier-qualifier: type-specifier type-qualifier alignment-specifier
member-declarator-list: member-declarator member-declarator-list , member-declarator member-declarator: declarator declaratoropt : constant-expression
2
Constraints A member declaration that does not declare an anonymous structure or anonymous union shall contain a member declarator list.
3
A structure or union shall not contain a member with incomplete or function type (hence, a structure shall not contain an instance of itself, but may contain a pointer to an instance of itself), except that the last member of a structure with more than one named member may have incomplete array type; such a structure (and any union containing, possibly recursively, a member that is such a structure) shall not be a member of a structure or an element of an array.
4
The expression that specifies the width of a bit-field shall be an integer constant expression with a nonnegative value that does not exceed the width of an object of the type that would be specified were the colon and expression omitted143) . If the value is zero, the declaration shall have no declarator.
5
A bit-field shall have a type that is a qualified or unqualified bool, signed int, unsigned int, a bit-precise integer type, or other implementation-defined type. It is implementation-defined whether atomic types are permitted.
6
An attribute specifier sequence shall not appear in a struct-or-union specifier without a member declaration list, except in a declaration of the form: struct-or-union attribute-specifier-sequence identifier ; The attributes in the attribute specifier sequence, if any, are thereafter considered attributes of the struct or union whenever it is named.
7
8
Semantics As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose storage is allocated in an ordered sequence, and a union is a type consisting of a sequence of members whose storage overlap. Structure and union specifiers have the same form. The keywords struct and union indicate that the type being specified is, respectively, a structure type or a union type. 143) While the number of bits in a bool object is at least CHAR_BIT, the width of a bool is just 1 bit.
§ 6.7.2.1
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The optional attribute specifier sequence in a struct-or-union specifier appertains to the structure or union type being declared. The optional attribute specifier sequence in a member declaration appertains to each of the members declared by the member declarator list; it shall not appear if the optional member declarator list is omitted. The optional attribute specifier sequence in a specifier qualifier list appertains to the type denoted by the preceding type specifier qualifiers. The attribute specifier sequence affects the type only for the member declaration or type name it appears in, not other types or declarations involving the same type.
10
The member declaration list is a sequence of declarations for the members of the structure or union. If the member declaration list does not contain any named members, either directly or via an anonymous structure or anonymous union, the behavior is undefined144) .
11
A member of a structure or union may have any complete object type other than a variably modified type.145) In addition, a member may be declared to consist of a specified number of bits (including a sign bit, if any). Such a member is called a bit-field 146) ; its width is preceded by a colon.
12
A bit-field is interpreted as having a signed or unsigned integer type consisting of the specified number of bits147) . If the value 0 or 1 is stored into a nonzero-width bit-field of type bool, the value of the bit-field shall compare equal to the value stored; a bool bit-field has the semantics of a bool.
13
An implementation may allocate any addressable storage unit large enough to hold a bit-field. If enough space remains, a bit-field that immediately follows another bit-field in a structure shall be packed into adjacent bits of the same unit. If insufficient space remains, whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is implementation-defined. The order of allocation of bit-fields within a unit (high-order to low-order or low-order to high-order) is implementation-defined. The alignment of the addressable storage unit is unspecified.
14
A bit-field declaration with no declarator, but only a colon and a width, indicates an unnamed bit-field.148) As a special case, a bit-field structure member with a width of zero indicates that no further bit-field is to be packed into the unit in which the previous bit-field, if any, was placed.
15
An unnamed member whose type specifier is a structure specifier with no tag is called an anonymous structure; an unnamed member whose type specifier is a union specifier with no tag is called an anonymous union. The members of an anonymous structure or union are members of the containing structure or union, keeping their structure or union layout. This applies recursively if the containing structure or union is also anonymous.
16
Each non-bit-field member of a structure or union object is aligned in an implementation-defined manner appropriate to its type.
17
Within a structure object, the non-bit-field members and the units in which bit-fields reside have addresses that increase in the order in which they are declared. A pointer to a structure object, suitably converted, points to its initial member (or if that member is a bit-field, then to the unit in which it resides), and vice versa. There may be unnamed padding within a structure object, but not at its beginning.
18
The size of a union is sufficient to contain the largest of its members. The value of at most one of the members can be stored in a union object at any time. A pointer to a union object, suitably converted, points to each of its members (or if a member is a bit-field, then to the unit in which it resides), and vice versa. The members of a union object overlap in such a way that pointers to them when converted to pointers to character type point to the same byte. There may be unnamed padding at the end of a union object, but not at its beginning.
19
There may be unnamed padding at the end of a structure or union. 144) For further rules affecting compatibility and completeness of structure or union types, see 6.2.7 and 6.7.2.3. 145) A structure or union cannot contain a member with a variably modified type because member names are not ordinary identifiers as defined in 6.2.3. 146) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to or arrays of bit-field objects. 147) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int, then it is implementation-defined whether the bit-field is signed or unsigned. This includes an int type specifier produced using the typeof specifiers (6.7.2.5). 148) An unnamed bit-field structure member is useful for padding to conform to externally imposed layouts.
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As a special case, the last member of a structure with more than one named member may have an incomplete array type; this is called a flexible array member. In most situations, the flexible array member is ignored. In particular, the size of the structure is as if the flexible array member were omitted except that it may have more trailing padding than the omission would imply. However, when a . (or ->) operator has a left operand that is (a pointer to) a structure with a flexible array member and the right operand names that member, it behaves as if that member were replaced with the longest array (with the same element type) that would not make the structure larger than the object being accessed; the offset of the array shall remain that of the flexible array member, even if this would differ from that of the replacement array. If this array would have no elements, it behaves as if it had one element but the behavior is undefined if any attempt is made to access that element or to generate a pointer one past it.
21
EXAMPLE 1 The following declarations illustrate the behavior when an attribute is written on a tag declaration: struct [[deprecated]] S; // valid, [[deprecated]] appertains to struct S void f(struct S *s); // valid, the struct S type has the [[deprecated]] // attribute struct S { // valid, struct S inherits the [[deprecated]] attribute int a; // from the previous declaration }; void g(struct [[deprecated]] S s); // invalid
22
EXAMPLE 2 The following illustrates anonymous structures and unions: struct v { union { // anonymous union struct { int i, j; }; // anonymous structure struct { long k, l; } w; }; int m; } v1; v1.i = 2; // valid v1.k = 3; // invalid: v1.w.k = 5; // valid
23
inner structure is not anonymous
EXAMPLE 3 After the declaration: struct s { int n; double d[]; };
the structure struct s has a flexible array member d. A typical way to use this is: int m = /* some value */; struct s *p = malloc(sizeof(struct s) + sizeof(double [m]));
and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if p had been declared as: struct { int n; double d[m]; } *p;
(there are circumstances in which this equivalence is broken; in particular, the offsets of member d might not be the same). 24
Following the above declaration: struct s t1 = { 0 }; struct s t2 = { 1, { 4.2 }}; t1.n = 4; t1.d[0] = 4.2;
§ 6.7.2.1
// valid // invalid // valid // might be undefined behavior
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The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that sizeof(struct s) >= offsetof(struct s, d) + sizeof(double)
in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming code. 25
After the further declaration: struct ss { int n; };
the expressions: sizeof(struct s) >= sizeof(struct ss) sizeof(struct s) >= offsetof(struct s, d)
are always equal to 1. 26
If sizeof(double) is 8, then after the following code is executed: struct s *s1; struct s *s2; s1 = malloc(sizeof(struct s) + 64); s2 = malloc(sizeof(struct s) + 46);
and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most purposes, as if the identifiers had been declared as: struct { int n; double d[8]; } *s1; struct { int n; double d[5]; } *s2; 27
Following the further successful assignments: s1 = malloc(sizeof(struct s) + 10); s2 = malloc(sizeof(struct s) + 6);
they then behave as if the declarations were: struct { int n; double d[1]; } *s1, *s2;
and: double *dp; dp = &(s1->d[0]); // valid // valid *dp = 42; dp = &(s2->d[0]); // valid // undefined behavior *dp = 42; 28
The assignment: *s1 = *s2;
only copies the member n; if any of the array elements are within the first sizeof(struct s) bytes of the structure, they are set to an indeterminate representation, that may or may not coincide with a copy of the representation of the elements of the source array. 29
EXAMPLE 4 Because members of anonymous structures and unions are considered to be members of the containing structure or union, struct s in the following example has more than one named member and thus the use of a flexible array member is valid: 106
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struct s { struct { int i; }; int a[]; };
Forward references: declarators (6.7.6), tags (6.7.2.3).
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6.7.2.2 Enumeration specifiers Syntax enum-specifier: enum attribute-specifier-sequenceopt identifieropt enum-type-specifieropt { enumerator-list } enum attribute-specifier-sequenceopt identifieropt enum-type-specifieropt { enumerator-list , } enum identifier enum-type-specifieropt enumerator-list: enumerator enumerator-list , enumerator enumerator: enumeration-constant attribute-specifier-sequenceopt enumeration-constant attribute-specifier-sequenceopt = constant-expression enum-type-specifier: : specifier-qualifier-list All enumerations have an underlying type. The underlying type can be explicitly specified using an enum type specifier and is its fixed underlying type. If it is not explicitly specified, the underlying type is the enumeration’s compatible type, which is either char or a standard or extended signed or unsigned integer type. Constraints For an enumeration with a fixed underlying type, the integer constant expression defining the value of the enumeration constant shall be representable in that fixed underlying type. If the value of an enumeration constant without a defining constant expression for an enumeration with fixed underlying type is obtained by adding 1 to the previous enumeration constant, the value of that previous enumeration constant shall not be the maximum value of the underlying type.
4
For an enumeration without a fixed underlying type, the expression that defines the value of an enumeration constant shall be an integer constant expression. For all the integer constant expressions which make up the values of the enumeration constants, there shall be a type capable of representing all the values that is a standard or extended signed or unsigned integer type, or char.
5
If an enum type specifier is present, then the longest possible sequence of tokens that can be interpreted as a specifier qualifier list is interpreted as part of the enum type specifier. It shall name an integer type that is neither an enumeration nor a bit-precise integer type. The underlying type of the enumeration is the unqualified, non-atomic version of the type specified by the type specifiers in the specifier qualifier list.149)
6
An enum specifier of the form enum identifier enum-type-specifier
may not appear except in a declaration of the form enum identifier enum-type-specifier ;
149) The specifier qualifier list is not a context listed in 6.7.5 as permitted for alignment specifiers, so the presence of an alignment specifier in the list violates a constraint.
§ 6.7.2.2
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unless it is immediately followed by an opening brace, an enumerator list (with an optional ending comma), and a closing brace. 7
8
If two enum specifiers that include an enum type specifier declare the same type, the underlying types shall be compatible. Semantics The optional attribute specifier sequence in the enum specifier appertains to the enumeration; the attributes in that attribute specifier sequence are thereafter considered attributes of the enumeration whenever it is named. The optional attribute specifier sequence in the enumerator appertains to that enumerator.
9
The identifiers in an enumerator list are declared as constants of the types specified below and may appear wherever such are permitted.150) An enumerator with = defines its enumeration constant as the value of the constant expression. If the first enumerator has no =, the value of its enumeration constant is zero. Each subsequent enumerator with no = defines its enumeration constant as the value of the constant expression obtained by adding 1 to the value of the previous enumeration constant. (The use of enumerators with = may produce enumeration constants with values that duplicate other values in the same enumeration.) The enumerators of an enumeration are also known as its members.
10
The type for the members of an enumeration is called the enumeration member type.
11
During the processing of each enumeration constant in the enumerator list, the type of the enumeration constant shall be: — the previously declared type, if it is a redeclaration of the same enumeration constant; or, — the enumerated type, for an enumeration with fixed underlying type; or, — int, if there are no previous enumeration constants in the enumerator list and no explicit = with a defining integer constant expression; or, — int, if given explicitly with = and the value of the integer constant expression is representable by an int; or, — the type of the integer constant expression, if given explicitly with = and if the value of the integer constant expression is not representable by int; or, — the type of the value from the previous enumeration constant with one added to it. If such an integer constant expression would overflow or wraparound the value of the previous enumeration constant from the addition of one, the type takes on either: — a suitably sized signed integer type, excluding the bit-precise signed integer types, capable of representing the value of the previous enumeration constant plus one; or, — a suitably sized unsigned integer type, excluding the bit-precise unsigned integer types, capable of representing the value of the previous enumeration constant plus one. A signed integer type is chosen if the previous enumeration constant being added is of signed integer type. An unsigned integer type is chosen if the previous enumeration constant is of unsigned integer type. If there is no suitably sized integer type described previously which can represent the new value, then the enumeration has no type which can represent all its values.151)
12
For all enumerations without a fixed underlying type, each enumerated type shall be compatible with char, a signed or an unsigned integer type that is not a bool or a bit-precise integer type. The 150) Thus, the identifiers of enumeration constants declared in the same scope are all required to be distinct from each other
and from other identifiers declared in ordinary declarators. 151) Therefore, a constraint has been violated.
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choice of type is implementation-defined152) , but shall be capable of representing the values of all the members of the enumeration153) . 13
Enumeration constants can be redefined in the same scope with the same value as part of a redeclaration of the same enumerated type.
14
The enumeration member type for an enumerated type without fixed underlying type upon completion is: — int if all the values of the enumeration are representable as an int; or, — the enumerated type.154)
15
The enumeration member type for an enumerated type with fixed underlying type is the enumerated type. The enumerated type is compatible with the underlying type of the enumeration. After possible lvalue conversion a value of the enumerated type behaves the same as the value with the underlying type, in particular with all aspects of promotion, conversion, and arithmetic.Conversion to the enumerated type has the same semantics as conversion to the underlying type.155)
16
EXAMPLE The following fragment: enum hue { chartreuse, burgundy, claret=20, winedark }; enum hue col, *cp; col = claret; cp = &col; if (*cp != burgundy) /* ... */
makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a pointer to an object that has that type. The enumerated values are in the set {0, 1, 20, 21}. 17
EXAMPLE Even if the value of an enumeration constant is generated by the implicit addition of one, an enumeration with a fixed underlying type does not exhibit typical overflow behavior: #include <limits.h> enum us : unsigned short { us_max = USHRT_MAX, us_violation, /* Constraint violation: USHRT_MAX + 1 would wraparound. */ _ _ us violation 2 = us_max + 1, /* Maybe constraint violation: USHRT_MAX + 1 may be promoted to "int", and result is too wide for the underlying type. */ us_wraparound_to_zero = (unsigned short)(USHRT_MAX + 1) /* Okay: conversion done in constant expression before conversion to underlying type: unsigned semantics okay. */ }; enum ui : unsigned int { ui_max = UINT_MAX, ui_violation, /* Constraint violation: UINT_MAX + 1 would wraparound. */ 152) An implementation can delay the choice of which integer type until all enumeration constants have been seen. 153) For further rules affecting compatibility and completeness of enumerated types see 6.2.7 and 6.7.2.3. 154) The integer type selected during processing of the enumerator list (before completion) of the enumeration may not be the same as the compatible implementation-defined integer type selected for the completed enumeration. 155) This means in particular that if the compatible type is bool, values of the enumerated type behave in all aspects the same as bool, conversion to the enumerated type behaves the same as bool (6.3.1.2), and the members only have values false and true. If it is a signed integer type and the constant expression of an enumeration constant overflows, a constraint for constant expressions (6.6) is violated.
§ 6.7.2.2
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ui_no_violation = ui_max + 1, /* Okay: Arithmetic performed as typical unsigned integer arithmetic: conversion from a value that is already 0 to 0. */ ui_wraparound_to_zero = (unsigned int)(UINT_MAX + 1) /* Okay: conversion done in constant expression before conversion to underlying type: unsigned semantics okay. */ }; int main () { // Same as return 0; return ui_wraparound_to_zero + us_wraparound_to_zero; }
18
EXAMPLE The following fragment: #include <limits.h> enum E1: short; enum E2: short; enum E3; /* Constraint violation: E3 forward declaration. */ enum E4 : unsigned long long; enum E1 : short { m11, m12 }; enum E1 x = m11; enum E2 : long { m21, m22 }; /* Constraint violation: different underlying types */ enum E3 { m31, m32, m33 = sizeof(enum E3) /* Constraint violation: E3 is not complete here. */ }; enum E3 : int; /* Constraint violation: E3 previously had no underlying type */ enum E4 : unsigned long long { m40 = sizeof(enum E4), m41 = ULLONG_MAX, m42 /* Constraint violation: unrepresentable value (wraparound) */ }; enum E5 y; /* Constraint violation: incomplete type */ enum E6 : long int z; /* Constraint violation: enum-type-specifier with identifier in declarator */ enum E7 : long int = 0; /* Syntax violation: enum-type-specifier with initializer */
demonstrates many of the properties of multiple declarations of enumerations with underlying types. Particularly, enum E3 is declared and defined without an underlying type first, therefore a redeclaration with an underlying type second is a violation. Because it not complete at that time within its enumerator list, sizeof(enum E3) is a constraint violation within the enum E3 definition. enum E4 is complete as it is being defined, therefore sizeof(enum E4) is not a constraint violation. 19
EXAMPLE The following fragment: enum no_underlying { a0 }; int main (void) { int a = _Generic(a0,
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int: 2, unsigned char: 1, default: 0 ); int b = _Generic((enum no_underlying)a0, int: 2, unsigned char: 1, default: 0 ); return a + b; }
demonstrates the implementation-defined nature of the underlying type of enumerations using generic selection (6.5.1.1). The value of a after its initialization is 2. The value of b after its initialization is implementation-defined: the enumeration must be compatible with a type large enough to fit the values of its enumeration constants. Because the only value is 0 for a0, b may hold any of 2, 1, or 0. Now, consider a similar fragment, but using a fixed underlying type: enum underlying : unsigned char { b0 }; int main (void) { int a = _Generic(b0, int: 2, unsigned char: 1, default: 0 ); int b = _Generic((enum underlying)b0, int: 2, unsigned char: 1, default: 0 ); return 0; }
Here, we are guaranteed that a and b are both initialized to 1. This makes enumerations with a fixed underlying type more portable. 20
EXAMPLE Enumerations with a fixed underlying type must have their braces and the enumerator list specified as part of their declaration if they are not a standalone declaration: void f1 (enum a : long b); /* Constraint violation */ void f2 (enum c : long { x } d); enum e : int f3(); /* Constraint violation */ typedef enum t u; /* Constraint violation: forward declaration of t. */ typedef enum v : short W; /* Constraint violation */ typedef enum q : short { s } R; struct s1 { int x; enum e : int : 1; /* Constraint violation */ int y; }; enum forward; /* Constraint violation */ extern enum forward fwd_val0; /* Constraint violation: incomplete type */ extern enum forward* fwd_ptr0; /* Constraint violation: enums cannot be
§ 6.7.2.2
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used like other incomplete types */ extern int* fwd_ptr0; /* Constraint violation: incompatible with incomplete type. */ enum forward1 : int; extern enum forward1 fwd_val1; extern int fwd_val1; extern enum forward1* fwd_ptr1; extern int* fwd_ptr1; int main () { enum e : short; enum e : short f = 0; /* Constraint violation */ enum g : short { y } h = y; return 0; } 21
EXAMPLE Enumerations with a fixed underlying type are complete when the enum type specifier for that specific enumeration is complete. The enumeration e in this snippet: enum e : typeof ((enum e : short { A })0, (short)0);
enum e is considered complete by the first opening brace within the typeof in this snippet.
Forward references: generic selection (6.5.1.1), tags (6.7.2.3), declarations (6.7), declarators (6.7.6), function declarators (6.7.6.3), type names (6.7.7).
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6.7.2.3 Tags Constraints Where two declarations that use the same tag declare the same type, they shall both use the same choice of struct, union, or enum. If two declarations of the same type have a member-declaration or enumerator-list, one shall not be nested within the other and both declarations shall fulfill all requirements of compatible types (6.2.7) with the additional requirement that corresponding members of structure or union types shall have the same (and not merely compatible) types. A type specifier of the form enum identifier
without an enumerator list shall only appear after the type it specifies is complete. 3
A type specifier of the form struct-or-union attribute-specifier-sequenceopt identifier shall not contain an attribute specifier sequence156) .
4
Semantics All declarations of structure, union, or enumerated types that have the same scope and use the same tag declare the same type.
5
Irrespective of whether there is a tag or what other declarations of the type are in the same translation unit, the type (except enumerated types with a fixed underlying type) is incomplete until immediately after the closing brace of the list defining the content for the first time and complete thereafter.
6
Enumerated types with fixed underlying type (6.7.2.2) are complete immediately after their first associated enum type specifier ends.
7
EXAMPLE 1 The following example shows allowed redeclarations of the same structure, union, or enumerated type in the same scope: 156) As specified in 6.7.2.1 above, the type specifier may be followed by a ; or a member declaration list.
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struct foo { struct { int x; }; }; struct foo { struct { int x; }; }; union bar { int x; float y; }; union bar { int x; float y; }; typedef struct q { int x; } q_t; typedef struct q { int x; } q_t; void foo(void) { struct S { int x; }; struct T { struct S s; }; struct S { int x; }; struct T { struct S s; }; } enum X { A = 1, B = 1 + 1 }; enum X { B = 2, A = 1 };
8
EXAMPLE 2 The following example shows invalid redeclarations of the same structure, union, or enumerated type in the same scope: struct foo { int (*p)[3]; }; struct foo { int (*p)[]; };
// member has different type
union bar { int x; float y; }; union bar { int z; float y; }; // member has different name union purr { int x; float y; }; union purr { float y; int x; }; // members have different order // Above only valid if each union "purr" is in // two different translation units typedef struct { int x; } q_t; typedef struct { int x; } q_t; // not the same type struct S { int x; }; void foo(void) { struct T { struct S s; }; struct S { int x; }; struct T { struct S s; }; // struct S not the same type } enum X { A = 1, B = 2 }; enum X { A = 1, B = 3 };
// different enumeration constant
enum R { C = 1 }; enum Q { C = 1 }; enum Q { C = C };
// conflicting enumeration constant // ok!
9
Two declarations of structure, union, or enumerated types which are in different scopes or use different tags declare distinct types. Each declaration of a structure, union, or enumerated type which does not include a tag declares a distinct type.
10
A type specifier of the form struct-or-union attribute-specifier-sequenceopt identifieropt { member-declaration-list } or enum attribute-specifier-sequenceopt identifieropt enum-type-specifieropt { enumerator-list }
or § 6.7.2.3
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enum attribute-specifier-sequenceopt identifieropt enum-type-specifieropt { enumerator-list , }
declares a structure, union, or enumerated type. The list defines the structure content, union content, or enumeration content. If an identifier is provided157) , the type specifier also declares the identifier to be the tag of that type. The optional attribute specifier sequence appertains to the structure, union, or enumerated type being declared; the attributes in that attribute specifier sequence are thereafter considered attributes of the structure, union, or enumerated type whenever it is named. 11
A declaration of the form struct-or-union attribute-specifier-sequenceopt identifier ; or enum identifier enum-type-specifier ;
specifies a structure, union, or enumerated type and declares the identifier as a tag of that type158) . The optional attribute specifier sequence appertains to the structure or union type being declared; the attributes in that attribute specifier sequence are thereafter considered attributes of the structure or union type whenever it is named. 12
If a type specifier of the form struct-or-union attribute-specifier-sequenceopt identifier occurs other than as part of one of the above forms, and no other declaration of the identifier as a tag is visible, then it declares an incomplete structure or union type, and declares the identifier as the tag of that type.158)
13
If a type specifier of the form struct-or-union attribute-specifier-sequenceopt identifier or enum identifier
occurs other than as part of one of the above forms, and a declaration of the identifier as a tag is visible, then it specifies the same type as that other declaration, and does not redeclare the tag. 14
EXAMPLE 3 This mechanism allows declaration of a self-referential structure. struct tnode { int count; struct tnode *left, *right; };
specifies a structure that contains an integer and two pointers to objects of the same type. Once this declaration has been given, the declaration struct tnode s, *sp;
declares s to be an object of the given type and sp to be a pointer to an object of the given type. With these declarations, the expression sp->left refers to the left struct tnode pointer of the object to which sp points; the expression s.right->count designates the count member of the right struct tnode pointed to from s. 15
The following alternative formulation uses the typedef mechanism: typedef struct tnode TNODE; struct tnode { int count; 157) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations can make use of that typedef name to declare objects having the specified structure, union, or enumerated type. 158) A similar construction for an enum that does not contain a fixed underlying type does not exist. Enumerations with a fixed underlying type are always complete after the enum type specifier.
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TNODE *left, *right; }; TNODE s, *sp;
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EXAMPLE 4 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential structures, the declarations struct s1 { struct s2 *s2p; /* ... */ }; // D1 struct s2 { struct s1 *s1p; /* ... */ }; // D2
specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in D2. To eliminate this context sensitivity, the declaration struct s2;
can be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then completes the specification of the new type. Forward references: declarators (6.7.6), type definitions (6.7.8).
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6.7.2.4 Atomic type specifiers Syntax atomic-type-specifier: _Atomic ( type-name )
Constraints Atomic type specifiers shall not be used if the implementation does not support atomic types (see 6.10.9.3). The type name in an atomic type specifier shall not refer to an array type, a function type, an atomic type, or a qualified type. Semantics The properties associated with atomic types are meaningful only for expressions that are lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is interpreted as a type specifier (with a type name), not as a type qualifier. 6.7.2.5 Typeof specifiers Syntax typeof-specifier: typeof ( typeof-specifier-argument ) typeof_unqual ( typeof-specifier-argument )
typeof-specifier-argument: expression type-name
2
The typeof and typeof_unqual tokens are collectively called the typeof operators.
3
Constraints The typeof operators shall not be applied to an expression that designates a bit-field member. § 6.7.2.5
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Semantics The typeof specifier applies the typeof operators to an expression (6.5) or a type name. If the typeof operators are applied to an expression, they yield the type of their operand159) . Otherwise, they designate the same type as the type name with any nested typeof specifier evaluated.160) If the type of the operand is a variably modified type, the operand is evaluated; otherwise, the operand is not evaluated.
5
The result of the typeof_unqual operator is the non-atomic unqualified type that would result from the typeof operator161) . The typeof operator preserves all qualifiers.
6
EXAMPLE 1 Type of an expression. typeof(1+1) main () { return 0; }
is equivalent to this program: int main () { return 0; } 7
EXAMPLE 2 The following program: const _Atomic int purr = 0; const int meow = 1; const char* const animals[] = { "aardvark", "bluejay", "catte", }; typeof_unqual(meow) main (int argc, char* argv[]) { typeof_unqual(purr) plain_purr; typeof(_Atomic typeof(meow)) atomic_meow; typeof(animals) animals_array; typeof_unqual(animals) animals2_array; return 0; }
is equivalent to this program: const _Atomic int purr = 0; const int meow = 1; const char* const animals[] = { "aardvark", "bluejay", "catte", }; int main (int argc, char* argv[]) { int plain_purr; const _Atomic int atomic_meow; const char* const animals_array[3]; const char* animals2_array[3]; return 0; 159) When applied to a parameter declared to have array or function type, the typeof operators yield the adjusted (pointer) type (see 6.9.1). 160) If the typeof specifier argument is itself a typeof specifier, the operand will be evaluated before evaluating the current typeof operator. This happens recursively until a typeof specifier is no longer the operand. 161) _Atomic ( type-name), with parentheses, is considered an _Atomic-qualified type.
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} 8
EXAMPLE 3 The equivalence between sizeof and typeof’s deduction of the type means this program has no constraint violations: int main (int argc, char* argv[]) { static_assert(sizeof(typeof(’p’)) == sizeof(int)); static_assert(sizeof(typeof(’p’)) == sizeof(’p’)); static_assert(sizeof(typeof((char)’p’)) == sizeof(char)); static_assert(sizeof(typeof((char)’p’)) == sizeof((char)’p’)); static_assert(sizeof(typeof("meow")) == sizeof(char[5])); static_assert(sizeof(typeof("meow")) == sizeof("meow")); static_assert(sizeof(typeof(argc)) == sizeof(int)); static_assert(sizeof(typeof(argc)) == sizeof(argc)); static_assert(sizeof(typeof(argv)) == sizeof(char**)); static_assert(sizeof(typeof(argv)) == sizeof(argv)); static_assert(sizeof(typeof_unqual(’p’)) == sizeof(int)); static_assert(sizeof(typeof_unqual(’p’)) == sizeof(’p’)); static_assert(sizeof(typeof_unqual((char)’p’)) == sizeof(char)); static_assert(sizeof(typeof_unqual((char)’p’)) == sizeof((char)’p’)); static_assert(sizeof(typeof_unqual("meow")) == sizeof(char[5])); static_assert(sizeof(typeof_unqual("meow")) == sizeof("meow")); static_assert(sizeof(typeof_unqual(argc)) == sizeof(int)); static_assert(sizeof(typeof_unqual(argc)) == sizeof(argc)); static_assert(sizeof(typeof_unqual(argv)) == sizeof(char**)); static_assert(sizeof(typeof_unqual(argv)) == sizeof(argv)); return 0; }
9
EXAMPLE 4 The following program with nested typeof(...): int main (int argc, char*[]) { float val = 6.0f; return (typeof(typeof_unqual(typeof(argc))))val; }
is equivalent to this program: int main (int argc, char*[]) { float val = 6.0f; return (int)val; } 10
EXAMPLE 5 Variable length arrays with typeof operators performs the operation at execution time rather than translation time. #include <stddef.h> size_t vla_size (int n) { typedef char vla_type[n + 3]; vla_type b; // variable length array return sizeof( typeof_unqual(b) ); // execution-time sizeof, translation-time typeof operation } int main () { return (int)vla_size(10); // vla_size returns 13 }
§ 6.7.2.5
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EXAMPLE 6 Nested typeof operators, arrays, and pointers do not perform array to pointer decay. int main () { typeof(typeof(const char*)[4]) y = { "a", "b", "c", "d" }; // 4-element array of "pointer to const char" return 0; }
12
EXAMPLE 7 Function, pointer, and array types may be substituted with typeof operations. void f(int); typeof(f(5)) g(double x) { printf("value %g\n", x); }
// g has type "void(double)"
typeof(g)* h; typeof(true ? g : NULL) k;
// h has type "void(*)(double)" // k has type "void(*)(double)"
void j(double A[5], typeof(A)* B); // j has type "void(double*, double**)" extern typeof(double[]) D; typeof(D) C = { 0.7, 99 };
// D has an incomplete type // C has type "double[2]"
typeof(D) D = { 5, 8.9, 0.1, 99 }; // D is now completed to "double[4]" typeof(D) E; // E has type "double[4]" from D’s completed type
6.7.3 1
Type qualifiers
Syntax type-qualifier: const restrict volatile _Atomic
2
Constraints Types other than pointer types whose referenced type is an object type and (possibly multidimensional) array types with such pointer types as element type shall not be restrict-qualified.
3
The _Atomic qualifier shall not be used if the implementation does not support atomic types (see 6.10.9.3).
4
The type modified by the _Atomic qualifier shall not be an array type or a function type.
5
Semantics The properties associated with qualified types are meaningful only for expressions that are lvalues.162)
6
If the same qualifier appears more than once in the same specifier-qualifier list or as declaration specifiers, either directly, via one or more typeof specifiers, or via one or more typedefs, the behavior is the same as if it appeared only once. If other qualifiers appear along with the _Atomic qualifier the resulting type is the so-qualified atomic type. 162) The implementation can place a const object that is not volatile in a read-only region of storage. Moreover, the implementation need not allocate storage for such an object if its address is never used.
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If an attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is made to refer to an object defined with a volatile-qualified type through use of an lvalue with non-volatile-qualified type, the behavior is undefined.163)
8
An object that has volatile-qualified type may be modified in ways unknown to the implementation or have other unknown side effects. Therefore, any expression referring to such an object shall be evaluated strictly according to the rules of the abstract machine, as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the object shall agree with that prescribed by the abstract machine, except as modified by the unknown factors mentioned previously.164) What constitutes an access to an object that has volatile-qualified type is implementation-defined.
9
An object that is accessed through a restrict-qualified pointer has a special association with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to that object use, directly or indirectly, the value of that pointer.165) The intended use of the restrict qualifier (like the register storage class) is to promote optimization, and deleting all instances of the qualifier from all preprocessing translation units composing a conforming program does not change its meaning (i.e., observable behavior), unless _Generic is used to distinguish whether or not a type has that qualifier.
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If the specification of an array type includes any type qualifiers, both the array and the element type are so-qualified. If the specification of a function type includes any type qualifiers, the behavior is undefined.166)
11
For two qualified types to be compatible, both shall have the identically qualified version of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers does not affect the specified type.
12
EXAMPLE 1 An object declared extern const volatile int real_time_clock;
might be modifiable by hardware, but cannot be assigned to, incremented, or decremented. 13
EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers modify an aggregate type: const struct s { int mem; } cs = { 1 }; struct s ncs; // the object ncs is modifiable typedef int A[2][3]; const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int int *pi; const int *pci; ncs = cs; // valid cs = ncs; // violates modifiable lvalue constraint for = pi = &ncs.mem; // valid pi = &cs.mem; // violates type constraints for = pci = &cs.mem; // valid pi = a[0]; // invalid: a[0] has type "const int *"
14
EXAMPLE 3 The declaration 163) This applies to those objects that behave as if they were defined with qualified types, even if they are never actually defined as objects in the program (such as an object at a memory-mapped input/output address). 164) A volatile declaration can be used to describe an object corresponding to a memory-mapped input/output port or an object accessed by an asynchronously interrupting function. Actions on objects so declared are not allowed to be "optimized out" by an implementation or reordered except as permitted by the rules for evaluating expressions. 165) For example, a statement that assigns a value returned by malloc to a single pointer establishes this association between the allocated object and the pointer. 166) This can occur with typedef s. Note that this rule does not apply to the _Atomic qualifier, and that qualifiers do not have any direct effect on the array type itself, but affect conversion rules for pointer types that reference an array type.
§ 6.7.3
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_Atomic volatile int *p;
specifies that p has the type "pointer to volatile atomic int", a pointer to a volatile-qualified atomic type.
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6.7.3.1 Formal definition of restrict Let D be a declaration of an ordinary identifier that provides a means of designating an object P as a restrict-qualified pointer to type T.
2
If D appears inside a block and does not have storage class extern, let B denote the block. If D appears in the list of parameter declarations of a function definition, let B denote the associated block. Otherwise, let B denote the block of main (or the block of whatever function is called at program startup in a freestanding environment).
3
In what follows, a pointer expression E is said to be based on object P if (at some sequence point in the execution of B prior to the evaluation of E) modifying P to point to a copy of the array object into which it formerly pointed would change the value of E.167) Note that "based" is defined only for expressions with pointer types.
4
During each execution of B, let L be any lvalue that has &L based on P. If L is used to access the value of the object X that it designates, and X is also modified (by any means), then the following requirements apply: T shall not be const-qualified. Every other lvalue used to access the value of X shall also have its address based on P. Every access that modifies X shall be considered also to modify P, for the purposes of this subclause. If P is assigned the value of a pointer expression E that is based on another restricted pointer object P2, associated with block B2, then either the execution of B2 shall begin before the execution of B, or the execution of B2 shall end prior to the assignment. If these requirements are not met, then the behavior is undefined.
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Here an execution of B means that portion of the execution of the program that would correspond to the lifetime of an object with scalar type and automatic storage duration associated with B.
6
A translator is free to ignore any or all aliasing implications of uses of restrict.
7
EXAMPLE 1 The file scope declarations int * restrict a; int * restrict b; extern int c[];
assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the program, then it is never accessed using either of the other two. 8
EXAMPLE 2 The function parameter declarations in the following example void f(int n, int * restrict p, int * restrict q) { while (n-- > 0) *p++ = *q++; }
assert that, during each execution of the function, if an object is accessed through one of the pointer parameters, then it is not also accessed through the other. The translator can make this no-aliasing inference based on the parameter declarations alone, without analyzing the function body. 9
The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence analysis of function f without examining any of the calls of f in the program. The cost is that the programmer has to examine all those calls to ensure that none give undefined behavior. For example, the second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through both p and q. 167) In other words, E depends on the value of P itself rather than on the value of an object referenced indirectly through P. For example, if identifier p has type (int **restrict), then the pointer expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer expressions *p and p[1] are not.
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void g(void) { extern int d[100]; f(50, d + 50, d); // valid f(50, d + 1, d); // undefined behavior } 10
EXAMPLE 3 The function parameter declarations void h(int n, int * restrict p, int * restrict q, int * restrict r) { int i; for (i = 0; i < n; i++) p[i] = q[i] + r[i]; }
illustrate how an unmodified object can be aliased through two restricted pointers. If a and b are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not modified within function h. 11
EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a function call and an equivalent nested block. With one exception, only "outer-to-inner" assignments between restricted pointers declared in nested blocks have defined behavior. { int * restrict p1; int * restrict q1; p1 = q1; // undefined behavior { int * restrict p2 = p1; // valid int * restrict q2 = q1; // valid p1 = q2; // undefined behavior p2 = q2; // undefined behavior } }
12
The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For example, this permits new_vector to return a vector. typedef struct { int n; float * restrict v; } vector; vector new_vector(int n) { vector t; t.n = n; t.v = malloc(n * sizeof(float)); return t; }
13
EXAMPLE 5 Suppose that a programmer knows that references of the form p[i] and q[j] are never aliases in the body of a function: void f(int n, int *p, int *q) { /* ... */ }
There are several ways that this information could be conveyed to a translator using the restrict qualifier. Example 2 shows the most effective way, qualifying all pointer parameters, and can be used provided that neither p nor q becomes based on the other in the function body. A potentially effective alternative is:
§ 6.7.3.1
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void f(int n, int * restrict p, int * const q) { /* ... */ }
Again, it is possible for a translator to make the no-aliasing inference based on the parameter declarations alone, though now it must use subtler reasoning: that the const-qualification of q precludes it becoming based on p. There is also a requirement that q is not modified, so this alternative cannot be used for the function in Example 2, as written. 14
EXAMPLE 6 Another potentially effective alternative is: void f(int n, int *p, int const * restrict q) { /* ... */ }
Again, it is possible for a translator to make the no-aliasing inference based on the parameter declarations alone, though now it must use even subtler reasoning: that this combination of restrict and const means that objects referenced using q cannot be modified, and so no modified object can be referenced using both p and q. 15
EXAMPLE 7 The least effective alternative is: void f(int n, int * restrict p, int *q) { /* ... */ }
Here the translator can make the no-aliasing inference only by analyzing the body of the function and proving that q cannot become based on p. Some translator designs may choose to exclude this analysis, given availability of the more effective alternatives above. Such a translator is required to assume that aliases are present because assuming that aliases are not present may result in an incorrect translation. Also, a translator that attempts the analysis may not succeed in all cases and consequently need to conservatively assume that aliases are present.
6.7.4 1
Function specifiers
Syntax function-specifier: inline _Noreturn
2
Constraints Function specifiers shall be used only in the declaration of an identifier for a function.
3
An inline definition of a function with external linkage shall not contain a definition of a modifiable object with static or thread storage duration, and shall not contain a reference to an identifier with internal linkage.
4
In a hosted environment, no function specifier(s) shall appear in a declaration of main.
5
Semantics A function specifier may appear more than once; the behavior is the same as if it appeared only once.
6
A function declared with an inline function specifier is an inline function. Making a function an inline function suggests that calls to the function be as fast as possible.168) The extent to which such suggestions are effective is implementation-defined.169)
7
Any function with internal linkage can be an inline function. For a function with external linkage, the following restrictions apply: If a function is declared with an inline function specifier, then it 168) By using, for example, an alternative to the usual function call mechanism, such as "inline substitution". Inline substitution is not textual substitution, nor does it create a new function. Therefore, for example, the expansion of a macro used within the body of the function uses the definition it had at the point the function body appears, and not where the function is called; and identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a single address, regardless of the number of inline definitions that occur in addition to the external definition. 169) For example, an implementation might never perform inline substitution, or might only perform inline substitutions to calls in the scope of an inline declaration.
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shall also be defined in the same translation unit. If all the file scope declarations for a function in a translation unit include the inline function specifier without extern, then the definition in that translation unit is an inline definition. An inline definition does not provide an external definition for the function and does not forbid an external definition in another translation unit. Inline definitions provide an alternative to external definitions, which a translator may use to implement any call to the function in the same translation unit. It is unspecified whether a call to the function uses the inline definition or the external definition.170) 8
9
10
A function declared with a _Noreturn function specifier shall not return to its caller. The attribute [[noreturn]] provides similar semantics. The _Noreturn function specifier is an obsolescent feature (6.7.12.6). Recommended practice The implementation should produce a diagnostic message for a function declared with a _Noreturn function specifier that appears to be capable of returning to its caller. EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external definition, or a definition available for use only within the translation unit. A file scope declaration with extern creates an external definition. The following example shows an entire translation unit. inline double fahr(double t) { return (9.0 * t) / 5.0 + 32.0; } inline double cels(double t) { return (5.0 * (t - 32.0)) / 9.0; } extern double fahr(double);
// creates an external definition
double convert(int is_fahr, double temp) { /* A translator may perform inline substitutions */ return is_fahr ? cels(temp): fahr(temp); } 11
Note that the definition of fahr is an external definition because fahr is also declared with extern, but the definition of cels is an inline definition. Because cels has external linkage and is referenced, an external definition has to appear in another translation unit (see 6.9); the inline definition and the external definition are distinct and either can be used for the call. Forward references: function definitions (6.9.1).
6.7.5 1
Alignment specifier
Syntax alignment-specifier: alignas ( type-name ) alignas ( constant-expression )
2
Constraints An alignment specifier shall appear only in the declaration specifiers of a declaration, or in the specifier-qualifier list of a member declaration, or in the type name of a compound literal. An 170) Since an inline definition is distinct from the corresponding external definition and from any other corresponding inline definitions in other translation units, all corresponding objects with static storage duration are also distinct in each of the definitions.
§ 6.7.5
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alignment specifier shall not be used in conjunction with either of the storage-class specifiers typedef or register, nor in a declaration of a function or bit-field. 3
The constant expression shall be an integer constant expression. It shall evaluate to a valid fundamental alignment, or to a valid extended alignment supported by the implementation for an object of the storage duration (if any) being declared, or to zero.
4
An object shall not be declared with an over-aligned type with an extended alignment requirement not supported by the implementation for an object of that storage duration.
5
The combined effect of all alignment specifiers in a declaration shall not specify an alignment that is less strict than the alignment that would otherwise be required for the type of the object or member being declared.
6
Semantics The first form is equivalent to alignas(alignof( type-name )).
7
The alignment requirement of the declared object or member is taken to be the specified alignment. An alignment specification of zero has no effect.171) When multiple alignment specifiers occur in a declaration, the effective alignment requirement is the strictest specified alignment.
8
If the definition of an object has an alignment specifier, any other declaration of that object shall either specify equivalent alignment or have no alignment specifier. If the definition of an object does not have an alignment specifier, any other declaration of that object shall also have no alignment specifier. If declarations of an object in different translation units have different alignment specifiers, the behavior is undefined.
6.7.6 1
Declarators
Syntax declarator: pointeropt direct-declarator direct-declarator: identifier attribute-specifier-sequenceopt ( declarator ) array-declarator attribute-specifier-sequenceopt function-declarator attribute-specifier-sequenceopt array-declarator: direct-declarator [ type-qualifier-listopt assignment-expressionopt ] direct-declarator [ static type-qualifier-listopt assignment-expression ] direct-declarator [ type-qualifier-list static assignment-expression ] direct-declarator [ type-qualifier-listopt * ] function-declarator: direct-declarator ( parameter-type-listopt ) pointer: * attribute-specifier-sequenceopt type-qualifier-listopt * attribute-specifier-sequenceopt type-qualifier-listopt pointer
type-qualifier-list: type-qualifier type-qualifier-list type-qualifier parameter-type-list: parameter-list parameter-list , ... ... 171) An alignment specification of zero also does not affect other alignment specifications in the same declaration.
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parameter-list: parameter-declaration parameter-list , parameter-declaration parameter-declaration: attribute-specifier-sequenceopt declaration-specifiers declarator attribute-specifier-sequenceopt declaration-specifiers abstract-declaratoropt
2
Semantics Each declarator declares an identifier for a single object, function, or type, within a declaration. The preceding specifiers indicate the type, storage class, or other properties of the identifier or identifiers being declared. Each declarator specifies one declaration and names it and/or modifies the type of the specifiers with operators such as * (pointer to) and () (function returning).
3
A full declarator is a declarator that is not part of another declarator. If, in the nested sequence of declarators in a full declarator, there is a declarator specifying a variable length array type, the type specified by the full declarator is said to be variably modified. Furthermore, any type derived by declarator type derivation from a variably modified type is itself variably modified.
4
In the following subclauses, consider a declaration T D1
where T contains the declaration specifiers that specify a type T (such as int) and D1 is a declarator that contains an identifier ident. The type specified for the identifier ident in the various forms of declarator is described inductively using this notation. 5
If, in the declaration "T D1", D1 has the form identifier attribute-specifier-sequenceopt then the type specified for ident is T and the optional attribute specifier sequence appertains to the entity that is declared.
6
If, in the declaration "T D1", D1 has the form (D )
then ident has the type specified by the declaration "T D". Thus, a declarator in parentheses is identical to the unparenthesized declarator, but the binding of complicated declarators may be altered by parentheses.
7
Implementation limits As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and function declarators that modify an arithmetic, structure, union, or void type, either directly or via one or more typedef s. Forward references: array declarators (6.7.6.2), type definitions (6.7.8).
1
6.7.6.1 Pointer declarators Semantics If, in the declaration "T D1", D1 has the form * attribute-specifier-sequenceopt type-qualifier-listopt D
and the type specified for ident in the declaration "T D" is "derived-declarator-type-list T", then the type specified for ident is "derived-declarator-type-list type-qualifier-list pointer to T". For each type qualifier in the list, ident is a so-qualified pointer. The optional attribute specifier sequence appertains to the pointer and not the object pointed to. 2
For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types.
3
EXAMPLE The following pair of declarations demonstrates the difference between a "object pointer to a constant value" and a "constant pointer to an object value". § 6.7.6.1
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const int *ptr_to_constant; int *const constant_ptr;
The contents of any object pointed to by ptr_to_constant cannot be modified through that pointer, but ptr_to_constant itself can be changed to point to another object. Similarly, the contents of the int pointed to by constant_ptr can be modified, but constant_ptr itself always points to the same location. 4
The declaration of the constant pointer constant_ptr can be clarified by including a definition for the type "pointer to int". typedef int *int_ptr; const int_ptr constant_ptr;
declares constant_ptr as an object that has type "const-qualified pointer to int".
1
2
3
6.7.6.2 Array declarators Constraints In addition to optional type qualifiers and the keyword static, the [ and ] may delimit an expression or *. If they delimit an expression (which specifies the size of an array), the expression shall have an integer type. If the expression is a constant expression, it shall have a value greater than zero. The element type shall not be an incomplete or function type. The optional type qualifiers and the keyword static shall appear only in a declaration of a function parameter with an array type, and then only in the outermost array type derivation. If an identifier is declared as having a variably modified type, it shall be an ordinary identifier (as defined in 6.2.3), have no linkage, and have either block scope or function prototype scope. If an identifier is declared to be an object with static or thread storage duration, it shall not have a variable length array type. Semantics If, in the declaration "T D1", D1 has one of the forms: D [ type-qualifier-listopt assignment-expressionopt ] attribute-specifier-sequenceopt D [ static type-qualifier-listopt assignment-expression ] attribute-specifier-sequenceopt D [ type-qualifier-list static assignment-expression ] attribute-specifier-sequenceopt D [ type-qualifier-listopt * ] attribute-specifier-sequenceopt
and the type specified for ident in the declaration "T D" is "derived-declarator-type-list T", then the type specified for ident is "derived-declarator-type-list array of T".172)173) The optional attribute specifier sequence appertains to the array. (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.) 4
If the size is not present, the array type is an incomplete type. If the size is * instead of being an expression, the array type is a variable length array type of unspecified size, which can only be used in declarations or type names with function prototype scope174) ; such arrays are nonetheless complete types. If the size is an integer constant expression and the element type has a known constant size, the array type is not a variable length array type; otherwise, the array type is a variable length array type. (Variable length arrays with automatic storage duration are a conditional feature that implementations need not support; see 6.10.9.3.)
5
If the size is an expression that is not an integer constant expression: if it occurs in a declaration at function prototype scope, it is treated as if it were replaced by *; otherwise, each time it is evaluated it shall have a value greater than zero. The size of each instance of a variable length array type does not change during its lifetime. Where a size expression is part of the operand of a typeof or sizeof operator and changing the value of the size expression would not affect the result of the operator, it 172) When several "array of" specifications are adjacent, a multidimensional array is declared. 173) The array is considered identically qualified to T according to 6.2.5. 174) Thus,
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* can be used only in function declarations that are not definitions (see 6.7.6.3).
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is unspecified whether or not the size expression is evaluated. Where a size expression is part of the operand of an alignof operator, that expression is not evaluated. 6
For two array types to be compatible, both shall have compatible element types, and if both size specifiers are present, and are integer constant expressions, then both size specifiers shall have the same constant value. If the two array types are used in a context which requires them to be compatible, it is undefined behavior if the two size specifiers evaluate to unequal values.
7
EXAMPLE 1 float fa[11], *afp[17];
declares an array of float numbers and an array of pointers to float numbers. 8
EXAMPLE 2 Note the distinction between the declarations extern int *x; extern int y[];
The first declares x to be a pointer to int; the second declares y to be an array of int of unknown size (an incomplete type), the storage for which is defined elsewhere. 9
EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types. extern int n; extern int m; void fcompat(void) { int a[n][6][m]; int (*p)[4][n+1]; int c[n][n][6][m]; int (*r)[n][n][n+1]; p = a; // invalid: not compatible because 4 != 6 r = c; // compatible, but defined behavior only if // n == 6 and m == n+1 }
10
EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or function prototype scope. Array objects declared with the thread_local, static, or extern storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of structures or unions. extern int n; int A[n]; extern int (*p2)[n]; int B[100];
// invalid: file scope VLA // invalid: file scope VM // valid: file scope but not VM
void fvla(int m, int C[m][m]);
// valid:
VLA with prototype scope
void fvla(int m, int C[m][m]) { typedef int VLA[m][m];
// valid:
adjusted to auto pointer to VLA
// valid:
block scope typedef VLA
struct tag { int (*y)[n]; int z[n]; }; int D[m];
§ 6.7.6.2
// invalid: // invalid: // valid:
Language
y not ordinary identifier z not ordinary identifier
auto VLA
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static int E[m]; extern int F[m]; int (*s)[m]; extern int (*r)[m]; static int (*q)[m] = &B;
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// invalid: static block scope VLA // invalid: F has linkage and is VLA // valid: auto pointer to VLA // invalid: r has linkage and points to VLA // valid: q is a static block pointer to VLA
}
Forward references: function declarators (6.7.6.3), function definitions (6.9.1), initialization (6.7.10).
1
6.7.6.3 Function declarators Constraints A function declarator shall not specify a return type that is a function type or an array type.
2
The only storage-class specifier that shall occur in a parameter declaration is register.
3
After adjustment, the parameters in a parameter type list in a function declarator that is part of a definition of that function shall not have incomplete type.
4
Semantics If, in the declaration "T D1", D1 has the form D ( parameter-type-listopt ) attribute-specifier-sequenceopt
and the type specified for ident in the declaration "T D" is "derived-declarator-type-list T", then the type specified for ident is "derived-declarator-type-list function returning the unqualified, non-atomic version of T". The optional attribute specifier sequence appertains to the function type. 5
A parameter type list specifies the types of, and may declare identifiers for, the parameters of the function.
6
A declaration of a parameter as "array of type" shall be adjusted to "qualified pointer to type", where the type qualifiers (if any) are those specified within the [ and ] of the array type derivation. If the keyword static also appears within the [ and ] of the array type derivation, then for each call to the function, the value of the corresponding actual argument shall provide access to the first element of an array with at least as many elements as specified by the size expression.
7
A declaration of a parameter as "function returning type" shall be adjusted to "pointer to function returning type", as in 6.3.2.1.
8
If the list terminates with an ellipsis (...), no information about the number or types of the parameters after the comma is supplied. 175)
9
The special case of an unnamed parameter of type void as the only item in the list specifies that the function has no parameters.
10
If, in a parameter declaration, an identifier can be treated either as a typedef name or as a parameter name, it shall be taken as a typedef name.
11
If the function declarator is not part of a definition of that function, parameters may have incomplete type and may use the [*] notation in their sequences of declarator specifiers to specify variable length array types.
12
The storage class specifier in the declaration specifiers for a parameter declaration, if present, is ignored unless the declared parameter is one of the members of the parameter type list for a function definition. The optional attribute specifier sequence in a parameter declaration appertains to the parameter.
13
For a function declarator without a parameter type list: the effect is as if it were declared with a parameter type list consisting of the keyword void. A function declarator provides a prototype for the function.
14
For two function types to be compatible, both shall specify compatible return types. Moreover, the parameter type lists shall agree in the number of parameters and in use of the final ellipsis; 175) The macros defined in the <stdarg.h> header (7.16) can be used to access arguments that correspond to the ellipsis.
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corresponding parameters shall have compatible types. In the determination of type compatibility and of a composite type, each parameter declared with function or array type is taken as having the adjusted type and each parameter declared with qualified type is taken as having the unqualified version of its declared type. 15
EXAMPLE 1 The declaration int f(void), *fip(), (*pfi)();
declares a function f with no parameters returning an int, a function fip with no parameters returning a pointer to an int, and a pointer pfi to a function with no parameters returning an int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the declaration suggests, and the same construction in an expression requires, the calling of a function fip, and then using indirection through the pointer result to yield an int. In the declarator (*pfi) (), the extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function designator, which is then used to call the function; it returns an int. 16
If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either internal or external linkage (depending on what file scope declarations for these identifiers are visible), and the identifier of the pointer pfi has block scope and no linkage.
17
EXAMPLE 2 The declaration int (*apfi[3])(int *x, int *y);
declares an array apfi of three pointers to functions returning int. Each of these functions has two parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and go out of scope at the end of the declaration of apfi. 18
EXAMPLE 3 The declaration int (*fpfi(int (*)(long), int))(int, ...);
declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two parameters: a pointer to a function returning an int (with one parameter of type long int), and an int. The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more additional arguments of any type. 19
EXAMPLE 4 The following prototype has a variably modified parameter. void addscalar(int n, int m, double a[n][n*m+300], double x); int main(void) { double b[4][308]; addscalar(4, 2, b, 2.17); return 0; } void addscalar(int n, int m, double a[n][n*m+300], double x) { for (int i = 0; i < n; i++) for (int j = 0, k = n*m+300; j < k; j++) // a is a pointer to a VLA with n*m+300 elements a[i][j] += x; }
20
EXAMPLE 5 The following are all compatible function prototype declarators. § 6.7.6.3
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double maximum(int n, int m, double a[n][m]); double maximum(int n, int m, double a[*][*]); double maximum(int n, int m, double a[ ][*]); double maximum(int n, int m, double a[ ][m]);
as are: void f(double (* restrict a)[5]); void f(double a[restrict][5]); void f(double a[restrict 3][5]); void f(double a[restrict static 3][5]);
(Note that the last declaration also specifies that the argument corresponding to a in any call to f can be expected to be a non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.) Forward references: function definitions (6.9.1), type names (6.7.7).
6.7.7 1
Type names
Syntax type-name: specifier-qualifier-list abstract-declaratoropt abstract-declarator: pointer pointeropt direct-abstract-declarator direct-abstract-declarator: ( abstract-declarator ) array-abstract-declarator attribute-specifier-sequenceopt function-abstract-declarator attribute-specifier-sequenceopt array-abstract-declarator: direct-abstract-declaratoropt [ type-qualifier-listopt assignment-expressionopt ] direct-abstract-declaratoropt [ static type-qualifier-listopt assignment-expression ] direct-abstract-declaratoropt [ type-qualifier-list static assignment-expression ] direct-abstract-declaratoropt [ * ] function-abstract-declarator: direct-abstract-declaratoropt ( parameter-type-listopt )
2
3
Semantics In several contexts, it is necessary to specify a type. This is accomplished using a type name, which is syntactically a declaration for a function or an object of that type that omits the identifier.176) The optional attribute specifier sequence in a direct abstract declarator appertains to the preceding array or function type. The attribute specifier sequence affects the type only for the declaration it appears in, not other declarations involving the same type. EXAMPLE The constructions (a) (b) (c) (d) (e) (f) (g)
int int * int *[3] int (*)[3] int (*)[*] int *() int (*)(void)
176) As indicated by the syntax, empty parentheses in a type name are interpreted as "function with no parameters", rather than redundant parentheses around the omitted identifier.
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int (*const [])(unsigned int, ...)
name respectively the types (a) (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an array of three int s, (e) pointer to a variable length array of an unspecified number of int s, (f) function with no parameters returning a pointer to int, (g) pointer to function with no parameters returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one parameter that has type unsigned int and an unspecified number of other parameters, returning an int.
6.7.8 1
Type definitions
Syntax typedef-name: identifier
2
3
Constraints If a typedef name specifies a variably modified type then it shall have block scope. Semantics In a declaration whose storage-class specifier is typedef, each declarator defines an identifier to be a typedef name that denotes the type specified for the identifier in the way described in 6.7.6. Any array size expressions associated with variable length array declarators and typeof operators are evaluated each time the declaration of the typedef name is reached in the order of execution. A typedef declaration does not introduce a new type, only a synonym for the type so specified. That is, in the following declarations: typedef T type_ident; type_ident D;
type_ident is defined as a typedef name with the type specified by the declaration specifiers in T (known as T), and the identifier in D has the type "derived-declarator-type-list T" where the deriveddeclarator-type-list is specified by the declarators of D. A typedef name shares the same name space
as other identifiers declared in ordinary declarators. If the identifier is redeclared in an enclosed block, the type of the inner declaration shall not be inferred (6.7.9). 4
EXAMPLE 1 After typedef int MILES, KLICKSP(); typedef struct { double hi, lo; } range;
the constructions MILES distance; extern KLICKSP *metricp; range x; range z, *zp;
§ 6.7.8
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are all valid declarations. The type of distance is int, that of metricp is "pointer to function with no parameters returning int", and that of x and z is the specified structure; zp is a pointer to such a structure. The object distance has a type compatible with any other int object. 5
EXAMPLE 2 After the declarations typedef struct s1 { int x; } t1, *tp1; typedef struct s2 { int x; } t2, *tp2;
type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int. 6
EXAMPLE 3 The following obscure constructions typedef signed int t; typedef int plain; struct tag { unsigned t:4; const t:5; plain r:5; };
declare a typedef name t with type signed int, a typedef name plain with type int, and a structure with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-qualified bit-field which (if it could be accessed) would contain values in the range [−16, +15], and one named r that contains values in one of the ranges [0, 31] or [−16, +15]. (The choice of range is implementation-defined.) The first two bit-field declarations differ in that unsigned is a type specifier (which forces t to be the name of a structure member), while const is a type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed in an inner scope by t f(t (t)); long t;
then a function f is declared with type "function returning signed int with one unnamed parameter with type pointer to function returning signed int with one unnamed parameter with type signed int", and an identifier t with type long int. 7
EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the following declarations of the signal function specify exactly the same type, the first without making use of any typedef names. typedef void fv(int), (*pfv)(int); void (*signal(int, void (*)(int)))(int); fv *signal(int, fv *); pfv signal(int, pfv);
8
EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the time the typedef name is defined, not each time it is used: void copyt(int n) { typedef int B[n]; // B is n ints, n evaluated now n += 1; B a; // a is n ints, n without += 1 int b[n]; // a and b are different sizes for (int i = 1; i < n; i++) a[i-1] = b[i]; }
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Type inference
1
Constraints A declaration for which the type is inferred shall contain the storage-class specifier auto.
2
Semantics For such a declaration that is the definition of an object the init-declarator shall have the form direct-declarator = assignment-expression The inferred type of the declared object is the type of the assignment expression after lvalue, array to pointer or function to pointer conversion, additionally qualified by qualifiers and amended by attributes as they appear in the declaration specifiers, if any.177) Implementations need not accept a direct declarator that is not of the form identifier attribute-specifier-sequenceopt optionally enclosed in balanced pairs of parentheses; if a direct declarator of a different form is accepted, the behavior is implementation-defined.178)
3
NOTE 1 Such a declaration that also defines a structure or union type violates a constraint. Here, the identifier x which is not ordinary but in the name space of the structure type is declared.
auto p = (struct { int x; } *)0; Even a forward declaration of a structure tag
struct s; auto p = (struct s { int x; } *)0; would not change that situation. A direct use of the structure definition as the type specifier ensures the validity of the declaration.
struct s { int x; } * p = 0; 4
EXAMPLE 1 Consider the following file scope definitions: static auto a = 3.5; auto p = &a;
They are interpreted as if they had been written as: static double a = 3.5; double * p = &a;
So effectively a is a double and p is a double*. Note that the restrictions on the syntax of such declarations does not allow the declarator to be *p, but that the final type here nevertheless is a pointer type. 5
EXAMPLE 2 The scope of the identifier for which the type is inferred only starts after the end of the initializer (6.2.1), so the assignment expression cannot use the identifier to refer to the object or function that is declared, for example to take its address. Any use of the identifier in the initializer is invalid, even if an entity with the same name exists in an outer scope. { double a = 7; double b = 9; { double b = b * b;
// undefined, uses uninitialized
177) The scope rules as described in 6.2.1 also prohibit the use of the identifier of the declarator within the assignment expression. 178) It is commended that implementations that accept different forms of direct declarators follow the syntax and semantics of the corresponding feature in ISO/IEC IS 14882.
§ 6.7.9
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// variable without address printf("%g\n", a); // valid, uses "a" from outer scope, prints 7 auto a = a * a; // invalid, "a" from outer scope is not // visible during initialization } { auto b = a * a; // valid, uses "a" from outer scope auto a = b; // valid, "a" from outer scope not visible now // ... printf("%g\n", a); // valid, uses "a" from inner scope, prints 49 } // ... } 6
EXAMPLE 3 In the following, declarations of pA and qA are valid. The type of A after array-topointer conversion is a pointer type, and qA is a pointer to array. double A[3] = { 0 }; auto pA = A; auto qA = &A;
7
EXAMPLE 4 Type inference can be used to capture the type of a call to a type-generic function. It ensures that the same type as the argument x is used. #include <tgmath.h> auto y = cos(x);
If instead the type of y is explicitly specified to a different type than x, a diagnosis of the mismatch is not enforced. 8
EXAMPLE 5 A type-generic macro that generalizes the div functions (7.24.6.2) is defined and used as follows. #define div(X, Y) _Generic((X)+(Y),\ int: div,\ long: ldiv,\ long long: lldiv)((X), (Y)) auto z = div(x, y); auto q = z.quot; auto r = z.rem;
9
EXAMPLE 6 Definitions of objects with inferred type are valid in all contexts that allow the initializer syntax as described. In particular they can be used to ensure type safety of for-loop controlling expressions. for (auto i = j; i < 2*j; ++i) { // ... }
Here, regardless of the integer rank or signedness of the type of j, i will have the non-atomic unqualified type of j. So, after lvalue conversion and possible promotion, the two operands of the < operator in the controlling expression are guaranteed to have the same type, and, in particular, the same signedness.
6.7.10 1
Initialization
Syntax braced-initializer: { } { initializer-list }
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{ initializer-list , }
initializer: assignment-expression braced-initializer initializer-list: designationopt initializer initializer-list , designationopt initializer designation: designator-list = designator-list: designator designator-list designator designator: [ constant-expression ] . identifier 2
An empty brace pair ({}) is called an empty initializer and is referred to as empty initialization.
3
Constraints No initializer shall attempt to provide a value for an object not contained within the entity being initialized.
4
The type of the entity to be initialized shall be an array of unknown size or a complete object type. An entity of variable length array type shall not be initialized except by an empty initializer. An array of unknown size shall not be initialized by an empty initializer.
5
All the expressions in an initializer for an object that has static or thread storage duration or is declared with the constexpr storage-class specifier shall be constant expressions or string literals.
6
If the declaration of an identifier has block scope, and the identifier has external or internal linkage, the declaration shall have no initializer for the identifier.
7
If a designator has the form [ constant-expression ]
then the current object (defined below) shall have array type and the expression shall be an integer constant expression. If the array is of unknown size, any nonnegative value is valid. 8
If a designator has the form . identifier
then the current object (defined below) shall have structure or union type and the identifier shall be the name of a member of that type.
9
Semantics An initializer specifies the initial value stored in an object. For objects with atomic type additional restrictions apply, see 7.17.2 and 7.17.8.
10
Except where explicitly stated otherwise, for the purposes of this subclause unnamed members of objects of structure and union type do not participate in initialization. Unnamed members of structure objects have indeterminate representation even after initialization.
11
If an object that has automatic storage duration is not initialized explicitly, its representation is indeterminate. If an object that has static or thread storage duration is not initialized explicitly, or any object is initialized with an empty initializer, then it is subject to default initialization, which initializes an object as follows: § 6.7.10
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— if it has pointer type, it is initialized to a null pointer; — if it has decimal floating type, it is initialized to positive zero, and the quantum exponent is implementation-defined179) ; — if it has arithmetic type, and it does not have decimal floating type, it is initialized to (positive or unsigned) zero; — if it is an aggregate, every member is initialized (recursively) according to these rules, and any padding is initialized to zero bits; — if it is a union, the first named member is initialized (recursively) according to these rules, and any padding is initialized to zero bits. 12
The initializer for a scalar shall be a single expression, optionally enclosed in braces, or it shall be an empty initializer. If the initializer is not the empty initializer, the initial value of the object is that of the expression (after conversion); the same type constraints and conversions as for simple assignment apply, taking the type of the scalar to be the unqualified version of its declared type.
13
The rest of this subclause deals with initializers for objects that have aggregate or union type.
14
The initializer for a structure or union object shall be either an initializer list as described below, or a single expression that has compatible structure or union type. In the latter case, the initial value of the object, including unnamed members, is that of the expression.180)
15
An array of character type may be initialized by a character string literal or UTF-8 string literal, optionally enclosed in braces. Successive bytes of the string literal (including the terminating null character if there is room or if the array is of unknown size) initialize the elements of the array.
16
An array with element type compatible with a qualified or unqualified wchar_t, char16_t, or char32_t may be initialized by a wide string literal with the corresponding encoding prefix (L, u, or U, respectively), optionally enclosed in braces. Successive wide characters of the wide string literal (including the terminating null wide character if there is room or if the array is of unknown size) initialize the elements of the array.
17
Otherwise, the initializer for an object that has aggregate or union type shall be a brace-enclosed list of initializers for the elements or named members.
18
Each brace-enclosed initializer list has an associated current object. When no designations are present, subobjects of the current object are initialized in order according to the type of the current object: array elements in increasing subscript order, structure members in declaration order, and the first named member of a union.181) In contrast, a designation causes the following initializer to begin initialization of the subobject described by the designator. Initialization then continues forward in order, beginning with the next subobject after that described by the designator.182)
19
Each designator list begins its description with the current object associated with the closest surrounding brace pair. Each item in the designator list (in order) specifies a particular member of its current object and changes the current object for the next designator (if any) to be that member.183) The current object that results at the end of the designator list is the subobject to be initialized by the following initializer.
20
The initialization shall occur in initializer list order, each initializer provided for a particular subobject overriding any previously listed initializer for the same subobject;184) all subobjects that are not 179) A representation with all bits zero results in a decimal floating-point zero with the most negative exponent. 180) If the object being initialized does not have automatic storage duration, this case violates a constraint unless the expression is a named constant or compound literal constant (6.6). 181) If the initializer list for a subaggregate or contained union does not begin with a left brace, its subobjects are initialized as usual, but the subaggregate or contained union does not become the current object: current objects are associated only with brace-enclosed initializer lists. 182) After a union member is initialized, the next object is not the next member of the union; instead, it is the next subobject of an object containing the union. 183) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with the surrounding brace pair. Note, too, that each separate designator list is independent. 184) Any initializer for the subobject which is overridden and so not used to initialize that subobject might not be evaluated at all.
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initialized explicitly are subject to default initialization. 21
If the aggregate or union contains elements or members that are aggregates or unions, these rules apply recursively to the subaggregates or contained unions. If the initializer of a subaggregate or contained union begins with a left brace, the initializers enclosed by that brace and its matching right brace initialize the elements or members of the subaggregate or the contained union. Otherwise, only enough initializers from the list are taken to account for the elements or members of the subaggregate or the first member of the contained union; any remaining initializers are left to initialize the next element or member of the aggregate of which the current subaggregate or contained union is a part.
22
If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate is subject to default initialization.
23
If an array of unknown size is initialized, its size is determined by the largest indexed element with an explicit initializer. The array type is completed at the end of its initializer list.
24
The evaluations of the initialization list expressions are indeterminately sequenced with respect to one another and thus the order in which any side effects occur is unspecified.185)
25
EXAMPLE 1 Provided that <complex.h> has been #included, the declarations int i = 3.5; double complex c = 5 + 3 * I;
define and initialize i with the value 3 and c with the value 5.0 + i3.0. 26
EXAMPLE 2 The declaration int x[] = { 1, 3, 5 };
defines and initializes x as a one-dimensional array object that has three elements, as no size was specified and there are three initializers. 27
EXAMPLE 3 The declaration int y[4][3] = { { 1, 3, 5 }, { 2, 4, 6 }, { 3, 5, 7 }, };
is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have been achieved by int y[4][3] = { 1, 3, 5, 2, 4, 6, 3, 5, 7 };
The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the next three are taken successively for y[1] and y[2]. 28
EXAMPLE 4 The declaration int z[4][3] = { { 1 }, { 2 }, { 3 }, { 4 } };
initializes the first column of z as specified and initializes the rest with zeros. 185) In particular, the evaluation order need not be the same as the order of subobject initialization.
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EXAMPLE 5 The declaration struct { int a[3], b; } w[] = { { 1 }, 2 };
is a definition with an inconsistently bracketed initialization. It defines an array with two element structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero. 30
EXAMPLE 6 The declaration short q[4][3][2] = { { 1 }, { 2, 3 }, { 4, 5, 6 } };
contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for q[0][0] does not begin with a left brace, so up to six items from the current list could be used. There is only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a diagnostic message would have been issued. The same initialization result could have been achieved by: short q[4][3][2] = { 1, 0, 0, 0, 0, 0, 2, 3, 0, 0, 0, 0, 4, 5, 6 };
or by: short q[4][3][2] = { { { 1 }, }, { { 2, 3 }, }, { { 4, 5 }, { 6 }, } };
in a fully bracketed form. 31
Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to cause confusion.
32
EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the declaration typedef int A[];
// OK - declared with block scope
the declaration A a = { 1, 2 }, b = { 3, 4, 5 };
is identical to 138
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int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
due to the rules for incomplete types. 33
EXAMPLE 8 The declaration char s[] = "abc", t[3] = "abc";
defines "plain" char array objects s and t whose elements are initialized with character string literals. This declaration is identical to char s[] = { ’a’, ’b’, ’c’, ’\0’ }, t[] = { ’a’, ’b’, ’c’ };
The contents of the arrays are modifiable. On the other hand, the declaration char *p = "abc";
defines p with type "pointer to char" and initializes it to point to an object with type "array of char" with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to modify the contents of the array, the behavior is undefined. 34
EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using designators: enum { member_one, member_two }; const char *nm[] = { [member_two] = "member two", [member_one] = "member one", };
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EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order: div_t answer = {.quot = 2, .rem = -1 };
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EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists might be misunderstood: struct { int a[3], b; } w[] = { [0].a = {1}, [1].a[0] = 2 };
37
EXAMPLE 12 struct T { int k; int l; }; struct S { int i; struct T t; }; struct T x = {.l = 43, .k = 42, }; void f(void) { struct S l = { 1, .t = x, .t.l = 41, };
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The value of l.t.k is 42, because implicit initialization does not override explicit initialization. 38
EXAMPLE 13 Space can be "allocated" from both ends of an array by using a single designator: int a[MAX] = { 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0 };
39
In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less than ten, some of the values provided by the first five initializers will be overridden by the second five.
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EXAMPLE 14 Any member of a union can be initialized: union { /* ... */ } u = {.any_member = 42 };
Forward references: common definitions <stddef.h> (7.21).
6.7.11 1
Static assertions
Syntax static_assert-declaration: static_assert ( constant-expression , string-literal ) ; static_assert ( constant-expression ) ;
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Constraints The constant expression shall compare unequal to 0. Semantics The constant expression shall be an integer constant expression. If the value of the constant expression compares unequal to 0, the declaration has no effect. Otherwise, the constraint is violated and the implementation shall produce a diagnostic message which should include the text of the string literal, if present. Forward references: diagnostics (7.2).
6.7.12
Attributes
1
Attributes specify additional information for various source constructs such as types, objects, identifiers, or blocks. They are identified by an attribute token, which can either be a attribute prefixed token (for implementation-specific attributes) or a standard attribute specified by an identifier (for attributes specified in this document).
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Support for any of the standard attributes specified in this document is implementation-defined and optional. For an attribute token (including an attribute prefixed token) not specified in this document, the behavior is implementation-defined. Any attribute token that is not supported by the implementation is ignored.
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Attributes are said to appertain to some source construct, identified by the syntactic context where they appear, and for each individual attribute, the corresponding clause constrains the syntactic context in which this appurtenance is valid. The attribute specifier sequence appertaining to some source construct shall contain only attributes that are allowed to apply to that source construct.
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In all aspects of the language, a standard attribute specified by this document as an identifier attr and an identifier of the form __attr__ shall behave the same when used as an attribute token, except for the spelling.186) 186) Thus, the attributes [[nodiscard]] and [[__nodiscard__]] can be freely interchanged. Implementations are encouraged to behave similarly for attribute tokens (including attribute prefixed tokens) they provide.
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For all standard attributes specified by this document, the current value when its token sequence is given to the __has_c_attribute conditional inclusion expression (6.10.1) is written in the associated subclause for that attribute. A history of those values can be found in Annex M (Annex M.1). Recommended practice It is recommended that implementations support all standard attributes as defined in this document. 6.7.12.1 General Syntax attribute-specifier-sequence: attribute-specifier-sequenceopt attribute-specifier attribute-specifier: [ [ attribute-list ] ] attribute-list: attributeopt attribute-list , attributeopt attribute: attribute-token attribute-argument-clauseopt attribute-token: standard-attribute attribute-prefixed-token standard-attribute: identifier attribute-prefixed-token: attribute-prefix :: identifier attribute-prefix: identifier attribute-argument-clause: ( balanced-token-sequenceopt ) balanced-token-sequence: balanced-token balanced-token-sequence balanced-token balanced-token: ( balanced-token-sequenceopt ) [ balanced-token-sequenceopt ] { balanced-token-sequenceopt } any token other than a parenthesis, a bracket, or a brace
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Constraints The identifier in a standard attribute shall be one of: deprecated fallthrough
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maybe_unused nodiscard
noreturn _Noreturn
unsequenced reproducible
Semantics An attribute specifier that contains no attributes has no effect. The order in which attribute tokens appear in an attribute list is not significant. If a keyword (6.4.1) that satisfies the syntactic requirements of an identifier (6.4.2) is contained in an attribute token, it is considered an identifier. A strictly conforming program using a standard attribute remains strictly conforming in the absence of that attribute.187) NOTE 1 For each standard attribute, the form of the balanced token sequence, if any, will be specified. 187) Standard attributes specified by this document can be parsed but ignored by an implementation without changing the semantics of a correct program; the same is not true for attributes not specified by this document.
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Recommended Practice Each implementation should choose a distinctive name for the attribute prefix in an attribute prefixed token. Implementations should not define attributes without an attribute prefix unless it is a standard attribute as specified in this document. EXAMPLE 1 Suppose that an implementation chooses the attribute prefix hal and provides specific attributes named daisy and rosie. [[deprecated, hal::daisy]] double nine1000(double); [[deprecated]] [[hal::daisy]] double nine1000(double); [[deprecated]] double nine1000 [[hal::daisy]] (double);
Then all the following declarations should be equivalent aside from the spelling: [[__deprecated__, __hal__::__daisy__]] double nine1000(double); [[__deprecated__]] [[__hal__::__daisy__]] double nine1000(double); [[__deprecated__]] double nine1000 [[__hal__::__daisy__]] (double);
These use the alternate spelling that is required for all standard attributes and recommended for prefixed attributes. These may be better-suited for use in header files, where the use of the alternate spelling avoids naming conflicts with user-provided macros. 7
EXAMPLE 2 For the same implementation, the following two declarations are equivalent, because the ordering inside attribute lists is not important. [[hal::daisy, hal::rosie]] double nine999(double); [[hal::rosie, hal::daisy]] double nine999(double);
On the other hand the following two declarations are not equivalent, because the ordering of different attribute specifiers may affect the semantics. [[hal::daisy]] [[hal::rosie]] double nine999(double); [[hal::rosie]] [[hal::daisy]] double nine999(double); // may have different semantics
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6.7.12.2 The nodiscard attribute Constraints The nodiscard attribute shall be applied to a function or to the definition of a structure, union, or enumerated type. If an attribute argument clause is present, it shall have the form: ( string-literal )
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Semantics The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given nodiscard as the pp-tokens operand if the implementation supports the attribute. A name or entity declared without the nodiscard attribute can later be redeclared with the attribute and vice versa. An entity is considered marked after the first declaration that marks it. Recommended Practice A nodiscard call is a function call expression that calls a function previously declared with attribute nodiscard, or whose return type is a structure, union, or enumerated type marked with attribute nodiscard. Evaluation of a nodiscard call as a void expression (6.8.3) is discouraged unless explicitly cast to void. Implementations are encouraged to issue a diagnostic in such cases. This is typically because immediately discarding the return value of a nodiscard call has surprising consequences.
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The diagnostic message should include text provided by the string literal within the attribute argument clause of any nodiscard attribute applied to the name or entity.
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EXAMPLE 1
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struct [[nodiscard]] error_info { /*...*/ }; struct error_info enable_missile_safety_mode(void); void launch_missiles(void); void test_missiles(void) { enable_missile_safety_mode(); launch_missiles(); }
A diagnostic for the call to enable_missile_safety_mode is encouraged. 7
EXAMPLE 2 [[nodiscard]] int important_func(void); void call(void) { int i = important_func(); }
No diagnostic for the call to important_func is encouraged despite the value of i not being used. 8
EXAMPLE 3 [[nodiscard("must check armed state")]] bool arm_detonator(int within); void call(void) { arm_detonator(3); detonate(); }
A diagnostic for the call to arm_detonator using the string literal "must check armed state" from the attribute argument clause is encouraged.
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6.7.12.3 The maybe_unused attribute Constraints The maybe_unused attribute shall be applied to the declaration of a structure, a union, a typedef name, an object, a structure or union member, a function, an enumeration, an enumerator, or a label. No attribute argument clause shall be present. Semantics The maybe_unused attribute indicates that a name or entity is possibly intentionally unused. The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given maybe_unused as the pp-tokens operand if the implementation supports the attribute. A name or entity declared without the maybe_unused attribute can later be redeclared with the attribute and vice versa. An entity is considered marked with the attribute after the first declaration that marks it.
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Recommended Practice For an entity marked maybe_unused, implementations are encouraged not to emit a diagnostic that the entity is unused, or that the entity is used despite the presence of the attribute.
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EXAMPLE [[maybe_unused]] void f([[maybe_unused]] int i) { [[maybe_unused]] int j = i + 100; assert(j); }
Implementations are encouraged not to diagnose that j is unused, even if NDEBUG is defined. § 6.7.12.3
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6.7.12.4 The deprecated attribute Constraints The deprecated attribute shall be applied to the declaration of a structure, a union, a typedef name, an object, a structure or union member, a function, an enumeration, or an enumerator. If an attribute argument clause is present, it shall have the form: ( string-literal )
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Semantics The deprecated attribute can be used to mark names and entities whose use is still allowed, but is discouraged for some reason.188)
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The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given deprecated as the pp-tokens operand if the implementation supports the attribute.
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A name or entity declared without the deprecated attribute can later be redeclared with the attribute and vice versa. An entity is considered marked with the attribute after the first declaration that marks it.
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Recommended Practice Implementations should use the deprecated attribute to produce a diagnostic message in case the program refers to a name or entity other than to declare it, after a declaration that specifies the attribute, when the reference to the name or entity is not within the context of a related deprecated entity. The diagnostic message should include text provided by the string literal within the attribute argument clause of any deprecated attribute applied to the name or entity. EXAMPLE struct [[deprecated]] S { int a; }; enum [[deprecated]] E1 { one }; enum E2 { two [[deprecated("use ’three’ instead")]], three }; [[deprecated]] typedef int Foo; void f1(struct S s) { // Diagnose use of S int i = one; // Diagnose use of E1 int j = two; // Diagnose use of two: "use ’three’ instead" int k = three; Foo f; // Diagnose use of Foo } [[deprecated]] void f2(struct S s) { int i = one; int j = two; int k = three; Foo f; } struct [[deprecated]] T { 188) In particular, deprecated is appropriate for names and entities that are obsolescent, insecure, unsafe, or otherwise unfit for purpose.
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Foo f; struct S s; };
Implementations are encouraged to diagnose the use of deprecated entities within a context which is not itself deprecated, as indicated for function f1, but not to diagnose within function f2 and struct T, as they are themselves deprecated.
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6.7.12.5 The fallthrough attribute Constraints The attribute token fallthrough shall only appear in an attribute declaration (6.7); such a declaration is a fallthrough declaration. No attribute argument clause shall be present. A fallthrough declaration may only appear within an enclosing switch statement (6.8.4.2). The next block item (6.8.2) that would be encountered after a fallthrough declaration shall be a case label or default label associated with the innermost enclosing switch statement and, if the fallthrough declaration is contained in an iteration statement, the next statement shall be part of the same execution of the secondary block of the innermost enclosing iteration statement. Semantics The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given fallthrough as the pp-tokens operand if the implementation supports the attribute. Recommended Practice The use of a fallthrough declaration is intended to suppress a diagnostic that an implementation might otherwise issue for a case or default label that is reachable from another case or default label along some path of execution. Implementations are encouraged to issue a diagnostic if a fallthrough declaration is not dynamically reachable. EXAMPLE void f(int n) { void g(void), h(void), i(void); switch (n) { case 1: /* diagnostic on fallthrough discouraged */ case 2: g(); [[fallthrough]]; case 3: /* diagnostic on fallthrough discouraged */ do { [[fallthrough]]; /* constraint violation: next statement is not part of the same secondary block execution */ } while(false); case 6: do { [[fallthrough]]; /* constraint violation: next statement is not part of the same secondary block execution */ } while (n--); case 7: while (false) { [[fallthrough]]; /* constraint violation: next statement is not part of the same secondary block execution */ } case 5: h(); case 4: /* fallthrough diagnostic encouraged */ i(); [[fallthrough]]; /* constraint violation */ } }
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6.7.12.6 The noreturn and _Noreturn attributes Description When _Noreturn is used as an attribute token (instead of a function specifier), the constraints and semantics are identical to that of the noreturn attribute token. Use of _Noreturn as an attribute token is an obsolescent feature189) . Constraints The noreturn attribute shall be applied to a function. No attribute argument clause shall be present. Semantics The first declaration of a function shall specify the noreturn attribute if any declaration of that function specifies the noreturn attribute. If a function is declared with the noreturn attribute in one translation unit and the same function is declared without the noreturn attribute in another translation unit, the behavior is undefined.
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If a function f is called where f was previously declared with the noreturn attribute and f eventually returns, the behavior is undefined.
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The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given noreturn as the pp-tokens operand if the implementation supports the attribute.
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Recommended Practice The implementation should produce a diagnostic message for a function declared with a noreturn attribute that appears to be capable of returning to its caller.
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EXAMPLE [[noreturn]] void f(void) { abort(); // ok } [[noreturn]] void g(int i) { // causes undefined behavior if i <= 0 if (i > 0) abort(); } [[noreturn]] int h(void);
Implementations are encouraged to diagnose the definition of g() because it is capable of returning to its caller. Implementations are similarly encouraged to diagnose the declaration of h() because it appears capable of returning to its caller due to the non-void return type.
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6.7.12.7 Standard attributes for function types Constraints The identifier in a standard function type attribute shall be one of: unsequenced
2
reproducible
An attribute for a function type shall be applied to a function declarator190) or to a type specifier that has a function type. The corresponding attribute is a property of the function type.191) No attribute argument clause shall be present. 189) [[_Noreturn]] and [[noreturn]] are equivalent attributes to support code that includes <stdnoreturn.h>, because that header defines noreturn as a macro that expands to _Noreturn. 190) That is, they appear in the attributes right after the closing parenthesis of the parameter list, independently of whether the function type is, for example, used directly to declare a function or whether it is used in a pointer to function type. 191) If several declarations of the same function or function pointer are visible, regardless whether an attribute is present at several or just one of the declarators, it is attached to the type of the corresponding function definition, function pointer object, or function pointer value.
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Description The main purpose of the function type properties and attributes defined in this clause is to provide the translator with information about the access of objects by a function such that certain properties of function calls can be deduced; the properties distinguish read operations (stateless and independent) and write operations (effectless, idempotent and reproducible) or a combination of both (unsequenced). Although semantically attached to a function type, the attributes described are not part of the prototype of such a annotated function, and redeclarations and conversions that drop such an attribute are valid and constitute compatible types. Conversely, if a definition that does not have the asserted property is accessed by a function declaration or a function pointer with a type that has the attribute, the behavior is undefined.192)
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To allow reordering of calls to functions as they are described here, possible access to objects with a lifetime that starts before or ends after a call has to be restricted; effects on all objects that are accessed during a function call are restricted to the same thread as the call and the based-on relation between pointer parameters and lvalues (6.7.3.1) models the fact that objects do not change inadvertently during the call. In the following, an operation is said to be sequenced during a function call if it is sequenced after the start of the function call193) and before the call terminates. An object definition of an object X in a function f escapes if an access to X happens while no call to f is active. An object is local to a call to a function f if its lifetime starts and ends during the call or if it is defined by f but does not escape. A function call and an object X synchronize if all accesses to X that are not sequenced during the call happen before or after the call. Execution state that is described in the library clause, such as the floating-point environment, conversion state, locale, input/output streams, external files or errno are considered as objects for the purposes of these attributes; operations that access this state, even indirectly, are considered as lvalue conversions for the purposes of these attributes, and operations that allow to change this state account as store operations.
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A function definition f is stateless if any definition of an object of static or thread storage duration in f or in a function that is called by f is const but not volatile qualified.
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An object X is observed by a function call if both synchronize, if X is not local to the call, if X has a lifetime that starts before the function call and if an access of X is sequenced during the call; the last value of X, if any, that is stored before the call is said to be the value of X that is observed by the call. A function pointer value f is independent if for any object X that is observed by some call to f through an lvalue that is not based on a parameter of the call, then all accesses to X in all calls to f during the same program execution observe the same value; otherwise if the access is based on a pointer parameter, there shall be a unique such pointer parameter P such that any access to X shall be to an lvalue that is based on P . A function definition is independent if the derived function pointer value is independent.
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A store operation to an object X that is sequenced during a function call such that both synchronize is said to be observable if X is not local to the call, if the lifetime of X ends after the call, if the stored value is different from the value observed by the call, if any, and if it is the last value written before the termination of the call. An evaluation of a function call194) is effectless if any store operation that is sequenced during the call is the modification of an object that synchronizes with the call; if additionally the operation is observable, there shall be a unique pointer parameter P of the function such that any access to X shall be to an lvalue that is based on P . A function pointer value f is effectless if any evaluation of a function call that calls f is effectless. A function definition is effectless if the derived function pointer value is effectless.
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An evaluation E is idempotent if a second evaluation of E can be sequenced immediately after the original one without changing the resulting value, if any, or the observable state of the execution. A function pointer value f is idempotent if any evaluation of a function call195) that calls f is 192) That is, the fact that a function has one of these properties is in general not determined by the specification of the translation unit in which it is found; other translation units and specific run time conditions also condition the possible assertion of the properties. 193) The initializations of the parameters is sequenced during the function call. 194) This considers the evaluation of the function call itself, not the evaluation of a full function call expression. Such an evaluation is sequenced after all evaluations that determine f and the call arguments, if any, have been performed. 195) This considers the evaluation of the function call itself, not the evaluation of a full function call expression. Such an evaluation is sequenced after all evaluations that determine f and the call arguments, if any, have been performed.
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idempotent. A function definition is idempotent if the derived function pointer value is idempotent. 9
A function is reproducible if it is effectless and idempotent; it is unsequenced if it is stateless, effectless, idempotent and independent.196)
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NOTE 1 The synchronization requirements with respect to any accessed object X for the independence of functions provide boundaries up to which a function call may safely be reordered without changing the semantics of the program. If X is const but not volatile qualified the reordering is unconstrained. If it is an object that is conditioned in an initialization phase, for a single threaded program a synchronization is provided by the sequenced before relation and the reordering may, in principle, move the call just after the initialization. For a multi-threaded program, synchronization guarantees can be given by calls to synchronizing functions of the <threads.h> header or by an appropriate call to atomic_thread_fence at the end of the initialization phase. If a function is known to be independent or effectless, adding restrict qualifications to the declarations of all pointer parameters does not change the semantics of any call. Similarly, changing the memory order to memory_order_relaxed for all atomic operations during a call to such a function preserves semantics.
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NOTE 2 In general the functions provided by the <math.h> header do not have the properties that are defined above; many of them change the floating-point state or errno when they encounter an error (so they have observable side effects) and the results of most of them depend on execution-wide state such as the rounding direction mode (so they are not independent). Whether a particular C library function is reproducible or unsequenced additionally often depends on properties of the implementation, such as implementation-defined behavior for certain error conditions.
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Recommended Practice If possible, it is recommended that implementations diagnose if an attribute of this clause is applied to a function definition that does not have the corresponding property. It is recommended that applications that assert the independent or effectless properties for functions qualify pointer parameters with restrict. Forward references: errors <errno.h> (7.5), floating-point environment <fenv.h> (7.6), localization <locale.h> (7.11), mathematics <math.h> (7.12), fences (7.17.4), input/output <stdio.h> (7.23), threads <threads.h> (7.28), extended multibyte and wide character utilities <wchar.h> (7.31).
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6.7.12.7.1 The reproducible type attribute Description The reproducible type attribute asserts that a function or pointed-to function with that type is reproducible.
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The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given reproducible as the pp-tokens operand if the implementation supports the attribute.
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EXAMPLE 1 The attribute in the following function declaration asserts that two consecutive calls to the function will result in the same return value. Changes to the abstract state during the call are possible as long as they are not observable, but no other side effects will occur. Thus the function definition may for example use local objects of static or thread storage duration to keep track of the arguments for which the function has been called and cache their computed return values. size_t hash(char const[static 32]) [[reproducible]];
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6.7.12.7.2 The unsequenced type attribute Description The unsequenced type attribute asserts that a function or pointed-to function with that type is unsequenced.
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The __has_c_attribute conditional inclusion expression (6.10.1) shall return the value 202311L when given unsequenced as the pp-tokens operand if the implementation supports the attribute.
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NOTE 1 The unsequenced type attribute asserts strong properties for such a function, in particular that certain sequencing requirements for function calls can be relaxed without affecting the state of the abstract machine. Thereby, calls to such functions are natural candidates for optimization techniques such as common subexpression elimination, local memoization or lazy evaluation. 196) A function call of an unsequenced function can be executed as early as the function pointer value, the values of the arguments and all objects that are accessible through them, and all values of globally accessible state have been determined, and it can be executed as late as the arguments and the objects they possibly target are unchanged and as any of its return value or modified pointed-to arguments are accessed.
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NOTE 2 A proof of validity of the annotation of a function type with the unsequenced attribute may depend on the property if a derived function pointer escapes the translation unit or not. For a function with internal linkage where no function pointer escapes the translation unit, all calling contexts are known and it is possible, in principle, to prove that no control flow exists such that a library function is called with arguments that trigger an exceptional condition. For a function with external linkage such a proof may not be possible and the use of such a function then has to ensure that no exceptional condition results from the provided arguments.
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NOTE 3 The unsequenced property does not necessarily imply that the function is reentrant or that calls can be executed concurrently. This is because an unsequenced function can read from and write to objects of static storage duration, as long as no change is observable after a call terminates.
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EXAMPLE 1 The attribute in the following function declaration asserts that it doesn’t depend on any modifiable state of the abstract machine. Calls to the function can be executed out of sequence before the return value is needed and two calls to the function with the same argument value will result in the same return value. bool tendency(signed char) [[unsequenced]];
Therefore such a call for a given argument value needs only to be executed once and the returned value can be reused when appropriate. For example, calls for all possible argument values can be executed during program startup and tabulated. 7
EXAMPLE 2 The attribute in the following function declaration asserts that it doesn’t depend on any modifiable state of the abstract machine. Within the same thread, calls to the function can be executed out of sequence before the return value is needed and two calls to the function will result in the same pointer return value. Therefore such a call needs only to be executed once in a given thread and the returned pointer value can be reused when appropriate. For example, a single call can be executed during thread startup and the return value p and the value of the object *p of type toto const can be cached. typedef struct toto toto; toto const* toto_zero(void) [[unsequenced]];
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EXAMPLE 3 The unsequenced property of a function f can be locally asserted within a function g that uses it. For example the library function sqrt is in generally not unsequenced because a negative argument will raise a domain error and because the result may depend on the rounding mode. Nevertheless in contexts similar to the following function a user can prove that it will not be called with invalid arguments, and, that the floating-point environment has the same value for all calls. #include <math.h> #include <fenv.h> inline double distance (double const x[static 2]) [[reproducible]] { #pragma FP_CONTRACT OFF #pragma FENV_ROUND FE_TONEAREST // We assert that sqrt will not be called with invalid arguments // and the result only depends on the argument value. extern typeof(sqrt) [[unsequenced]] sqrt; return sqrt(x[0]*x[0] + x[1]*x[1]); }
The function distance potentially has the side effect of changing the floating-point environment. Nevertheless the floating environment is thread local, thus a change to that state outside the function is sequenced with the change within and additionally the observed value is restored when the function returns. Thus this side effect is not observable for a caller. Overall the function distance is stateless, effectless and idempotent and in particular it is reproducible as the attribute indicates. Because the function can be called in a context where the floating-point environment has different state, distance is not independent and thus it is also not unsequenced. Nevertheless, adding an unsequenced attribute where this is justified may introduce optimization opportunities.
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double g (double y[static 1], double const x[static 2]) { // We assert that distance will not see different states of the floating // point environment. extern double distance (double const x[static 2]) [[unsequenced]]; y[0] = distance(x); ... return distance(x); // replacement by y[0] is valid }
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Statements and blocks
Syntax statement: labeled-statement unlabeled-statement unlabeled-statement: expression-statement attribute-specifier-sequenceopt primary-block attribute-specifier-sequenceopt jump-statement primary-block: compound-statement selection-statement iteration-statement secondary-block: statement
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Semantics A statement specifies an action to be performed. Except as indicated, statements are executed in sequence. The optional attribute specifier sequence appertains to the respective statement.
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A block is either a primary block, a secondary block, or the block associated with a function definition; it allows a set of declarations and statements to be grouped into one syntactic unit. Whenever a block B appears in the syntax production as part of the definition of an enclosing block A, scopes of identifiers and lifetimes of objects that are associated with B do not extend to the parts of A that are outside of B. The initializers of objects that have automatic storage duration, and any size expressions and typeof operators in declarations of ordinary identifiers with block scope, are evaluated and the values are stored in the objects (the representation of objects without an initializer becomes indeterminate) each time the declaration is reached in the order of execution, as if it were a statement, and within each declaration in the order that declarators appear.
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A full expression is an expression that is not part of another expression, nor part of a declarator or abstract declarator. There is also an implicit full expression in which the non-constant size expressions for a variably modified type are evaluated; within that full expression, the evaluation of different size expressions are unsequenced with respect to one another. There is a sequence point between the evaluation of a full expression and the evaluation of the next full expression to be evaluated.
5
NOTE Each of the following is a full expression: — a full declarator for a variably modified type, — an initializer that is not part of a compound literal, — the expression in an expression statement, — the controlling expression of a selection statement (if or switch), — the controlling expression of a while or do statement, — each of the (optional) expressions of a for statement, — the (optional) expression in a return statement. While a constant expression satisfies the definition of a full expression, evaluating it does not depend on nor produce any side effects, so the sequencing implications of being a full expression are not relevant to a constant expression.
Forward references: expression and null statements (6.8.3), selection statements (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
6.8.1 1
Labeled statements
Syntax label: attribute-specifier-sequenceopt identifier : § 6.8.1
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attribute-specifier-sequenceopt case constant-expression : attribute-specifier-sequenceopt default : labeled-statement: label statement
2
Constraints A case or default label shall appear only in a switch statement. Further constraints on such labels are discussed under the switch statement.
3
Label names shall be unique within a function.
4
Semantics Any statement or declaration in a compound statement may be preceded by a prefix that declares an identifier as a label name. The optional attribute specifier sequence appertains to the label. Labels in themselves do not alter the flow of control, which continues unimpeded across them. Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2) .
6.8.2 1
Compound statement
Syntax compound-statement: { block-item-listopt }
block-item-list: block-item block-item-list block-item block-item: declaration unlabeled-statement label
2
Semantics A compound statement that is a function body together with the parameter type list and the optional attribute specifier sequence between them forms the block associated with the function definition in which it appears. Otherwise, it is a block that is different from any other block. A label shall be translated as if it were followed by a null statement.
6.8.3 1
Expression and null statements
Syntax expression-statement: expressionopt ; attribute-specifier-sequence expression ;
2
Semantics The attribute specifier sequence appertains to the expression. The expression in an expression statement is evaluated as a void expression for its side effects.197)
3
A null statement (consisting of just a semicolon) performs no operations.
4
EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the discarding of its value can be made explicit by converting the expression to a void expression by means of a cast: int p(int); /* ... */ 197) Such as assignments, and function calls which have side effects.
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(void)p(0); 5
EXAMPLE 2 In the program fragment char *s; /* ... */ while (*s++ != ’\0’) ;
a null statement is used to supply an empty loop body to the iteration statement. Forward references: iteration statements (6.8.5).
6.8.4 1
Selection statements
Syntax selection-statement: if ( expression ) secondary-block if ( expression ) secondary-block else secondary-block switch ( expression ) secondary-block
2
1
2
Semantics A selection statement selects among a set of secondary blocks depending on the value of a controlling expression. 6.8.4.1 The if statement Constraints The controlling expression of an if statement shall have scalar type. Semantics In both forms, the first substatement is executed if the expression compares unequal to 0. In the else form, the second substatement is executed if the expression compares equal to 0. If the first substatement is reached via a label, the second substatement is not executed.
3
An else is associated with the lexically nearest preceding if that is allowed by the syntax.
1
6.8.4.2 The switch statement Constraints The controlling expression of a switch statement shall have integer type.
2
If a switch statement has an associated case or default label within the scope of an identifier with a variably modified type, the entire switch statement shall be within the scope of that identifier.198)
3
The expression of each case label shall be an integer constant expression and no two of the case constant expressions associated to the same switch statement shall have the same value after conversion. There may be at most one default label associated to a switch statement. (Any enclosed switch statement may have a default label or case constant expressions with values that duplicate case constant expressions in the enclosing switch statement.)
4
5
Semantics A switch statement causes control to jump to, into, or past the statement that is the switch body, depending on the value of a controlling expression, and on the presence of a default label and the values of any case labels on or in the switch body. A case or default label is accessible only within the closest enclosing switch statement. The integer promotions are performed on the controlling expression. The constant expression in each case label is converted to the promoted type of the controlling expression. If a converted value matches that of the promoted controlling expression, control jumps to the statement or declaration 198) That is, the declaration either precedes the switch statement, or it follows the last case or default label associated with the switch that is in the block containing the declaration.
§ 6.8.4.2
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following the matched case label. Otherwise, if there is a default label, control jumps to the statement or declaration following the default label. If no converted case constant expression matches and there is no default label, no part of the switch body is executed.
6
Implementation limits As discussed in 5.2.4.1, the implementation may limit the number of case values in a switch statement.
7
EXAMPLE In the artificial program fragment switch (expr) { int i = 4; f(i); case 0: i = 17; /* falls through into default code */ default: printf("%d\n", i); }
the object whose identifier is i exists with automatic storage duration (within the block) but is never initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will access an object with an indeterminate representation. Similarly, the call to the function f cannot be reached.
6.8.5 1
Iteration statements
Syntax iteration-statement: while ( expression ) secondary-block do secondary-block while ( expression ) ; for ( expressionopt ; expressionopt ; expressionopt ) secondary-block for ( declaration expressionopt ; expressionopt ) secondary-block
2
3
4
Constraints The controlling expression of an iteration statement shall have scalar type. Semantics An iteration statement causes a secondary block called the loop body to be executed repeatedly until the controlling expression compares equal to 0. The repetition occurs regardless of whether the loop body is entered from the iteration statement or by a jump199) . An iteration statement may be assumed by the implementation to terminate if its controlling expression is not a constant expression200) , and none of the following operations are performed in its body, controlling expression or (in the case of a for statement) its expression-3201) : — input/output operations — accessing a volatile object — synchronization or atomic operations.
1
6.8.5.1 The while statement The evaluation of the controlling expression takes place before each execution of the loop body. 199) Code jumped over is not executed. In particular, the controlling expression of a for or while statement is not evaluated before entering the loop body, nor is clause-1 (6.8.5.3) of a for statement. 200) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression. 201) This is intended to allow compiler transformations such as removal of empty loops even when termination cannot be proven.
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6.8.5.2 The do statement The evaluation of the controlling expression takes place after each execution of the loop body.
1
6.8.5.3 The for statement The statement for (clause-1; expression-2; expression-3) statement
behaves as follows: The expression expression-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expression-3 is evaluated as a void expression after each execution of the loop body. If clause-1 is a declaration, the scope of any identifiers it declares is the remainder of the declaration and the entire loop, including the other two expressions; it is reached in the order of execution before the first evaluation of the controlling expression. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.202) 2
Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a nonzero constant.
6.8.6 1
Jump statements
Syntax jump-statement: goto identifier ; continue ; break ; return expressionopt ;
2
Semantics A jump statement causes an unconditional jump to another place.
1
6.8.6.1 The goto statement Constraints The identifier in a goto statement shall name a label located somewhere in the enclosing function. A goto statement shall not jump from outside the scope of an identifier having a variably modified type to inside the scope of that identifier.
2
Semantics A goto statement causes an unconditional jump to the statement prefixed by the named label in the enclosing function.
3
EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The following outline presents one possible approach to a problem based on these three assumptions: 1. The general initialization code accesses objects only visible to the current function. 2. The general initialization code is too large to warrant duplication. 3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by continue statements, for example.) /* ... */ goto first_time; for (;;) { // determine next operation 202) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration, such that execution of the loop continues until the expression compares equal to 0; and expression-3 specifies an operation (such as incrementing) that is performed after each iteration.
§ 6.8.6.1
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/* ... */ if (need to reinitialize) { // reinitialize-only code /* ... */ first_time: // general initialization code /* ... */ continue; } // handle other operations /* ... */ }
4
EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably modified types. A jump within the scope, however, is permitted. goto lab3; { double a[n]; a[j] = 4.4; lab3: a[j] = 3.3; goto lab4; a[j] = 5.5; lab4: a[j] = 6.6; } goto lab4;
1
2
// invalid:
// valid:
going INTO scope of VLA.
going WITHIN scope of VLA.
// invalid:
going INTO scope of VLA.
6.8.6.2 The continue statement Constraints A continue statement shall appear only in or as a loop body. Semantics A continue statement causes a jump to the loop-continuation portion of the innermost enclosing iteration statement; that is, to the end of the loop body. More precisely, in each of the statements while (/* ... /* ... */ continue; /* ... */ contin: }
*/) {
do { /* ... */ continue; /* ... */ contin:; } while (/* ...
*/);
for (/* ... */) { /* ... */ continue; /* ... */ contin: }
unless the continue statement shown is in an enclosed iteration statement (in which case it is interpreted within that statement), it is equivalent to goto contin; 203) .
1
6.8.6.3 The break statement Constraints A break statement shall appear only in or as a switch body or loop body.
2
Semantics A break statement terminates execution of the innermost enclosing switch or iteration statement. 203) Following the contin: label in the 2nd example is a null statement. The null statement in the first and third example is implied by the label (6.8.2).
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6.8.6.4 The return statement Constraints A return statement with an expression shall not appear in a function whose return type is void. A return statement without an expression shall only appear in a function whose return type is void. Semantics A return statement terminates execution of the current function and returns control to its caller. A function may have any number of return statements.
3
If a return statement with an expression is executed, the value of the expression is returned to the caller as the value of the function call expression. If the expression has a type different from the return type of the function in which it appears, the value is converted as if by assignment to an object having the return type of the function.204)
4
EXAMPLE In: struct s { double i; } f(void); union { struct { int f1; struct s f2; } u1; struct { struct s f3; int f4; } u2; } g; struct s f(void) { return g.u1.f2; } /* ... */ g.u2.f3 = f();
there is no undefined behavior, although there would be if the assignment were done directly (without using a function call to fetch the value).
204) The return statement is not an assignment. The overlap restriction of 6.5.16.1 does not apply to the case of function return. The representation of floating-point values can have wider range or precision than implied by the type; a cast can be used to remove this extra range and precision.
§ 6.8.6.4
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External definitions
Syntax translation-unit: external-declaration translation-unit external-declaration external-declaration: function-definition declaration
2
3
Constraints The storage-class specifier register shall not appear in the declaration specifiers in an external declaration. The storage-class specifier auto shall only appear in the declaration specifiers in an external declaration if the type is inferred. There shall be no more than one external definition for each identifier declared with internal linkage in a translation unit. Moreover, if an identifier declared with internal linkage is used in an expression there shall be exactly one external definition for the identifier in the translation unit, unless it is: — part of the operand of a sizeof operator whose result is an integer constant; — part of the operand of an alignof operator whose result is an integer constant; — or, part of the operand of any typeof operator whose result is not a variably modified type.
4
5
Semantics As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit, which consists of a sequence of external declarations. These are described as "external" because they appear outside any function (and hence have file scope). As discussed in 6.7, a declaration that also causes storage to be reserved for an object or a function named by the identifier is a definition. An external definition is an external declaration that is also a definition of a function (other than an inline definition) or an object. If an identifier declared with external linkage is used in an expression (other than as part of the operand of a typeof operator whose result is not a variably modified type, or a sizeof or alignof operator whose result is an integer constant expression), somewhere in the entire program there shall be exactly one external definition for the identifier; otherwise, there shall be no more than one.205)
6.9.1 1
Function definitions
Syntax function-definition: attribute-specifier-sequenceopt declaration-specifiers declarator function-body function-body: compound-statement
2
Constraints The identifier declared in a function definition (which is the name of the function) shall have a function type, as specified by the declarator portion of the function definition.
3
The return type of a function shall be void or a complete object type other than array type. 205) Thus, if an identifier declared with external linkage is not used in an expression, there need be no external definition for
it.
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The storage-class specifier, if any, in the declaration specifiers shall be either extern or static.
5
If the parameter list consists of a single parameter of type void, the parameter declarator shall not include an identifier.
6
Semantics The optional attribute specifier sequence in a function definition appertains to the function.
7
The declarator in a function definition specifies the name of the function being defined and the types (and optionally the names) of all the parameters; the declarator also serves as a function prototype for later calls to the same function in the same translation unit. The type of each parameter is adjusted as described in 6.7.6.3.
8
If a function that accepts a variable number of arguments is defined without a parameter type list that ends with the ellipsis notation, the behavior is undefined.
9
The parameter type list, the attribute specifier sequence of the declarator that follows the parameter type list, and the compound statement of the function body form a single block.206) Each parameter has automatic storage duration; its identifier, if any207) , is an lvalue.208) The layout of the storage for parameters is unspecified.
10
On entry to the function, the size expressions of each variably modified parameter are evaluated and the value of each argument expression is converted to the type of the corresponding parameter as if by assignment. (Array expressions and function designators as arguments were converted to pointers before the call.)
11
After all parameters have been assigned, the compound statement of the function body is executed.
12
Unless otherwise specified, if the } that terminates the function body is reached, and the value of the function call is used by the caller, the behavior is undefined.
13
NOTE 1 In a function definition, the type of the function and its prototype cannot be inherited from a typedef:
typedef int F(void); F f, g; F f { /* ... */ } F g() { /* ... */ } int f(void) { /* ... */ } int g() { /* ... */ } F *e(void) { /* ... */ } F *((e))(void) { /* ... */ } int (*fp)(void); F *Fp; 14
// type F is "function with no parameters // returning int" // f and g both have type compatible with F // WRONG: syntax/constraint error // WRONG: declares that g returns a function // RIGHT: f has type compatible with F // RIGHT: g has type compatible with F // e returns a pointer to a function // same: parentheses irrelevant // fp points to a function that has type F // Fp points to a function that has type F
EXAMPLE 1 In the following: extern int max(int a, int b) { return a > b ? a: b; }
extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the function
declarator; and { return a
>
b ? a: b; }
206) The visibility scope of a parameter in a function definition starts when its declaration is completed, extends to following parameter declarations, to possible attributes that follow the parameter type list, and then to the entire function body. The lifetime of each instance of a parameter starts when the declaration is evaluated starting a call and ends when that call terminates. 207) A parameter that has no declared name is inaccessible within the function body. 208) A parameter identifier cannot be redeclared in the function body except in an enclosed block.
§ 6.9.1
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is the function body. 15
EXAMPLE 2 To pass one function to another, one might say int f(void); /* ... */ g(f);
Then the definition of g might read void g(int (*funcp)(void)) { /* ... */ (*funcp)(); /* or funcp(); ...*/ }
or, equivalently, void g(int func(void)) { /* ... */ func(); /* or (*func)(); ...*/ }
6.9.2 1
2
External object definitions
Semantics If the declaration of an identifier for an object has file scope and an initializer, or has file scope and storage-class specifier thread_local, the declaration is an external definition for the identifier. A declaration of an identifier for an object that has file scope without an initializer, and without the storage-class specifier extern or thread_local, constitutes a tentative definition. If a translation unit contains one or more tentative definitions for an identifier, and the translation unit contains no external definition for that identifier, then the behavior is exactly as if the translation unit contains a file scope declaration of that identifier, with the composite type as of the end of the translation unit, with an empty initializer and a type determined as follows: — if the composite type as of the end of the translation unit is an array of unknown size, then an array of size one with the composite element type; — otherwise, the composite type at the end of the translation unit.
3
If the declaration of an identifier for an object is a tentative definition and has internal linkage, the declared type shall not be an incomplete type.
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EXAMPLE 1 int i1 = 1; static int i2 = 2; extern int i3 = 3; int i4; static int i5;
// definition, external linkage // definition, internal linkage // definition, external linkage // tentative definition, external linkage // tentative definition, internal linkage
int i1; int i2; int i3; int i4; int i5;
// valid tentative definition, refers to previous // 6.2.2 renders undefined, linkage disagreement // valid tentative definition, refers to previous // valid tentative definition, refers to previous // 6.2.2 renders undefined, linkage disagreement
extern int i1; extern int i2; extern int i3; extern int i4; extern int i5;
// refers to previous, whose linkage is external // refers to previous, whose linkage is internal // refers to previous, whose linkage is external // refers to previous, whose linkage is external // refers to previous, whose linkage is internal
EXAMPLE 2 If at the end of the translation unit containing int i[];
the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to zero on program startup.
§ 6.9.2
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Preprocessing directives
Syntax 1
preprocessing-file: groupopt group: group-part group group-part group-part: if-section control-line text-line # non-directive if-section: if-group elif-groupsopt else-groupopt endif-line if-group: # if constant-expression new-line groupopt # ifdef identifier new-line groupopt # ifndef identifier new-line groupopt
elif-groups: elif-group elif-groups elif-group elif-group: # elif constant-expression new-line groupopt # elifdef identifier new-line groupopt # elifndef identifier new-line groupopt
else-group: # else new-line groupopt
endif-line: # endif new-line
control-line: # include pp-tokens new-line # embed pp-tokens new-line # define identifier replacement-list new-line # define identifier lparen identifier-listopt ) replacement-list new-line # define identifier lparen ... ) replacement-list new-line # define identifier lparen identifier-list , ... ) replacement-list new-line # undef identifier new-line # line pp-tokens new-line # error pp-tokensopt new-line # warning pp-tokensopt new-line # pragma pp-tokensopt new-line # new-line
text-line: pp-tokensopt new-line non-directive: pp-tokens new-line lparen: a ( character not immediately preceded by white space replacement-list: pp-tokensopt 162
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pp-tokens: preprocessing-token pp-tokens preprocessing-token new-line: the new-line character identifier-list: identifier identifier-list , identifier pp-parameter: pp-parameter-name pp-parameter-clauseopt pp-parameter-name: pp-standard-parameter pp-prefixed-parameter pp-standard-parameter: identifier pp-prefixed-parameter: identifier :: identifier pp-parameter-clause: ( pp-balanced-token-sequenceopt )
pp-balanced-token-sequence: pp-balanced-token pp-balanced-token-sequence pp-balanced-token pp-balanced-token: ( pp-balanced-token-sequenceopt ) [ pp-balanced-token-sequenceopt ] { pp-balanced-token-sequenceopt }
any pp-token other than a parenthesis, a bracket, or a brace embed-parameter-sequence: pp-parameter embed-parameter-sequence pp-parameter
2
Description A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the following constraints: The first token in the sequence is a # preprocessing token that (at the start of translation phase 4) is either the first character in the source file (optionally after white space containing no new-line characters) or that follows white space containing at least one new-line character. The last token in the sequence is the first new-line character that follows the first token in the sequence. 209) 209) Thus, preprocessing directives are commonly called "lines". These "lines" have no other syntactic significance, as all white space is equivalent except in certain situations during preprocessing (see the # character string literal creation operator
§ 6.10
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A new-line character ends the preprocessing directive even if it occurs within what would otherwise be an invocation of a function-like macro. 3
A text line shall not begin with a # preprocessing token. A non-directive shall not begin with any of the directive names appearing in the syntax.
4
Some preprocessing directives take additional information using preprocessor parameters. A preprocessing parameter (pp-parameter) shall be either a preprocessor prefixed parameter (identified by a pp-prefixed-parameter, for implementation-defined preprocessor parameters) or a preprocessor standard parameter (identified with a pp-standard-parameter, for pp-parameters specified by this document).
5
In all aspects, a preprocessor standard parameter specified by this document as an identifier pp_param and an identifier of the form __pp_param__ shall behave the same when used as a preprocessor parameter, except for the spelling.
6
EXAMPLE 1 Thus, the preprocessor parameters on the two binary resource inclusion directives (6.10.3.1): #embed "boop.h" limit(5) #embed "boop.h" __limit__(5)
behave the same, and can be freely interchanged. Implementations are encouraged to behave similarly for preprocessor parameters (including preprocessor prefixed parameters) they provide. 7
8
9
10
When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any sequence of preprocessing tokens to occur between the directive name and the following new-line character. Constraints The only white-space characters that shall appear between preprocessing tokens within a preprocessing directive (from just after the introducing # preprocessing token through just before the terminating new-line character) are space and horizontal-tab (including spaces that have replaced comments or possibly other white-space characters in translation phase 3). A preprocessor parameter shall be either a preprocessor standard parameter, or an implementationdefined preprocessor prefixed parameter210) . Semantics The implementation can process and skip sections of source files conditionally, include other source files, and replace macros. These capabilities are called preprocessing, because conceptually they occur before translation of the resulting translation unit.
11
The preprocessing tokens within a preprocessing directive are not subject to macro expansion unless otherwise stated.
12
EXAMPLE In: #define EMPTY EMPTY # include <file.h>
the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been replaced. 13
The execution of a non-directive preprocessing directive results in undefined behavior.
6.10.1 1
Conditional inclusion
Syntax defined-macro-expression: defined identifier in 6.10.4.2, for example). 210) An unrecognized preprocessor prefixed parameter is a constraint violation, except within has_embed expressions (6.10.1).
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defined ( identifier ) h-preprocessing-token: any preprocessing-token other than > h-pp-tokens: h-preprocessing-token h-pp-tokens h-preprocessing-token header-name-tokens: string-literal < h-pp-tokens > has-include-expression: __has_include ( header-name ) __has_include ( header-name-tokens ) has-embed-expression: __has_embed ( header-name embed-parameter-sequenceopt ) __has_embed ( header-name-tokens pp-balanced-token-sequenceopt ) has-c-attribute-express: __has_c_attribute ( pp-tokens )
2
3
The #if and #elif directives are collectively known as the conditional expression inclusion preprocessing directives. The conditional expression inclusion preprocessing directives, #ifdef, #ifndef, #elifdef, and #elifndef directives are collectively known as the conditional inclusion preprocessing directives. Constraints The expression that controls conditional inclusion shall be an integer constant expression except that: identifiers (including those lexically identical to keywords) are interpreted as described below211) and it may contain zero or more defined macro expressions, has_include expressions, has_embed expressions, and/or has_c_attribute expressions as unary operator expressions.
4
A defined macro expression evaluates to 1 if the identifier is currently defined as a macro name (that is, if it is predefined or if it has been the subject of a #define preprocessing directive without an intervening #undef directive with the same subject identifier), 0 if it is not.
5
The second form of the has_include expression and has_embed expression is considered only if the first form does not match, in which case the preprocessing tokens are processed just as in normal text.
6
The header or source file identified by the parenthesized preprocessing token sequence in each contained has_include expression is searched for as if that preprocessing token were the pp-tokens in a #include directive, except that no further macro expansion is performed. Such a directive shall satisfy the syntactic requirements of a #include directive. The has_include expression evaluates to 1 if the search for the source file succeeds, and to 0 if the search fails.
7
The resource (6.10.3.1) identified by the header-name preprocessing token sequence in each contained has_embed expression is searched for as if those preprocessing token were the pp-tokens in a #embed directive, except that no further macro expansion is performed. Such a directive shall satisfy the syntactic requirements of a #embed directive. The has_embed expression evaluates to: — __STDC_EMBED_NOT_FOUND__ , if the search fails or if any of the embed parameters in the embed parameter sequence specified are not supported by the implementation for the #embed directive; or, — __STDC_EMBED_FOUND__ , if the search for the resource succeeds and all embed parameters in the embed parameter sequence specified are supported by the implementation for the #embed directive and the resource is not empty; or, 211) Because the controlling constant expression is evaluated during translation phase 4, all identifiers either are or are not macro names — there simply are no keywords, enumeration constants, etc.
§ 6.10.1
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— __STDC_EMBED_EMPTY__ , if the search for the resource succeeds and all embed parameters in the embed parameter sequence specified are supported by the implementation for the #embed directive and the resource is empty. 8
NOTE 1 Unrecognized preprocessor prefixed parameters in has_embed expressions are not a constraint violation and instead cause the expression to be evaluate to 0, as specified above.
9
Each has_c_attribute expression is replaced by a nonzero pp-number matching the form of an integer constant if the implementation supports an attribute with the name specified by interpreting the pp-tokens as an attribute token, and by 0 otherwise. The pp-tokens shall match the form of an attribute token.
10
Each preprocessing token that remains (in the list of preprocessing tokens that will become the controlling expression) after all macro replacements have occurred shall be in the lexical form of a token (6.4).
11
12
Semantics The #ifdef, #ifndef, #elifdef, and #elifndef directives, and the defined conditional inclusion operator, shall treat __has_include, __has_embed and __has_c_attribute as if they were the name of defined macros. The identifiers __has_include, __has_embed, and __has_c_attribute shall not appear in any context not mentioned in this subclause. Preprocessing directives of the forms # if constant-expression new-line groupopt # elif constant-expression new-line groupopt
check whether the controlling constant expression evaluates to nonzero. 13
Prior to evaluation, macro invocations in the list of preprocessing tokens that will become the controlling constant expression are replaced (except for those macro names modified by the defined unary operator), just as in normal text. If the token defined is generated as a result of this replacement process or use of the defined unary operator does not match one of the two specified forms prior to macro replacement, the behavior is undefined. After all replacements due to macro expansion and evaluations of defined macro expressions, has_include expressions, has_embed expressions, and has_c_attribute expressions have been performed, all remaining identifiers other than true (including those lexically identical to keywords such as false) are replaced with the pp-number 0, true is replaced with pp-number 1, and then each preprocessing token is converted into a token. The resulting tokens compose the controlling constant expression which is evaluated according to the rules of 6.6. For the purposes of this token conversion and evaluation, all signed integer types and all unsigned integer types act as if they have the same representation as, respectively, the types intmax_t and uintmax_t defined in the header <stdint.h>. 212) This includes interpreting character constants, which may involve converting escape sequences into execution character set members. Whether the numeric value for these character constants matches the value obtained when an identical character constant occurs in an expression (other than within a #if or #elif directive) is implementation-defined213) . Also, whether a single-character character constant may have a negative value is implementationdefined.
14
Preprocessing directives of the forms # ifdef identifier new-line groupopt # ifndef identifier new-line groupopt 212) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant 0x8000 is signed and positive within a #if expression even though it would be unsigned in translation phase 7. 213) Thus, the constant expression in the following #if directive and if statement is not guaranteed to evaluate to the same value in these two contexts.
#if ’z’ - ’a’ == 25 if (’z’ - ’a’ == 25)
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# elifdef identifier new-line groupopt # elifndef identifier new-line groupopt
check whether the identifier is or is not currently defined as a macro name. Their conditions are equivalent to #if defined identifier, #if !defined identifier, #elif defined identifier, and #elif !defined identifier respectively. 15
Each directive’s condition is checked in order. If it evaluates to false (zero), the group that it controls is skipped: directives are processed only through the name that determines the directive to keep track of the level of nested conditionals; the rest of the directives’ preprocessing tokens are ignored, as are the other preprocessing tokens in the group. Only the first group whose control condition evaluates to true (nonzero) is processed; any following groups are skipped and their controlling directives are processed as if they were in a group that is skipped. If none of the conditions evaluates to true, and there is a #else directive, the group controlled by the #else is processed; lacking a #else directive, all the groups until the #endif are skipped. 214)
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EXAMPLE This demonstrates a way to include a header file only if it is available. #if __has_include(<optional.h>) # include <optional.h> # define have_optional 1 #elif __has_include(<experimental/optional.h>) # include <experimental/optional.h> # define have_optional 1 # define have_experimental_optional 1 #endif #ifndef have_optional # define have_optional 0 #endif
17
EXAMPLE /* Fallback for compilers not yet implementing this feature. */ #ifndef __has_c_attribute #define __has_c_attribute(x) 0 #endif /* __has_c_attribute */ #if __has_c_attribute(fallthrough) /* Standard attribute is available, use it. */ #define FALLTHROUGH [[fallthrough]] #elif __has_c_attribute(vendor::fallthrough) /* Vendor attribute is available, use it. */ #define FALLTHROUGH [[vendor::fallthrough]] #else /* Fallback implementation. */ #define FALLTHROUGH #endif
18
EXAMPLE #ifdef __STDC__ #define TITLE "ISO C Compilation" #elifndef __cplusplus #define TITLE "Non-ISO C Compilation" #else /* C++ */ #define TITLE "C++ Compilation" #endif 214) As indicated by the syntax, no preprocessing tokens are allowed to follow a #else or #endif directive before the terminating new-line character. However, comments can appear anywhere in a source file, including within a preprocessing directive.
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EXAMPLE 1 A combination of __FILE__ (6.10.9.1) and __has_embed could be used to check for support of specific implementation extensions for the #embed (6.10.3.1) directive’s parameters. #if __has_embed(__FILE__ ext::token(0xB055)) #define DESCRIPTION "Supports extended token embed parameter" #else #define DESCRIPTION "Does not support extended token embed parameter" #endif
20
EXAMPLE 2 The snippet below uses __has_embed to check for support of a specific implementation-defined embed parameter, and otherwise uses standard behavior to produce the same effect. void parse_into_s(short* ptr, unsigned char* ptr_bytes, unsigned long long size); int main () { #if __has_embed ("bits.bin" ds9000::element_type(short)) /* Implementation extension: create short integers from the */ /* translation environment resource into */ /* a sequence of integer constants */ short meow[] = { #embed "bits.bin" ds9000::element_type(short) }; #elif __has_embed ("bits.bin") /* no support for implementation-specific */ /* ds9000::element_type(short) parameter */ const unsigned char meow_bytes[] = { #embed "bits.bin" }; short meow[sizeof(meow_bytes) / sizeof(short)] = {}; /* parse meow_bytes into short values by-hand! */ parse_into_s(meow, meow_bytes, sizeof(meow_bytes)); #else #error "cannot find bits.bin resource" #endif return (int)(meow[0] + meow[(sizeof(meow) / sizeof(*meow)) - 1]); }
21
EXAMPLE 3 If the search for the resource is successful, this resource is always considered empty due to the limit(0) embed parameter, including in __has_embed expressions. int main () { #if __has_embed(<infinite-resource> limit(0)) == 2 // if <infinite-resource> exists, this // token sequence is always taken. return 0; #else // the ’infinite-resource’ resource does not exist #error "The resource does not exist" #endif }
Forward references: macro replacement (6.10.4), source file inclusion (6.10.2), mandatory macros (6.10.9.1), largest integer types (7.22.1.5).
6.10.2 1
Source file inclusion
Constraints A #include directive shall identify a header or source file that can be processed by the implementation. 168
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Semantics A preprocessing directive of the form # include < h-char-sequence > new-line
searches a sequence of implementation-defined places for a header identified uniquely by the specified sequence between the < and > delimiters, and causes the replacement of that directive by the entire contents of the header. How the places are specified or the header identified is implementation-defined. 3
A preprocessing directive of the form # include " q-char-sequence " new-line
causes the replacement of that directive by the entire contents of the source file identified by the specified sequence between the " delimiters. The named source file is searched for in an implementation-defined manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read # include < h-char-sequence > new-line
with the identical contained sequence (including > characters, if any) from the original directive. 4
A preprocessing directive of the form # include pp-tokens new-line
(that does not match one of the two previous forms) is permitted. The preprocessing tokens after include in the directive are processed just as in normal text. (Each identifier currently defined as a macro name is replaced by its replacement list of preprocessing tokens.) The directive resulting after all replacements shall match one of the two previous forms.215) The method by which a sequence of preprocessing tokens between a < and a > preprocessing token pair or a pair of " characters is combined into a single header name preprocessing token is implementation-defined. 5
The implementation shall provide unique mappings for sequences consisting of one or more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The first character shall not be a digit. The implementation may ignore distinctions of alphabetical case and restrict the mapping to eight significant characters before the period.
6
A #include preprocessing directive may appear in a source file that has been read because of a #include directive in another file, up to an implementation-defined nesting limit (see 5.2.4.1).
7
EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following: #include <stdio.h> #include "myprog.h"
8
EXAMPLE 2 This illustrates macro-replaced #include directives: #if VERSION == 1 #define INCFILE #elif VERSION == 2 #define INCFILE #else #define INCFILE #endif #include INCFILE
"vers1.h" "vers2.h"
// and so on
"versN.h"
Forward references: macro replacement (6.10.4). 215) Note that adjacent string literals are not concatenated into a single string literal (see the translation phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.
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Binary resource inclusion
6.10.3.1 #embed preprocessing directive Description A resource is a source of data accessible from the translation environment. An embed parameter is a single preprocessor parameter in the embed parameter sequence. It has an implementation resource width, which is the implementation-defined size in bits of the located resource. It also has a resource width, which is either: — the number of bits as computed from the optionally-provided limit embed parameter (6.10.3.2), if present; or, — the implementation resource width.
2
3
An embed parameter sequence is a whitespace-delimited list of preprocessor parameters which may modify the result of the replacement for the #embed preprocessing directive. Constraints An #embed directive shall identify a resource that can be processed by the implementation as a binary data sequence given the provided embed parameters.
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Embed parameters not specified in this document shall be implementation-defined. Implementationdefined embed parameters may change the below-defined semantics of the directive; otherwise, #embed directives which do not contain implementation-defined embed parameters shall behave as described in this document.
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A resource is considered empty when its resource width is zero.
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Let embed element width be either: — an integer constant expression greater than zero determined by an implementation-defined embed parameter; or, — CHAR_BIT (5.2.4.2.1). The result of (resource width) % (embed element width) shall be zero216) .
7
8
Semantics The expansion of a #embed directive is a token sequence formed from the list of integer constant expressions described below. The group of tokens for each integer constant expression in the list is separated in the token sequence from the group of tokens for the previous integer constant expression in the list by a comma. The sequence neither begins nor ends in a comma. If the list of integer constant expressions is empty, the token sequence is empty. The directive is replaced by its expansion and, with the presence of certain embed parameters, additional or replacement token sequences. A preprocessing directive of the form # embed < h-char-sequence > embed-parameter-sequenceopt new-line
searches a sequence of implementation-defined places for a resource identified uniquely by the specified sequence between the < and >. The search for the named resource is done in an implementationdefined manner. 9
A preprocessing directive of the form # embed " q-char-sequence " embed-parameter-sequenceopt new-line
searches a sequence of implementation-defined places for a resource identified uniquely by the specified sequence between the " delimiters. The search for the named resource is done in an 216) This constraint helps ensure data is neither filled with padding values nor truncated in a given environment, and helps ensure the data is portable with respect to usages of memcpy (7.26.2.1) with character type arrays initialized from the data.
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implementation-defined manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read # embed < h-char-sequence > embed-parameter-sequenceopt new-line
with the identical contained q-char-sequence (including > characters, if any) from the original directive. 10
Either form of the #embed directive specified previously behaves as specified below. The values of the integer constant expressions in the expanded sequence are determined by an implementationdefined mapping of the resource’s data. Each integer constant expression’s value is in the range from 0 to (2embed element width ) − 1, inclusive.217) If: — the list of integer constant expressions is used to initialize an array of a type compatible with unsigned char, or compatible with char if char cannot hold negative values; and, — the embed element width is equal to CHAR_BIT (5.2.4.2.1), then the contents of the initialized elements of the array are as-if the resource’s binary data is fread (7.23.8.1) into the array at translation time.
11
A preprocessing directive of the form # embed pp-tokens new-line
(that does not match one of the two previous forms) is permitted. The preprocessing tokens after embed in the directive are processed just as in normal text. (Each identifier currently defined as a macro name is replaced by its replacement list of preprocessing tokens.) The directive resulting after all replacements shall match one of the two previous forms218) . The method by which a sequence of preprocessing tokens between a < and a > preprocessing token pair or a pair of " characters is combined into a single resource name preprocessing token is implementation-defined. 12
An embed parameter with a preprocessor parameter token that is one of the following is a standard embed parameter: limit
prefix
suffix
if_empty
The significance of these standard embed parameters is specified below.
13
Recommended practice The #embed directive is meant to translate binary data in a resource to a sequence of integer constant expressions in a way that preserves the value of the resource’s bit stream where possible.
14
A mechanism similar to, but distinct from, the implementation-defined search paths used for source file inclusion (6.10.2) is encouraged.
15
Implementations should take into account translation-time bit and byte orders as well as executiontime bit and byte orders to more appropriately represent the resource’s binary data from the directive. This maximizes the chance that, if the resource referenced at translation time through the #embed directive is the same one accessed through execution-time means, the data that is e.g. fread or similar into contiguous storage will compare bit-for-bit equal to an array of character type initialized from an #embed directive’s expanded contents.
16
EXAMPLE 1 Placing a small image resource. #include <stddef.h> void have_you_any_wool(const unsigned char*, size_t);
217) For example, an embed element width of 8 will yield a range of values from 0 to 255, inclusive. 218) Note that adjacent string literals are not concatenated into a single string literal (see the translation phases in 5.1.1.2);
thus, an expansion that results in two string literals is an invalid directive.
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int main (int, char*[]) { static const unsigned char baa_baa[] = { #embed "black_sheep.ico" }; have_you_any_wool(baa_baa, sizeof(baa_baa)); return 0; } 17
EXAMPLE 2 This snippet: int main (int, char*[]) { static const unsigned char coefficients[] = { #embed "only_8_bits.bin" // potential constraint violation }; return 0; }
may violate the constraint that (resource width) % (embed element width) must be 0. The 8 bits might not be evenly divisible by the embed element width (e.g., on a system where CHAR_BIT is 16). Issuing a diagnostic in this case may aid in portability by calling attention to potentially incompatible expectations between implementations and their resources. 18
EXAMPLE 3 Initialization of non-arrays. int main () { /* Braces may be kept or elided as per normal initialization rules */ int i = { #embed "i.dat" }; /* valid if i.dat produces 1 value, i value is [0, 2(embedelementwidth) ) */ int i2 = #embed "i.dat" ; /* i2 value is [0, 2^(embed element width)) */ struct s { double a, b, c; struct { double e, f, g; }; double h, i, j; }; struct s x = { /* initializes each element in order according to initialization rules with comma-separated list of integer constant expressions inside of braces */ #embed "s.dat" }; return 0; }
Non-array types can still be initialized since the directive produces a comma-delimited list of integer constant expressions, a single integer constant expression, or nothing. 19
EXAMPLE 4 Equivalency of bit sequence and bit order between a translation-time read and an execution-time read of the same resource/file. #include <string.h> #include <stddef.h> #include <stdio.h> int main(void) {
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static const unsigned char embed_data[] = { #embed <data.dat> }; const size_t f_size = sizeof(embed_data); unsigned char f_data[f_size]; FILE* f_source = fopen("data.dat", "rb"); if (f_source == NULL); return 1; char* f_ptr = (char*)&f_data[0]; if (fread(f_ptr, 1, f_size, f_source) != f_size) { fclose(f_source); return 1; } fclose(f_source); int is_same = memcmp(&embed_data[0], f_ptr, f_size); // if both operations refers to the same resource/file at // execution time and translation time, "is_same" should be 0 return is_same == 0 ? 0 : 1; }
1
6.10.3.2 limit parameter Constraints The limit standard embed parameter may appear zero times or one time in the embed parameter sequence. Its preprocessor argument clause shall be present and have the form: ( constant-expression )
and shall be an integer constant expression. The integer constant expression shall not evaluate to a value less than 0. 2
3
4
The token defined shall not appear within the constant expression. Semantics The embed parameter with a preprocessor parameter token limit denotes a balanced preprocessing token sequence that will be used to compute the resource width. Independently of any macro replacement done previously (e.g. when matching the form of #embed), the constant expression is evaluated after the balanced preprocessing token sequence is processed as in normal text, using the rules specified for conditional inclusion (6.10.1), with the exception that any defined macro expressions are not permitted. The resource width is: — 0, if the integer constant expression evaluates to 0; or, — the implementation resource width if it is less than the embed element width multiplied by the integer constant expression; or, — the embed element width multiplied by the integer constant expression, if it is less than or equal to the implementation resource width.
5
EXAMPLE 1 Checking the first 4 elements of a sound resource. #include <assert.h> int main (int, char*[]) { static const char sound_signature[] = { #embed <sdk/jump.wav> limit(2+2) }; static_assert((sizeof(sound_signature) / sizeof(*sound_signature)) == 4,
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"There should only be 4 elements in this array."); // verify PCM WAV resource assert(sound_signature[0] == ’R’); assert(sound_signature[1] == ’I’); assert(sound_signature[2] == ’F’); assert(sound_signature[3] == ’F’); assert(sizeof(sound_signature) == 4); return 0; } 6
EXAMPLE 2 Similar to a previous example, except it illustrates macro expansion specifically done for the limit(...) parameter. #include <assert.h> #define TWO_PLUS_TWO 2+2 int main (int, char*[]) { const char sound_signature[] = { /* the token sequence within the parentheses for the "limit" parameter undergoes macro expansion, at least once, resulting in #embed <sdk/jump.wav> limit(2+2) */ #embed <sdk/jump.wav> limit(TWO_PLUS_TWO) }; static_assert((sizeof(sound_signature) / sizeof(*sound_signature)) == 4, "There should only be 4 elements in this array."); // verify PCM WAV resource assert(sound_signature[0] == ’R’); assert(sound_signature[1] == ’I’); assert(sound_signature[2] == ’F’); assert(sound_signature[3] == ’F’); assert(sizeof(sound_signature) == 4); return 0; }
7
EXAMPLE 3 A potential constraint violation from a resource that may not have enough information in an environment that has a CHAR_BIT greater than 24. int main (int, char*[]) { const unsigned char arr[] = { #embed "24_bits.bin" limit(1) // may be a constraint violation }; return 0; }
8
EXAMPLE 4 Resources interfacing with certain implementations may have an infinite stream of data, such as the </owo/uwurandom> resource used in the snippet below: int main (int, char*[]) { const unsigned char arr[] = { #embed </owo/uwurandom> limit(513) }; return 0;
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}
The limit parameter may help process only a portion of that information and prevent exhaustion of an implementation’s internal resources when processing such data.
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6.10.3.3 suffix parameter Constraints The suffix standard embed parameter may appear zero times or one time in the embed parameter sequence. Its preprocessor argument clause shall be present and have the form: ( pp-balanced-token-sequenceopt )
2
Semantics The embed parameter with a preprocessing parameter token suffix denotes a balanced preprocessing token sequence within its preprocessor argument clause that will be placed immediately after the result of the associated #embed directive’s expansion.
3
If the resource is empty, then suffix has no effect and is ignored.
4
EXAMPLE 1 Extra elements added to array initializer. #include <string.h> #ifndef SHADER_TARGET #define SHADER_TARGET "edith-impl.glsl" #endif extern char* null_term_shader_data; void fill_in_data () { const char internal_data[] = { #embed SHADER_TARGET \ suffix(,) 0 }; strcpy(null_term_shader_data, internal_data); }
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6.10.3.4 prefix parameter Constraints The prefix standard embed parameter may appear zero times or one time in the embed parameter sequence. Its preprocessor parameter clause shall be present and have the form: ( pp-balanced-token-sequenceopt )
2
Semantics The embed parameter with a preprocessor parameter token prefix denotes a balanced preprocessing token sequence within its preprocessor argument clause that will be placed immediately before the result of the associated #embed directive’s expansion, if any.
3
If the resource is empty, then prefix has no effect and is ignored.
4
EXAMPLE 1 A null-terminated character array with prefixed and suffixed additional tokens when the resource is not empty, providing null termination and a byte order mark. #include <assert.h> #include <string.h> #ifndef SHADER_TARGET #define SHADER_TARGET "ches.glsl"
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#endif extern char* merp; void init_data () { const char whl[] = { #embed SHADER_TARGET \ prefix(0xEF, 0xBB, 0xBF, ) /* UTF-8 BOM */ \ suffix(,) 0 }; // always null terminated, // contains BOM if not-empty int is_good = (sizeof(whl) == 1 && whl[0] == ’\0’) || (whl[0] == ’\xEF’ && whl[1] == ’\xBB’ && whl[2] == ’\xBF’ && whl[sizeof(whl) - 1] == ’\0’); assert(is_good); strcpy(merp, whl); }
1
6.10.3.5 if_empty parameter Constraints The if_empty standard embed parameter may appear zero times or one time in the embed parameter sequence. Its preprocessor argument clause shall be present and have the form: ( pp-balanced-token-sequenceopt )
2
Semantics The embed parameter with a preprocessing parameter token if_empty denotes a balanced preprocessing token sequence within its preprocessor argument clause that will replace the #embed directive entirely. If the resource is not empty, then if_empty has no effect and is ignored.
3
EXAMPLE 1 If the search for the resource is successful, this resource is always considered empty due to the limit(0) embed parameter. This program always returns 0, even if the resource is searched for and found successfully by the implementation and has an implementation resource width greater than 0. int main () { return #embed <some_resource> limit(0) prefix(1) if_empty(0) ; // becomes: // return 0; }
4
EXAMPLE 2 An example similar to using the suffix embed parameter, but changed slightly. #include <string.h> #ifndef SHADER_TARGET #define SHADER_TARGET "edith-impl.glsl" #endif extern char* null_term_shader_data; void fill_in_data () { const char internal_data[] = { #embed SHADER_TARGET \ suffix(, 0) \
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if_empty(0) }; strcpy(null_term_shader_data, internal_data); }
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EXAMPLE 3 This resource is considered empty due to the limit(0) embed parameter, meaning an if_empty expression replaces the directive as specified above. A constraint is still violated if the search for the resource is unsuccessful. int main () { return #embed <infinite-resource> limit(0) if_empty(45540) ; }
becomes: int main () { return 45540; }
6.10.4 1
Macro replacement
Constraints Two replacement lists are identical if and only if the preprocessing tokens in both have the same number, ordering, spelling, and white-space separation, where all white-space separations are considered identical.
2
An identifier currently defined as an object-like macro shall not be redefined by another #define preprocessing directive unless the second definition is an object-like macro definition and the two replacement lists are identical. Likewise, an identifier currently defined as a function-like macro shall not be redefined by another #define preprocessing directive unless the second definition is a function-like macro definition that has the same number and spelling of parameters, and the two replacement lists are identical.
3
There shall be white space between the identifier and the replacement list in the definition of an object-like macro.
4
If the identifier-list in the macro definition does not end with an ellipsis, the number of arguments (including those arguments consisting of no preprocessing tokens) in an invocation of a function-like macro shall equal the number of parameters in the macro definition. Otherwise, there shall be at least as many arguments in the invocation as there are parameters in the macro definition (excluding the ...). There shall exist a ) preprocessing token that terminates the invocation.
5
The identifiers __VA_ARGS__ and __VA_OPT__ shall occur only in the replacement-list of a functionlike macro that uses the ellipsis notation in the parameters.
6
A parameter identifier in a function-like macro shall be uniquely declared within its scope.
7
Semantics The identifier immediately following the define is called the macro name. There is one name space for macro names. Any white-space characters preceding or following the replacement list of preprocessing tokens are not considered part of the replacement list for either form of macro.
8
If a # preprocessing token, followed by an identifier, occurs lexically at the point at which a preprocessing directive could begin, the identifier is not subject to macro replacement.
9
A preprocessing directive of the form # define identifier replacement-list new-line
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defines an object-like macro that causes each subsequent instance of the macro name219) to be replaced by the replacement list of preprocessing tokens that constitute the remainder of the directive. The replacement list is then rescanned for more macro names as specified below. 10
A preprocessing directive of the form # define identifier lparen identifier-listopt ) replacement-list new-line # define identifier lparen ... ) replacement-list new-line # define identifier lparen identifier-list , ... ) replacement-list new-line
defines a function-like macro with parameters, whose use is similar syntactically to a function call. The parameters are specified by the optional list of identifiers, whose scope extends from their declaration in the identifier list until the new-line character that terminates the #define preprocessing directive. Each subsequent instance of the function-like macro name followed by a ( as the next preprocessing token introduces the sequence of preprocessing tokens that is replaced by the replacement list in the definition (an invocation of the macro). The replaced sequence of preprocessing tokens is terminated by the matching ) preprocessing token, skipping intervening matched pairs of left and right parenthesis preprocessing tokens. Within the sequence of preprocessing tokens making up an invocation of a function-like macro, new-line is considered a normal white-space character. 11
The sequence of preprocessing tokens bounded by the outside-most matching parentheses forms the list of arguments for the function-like macro. The individual arguments within the list are separated by comma preprocessing tokens, but comma preprocessing tokens between matching inner parentheses do not separate arguments. If there are sequences of preprocessing tokens within the list of arguments that would otherwise act as preprocessing directives,220) the behavior is undefined.
12
If there is a ... in the identifier-list in the macro definition, then the trailing arguments (if any), including any separating comma preprocessing tokens, are merged to form a single item: the variable arguments. The number of arguments so combined is such that, following merger, the number of arguments is one more than the number of parameters in the macro definition (excluding the ...), except that if there are as many arguments as named parameters, the macro invocation behaves as if a comma token has been appended to the argument list such that variable arguments are formed that contain no pp-tokens.
1
6.10.4.1 Argument substitution Syntax va-opt-replacement: __VA_OPT__ ( pp-tokensopt )
2
3
Description Argument substitution is a process during macro expansion in which identifiers corresponding to the parameters of the macro definition and the special constructs __VA_ARGS__ and __VA_OPT__ are replaced with token sequences from the arguments of the macro invocation and possibly of the argument of the feature __VA_OPT__. The latter process allows to control a substitute token sequence that is only expanded if the argument list that corresponds to a trailing ... of the parameter list is present and has a non-empty substitution. Constraints The identifier __VA_OPT__ shall always occur as part of the preprocessing token sequence va-optreplacement; its closing ) is determined by skipping intervening pairs of matching left and right parentheses in its pp-tokens. The pp-tokens of a va-opt-replacement shall not contain __VA_OPT__. The pp-tokens shall form a valid replacement list for the current function-like macro. 219) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens, not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they are never scanned for macro names or parameters. 220) Despite the name, a non-directive is a preprocessing directive.
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Semantics After the arguments for the invocation of a function-like macro have been identified, argument substitution takes place. A va-opt-replacement is treated as if it were a parameter. For each parameter in the replacement list that is neither preceded by a # or ## preprocessing token nor followed by a ## preprocessing token, the preprocessing tokens naming the parameter are replaced by a token sequence determined as follows: — If the parameter is of the form va-opt-replacement, the replacement preprocessing tokens are the preprocessing token sequence for the corresponding argument, as specified below. — Otherwise, the replacement preprocessing tokens are the preprocessing tokens of the corresponding argument after all macros contained therein have been expanded. The argument’s preprocessing tokens are completely macro replaced before being substituted as if they formed the rest of the preprocessing file with no other preprocessing tokens being available.
5
EXAMPLE 1 #define LPAREN() ( #define G(Q) 42 #define F(R, X, ...) __VA_OPT__(G R X) ) int x = F(LPAREN(), 0, <:-); // replaced by int x = 42;
6
An identifier __VA_ARGS__ that occurs in the replacement list is treated as if it were a parameter, and the variable arguments form the preprocessing tokens used to replace it.
7
The preprocessing token sequence for the corresponding argument of a va-opt-replacement is defined as follows. If a (hypothetical) substitution of __VA_ARGS__ as neither an operand of # nor ## consists of no preprocessing tokens, the argument consists of a single placemarker preprocessing token (6.10.4.3, 6.10.4.4). Otherwise, the argument consists of the results of the expansion of the contained pp-tokens as the replacement list of the current function-like macro before removal of placemarker tokens, rescanning, and further replacement.
8
NOTE 1 The placemarker tokens are removed before stringization (6.10.4.2), and can be removed by rescanning and further replacement (6.10.4.4).
9
EXAMPLE 2 #define F(...) f(0 __VA_OPT__(,) __VA_ARGS__) #define G(X, ...) f(0, X __VA_OPT__(,) __VA_ARGS__) #define SDEF(sname, ...) S sname __VA_OPT__(= { __VA_ARGS__ }) #define EMP F(a, b, c) F() F(EMP)
// replaced by f(0, a, b, c) // replaced by f(0) // replaced by f(0)
G(a, b, c) G(a, ) G(a)
// replaced by f(0, a, b, c) // replaced by f(0, a) // replaced by f(0, a)
SDEF(foo); SDEF(bar, 1, 2);
// replaced by S foo; // replaced by S bar = { 1, 2 };
#define H1(X, ...) X __VA_OPT__(##) __VA_ARGS__ // error: ## on line above // may not appear at the beginning of a replacement // list (6.10.4.3) #define H2(X, Y, ...) __VA_OPT__(X ## Y,) __VA_ARGS__ H2(a, b, c, d)
§ 6.10.4.1
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#define H3(X, ...) #__VA_OPT__(X##X X##X) H3(, 0) // replaced by "" __VA_OPT__(a X ## X) ## b #define H4(X, ...) H4(, 1) // replaced by a b #define H5A(...) #define H5B(X) #define H5C(X) H5C(H5A())
1
2
1
2
3
__VA_OPT__()/**/__VA_OPT__() a ## X ## b H5B(X) // replaced by ab
6.10.4.2 The # operator Constraints Each # preprocessing token in the replacement list for a function-like macro shall be followed by a parameter as the next preprocessing token in the replacement list. Semantics If, in the replacement list, a parameter is immediately preceded by a # preprocessing token, both are replaced by a single character string literal preprocessing token that contains the spelling of the preprocessing token sequence for the corresponding argument (excluding placemarker tokens). Let the stringizing argument be the preprocessing token sequence for the corresponding argument with placemarker tokens removed. Each occurrence of white space between the stringizing argument’s preprocessing tokens becomes a single space character in the character string literal. White space before the first preprocessing token and after the last preprocessing token composing the stringizing argument is deleted. Otherwise, the original spelling of each preprocessing token in the stringizing argument is retained in the character string literal, except for special handling for producing the spelling of string literals and character constants: a \ character is inserted before each " and \ character of a character constant or string literal (including the delimiting " characters), except that it is implementation-defined whether a \ character is inserted before the \ character beginning a universal character name. If the replacement that results is not a valid character string literal, the behavior is undefined. The character string literal corresponding to an empty stringizing argument is "". The order of evaluation of # and ## operators is unspecified. 6.10.4.3 The ## operator Constraints A ## preprocessing token shall not occur at the beginning or at the end of a replacement list for either form of macro definition. Semantics If, in the replacement list of a function-like macro, a parameter is immediately preceded or followed by a ## preprocessing token, the parameter is replaced by the corresponding argument’s preprocessing token sequence; however, if an argument consists of no preprocessing tokens, the parameter is replaced by a placemarker preprocessing token instead.221) For both object-like and function-like macro invocations, before the replacement list is reexamined for more macro names to replace, each instance of a ## preprocessing token in the replacement list (not from an argument) is deleted and the preceding preprocessing token is concatenated with the following preprocessing token. Placemarker preprocessing tokens are handled specially: concatenation of two placemarkers results in a single placemarker preprocessing token, and concatenation of a placemarker with a non-placemarker preprocessing token results in the non-placemarker preprocessing token. If the result is not a valid preprocessing token, the behavior is undefined. The resulting token is available for further macro replacement. The order of evaluation of ## operators is unspecified. 221) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that exist only within translation phase 4.
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EXAMPLE In the following fragment: #define hash_hash # ## # #define mkstr(a) # a #define in_between(a) mkstr(a) #define join(c, d) in_between(c hash_hash d) char p[] = join(x, y); // equivalent to // char p[] = "x ## y";
The expansion produces, at various stages: join(x, y) in_between(x hash_hash y) in_between(x ## y) mkstr(x ## y) "x ## y"
In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but this new token is not the ## operator.
1
6.10.4.4 Rescanning and further replacement After all parameters in the replacement list have been substituted and # and ## processing has taken place, all placemarker preprocessing tokens are removed. The resulting preprocessing token sequence is then rescanned, along with all subsequent preprocessing tokens of the source file, for more macro names to replace.
2
If the name of the macro being replaced is found during this scan of the replacement list (not including the rest of the source file’s preprocessing tokens), it is not replaced. Furthermore, if any nested replacements encounter the name of the macro being replaced, it is not replaced. These nonreplaced macro name preprocessing tokens are no longer available for further replacement even if they are later (re)examined in contexts in which that macro name preprocessing token would otherwise have been replaced.
3
The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one, but all pragma unary operator expressions within it are then processed as specified in 6.10.10 below.
4
EXAMPLE There are cases where it is not clear whether a replacement is nested or not. For example, given the following macro definitions: #define f(a) a*g #define g(a) f(a)
the invocation f(2)(9)
could expand to either 2*f(9)
or 2*9*g
Strictly conforming programs are not permitted to depend on such unspecified behavior. § 6.10.4.4
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6.10.4.5 Scope of macro definitions A macro definition lasts (independent of block structure) until a corresponding #undef directive is encountered or (if none is encountered) until the end of the preprocessing translation unit. Macro definitions have no significance after translation phase 4. A preprocessing directive of the form # undef identifier new-line
causes the specified identifier no longer to be defined as a macro name. It is ignored if the specified identifier is not currently defined as a macro name. 3
EXAMPLE 1 The simplest use of this facility is to define a "manifest constant", as in #define TABSIZE 100 int table[TABSIZE];
4
EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments. It has the advantages of working for any compatible types of the arguments and of generating in-line code without the overhead of function calling. It has the disadvantages of evaluating one or the other of its arguments a second time (including side effects) and generating more code than a function if invoked several times. It also cannot have its address taken, as it has none. #define max(a, b) ((a)
>
(b) ? (a): (b))
The parentheses ensure that the arguments and the resulting expression are bound properly. 5
EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence #define x 3 #define f(a) f(x * (a)) #undef x #define x 2 #define g f #define z z[0] #define h g(\~{ } #define m(a) a(w) #define w 0,1 #define t(a) a #define p() int #define q(x) x #define r(x,y) x ## y #define str(x) # x f(y+1) + f(f(z)) % t(t(g)(0) + t)(1); g(x+(3,4)-w) | h 5) & m (f)^m(m); p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) }; char c[2][6] = { str(hello), str() };
results in f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1); f(2 * (2+(3,4)-0,1)) | f(2 * (\~{ } 5)) & f(2 * (0,1))^m(0,1); int i[] = { 1, 23, 4, 5, }; char c[2][6] = { "hello", "" };
6
EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the sequence 182
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#define str(s) # s #define xstr(s) str(s) #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \ x ## s, x ## t) #define INCFILE(n) vers ## n #define glue(a, b) a ## b #define xglue(a, b) glue(a, b) #define HIGHLOW "hello" #define LOW LOW ", world" debug(1, 2); fputs(str(strncmp("abc\0d", "abc", ’\4’) // this goes away == 0) str(: @\n), s); #include xstr(INCFILE(2).h) glue(HIGH, LOW); xglue(HIGH, LOW)
results in printf("x" "1" "= %d, x" "2" "= %s", x1, x2); fputs( "strncmp(\"abc\\0d\", \"abc\", ’\\4’) == 0" ": @\n", s); #include "vers2.h" (after macro replacement, before file access) "hello"; "hello" ", world"
or, after concatenation of the character string literals, printf("x1= %d, x2= %s", x1, x2); fputs( "strncmp(\"abc\\0d\", \"abc\", ’\\4’) == 0: @\n", s); #include "vers2.h" (after macro replacement, before file access) "hello"; "hello, world"
Space around the # and ## tokens in the macro definition is optional. 7
EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence #define t(x,y,z) x ## y ## z int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,), t(10,,), t(,11,), t(,,12), t(,,) };
results in int j[] = { 123, 45, 67, 89, 10, 11, 12, }; 8
EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid. #define OBJ_LIKE (1-1) #define OBJ_LIKE /* white space */ (1-1) /* other */ #define FUNC_LIKE(a) (a) #define FUNC_LIKE( a ) (a) #define FUNC_LIKE(a)( /* note the white space */ \ a /* other stuff on this line */)
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But the following redefinitions of the preceding definitions are invalid: #define OBJ_LIKE (0) // different token sequence #define OBJ_LIKE (1 - 1) // different white space #define FUNC_LIKE(b) (a) // different parameter usage #define FUNC_LIKE(b) (b) // different parameter spelling 9
EXAMPLE 7 Finally, to show the variable argument list macro facilities: #define debug(...) fprintf(stderr, __VA_ARGS__) #define showlist(...) puts(#__VA_ARGS__) #define report(test, ...) ((test)?puts(#test):\ printf(__VA_ARGS__)) debug("Flag"); debug("X = %d\n", x); showlist(The first, second, and third items.); report(x>y, "x is %d but y is %d", x, y);
results in fprintf(stderr, "Flag"); fprintf(stderr, "X = %d\n", x); puts("The first, second, and third items."); ((x>y)?puts("x>y"): printf("x is %d but y is %d", x, y));
6.10.5 1
2
Line control
Constraints The string literal of a #line directive, if present, shall be a character string literal. Semantics The line number of the current source line is one greater than the number of new-line characters read or introduced in translation phase 1 (5.1.1.2) while processing the source file to the current token.
3
If a preprocessing token (in particular __LINE__) spans two or more physical lines, it is unspecified which of those line numbers is associated with that token. If a preprocessing directive spans two or more physical lines, it is unspecified which of those line numbers is associated with the preprocessing directive. If a macro invocation spans multiple physical lines, it is unspecified which of those line numbers is associated with that invocation. The line number of a preprocessing token is independent of the context (in particular, as a macro argument or in a preprocessing directive). The line number of a __LINE__ in a macro body is the line number of the macro invocation.
4
A preprocessing directive of the form # line digit-sequence new-line
causes the implementation to behave as if the following sequence of source lines begins with a source line that has a line number as specified by the digit sequence (interpreted as a decimal integer, ignoring any optional digit separators (6.4.4.1) in the digit sequence). The digit sequence shall not specify zero, nor a number greater than 2147483647. 5
A preprocessing directive of the form # line digit-sequence " s-char-sequenceopt " new-line
sets the presumed line number similarly and changes the presumed name of the source file to be the contents of the character string literal. 6
A preprocessing directive of the form # line pp-tokens new-line
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line on the directive are processed just as in normal text (each identifier currently defined as a
macro name is replaced by its replacement list of preprocessing tokens). The directive resulting after all replacements shall match one of the two previous forms and is then processed as appropriate.222)
7
Recommended practice The line number associated with a pp-token should be the line number of the first character of the pp-token. The line number associated with a preprocessing directive should be the line number of the line with the first # token. The line number associated with a macro invocation should be the line number of the first character of the macro name in the invocation.
6.10.6 1
Diagnostic directives
Semantics A preprocessing directive of either form # error pp-tokensopt new-line # warning pp-tokensopt new-line
causes the implementation to produce a diagnostic message that includes the specified sequence of preprocessing tokens.
6.10.7 1
Pragma directive
Semantics A preprocessing directive of the form # pragma pp-tokensopt new-line
where the preprocessing token STDC does not immediately follow pragma in the directive (prior to any macro replacement)223) causes the implementation to behave in an implementation-defined manner. The behavior might cause translation to fail or cause the translator or the resulting program to behave in a non-conforming manner. Any such pragma that is not recognized by the implementation is ignored. 2
If the preprocessing token STDC does immediately follow pragma in the directive (prior to any macro replacement), then no macro replacement is performed on the directive, and the directive shall have one of the following forms224) whose meanings are described elsewhere: standard-pragma: # pragma STDC FP_CONTRACT on-off-switch # pragma STDC FENV_ACCESS on-off-switch # pragma STDC FENV_DEC_ROUND dec-direction # pragma STDC FENV_ROUND direction # pragma STDC CX_LIMITED_RANGE on-off-switch
on-off-switch: one of ON
OFF
DEFAULT
direction: one of FE_DOWNWARD FE_TOWARDZERO
FE_TONEAREST FE_UPWARD
FE_TONEARESTFROMZERO FE_DYNAMIC
dec-direction: one of FE_DEC_DOWNWARD
FE_DEC_TONEAREST
FE_DEC_TONEARESTFROMZERO
222) Because a new-line is explicitly included as part of the #line directive, the number of new-line characters read while processing to the first pp-token can be different depending on whether the implementation uses a one-pass preprocessor. Therefore, there are two possible values for the line number following a directive of the form #line __LINE__ new-line. 223) An implementation is not required to perform macro replacement in pragmas, but it is permitted except for in standard pragmas (where STDC immediately follows pragma). If the result of macro replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still implementation-defined; an implementation is permitted to behave as if it were the standard pragma, but is not required to. 224) See "future language directions" (6.11.6).
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the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma Forward references: (7.6.1), the FENV_DEC_ROUND pragma (7.6.3), the FENV_ROUND pragma (7.6.2), the CX_LIMITED_RANGE pragma (7.3.4).
6.10.8 1
Null directive
Semantics A preprocessing directive of the form # new-line
has no effect.
6.10.9
Predefined macro names
1
The values of the predefined macros listed in the following subclauses225) (except for __FILE__ and __LINE__) remain constant throughout the translation unit.
2
None of these macro names nor the identifiers defined, __has_c_attribute, __has_include , or __has_embed shall be the subject of a #define or a #undef preprocessing directive. Any other predefined macro names: shall begin with a leading underscore followed by an uppercase letter; or, a second underscore; or, shall be any of the identifiers alignas, alignof, bool, false, static_assert, thread_local, or true.
3
The implementation shall not predefine the macro __cplusplus, nor shall it define it in any standard header. Forward references: standard headers (7.1.2).
1
6.10.9.1 Mandatory macros The following macro names shall be defined by the implementation: __DATE__ The date of translation of the preprocessing translation unit: a character string literal of the form "Mmm dd yyyy", where the names of the months are the same as those generated by the asctime function, and the first character of dd is a space character if the value is
less than 10. If the date of translation is not available, an implementation-defined valid date shall be supplied. __FILE__ The presumed name of the current source file (a character string literal).226) __LINE__ The presumed line number (within the current source file) of the current source line (an
integer constant).226) __STDC__ The integer constant 1, intended to indicate a conforming implementation. __STDC_EMBED_NOT_FOUND__ , __STDC_EMBED_FOUND__ , __STDC_EMBED_EMPTY__ The integer constants 0, 1, and 2, respectively. __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted implementation or the integer constant 0 if it is not. __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type char16_t are
UTF-16 encoded. __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type char32_t are
UTF-32 encoded. 225) See "future language directions" (6.11.7). 226) The presumed source file name and line number can be changed by the #line directive.
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__STDC_VERSION__ The integer constant 202311L.227) __TIME__ The time of translation of the preprocessing translation unit: a character string literal of the form "hh:mm:ss" as in the time generated by the asctime function. If the time of
translation is not available, an implementation-defined valid time shall be supplied. Forward references: the asctime function (7.29.3.1).
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6.10.9.2 Environment macros The following macro names are conditionally defined by the implementation: __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example, 202012L). If this
symbol is defined, then every character in the Unicode required set, when stored in an object of type wchar_t, has the same value as the short identifier of that character. The Unicode required set consists of all the characters that are defined by ISO/IEC 10646, along with all amendments and technical corrigenda, as of the specified year and month. If some other encoding is used, the macro shall not be defined and the actual encoding used is implementation-defined. __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in the encoding for wchar_t, a member of the basic character set need not have a code value equal to its
value when used as the lone character in an integer character constant. Forward references: common definitions (7.21), Unicode utilities (7.30).
1
6.10.9.3 Conditional feature macros The following macro names are conditionally defined by the implementation: __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to the specifica-
tions in Annex L (Analyzability). __STDC_IEC_60559_BFP__ The integer constant 202311L, intended to indicate conformance to
Annex F (IEC 60559 floating-point arithmetic) for binary floating-point arithmetic. __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the specifications
in Annex F (IEC 60559 floating-point arithmetic) for binary floating-point arithmetic. Use of this macro is an obsolescent feature. __STDC_IEC_60559_DFP__ The integer constant 202311L, intended to indicate support of decimal
floating types and conformance to Annex F (IEC 60559 floating-point arithmetic) for decimal floating-point arithmetic. __STDC_IEC_60559_COMPLEX__ The integer constant 202311L, intended to indicate conformance
to the specifications in Annex G (IEC 60559 compatible complex arithmetic). __STDC_IEC_60559_TYPES__ The integer constant 202311L, intended to indicate conformance to
the specification in Annex H (IEC 60559 interchange and extended types). __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate adherence to the specifi-
cations in Annex G (IEC 60559 compatible complex arithmetic). Use of this macro is an obsolescent feature. __STDC_LIB_EXT1__ The integer constant 202311L, intended to indicate support for the extensions
defined in Annex K (Bounds-checking interfaces). __STDC_NO_ATOMICS__ The integer constant 1, intended to indicate that the implementation does not support atomic types (including the _Atomic type qualifier) and the <stdatomic.h>
header. 227) See Annex M for the values in previous revisions. The intention is that this will remain an integer constant of type
long int that is increased with each revision of this document.
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__STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the implementation does not support complex types or the <complex.h> header. __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the implementation does not support the <threads.h> header. __STDC_NO_VLA__ The integer constant 1, intended to indicate that the implementation does not
support variable length arrays with automatic storage duration. Parameters declared with variable length array types are adjusted and then define objects of automatic storage duration with pointer types. Thus, support for such declarations is mandatory. 2
NOTE 1 The intention for the macros __STDC_LIB_EXT1__, __STDC_IEC_60559_BFP__, __STDC_IEC_60559_DFP__, __STDC_IEC_60559_COMPLEX__, and __STDC_IEC_60559_TYPES__, with the value 202311L, is that this will remain an integer constant of type long int that is increased with each revision of this document.
3
An implementation that defines __STDC_NO_COMPLEX__ shall not define __STDC_IEC_60559_COMPLEX__ or __STDC_IEC_559_COMPLEX__.
6.10.10 1
Pragma operator
Semantics A unary operator expression of the form: _Pragma ( string-literal )
is processed as follows: The string literal is destringized by deleting any encoding prefix, deleting the leading and trailing double-quotes, replacing each escape sequence \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The resulting sequence of characters is processed through translation phase 3 to produce preprocessing tokens that are executed as if they were the pp-tokens in a pragma directive. The original four preprocessing tokens in the unary operator expression are removed. 2
EXAMPLE A directive of the form: #pragma listing on "..\listing.dir"
can also be expressed as: _Pragma ("listing on \"..\\listing.dir\"")
The latter form is processed in the same way whether it appears literally as shown, or results from macro replacement, as in: #define LISTING(x) PRAGMA(listing on #x) #define PRAGMA(x) _Pragma(#x) LISTING (..\listing.dir)
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6.11 Future language directions 6.11.1 Floating types 1
Future standardization may include additional floating types, including those with greater range, precision, or both than long double.
6.11.2 1
6.11.3 1
Storage-class specifiers
The placement of a storage-class specifier other than at the beginning of the declaration specifiers in a declaration is an obsolescent feature.
6.11.6 1
Character escape sequences
Lowercase letters as escape sequences are reserved for future standardization. Other characters may be used in extensions.
6.11.5 1
External names
Restriction of the significance of an external name to fewer than 255 characters (considering each universal character name or extended source character as a single character) is an obsolescent feature that is a concession to existing implementations.
6.11.4 1
Linkages of identifiers
Declaring an identifier with internal linkage at file scope without the static or constexpr storageclass specifier is an obsolescent feature.
Pragma directives
Pragmas whose first preprocessing token is STDC are reserved for future standardization.
6.11.7
Predefined macro names
1
Macro names beginning with __STDC_ are reserved for future standardization.
2
Uses of the __STDC_IEC_559__ and __STDC_IEC_559_COMPLEX__ macros are obsolescent features.
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7. Library 7.1 Introduction 7.1.1 Definitions of terms 1
A string is a contiguous sequence of characters terminated by and including the first null character. The term multibyte string is sometimes used instead to emphasize special processing given to multibyte characters contained in the string or to avoid confusion with a wide string. A pointer to a string is a pointer to its initial (lowest addressed) character. The length of a string is the number of bytes preceding the null character and the value of a string is the sequence of the values of the contained characters, in order.
2
The decimal-point character is the character used by functions that convert floating-point numbers to or from character sequences to denote the beginning of the fractional part of such character sequences.228) It is represented in the text and examples by a period, but may be changed by the setlocale function.
3
A null wide character is a wide character with code value zero.
4
A wide string is a contiguous sequence of wide characters terminated by and including the first null wide character. A pointer to a wide string is a pointer to its initial (lowest addressed) wide character. The length of a wide string is the number of wide characters preceding the null wide character and the value of a wide string is the sequence of code values of the contained wide characters, in order.
5
A shift sequence is a contiguous sequence of bytes within a multibyte string that (potentially) causes a change in shift state (see 5.2.1.1). A shift sequence shall not have a corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte character.229) In this clause, "white-space character" refers to (execution) white-space character as defined by isspace. "White-space wide character" refers to (execution) white-space wide character as defined by iswspace. Forward references: character handling (7.4), the setlocale function (7.11.1.1).
7.1.2
Standard headers
1
Each library function is declared in a header,230) whose contents are made available by the #include preprocessing directive. The header declares a set of related functions, plus any types and additional macros needed to facilitate the use of such related functions. In addition to the provisions given in this clause, an implementation that defines __STDC_IEC_60559_BFP__, __STDC_IEC_559__ , or __STDC_IEC_60559_DFP__ shall conform to the specifications in Annex F, one that defines __STDC_IEC_60559_COMPLEX__ or __STDC_IEC_559_COMPLEX__ shall conform to the specifications in Annex G, one that defines __STDC_IEC_60559_TYPES__ shall conform to the specifications in Annex H and one that defines __STDC_LIB_EXT1__ shall conform to the specifications in Annex K, and those Annexes should be read as if they were merged into the parallel structure of named subclauses of this clause. Declarations of types described here or in Annex K shall not include type qualifiers, unless explicitly stated otherwise.
2
An implementation that does not support decimal floating types (6.10.9.3) need not support interfaces or aspects of interfaces that are specific to these types.
3
The standard headers are231)
228) The functions that make use of the decimal-point character are the numeric conversion functions (7.24.1, 7.31.4.1) and the formatted input/output functions (7.23.6, 7.31.2). 229) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX are thus required to be large enough to count all the bytes in any complete multibyte character plus at least one adjacent shift sequence of maximum length. Whether these counts provide for more than one shift sequence is the implementation’s choice. 230) A header is not necessarily a source file, nor are the < and > delimited sequences in header names necessarily valid source file names. 231) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that implementations need not support; see 6.10.9.3.
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<assert.h> <complex.h> <ctype.h> <errno.h> <fenv.h> <float.h> <inttypes.h> <iso646.h> <limits.h> <locale.h> <math.h>
<setjmp.h> <signal.h> <stdalign.h> <stdarg.h> <stdatomic.h> <stdbit.h> <stdbool.h> <stdckdint.h> <stddef.h> <stdint.h> <stdio.h>
ISO/IEC 9899:2023 (E)
<stdlib.h> <stdnoreturn.h> <string.h> <tgmath.h> <threads.h> <time.h> <uchar.h> <wchar.h> <wctype.h>
4
If a file with the same name as one of the above < and > delimited sequences, not provided as part of the implementation, is placed in any of the standard places that are searched for included source files, the behavior is undefined.
5
Standard headers may be included in any order; each may be included more than once in a given scope, with no effect different from being included only once, except that the effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If used, a header shall be included outside of any external declaration or definition, and it shall first be included before the first reference to any of the functions or objects it declares, or to any of the types or macros it defines. However, if an identifier is declared or defined in more than one header, the second and subsequent associated headers may be included after the initial reference to the identifier. The program shall not have any macros with names lexically identical to keywords currently defined prior to the inclusion of the header or when any macro defined in the header is expanded.
6
Some standard headers define or declare identifiers that had not been present in previous versions of this document. To allow implementations and users to adapt to that situation, they also define a version macro for feature test of the form __STDC_VERSION_XXXX_H__ which expands to 202311L, where XXXX is the all-caps spelling of the corresponding header <xxxx.h>.
7
Any definition of an object-like macro described in this clause or Annex F, Annex G, Annex H, and Annex K shall expand to code that is fully protected by parentheses where necessary, so that it groups in an arbitrary expression as if it were a single identifier.
8
Any declaration of a library function shall have external linkage.
9
A summary of the contents of the standard headers is given in Annex B. Forward references: diagnostics (7.2).
7.1.3 1
Reserved identifiers
Each header declares or defines all identifiers listed in its associated subclause, and optionally declares or defines identifiers listed in its associated future library directions subclause and identifiers which are always reserved either for any use or for use as file scope identifiers. — All potentially reserved identifiers (including ones listed in the future library directions) that are provided by an implementation with an external definition are reserved for any use. An implementation shall not provide an external definition of a potentially reserved identifier unless that identifier is reserved for a use where it would have external linkage.232) All other potentially reserved identifiers that are provided by an implementation (including in the form of a macro) are reserved for any use when the associated header is included. No other potentially reserved identifiers are reserved.233) — Each macro name in any of the following subclauses (including the future library directions) is reserved for use as specified if any of its associated headers is included; unless explicitly stated otherwise (see 7.1.4). 232) All library functions have external linkage. 233) A potentially reserved identifier becomes a reserved identifier when an implementation begins using it or a future standard reserves it, but is otherwise available for use by the programmer.
§ 7.1.3
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— All identifiers with external linkage in any of the following subclauses (including the future library directions) and errno are always reserved for use as identifiers with external linkage234) . — Each identifier with file scope listed in any of the following subclauses (including the future library directions) is reserved for use as a macro name and as an identifier with file scope in the same name space if any of its associated headers is included.
7.1.4 1
Use of library functions
Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow: — If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointer to non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after default argument promotion) not expected by a function with a variable number of arguments, the behavior is undefined. — If a function argument is described as being an array, the pointer passed to the function shall have a value such that all address computations and accesses to objects (that would be valid if the pointer did point to the first element of such an array) are valid.235) — Any function declared in a header may be additionally implemented as a function-like macro defined in the header, so if a library function is declared explicitly when its header is included, one of the techniques shown below can be used to ensure the declaration is not affected by such a macro. Any macro definition of a function can be suppressed locally by enclosing the name of the function in parentheses, because the name is then not followed by the left parenthesis that indicates expansion of a macro function name. For the same syntactic reason, it is permitted to take the address of a library function even if it is also defined as a macro.236) The use of #undef to remove any macro definition will also ensure that an actual function is referred to. — Any invocation of a library function that is implemented as a macro shall expand to code that evaluates each of its arguments exactly once, fully protected by parentheses where necessary, so it is generally safe to use arbitrary expressions as arguments.237) — Likewise, those function-like macros described in the following subclauses may be invoked in an expression anywhere a function with a compatible return type could be called. 238) — All object-like macros listed as expanding to integer constant expressions shall additionally be suitable for use in conditional expression inclusion preprocessing directives. 234) The list of reserved identifiers with external linkage includes math_errhandling, setjmp, va_copy, and va_end. 235) This includes, for example, passing a valid pointer that points one-past-the-end of an array along with a size of 0, or using any valid pointer with a size of 0. 236) This means that an implementation is required to provide an actual function for each library function, even if it also provides a macro for that function. 237) Such macros might not contain the sequence points that the corresponding function calls do. 238) Because external identifiers and some macro names beginning with an underscore are reserved, implementations can provide special semantics for such names. For example, the identifier _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the appropriate header could specify
#define abs(x) _BUILTIN_abs(x) for a compiler whose code generator will accept it. In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine function can write
#undef abs whether the implementation’s header provides a macro implementation of abs or a built-in implementation. The prototype for the function, which precedes and is hidden by any macro definition, is thereby revealed also.
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2
Provided that a library function can be declared without reference to any type defined in a header, it is also permissible to declare the function and use it without including its associated header.
3
There is a sequence point immediately before a library function returns.
4
The functions in the standard library are not guaranteed to be reentrant and may modify objects with static or thread storage duration. 239)
5
Unless explicitly stated otherwise in the detailed descriptions that follow, library functions shall prevent data races as follows: A library function shall not directly or indirectly access objects accessible by threads other than the current thread unless the objects are accessed directly or indirectly via the function’s arguments. A library function shall not directly or indirectly modify objects accessible by threads other than the current thread unless the objects are accessed directly or indirectly via the function’s non-const arguments. 240) Implementations may share their own internal objects between threads if the objects are not visible to users and are protected against data races.
6
Unless otherwise specified, library functions shall perform all operations solely within the current thread if those operations have effects that are visible to users.241)
7
EXAMPLE The function atoi can be used in any of several ways: — by use of its associated header (possibly generating a macro expansion) #include <stdlib.h> const char *str; /* ... */ i = atoi(str);
— by use of its associated header (assuredly generating a true function reference) #include <stdlib.h> #undef atoi const char *str; /* ... */ i = atoi(str);
or #include <stdlib.h> const char *str; /* ... */ i = (atoi)(str);
— by explicit declaration extern int atoi(const char *); const char *str; /* ... */ i = atoi(str);
239) Thus, a signal handler cannot, in general, call standard library functions. 240) This means, for example, that an implementation is not permitted to use a static object for internal purposes without synchronization because it could cause a data race even in programs that do not explicitly share objects between threads. Similarly, an implementation of memcpy is not permitted to copy bytes beyond the specified length of the destination object and then restore the original values because it could cause a data race if the program shared those bytes between threads. 241) This allows implementations to parallelize operations if there are no visible side effects.
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Diagnostics <assert.h>
The header <assert.h> defines the assert and __STDC_VERSION_ASSERT_H__ macros and refers to another macro, NDEBUG
which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the point in the source file where <assert.h> is included, the assert macro is defined simply as #define assert(...) ((void)0)
The assert macro is redefined according to the current state of NDEBUG each time that <assert.h> is included. 2
The assert macro shall be implemented as a macro with an ellipsis parameter, not as an actual function. If the macro definition is suppressed to access an actual function, the behavior is undefined.
3
NOTE 1 Nevertheless, when NDEBUG is not defined, the macro acts as a function taking one parameter as indicated by the given prototype. For both assert() and assert(1, 1), the number of arguments do not agree with the number of parameters. A diagnostic is required by 6.5.2.2.
4
The assert macro shall be implemented as a macro with an ellipsis parameter, not as an actual function. If the macro definition is suppressed to access an actual function, the behavior is undefined.
5
The macro __STDC_VERSION_ASSERT_H__
is an integer constant expression with a value equivalent to 202311L.
7.2.1
Program diagnostics
7.2.1.1 The assert macro Synopsis #include <assert.h> void assert(scalar expression);
1
2
Description The assert macro puts diagnostic tests into programs; it expands to a void expression. When it is executed, if expression (which shall have a scalar type) is false (that is, compares equal to 0), the assert macro writes information about the particular call that failed (including the text of the argument, the name of the source file, the source line number, and the name of the enclosing function — the latter are respectively the values of the preprocessing macros __FILE__ and __LINE__ and of the identifier __func__) on the standard error stream in an implementation-defined format.242) It then calls the abort function.
3
Returns The assert macro returns no value. Forward references: the abort function (7.24.4.1).
242) The message written might be of the form:
Assertion failed:
194
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7.3 Complex arithmetic <complex.h> 7.3.1 Introduction 1
The header <complex.h> defines macros and declares functions that support complex arithmetic.243)
2
Implementations that define the macro __STDC_NO_COMPLEX__ need not provide this header nor support any of its facilities.
3
The macro __STDC_VERSION_COMPLEX_H__
is an integer constant expression with a value equivalent to 202311L. 4
Each synopsis, other than for the CMPLX macros, specifies a family of functions consisting of a principal function with one or more double complex parameters and a double complex or double return value; and other functions with the same name but with f and l suffixes which are corresponding functions with float and long double parameters and return values.
5
The macro complex
expands to _Complex; the macro _Complex_I
expands to a arithmetic constant expression of type float _Complex, with the value of the imaginary unit.244) 6
The macros imaginary
and _Imaginary_I
are defined if and only if the implementation supports imaginary types245) ; and, if defined, they expand to _Imaginary and a arithmetic constant expression of type float _Imaginary with the value of the imaginary unit. 7
The macro I
expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not defined, I shall expand to _Complex_I. 8
Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then redefine the macros complex, imaginary, and I. Forward references: the CMPLX macros (7.3.9.3), IEC 60559-compatible complex arithmetic (Annex G).
7.3.2 1
Conventions
Values are interpreted as radians, not degrees. An implementation may set errno but is not required to do so. 243) See "future library directions" (7.33.1). 244) The imaginary unit is a number i such that i2 = −1. 245) A specification for imaginary types is inAnnex G.
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Branch cuts
1
Some of the functions below have branch cuts, across which the function is discontinuous. For implementations with a signed zero (including all IEC 60559 implementations) that follow the specifications of Annex G, the sign of zero distinguishes one side of a cut from another so that the function is continuous (except for format limitations) as the cut is approached from either side. For example, for the square root function, which has a branch cut along the negative real axis, the top of the cut, with imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with imaginary part -0, maps to the negative imaginary axis.
2
Implementations that do not support a signed zero (see Annex F) cannot distinguish the sides of branch cuts. These implementations shall map a cut so that the function is continuous as the cut is approached coming around the finite endpoint of the cut in a counter clockwise direction. (Branch cuts for the functions specified here have just one finite endpoint.) For example, in the square root function, coming counter clockwise around the finite endpoint of the cut along the negative real axis approaches the cut from above, so that the cut maps to the positive imaginary axis.
7.3.4
The CX_LIMITED_RANGE pragma
Synopsis #include <complex.h> #pragma STDC CX_LIMITED_RANGE on-off-switch
1
2
Description The usual mathematical formulas for complex multiply, divide, and absolute value are problematic because of their treatment of infinities and because of undue overflow and underflow. The CX_LIMITED_RANGE pragma can be used to inform the implementation that (where the state is "on") the usual mathematical formulas are acceptable.246) The pragma can occur either outside external declarations or preceding all explicit declarations and statements inside a compound statement. When outside external declarations, the pragma takes effect from its occurrence until another CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit. When inside a compound statement, the pragma takes effect from its occurrence until another CX_LIMITED_RANGE pragma is encountered (including within a nested compound statement), or until the end of the compound statement; at the end of a compound statement the state for the pragma is restored to its condition just before the compound statement. If this pragma is used in any other context, the behavior is undefined. The default state for the pragma is "off".
7.3.5
Trigonometric functions
7.3.5.1 The cacos functions Synopsis #include <complex.h> double complex cacos(double complex z); float complex cacosf(float complex z); long double complex cacosl(long double complex z);
1
2
Description The cacos functions compute the complex arc cosine of z, with branch cuts outside the interval [−1, +1] along the real axis. 246) The purpose of the pragma is to allow the implementation to use the formulas:
(x + iy) × (u + iv)
=
(xu − yv) + i(yu + xv)
(x + iy) / (u + iv)
=
|x + iy|
=
[(xu + yv) + i(yu − xv)]/(u2 + v 2 ) p x2 + y 2
where the programmer can determine they are safe.
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Returns The cacos functions return the complex arc cosine value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [0, π] along the real axis. 7.3.5.2 The casin functions Synopsis #include <complex.h> double complex casin(double complex z); float complex casinf(float complex z); long double complex casinl(long double complex z);
1
2
Description The casin functions compute the complex arc sine of z, with branch cuts outside the interval [−1, +1] along the real axis.
3
Returns The casin functions return the complex arc sine value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [− π2 , + π2 ] along the real axis. 7.3.5.3 The catan functions Synopsis #include <complex.h> double complex catan(double complex z); float complex catanf(float complex z); long double complex catanl(long double complex z);
1
2
Description The catan functions compute the complex arc tangent of z, with branch cuts outside the interval [−i, +i] along the imaginary axis.
3
Returns The catan functions return the complex arc tangent value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [− π2 , + π2 ] along the real axis. 7.3.5.4 The ccos functions Synopsis #include <complex.h> double complex ccos(double complex z); float complex ccosf(float complex z); long double complex ccosl(long double complex z);
1
2
Description The ccos functions compute the complex cosine of z.
3
Returns The ccos functions return the complex cosine value. 7.3.5.5 The csin functions Synopsis #include <complex.h> double complex csin(double complex z); float complex csinf(float complex z); long double complex csinl(long double complex z);
1
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Description The csin functions compute the complex sine of z.
3
Returns The csin functions return the complex sine value.
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7.3.5.6 The ctan functions Synopsis #include <complex.h> double complex ctan(double complex z); float complex ctanf(float complex z); long double complex ctanl(long double complex z);
1
2
Description The ctan functions compute the complex tangent of z.
3
Returns The ctan functions return the complex tangent value.
7.3.6
Hyperbolic functions
7.3.6.1 The cacosh functions Synopsis #include <complex.h> double complex cacosh(double complex z); float complex cacoshf(float complex z); long double complex cacoshl(long double complex z);
1
2
Description The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch cut at values less than 1 along the real axis.
3
Returns The cacosh functions return the complex arc hyperbolic cosine value, in the range of a half-strip of nonnegative values along the real axis and in the interval [−iπ, +iπ] along the imaginary axis. 7.3.6.2 The casinh functions Synopsis #include <complex.h> double complex casinh(double complex z); float complex casinhf(float complex z); long double complex casinhl(long double complex z);
1
2
Description The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts outside the interval [−i, +i] along the imaginary axis.
3
Returns The casinh functions return the complex arc hyperbolic sine value, in the range of a strip matheiπ matically unbounded along the real axis and in the interval [− iπ 2 , + 2 ] along the imaginary axis. 7.3.6.3 The catanh functions Synopsis #include <complex.h>
1
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double complex catanh(double complex z); float complex catanhf(float complex z); long double complex catanhl(long double complex z);
2
3
Description The catanh functions compute the complex arc hyperbolic tangent of z, with branch cuts outside the interval [−1, +1] along the real axis. Returns The catanh functions return the complex arc hyperbolic tangent value, in the range of a strip iπ mathematically unbounded along the real axis and in the interval [− iπ 2 , + 2 ] along the imaginary axis. 7.3.6.4 The ccosh functions Synopsis #include <complex.h> double complex ccosh(double complex z); float complex ccoshf(float complex z); long double complex ccoshl(long double complex z);
1
2
Description The ccosh functions compute the complex hyperbolic cosine of z.
3
Returns The ccosh functions return the complex hyperbolic cosine value. 7.3.6.5 The csinh functions Synopsis #include <complex.h> double complex csinh(double complex z); float complex csinhf(float complex z); long double complex csinhl(long double complex z);
1
2
Description The csinh functions compute the complex hyperbolic sine of z.
3
Returns The csinh functions return the complex hyperbolic sine value. 7.3.6.6 The ctanh functions Synopsis #include <complex.h> double complex ctanh(double complex z); float complex ctanhf(float complex z); long double complex ctanhl(long double complex z);
1
2
Description The ctanh functions compute the complex hyperbolic tangent of z.
3
Returns The ctanh functions return the complex hyperbolic tangent value.
7.3.7
Exponential and logarithmic functions
7.3.7.1
The cexp functions
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Synopsis #include <complex.h> double complex cexp(double complex z); float complex cexpf(float complex z); long double complex cexpl(long double complex z);
1
2
Description The cexp functions compute the complex base-e exponential of z.
3
Returns The cexp functions return the complex base-e exponential value. 7.3.7.2 The clog functions Synopsis #include <complex.h> double complex clog(double complex z); float complex clogf(float complex z); long double complex clogl(long double complex z);
1
2
Description The clog functions compute the complex natural (base-e) logarithm of z, with a branch cut along the negative real axis.
3
Returns The clog functions return the complex natural logarithm value, in the range of a strip mathematically unbounded along the real axis and in the interval [−iπ, +iπ] along the imaginary axis.
7.3.8
Power and absolute-value functions
7.3.8.1 The cabs functions Synopsis #include <complex.h> double cabs(double complex z); float cabsf(float complex z); long double cabsl(long double complex z);
1
2
3
Description The cabs functions compute the complex absolute value (also called norm, modulus, or magnitude) of z. Returns The cabs functions return the complex absolute value. 7.3.8.2 The cpow functions Synopsis #include <complex.h> double complex cpow(double complex x, double complex y); float complex cpowf(float complex x, float complex y); long double complex cpowl(long double complex x, long double complex y);
1
2
Description The cpow functions compute the complex power function xy , with a branch cut for the first parameter along the negative real axis. 200
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Returns The cpow functions return the complex power function value. 7.3.8.3 The csqrt functions Synopsis #include <complex.h> double complex csqrt(double complex z); float complex csqrtf(float complex z); long double complex csqrtl(long double complex z);
1
2
Description The csqrt functions compute the complex square root of z, with a branch cut along the negative real axis.
3
Returns The csqrt functions return the complex square root value, in the range of the right half-plane (including the imaginary axis).
7.3.9
Manipulation functions
7.3.9.1 The carg functions Synopsis #include <complex.h> double carg(double complex z); float cargf(float complex z); long double cargl(long double complex z);
1
2
3
Description The carg functions compute the argument (also called phase (which is an angle)) of z, with a branch cut along the negative real axis. Returns The carg functions return the value of the argument in the interval [−π, +π]. 7.3.9.2 The cimag functions Synopsis #include <complex.h> double cimag(double complex z); float cimagf(float complex z); long double cimagl(long double complex z);
1
Description 2
The cimag functions compute the imaginary part of z.247)
3
Returns The cimag functions return the imaginary part value (as a real). 7.3.9.3 The CMPLX macros Synopsis #include <complex.h> double complex CMPLX(double x, double y); float complex CMPLXF(float x, float y);
1
247) For a complex variable z, z and CMPLX(creal(z), cimag(z)) are equivalent expressions. If imaginary types are supported, z and creal(z)+ cimag(z)* I are equivalent expressions.
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long double complex CMPLXL(long double x, long double y);
2
Description The CMPLX macros expand to an expression of the specified complex type, with the real part having the (converted) value of x and the imaginary part having the (converted) value of y. The resulting expression shall be suitable for use as an initializer for an object with static or thread storage duration, provided both arguments are likewise suitable. The resulting expression shall be an arithmetic constant expression, provided both arguments are arithmetic constant expressions.
3
Returns The CMPLX macros return the complex value x + iy.
4
NOTE 1 These macros act as if the implementation supported imaginary types and the definitions were:
#define CMPLX(x, y)
((double complex)((double)(x) + \ _Imaginary_I * (double)(y))) #define CMPLXF(x, y) ((float complex)((float)(x) + \ _Imaginary_I * (float)(y))) #define CMPLXL(x, y) ((long double complex)((long double)(x) + \ _Imaginary_I * (long double)(y)))
7.3.9.4 The conj functions Synopsis #include <complex.h> double complex conj(double complex z); float complex conjf(float complex z); long double complex conjl(long double complex z);
1
2
Description The conj functions compute the complex conjugate of z, by negating the sign of its imaginary part.
3
Returns The conj functions return the complex conjugate value. 7.3.9.5 The cproj functions Synopsis #include <complex.h> double complex cproj(double complex z); float complex cprojf(float complex z); long double complex cprojl(long double complex z);
1
2
Description The cproj functions compute a projection of z onto the Riemann sphere where z projects to z except that all complex infinities (even those with one infinite part and one NaN part) project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is equivalent to INFINITY + I * copysign(0.0, cimag(z))
3
Returns The cproj functions return the value of the projection onto the Riemann sphere. 7.3.9.6 The creal functions Synopsis #include <complex.h> double creal(double complex z);
1
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float crealf(float complex z); long double creall(long double complex z);
Description 2
The creal functions compute the real part of z.248)
3
Returns The creal functions return the real part value.
248) For a variable z of complex type, z == creal(z)+cimag(z) I. *
§ 7.3.9.6
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Character handling <ctype.h>
1
The header <ctype.h> declares several functions useful for classifying and mapping characters.249) In all cases the argument is an int, the value of which shall be representable as an unsigned char or shall equal the value of the macro EOF. If the argument has any other value, the behavior is undefined.
2
The behavior of these functions is affected by the current locale. Those functions that have localespecific aspects only when not in the "C" locale are noted below.
3
The term printing character refers to a member of a locale-specific set of characters, each of which occupies one printing position on a display device; the term control character refers to a member of a locale-specific set of characters that are not printing characters.250) All letters and digits are printing characters. Forward references: EOF (7.23.1), localization (7.11).
7.4.1 1
Character classification functions
The functions in this subclause return nonzero (true) if and only if the value of the argument c conforms to that in the description of the function. 7.4.1.1 The isalnum function Synopsis #include <ctype.h> int isalnum(int c);
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Description The isalnum function tests for any character for which isalpha or isdigit is true. 7.4.1.2 The isalpha function Synopsis #include <ctype.h> int isalpha(int c);
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2
Description The isalpha function tests for any character for which isupper or islower is true, or any character that is one of a locale-specific set of alphabetic characters for which none of iscntrl, isdigit, ispunct, or isspace is true.251) In the "C" locale, isalpha returns true only for the characters for which isupper or islower is true. 7.4.1.3 The isblank function Synopsis #include <ctype.h> int isblank(int c);
1
2
Description The isblank function tests for any character that is a standard blank character or is one of a localespecific set of characters for which isspace is true and that is used to separate words within a line of text. The standard blank characters are the following: space (’ ’), and horizontal tab (’\t’). In the "C" locale, isblank returns true only for the standard blank characters. 249) See "future library directions" (7.33.2). 250) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL). 251) The functions islower and isupper test true or false separately for each of these additional characters; all four combinations are possible.
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7.4.1.4 The iscntrl function Synopsis #include <ctype.h> int iscntrl(int c);
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Description The iscntrl function tests for any control character. 7.4.1.5 The isdigit function Synopsis #include <ctype.h> int isdigit(int c);
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Description The isdigit function tests for any decimal-digit character (as defined in 5.2.1). 7.4.1.6 The isgraph function Synopsis #include <ctype.h> int isgraph(int c);
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Description The isgraph function tests for any printing character except space (’ ’). 7.4.1.7 The islower function Synopsis #include <ctype.h> int islower(int c);
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Description The islower function tests for any character that is a lowercase letter or is one of a locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or isspace is true. In the "C" locale, islower returns true only for the lowercase letters (as defined in 5.2.1). 7.4.1.8 The isprint function Synopsis #include <ctype.h> int isprint(int c);
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Description The isprint function tests for any printing character including space (’ ’). 7.4.1.9 The ispunct function Synopsis #include <ctype.h> int ispunct(int c);
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Description The ispunct function tests for any printing character that is one of a locale-specific set of punctuation characters for which neither isspace nor isalnum is true. In the "C" locale, ispunct returns true for every printing character for which neither isspace nor isalnum is true. § 7.4.1.9
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7.4.1.10 The isspace function Synopsis #include <ctype.h> int isspace(int c);
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Description The isspace function tests for any character that is a standard white-space character or is one of a locale-specific set of characters for which isalnum is false. The standard white-space characters are the following: space (’ ’), form feed (’\f’), new-line (’\n’), carriage return (’\r’), horizontal tab (’\t’), and vertical tab (’\v’). In the "C" locale, isspace returns true only for the standard white-space characters. 7.4.1.11 The isupper function Synopsis #include <ctype.h> int isupper(int c);
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Description The isupper function tests for any character that is an uppercase letter or is one of a locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or isspace is true. In the "C" locale, isupper returns true only for the uppercase letters (as defined in 5.2.1). 7.4.1.12 The isxdigit function Synopsis #include <ctype.h> int isxdigit(int c);
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Description The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).
7.4.2
Character case mapping functions
7.4.2.1 The tolower function Synopsis #include <ctype.h> int tolower(int c);
1
2
3
Description The tolower function converts an uppercase letter to a corresponding lowercase letter. Returns If the argument is a character for which isupper is true and there are one or more corresponding characters, as specified by the current locale, for which islower is true, the tolower function returns one of the corresponding characters (always the same one for any given locale); otherwise, the argument is returned unchanged. 7.4.2.2 The toupper function Synopsis #include <ctype.h> int toupper(int c);
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Description The toupper function converts a lowercase letter to a corresponding uppercase letter. 206
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Returns If the argument is a character for which islower is true and there are one or more corresponding characters, as specified by the current locale, for which isupper is true, the toupper function returns one of the corresponding characters (always the same one for any given locale); otherwise, the argument is returned unchanged.
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Errors <errno.h>
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The header <errno.h> defines several macros, all relating to the reporting of error conditions.
2
The macros are EDOM EILSEQ ERANGE
which expand to integer constant expressions with type int, distinct positive values, and which are suitable for use in conditional expression inclusion preprocessing directives; and errno
which expands to a modifiable lvalue252) that has type int and thread storage duration, the value of which is set to a positive error number by several library functions. If a macro definition is suppressed to access an actual object, or a program defines an identifier with the name errno, the behavior is undefined. 3
The value of errno in the initial thread is zero at program startup (the initial representation of the object designated by errno in other threads is indeterminate), but is never set to zero by any library function253) . The value of errno may be set to nonzero by a library function call whether or not there is an error, provided the use of errno is not documented in the description of the function in this document.
4
Additional macro definitions, beginning with E and a digit or E and an uppercase letter,254) may also be specified by the implementation.
252) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue resulting from a function call (for example, (*errno())). 253) Thus, a program that uses errno for error checking would set it to zero before a library function call, then inspect it before a subsequent library function call. Of course, a library function can save the value of errno on entry and then set it to zero, as long as the original value is restored if errno’s value is still zero just before the return. 254) See "future library directions" (7.33.3).
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Floating-point environment <fenv.h>
The header <fenv.h> defines several macros, and declares types and functions that provide access to the floating-point environment. The floating-point environment refers collectively to any floating-point status flags and control modes supported by the implementation.255) A floating-point status flag is a system variable whose value is set (but never cleared) when a floatingpoint exception is raised, which occurs as a side effect of exceptional floating-point arithmetic to provide auxiliary information.256) A floating-point control mode is a system variable whose value may be set by the user to affect the subsequent behavior of floating-point arithmetic.
2
A floating-point control mode may be constant (7.6.2) or dynamic. The dynamic floating-point environment includes the dynamic floating-point control modes and the floating-point status flags.
3
The dynamic floating-point environment has thread storage duration. The initial state for a thread’s dynamic floating-point environment is the current state of the dynamic floating-point environment of the thread that creates it. It is initialized at the time of the thread’s creation.
4
Certain programming conventions support the intended model of use for the dynamic floating-point environment:257) — a function call does not alter its caller’s floating-point control modes, clear its caller’s floatingpoint status flags, nor depend on the state of its caller’s floating-point status flags unless the function is so documented; — a function call is assumed to require default floating-point control modes, unless its documentation promises otherwise; — a function call is assumed to have the potential for raising floating-point exceptions, unless its documentation promises otherwise.
5
The feature test macro __STDC_VERSION_FENV_H__ expands to the token 202311L.
6
The type fenv_t
represents the entire dynamic floating-point environment. 7
The type femode_t
represents the collection of dynamic floating-point control modes supported by the implementation, including the dynamic rounding direction mode. 8
The type fexcept_t
represents the floating-point status flags collectively, including any status the implementation associates with the flags. 9
Each of the macros 255) This header is designed to support the floating-point exception status flags and rounding-direction control modes required by IEC 60559, and other similar floating-point state information. It is also designed to facilitate code portability among all systems. 256) A floating-point status flag is not an object and can be set more than once within an expression. 257) With these conventions, a programmer can safely assume default floating-point control modes (or be unaware of them). The responsibilities associated with accessing the floating-point environment fall on the programmer or program that does so explicitly.
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FE_DIVBYZERO FE_INEXACT FE_INVALID FE_OVERFLOW FE_UNDERFLOW
is defined if and only if the implementation supports the floating-point exception by means of the functions in 7.6.4.258) Additional implementation-defined floating-point exceptions, with macro definitions beginning with FE_ and an uppercase letter,259) may also be specified by the implementation. The defined macros expand to integer constant expressions with values such that bitwise ORs of all combinations of the macros result in distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in zero.260) 10
Decimal floating-point operations and IEC 60559 binary floating-point operations (Annex F) access the same floating-point exception status flags.
11
The macro FE_DFL_MODE
represents the default state for the collection of dynamic floating-point control modes supported by the implementation – and has type "pointer to const-qualified femode_t". Additional implementation-defined states for the dynamic mode collection, with macro definitions beginning with FE_ and an uppercase letter, and having type "pointer to const-qualified femode_t", may also be specified by the implementation. 12
The macro FE_ALL_EXCEPT
is the bitwise OR of all floating-point exception macros defined by the implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0. 13
Each of the macros FE_DOWNWARD FE_TONEAREST FE_TONEARESTFROMZERO FE_TOWARDZERO FE_UPWARD
is defined if and only if the implementation supports getting and setting the represented rounding direction by means of the fegetround and fesetround functions. The defined macros expand to integer constant expressions whose values are distinct nonnegative values. Additional implementation-defined rounding directions, with macro definitions beginning with FE_ and an uppercase letter,261) may also be specified by the implementation.262) 14
If the implementation supports decimal floating types, each of the macros FE_DEC_DOWNWARD FE_DEC_TONEAREST FE_DEC_TONEARESTFROMZERO FE_DEC_TOWARDZERO 258) The implementation supports a floating-point exception if there are circumstances where a call to at least one of the functions in 7.6.4, using the macro as the appropriate argument, will succeed. It is not necessary for all the functions to succeed all the time. 259) See "future library directions" (7.33.4). 260) The macros are typically distinct powers of two. 261) See "future library directions" (7.33.4). 262) Even though the rounding direction macros might expand to constants corresponding to the values of FLT_ROUNDS, they are not required to do so.
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FE_DEC_UPWARD
is defined for use with the fe_dec_getround and fe_dec_setround functions for getting and setting the dynamic rounding direction mode for decimal floating-point operations. The decimal rounding direction affects all (inexact) operations that produce a result of decimal floating type and all operations that produce an integer or character sequence result and have an operand of decimal floating type, unless stated otherwise. The macros expand to integer constant expressions whose values are distinct nonnegative values. 15
During translation, constant rounding direction modes for decimal floating-point arithmetic are in effect where specified. Elsewhere, during translation the decimal rounding direction mode is FE_DEC_TONEAREST.
16
At program startup the dynamic rounding direction mode for decimal floating-point arithmetic is initialized to FE_DEC_TONEAREST.
17
The macro FE_DFL_ENV
represents the default dynamic floating-point environment — the one installed at program startup — and has type "pointer to const-qualified fenv_t". It can be used as an argument to <fenv.h> functions that manage the dynamic floating-point environment. 18
Additional implementation-defined environments, with macro definitions beginning with FE_ and an uppercase letter,263) and having type "pointer to const-qualified fenv_t", may also be specified by the implementation.
7.6.1
The FENV_ACCESS pragma
Synopsis #include <fenv.h> #pragma STDC FENV_ACCESS on-off-switch
1
2
3
Description The FENV_ACCESS pragma provides a means to inform the implementation when a program might access the floating-point environment to test floating-point status flags or run under non-default floating-point control modes.264) The pragma shall occur either outside external declarations or preceding all explicit declarations and statements inside a compound statement. When outside external declarations, the pragma takes effect from its occurrence until another FENV_ACCESS pragma is encountered, or until the end of the translation unit. When inside a compound statement, the pragma takes effect from its occurrence until another FENV_ACCESS pragma is encountered (including within a nested compound statement), or until the end of the compound statement. At the end of a compound statement, the state for the pragma is restored to its condition just before the compound statement. If this pragma is used in any other context, the behavior is undefined. If part of a program tests floating-point status flags or establishes or is executed with non-default floating-point mode settings using any means other than the FENV_ROUND pragmas, but was translated with the state for the FENV_ACCESS pragma "off", the behavior is undefined. The default state ("on" or "off") for the pragma is implementation-defined. (When execution passes from a part of the program translated with FENV_ACCESS "off" to a part translated with FENV_ACCESS "on", the state of the floating-point status flags is unspecified and the floating-point control modes have their default settings.) EXAMPLE #include <fenv.h> 263) See "future library directions" (7.33.4). 264) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag tests and mode changes (e.g., global common subexpression elimination, code motion, and constant folding). In general, if the state of FENV_ACCESS is "off", the translator can assume that the flags are not tested, and that default modes are in effect, except where specified otherwise by an FENV_ROUND pragma.
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void f(double x) { #pragma STDC FENV_ACCESS ON void g(double); void h(double); /* ... */ g(x + 1); h(x + 1); /* ... */ } 4
If the function g might depend on status flags set as a side effect of the first x + 1, or if the second x + 1 might depend on control modes set as a side effect of the call to function g, then the program has to contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON as shown.265)
7.6.2
The FENV_ROUND pragma
Synopsis #include <fenv.h> #pragma STDC FENV_ROUND direction #pragma STDC FENV_ROUND FE_DYNAMIC
1
2
Description The FENV_ROUND pragma provides a means to specify a constant rounding direction for floating-point operations for standard floating types within a translation unit or compound statement. The pragma shall occur either outside external declarations or before all explicit declarations and statements inside a compound statement. When outside external declarations, the pragma takes effect from its occurrence until another FENV_ROUND pragma is encountered, or until the end of the translation unit. When inside a compound statement, the pragma takes effect from its occurrence until another FENV_ROUND pragma is encountered (including within a nested compound statement), or until the end of the compound statement; at the end of a compound statement the static rounding mode is restored to its condition just before the compound statement. If this pragma is used in any other context, its behavior is undefined.
3
direction shall be one of the names of the supported rounding direction macros for operations for standard floating types (7.6), or FE_DYNAMIC. If any other value is specified, the behavior is undefined. If no FENV_ROUND pragma is in effect, or the specified constant rounding mode is FE_DYNAMIC, rounding is according to the mode specified by the dynamic floating-point environment, which is the dynamic rounding mode that was established either at thread creation or by a call to fesetround, fesetmode, fesetenv, or feupdateenv. If the FE_DYNAMIC mode is specified and FENV_ACCESS is "off", the translator may assume that the default rounding mode is in effect.
4
The FENV_ROUND pragma affects operations for standard floating types. Within the scope of an FENV_ROUND pragma establishing a mode other than FE_DYNAMIC, floating-point operators, implicit conversions (including the conversion of a value represented in a format wider than its semantic types to its semantic type, as done by classification macros), and invocations of functions indicated in the table below, for which macro replacement has not been suppressed (7.1.4), shall be evaluated according to the specified constant rounding mode (as though no constant mode was specified and the corresponding dynamic rounding mode had been established by a call to fesetround). Invocations of functions for which macro replacement has been suppressed and invocations of functions other than those indicated in the table below shall not be affected by constant rounding modes – they are affected by (and affect) only the dynamic mode. Floating constants (6.4.4.2) of a standard floating type that occur in the scope of a constant rounding mode shall be interpreted according to that mode.
265) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is "off", just one evaluation of x + 1 would suffice.
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Functions affected by constant rounding modes – for standard floating types Header <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <stdlib.h> <wchar.h> <stdio.h> <wchar.h>
Function families acos, acospi, asin, asinpi, atan, atan2, atan2pi, atanpi cos, cospi, sin, sinpi, tan, tanpi acosh, asinh, atanh cosh, sinh, tanh exp, exp10, exp10m1, exp2, exp2m1, expm1 log, log10, log10p1, log1p, log2, log2p1, logp1 scalbn, scalbln, ldexp cbrt, compoundn, hypot, pow, pown, powr, rootn, rsqrt, sqrt erf, erfc lgamma, tgamma rint, nearbyint, lrint, llrint fdim fma fadd, dadd, fsub, dsub, fmul, dmul, fdiv, ddiv, ffma, dfma, fsqrt, dsqrt atof, strfrom, strto wcsto printf and scanf families wprintf and wscanf families
A function family listed in the table above indicates the functions for all standard floating types, where the function family is represented by the name of the functions without a suffix. For example, acos indicates the functions acos, acosf, and acosl. 5
NOTE 1 Constant rounding modes (other than FE_DYNAMIC) could be implemented using dynamic rounding modes as illustrated in the following example:
{ #pragma STDC FENV_ROUND direction // compiler inserts: // #pragma STDC FENV_ACCESS ON // int __savedrnd; // __savedrnd = __swapround(direction); ... operations affected by constant rounding mode ... // compiler inserts: // __savedrnd = __swapround(__savedrnd); ... operations not affected by constant rounding mode ... // compiler inserts: // __savedrnd = __swapround(__savedrnd); ... operations affected by constant rounding mode ... // compiler inserts: // __swapround(__savedrnd); } where __swapround is defined by:
static inline int __swapround(const int new) { const int old = fegetround(); fesetround(new); return old; }
7.6.3
The FENV_DEC_ROUND pragma
Synopsis #include <fenv.h>
1
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#ifdef __STDC_IEC_60559_DFP__ #pragma STDC FENV_DEC_ROUND dec-direction #endif
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Description The FENV_DEC_ROUND pragma is a decimal floating-point analog of the FENV_ROUND pragma. If FLT_RADIX is not 10, the FENV_DEC_ROUND pragma affects operators, functions, and floating constants only for decimal floating types. The affected functions are listed in the table below. If FLT_RADIX is 10, whether the FENV_ROUND and FENV_DEC_ROUND pragmas alter the rounding direction of both standard and decimal floating-point operations is implementation-defined. dec-direction shall be one of the decimal rounding direction macro names (FE_DEC_DOWNWARD, FE_DEC_TONEAREST , FE_DEC_TONEARESTFROMZERO, FE_DEC_TOWARDZERO, and FE_DEC_UPWARD) defined in 7.6, to specify a constant rounding mode, or FE_DEC_DYNAMIC, to specify dynamic rounding. The corresponding dynamic rounding mode can be established by a call to fe_dec_setround. Functions affected by constant rounding modes – for decimal floating types Header <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <math.h> <stdlib.h> <wchar.h> <stdio.h> <wchar.h>
Function families acos, acospi, asin, asinpi, atan, atan2, atan2pi, atanpi cos, cospi, sin, sinpi, tan, tanpi acosh, asinh, atanh cosh, sinh, tanh exp, exp10, exp10m1, exp2, exp2m1, expm1 log, log10, log10p1, log1p, log2, log2p1, logp1 scalbn, scalbln, ldexp cbrt, compoundn, hypot, pow, pown, powr, rootn, rsqrt, sqrt erf, erfc lgamma, tgamma rint, nearbyint, lrint, llrint quantize fdim fma d32add, d64add, d32sub, d64sub, d32mul, d64mul, d32div, d64div, d32fma, d64fma, d32sqrt, d64sqrt strfrom, strto wcsto printf and scanf families wprintf and wscanf families
A function family listed in the table above indicates the functions for all decimal floating types, where the function family is represented by the name of the functions without a suffix. For example, acos indicates the functions acosd32, acosd64, and acosd128.
7.6.4 1
Floating-point exceptions
The following functions provide access to the floating-point status flags.266) The int input argument for the functions represents a subset of floating-point exceptions, and can be zero or the bitwise OR of one or more floating-point exception macros, for example FE_OVERFLOW | FE_INEXACT. For other argument values, the behavior of these functions is undefined. 7.6.4.1
The feclearexcept function
266) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic abstraction of flags that are either set or clear. An implementation can endow floating-point status flags with more information — for example, the address of the code which first raised the floating-point exception; the functions fegetexceptflag and fesetexceptflag deal with the full content of flags.
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Synopsis #include <fenv.h> int feclearexcept(int excepts);
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Description The feclearexcept function attempts to clear the supported floating-point exceptions represented by its argument.
3
Returns The feclearexcept function returns zero if the excepts argument is zero or if all the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value. 7.6.4.2 The fegetexceptflag function Synopsis #include <fenv.h> int fegetexceptflag(fexcept_t *flagp, int excepts);
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Description The fegetexceptflag function attempts to store an implementation-defined representation of the states of the floating-point status flags indicated by the argument excepts in the object pointed to by the argument flagp. Returns The fegetexceptflag function returns zero if the representation was successfully stored. Otherwise, it returns a nonzero value. 7.6.4.3 The feraiseexcept function Synopsis #include <fenv.h> int feraiseexcept(int excepts);
1
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Description The feraiseexcept function attempts to raise the supported floating-point exceptions represented by its argument. 267) The order in which these floating-point exceptions are raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function additionally raises the "inexact" floating-point exception whenever it raises the "overflow" or "underflow" floating-point exception is implementation-defined. Returns The feraiseexcept function returns zero if the excepts argument is zero or if all the specified exceptions were successfully raised. Otherwise, it returns a nonzero value. Recommended Practice Implementation extensions associated with raising a floating-point exception (for example, enabled traps or IEC 60559 alternate exception handling) should be honored by this function. 7.6.4.4 The fesetexcept function Synopsis #include <fenv.h> int fesetexcept(int excepts);
1
267) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations. Hence, implementation extensions associated with raising a floating-point exception (for example, enabled traps or IEC 60559 alternate exception handling) should be honored. The specification in F.8.6 is in the same spirit.
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Description The fesetexcept function attempts to set the supported floating-point exception flags represented by its argument. This function does not clear any floating-point exception flags. This function changes the state of the floating-point exception flags, but does not cause any other side effects that might be associated with raising floating-point exceptions. 268) Returns The fesetexcept function returns zero if all the specified exceptions were successfully set or if the excepts argument is zero. Otherwise, it returns a nonzero value. 7.6.4.5 The fesetexceptflag function Synopsis #include <fenv.h> int fesetexceptflag(const fexcept_t *flagp, int excepts);
1
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3
Description The fesetexceptflag function attempts to set the floating-point status flags indicated by the argument excepts to the states stored in the object pointed to by flagp. The value of *flagp shall have been set by a previous call to fegetexceptflag whose second argument represented at least those floating-point exceptions represented by the argument excepts. Like fesetexcept, this function does not raise floating-point exceptions, but only sets the state of the flags. Returns The fesetexceptflag function returns zero if the excepts argument is zero or if all the specified flags were successfully set to the appropriate state. Otherwise, it returns a nonzero value. 7.6.4.6 The fetestexceptflag function Synopsis #include <fenv.h> int fetestexceptflag(const fexcept_t * flagp, int excepts);
1
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3
Description The fetestexceptflag function determines which of a specified subset of the floating-point exception flags are set in the object pointed to by flagp. The value of *flagp shall have been set by a previous call to fegetexceptflag whose second argument represented at least those floating-point exceptions represented by the argument excepts. The excepts argument specifies the floating-point status flags to be queried. Returns The fetestexceptflag function returns the value of the bitwise OR of the floating-point exception macros included in excepts corresponding to the floating-point exceptions set in *flagp. 7.6.4.7 The fetestexcept function Synopsis #include <fenv.h> int fetestexcept(int excepts);
1
2
Description The fetestexcept function determines which of a specified subset of the floating-point exception flags are currently set. The excepts argument specifies the floating-point status flags to be queried.269) 268) Implementation extensions like traps for floating-point exceptions and IEC 60559 exception handling do not occur. 269) This mechanism allows testing several floating-point exceptions with just one function call.
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Returns The fetestexcept function returns the value of the bitwise OR of the floating-point exception macros corresponding to the currently set floating-point exceptions included in excepts.
4
EXAMPLE Call f if "invalid" is set, then g if "overflow" is set: #include <fenv.h> /* ... */ { #pragma STDC FENV_ACCESS ON int set_excepts; feclearexcept(FE_INVALID | FE_OVERFLOW); // maybe raise exceptions set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW); if (set_excepts & FE_INVALID) f(); if (set_excepts & FE_OVERFLOW) g(); /* ... */ }
7.6.5 1
Rounding and other control modes
The fegetround and fesetround functions provide control of rounding direction modes. The fegetmode and fesetmode functions manage all the implementation’s dynamic floating-point control modes collectively. 7.6.5.1 The fegetmode function Synopsis #include <fenv.h> int fegetmode(femode_t *modep);
1
2
Description The fegetmode function attempts to store all the dynamic floating-point control modes in the object pointed to by modep.
3
Returns The fegetmode function returns zero if the modes were successfully stored. Otherwise, it returns a nonzero value. 7.6.5.2 The fegetround function Synopsis #include <fenv.h> int fegetround(void);
1
2
3
Description The fegetround function gets the current value of the dynamic rounding direction mode. Returns The fegetround function returns the value of the rounding direction macro representing the current dynamic rounding direction or a negative value if there is no such rounding direction macro or the current dynamic rounding direction is not determinable. 7.6.5.3 The fe_dec_getround function Synopsis #include <fenv.h> #ifdef __STDC_IEC_60559_DFP__ int fe_dec_getround(void);
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2
3
Description The fe_dec_getround function gets the current value of the dynamic rounding direction mode for decimal floating-point operations. Returns The fe_dec_getround function returns the value of the rounding direction macro representing the current dynamic rounding direction for decimal floating-point operations, or a negative value if there is no such rounding macro or the current rounding direction is not determinable. 7.6.5.4 The fesetmode function Synopsis #include <fenv.h> int fesetmode(const femode_t *modep);
1
2
Description The fesetmode function attempts to establish the dynamic floating-point modes represented by the object pointed to by modep. The argument modep shall point to an object set by a call to fegetmode, or equal FE_DFL_MODE or a dynamic floating-point mode state macro defined by the implementation. Returns The fesetmode fesetmode function returns zero if the modes were successfully established. Otherwise, it returns a nonzero value. 7.6.5.5 The fesetround function Synopsis #include <fenv.h> int fesetround(int rnd);
1
2
3
4
Description The fesetround function establishes the rounding direction represented by its argument rnd. If the argument is not equal to the value of a rounding direction macro, the rounding direction is not changed. Returns The fesetround function returns zero if and only if the dynamic rounding direction mode was set to the requested rounding direction. EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the rounding direction fails. #include <fenv.h> #include <assert.h> void f(int rnd_dir) { #pragma STDC FENV_ACCESS ON int save_round; int setround_ok; save_round = fegetround(); setround_ok = fesetround(rnd_dir); assert(setround_ok == 0); /* ... */ fesetround(save_round); /* ... */
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}
7.6.5.6 The fe_dec_setround function Synopsis #include <fenv.h> #ifdef __STDC_IEC_60559_DFP__ int fe_dec_setround(int rnd);
1
#endif
2
3
4
Description The fe_dec_setround function sets the dynamic rounding direction mode for decimal floatingpoint operations to be the rounding direction represented by its argument rnd. If the argument is not equal to the value of a decimal rounding direction macro, the rounding direction is not changed. If FLT_RADIX is not 10, the rounding direction altered by the fesetround function is independent of the rounding direction altered by the fe_dec_setround function; otherwise if FLT_RADIX is 10, whether the fesetround and fe_dec_setround functions alter the rounding direction of both standard and decimal floating-point operations is implementation-defined. Returns The fe_dec_setround function returns a zero value if and only if the argument is equal to a decimal rounding direction macro (that is, if and only if the dynamic rounding direction mode for decimal floating-point operations was set to the requested rounding direction).
7.6.6 1
Environment
The functions in this section manage the floating-point environment — status flags and control modes — as one entity. 7.6.6.1 The fegetenv function Synopsis #include <fenv.h> int fegetenv(fenv_t *envp);
1
2
Description The fegetenv function attempts to store the current dynamic floating-point environment in the object pointed to by envp.
3
Returns The fegetenv function returns zero if the environment was successfully stored. Otherwise, it returns a nonzero value. 7.6.6.2 The feholdexcept function Synopsis #include <fenv.h> int feholdexcept(fenv_t *envp);
1
2
Description The feholdexcept function saves the current dynamic floating-point environment in the object pointed to by envp, clears the floating-point status flags, and then installs a non-stop (continue on floating-point exceptions) mode, if available, for all floating-point exceptions.270) 270) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For such systems, the feholdexcept function can be used in conjunction with the feupdateenv function to write routines that hide spurious floating-point exceptions from their callers.
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Returns The feholdexcept function returns zero if and only if non-stop floating-point exception handling was successfully installed. 7.6.6.3 The fesetenv function Synopsis #include <fenv.h> int fesetenv(const fenv_t *envp);
1
2
3
Description The fesetenv function attempts to establish the dynamic floating-point environment represented by the object pointed to by envp. The argument envp shall point to an object set by a call to fegetenv or feholdexcept, or equal a dynamic floating-point environment macro. Note that fesetenv merely installs the state of the floating-point status flags represented through its argument, and does not raise these floating-point exceptions. Returns The fesetenv function returns zero if the environment was successfully established. Otherwise, it returns a nonzero value. 7.6.6.4 The feupdateenv function Synopsis #include <fenv.h> int feupdateenv(const fenv_t *envp);
1
2
Description The feupdateenv function attempts to save the currently raised floating-point exceptions in its automatic storage, install the dynamic floating-point environment represented by the object pointed to by envp, and then raise the saved floating-point exceptions. The argument envp shall point to an object set by a call to feholdexcept or fegetenv, or equal a dynamic floating-point environment macro.
3
Returns The feupdateenv function returns zero if all the actions were successfully carried out. Otherwise, it returns a nonzero value.
4
EXAMPLE Hide spurious underflow floating-point exceptions: #include <fenv.h> double f(double x) { #pragma STDC FENV_ACCESS ON double result; fenv_t save_env; if (feholdexcept(&save_env)) return /* indication of an environmental problem */; // compute result if (/* test spurious underflow */) if (feclearexcept(FE_UNDERFLOW)) return /* indication of an environmental problem */; if (feupdateenv(&save_env)) return /* indication of an environmental problem */; return result; }
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Characteristics of floating types <float.h>
1
The header <float.h> defines several macros that expand to various limits and parameters of the real floating types.
2
The macro __STDC_VERSION_FLOAT_H__
is an integer constant expression with a value equivalent to 202311L. 3
The rest of the macros, their meanings, and the constraints (or restrictions) on their values are listed in 5.2.4.2.2 and 5.2.4.2.3. A summary is given in Annex E.
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Format conversion of integer types <inttypes.h>
1
The header <inttypes.h> includes the header <stdint.h> and extends it with additional facilities provided by hosted implementations.
2
It declares functions for manipulating greatest-width integers and converting numeric character strings to greatest-width integers, and it declares the type imaxdiv_t
which is a structure type that is the type of the value returned by the imaxdiv function. For each type declared in <stdint.h>, it defines corresponding macros for conversion specifiers for use with the formatted input/output functions.271) Forward references: integer types <stdint.h> (7.22), formatted input/output functions (7.23.6), formatted wide character input/output functions (7.31.2).
7.8.1
Macros for format specifiers
1
Each of the following object-like macros expands to a character string literal containing a conversion specifier, possibly modified by a length modifier, suitable for use within the format argument of a formatted input/output function when converting the corresponding integer type. These macro names have the general form of PRI (character string literals for the fprintf and fwprintf family) or SCN (character string literals for the fscanf and fwscanf family),272) followed by the conversion specifier, followed by a name corresponding to a similar type name in 7.22.1. In these names, N represents the width of the type as described in 7.22.1. For example, PRIdFAST32 can be used in a format string to print the value of an integer of type int_fast32_t.
2
The fprintf macros for signed integers are: PRIdN PRIiN
3
PRIdFASTN PRIiFASTN
PRIdMAX PRIiMAX
PRIdPTR PRIiPTR
The fprintf macros for unsigned integers are: PRIbN PRIoN PRIuN PRIxN PRIXN
4
PRIdLEASTN PRIiLEASTN
PRIbLEASTN PRIoLEASTN PRIuLEASTN PRIxLEASTN PRIXLEASTN
PRIbFASTN PRIoFASTN PRIuFASTN PRIxFASTN PRIXFASTN
PRIbMAX PRIoMAX PRIuMAX PRIxMAX PRIXMAX
PRIbPTR PRIoPTR PRIuPTR PRIxPTR PRIXPTR
The following fprintf macros for unsigned integer types are optional: PRIBN
PRIBLEASTN
PRIBFASTN
PRIBMAX
PRIBPTR
They shall be defined if the implementation supports the B specifier as indicated in 7.23.6.1 and ??; otherwise they shall not be defined. 5
The fscanf macros for signed integers are: SCNbN SCNdN SCNiN
6
SCNbFASTN SCNdFASTN SCNiFASTN
SCNbMAX SCNdMAX SCNiMAX
SCNbPTR SCNdPTR SCNiPTR
The fscanf macros for unsigned integers are: SCNoN SCNuN SCNxN
7
SCNbLEASTN SCNdLEASTN SCNiLEASTN
SCNoLEASTN SCNuLEASTN SCNxLEASTN
SCNoFASTN SCNuFASTN SCNxFASTN
SCNoMAX SCNuMAX SCNxMAX
SCNoPTR SCNuPTR SCNxPTR
For each type that the implementation provides in <stdint.h>, the corresponding fprintf macros shall be defined and the corresponding fscanf macros shall be defined unless the implementation does not have a suitable fscanf length modifier for the type. 271) See "future library directions" (7.33.6). 272) Separate macros are given for use with fprintf and fscanf functions because, in the general case, different format specifiers might be required for fprintf and fscanf, even when the type is the same.
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EXAMPLE #include <inttypes.h> #include <wchar.h> int main(void) { uintmax_t i = UINTMAX_MAX; // this type always exists wprintf(L"The largest integer value is %020" PRIxMAX "\n", i); return 0; }
7.8.2
Functions for greatest-width integer types
7.8.2.1 The imaxabs function Synopsis 1
2
3
#include <inttypes.h> intmax_t imaxabs(intmax_t j);
Description The imaxabs function computes the absolute value of an integer j. If the result cannot be represented, the behavior is undefined.273) Returns The imaxabs function returns the absolute value. 7.8.2.2 The imaxdiv function Synopsis
1
2
3
#include <inttypes.h> imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
Description The imaxdiv function computes numer / denom and numer % denom in a single operation. Returns The imaxdiv function returns a structure of type imaxdiv_t comprising both the quotient and the remainder. The structure shall contain (in either order) the members quot (the quotient) and rem (the remainder), each of which has type intmax_t. If either part of the result cannot be represented, the behavior is undefined. 7.8.2.3 The strtoimax and strtoumax functions Synopsis
1
2
3
#include <inttypes.h> intmax_t strtoimax(const char * restrict nptr, char ** restrict endptr, int base); uintmax_t strtoumax(const char * restrict nptr, char ** restrict endptr, int base);
Description The strtoimax and strtoumax functions are equivalent to the strtol, strtoll, strtoul, and strtoull functions, except that the initial portion of the string is converted to intmax_t and uintmax_t representation, respectively. Returns The strtoimax and strtoumax functions return the converted value, if any. If no conversion could be performed, zero is returned. If the correct value is outside the range of representable values, 273) The absolute value of the most negative number is not representable.
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INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the return type and sign of the value, if any), and the value of the macro ERANGE is stored in errno.
Forward references: the strtol, strtoll, strtoul, and strtoull functions (7.24.1.7). 7.8.2.4 The wcstoimax and wcstoumax functions Synopsis 1
2
3
#include <stddef.h> // for wchar_t #include <inttypes.h> intmax_t wcstoimax(const wchar_t *restrict nptr, wchar_t **restrict endptr, int base); uintmax_t wcstoumax(const wchar_t *restrict nptr, wchar_t **restrict endptr, int base);
Description The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll, wcstoul, and wcstoull functions except that the initial portion of the wide string is converted to intmax_t and uintmax_t representation, respectively. Returns The wcstoimax function returns the converted value, if any. If no conversion could be performed, zero is returned. If the correct value is outside the range of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the return type and sign of the value, if any), and the value of the macro ERANGE is stored in errno. Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions (7.31.4.1.4).
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Alternative spellings <iso646.h>
The header <iso646.h> defines the following eleven macros (on the left) that expand to the corresponding tokens (on the right): and and_eq bitand bitor compl not not_eq or or_eq xor xor_eq
§ 7.9
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Characteristics of integer types <limits.h>
1
The header <limits.h> defines several macros that expand to various limits and parameters of the standard integer types.
2
The macro __STDC_VERSION_LIMITS_H__
is an integer constant expression with a value equivalent to 202311L. 3
The rest of the macros, their meanings, and the constraints (or restrictions) on their values are listed in 5.2.4.2.1. A summary is given in Annex E.
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Localization <locale.h>
1
The header <locale.h> declares two functions, one type, and defines several macros.
2
The type is struct lconv
which contains members related to the formatting of numeric values. The structure shall contain at least the following members, in any order. The semantics of the members and their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have the values specified in the comments. char *decimal_point; char *thousands_sep; char *grouping; char *mon_decimal_point; char *mon_thousands_sep; char *mon_grouping; char *positive_sign; char *negative_sign; char *currency_symbol; char frac_digits; char p_cs_precedes; char n_cs_precedes; char p_sep_by_space; char n_sep_by_space; char p_sign_posn; char n_sign_posn; char *int_curr_symbol; char int_frac_digits; char int_p_cs_precedes; char int_n_cs_precedes; char int_p_sep_by_space; char int_n_sep_by_space; char int_p_sign_posn; char int_n_sign_posn; 3
// "." // "" // "" // "" // "" // "" // "" // "" // "" // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // "" // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX // CHAR_MAX
The macros defined are NULL (described in 7.21); and LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME
which expand to integer constant expressions with distinct values, suitable for use as the first argument to the setlocale function.274) Additional macro definitions, beginning with the characters LC_ and an uppercase letter,275) may also be specified by the implementation.
7.11.1
Locale control
7.11.1.1 The setlocale function Synopsis 1
#include <locale.h> char *setlocale(int category, const char *locale);
274) ISO/IEC 9945 specifies locale and charmap formats that can be used to specify locales for C. 275) See "future library directions" (7.33.7).
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Description The setlocale function selects the appropriate portion of the program’s locale as specified by the category and locale arguments. The setlocale function may be used to change or query the program’s entire current locale or portions thereof. The value LC_ALL for category names the program’s entire locale; the other values for category name only a portion of the program’s locale. LC_COLLATE affects the behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of the character handling functions276) and the multibyte and wide character functions. LC_MONETARY affects the monetary formatting information returned by the localeconv function. LC_NUMERIC affects the decimal-point character for the formatted input/output functions and the string conversion functions, as well as the nonmonetary formatting information returned by the localeconv function. LC_TIME affects the behavior of the strftime and wcsftime functions.
3
A value of "C" for locale specifies the minimal environment for C translation; a value of "" for locale specifies the locale-specific native environment. Other implementation-defined strings may be passed as the second argument to setlocale.
4
At program startup, the equivalent of setlocale(LC_ALL, "C");
is executed. 5
6
A call to the setlocale function may introduce a data race with other calls to the setlocale function or with calls to functions that are affected by the current locale. The implementation shall behave as if no library function calls the setlocale function. Returns If a pointer to a string is given for locale and the selection can be honored, the setlocale function returns a pointer to the string associated with the specified category for the new locale. If the selection cannot be honored, the setlocale function returns a null pointer and the program’s locale is not changed.
7
A null pointer for locale causes the setlocale function to return a pointer to the string associated with the category for the program’s current locale; the program’s locale is not changed.277)
8
The pointer to string returned by the setlocale function is such that a subsequent call with that string value and its associated category will restore that part of the program’s locale. The string pointed to shall not be modified by the program. The behavior is undefined if the returned value is used after a subsequent call to the setlocale function, or after the thread which called the setlocale function to obtain the returned value has exited. Forward references: formatted input/output functions (7.23.6), multibyte/wide character conversion functions (7.24.7), multibyte/wide string conversion functions (7.24.8), numeric conversion functions (7.24.1), the strcoll function (7.26.4.3), the strftime function (7.29.3.5), the strxfrm function (7.26.4.5).
7.11.2
Numeric formatting convention inquiry
7.11.2.1 The localeconv function Synopsis #include <locale.h> struct lconv *localeconv(void);
1
2
Description The localeconv function sets the components of an object with type struct lconv with values appropriate for the formatting of numeric quantities (monetary and otherwise) according to the rules of the current locale. 276) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and isxdigit. 277) The implementation is thus required to arrange to encode in a string the various categories due to a heterogeneous locale
when category has the value LC_ALL.
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The members of the structure with type char * are pointers to strings, any of which (except decimal_point) can point to "", to indicate that the value is not available in the current locale or is of zero length. Apart from grouping and mon_grouping, the strings shall start and end in the initial shift state. The members with type char are nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not available in the current locale. The members include the following: char *decimal_point
The decimal-point character used to format nonmonetary quantities. char *thousands_sep
The character used to separate groups of digits before the decimal-point character in formatted nonmonetary quantities. char *grouping
A string whose elements indicate the size of each group of digits in formatted nonmonetary quantities. char *mon_decimal_point
The decimal-point used to format monetary quantities. char *mon_thousands_sep
The separator for groups of digits before the decimal-point in formatted monetary quantities. char *mon_grouping
A string whose elements indicate the size of each group of digits in formatted monetary quantities. char *positive_sign
The string used to indicate a nonnegative-valued formatted monetary quantity. char *negative_sign
The string used to indicate a negative-valued formatted monetary quantity. char *currency_symbol
The local currency symbol applicable to the current locale. char frac_digits
The number of fractional digits (those after the decimal-point) to be displayed in a locally formatted monetary quantity. char p_cs_precedes
Set to 1 or 0 if the currency_symbol respectively precedes or succeeds the value for a nonnegative locally formatted monetary quantity. char n_cs_precedes
Set to 1 or 0 if the currency_symbol respectively precedes or succeeds the value for a negative locally formatted monetary quantity. char p_sep_by_space
Set to a value indicating the separation of the currency_symbol, the sign string, and the value for a nonnegative locally formatted monetary quantity. char n_sep_by_space
Set to a value indicating the separation of the currency_symbol, the sign string, and the value for a negative locally formatted monetary quantity. char p_sign_posn
Set to a value indicating the positioning of the positive_sign for a nonnegative locally formatted monetary quantity. § 7.11.2.1
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char n_sign_posn
Set to a value indicating the positioning of the negative_sign for a negative locally formatted monetary quantity. char *int_curr_symbol
The international currency symbol applicable to the current locale. The first three characters contain the alphabetic international currency symbol in accordance with those specified in ISO 4217. The fourth character (immediately preceding the null character) is the character used to separate the international currency symbol from the monetary quantity. char int_frac_digits
The number of fractional digits (those after the decimal-point) to be displayed in an internationally formatted monetary quantity. char int_p_cs_precedes
Set to 1 or 0 if the int_curr_symbol respectively precedes or succeeds the value for a nonnegative internationally formatted monetary quantity. char int_n_cs_precedes
Set to 1 or 0 if the int_curr_symbol respectively precedes or succeeds the value for a negative internationally formatted monetary quantity. char int_p_sep_by_space
Set to a value indicating the separation of the int_curr_symbol, the sign string, and the value for a nonnegative internationally formatted monetary quantity. char int_n_sep_by_space
Set to a value indicating the separation of the int_curr_symbol, the sign string, and the value for a negative internationally formatted monetary quantity. char int_p_sign_posn
Set to a value indicating the positioning of the positive_sign for a nonnegative internationally formatted monetary quantity. char int_n_sign_posn
Set to a value indicating the positioning of the negative_sign for a negative internationally formatted monetary quantity. 4
5
The elements of grouping and mon_grouping are interpreted according to the following: CHAR_MAX
No further grouping is to be performed.
0
The previous element is to be repeatedly used for the remainder of the digits.
other
The integer value is the number of digits that compose the current group. The next element is examined to determine the size of the next group of digits before the current group.
values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space, _ _ _ _ int n sep by space are interpreted according to the following: The
and
0
No space separates the currency symbol and value.
1
If the currency symbol and sign string are adjacent, a space separates them from the value; otherwise, a space separates the currency symbol from the value.
2
If the currency symbol and sign string are adjacent, a space separates them; otherwise, a space separates the sign string from the value.
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For int_p_sep_by_space and int_n_sep_by_space, the fourth character of int_curr_symbol is used instead of a space. 6
7
8
9
The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and int_n_sign_posn are interpreted according to the following: 0
Parentheses surround the quantity and currency symbol.
1
The sign string precedes the quantity and currency symbol.
2
The sign string succeeds the quantity and currency symbol.
3
The sign string immediately precedes the currency symbol.
4
The sign string immediately succeeds the currency symbol.
The implementation shall behave as if no library function calls the localeconv function. Returns The localeconv function returns a pointer to the filled-in object. The structure pointed to by the return value shall not be modified by the program, but may be overwritten by a subsequent call to the localeconv function. In addition, calls to the setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may overwrite the contents of the structure. EXAMPLE 1 The following table illustrates rules which might have been used by four countries to format monetary quantities. Country Country1 Country2 Country3 Country4
10
Positive
Local format Negative
1.234,56 mk L.1.234 ƒ 1.234,56 SFrs.1,234.56
-1.234,56 mk -L.1.234 ƒ -1.234,56 SFrs.1,234.56C
International format Positive Negative FIM 1.234,56 ITL 1.234 NLG 1.234,56 CHF 1,234.56
FIM -1.234,56 -ITL 1.234 NLG -1.234,56 CHF 1,234.56C
For these four countries, the respective values for the monetary members of the structure returned by localeconv could be: mon_decimal_point mon_thousands_sep mon_grouping positive_sign negative_sign currency_symbol frac_digits p_cs_precedes n_cs_precedes p_sep_by_space n_sep_by_space p_sign_posn n_sign_posn int_curr_symbol int_frac_digits int_p_cs_precedes int_n_cs_precedes int_p_sep_by_space int_n_sep_by_space int_p_sign_posn int_n_sign_posn
§ 7.11.2.1
Country1
Country2
Country3
Country4
"," "." "\3" "" "-" "mk" 2 0 0 1 1 1 1 "FIM " 2 1 1 1 2 1 4
"" "." "\3" "" "-" "L." 0 1 1 0 0 1 1 "ITL " 0 1 1 1 1 1 1
"," "." "\3" "" "-" "\u0192" 2 1 1 1 2 1 4 "NLG " 2 1 1 1 2 1 4
"." "," "\3" "" "C" "SFrs." 2 1 1 0 0 1 2 "CHF " 2 1 1 1 1 1 2
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EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members affect the formatted value. p_cs_precedes
p_sign_posn
0
0 1 2 3 4 0 1 2 3 4
1
232
0
p_sep_by_space 1 2
(1.25$) +1.25$ 1.25$+ 1.25+$ 1.25$+ ($1.25) +$1.25 $1.25+ +$1.25 $+1.25
(1.25 $) +1.25 $ 1.25 $+ 1.25 +$ 1.25 $+ ($ 1.25) +$ 1.25 $ 1.25+ +$ 1.25 $+ 1.25
Library
(1.25$) + 1.25$ 1.25$ + 1.25+ $ 1.25$ + ($1.25) + $1.25 $1.25 + + $1.25 $ +1.25
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Mathematics <math.h>
1
The header <math.h> declares two types and many mathematical functions and defines several macros. Most synopses specify a family of functions consisting of a principal function with one or more double parameters, a double return value, or both; and other functions with the same name but with f and l suffixes, which are corresponding functions with float and long double parameters, return values, or both.278) Integer arithmetic functions and conversion functions are discussed later.
2
The feature test macro __STDC_VERSION_MATH_H__ expands to the token 202311L.
3
The types float_t double_t
are floating types at least as wide as float and double, respectively, and such that double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0, float_t and double_t are float and double, respectively; if FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are otherwise implementation-defined.279) 4
The types _Decimal32_t _Decimal64_t
are decimal floating types at least as wide as _Decimal32 and _Decimal64, respectively, and such that _Decimal64_t is at least as wide as _Decimal32_t. They are present only if the implementation defines __STDC_IEC_60559_DFP__ and additionally the user code defines __STDC_WANT_IEC_60559_EXT__ before any inclusion of <math.h>. If DEC_EVAL_METHOD _ _ _ _ _ _ equals 0, Decimal32 t and Decimal64 t are Decimal32 and Decimal64, respectively; if DEC_EVAL_METHOD equals 1, they are both _Decimal64; if DEC_EVAL_METHOD equals 2, they are both _Decimal128; and for other values of DEC_EVAL_METHOD, they are otherwise implementationdefined. 5
The macro HUGE_VAL
expands to a double arithmetic constant expression, not necessarily representable as a float, whose value is the maximum value returned by library functions when a floating result of type double overflows under the default rounding mode, either maximum finite number in the type or positive or unsigned infinity. The macros HUGE_VALF HUGE_VALL
are respectively float and long double analogs of HUGE_VAL280) . 6
The macros in this paragraph are only present if the implementation defines __STDC_IEC_60559_DFP__ and additionally the user code defines __STDC_WANT_IEC_60559_EXT__ before any inclusion of <math.h>. The macro HUGE_VAL_D32 278) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments and return values in wider format than the synopsis prototype indicates. 279) The types float_t and double_t are intended to be the implementation’s most efficient types at least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the type float_t is the narrowest type used by the implementation to evaluate floating expressions. 280) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that supports infinities.
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expands to a arithmetic constant expression of type _Decimal32 representing positive infinity. The macros HUGE_VAL_D64 HUGE_VAL_D128
are respectively _Decimal64 and _Decimal128 analogs of HUGE_VAL_D32. 7
The macro INFINITY
is defined if and only if the implementation supports an infinity for the type float. It expands to a arithmetic constant expression of type float representing positive or unsigned infinity. 8
The macro DEC_INFINITY
expands to a arithmetic constant expression of type _Decimal32 representing positive infinity. 9
The macro NAN
is defined if and only if the implementation supports quiet NaNs for the float type. It expands to a arithmetic constant expression of type float representing a quiet NaN. 10
The macro DEC_NAN
expands to a arithmetic constant expression of type _Decimal32 representing a quiet NaN. 11
Use of the macros INFINITY, DEC_INFINITY, NAN, and DEC_NAN in <math.h> is an obsolescent feature. Instead, use the same macros in <float.h>.
12
The number classification macros FP_INFINITE FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO
represent mutually exclusive kinds of floating-point values. They expand to integer constant expressions with distinct values. Additional implementation-defined floating-point classifications, with macro definitions beginning with FP_ and an uppercase letter, may also be specified by the implementation. 13
The math rounding direction macros FP_INT_UPWARD FP_INT_DOWNWARD FP_INT_TOWARDZERO FP_INT_TONEARESTFROMZERO FP_INT_TONEAREST
represent the rounding directions of the functions ceil, floor, trunc, round, and roundeven, respectively, that convert to integral values in floating-point formats. They expand to integer constant expressions with distinct values suitable for use as the second argument to the fromfp, ufromfp, fromfpx, and ufromfpx functions. 234
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The macro FP_FAST_FMA
is optionally defined. If defined, it indicates that the fma function generally executes about as fast as, or faster than, a multiply and an add of double operands.281) The macros FP_FAST_FMAF FP_FAST_FMAL
are, respectively, float and long double analogs of FP_FAST_FMA. If defined, these macros expand to the integer constant 1. 15
The macros FP_FAST_FMAD32 FP_FAST_FMAD64 FP_FAST_FMAD128
are, respectively, _Decimal32, _Decimal64, and _Decimal128 analogs of FP_FAST_FMA. 16
Each of the macros FP_FAST_FADD FP_FAST_FADDL FP_FAST_DADDL FP_FAST_FSUB FP_FAST_FSUBL
FP_FAST_DSUBL FP_FAST_FMUL FP_FAST_FMULL FP_FAST_DMULL FP_FAST_FDIV
FP_FAST_FDIVL FP_FAST_DDIVL FP_FAST_FSQRT FP_FAST_FSQRTL FP_FAST_DSQRTL
FP_FAST_FFMA FP_FAST_FFMAL FP_FAST_DFMAL
is optionally defined. If defined, it indicates that the corresponding function generally executes about as fast, or faster, than the corresponding operation or function of the argument type with result type the same as the argument type followed by conversion to the narrower type. For FP_FAST_FFMA, FP_FAST_FFMAL, and FP_FAST_DFMAL, the comparison is to a call to fma or fmal followed by a conversion, not to separate multiply, add, and conversion. If defined, these macros expand to the integer constant 1. 17
The macros FP_FAST_D32ADDD64 FP_FAST_D32ADDD128 FP_FAST_D64ADDD128 FP_FAST_D32SUBD64 FP_FAST_D32SUBD128 FP_FAST_D64SUBD128
FP_FAST_D32MULD64 FP_FAST_D32MULD128 FP_FAST_D64MULD128 FP_FAST_D32DIVD64 FP_FAST_D32DIVD128 FP_FAST_D64DIVD128
FP_FAST_D32FMAD64 FP_FAST_D32FMAD128 FP_FAST_D64FMAD128 FP_FAST_D32SQRTD64 FP_FAST_D32SQRTD128 FP_FAST_D64SQRTD128
are analogs of FP_FAST_FADD, FP_FAST_FADDL, FP_FAST_DADDL, etc., for decimal floating types. 18
The macros FP_ILOGB0 FP_ILOGBNAN
expand to integer constant expressions whose values are returned by ilogb(x) if x is zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN. 19
The macros 281) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented directly with a hardware multiply-add instruction. Software implementations are expected to be substantially slower.
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FP_LLOGB0 FP_LLOGBNAN
expand to integer constant expressions whose values are returned by llogb(x) if x is zero or NaN, respectively. The value of FP_LLOGB0 shall be LONG_MIN if the value of FP_ILOGB0 is INT_MIN, and shall be -LONG_MAX if the value of FP_ILOGB0 is -INT_MAX. The value of FP_LLOGBNAN shall be LONG_MAX if the value of FP_ILOGBNAN is INT_MAX, and shall be LONG_MIN if the value of FP_ILOGBNAN is INT_MIN. 20
The macros MATH_ERRNO MATH_ERREXCEPT
expand to the integer constants 1 and 2, respectively; the macro math_errhandling
expands to an expression that has type int and the value MATH_ERRNO, MATH_ERREXCEPT, the bitwise OR of both, or 0; the value shall not be 0 in a hosted implementation. The value of math_errhandling is constant for the duration of the program. It is unspecified whether math_errhandling is a macro or an identifier with external linkage. If a macro definition is suppressed or a program defines an identifier with the name math_errhandling, the behavior is undefined. If the expression math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in <fenv.h>.
7.12.1
Treatment of error conditions
1
The behavior of each of the functions in <math.h> is specified for all representable values of its input arguments, except where explicitly stated otherwise. Each function shall execute as if it were a single operation without raising SIGFPE and without generating any of the floating-point exceptions "invalid", "divide-by-zero", or "overflow" except to reflect the result of the function.
2
For all functions, a domain error occurs if and only if an input argument is outside the domain over which the mathematical function is defined. The description of each function lists any required domain errors; an implementation may define additional domain errors, provided that such errors are consistent with the mathematical definition of the function.282) Whether a signaling NaN input causes a domain error is implementation-defined. On a domain error, the function returns an implementation-defined value; if the integer expression math_errhandling & MATH_ERRNO is nonzero, the integer expression errno acquires the value EDOM; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the "invalid" floating-point exception is raised.
3
Similarly, a pole error (also known as a singularity or infinitary) occurs if and only if the mathematical function has an exact infinite result as the finite input argument(s) are approached in the limit (for example, log(0.0)). The description of each function lists any required pole errors; an implementation may define additional pole errors, provided that such errors are consistent with the mathematical definition of the function. On a pole error, the function returns an implementation-defined value; if the integer expression math_errhandling & MATH_ERRNO is nonzero, the integer expression errno acquires the value ERANGE; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the "divide-by-zero" floating-point exception is raised.
4
Likewise, a range error occurs if and only if the result overflows or underflows, as defined below. The description of each function lists any required range errors; an implementation may define additional range errors, provided that such errors are consistent with the mathematical definition of the function and are the result of either overflow or underflow.283) 282) In an implementation that supports infinities, this allows an infinity as an argument to be a domain error if the
mathematical domain of the function does not include the infinity. 283) Range errors that are required or implementation-defined shall or may be reported, as specified in this subclause.
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A floating result overflows if a finite result value with ordinary accuracy284) would have magnitude (absolute value) too large for the representation with full precision in the specified type. A result that is exactly an infinity does not overflow. If a floating result overflows and default rounding is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or HUGE_VALL according to the return type, with the same sign as the correct value of the function; however, for the types with reduced-precision representations of numbers beyond the overflow threshold, the function may return a representation of the result with less than full precision for the type. If a floating result overflows, default rounding is in effect and the integer expression math_errhandling & MATH_ERRNO is nonzero, the integer expression errno acquires the value ERANGE. If a floating result overflows, and the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the "overflow" floating-point exception is raised (regardless of whether default rounding is in effect).
6
The result underflows if a nonzero result value with ordinary accuracy would have magnitude (absolute value) less than the minimum normalized number in the type; however a zero result that is specified to be an exact zero does not underflow. Also, a result with ordinary accuracy and the magnitude of the minimum normalized number may underflow285) . If the result underflows, the function returns an implementation-defined value whose magnitude is no greater than the smallest normalized positive number in the specified type; if the integer expression math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the value ERANGE is implementation-defined; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point exception is raised is implementation-defined.
7
If a domain, pole, or range error occurs and the integer expression math_errhandling & MATH_ERRNO is zero,286) then errno shall either be set to the value corresponding to the error or left unmodified. If no such error occurs, errno shall be left unmodified regardless of the setting of math_errhandling.
The FP_CONTRACT pragma
7.12.2 Synopsis
#include <math.h> #pragma STDC FP_CONTRACT on-off-switch
1
2
Description The FP_CONTRACT pragma can be used to allow (if the state is "on") or disallow (if the state is "off") the implementation to contract expressions (6.5). Each pragma can occur either outside external declarations or preceding all explicit declarations and statements inside a compound statement. When outside external declarations, the pragma takes effect from its occurrence until another FP_CONTRACT pragma is encountered, or until the end of the translation unit. When inside a compound statement, the pragma takes effect from its occurrence until another FP_CONTRACT pragma is encountered (including within a nested compound statement), or until the end of the compound statement; at the end of a compound statement the state for the pragma is restored to its condition just before the compound statement. If this pragma is used in any other context, the behavior is undefined. The default state ("on" or "off") for the pragma is implementation-defined.
7.12.3 1
Classification macros
Floating-point values can be classified as NaN, infinite, normal, subnormal, or zero, or into other implementation-defined categories. Numbers whose magnitude is at least bemin −1 (the minimum magnitude of normalized floating-point numbers in the type) and at most (1 − b−p )bemax (the maximum magnitude of normalized floating-point numbers in the type), where b, p, emin , and emax are as in 5.2.4.2.2, are classified as normal. Larger magnitude finite numbers represented with full precision in the type may also be classified as normal. Nonzero numbers whose magnitude is less than bemin −1 are classified as subnormal. 284) Ordinary accuracy is determined by the implementation. It refers to the accuracy of the function where results are not compromised by extreme magnitude. 285) The term underflow here is intended to encompass both "gradual underflow" as in IEC 60559 and also "flush-to-zero" underflow. IEC 60559 underflow can occur in cases where the magnitude of the rounded result (accurate to the full precision of the type) equals the minimum normalized number in the format. 286) Math errors are being indicated by the floating-point exception flags rather than by errno.
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In the synopses in this subclause, real-floating indicates that the argument shall be an expression of real floating type. 7.12.3.1 The fpclassify macro Synopsis #include <math.h> int fpclassify(real-floating x);
1
2
3
Description The fpclassify macro classifies its argument value as NaN, infinite, normal, subnormal, zero, or into another implementation-defined category. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then classification is based on the type of the argument.287) Returns The fpclassify macro returns the value of the number classification macro appropriate to the value of its argument. 7.12.3.2 The iscanonical macro Synopsis #include <math.h> int iscanonical(real-floating x);
1
2
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Description The iscanonical macro determines whether its argument value is canonical (5.2.4.2.2). First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then, determination is based on the type of the argument. Returns The iscanonical macro returns a nonzero value if and only if its argument is canonical. 7.12.3.3 The isfinite macro Synopsis #include <math.h> int isfinite(real-floating x);
1
2
3
Description The isfinite macro determines whether its argument has a finite value (zero, subnormal, or normal, and not infinite or NaN). First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument. Returns The isfinite macro returns a nonzero value if and only if its argument has a finite value. 7.12.3.4 The isinf macro Synopsis #include <math.h> int isinf(real-floating x);
1
287) Since an expression can be evaluated with more range and precision than its type has, it is important to know the type that classification is based on. For example, a normal long double value might become subnormal when converted to double, and zero when converted to float.
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Description The isinf macro determines whether its argument value is (positive or negative) infinity. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument. Returns The isinf macro returns a nonzero value if and only if its argument has an infinite value. 7.12.3.5 The isnan macro Synopsis #include <math.h> int isnan(real-floating x);
1
2
3
Description The isnan macro determines whether its argument value is a NaN. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument.288) Returns The isnan macro returns a nonzero value if and only if its argument has a NaN value. 7.12.3.6 The isnormal macro Synopsis #include <math.h> int isnormal(real-floating x);
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Description The isnormal macro determines whether its argument value is normal (neither zero, subnormal, infinite, nor NaN). First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument. Returns The isnormal macro returns a nonzero value if and only if its argument has a normal value. 7.12.3.7 The signbit macro Synopsis #include <math.h> int signbit(real-floating x);
1
Description 2
3
The signbit macro determines whether the sign of its argument value is negative289) . If the argument value is an unsigned zero, its sign is regarded as positive. Otherwise, if the argument value is unsigned, the result value (zero or nonzero) is implementation-defined. Returns The signbit macro returns a nonzero value if and only if the sign of its argument value is determined to be negative. 7.12.3.8
The issignaling macro
288) For the isnan macro, the type for determination does not matter unless the implementation supports NaNs in the
evaluation type but not in the semantic type. 289) The signbit macro determines the sign of all values, including infinities, zeros, and NaNs.
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Synopsis #include <math.h> int issignaling(real-floating x);
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Description The issignaling macro determines whether its argument value is a signaling NaN. Returns
3
The issignaling macro returns a nonzero value if and only if its argument is a signaling NaN.290) 7.12.3.9 The issubnormal macro Synopsis #include <math.h> int issubnormal(real-floating x);
1
2
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Description The issubnormal macro determines whether its argument value is subnormal. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument. Returns The issubnormal macro returns a nonzero value if and only if its argument is subnormal. 7.12.3.10 The iszero macro Synopsis #include <math.h> int iszero(real-floating x);
1
2
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Description The iszero macro determines whether its argument value is (positive, negative, or unsigned) zero. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then, determination is based on the type of the argument. Returns The iszero macro returns a nonzero value if and only if its argument is zero.
7.12.4
Trigonometric functions
7.12.4.1 The acos functions Synopsis #include <math.h> double acos(double x); float acosf(float x); long double acosl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 acosd32(_Decimal32 x); _Decimal64 acosd64(_Decimal64 x); _Decimal128 acosd128(_Decimal128 x); #endif
1
290) F.3 specifies that issignaling (and all the other classification macros), raise no floating-point exception if the argument is a variable, or any other expression whose value is represented in the format of its semantic type, even if the value is a signaling NaN.
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Description The acos functions compute the principal value of the arc cosine of x. A domain error occurs for arguments not in the interval [−1, +1]. Returns The acos functions return arccos x in the interval [0, π] radians. 7.12.4.2 The asin functions Synopsis
1
2
3
#include <math.h> double asin(double x); float asinf(float x); long double asinl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 asind32(_Decimal32 x); _Decimal64 asind64(_Decimal64 x); _Decimal128 asind128(_Decimal128 x); #endif
Description The asin functions compute the principal value of the arc sine of x. A domain error occurs for arguments not in the interval [−1, +1]. A range error occurs if nonzero x is too close to zero. Returns The asin functions return arcsin x in the interval [− π2 , + π2 ] radians. 7.12.4.3 The atan functions Synopsis
1
#include <math.h> double atan(double x); float atanf(float x); long double atanl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 atand32(_Decimal32 x); _Decimal64 atand64(_Decimal64 x); _Decimal128 atand128(_Decimal128 x); #endif
2
3
Description The atan functions compute the principal value of the arc tangent of x. A range error occurs if nonzero x is too close to zero. Returns The atan functions return arctan x in the interval [− π2 , + π2 ] radians. 7.12.4.4 The atan2 functions Synopsis
1
#include <math.h> double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 atan2d32(_Decimal32 y, _Decimal32 x); _Decimal64 atan2d64(_Decimal64 y, _Decimal64 x); _Decimal128 atan2d128(_Decimal128 y, _Decimal128 x); #endif
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Description The atan2 functions compute the value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value. A domain error may occur if both arguments are zero. A range error occurs if x is positive and nonzero xy is too close to zero. Returns The atan2 functions return arctan(y/x) in the interval [−π, +π] radians. 7.12.4.5 The cos functions Synopsis #include <math.h> double cos(double x); float cosf(float x); long double cosl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 cosd32(_Decimal32 x); _Decimal64 cosd64(_Decimal64 x); _Decimal128 cosd128(_Decimal128 x); #endif
1
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Description The cos functions compute the cosine of x (measured in radians).
3
Returns The cos functions return cos x. 7.12.4.6 The sin functions Synopsis #include <math.h> double sin(double x); float sinf(float x); long double sinl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 sind32(_Decimal32 x); _Decimal64 sind64(_Decimal64 x); _Decimal128 sind128(_Decimal128 x);
1
#endif
2
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Description The sin functions compute the sine of x (measured in radians). A range error occurs if nonzero x is too close to zero. Returns The sin functions return sin x. 7.12.4.7 The tan functions Synopsis #include <math.h> double tan(double x); float tanf(float x); long double tanl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 tand32(_Decimal32 x); _Decimal64 tand64(_Decimal64 x); _Decimal128 tand128(_Decimal128 x);
1
#endif
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Description The tan functions return the tangent of x (measured in radians). A range error occurs if nonzero x is too close to zero. Returns The tan functions return tan x. 7.12.4.8 The acospi functions Synopsis #include <math.h> double acospi(double x); float acospif(float x); long double acospil(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 acospid32(_Decimal32 x); _Decimal64 acospid64(_Decimal64 x); _Decimal128 acospid128(_Decimal128 x); #endif
1
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Description The acospi functions compute the principal value of the arc cosine of x, divided by π, thus measuring the angle in half-revolutions. A domain error occurs for arguments not in the interval [−1, +1]. Returns The acospi functions return arccos(x)/π in the interval [0, 1]. 7.12.4.9 The asinpi functions Synopsis #include <math.h> double asinpi(double x); float asinpif(float x); long double asinpil(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 asinpid32(_Decimal32 x); _Decimal64 asinpid64(_Decimal64 x); _Decimal128 asinpid128(_Decimal128 x);
1
#endif
2
Description The asinpi functions compute the principal value of the arc sine of x, divided by π, thus measuring the angle in half-revolutions. A domain error occurs for arguments not in the interval [−1, +1]. A range error occurs if nonzero x is too close to zero. Returns
3
The asinpi functions return arcsin(x)/π in the interval [− 12 , + 12 ]. 7.12.4.10 The atanpi functions Synopsis
1
#include <math.h> double atanpi(double x); float atanpif(float x); long double atanpil(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 atanpid32(_Decimal32 x); _Decimal64 atanpid64(_Decimal64 x);
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_Decimal128 atanpid128(_Decimal128 x); #endif
2
Description The atanpi functions compute the principal value of the arc tangent of x, divided by π, thus measuring the angle in half-revolutions. A range error occurs if nonzero x is too close to zero. Returns
3
The atanpi functions return arctan(x)/π. in the interval [− 12 , + 12 ]. 7.12.4.11 The atan2pi functions Synopsis #include <math.h> double atan2pi(double y, double x); float atan2pif(float y, float x); long double atan2pil(long double y, long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 atan2pid32(_Decimal32 y, _Decimal32 x); _Decimal64 atan2pid64(_Decimal64 y, _Decimal64 x); _Decimal128 atan2pid128(_Decimal128 y, _Decimal128 x);
1
#endif
2
3
Description The atan2pi functions compute the angle, measured in half-revolutions, subtended at the origin by the point (x, y) and the positive x-axis. Thus, the atan2pi functions compute arctan( xy )/π, in the range [−1, +1]. A domain error may occur if both arguments are zero. A range error occurs if x is positive and nonzero xy is too close to zero. Returns The atan2pi functions return the computed angle, in the interval [−1, +1]. 7.12.4.12 The cospi functions Synopsis #include <math.h> double cospi(double x); float cospif(float x); long double cospil(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 cospid32(_Decimal32 x); _Decimal64 cospid64(_Decimal64 x); _Decimal128 cospid128(_Decimal128 x);
1
#endif
2
3
Description The cospi functions compute the cosine of π × x, thus regarding x as a measurement in halfrevolutions. Returns The cospi functions return cos(π × x). 7.12.4.13 The sinpi functions Synopsis #include <math.h> double sinpi(double x); float sinpif(float x);
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long double sinpil(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 sinpid32(_Decimal32 x); _Decimal64 sinpid64(_Decimal64 x); _Decimal128 sinpid128(_Decimal128 x); #endif
2
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Description The sinpi functions compute the sine of π× x, thus regarding x as a measurement in half-revolutions. A range error occurs if nonzero x is too close to zero. Returns The sinpi functions return sin(π × x). 7.12.4.14 The tanpi functions Synopsis #include <math.h> double tanpi(double x); float tanpif(float x); long double tanpil(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 tanpid32(_Decimal32 x); _Decimal64 tanpid64(_Decimal64 x); _Decimal128 tanpid128(_Decimal128 x);
1
#endif
2
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Description The tanpi functions compute the tangent of π × x, thus regarding x as a measurement in halfrevolutions. A range error occurs if nonzero x is too close to zero. A pole error may occur if |x| is (n + 0.5) for integer n. Returns The tanpi functions return tan(π × x).
7.12.5
Hyperbolic functions
7.12.5.1 The acosh functions Synopsis #include <math.h> double acosh(double x); float acoshf(float x); long double acoshl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 acoshd32(_Decimal32 x); _Decimal64 acoshd64(_Decimal64 x); _Decimal128 acoshd128(_Decimal128 x);
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Description The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain error occurs for arguments less than 1. Returns The acosh functions return arcosh x in the interval [0, +∞]. 7.12.5.2 § 7.12.5.2
The asinh functions Library
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Synopsis #include <math.h> double asinh(double x); float asinhf(float x); long double asinhl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 asinhd32(_Decimal32 x); _Decimal64 asinhd64(_Decimal64 x); _Decimal128 asinhd128(_Decimal128 x);
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Description The asinh functions compute the arc hyperbolic sine of x. A range error occurs if nonzero x is too close to zero. Returns The asinh functions return arsinh x. 7.12.5.3 The atanh functions Synopsis #include <math.h> double atanh(double x); float atanhf(float x); long double atanhl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 atanhd32(_Decimal32 x); _Decimal64 atanhd64(_Decimal64 x); _Decimal128 atanhd128(_Decimal128 x); #endif
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Description The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs for arguments not in the interval [−1, +1]. A pole error may occur if the argument equals -1 or +1. A range error occurs if nonzero x is too close to zero. Returns The atanh functions return artanh x. 7.12.5.4 The cosh functions Synopsis #include <math.h> double cosh(double x); float coshf(float x); long double coshl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 coshd32(_Decimal32 x); _Decimal64 coshd64(_Decimal64 x); _Decimal128 coshd128(_Decimal128 x);
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Description The cosh functions compute the hyperbolic cosine of x. A range error occurs if the magnitude of finite x is too large. Returns The cosh functions return cosh x. 246
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7.12.5.5 The sinh functions Synopsis #include <math.h> double sinh(double x); float sinhf(float x); long double sinhl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 sinhd32(_Decimal32 x); _Decimal64 sinhd64(_Decimal64 x); _Decimal128 sinhd128(_Decimal128 x);
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Description The sinh functions compute the hyperbolic sine of x. A range error occurs if the magnitude of finite x is too large or if nonzero x is too close to zero. Returns The sinh functions return sinh x. 7.12.5.6 The tanh functions Synopsis #include <math.h> double tanh(double x); float tanhf(float x); long double tanhl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 tanhd32(_Decimal32 x); _Decimal64 tanhd64(_Decimal64 x); _Decimal128 tanhd128(_Decimal128 x); #endif
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Description The tanh functions compute the hyperbolic tangent of x. A range error occurs if nonzero x is too close to zero. Returns The tanh functions return tanh x.
7.12.6
Exponential and logarithmic functions
7.12.6.1 The exp functions Synopsis 1
#include <math.h> double exp(double x); float expf(float x); long double expl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 expd32(_Decimal32 x); _Decimal64 expd64(_Decimal64 x); _Decimal128 expd128(_Decimal128 x); #endif
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Description The exp functions compute the base-e exponential of x. A range error occurs if the magnitude of finite x is too large. § 7.12.6.1
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Returns The exp functions return ex . 7.12.6.2 The exp10 functions Synopsis #include <math.h> double exp10(double x); float exp10f(float x); long double exp10l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 exp10d32(_Decimal32 x); _Decimal64 exp10d64(_Decimal64 x); _Decimal128 exp10d128(_Decimal128 x); #endif
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Description The exp10 functions compute the base-10 exponential of x. A range error occurs if the magnitude of finite x is too large. Returns The exp10 functions return 10x . 7.12.6.3 The exp10m1 functions Synopsis #include <math.h> double exp10m1(double x); float exp10m1f(float x); long double exp10m1l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 exp10m1d32(_Decimal32 x); _Decimal64 exp10m1d64(_Decimal64 x); _Decimal128 exp10m1d128(_Decimal128 x);
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Description The exp10m1 functions compute the base-10 exponential of the argument, minus 1. A range error occurs if positive finite x is too large or if nonzero x is too close to zero. Returns The exp10m1 functions return 10x − 1. 7.12.6.4 The exp2 functions Synopsis #include <math.h> double exp2(double x); float exp2f(float x); long double exp2l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 exp2d32(_Decimal32 x); _Decimal64 exp2d64(_Decimal64 x); _Decimal128 exp2d128(_Decimal128 x);
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Description The exp2 functions compute the base-2 exponential of x. A range error occurs if the magnitude of finite x is too large. 248
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Returns The exp2 functions return 2x . 7.12.6.5 The exp2m1 functions Synopsis
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#include <math.h> double exp2m1(double x); float exp2m1f(float x); long double exp2m1l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 exp2m1d32(_Decimal32 x); _Decimal64 exp2m1d64(_Decimal64 x); _Decimal128 exp2m1d128(_Decimal128 x); #endif
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Description The exp2m1 functions compute the base-2 exponential of the argument, minus 1. A range error occurs if positive finite x is too large or if nonzero x is too close to zero. Returns The exp2m1 functions return 2x − 1. 7.12.6.6 The expm1 functions Synopsis
1
#include <math.h> double expm1(double x); float expm1f(float x); long double expm1l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 expm1d32(_Decimal32 x); _Decimal64 expm1d64(_Decimal64 x); _Decimal128 expm1d128(_Decimal128 x); #endif
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Description The expm1 functions compute the base-e exponential of the argument, minus 1. A range error occurs if positive finite x is too large or if nonzero x is too close to zero. 291) Returns The expm1 functions return ex − 1. 7.12.6.7 The frexp functions Synopsis
1
#include <math.h> double frexp(double value, int *p); float frexpf(float value, int *p); long double frexpl(long double value, int *p); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 frexpd32(_Decimal32 value, int *p); _Decimal64 frexpd64(_Decimal64 value, int *p); _Decimal128 frexpd128(_Decimal128 value, int *p); #endif
291) For small magnitude x, expm1(x) is expected to be more accurate than exp(x)-1.
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Description The frexp functions break a floating-point number into a normalized fraction and an integer exponent. They store the integer in the int object pointed to by p. If the type of the function is a standard floating type, the exponent is an integral power of 2. If the type of the function is a decimal floating type, the exponent is an integral power of 10. Returns If value is not a floating-point number or if the integral power is outside the range of int, the results are unspecified. Otherwise, the frexp functions return the value x, such that x has a magnitude in the interval [ 12 , 1) or zero, and value equals x × 2*p , when the type of the function is a standard floating type; or x has a magnitude in the interval [1/10, 1) or zero, and value equals x × 10*p , when the type of the function is a decimal floating type. If value is zero, both parts of the result are zero. 7.12.6.8 The ilogb functions Synopsis #include <math.h> int ilogb(double x); int ilogbf(float x); int ilogbl(long double x); #ifdef __STDC_IEC_60559_DFP__ int ilogbd32(_Decimal32 x); int ilogbd64(_Decimal64 x); int ilogbd128(_Decimal128 x); #endif
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Description The ilogb functions extract the exponent of x as a signed int value. If x is zero they compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling the corresponding logb function and converting the returned value to type int. A domain error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur. Returns The ilogb functions return the exponent of x as a signed int value. Forward references: the logb functions (7.12.6.17). 7.12.6.9 The ldexp functions Synopsis #include <math.h> double ldexp(double x, int p); float ldexpf(float x, int p); long double ldexpl(long double x, int p); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 ldexpd32(_Decimal32 x, int p); _Decimal64 ldexpd64(_Decimal64 x, int p); _Decimal128 ldexpd128(_Decimal128 x, int p); #endif
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Description The ldexp functions multiply a floating-point number by an integral power of 2 when the type of the function is a standard floating type, or by an integral power of 10 when the type of the function is a decimal floating type. A range error occurs for some finite x, depending on p. 250
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Returns The ldexp functions return x × 2p when the type of the function is a standard floating type, or return x × 10p when the type of the function is a decimal floating type. 7.12.6.10 The llogb functions Synopsis
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#include <math.h> long int llogb(double x); long int llogbf(float x); long int llogbl(long double x); #ifdef __STDC_IEC_60559_DFP__ long int llogbd32(_Decimal32 x); long int llogbd64(_Decimal64 x); long int llogbd128(_Decimal128 x); #endif
Description The llogb functions extract the exponent of x as a signed long int value. If x is zero they compute the value FP_LLOGB0; if x is infinite they compute the value LONG_MAX; if x is a NaN they compute the value FP_LLOGBNAN; otherwise, they are equivalent to calling the corresponding logb function and converting the returned value to type long int. A domain error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside the range of the return type, the numeric result is unspecified. Returns The llogb functions return the exponent of x as a signed long int value. Forward references: the logb functions (7.12.6.17). 7.12.6.11 The log functions Synopsis
1
#include <math.h> double log(double x); float logf(float x); long double logl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 logd32(_Decimal32 x); _Decimal64 logd64(_Decimal64 x); _Decimal128 logd128(_Decimal128 x); #endif
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Description The log functions compute the base-e (natural) logarithm of x. A domain error occurs if the argument is less than zero. A pole error may occur if the argument is zero. Returns The log functions return loge x. 7.12.6.12 The log10 functions Synopsis
1
#include <math.h> double log10(double x); float log10f(float x); long double log10l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 log10d32(_Decimal32 x); _Decimal64 log10d64(_Decimal64 x);
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_Decimal128 log10d128(_Decimal128 x); #endif
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Description The log10 functions compute the base-10 (common) logarithm of x. A domain error occurs if the argument is less than zero. A pole error may occur if the argument is zero. Returns The log10 functions return log10 x. 7.12.6.13 The log10p1 functions Synopsis #include <math.h> double log10p1(double x); float log10p1f(float x); long double log10p1l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 log10p1d32(_Decimal32 x); _Decimal64 log10p1d64(_Decimal64 x); _Decimal128 log10p1d128(_Decimal128 x);
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Description The log10p1 functions compute the base-10 logarithm of 1 plus the argument. A domain error occurs if the argument is less than −1. A pole error may occur if the argument equals −1. A range error occurs if nonzero x is too close to zero. Returns The log10p1 functions return log10 (1 + x). 7.12.6.14 The log1p and logp1 functions Synopsis #include <math.h> double log1p(double x); float log1pf(float x); long double log1pl(long double x); double logp1(double x); float logp1f(float x); long double logp1l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 log1pd32(_Decimal32 x); _Decimal64 log1pd64(_Decimal64 x); _Decimal128 log1pd128(_Decimal128 x); _Decimal32 logp1d32(_Decimal32 x); _Decimal64 logp1d64(_Decimal64 x); _Decimal128 logp1d128(_Decimal128 x); #endif
1
Description 2
The log1p functions are equivalent to the logp1 functions.292) These functions compute the base-e (natural) logarithm of 1 plus the argument.293) A domain error occurs if the argument is less than −1. A pole error may occur if the argument equals −1. A range error occurs if nonzero x is too close to zero. 292) The logp1 functions are preferred for name consistency with the log10p1 and log2p1 functions. 293) For small magnitude x, logp1(x) is expected to be more accurate than log(1 + x).
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Returns The log1p and logp1 functions return loge (1 + x). 7.12.6.15 The log2 functions Synopsis
1
#include <math.h> double log2(double x); float log2f(float x); long double log2l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 log2d32(_Decimal32 x); _Decimal64 log2d64(_Decimal64 x); _Decimal128 log2d128(_Decimal128 x); #endif
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Description The log2 functions compute the base-2 logarithm of x. A domain error occurs if the argument is less than zero. A pole error may occur if the argument is zero. Returns The log2 functions return log2 x. 7.12.6.16 The log2p1 functions Synopsis
1
#include <math.h> double log2p1(double x); float log2p1f(float x); long double log2p1l(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 log2p1d32(_Decimal32 x); _Decimal64 log2p1d64(_Decimal64 x); _Decimal128 log2p1d128(_Decimal128 x); #endif
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Description The log2p1 functions compute the base-2 logarithm of 1 plus the argument. A domain error occurs if the argument is less than −1. A pole error may occur if the argument equals −1. A range error occurs if nonzero x is too close to zero. Returns The log2p1 functions return log2 (1+x). 7.12.6.17 The logb functions Synopsis
1
#include <math.h> double logb(double x); float logbf(float x); long double logbl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 logbd32(_Decimal32 x); _Decimal64 logbd64(_Decimal64 x); _Decimal128 logbd128(_Decimal128 x); #endif
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Description The logb functions extract the exponent of x, as a signed integer value in floating-point format. If x is subnormal it is treated as though it were normalized; thus, for positive finite x, 1 ≤ x × b−logb(x) < b where b = FLT_RADIX if the type of the function is a standard floating type, or b = 10 if the type of the function is a decimal floating type. A domain error or pole error may occur if the argument is zero.
3
Returns The logb functions return the signed exponent of x. 7.12.6.18 The modf functions Synopsis #include <math.h> double modf(double value, double *iptr); float modff(float value, float *iptr); long double modfl(long double value, long double *iptr); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 modfd32(_Decimal32 x, _Decimal32 *iptr); _Decimal64 modfd64(_Decimal64 x, _Decimal64 *iptr); _Decimal128 modfd128(_Decimal128 x, _Decimal128 *iptr);
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#endif
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Description The modf functions break the argument value into integral and fractional parts, each of which has the same type and sign as the argument. They store the integral part (in floating-point format) in the object pointed to by iptr. Returns The modf functions return the signed fractional part of value. 7.12.6.19 The scalbn and scalbln functions Synopsis #include <math.h> double scalbn(double x, int n); float scalbnf(float x, int n); long double scalbnl(long double x, int n); double scalbln(double x, long int n); float scalblnf(float x, long int n); long double scalblnl(long double x, long int n); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 scalbnd32(_Decimal32 x, int n); _Decimal64 scalbnd64(_Decimal64 x, int n); _Decimal128 scalbnd128(_Decimal128 x, int n); _Decimal32 scalblnd32(_Decimal32 x, long int n); _Decimal64 scalblnd64(_Decimal64 x, long int n); _Decimal128 scalblnd128(_Decimal128 x, long int n); #endif
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Description The scalbn and scalbln functions compute x × bn , where b = FLT_RADIX if the type of the function is a standard floating type, or b = 10 if the type of the function is a decimal floating type. A range error occurs for some finite x, depending on n. Returns The scalbn and scalbln functions return x × bn . 254
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7.12.7
ISO/IEC 9899:2023 (E)
Power and absolute-value functions
7.12.7.1 The cbrt functions Synopsis #include <math.h> double cbrt(double x); float cbrtf(float x); long double cbrtl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 cbrtd32(_Decimal32 x); _Decimal64 cbrtd64(_Decimal64 x); _Decimal128 cbrtd128(_Decimal128 x); #endif
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Description The cbrt functions compute the real cube root of x. Returns
3
1
The cbrt functions return x 3 . 7.12.7.2 The compoundn functions Synopsis
1
#include <stdint.h> #include <math.h> double compoundn(double x, long long int n); float compoundnf(float x, long long int n); long double compoundnl(long double x, long long int n); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 compoundnd32(_Decimal32 x, long long int n); _Decimal64 compoundnd64(_Decimal64 x, long long int n); _Decimal128 compoundnd128(_Decimal128 x, long long int n); #endif
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Description The compoundn functions compute 1 plus x, raised to the power n. A domain error occurs if x < −1. Depending on n, a range error occurs if either positive finite x is too large or if x is too near but not equal to -1. A pole error may occur if x equals −1 and n < 0. Returns The compoundn functions return (1 + x)n . 7.12.7.3 The fabs functions Synopsis
1
#include <math.h> double fabs(double x); float fabsf(float x); long double fabsl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fabsd32(_Decimal32 x); _Decimal64 fabsd64(_Decimal64 x); _Decimal128 fabsd128(_Decimal128 x); #endif
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Description The fabs functions compute the absolute value of x. § 7.12.7.3
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Returns The fabs functions return |x|. 7.12.7.4 The hypot functions Synopsis #include <math.h> double hypot(double x, double y); float hypotf(float x, float y); long double hypotl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 hypotd32(_Decimal32 x, _Decimal32 y); _Decimal64 hypotd64(_Decimal64 x, _Decimal64 y); _Decimal128 hypotd128(_Decimal128 x, _Decimal128 y); #endif
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Description The hypot functions compute the square root of the sum of the squares of x and y, without undue overflow or underflow. A range error occurs for some finite arguments. Returns
3
The hypot functions return
p
x 2 + y2 .
7.12.7.5 The pow functions Synopsis #include <math.h> double pow(double x, double y); float powf(float x, float y); long double powl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 powd32(_Decimal32 x, _Decimal32 y); _Decimal64 powd64(_Decimal64 x, _Decimal64 y); _Decimal128 powd128(_Decimal128 x, _Decimal128 y);
1
#endif
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Description The pow functions compute x raised to the power y. A domain error occurs if x is finite and less than zero and y is finite and not an integer value. A domain error may occur if x is zero and y is zero. Depending on y, a range error occurs if either the magnitude of nonzero finite x is too large or too near zero. A domain error or pole error may occur if x is zero and y is less than zero. Returns The pow functions return xy . 7.12.7.6 The pown functions Synopsis #include <stdint.h> #include <math.h> double pown(double x, long long int n); float pownf(float x, long long int n); long double pownl(long double x, long long int n); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 pownd32(_Decimal32 x, long long int n); _Decimal64 pownd64(_Decimal64 x, long long int n); _Decimal128 pownd128(_Decimal128 x, long long int n); #endif
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Description 2
3
The pown functions compute x raised to the nth power. A pole error may occur if x equals 0 and n < 0. Depending on n, a range error occurs if either the magnitude of nonzero finite x is too large or too near zero. Returns The pown functions return xn . 7.12.7.7 The powr functions Synopsis #include <math.h> double powr(double y, double x); float powrf(float y, float x); long double powrl(long double y, long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 powrd32(_Decimal32 y, _Decimal32 x); _Decimal64 powrd64(_Decimal64 y, _Decimal64 x); _Decimal128 powrd128(_Decimal128 y, _Decimal128 x); #endif
1
Description 2
The powr functions compute x raised to the power y as ey loge x .294) A domain error occurs if x < 0 or if x and y are both zero. Depending on y, a range error occurs if either positive nonzero finite x is too large or too near zero. A pole error may occur if x equals zero and finite y < 0. Returns
3
The powr functions return ey loge x . 7.12.7.8 The rootn functions Synopsis #include <stdint.h> #include <math.h> double rootn(double x, long long int n); float rootnf(float x, long long int n); long double rootnl(long double x, long long int n); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 rootnd32(_Decimal32 x, long long int n); _Decimal64 rootnd64(_Decimal64 x, long long int n); _Decimal128 rootnd128(_Decimal128 x, long long int n); #endif
1
Description 2
The rootn functions compute the principal nth root of x. A domain error occurs if n is 0 or if x < 0 and n is even. If n is −1, a range error occurs if either the magnitude of nonzero finite x is too large or too near zero. A pole error may occur if x equals zero and n < 0. Returns
3
1
The rootn functions return x n . 7.12.7.9 The rsqrt functions Synopsis
1
#include <math.h> double rsqrt(double x); 294) Restricting the domain to that of the formula ey loge x is intended to better meet expectations for a continuous power function and to allow implementations with fewer tests for special cases.
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float rsqrtf(float x); long double rsqrtl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 rsqrtd32(_Decimal32 x); _Decimal64 rsqrtd64(_Decimal64 x); _Decimal128 rsqrtd128(_Decimal128 x); #endif
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Description The rsqrt functions compute the reciprocal of the nonnegative square root of the argument. A domain error occurs if the argument is less than zero. A pole error may occur if the argument equals zero. Returns
3
The rsqrt functions return √1x . 7.12.7.10 The sqrt functions Synopsis #include <math.h> double sqrt(double x); float sqrtf(float x); long double sqrtl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 sqrtd32(_Decimal32 x); _Decimal64 sqrtd64(_Decimal64 x); _Decimal128 sqrtd128(_Decimal128 x); #endif
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Description The sqrt functions compute the nonnegative square root of x. A domain error occurs if the argument is less than zero. Returns √ The sqrt functions return x.
7.12.8
Error and gamma functions
7.12.8.1 The erf functions Synopsis #include <math.h> double erf(double x); float erff(float x); long double erfl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 erfd32(_Decimal32 x); _Decimal64 erfd64(_Decimal64 x); _Decimal128 erfd128(_Decimal128 x);
1
#endif
2
Description The erf functions compute the error function of x. A range error occurs if nonzero x is too close to zero. Returns
3
The erf functions return erf x = √2π 258
Rx −t2 e dt. 0
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7.12.8.2 The erfc functions Synopsis #include <math.h> double erfc(double x); float erfcf(float x); long double erfcl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 erfcd32(_Decimal32 x); _Decimal64 erfcd64(_Decimal64 x); _Decimal128 erfcd128(_Decimal128 x);
1
#endif
2
Description The erfc functions compute the complementary error function of x. A range error occurs if positive finite x is too large. Returns
3
The erfc functions return erfc x = 1 − erf x = √2π
R∞ −t2 e dt. x
7.12.8.3 The lgamma functions Synopsis 1
2
3
#include <math.h> double lgamma(double x); float lgammaf(float x); long double lgammal(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 lgammad32(_Decimal32 x); _Decimal64 lgammad64(_Decimal64 x); _Decimal128 lgammad128(_Decimal128 x); #endif
Description The lgamma functions compute the natural logarithm of the absolute value of gamma of x. A range error occurs if positive finite x is too large. A pole error may occur if x is a negative integer or zero. Returns The lgamma functions return loge |Γ(x)|. 7.12.8.4 The tgamma functions Synopsis
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#include <math.h> double tgamma(double x); float tgammaf(float x); long double tgammal(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 tgammad32(_Decimal32 x); _Decimal64 tgammad64(_Decimal64 x); _Decimal128 tgammad128(_Decimal128 x); #endif
Description The tgamma functions compute the gamma function of x. A domain error or pole error may occur if x is a negative integer or zero. A range error occurs for some finite x less than zero, if positive finite x is too large, or nonzero x is too close to zero. § 7.12.8.4
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Returns The tgamma functions return Γ(x).
7.12.9
Nearest integer functions
7.12.9.1 The ceil functions Synopsis #include <math.h> double ceil(double x); float ceilf(float x); long double ceill(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 ceild32(_Decimal32 x); _Decimal64 ceild64(_Decimal64 x); _Decimal128 ceild128(_Decimal128 x);
1
#endif
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Description The ceil functions compute the smallest integer value not less than x.
3
Returns The ceil functions return ⌈x⌉, expressed as a floating-point number. 7.12.9.2 The floor functions Synopsis #include <math.h> double floor(double x); float floorf(float x); long double floorl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 floord32(_Decimal32 x); _Decimal64 floord64(_Decimal64 x); _Decimal128 floord128(_Decimal128 x);
1
#endif
2
Description The floor functions compute the largest integer value not greater than x.
3
Returns The floor functions return ⌊x⌋, expressed as a floating-point number. 7.12.9.3 The nearbyint functions Synopsis #include <math.h> double nearbyint(double x); float nearbyintf(float x); long double nearbyintl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 nearbyintd32(_Decimal32 x); _Decimal64 nearbyintd64(_Decimal64 x); _Decimal128 nearbyintd128(_Decimal128 x);
1
#endif
2
Description The nearbyint functions round their argument to an integer value in floating-point format, using the current rounding direction and without raising the "inexact" floating-point exception. 260
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Returns The nearbyint functions return the rounded integer value. 7.12.9.4 The rint functions Synopsis
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#include <math.h> double rint(double x); float rintf(float x); long double rintl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 rintd32(_Decimal32 x); _Decimal64 rintd64(_Decimal64 x); _Decimal128 rintd128(_Decimal128 x); #endif
Description The rint functions differ from the nearbyint functions (7.12.9.3) only in that the rint functions may raise the "inexact" floating-point exception if the result differs in value from the argument. Returns The rint functions return the rounded integer value. 7.12.9.5 The lrint and llrint functions Synopsis
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#include <math.h> long int lrint(double x); long int lrintf(float x); long int lrintl(long double x); long long int llrint(double x); long long int llrintf(float x); long long int llrintl(long double x); #ifdef __STDC_IEC_60559_DFP__ long int lrintd32(_Decimal32 x); long int lrintd64(_Decimal64 x); long int lrintd128(_Decimal128 x); long long int llrintd32(_Decimal32 x); long long int llrintd64(_Decimal64 x); long long int llrintd128(_Decimal128 x); #endif
Description The lrint and llrint functions round their argument to the nearest integer value, rounding according to the current rounding direction. If the rounded value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur. Returns The lrint and llrint functions return the rounded integer value. 7.12.9.6 The round functions Synopsis
1
#include <math.h> double round(double x); float roundf(float x); long double roundl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 roundd32(_Decimal32 x);
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_Decimal64 roundd64(_Decimal64 x); _Decimal128 roundd128(_Decimal128 x); #endif
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Description The round functions round their argument to the nearest integer value in floating-point format, rounding halfway cases away from zero, regardless of the current rounding direction. Returns The round functions return the rounded integer value. 7.12.9.7 The lround and llround functions Synopsis #include <math.h> long int lround(double x); long int lroundf(float x); long int lroundl(long double x); long long int llround(double x); long long int llroundf(float x); long long int llroundl(long double x); #ifdef __STDC_IEC_60559_DFP__ long int lroundd32(_Decimal32 x); long int lroundd64(_Decimal64 x); long int lroundd128(_Decimal128 x); long long int llroundd32(_Decimal32 x); long long int llroundd64(_Decimal64 x); long long int llroundd128(_Decimal128 x);
1
#endif
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Description The lround and llround functions round their argument to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction. If the rounded value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur. Returns The lround and llround functions return the rounded integer value. 7.12.9.8 The roundeven functions Synopsis #include <math.h> double roundeven(double x); float roundevenf(float x); long double roundevenl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 roundevend32(_Decimal32 x); _Decimal64 roundevend64(_Decimal64 x); _Decimal128 roundevend128(_Decimal128 x);
1
#endif
2
Description The roundeven functions round their argument to the nearest integer value in floating-point format, rounding halfway cases to even (that is, to the nearest value that is an even integer), regardless of the current rounding direction. 262
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Returns The roundeven functions return the rounded integer value. 7.12.9.9 The trunc functions Synopsis
1
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#include <math.h> double trunc(double x); float truncf(float x); long double truncl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 truncd32(_Decimal32 x); _Decimal64 truncd64(_Decimal64 x); _Decimal128 truncd128(_Decimal128 x); #endif
Description The trunc functions round their argument to the integer value, in floating format, nearest to but no larger in magnitude than the argument. Returns The trunc functions return the truncated integer value. 7.12.9.10 The fromfp and ufromfp functions Synopsis
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2
#include <stdint.h> #include <math.h> double fromfp(double x, int rnd, unsigned int width); float fromfpf(float x, int rnd, unsigned int width); long double fromfpl(long double x, int rnd, unsigned int width); double ufromfp(double x, int rnd, unsigned int width); float ufromfpf(float x, int rnd, unsigned int width); long double ufromfpl(long double x, int rnd, unsigned int width); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fromfpd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 fromfpd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 fromfpd128(_Decimal128 x, int rnd, unsigned int width); _Decimal32 ufromfpd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 ufromfpd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 ufromfpd128(_Decimal128 x, int rnd, unsigned int width); #endif
Description The fromfp and ufromfp functions round x, using the math rounding direction indicated by rnd, to a signed or unsigned integer, respectively. If width is nonzero and the resulting integer is within the range — [−2(width−1) , 2(width−1) − 1], for signed — [0, 2width − 1], for unsigned then the functions return the integer value (represented in floating type). Otherwise, if width is zero or x does not round to an integer within the range, the functions return a NaN (of the type of the x argument, if available), else the value of x, and a domain error occurs. If the value of the rnd argument is not equal to the value of a math rounding direction macro (7.12), the direction of rounding is unspecified. The fromfp and ufromfp functions do not raise the "inexact" floating-point exception. § 7.12.9.10
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Returns The fromfp and ufromfp functions return the rounded integer value. EXAMPLE Upward rounding of double x to type int, without raising the "inexact" floating-point exception, is achieved by (int)fromfp(x, FP_INT_UPWARD, INT_WIDTH)
5
EXAMPLE Unsigned integer wrapping is not performed in ufromfp(-3.0, FP_INT_UPWARD, UINT_WIDTH) /* domain error */
7.12.9.11 The fromfpx and ufromfpx functions Synopsis #include <stdint.h> #include <math.h> double fromfpx(double x, int rnd, unsigned int width); float fromfpxf(float x, int rnd, unsigned int width); long double fromfpxl(long double x, int rnd, unsigned int width); double ufromfpx(double x, int rnd, unsigned int width); float ufromfpxf(float x, int rnd, unsigned int width); long double ufromfpxl(long double x, int rnd, unsigned int width); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fromfpxd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 fromfpxd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 fromfpxd128(_Decimal128 x, int rnd, unsigned int width); _Decimal32 ufromfpxd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 ufromfpxd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 ufromfpxd128(_Decimal128 x, int rnd, unsigned int width); #endif
1
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Description The fromfpx and ufromfpx functions differ from the fromfp and ufromfp functions, respectively, only in that the fromfpx and ufromfpx functions raise the "inexact" floating-point exception if a rounded result not exceeding the specified width differs in value from the argument x. Returns The fromfpx and ufromfpx functions return the rounded integer value. NOTE 1 Conversions to integer types that are not required to raise the inexact exception can be done simply by rounding to integral value in floating type and then converting to the target integer type. For example, the conversion of long double x to uint64_t, using upward rounding, is done by
(uint64_t)ceill(x)
7.12.10
Remainder functions
7.12.10.1 The fmod functions Synopsis #include <math.h> double fmod(double x, double y); float fmodf(float x, float y); long double fmodl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmodd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmodd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmodd128(_Decimal128 x, _Decimal128 y);
1
#endif
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Description The fmod functions compute the floating-point remainder of x/y. Returns The fmod functions return the value x − ny, for some integer n such that, if y is nonzero, the result has the same sign as x and magnitude less than the magnitude of y. If y is zero, whether a domain error occurs or the fmod functions return zero is implementation-defined. 7.12.10.2 The remainder functions Synopsis #include <math.h> double remainder(double x, double y); float remainderf(float x, float y); long double remainderl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 remainderd32(_Decimal32 x, _Decimal32 y); _Decimal64 remainderd64(_Decimal64 x, _Decimal64 y); _Decimal128 remainderd128(_Decimal128 x, _Decimal128 y); #endif
1
Description 2
The remainder functions compute the remainder x REM y required by IEC 60559. 295)
3
Returns The remainder functions return x REM y. If y is zero, whether a domain error occurs or the functions return zero is implementation-defined. 7.12.10.3 The remquo functions Synopsis #include <math.h> double remquo(double x, double y, int *quo); float remquof(float x, float y, int *quo); long double remquol(long double x, long double y, int *quo);
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Description The remquo functions compute the same remainder as the remainder functions. In the object pointed to by quo they store a value whose sign is the sign of x/y and whose magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where n is an implementation-defined integer greater than or equal to 3. Returns The remquo functions return x REM y. If y is zero, the value stored in the object pointed to by quo is unspecified and whether a domain error occurs or the functions return zero is implementationdefined. NOTE 1 There are no decimal floating-point versions of the remquo functions.
7.12.11
Manipulation functions
7.12.11.1 The copysign functions Synopsis 1
#include <math.h> double copysign(double x, double y); 295) "When y ̸= 0, the remainder r = x REM y is defined regardless of the rounding mode by the mathematical relation r = x − ny, where n is the integer nearest the exact value of x ; whenever |n − x | = 12 , then n is even. If r = 0, its sign shall y y be that of x." This definition is applicable for all implementations.
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float copysignf(float x, float y); long double copysignl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 copysignd32(_Decimal32 x, _Decimal32 y); _Decimal64 copysignd64(_Decimal64 x, _Decimal64 y); _Decimal128 copysignd128(_Decimal128 x, _Decimal128 y); #endif
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Description The copysign functions produce a value with the magnitude of x and the sign of y. If x or y is an unsigned value, the sign (if any) of the result is implementation-defined. On implementations that represent a signed zero but do not treat negative zero consistently in arithmetic operations, the copysign functions should regard the sign of zero as positive. Returns The copysign functions return a value with the magnitude of x and the sign of y. 7.12.11.2 The nan functions Synopsis #include <math.h> double nan(const char *tagp); float nanf(const char *tagp); long double nanl(const char *tagp); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 nand32(const char *tagp); _Decimal64 nand64(const char *tagp); _Decimal128 nand128(const char *tagp);
1
#endif
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Description The nan, nanf, and nanl functions convert the string pointed to by tagp according to the following rules. The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-sequence)", nullptr); the call nan("") is equivalent to strtod("NAN()", nullptr). If tagp does not point to an empty string or an n-char sequence, the call is equivalent to strtod("NAN", nullptr). Calls to nanf and nanl are equivalent to the corresponding calls to strtof and strtold. Returns The nan functions return a quiet NaN, if available, with content indicated through tagp. If the implementation does not support quiet NaNs, the functions return zero. Forward references: the strtod, strtof, and strtold functions (7.24.1.5). 7.12.11.3 The nextafter functions Synopsis #include <math.h> double nextafter(double x, double y); float nextafterf(float x, float y); long double nextafterl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 nextafterd32(_Decimal32 x, _Decimal32 y); _Decimal64 nextafterd64(_Decimal64 x, _Decimal64 y); _Decimal128 nextafterd128(_Decimal128 x, _Decimal128 y);
1
#endif
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Description The nextafter functions determine the next representable value, in the type of the function, after x in the direction of y, where x and y are first converted to the type of the function.296) The nextafter functions return y if x equals y. A range error occurs if the magnitude of x is the largest finite value representable in the type and the result is infinite or not representable in the type. If x != y, a range error occurs for either subnormal or zero results.
3
Returns The nextafter functions return the next representable value in the specified format after x in the direction of y. 7.12.11.4 The nexttoward functions Synopsis
1
#include <math.h> double nexttoward(double x, long double y); float nexttowardf(float x, long double y); long double nexttowardl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 nexttowardd32(_Decimal32 x, _Decimal128 y); _Decimal64 nexttowardd64(_Decimal64 x, _Decimal128 y); _Decimal128 nexttowardd128(_Decimal128 x, _Decimal128 y); #endif
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Description The nexttoward functions are equivalent to the nextafter functions except that the second parameter has type long double or _Decimal128 and the functions return y converted to the type of the function if x equals y.297) Returns The nexttoward functions return the next representable value in the specified format after x in the direction of y. 7.12.11.5 The nextup functions Synopsis
1
#include <math.h> double nextup(double x); float nextupf(float x); long double nextupl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 nextupd32(_Decimal32 x); _Decimal64 nextupd64(_Decimal64 x); _Decimal128 nextupd128(_Decimal128 x); #endif
2
Description The nextup functions determine the next representable value, in the type of the function, greater than x. If x is the negative number of least magnitude in the type of x, nextup(x) is −0 if the type has signed zeros and is 0 otherwise. If x is zero, nextup(x) is the positive number of least magnitude in the type of x. If x is the positive number (finite or infinite) of maximum magnitude in the type, nextup(x) is x. 296) The argument values are converted to the type of the function, even by a macro implementation of the function. 297) The result of the nexttoward functions is determined in the type of the function, without loss of range or precision in a floating second argument.
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Returns The nextup functions return the next representable value in the specified type greater than x. 7.12.11.6 The nextdown functions Synopsis #include <math.h> double nextdown(double x); float nextdownf(float x); long double nextdownl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 nextdownd32(_Decimal32 x); _Decimal64 nextdownd64(_Decimal64 x); _Decimal128 nextdownd128(_Decimal128 x); #endif
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Description The nextdown functions determine the next representable value, in the type of the function, less than x. If x is the positive number of least magnitude in the type of x, nextdown(x) is +0 if the type has signed zeros and is 0 otherwise. If x is zero, nextdown(x) is the negative number of least magnitude in the type of x. If x is the negative number (finite or infinite) of maximum magnitude in the type, nextdown(x) is x. Returns The nextdown functions return the next representable value in the specified type less than x. 7.12.11.7 The canonicalize functions Synopsis #include <math.h> int canonicalize(double * cx, const double * x); int canonicalizef(float * cx, const float * x); int canonicalizel(long double * cx, const long double * x); #ifdef __STDC_IEC_60559_DFP__ int canonicalized32(_Decimal32 * cx, const _Decimal32 * x); int canonicalized64(_Decimal64 * cx, const _Decimal64 * x); int canonicalized128(_Decimal128 * cx, const _Decimal128 * x);
1
#endif
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Description The canonicalize functions attempt to produce a canonical version of the floating-point representation in the object pointed to by the argument x, as if to a temporary object of the specified type, and store the canonical result in the object pointed to by the argument cx.298) If the input *x is a signaling NaN, the canonicalize functions are intended to store a canonical quiet NaN. If a canonical result is not produced the object pointed to by cx is unchanged. Returns The canonicalize functions return zero if a canonical result is stored in the object pointed to by cx. Otherwise they return a nonzero value.
7.12.12
Maximum, minimum, and positive difference functions
7.12.12.1 The fdim functions Synopsis #include <math.h> double fdim(double x, double y);
1
298) Arguments x and cx may point to the same object.
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float fdimf(float x, float y); long double fdiml(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fdimd32(_Decimal32 x, _Decimal32 y); _Decimal64 fdimd64(_Decimal64 x, _Decimal64 y); _Decimal128 fdimd128(_Decimal128 x, _Decimal128 y); #endif
2
Description The fdim functions determine the positive difference between their arguments: (
x−y
+0
if x > y if x ≤ y
A range error occurs for some finite arguments.
3
Returns The fdim functions return the positive difference value. 7.12.12.2 The fmax functions Synopsis
1
#include <math.h> double fmax(double x, double y); float fmaxf(float x, float y); long double fmaxl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmaxd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaxd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaxd128(_Decimal128 x, _Decimal128 y); #endif
Description 2
The fmax functions determine the maximum numeric value of their arguments.299)
3
Returns The fmax functions return the maximum numeric value of their arguments. 7.12.12.3 The fmin functions Synopsis
1
#include <math.h> double fmin(double x, double y); float fminf(float x, float y); long double fminl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmind32(_Decimal32 x, _Decimal32 y); _Decimal64 fmind64(_Decimal64 x, _Decimal64 y); _Decimal128 fmind128(_Decimal128 x, _Decimal128 y); #endif
Description 2
The fmin functions determine the minimum numeric value of their arguments. 300) 299) Quiet NaN arguments are treated as missing data: if one argument is a quiet NaN and the other numeric, then the fmax
functions choose the numeric value. See F.10.9.2. 300) The fmin functions are analogous to the fmax functions in their treatment of quiet NaNs.
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Returns The fmin functions return the minimum numeric value of their arguments. NOTE 1 The fmax and fmin functions are similar to the fmaximum_num and fminimum_num functions, though may differ in which signed zero is returned when the arguments are differently signed zeros and in their treatment of signaling NaNs (see F.10.9.5).
7.12.12.4 The fmaximum functions Synopsis #include <math.h> double fmaximum(double x, double y); float fmaximumf(float x, float y); long double fmaximuml(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmaximumd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximumd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximumd128(_Decimal128 x, _Decimal128 y);
1
#endif
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Description The fmaximum functions determine the maximum value of their arguments. For these functions, +0 is considered greater than −0. These functions differ from the fmaximum_num functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fmaximum functions return the maximum value of their arguments. 7.12.12.5 The fminimum functions Synopsis #include <math.h> double fminimum(double x, double y); float fminimumf(float x, float y); long double fminimuml(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fminimumd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimumd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimumd128(_Decimal128 x, _Decimal128 y); #endif
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Description The fminimum functions determine the minimum value of their arguments. For these functions, −0 is considered less than +0. These functions differ from the fminimum_num functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fminimum functions return the minimum value of their arguments. 7.12.12.6 The fmaximum_mag functions Synopsis #include <math.h> double fmaximum_mag(double x, double y); float fmaximum_magf(float x, float y); long double fmaximum_magl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmaximum_magd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximum_magd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximum_magd128(_Decimal128 x, _Decimal128 y);
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#endif
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Description The fmaximum_mag functions determine the value of the argument of maximum magnitude: x if |x| > |y|, y if |y| > |x|, and fmaximum(x, y) otherwise. These functions differ from the fmaximum_mag_num functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fmaximum_mag functions return the value of the argument of maximum magnitude. 7.12.12.7 The fminimum_mag functions Synopsis
1
#include <math.h> double fminimum_mag(double x, double y); float fminimum_magf(float x, float y); long double fminimum_magl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fminimum_magd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimum_magd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimum_magd128(_Decimal128 x, _Decimal128 y); #endif
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Description The fminimum_mag functions determine the value of the argument of minimum magnitude: x if |x| < |y|, y if |y| < |x|, and fminimum(x, y) otherwise. These functions differ from the fminimum_mag_num functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fminimum_mag functions return the value of the argument of minimum magnitude. 7.12.12.8 The fmaximum_num functions Synopsis
1
#include <math.h> double fmaximum_num(double x, double y); float fmaximum_numf(float x, float y); long double fmaximum_numl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmaximum_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximum_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximum_numd128(_Decimal128 x, _Decimal128 y); #endif
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Description The fmaximum_num functions determine the maximum value of their numeric arguments. They determine the number if one argument is a number and the other is a NaN. These functions differ from the fmaximum functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fmaximum_num functions return the maximum value of their numeric arguments. 7.12.12.9 The fminimum_num functions Synopsis
1
#include <math.h> double fminimum_num(double x, double y); float fminimum_numf(float x, float y);
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long double fminimum_numl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fminimum_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimum_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimum_numd128(_Decimal128 x, _Decimal128 y); #endif
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Description The fminimum_num functions determine the minimum value of their numeric arguments. They determine the number if one argument is a number and the other is a NaN. These functions differ from the fminimum functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fminimum_num functions return the minimum value of their numeric arguments. 7.12.12.10 Synopsis
#include <math.h> double fmaximum_mag_num(double x, double y); float fmaximum_mag_numf(float x, float y); long double fmaximum_mag_numl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmaximum_mag_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximum_mag_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximum_mag_numd128(_Decimal128 x, _Decimal128 y); #endif
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The fmaximum_mag_num functions
Description The fmaximum_mag_num functions determine the value of a numeric argument of maximum magnitude. They determine the number if one argument is a number and the other is a NaN. These functions differ from the fmaximum_mag functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fmaximum_mag_num functions return the value of a numeric argument of maximum magnitude. 7.12.12.11 Synopsis
The fminimum_mag_num functions
#include <math.h> double fminimum_mag_num(double x, double y); float fminimum_mag_numf(float x, float y); long double fminimum_mag_numl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fminimum_mag_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimum_mag_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimum_mag_numd128(_Decimal128 x, _Decimal128 y);
1
#endif
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Description The fminimum_mag_num functions determine the value of a numeric argument of minimum magnitude. They determine the number if one argument is a number and the other is a NaN. These functions differ from the fminimum_mag functions only in their treatment of NaN arguments (see F.10.9.4, F.10.9.5). Returns The fminimum_mag_num functions return the value of a numeric argument of minimum magnitude. 272
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7.12.13
ISO/IEC 9899:2023 (E)
Fused multiply-add
7.12.13.1 The fma functions Synopsis #include <math.h> double fma(double x, double y, double z); float fmaf(float x, float y, float z); long double fmal(long double x, long double y, long double z); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 fmad32(_Decimal32 x, _Decimal32 y, _Decimal32 z); _Decimal64 fmad64(_Decimal64 x, _Decimal64 y, _Decimal64 z); _Decimal128 fmad128(_Decimal128 x, _Decimal128 y, _Decimal128 z);
1
#endif
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Description The fma functions compute (x × y) + z, rounded as one ternary operation: they compute the value (as if) to infinite precision and round once to the result format, according to the current rounding mode. A range error occurs for some finite arguments. A domain error occurs for some infinite arguments. Returns The fma functions return (x × y) + z, rounded as one ternary operation.
7.12.14 1
Functions that round result to narrower type
The functions in this subclause round their results to a type typically narrower301) than the parameter types. 7.12.14.1 Add and round to narrower type Synopsis
1
#include <math.h> float fadd(double x, double y); float faddl(long double x, long double y); double daddl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32addd64(_Decimal64 x, _Decimal64 y); _Decimal32 d32addd128(_Decimal128 x, _Decimal128 y); _Decimal64 d64addd128(_Decimal128 x, _Decimal128 y); #endif
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Description These functions compute the sum of x + y, rounded to the type of the function. They compute the sum (as if) to infinite precision and round once to the result format, according to the current rounding mode. A range error occurs for some finite arguments. A domain error may occur for infinite arguments. Returns These functions return the sum of x + y, rounded to the type of the function. 7.12.14.2 Subtract and round to narrower type Synopsis
1
#include <math.h> float fsub(double x, double y); float fsubl(long double x, long double y); double dsubl(long double x, long double y); 301) In some cases the destination type might not be narrower than the parameter types. For example, double might not be narrower than long double.
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#ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32subd64(_Decimal64 x, _Decimal64 y); _Decimal32 d32subd128(_Decimal128 x, _Decimal128 y); _Decimal64 d64subd128(_Decimal128 x, _Decimal128 y); #endif
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Description These functions compute the difference of x − y, rounded to the type of the function. They compute the difference (as if) to infinite precision and round once to the result format, according to the current rounding mode. A range error occurs for some finite arguments. A domain error may occur for infinite arguments. Returns These functions return the difference of x − y, rounded to the type of the function. 7.12.14.3 Multiply and round to narrower type Synopsis #include <math.h> float fmul(double x, double y); float fmull(long double x, long double y); double dmull(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32muld64(_Decimal64 x, _Decimal64 y); _Decimal32 d32muld128(_Decimal128 x, _Decimal128 y); _Decimal64 d64muld128(_Decimal128 x, _Decimal128 y); #endif
1
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Description These functions compute the product x × y, rounded to the return type of the function. They compute the product (as if) to infinite precision and round once to the result format, according to the current rounding mode. A range error occurs for some finite arguments. A domain error occurs for one infinite argument and one zero argument. Returns These functions return the product of x × y, rounded to the return type of the function. 7.12.14.4 Divide and round to narrower type Synopsis #include <math.h> float fdiv(double x, double y); float fdivl(long double x, long double y); double ddivl(long double x, long double y); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32divd64(_Decimal64 x, _Decimal64 y); _Decimal32 d32divd128(_Decimal128 x, _Decimal128 y); _Decimal64 d64divd128(_Decimal128 x, _Decimal128 y); #endif
1
2
Description These functions compute the quotient x ÷ y, rounded to the return type of the function. They compute the quotient (as if) to infinite precision and round once to the result format, according to the current rounding mode. A range error occurs for some finite arguments. A domain error occurs for either both arguments infinite or both arguments zero. A pole error occurs for a finite x and a zero y. 274
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Returns These functions return the quotient x ÷ y, rounded to the type of the function. 7.12.14.5 Fused multiply-add and round to narrower type Synopsis #include <math.h> float ffma(double x, double y, double z); float ffmal(long double x, long double y, long double z); double dfmal(long double x, long double y, long double z); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32fmad64(_Decimal64 x, _Decimal64 y, _Decimal64 z); _Decimal32 d32fmad128(_Decimal128 x, _Decimal128 y, _Decimal128 z); _Decimal64 d64fmad128(_Decimal128 x, _Decimal128 y, _Decimal128 z);
1
#endif
2
3
Description These functions compute (x × y) + z (as if) to infinite precision and round once to the result format (the return type), according to the current rounding mode. A range error occurs for some finite arguments. A domain error may occur for an infinite argument. Returns These functions return (x × y) + z, rounded to the return type of the function. 7.12.14.6 Square root rounded to narrower type Synopsis #include <math.h> float fsqrt(double x); float fsqrtl(long double x); double dsqrtl(long double x); #ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32sqrtd64(_Decimal64 x); _Decimal32 d32sqrtd128(_Decimal128 x); _Decimal64 d64sqrtd128(_Decimal128 x);
1
#endif
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3
Description These functions compute the square root of x, rounded to the type of the function. They compute the square root (as if) to infinite precision and round once to the result format, according to the current rounding mode. A range error occurs for some finite positive arguments. A domain error occurs if the argument is less than zero. Returns These functions return the nonnegative square root of x, rounded to the return type of the function.
7.12.15
Quantum and quantum exponent functions
7.12.15.1 The quantizedN functions Synopsis 1
#include <math.h> #ifdef __STDC_IEC_60559_DFP__ _Decimal32 quantized32(_Decimal32 x, _Decimal32 y); _Decimal64 quantized64(_Decimal64 x, _Decimal64 y); _Decimal128 quantized128(_Decimal128 x, _Decimal128 y); #endif
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Description The quantizedN functions compute, if possible, a value with the numerical value of x and the quantum exponent of y. If the quantum exponent is being increased, the value shall be correctly rounded; if the result does not have the same value as x, the "inexact" floating-point exception shall be raised. If the quantum exponent is being decreased and the significand of the result has more digits than the type would allow, the result is NaN, the "invalid" floating-point exception is raised, and a domain error occurs. If one or both operands are NaN the result is NaN. Otherwise if only one operand is infinite, the result is NaN, the "invalid" floating-point exception is raised, and a domain error occurs. If both operands are infinite, the result is DEC_INFINITY with the sign of x, converted to the type of the function. The quantizedN functions do not raise the "overflow" and "underflow" floating-point exceptions. Returns The quantizedN functions return a value with the numerical value of x (except for any rounding) and the quantum exponent of y. 7.12.15.2 The samequantumdN functions Synopsis #include <math.h> #ifdef __STDC_IEC_60559_DFP__ bool samequantumd32(_Decimal32 x, _Decimal32 y); bool samequantumd64(_Decimal64 x, _Decimal64 y); bool samequantumd128(_Decimal128 x, _Decimal128 y);
1
#endif
2
3
Description The samequantumdN functions determine if the quantum exponents of x and y are the same. If both x and y are NaN, or both infinite, they have the same quantum exponents; if exactly one operand is infinite or exactly one operand is NaN, they do not have the same quantum exponents. The samequantumdN functions raise no floating-point exception. Returns The samequantumdN functions return nonzero (true) when x and y have the same quantum exponents, zero (false) otherwise. 7.12.15.3 The quantumdN functions Synopsis #include <math.h> #ifdef __STDC_IEC_60559_DFP__ _Decimal32 quantumd32(_Decimal32 x); _Decimal64 quantumd64(_Decimal64 x); _Decimal128 quantumd128(_Decimal128 x);
1
#endif
2
3
Description The quantumdN functions compute the quantum (5.2.4.2.3) of a finite argument. If x is infinite, the result is +∞. Returns The quantumdN functions return the quantum of x. 7.12.15.4 The llquantexpdN functions Synopsis #include <math.h> #ifdef __STDC_IEC_60559_DFP__
1
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long long int llquantexpd32(_Decimal32 x); long long int llquantexpd64(_Decimal64 x); long long int llquantexpd128(_Decimal128 x); #endif
2
3
Description The llquantexpdN functions compute the quantum exponent (5.2.4.2.3) of a finite argument. If x is infinite or NaN, they compute LLONG_MIN, the "invalid" floating-point exception is raised, and a domain error occurs. Returns The llquantexpdN functions return the quantum exponent of x.
7.12.16 1
Decimal re-encoding functions
IEC 60559 specifies two different schemes to encode significands in the object representation of a decimal floating-point object: one based on decimal encoding (which packs three decimal digits into 10 bits), the other based on binary encoding (as a binary integer). An implementation may use either of these encoding schemes for its decimal floating types. The re-encoding functions in this subclause provide conversions between external decimal data with a given encoding scheme and the implementation’s corresponding decimal floating type. 7.12.16.1 The encodedecdN functions Synopsis
1
2
3
#include <math.h> #ifdef __STDC_IEC_60559_DFP__ void encodedecd32(unsigned char encptr[restrict static 4], const _Decimal32*restrict xptr); void encodedecd64(unsigned char encptr[restrict static 8], const _Decimal64*restrict xptr); void encodedecd128(unsigned char encptr[restrict static 16], const _Decimal128*restrict xptr); #endif
Description The encodedecdN functions convert *xptr into an IEC 60559 decimalN encoding in the encoding scheme based on decimal encoding of the significand and store the resulting encoding as an N/8 element array, with 8 bits per array element, in the object pointed to by encptr. The order of bytes in the array follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). These functions preserve the value of *xptr and raise no floating-point exceptions. If *xptr is non-canonical, these functions may or may not produce a canonical encoding. Returns The encodedecdN functions return no value. 7.12.16.2 The decodedecdN functions Synopsis
1
#include <math.h> #ifdef __STDC_IEC_60559_DFP__ void decodedecd32(_Decimal32 * restrict xptr, const unsigned char encptr[restrict static 4]); void decodedecd64(_Decimal64 * restrict xptr, const unsigned char encptr[restrict static 8]); void decodedecd128(_Decimal128 * restrict xptr, const unsigned char encptr[restrict static 16]); #endif
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Description The decodedecdN functions interpret the N/8 element array pointed to by encptr as an IEC 60559 decimalN encoding, with 8 bits per array element, in the encoding scheme based on decimal encoding of the significand. The order of bytes in the array is implementation-defined. These functions convert the given encoding into a value of the decimal floating type, and store the result in the object pointed to by xptr. These functions preserve the encoded value and raise no floating-point exceptions. If the encoding is non-canonical, these functions may or may not produce a canonical representation. Returns The decodedecdN functions return no value. 7.12.16.3 The encodebindN functions Synopsis #include <math.h> #ifdef __STDC_IEC_60559_DFP__ void encodebind32(unsigned char encptr[restrict static 4], const _Decimal32 * restrict xptr); void encodebind64(unsigned char encptr[restrict static 8], const _Decimal64 * restrict xptr); void encodebind128(unsigned char encptr[restrict static 16], const _Decimal128 * restrict xptr); #endif
1
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Description The encodebindN functions convert *xptr into an IEC 60559 decimalN encoding in the encoding scheme based on binary encoding of the significand and store the resulting encoding as an N/8 element array, with 8 bits per array element, in the object pointed to by encptr. The order of bytes in the array follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). These functions preserve the value of *xptr and raise no floating-point exceptions. If *xptr is non-canonical, these functions may or may not produce a canonical encoding. Returns The encodebindN functions return no value. 7.12.16.4 The decodebindN functions Synopsis #include <math.h> #ifdef __STDC_IEC_60559_DFP__ void decodebind32(_Decimal32 * restrict xptr, const unsigned char encptr[restrict static 4]); void decodebind64(_Decimal64 * restrict xptr, const unsigned char encptr[restrict static 8]); void decodebind128(_Decimal128 * restrict xptr, const unsigned char encptr[restrict static 16]); #endif
1
2
Description The decodebindN functions interpret the N/8 element array pointed to by encptr as an IEC 60559 decimalN encoding, with 8 bits per array element, in the encoding scheme based on binary encoding of the significand. The order of bytes in the array follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). These functions convert the given encoding into a value of decimal floating type, and store the result in the object pointed to by xptr. These functions preserve the encoded value and raise no floating-point exceptions. If the encoding is non-canonical, these functions may or may not produce a canonical representation. 278
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Returns The decodebindN functions return no value.
7.12.17 1
ISO/IEC 9899:2023 (E)
Comparison macros
The relational and equality operators support the usual mathematical relationships between numeric values. For any ordered pair of numeric values exactly one of the relationships — less, greater, and equal — is true. Relational operators may raise the "invalid" floating-point exception when argument values are NaNs. For a NaN and a numeric value, or for two NaNs, just the unordered relationship is true.302) Subclauses 7.12.17.1 through 7.12.17.6 provide macros that are quiet versions of the relational operators: the macros do not raise the "invalid" floating-point exception as an effect of quiet NaN arguments. The comparison macros facilitate writing efficient code that accounts for quiet NaNs without suffering the "invalid" floating-point exception. In the synopses in this subclause, real-floating indicates that the argument shall be an expression of real floating type303) (both arguments need not have the same type).304) If either argument has decimal floating type, the other argument shall have decimal floating type as well. 7.12.17.1 The isgreater macro Synopsis
1
2
#include <math.h> int isgreater(real-floating x, real-floating y);
Description The isgreater macro determines whether its first argument is greater than its second argument. The value of isgreater(x,y) is always equal to (x)> (y). However, unlike (x)> (y), isgreater(x,y) does not raise the "invalid" floating-point exception when x and y are unordered and neither is a signaling NaN.
3
Returns The isgreater macro returns the value of (x)> (y). 7.12.17.2 The isgreaterequal macro Synopsis
1
2
#include <math.h> int isgreaterequal(real-floating x, real-floating y);
Description The isgreaterequal macro determines whether its first argument is greater than or equal to its second argument. The value of isgreaterequal(x,y) is always equal to (x)>= (y). However, unlike (x)>= (y), isgreaterequal(x,y) does not raise the "invalid" floating-point exception when x and y are unordered and neither is a signaling NaN.
3
Returns The isgreaterequal macro returns the value of (x)>= (y). 7.12.17.3 The isless macro Synopsis
1
#include <math.h> int isless(real-floating x, real-floating y); 302) IEC 60559 requires that the built-in relational operators raise the "invalid" floating-point exception if the operands compare unordered, as an error indicator for programs written without consideration of NaNs; the result in these cases is false. 303) If any argument is of integer type, or any other type that is not a real floating type, the behavior is undefined. 304) Whether an argument represented in a format wider than its semantic type is converted to the semantic type is unspecified.
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Description The isless macro determines whether its first argument is less than its second argument. The value of isless(x,y) is always equal to (x)< (y). However, unlike (x)< (y), isless(x,y) does not raise the "invalid" floating-point exception when x and y are unordered and neither is a signaling NaN.
3
Returns The isless macro returns the value of (x)< (y). 7.12.17.4 The islessequal macro Synopsis #include <math.h> int islessequal(real-floating x, real-floating y);
1
2
Description The islessequal macro determines whether its first argument is less than or equal to its second argument. The value of islessequal(x,y) is always equal to (x)<= (y). However, unlike (x)<= (y), islessequal(x,y) does not raise the "invalid" floating-point exception when x and y are unordered and neither is a signaling NaN.
3
Returns The islessequal macro returns the value of (x)<= (y). 7.12.17.5 The islessgreater macro Synopsis #include <math.h> int islessgreater(real-floating x, real-floating y);
1
2
Description The islessgreater macro determines whether its first argument is less than or greater than its second argument. The islessgreater(x,y) macro is similar to (x)< (y)|| (x)> (y). However, islessgreater(x,y) does not raise the "invalid" floating-point exception when x and y are unordered and neither is a signaling NaN (nor does it evaluate x and y twice).
3
Returns The islessgreater macro returns the value of (x)< (y)|| (x)> (y). 7.12.17.6 The isunordered macro Synopsis #include <math.h> int isunordered(real-floating x, real-floating y);
1
2
3
Description The isunordered macro determines whether its arguments are unordered. It raises no floating-point exceptions if neither argument is a signaling NaN. Returns The isunordered macro returns 1 if its arguments are unordered and 0 otherwise. 7.12.17.7 The iseqsig macro Synopsis #include <math.h>
1
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int iseqsig(real-floating x, real-floating y);
2
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Description The iseqsig macro determines whether its arguments are equal. If an argument is a NaN, a domain error occurs for the macro, as if a domain error occurred for a function (7.12.1). Returns The iseqsig macro returns 1 if its arguments are equal and 0 otherwise.
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Non-local jumps <setjmp.h>
1
The header <setjmp.h> defines the macros setjmp and __STDC_VERSION_SETJMP_H__, and declares one function and one type, for bypassing the normal function call and return discipline.305)
2
The macro __STDC_VERSION_SETJMP_H__
is an integer constant expression with a value equivalent to 202311L. 3
The type declared is jmp_buf
which is an array type suitable for holding the information needed to restore a calling environment. The environment of a call to the setjmp macro consists of information sufficient for a call to the longjmp function to return execution to the correct block and invocation of that block, were it called recursively. It does not include the state of the floating-point environment, of open files, or of any other component of the abstract machine. 4
It is unspecified whether setjmp is a macro or an identifier declared with external linkage. If a macro definition is suppressed to access an actual function, or a program defines an external identifier with the name setjmp, the behavior is undefined.
7.13.1
Save calling environment
7.13.1.1 The setjmp macro Synopsis #include <setjmp.h> int setjmp(jmp_buf env);
1
2
Description The setjmp macro saves its calling environment in its jmp_buf argument for later use by the longjmp function.
3
Returns If the return is from a direct invocation, the setjmp macro returns the value zero. If the return is from a call to the longjmp function, the setjmp macro returns a nonzero value.
4
Environmental limits An invocation of the setjmp macro shall appear only in one of the following contexts: — the entire controlling expression of a selection or iteration statement; — one operand of a relational or equality operator with the other operand an integer constant expression, with the resulting expression being the entire controlling expression of a selection or iteration statement; — the operand of a unary ! operator with the resulting expression being the entire controlling expression of a selection or iteration statement; or — the entire expression of an expression statement (possibly cast to void).
5
If the invocation appears in any other context, the behavior is undefined.
7.13.2
Restore calling environment
7.13.2.1
The longjmp function
305) These functions are useful for dealing with unusual conditions encountered in a low-level function of a program.
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Synopsis 1
2
3
4
5
#include <setjmp.h> [[noreturn]] void longjmp(jmp_buf env, int val);
Description The longjmp function restores the environment saved by the most recent invocation of the setjmp macro in the same invocation of the program with the corresponding jmp_buf argument. If there has been no such invocation, or if the invocation was from another thread of execution, or if the function containing the invocation of the setjmp macro has terminated execution306) in the interim, or if the invocation of the setjmp macro was within the scope of an identifier with variably modified type and execution has left that scope in the interim, the behavior is undefined. All accessible objects have values, and all other components of the abstract machine307) have state, as of the time the longjmp function was called, except that the representation of objects of automatic storage duration that are local to the function containing the invocation of the corresponding setjmp macro that do not have volatile-qualified type and have been changed between the setjmp invocation and longjmp call is indeterminate. Returns After longjmp is completed, thread execution continues as if the corresponding invocation of the setjmp macro had just returned the value specified by val. The longjmp function cannot cause the setjmp macro to return the value 0; if val is 0, the setjmp macro returns the value 1. EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation might cause memory associated with a variable length array object to be squandered. #include <setjmp.h> jmp_buf buf; void g(int n); void h(int n); int n = 6; void f(void) { int x[n]; setjmp(buf); g(n); } void g(int n) { int a[n]; h(n); } void h(int n) { int b[n]; longjmp(buf, 2); }
// valid:
f is not terminated
// a may remain allocated
// b may remain allocated // might cause memory loss
306) For example, by executing a return statement or because another longjmp call has caused a transfer to a setjmp
invocation in a function earlier in the set of nested calls. 307) This includes, but is not limited to, the floating-point environment and the state of open files.
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Signal handling <signal.h>
1
The header <signal.h> declares a type and two functions and defines several macros, for handling various signals (conditions that may be reported during program execution).
2
The type defined is sig_atomic_t
which is the (possibly volatile-qualified) integer type of an object that can be accessed as an atomic entity, even in the presence of asynchronous interrupts. 3
The macros defined are SIG_DFL SIG_ERR SIG_IGN
which expand to constant expressions with distinct values that have type compatible with the second argument to, and the return value of, the signal function, and whose values compare unequal to the address of any declarable function; and the following, which expand to positive integer constant expressions with type int and distinct values that are the signal numbers, each corresponding to the specified condition: SIGABRT abnormal termination, such as is initiated by the abort function SIGFPE
an erroneous arithmetic operation, such as zero divide or an operation resulting in overflow
SIGILL
detection of an invalid function image, such as an invalid instruction
SIGINT
receipt of an interactive attention signal
SIGSEGV an invalid access to storage SIGTERM a termination request sent to the program 4
An implementation need not generate any of these signals, except as a result of explicit calls to the raise function. Additional signals and pointers to undeclarable functions, with macro definitions beginning, respectively, with the letters SIG and an uppercase letter or with SIG_ and an uppercase letter,308) may also be specified by the implementation. The complete set of signals, their semantics, and their default handling is implementation-defined; all signal numbers shall be positive.
7.14.1
Specify signal handling
7.14.1.1 The signal function Synopsis #include <signal.h> void (*signal(int sig, void (*func)(int)))(int);
1
2
Description The signal function chooses one of three ways in which receipt of the signal number sig is to be subsequently handled. If the value of func is SIG_DFL, default handling for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored. Otherwise, func shall point to a function to be called when that signal occurs. An invocation of such a function because of a signal, or (recursively) of any further functions called by that invocation (other than functions in the standard library),309) is called a signal handler. 308) See "future library directions" (7.33.9). The names of the signal numbers reflect the following terms (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation, and termination. 309) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler called via the abort function).
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When a signal occurs and func points to a function, it is implementation-defined whether the equivalent of signal(sig, SIG_DFL); is executed or the implementation prevents some implementationdefined set of signals (at least including sig) from occurring until the current signal handling has completed; in the case of SIGILL, the implementation may alternatively define that no action is taken. Then the equivalent of (*func)(sig); is executed. If and when the function returns, if the value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined value corresponding to a computational exception, the behavior is undefined; otherwise the program will resume execution at the point it was interrupted.
4
If the signal occurs as the result of calling the abort or raise function, the signal handler shall not call the raise function.
5
If the signal occurs other than as the result of calling the abort or raise function, the behavior is undefined if the signal handler refers to any object with static or thread storage duration that is not a lock-free atomic object and that is not declared with the constexpr storage-class specifier other than by assigning a value to an object declared as volatile sig_atomic_t, or the signal handler calls any function in the standard library other than — the abort function, — the _Exit function, — the quick_exit function, — the functions in <stdatomic.h> (except where explicitly stated otherwise) when the atomic arguments are lock-free, — the atomic_is_lock_free function with any atomic argument, or — the signal function with the first argument equal to the signal number corresponding to the signal that caused the invocation of the handler. Furthermore, if such a call to the signal function results in a SIG_ERR return, the object designated by errno has an indeterminate representation.310)
6
At program startup, the equivalent of signal(sig, SIG_IGN);
may be executed for some signals selected in an implementation-defined manner; the equivalent of signal(sig, SIG_DFL);
is executed for all other signals defined by the implementation. 7
8
Use of this function in a multi-threaded program results in undefined behavior. The implementation shall behave as if no library function calls the signal function. Returns If the request can be honored, the signal function returns the value of func for the most recent successful call to signal for the specified signal sig. Otherwise, a value of SIG_ERR is returned and a positive value is stored in errno. Forward references: the abort function (7.24.4.1), the exit function (7.24.4.4), the _Exit function (7.24.4.5), the quick_exit function (7.24.4.7).
7.14.2
Send signal
7.14.2.1
The raise function
310) If any signal is generated by an asynchronous signal handler, the behavior is undefined.
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Synopsis #include <signal.h> int raise(int sig);
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Description The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a signal handler is called, the raise function shall not return until after the signal handler does. Returns The raise function returns zero if successful, nonzero if unsuccessful.
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Alignment <stdalign.h>
The header <stdalign.h> provides no content.
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Variable arguments <stdarg.h>
1
The header <stdarg.h> declares a type and defines five macros, for advancing through a list of arguments whose number and types are not known to the called function when it is translated.
2
The macro __STDC_VERSION_STDARG_H__
is an integer constant expression with a value equivalent to 202311L. 3
A function may be called with a variable number of arguments of varying types if its parameter type list ends with an ellipsis.
4
The type declared is va_list
which is a complete object type suitable for holding information needed by the macros va_start, va_arg, va_end, and va_copy. If access to the varying arguments is desired, the called function shall declare an object (generally referred to as ap in this subclause) having type va_list. The object ap may be passed as an argument to another function; if that function invokes the va_arg macro with parameter ap, the representation of ap in the calling function is indeterminate and shall be passed to the va_end macro prior to any further reference to ap311) .
7.16.1 1
Variable argument list access macros
The va_start and va_arg macros described in this subclause shall be implemented as macros, not functions. It is unspecified whether va_copy and va_end are macros or identifiers declared with external linkage. If a macro definition is suppressed to access an actual function, or a program defines an external identifier with the same name, the behavior is undefined. Each invocation of the va_start and va_copy macros shall be matched by a corresponding invocation of the va_end macro in the same function. 7.16.1.1 The va_arg macro Synopsis #include <stdarg.h> type va_arg(va_list ap, type);
1
2
Description The va_arg macro expands to an expression that has the specified type and the value of the next argument in the call. The parameter ap shall have been initialized by the va_start or va_copy macro (without an intervening invocation of the va_end macro for the same ap). Each invocation of the va_arg macro modifies ap so that the values of successive arguments are returned in turn. The behavior is undefined if there is no actual next argument. The parameter type shall be a type name specified such that the type of a pointer to an object that has the specified type can be obtained simply by postfixing a * to type. If type is not compatible with the type of the actual next argument (as promoted according to the default argument promotions), the behavior is undefined, except for the following cases: — both types are pointers to qualified or unqualified versions of compatible types; — one type is a signed integer type, the other type is the corresponding unsigned integer type, and the value is representable in both types; — one type is pointer to qualified or unqualified void and the other is a pointer to a qualified or unqualified character type; 311) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which case the original function can make further use of the original list after the other function returns.
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— or, the type of the next argument is nullptr_t and type is a pointer type that has the same representation and alignment requirements as a pointer to a character type.312)
3
Returns The first invocation of the va_arg macro after that of the va_start macro returns the value of the first argument without an explicit parameter, which matches the position of the ... in the parameter list. Successive invocations return the values of the remaining arguments in succession. 7.16.1.2 The va_copy macro Synopsis
1
2
3
#include <stdarg.h> void va_copy(va_list dest, va_list src);
Description The va_copy macro initializes dest as a copy of src, as if the va_start macro had been applied to dest followed by the same sequence of uses of the va_arg macro as had previously been used to reach the present state of src. Neither the va_copy nor va_start macro shall be invoked to reinitialize dest without an intervening invocation of the va_end macro for the same dest. Returns The va_copy macro returns no value. 7.16.1.3 The va_end macro Synopsis
1
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#include <stdarg.h> void va_end(va_list ap);
Description The va_end macro facilitates a normal return from the function whose variable argument list was referred to by the expansion of the va_start macro, or the function containing the expansion of the va_copy macro, that initialized the va_list ap. The va_end macro may modify ap so that it is no longer usable (without being reinitialized by the va_start or va_copy macro). If there is no corresponding invocation of the va_start or va_copy macro, or if the va_end macro is not invoked before the return, the behavior is undefined. Returns The va_end macro returns no value. 7.16.1.4 The va_start macro Synopsis
1
2
#include <stdarg.h> void va_start(va_list ap, ...);
Description The va_start macro shall be invoked before any access to the unnamed arguments.
3
The va_start macro initializes ap for subsequent use by the va_arg and va_end macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap without an intervening invocation of the va_end macro for the same ap.
4
Only the first argument passed to va_start is evaluated.
5
NOTE 1 The macro allows additional arguments to be passed for va_start for compatibility with older versions of the library only. 312) Such types are in particular pointers to qualified or unqualified versions of void.
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Returns The va_start macro returns no value. Recommended Practice Additional arguments beyond the first given to the va_start macro may be expanded and used in unspecified contexts where they are unevaluated. For example, an implementation diagnoses potentially erroneous input for a call to va_start such as: #include <stdarg.h> void miaou (...) { va_list vl; va_start(vl, 1, 3.0, "12", xd); // diagnostic encouraged /* ... */ va_end(vl); }
Simultaneously, va_start usage consistent with older revisions of this document should not produce a diagnostic: #include <stdarg.h> void neigh (int last_arg, ...) { va_list vl; va_start(vl, last_arg); // no diagnostic /* ... */ va_end(vl); } 8
EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of pointers is specified by the first argument to f1. #include <stdarg.h> #define MAXARGS 31 void f1(int n_ptrs, ...) { va_list ap; char *array[MAXARGS]; int ptr_no = 0; if (n_ptrs > MAXARGS) n_ptrs = MAXARGS; va_start(ap); while (ptr_no < n_ptrs) array[ptr_no++] = va_arg(ap, char *); _ va end(ap); f2(n_ptrs, array); }
Each call to f1 is required to have visible the definition of the function or a declaration such as void f1(int, ...); 9
EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list is gathered again and passed to function f4.
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#include <stdarg.h> #define MAXARGS 31 void f3(int n_ptrs, int f4_after, ...) { va_list ap, ap_save; char *array[MAXARGS]; int ptr_no = 0; if (n_ptrs > MAXARGS) n_ptrs = MAXARGS; _ va start(ap); while (ptr_no < n_ptrs) { array[ptr_no++] = va_arg(ap, char *); if (ptr_no == f4_after) va_copy(ap_save, ap); } va_end(ap); f2(n_ptrs, array); // Now process the saved copy. n_ptrs -= f4_after; ptr_no = 0; while (ptr_no < n_ptrs) array[ptr_no++] = va_arg(ap_save, char *); _ va end(ap_save); f4(n_ptrs, array); } 10
EXAMPLE 3 The function f5 is similar to f1, but instead of passing an explicit number of strings as the first argument, the argument list is terminated with a null pointer. #include <stdarg.h> #define MAXARGS 31 void f5(...) { va_list ap; char *array[MAXARGS]; int ptr_no = 0; va_start(ap); while (ptr_no < MAXARGS) { char *ptr = va_arg(ap, char *); if (!ptr) break; array[ptr_no++] = ptr; } va_end(ap); f6(ptr_no, array); }
Each call to f5 is required to have visible the definition of the function or a declaration such as void f5(...);
and implicitly requires the last argument to be a null pointer.
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7.17 Atomics <stdatomic.h> 7.17.1 Introduction 1
The header <stdatomic.h> defines several macros and declares several types and functions for performing atomic operations on data shared between threads.313)
2
Implementations that define the macro __STDC_NO_ATOMICS__ need not provide this header nor support any of its facilities.
3
The macro __STDC_VERSION_STDATOMIC_H__
is an integer constant expression with a value equivalent to 202311L. 4
The macros defined are the atomic lock-free macros ATOMIC_BOOL_LOCK_FREE ATOMIC_CHAR_LOCK_FREE ATOMIC_CHAR8_T_LOCK_FREE ATOMIC_CHAR16_T_LOCK_FREE ATOMIC_CHAR32_T_LOCK_FREE ATOMIC_WCHAR_T_LOCK_FREE ATOMIC_SHORT_LOCK_FREE ATOMIC_INT_LOCK_FREE ATOMIC_LONG_LOCK_FREE ATOMIC_LLONG_LOCK_FREE ATOMIC_POINTER_LOCK_FREE
which expand to constant expressions suitable for use in conditional expression inclusion preprocessing directives and which indicate the lock-free property of the corresponding atomic types (both signed and unsigned); and ATOMIC_FLAG_INIT
which expands to an initializer for an object of type atomic_flag. 5
The types include memory_order
which is an enumerated type whose enumerators identify memory ordering constraints; atomic_flag
which is a structure type representing a lock-free, primitive atomic flag; and several atomic analogs of integer types. 6
In the following synopses: — An A refers to an atomic type. — A C refers to its corresponding non-atomic type. — An M refers to the type of the other argument for arithmetic operations. For atomic integer types, M is C. For atomic pointer types, M is ptrdiff_t. — The functions not ending in _explicit have the same semantics as the corresponding _explicit function with memory_order_seq_cst for the memory_order argument. 313) See "future library directions" (7.33.10).
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It is unspecified whether any generic function declared in <stdatomic.h> is a macro or an identifier declared with external linkage. If a macro definition is suppressed to access an actual function, or a program defines an external identifier with the name of a generic function, the behavior is undefined.
8
NOTE 1 Many operations are volatile-qualified. The "volatile as device register" semantics have not changed in the standard. This qualification means that volatility is preserved when applying these operations to volatile objects.
7.17.2
Initialization
1
An atomic object with automatic storage duration that is not initialized or such an object with allocated storage duration initially has an indeterminate representation; equally, a non-atomic store to any byte of the representation (either directly or, for example, by calls to memcpy or memset) makes any atomic object have an indeterminate representation. Explicit, default initialization for atomic objects with static or thread storage duration that do not have the type atomic_flag is guaranteed to produce a valid state.314) .
2
Concurrent access to an atomic object before it is set to a valid state, even via an atomic operation, constitutes a data race. If a signal occurs other than as the result of calling the abort or raise functions, the behavior is undefined if the signal handler reads or modifies an atomic object that has an indeterminate representation.
3
EXAMPLE The following definition ensure valid states for guide and head regardless if these are found in file scope or block scope. Thus any atomic operation that is performed on them after their initialization has been met is well defined. _Atomic int guide = 42; static _Atomic(void*) head;
7.17.2.1 The atomic_init generic function Synopsis #include <stdatomic.h> void atomic_init(volatile A *obj, C value);
1
2
Description The atomic_init generic function initializes the atomic object pointed to by obj to the value value, while also initializing any additional state that the implementation might need to carry for the atomic object. If the object has no declared type, after the call the effective type is the atomic type A.
3
Although this function initializes an atomic object, it does not avoid data races; concurrent access to the object being initialized, even via an atomic operation, constitutes a data race.
4
If a signal occurs other than as the result of calling the abort or raise functions, the behavior is undefined if the signal handler calls the atomic_init generic function.
5
Returns The atomic_init generic function returns no value.
6
EXAMPLE atomic_int guide; atomic_init(&guide, 42);
7.17.3 1
Order and consistency
The enumerated type memory_order specifies the detailed regular (non-atomic) memory synchronization operations as defined in 5.1.2.4 and may provide for operation ordering. Its enumeration constants are as follows:315) 314) See "future library directions" (7.33.10). 315) See "future library directions" (7.33.10).
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memory_order_relaxed memory_order_consume memory_order_acquire memory_order_release memory_order_acq_rel memory_order_seq_cst 2
For memory_order_relaxed, no operation orders memory.
3
For memory_order_release, memory_order_acq_rel, and memory_order_seq_cst, a store operation performs a release operation on the affected memory location.
4
For memory_order_acquire, memory_order_acq_rel, and memory_order_seq_cst, a load operation performs an acquire operation on the affected memory location.
5
For memory_order_consume, a load operation performs a consume operation on the affected memory location.
6
There shall be a single total order S on all memory_order_seq_cst operations, consistent with the "happens before" order and modification orders for all affected locations, such that each memory_order_seq_cst operation B that loads a value from an atomic object M observes one of the following values: — the result of the last modification A of M that precedes B in S, if it exists, or — if A exists, the result of some modification of M that is not memory_order_seq_cst and that does not happen before A, or — if A does not exist, the result of some modification of M that is not memory_order_seq_cst.
7
NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to an order that does include lock and unlock operations, since the ordering between those is already included in the "happens before" ordering.
8
NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to memory ordering. Implementations still guarantee that any given atomic access to a particular atomic object is indivisible with respect to all other atomic accesses to that object.
9
For an atomic operation B that reads the value of an atomic object M , if there is a memory_order_seq_cst fence X sequenced before B, then B observes either the last memory_order_seq_cst modification of M preceding X in the total order S or a later modification of M in its modification order.
10
For atomic operations A and B on an atomic object M , where A modifies M and B takes its value, if there is a memory_order_seq_cst fence X such that A is sequenced before X and B follows X in S, then B observes either the effects of A or a later modification of M in its modification order.
11
For atomic modifications A and B of an atomic object M , B occurs later than A in the modification order of M if: — there is a memory_order_seq_cst fence X such that A is sequenced before X, and X precedes B in S, or — there is a memory_order_seq_cst fence Y such that Y is sequenced before B, and A precedes Y in S, or — there are memory_order_seq_cst fences X and Y such that A is sequenced before X, Y is sequenced before B, and X precedes Y in S.
12
Atomic read-modify-write operations shall always read the last value (in the modification order) stored before the write associated with the read-modify-write operation.
13
An atomic store shall only store a value that has been computed from constants and program input values by a finite sequence of program evaluations, such that each evaluation observes the stored values of the objects as computed by the last prior assignment in the sequence. The ordering of evaluations in this sequence shall be such that 294
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— If an evaluation B observes a value computed by A in a different thread, then B does not happen before A. — If an evaluation A is included in the sequence, then all evaluations that assign to the same object and happen before A are also included. 14
NOTE 3 The second requirement disallows "out-of-thin-air", or "speculative" stores of atomics when relaxed atomics are used. Since unordered operations are involved, evaluations can appear in this sequence out of thread order. For example, with x and y initially zero,
// Thread 1: r1 = atomic_load_explicit(&y, memory_order_relaxed); atomic_store_explicit(&x, r1, memory_order_relaxed); // Thread 2: r2 = atomic_load_explicit(&x, memory_order_relaxed); atomic_store_explicit(&y, 42, memory_order_relaxed); is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:
atomic_store_explicit(&y, 42, memory_order_relaxed); r1 = atomic_load_explicit(&y, memory_order_relaxed); atomic_store_explicit(&x, r1, memory_order_relaxed); r2 = atomic_load_explicit(&x, memory_order_relaxed); On the other hand,
// Thread 1: r1 = atomic_load_explicit(&y, memory_order_relaxed); atomic_store_explicit(&x, r1, memory_order_relaxed); // Thread 2: r2 = atomic_load_explicit(&x, memory_order_relaxed); atomic_store_explicit(&y, r2, memory_order_relaxed); is not allowed to produce r1 == 42 && r2 == 42, since there is no sequence of evaluations that results in the computation of 42. In the absence of "relaxed" operations and read-modify-write operations with weaker than memory_order_acq_rel ordering, the second requirement has no impact.
15
Recommended practice The requirements do not forbid r1 == 42 && r2 == 42 in the following example, with x and y initially zero: // Thread 1: r1 = atomic_load_explicit(&x, memory_order_relaxed); if (r1 == 42) atomic_store_explicit(&y, r1, memory_order_relaxed); // Thread 2: r2 = atomic_load_explicit(&y, memory_order_relaxed); if (r2 == 42) atomic_store_explicit(&x, 42, memory_order_relaxed);
However, this is not useful behavior, and implementations should not allow it. 16
Implementations should make atomic stores visible to atomic loads within a reasonable amount of time. 7.17.3.1 The kill_dependency macro Synopsis
1
#include <stdatomic.h> type kill_dependency(type y);
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Description The kill_dependency macro terminates a dependency chain; the argument does not carry a dependency to the return value. Returns The kill_dependency macro returns the value of y.
7.17.4
Fences
1
This subclause introduces synchronization primitives called fences. Fences can have acquire semantics, release semantics, or both. A fence with acquire semantics is called an acquire fence; a fence with release semantics is called a release fence.
2
A release fence A synchronizes with an acquire fence B if there exist atomic operations X and Y , both operating on some atomic object M , such that A is sequenced before X, X modifies M , Y is sequenced before B, and Y reads the value written by X or a value written by any side effect in the hypothetical release sequence X would head if it were a release operation.
3
A release fence A synchronizes with an atomic operation B that performs an acquire operation on an atomic object M if there exists an atomic operation X such that A is sequenced before X, X modifies M , and B reads the value written by X or a value written by any side effect in the hypothetical release sequence X would head if it were a release operation.
4
An atomic operation A that is a release operation on an atomic object M synchronizes with an acquire fence B if there exists some atomic operation X on M such that X is sequenced before B and reads the value written by A or a value written by any side effect in the release sequence headed by A. 7.17.4.1 The atomic_thread_fence function Synopsis #include <stdatomic.h> void atomic_thread_fence(memory_order order);
1
2
Description Depending on the value of order, this operation: — has no effects, if order == memory_order_relaxed; — is an acquire fence, if order == memory_order_acquire or order == memory_order_consume; — is a release fence, if order == memory_order_release; — is both an acquire fence and a release fence, if order == memory_order_acq_rel; — is a sequentially consistent acquire and release fence, if order == memory_order_seq_cst.
3
Returns The atomic_thread_fence function returns no value. 7.17.4.2 The atomic_signal_fence function Synopsis #include <stdatomic.h> void atomic_signal_fence(memory_order order);
1
2
Description Equivalent to atomic_thread_fence(order), except that the resulting ordering constraints are established only between a thread and a signal handler executed in the same thread. 296
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NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions performed by the thread become visible to the signal handler.
4
NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would have inserted are not emitted.
5
Returns The atomic_signal_fence function returns no value.
7.17.5 1
2
Lock-free property
The atomic lock-free macros indicate the lock-free property of integer and address atomic types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free. Recommended practice Operations that are lock-free should also be address-free. That is, atomic operations on the same memory location via two different addresses will communicate atomically. The implementation should not depend on any per-process state. This restriction enables communication via memory mapped into a process more than once and memory shared between two processes. 7.17.5.1 The atomic_is_lock_free generic function Synopsis #include <stdatomic.h> bool atomic_is_lock_free(const volatile A *obj);
1
2
3
Description The atomic_is_lock_free generic function indicates whether atomic operations on objects of the type pointed to by obj are lock-free. Returns The atomic_is_lock_free generic function returns nonzero (true) if and only if atomic operations on objects of the type pointed to by the argument are lock-free. In any given program execution, the result of the lock-free query shall be consistent for all pointers of the same type.316)
7.17.6 1
Atomic integer types
For each line in the following table,317) the atomic type name is declared as a type that has the same representation and alignment requirements as the corresponding direct type.318) Atomic type name
Direct type
atomic_bool atomic_char atomic_schar atomic_uchar atomic_short atomic_ushort atomic_int atomic_uint atomic_long atomic_ulong atomic_llong atomic_ullong atomic_char8_t
_Atomic bool _Atomic char _Atomic signed char _Atomic unsigned char _Atomic short _Atomic unsigned short _Atomic int _Atomic unsigned int _Atomic long _Atomic unsigned long _Atomic long long _Atomic unsigned long long _Atomic char8_t
316) obj can be a null pointer. 317) See "future library directions" (7.33.10). 318) The same representation and alignment requirements are meant to imply interchangeability as arguments to functions, return values from functions, and members of unions.
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Atomic type name
Direct type
atomic_char16_t atomic_char32_t atomic_wchar_t atomic_int_least8_t atomic_uint_least8_t atomic_int_least16_t atomic_uint_least16_t atomic_int_least32_t atomic_uint_least32_t atomic_int_least64_t atomic_uint_least64_t atomic_int_fast8_t atomic_uint_fast8_t atomic_int_fast16_t atomic_uint_fast16_t atomic_int_fast32_t atomic_uint_fast32_t atomic_int_fast64_t atomic_uint_fast64_t atomic_intptr_t atomic_uintptr_t atomic_size_t atomic_ptrdiff_t atomic_intmax_t atomic_uintmax_t
_Atomic char16_t _Atomic char32_t _Atomic wchar_t _Atomic int_least8_t _Atomic uint_least8_t _Atomic int_least16_t _Atomic uint_least16_t _Atomic int_least32_t _Atomic uint_least32_t _Atomic int_least64_t _Atomic uint_least64_t _Atomic int_fast8_t _Atomic uint_fast8_t _Atomic int_fast16_t _Atomic uint_fast16_t _Atomic int_fast32_t _Atomic uint_fast32_t _Atomic int_fast64_t _Atomic uint_fast64_t _Atomic intptr_t _Atomic uintptr_t _Atomic size_t _Atomic ptrdiff_t _Atomic intmax_t _Atomic uintmax_t
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Conversions to atomic_bool behave the same as conversions to bool. Recommended practice The representation of an atomic integer type is not required to have the same size as the corresponding regular type but it should have the same size whenever possible, as it eases effort required to port existing code.
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Operations on atomic types
There are only a few kinds of operations on atomic types, though there are many instances of those kinds. This subclause specifies each general kind. 7.17.7.1 The atomic_store generic functions Synopsis #include <stdatomic.h> void atomic_store(volatile A *object, C desired); void atomic_store_explicit(volatile A *object, C desired, memory_order order);
1
2
3
Description The order argument shall not be memory_order_acquire, memory_order_consume, nor memory_order_acq_rel. Atomically replace the value pointed to by object with the value of desired. Memory is affected according to the value of order. Returns The atomic_store generic functions return no value. 7.17.7.2 The atomic_load generic functions Synopsis #include <stdatomic.h>
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C atomic_load(const volatile A *object); C atomic_load_explicit(const volatile A *object, memory_order order);
2
3
Description The order argument shall not be memory_order_release nor memory_order_acq_rel. Memory is affected according to the value of order. Returns Atomically returns the value pointed to by object. 7.17.7.3 The atomic_exchange generic functions Synopsis
1
2
3
#include <stdatomic.h> C atomic_exchange(volatile A *object, C desired); C atomic_exchange_explicit(volatile A *object, C desired, memory_order order);
Description Atomically replace the value pointed to by object with desired. Memory is affected according to the value of order. These operations are read-modify-write operations (5.1.2.4). Returns Atomically returns the value pointed to by object immediately before the effects. 7.17.7.4 The atomic_compare_exchange generic functions Synopsis
1
2
#include <stdatomic.h> bool atomic_compare_exchange_strong(volatile A *object, C *expected, C desired); bool atomic_compare_exchange_strong_explicit(volatile A *object, C *expected, C desired, memory_order success, memory_order failure); bool atomic_compare_exchange_weak(volatile A *object, C *expected, C desired); bool atomic_compare_exchange_weak_explicit(volatile A *object, C *expected, C desired, memory_order success, memory_order failure);
Description The failure argument shall not be memory_order_release nor memory_order_acq_rel. The failure argument shall be no stronger than the success argument.
3
Atomically, compares the contents of the memory pointed to by object for equality with that pointed to by expected, and if true, replaces the contents of the memory pointed to by object with desired, and if false, updates the contents of the memory pointed to by expected with that pointed to by object. Further, if the comparison is true, memory is affected according to the value of success, and if the comparison is false, memory is affected according to the value of failure. These operations are atomic read-modify-write operations (5.1.2.4).
4
NOTE 1 For example, the effect of atomic_compare_exchange_strong is
if (memcmp(object, expected, sizeof(*object)) == 0) memcpy(object, &desired, sizeof(*object)); else memcpy(expected, object, sizeof(*object)); 5
A weak compare-and-exchange operation may fail spuriously. That is, even when the contents of memory referred to by expected and object are equal, it may return zero and store back to expected the same memory contents that were originally there.
6
NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of machines, e.g. load-locked store-conditional machines.
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EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will be in a loop. exp = atomic_load(&cur); do { des = function(exp); } while (!atomic_compare_exchange_weak(&cur, &exp, des));
When a compare-and-exchange is in a loop, the weak version will yield better performance on some platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the strong one is preferable.
8
1
Returns The result of the comparison. 7.17.7.5 The atomic_fetch and modify generic functions The following operations perform arithmetic and bitwise computations. All these operations are applicable to an object of any atomic integer type other than _Atomic bool or the atomic version of an enumeration with underlying type bool. The key, operator, and computation correspondence is: key op add + sub or | xor ^ and &
computation addition subtraction bitwise inclusive or bitwise exclusive or bitwise and
Synopsis #include <stdatomic.h> C atomic_fetch_key(volatile A *object, M operand); C atomic_fetch_key_explicit(volatile A *object, M operand, memory_order order);
2
3
4
Description Atomically replaces the value pointed to by object with the result of the computation applied to the value pointed to by object and the given operand. Memory is affected according to the value of order. These operations are atomic read-modify-write operations (5.1.2.4). For signed integer types, arithmetic performs silent wraparound on integer overflow; there are no undefined results. For address types, the result may be an undefined address, but the operations otherwise have no undefined behavior. Returns Atomically, the value pointed to by object immediately before the effects.
7.17.8
Atomic flag type and operations
1
The atomic_flag type provides the classic test-and-set functionality. It has two states, set and clear.
2
Operations on an object of type atomic_flag shall be lock free.
3
NOTE 1 Hence, as per 7.17.5, the operations should also be address-free. No other type requires lock-free operations, so the atomic_flag type is the minimum hardware-implemented type needed to conform to this document. The remaining types can be emulated with atomic_flag, though with less than ideal properties.
4
The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the clear state. An atomic_flag that is not explicitly initialized with ATOMIC_FLAG_INIT has initially an indeterminate representation.
5
EXAMPLE atomic_flag guard = ATOMIC_FLAG_INIT;
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7.17.8.1 The atomic_flag_test_and_set functions Synopsis 1
2
3
#include <stdatomic.h> bool atomic_flag_test_and_set(volatile atomic_flag *object); bool atomic_flag_test_and_set_explicit(volatile atomic_flag *object, memory_order order);
Description Atomically places the atomic flag pointed to by object in the set state and returns the value corresponding to the immediately preceding state. Memory is affected according to the value of order. These operations are atomic read-modify-write operations (5.1.2.4). Returns The atomic_flag_test_and_set functions return the value that corresponds to the state of the atomic flag immediately before the effects. The return value true corresponds to the set state and the return value false corresponds to the clear state. 7.17.8.2 The atomic_flag_clear functions Synopsis
1
2
3
#include <stdatomic.h> void atomic_flag_clear(volatile atomic_flag *object); void atomic_flag_clear_explicit(volatile atomic_flag *object, memory_order order);
Description The order argument shall not be memory_order_acquire nor memory_order_acq_rel. Atomically places the atomic flag pointed to by object into the clear state. Memory is affected according to the value of order. Returns The atomic_flag_clear functions return no value.
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7.18 Bit and byte utilities <stdbit.h> 7.18.1 General 1
The header <stdbit.h> defines the following macros, types, and functions, to work with the byte and bit representation of many types, typically integer types. This header makes available the size_t type name (7.21) and any uintN_t, intN_t, uint_leastN_t, or int_leastN_t type names defined by the implementation (7.22).
2
The macro __STDC_VERSION_STDBIT_H__
is an integer constant expression with a value equivalent to 202311L. 3
The most significant index is the 0-based index counting from the most significant bit, 0, to the least significant bit, w − 1, where w is the width of the type that is having its most significant index computed.
4
The least significant index is the 0-based index counting from the least significant bit, 0, to the most significant bit, w − 1, where w is the width of the type that is having its least significant index computed.
5
It is unspecified whether any generic function declared in <stdbit.h> is a macro or an identifier declared with external linkage. If a macro definition is suppressed to access an actual function, or a program defines an external identifier with the name of a generic function, the behavior is unspecified.
7.18.2
Endian
1
Two common methods of byte ordering in multi-byte scalar types are little-endian and big-endian. Little-endian is a format for storage or transmission of binary data in which the least significant byte is placed first, with the rest in ascending order. Or, that the least significant byte is stored at the smallest memory address. Big-endian is a format for storage or transmission of binary data in which the most significant byte is placed first, with the rest in descending order. Or, that the most significant byte is stored at the smallest memory address. Other byte orderings are also possible.
2
The macros are: __STDC_ENDIAN_LITTLE__
which represents a method of byte order storage in which the least significant byte is placed first and the rest are in ascending order, and is an integer constant expression; __STDC_ENDIAN_BIG__
which represents a method of byte order storage in which the most significant byte is placed first and the rest are in descending order, and is an integer constant expression; __STDC_ENDIAN_NATIVE__ /* see below */
which represents the method of byte order storage for the execution environment and is an integer constant expression. __STDC_ENDIAN_NATIVE__ describes the endianness of the execution environment with respect to bit-precise integer types, standard integer types, and extended integer types which do not have padding bits. 3
__STDC_ENDIAN_NATIVE__ shall expand to an integer constant expression whose value is equivalent to the value of __STDC_ENDIAN_LITTLE__ if the execution environment is littleendian. Otherwise, __STDC_ENDIAN_NATIVE__ shall expand to an integer constant expression whose value is equivalent to the value of __STDC_ENDIAN_BIG__ if the execution environment is big-endian. If the execution environment is neither little-endian nor big-endian, it then has some other implementation-defined byte order and the macro __STDC_ENDIAN_NATIVE__ shall expand to an integer constant expression whose value is different from the values of
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__STDC_ENDIAN_LITTLE__ and __STDC_ENDIAN_BIG__. The values of the integer constant expressions for __STDC_ENDIAN_LITTLE__ and __STDC_ENDIAN_BIG__ are not equal.
7.18.3
Count Leading Zeros
Synopsis #include <stdbit.h> unsigned int stdc_leading_zeros_uc(unsigned char value); unsigned int stdc_leading_zeros_us(unsigned short value); unsigned int stdc_leading_zeros_ui(unsigned int value); unsigned int stdc_leading_zeros_ul(unsigned long value); unsigned int stdc_leading_zeros_ull(unsigned long long value); generic_return_type stdc_leading_zeros(generic_value_type value);
1
2
Returns Returns the number of consecutive 0 bits in value, starting from the most significant bit. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.4
Count Leading Ones
Synopsis #include <stdbit.h> unsigned int stdc_leading_ones_uc(unsigned char value); unsigned int stdc_leading_ones_us(unsigned short value); unsigned int stdc_leading_ones_ui(unsigned int value); unsigned int stdc_leading_ones_ul(unsigned long value); unsigned int stdc_leading_ones_ull(unsigned long long value); generic_return_type stdc_leading_ones(generic_value_type value);
1
2
Returns Returns the number of consecutive 1 bits in value, starting from the most significant bit. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.5 § 7.18.5
Count Trailing Zeros Library
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Synopsis #include <stdbit.h> unsigned int stdc_trailing_zeros_uc(unsigned char value); unsigned int stdc_trailing_zeros_us(unsigned short value); unsigned int stdc_trailing_zeros_ui(unsigned int value); unsigned int stdc_trailing_zeros_ul(unsigned long value); unsigned int stdc_trailing_zeros_ull(unsigned long long value); generic_return_type stdc_trailing_zeros(generic_value_type value);
1
2
Returns Returns the number of consecutive 0 bits in value, starting from the least significant bit. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.6
Count Trailing Ones
Synopsis #include <stdbit.h> unsigned int stdc_trailing_ones_uc(unsigned char value); unsigned int stdc_trailing_ones_us(unsigned short value); unsigned int stdc_trailing_ones_ui(unsigned int value); unsigned int stdc_trailing_ones_ul(unsigned long value); unsigned int stdc_trailing_ones_ull(unsigned long long value); generic_return_type stdc_trailing_ones(generic_value_type value);
1
2
Returns Returns the number of consecutive 1 bits in value, starting from the least significant bit. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.7
First Leading Zero
Synopsis #include <stdbit.h> unsigned int stdc_first_leading_zero_uc(unsigned char value); unsigned int stdc_first_leading_zero_us(unsigned short value); unsigned int stdc_first_leading_zero_ui(unsigned int value);
1
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unsigned int stdc_first_leading_zero_ul(unsigned long value); unsigned int stdc_first_leading_zero_ull(unsigned long long value); generic_return_type stdc_first_leading_zero(generic_value_type value);
2
Returns Returns the most significant index of the first 0 bit in value, plus 1. If it is not found, this function returns 0. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.8
First Leading One
Synopsis #include <stdbit.h> unsigned int stdc_first_leading_one_uc(unsigned char value); unsigned int stdc_first_leading_one_us(unsigned short value); unsigned int stdc_first_leading_one_ui(unsigned int value); unsigned int stdc_first_leading_one_ul(unsigned long value); unsigned int stdc_first_leading_one_ull(unsigned long long value); generic_return_type stdc_first_leading_one(generic_value_type value);
1
2
Returns Returns the most significant index of the first 1 bit in value, plus 1. If it is not found, this function returns 0. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.9
First Trailing Zero
Synopsis #include <stdbit.h> unsigned int stdc_first_trailing_zero_uc(unsigned char value); unsigned int stdc_first_trailing_zero_us(unsigned short value); unsigned int stdc_first_trailing_zero_ui(unsigned int value); unsigned int stdc_first_trailing_zero_ul(unsigned long value); unsigned int stdc_first_trailing_zero_ull(unsigned long long value); generic_return_type stdc_first_trailing_zero(generic_value_type value);
1
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Returns Returns the least significant index of the first 0 bit in value, plus 1. If it is not found, this function returns 0. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.10
First Trailing One
Synopsis #include <stdbit.h> unsigned int stdc_first_trailing_one_uc(unsigned char value); unsigned int stdc_first_trailing_one_us(unsigned short value); unsigned int stdc_first_trailing_one_ui(unsigned int value); unsigned int stdc_first_trailing_one_ul(unsigned long value); unsigned int stdc_first_trailing_one_ull(unsigned long long value); generic_return_type stdc_first_trailing_one(generic_value_type value);
1
2
Returns Returns the least significant index of the first 1 bit in value, plus 1. If it is not found, this function returns 0. The type-generic function (marked by its generic_value_type argument) returns the appropriate value based on the type of the input value, so long as it is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.11
Count Zeros
Synopsis #include <stdbit.h> unsigned int stdc_count_zeros_uc(unsigned char value); unsigned int stdc_count_zeros_us(unsigned short value); unsigned int stdc_count_zeros_ui(unsigned int value); unsigned int stdc_count_zeros_ul(unsigned long value); unsigned int stdc_count_zeros_ull(unsigned long long value); generic_return_type stdc_count_zeros(generic_value_type value);
1
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Returns Returns the total number of 0 bits within the given value. The type-generic function (marked by its generic_value_type argument) returns the previously described result for a given input value so long as the generic_value_type is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.12
Count Ones
Synopsis #include <stdbit.h> unsigned int stdc_count_ones_uc(unsigned char value); unsigned int stdc_count_ones_us(unsigned short value); unsigned int stdc_count_ones_ui(unsigned int value); unsigned int stdc_count_ones_ul(unsigned long value); unsigned int stdc_count_ones_ull(unsigned long long value); generic_return_type stdc_count_ones(generic_value_type value);
1
2
Returns Returns the total number of 1 bits within the given value. The type-generic function (marked by its generic_value_type argument) returns the previously described result for a given input value so long as the generic_value_type is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.13
Single-bit Check
Synopsis 1
2
#include <stdbit.h> bool stdc_has_single_bit_uc(unsigned char value); bool stdc_has_single_bit_us(unsigned short value); bool stdc_has_single_bit_ui(unsigned int value); bool stdc_has_single_bit_ul(unsigned long value); bool stdc_has_single_bit_ull(unsigned long long value); bool stdc_has_single_bit(generic_value_type value);
Returns The stdc_has_single_bit functions return true if and only if there is a single 1 bit in value. The type-generic function (marked by its generic_value_type argument) returns the previously described result for a given input value so long as the generic_value_type is a: § 7.18.13
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— standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool.
7.18.14
Bit Width
Synopsis #include <stdbit.h> unsigned int stdc_bit_width_uc(unsigned char value); unsigned int stdc_bit_width_us(unsigned short value); unsigned int stdc_bit_width_ui(unsigned int value); unsigned int stdc_bit_width_ul(unsigned long value); unsigned int stdc_bit_width_ull(unsigned long long value); generic_return_type stdc_bit_width(generic_value_type value);
1
2
Description The stdc_bit_width functions compute the smallest number of bits needed to store value.
3
Returns The stdc_bit_width functions return 0 if value is 0. Otherwise, they return 1 + ⌊log2 (value)⌋. The type-generic function (marked by its generic_value_type argument) returns the previously described result for a given input value so long as the generic_value_type is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool. The generic_return_type type shall be a suitable large unsigned integer type capable of representing the computed result.
7.18.15
Bit Floor
Synopsis #include <stdbit.h> unsigned char stdc_bit_floor_uc(unsigned char value); unsigned short stdc_bit_floor_us(unsigned short value); unsigned int stdc_bit_floor_ui(unsigned int value); unsigned long stdc_bit_floor_ul(unsigned long value); unsigned long long stdc_bit_floor_ull(unsigned long long value); generic_value_type stdc_bit_floor(generic_value_type value);
1
2
Description The stdc_bit_floor functions compute the largest integral power of 2 that is not greater than value.
3
Returns The stdc_bit_floor functions return 0 if value is 0. Otherwise, they return the largest integral power of 2 that is not greater than value. The type-generic function (marked by its generic_value_type argument) returns the previously described result for a given input value so long as the generic_value_type is a: 308
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— standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool.
7.18.16
Bit Ceiling
Synopsis 1
2
3
#include <stdbit.h> unsigned char stdc_bit_ceil_uc(unsigned char value); unsigned short stdc_bit_ceil_us(unsigned short value); unsigned int stdc_bit_ceil_ui(unsigned int value); unsigned long stdc_bit_ceil_ul(unsigned long value); unsigned long long stdc_bit_ceil_ull(unsigned long long value); generic_value_type stdc_bit_ceil(generic_value_type value);
Description The stdc_bit_ceil functions compute the smallest integral power of 2 that is not less than value. If the computation does not fit in the given return type, the behavior is undefined. Returns The stdc_bit_ceil functions return the smallest integral power of 2 that is not less than value. The type-generic function (marked by its generic_value_type argument) returns the previously described result for a given input value so long as the generic_value_type is a: — standard unsigned integer type, excluding bool; — extended unsigned integer type; — or, bit-precise unsigned integer type whose width matches a standard or extended integer type, excluding bool.
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Boolean type and values <stdbool.h>
The header <stdbool.h> provides the obsolescent macro __bool_true_false_are_defined which expands to the integer constant 1.
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Checked Integer Arithmetic <stdckdint.h>
1
The header <stdckdint.h> defines several macros for performing checked integer arithmetic.
2
The macro __STDC_VERSION_STDCKDINT_H__
is an integer constant expression with a value equivalent to 202311L.
The ckd_ Checked Integer Operation Macros
7.20.1 Synopsis
#include <stdckdint.h> bool ckd_add(type1 *result, type2 a, type3 b); bool ckd_sub(type1 *result, type2 a, type3 b); bool ckd_mul(type1 *result, type2 a, type3 b);
1
2
3
4
5
6
Description These macros perform addition, subtraction, or multiplication of the mathematical values of a and b, storing the result of the operation in *result, (that is, *result is assigned the result of computing a + b, a - b, or a * b). Each operation is performed as if both operands were represented in a signed integer type with infinite range, and the result was then converted from this integer type to type1. Both type2 and type3 shall be any integer type other than "plain" char, bool, a bit-precise integer type, or an enumerated type, and they need not be the same. *result shall be a modifiable lvalue of any integer type other than "plain" char, bool, a bit-precise integer type, or an enumerated type. Recommended practice It is recommended to produce a diagnostic message if type2 or type3 are not suitable integer types, or if *result is not a modifiable lvalue of a suitable integer type. Returns If these macros return false, the value assigned to *result correctly represents the mathematical result of the operation. Otherwise, these macros return true. In this case, the value assigned to *result is the mathematical result of the operation wrapped around to the width of *result. EXAMPLE 1 If a and b are values of type signed int, and result is a signed long, then ckd_sub(&result, a, b);
will indicate if a - b can be expressed as a signed long. If signed long has a greater width than signed int, this will always be possible and this macro will return false.
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Common definitions <stddef.h>
1
The header <stddef.h> defines the following macros and declares the following types. Some are also defined in other headers, as noted in their respective subclauses.
2
The macro __STDC_VERSION_STDDEF_H__
is an integer constant expression with a value equivalent to 202311L. 3
The types are ptrdiff_t
which is the signed integer type of the result of subtracting two pointers; size_t
which is the unsigned integer type of the result of the sizeof operator; max_align_t
which is an object type whose alignment is the greatest fundamental alignment; wchar_t
which is an integer type whose range of values can represent distinct codes for all members of the largest extended character set specified among the supported locales; the null character shall have the code value zero. Each member of the basic character set shall have a code value equal to its value when used as the lone character in an integer character constant if an implementation does not define __STDC_MB_MIGHT_NEQ_WC__; and, nullptr_t
which is the type of the nullptr predefined constant, see below. 4
The macros are NULL
which expands to an implementation-defined null pointer constant; unreachable()
which expands to a void expression that invokes undefined behavior if it is reached during execution; and offsetof(type, member-designator)
which expands to an integer constant expression that has type size_t, the value of which is the offset in bytes, to the subobject (designated by member-designator), from the beginning of any object of type type. The type and member designator shall be such that given static type t;
then the expression &(t. member-designator) evaluates to an address constant. If the specified type defines a new type or if the specified member is a bit-field, the behavior is undefined. 312
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Recommended practice The types used for size_t and ptrdiff_t should not have an integer conversion rank greater than that of signed long int unless the implementation supports objects large enough to make this necessary.
7.21.1
The unreachable macro
Synopsis #include <stddef.h> void unreachable(void);
1
2
3 4
Description A call to the function-like macro unreachable indicates that the particular flow control that leads to the call will never be taken; it receives no arguments and expands to a void expression. The program execution shall not reach such a call. Returns If a macro call unreachable() is reached during execution, the behavior is undefined. EXAMPLE 1 The following program assumes that each execution is provided with at least one command line argument. The behavior of an execution with no arguments is undefined. #include <stddef.h> #include <stdio.h> int main (int argc, char* argv[static argc + 1]) { if (argc <= 2) unreachable(); else return printf("%s: we see %s", argv[0], argv[1]); return puts("this should never be reached"); }
Here, the static array size expression and the annotation of the control flow with unreachable indicates that the pointed-to parameter array argv will hold at least three elements, regardless of the circumstances. A possible optimization is that the resulting executable never performs the comparison and unconditionally executes a tail call to printf that never returns to the main function. In particular, the entire call and reference to puts can be omitted from the executable. No diagnostic is expected.
The nullptr_t type
7.21.2 Synopsis
#include <stddef.h> typedef typeof_unqual(nullptr) nullptr_t;
1
2
3
Description The nullptr_t type is the type of the nullptr predefined constant. It has only a very limited use in contexts where this type is needed to distinguish nullptr from other expression types. It is an unqualified complete scalar type that is different from all pointer or arithmetic types and is neither an atomic or array type and has exactly one value, nullptr. Default or empty initialization of an object of this type is equivalent to an initialization by nullptr. The size and alignment of nullptr_t is the same as for a pointer to character type. An object representation of the value nullptr is the same as the object representation of a null pointer value of type void*. An lvalue conversion of an object of type nullptr_t with such an object representation § 7.21.2
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has the value nullptr; if the object representation is different, the behavior is undefined319) . 4
NOTE Because it is considered to be a scalar type, nullptr_t may appear in many context where (void*)0 would be valid, for example, — as the operand of alignas, sizeof or typeof operators, — as the operand of an implicit or explicit conversion to a pointer type, — as the assignment expression in an assignment or initialization of an object of type nullptr_t, — as an argument to a parameter of type nullptr_t or in a variable argument list, — as a void expression, — as the operand of an implicit or explicit conversion to bool, — as an operand of a _Generic primary expression, — as an operand of the !, &&, || or conditional operators, or — as the controlling expression of an if or iteration statement.
319) Thus, during the whole program execution an object of type nullptr_t evaluates to the assumed value nullptr.
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Integer types <stdint.h>
1
The header <stdint.h> declares sets of integer types having specified widths, and defines corresponding sets of macros.320) It also defines macros that specify limits of integer types corresponding to types defined in other standard headers.
2
Types are defined in the following categories: — integer types having certain exact widths; — integer types having at least certain specified widths; — fastest integer types having at least certain specified widths; — integer types wide enough to hold pointers to objects; — integer types having greatest width. (Some of these types may denote the same type.)
3
Corresponding macros specify limits of the declared types and construct suitable constants.
4
For each type described herein that the implementation provides,321) <stdint.h> shall declare that typedef name and define the associated macros. Conversely, for each type described herein that the implementation does not provide, <stdint.h> shall not declare that typedef name nor shall it define the associated macros. An implementation shall provide those types described as "required", but need not provide any of the others (described as "optional"). None of the types shall be defined as a synonym for a bit-precise integer type.
5
The feature test macro __STDC_VERSION_STDINT_H__ expands to the token 202311L.
7.22.1
Integer types
1
When typedef names differing only in the absence or presence of the initial u are defined, they shall denote corresponding signed and unsigned types as described in 6.2.5; an implementation providing one of these corresponding types shall also provide the other.
2
In the following descriptions, the symbol N represents an unsigned decimal integer with no leading zeros (e.g., 8 or 24, but not 04 or 048).
1
7.22.1.1 Exact-width integer types The typedef name intN_t designates a signed integer type with width N and no padding bits. Thus, int8_t denotes such a signed integer type with a width of exactly 8 bits.
2
The typedef name uintN_t designates an unsigned integer type with width N and no padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of exactly 24 bits.
3
If an implementation provides standard or extended integer types with a particular width and no padding bits, it shall define the corresponding typedef names.
1
7.22.1.2 Minimum-width integer types The typedef name int_leastN_t designates a signed integer type with a width of at least N, such that no signed integer type with lesser size has at least the specified width. Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
2
The typedef name uint_leastN_t designates an unsigned integer type with a width of at least N, such that no unsigned integer type with lesser size has at least the specified width. Thus, uint_least16_t denotes an unsigned integer type with a width of at least 16 bits.
3
If the typedef name intN_t is defined, int_leastN_t designates the same type. If the typedef name uintN_t is defined, uint_leastN_t designates the same type.
4
The following types are required: 320) See "future library directions" (7.33.14). 321) Some of these types might denote implementation-defined extended integer types.
§ 7.22.1.2
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int_least8_t int_least16_t int_least32_t int_least64_t
N3096
uint_least8_t uint_least16_t uint_least32_t uint_least64_t
All other types of this form are optional. 7.22.1.3
Fastest minimum-width integer types
1
Each of the following types designates an integer type that is usually fastest322) to operate with among all integer types that have at least the specified width.
2
The typedef name int_fastN_t designates the fastest signed integer type with a width of at least N. The typedef name uint_fastN_t designates the fastest unsigned integer type with a width of at least N.
3
The following types are required: int_fast8_t int_fast16_t int_fast32_t int_fast64_t
uint_fast8_t uint_fast16_t uint_fast32_t uint_fast64_t
All other types of this form are optional.
1
7.22.1.4 Integer types capable of holding object pointers The following type designates a signed integer type, other than a bit-precise integer type, with the property that any valid pointer to void can be converted to this type, then converted back to pointer to void, and the result will compare equal to the original pointer: intptr_t
The following type designates an unsigned integer type, other than a bit-precise integer type, with the property that any valid pointer to void can be converted to this type, then converted back to pointer to void, and the result will compare equal to the original pointer: uintptr_t
These types are optional.
1
7.22.1.5 Greatest-width integer types The following type designates a signed integer type, other than a bit-precise integer type, capable of representing any value of any signed integer type with the possible exceptions of signed bit-precise integer types and of signed extended integer types that are wider than long long and that are referred by the type definition for an exact width integer type: intmax_t
The following type designates the unsigned integer type that corresponds to intmax_t323) : uintmax_t
These types are required. 322) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear grounds for choosing one type over another, it will simply pick some integer type satisfying the signedness and width requirements. 323) Thus this type is capable of representing any value of any unsigned integer type with the possible exception of bit-precise integer types and particular extended integer types that are wider than unsigned long long.
316
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Widths of specified-width integer types
1
The following object-like macros specify the width of the types declared in <stdint.h>. Each macro name corresponds to a similar type name in 7.22.1.
2
Each instance of any defined macro shall be replaced by a constant expression suitable for use in #if preprocessing directives. Its implementation-defined value shall be equal to or greater than the value given below, except where stated to be exactly the given value. An implementation shall define only the macros corresponding to those typedef names it actually provides.324) 7.22.2.1
1
INTN_WIDTH UINTN_WIDTH
7.22.2.2 1
1
1
exactly UINTPTR_WIDTH 16
Width of greatest-width integer types
INTMAX_WIDTH UINTMAX_WIDTH
7.22.3
exactly UINT_FASTN_WIDTH N
Width of integer types capable of holding object pointers
INTPTR_WIDTH UINTPTR_WIDTH
7.22.2.5
exactly UINT_LEASTN_WIDTH N
Width of fastest minimum-width integer types
INT_FASTN_WIDTH UINT_FASTN_WIDTH
7.22.2.4
exactly N exactly N
Width of minimum-width integer types
INT_LEASTN_WIDTH UINT_LEASTN_WIDTH
7.22.2.3 1
Width of exact-width integer types
exactly UINTMAX_WIDTH 64
Width of other integer types
1
The following object-like macros specify the width of integer types corresponding to types defined in other standard headers.
2
Each instance of these macros shall be replaced by a constant expression suitable for use in #if preprocessing directives. Its implementation-defined value shall be equal to or greater than the corresponding value given below. An implementation shall define only the macros corresponding to those typedef names it actually provides.325) 7.22.3.1
1
PTRDIFF_WIDTH
7.22.3.2 1
Width of ptrdiff_t 16
Width of sig_atomic_t
SIG_ATOMIC_WIDTH
8
324) The exact-width and pointer-holding integer types are optional. 325) A freestanding implementation need not provide all these types.
§ 7.22.3.2
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7.22.3.3 1
1
1
8
Width of wint_t
WINT_WIDTH
7.22.4
16
Width of wchar_t
WCHAR_WIDTH
7.22.3.5
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Width of size_t
SIZE_WIDTH
7.22.3.4
working draft — April 1, 2023
16
Macros for integer constants
1
The following function-like macros expand to integer constants suitable for initializing objects that have integer types corresponding to types defined in <stdint.h>. Each macro name corresponds to a similar type name in 7.22.1.2 or 7.22.1.5.
2
The argument in any instance of these macros shall be an unsuffixed integer constant (as defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
3
Each invocation of one of these macros shall expand to an integer constant expression. The type of the expression shall have the same type as would an expression of the corresponding type converted according to the integer promotions. The value of the expression shall be that of the argument. If the value is in the range of the type intmax_t (for a signed type) or the type uintmax_t (for an unsigned type), see 7.22.1.5, the expression is suitable for use in conditional expression inclusion preprocessing directives.
1
1
7.22.4.1 Macros for minimum-width integer constants The macro INTN_C( value) expands to an integer constant expression corresponding to the type int_leastN_t. The macro UINTN_C( value) expands to an integer constant expression corresponding to the type uint_leastN_t . For example, if uint_least64_t is a name for the type unsigned long long int, then UINT64_C(0x123) might expand to the integer constant 0x123ULL. 7.22.4.2 Macros for greatest-width integer constants The following macro expands to an integer constant expression having the value specified by its argument and the type intmax_t: INTMAX_C(value)
The following macro expands to an integer constant expression having the value specified by its argument and the type uintmax_t: UINTMAX_C(value)
7.22.5 1
Maximal and minimal values of integer types
For all integer types for which there is a macro with suffix _WIDTH holding the width, maximum macros with suffix _MAX and, for all signed types, minimum macros with suffix _MIN are defined as by 5.2.4.2. If it is unspecified if a type is signed or unsigned and the implementation has it as an unsigned type, a minimum macro with extension _MIN and value 0 of the corresponding type, according to the integer promotions, is defined.
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7.23 Input/output <stdio.h> 7.23.1 Introduction 1
The header <stdio.h> defines several macros, and declares three types and many functions for performing input and output.
2
The macro __STDC_VERSION_STDIO_H__
is an integer constant expression with a value equivalent to 202311L. 3
The types declared are size_t (described in 7.21); FILE
which is an object type capable of recording all the information needed to control a stream, including its file position indicator, a pointer to its associated buffer (if any), an error indicator that records whether a read/write error has occurred, and an end-of-file indicator that records whether the end of the file has been reached; and fpos_t
which is a complete object type other than an array type capable of recording all the information needed to specify uniquely every position within a file. 4
The macros are NULL (described in 7.21); _IOFBF _IOLBF _IONBF
which expand to integer constant expressions with distinct values, suitable for use as the third argument to the setvbuf function; BUFSIZ
which expands to an integer constant expression that is the size of the buffer used by the setbuf function; EOF
which expands to an integer constant expression, with type int and a negative value, that is returned by several functions to indicate end-of-file, that is, no more input from a stream; FOPEN_MAX
which expands to an integer constant expression that is the minimum number of files that the implementation guarantees can be open simultaneously; FILENAME_MAX
which expands to an integer constant expression that is the size needed for an array of char large enough to hold the longest file name string that the implementation guarantees can be opened or, if the implementation imposes no practical limit on the length of file name strings, the recommended size of an array intended to hold a file name string326) ; 326) Of course, file name string contents are subject to other system-specific constraints; therefore all possible strings of length
FILENAME_MAX cannot be expected to be opened successfully.
§ 7.23.1
Library
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_PRINTF_NAN_LEN_MAX
which expands to an integer constant expression (suitable for use in conditional expression inclusion preprocessing directives) that is the maximum number of characters output for any [-]NAN(n-char-sequence) sequence.327) If an implementation has no support for NaNs, it shall be 0. _PRINTF_NAN_LEN_MAX shall be less than 64; L_tmpnam
which expands to an integer constant expression that is the size needed for an array of char large enough to hold a temporary file name string generated by the tmpnam function; SEEK_CUR SEEK_END SEEK_SET
which expand to integer constant expressions with distinct values, suitable for use as the third argument to the fseek function; TMP_MAX
which expands to an integer constant expression that is the minimum number of unique file names that can be generated by the tmpnam function; stderr stdin stdout
which are expressions of type "pointer to FILE" that point to the FILE objects associated, respectively, with the standard error, input, and output streams. 5
The header <wchar.h> declares functions for wide character input and output. The wide character input/output functions described in that subclause provide operations analogous to most of those described here, except that the fundamental units internal to the program are wide characters. The external representation (in the file) is a sequence of generalized multibyte characters, as described further in 7.23.3.
6
The input/output functions are given the following collective terms: — The wide character input functions — those functions described in 7.31 that perform input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar, fwscanf, wscanf, vfwscanf, and vwscanf. — The wide character output functions — those functions described in 7.31 that perform output from wide characters and wide strings: fputwc, fputws, putwc, putwchar, fwprintf, wprintf, vfwprintf, and vwprintf. — The wide character input/output functions — the union of the ungetwc function, the wide character input functions, and the wide character output functions. — The byte input/output functions — those functions described in this subclause that perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread, fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf, ungetc, vfprintf, vfscanf, vprintf, and vscanf. Forward references: files (7.23.3), the fseek function (7.23.9.2), streams (7.23.2), the tmpnam function (7.23.4.4), <wchar.h> (7.31). 327) If the implementation only uses the [-]NAN style, then _PRINTF_NAN_LEN_MAX would have the value 4.
320
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§ 7.23.1
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Streams
1
Input and output, whether to or from physical devices such as terminals and tape drives, or whether to or from files supported on structured storage devices, are mapped into logical data streams, whose properties are more uniform than their various inputs and outputs. Two forms of mapping are supported, for text streams and for binary streams.328)
2
A text stream is an ordered sequence of characters composed into lines, each line consisting of zero or more characters plus a terminating new-line character. Whether the last line requires a terminating new-line character is implementation-defined. Characters may have to be added, altered, or deleted on input and output to conform to differing conventions for representing text in the host environment. Thus, there need not be a one-to-one correspondence between the characters in a stream and those in the external representation. Data read in from a text stream will necessarily compare equal to the data that were earlier written out to that stream only if: the data consist only of printing characters and the control characters horizontal tab and new-line; no new-line character is immediately preceded by space characters; and the last character is a new-line character. Whether space characters that are written out immediately before a new-line character appear when read in is implementation-defined.
3
A binary stream is an ordered sequence of characters that can transparently record internal data. Data read in from a binary stream shall compare equal to the data that were earlier written out to that stream, under the same implementation. Such a stream may, however, have an implementationdefined number of null characters appended to the end of the stream.
4
Each stream has an orientation. After a stream is associated with an external file, but before any operations are performed on it, the stream is unoriented. Once a wide character input/output function has been applied to an unoriented stream, the stream becomes a wide-oriented stream. Similarly, once a byte input/output function has been applied to an unoriented stream, the stream becomes a byte-oriented stream. Only a call to the freopen function or the fwide function can otherwise alter the orientation of a stream. (A successful call to freopen removes any orientation.)329)
5
Byte input/output functions shall not be applied to a wide-oriented stream and wide character input/output functions shall not be applied to a byte-oriented stream. The remaining stream operations do not affect, and are not affected by, a stream’s orientation, except for the following additional restrictions: — Binary wide-oriented streams have the file-positioning restrictions ascribed to both text and binary streams. — For wide-oriented streams, after a successful call to a file-positioning function that leaves the file position indicator prior to the end-of-file, a wide character output function can overwrite a partial multibyte character; any file contents beyond the byte(s) written may henceforth not consist of valid multibyte characters.
6
Each wide-oriented stream has an associated mbstate_t object that stores the current parse state of the stream. A successful call to fgetpos stores a representation of the value of this mbstate_t object as part of the value of the fpos_t object. A later successful call to fsetpos using the same stored fpos_t value restores the value of the associated mbstate_t object as well as the position within the controlled stream.
7
Each stream has an associated lock that is used to prevent data races when multiple threads of execution access a stream, and to restrict the interleaving of stream operations performed by multiple threads. Only one thread may hold this lock at a time. The lock is reentrant: a single thread may hold the lock multiple times at a given time.
8
All functions that read, write, position, or query the position of a stream lock the stream before accessing it. They release the lock associated with the stream when the access is complete. 328) An implementation need not distinguish between text streams and binary streams. In such an implementation, there
need be no new-line characters in a text stream nor any limit to the length of a line. 329) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.
§ 7.23.2
Library
321
ISO/IEC 9899:2023 (E)
9
working draft — April 1, 2023
N3096
Environmental limits An implementation shall support text files with lines containing at least 254 characters, including the terminating new-line character. The value of the macro BUFSIZ shall be at least 256. Forward references: the freopen function (7.23.5.4), the fwide function (7.31.3.5), mbstate_t (7.31.1), the fgetpos function (7.23.9.1), the fsetpos function (7.23.9.3).
7.23.3
Files
1
A stream is associated with an external file (which may be a physical device) by opening a file, which may involve creating a new file. Creating an existing file causes its former contents to be discarded, if necessary. If a file can support positioning requests (such as a disk file, as opposed to a terminal), then a file position indicator associated with the stream is positioned at the start (character number zero) of the file, unless the file is opened with append mode in which case it is implementationdefined whether the file position indicator is initially positioned at the beginning or the end of the file. The file position indicator is maintained by subsequent reads, writes, and positioning requests, to facilitate an orderly progression through the file.
2
Binary files are not truncated, except as defined in 7.23.5.3. Whether a write on a text stream causes the associated file to be truncated beyond that point is implementation-defined.
3
When a stream is unbuffered, characters are intended to appear from the source or at the destination as soon as possible. Otherwise characters may be accumulated and transmitted to or from the host environment as a block. When a stream is fully buffered, characters are intended to be transmitted to or from the host environment as a block when a buffer is filled. When a stream is line buffered, characters are intended to be transmitted to or from the host environment as a block when a new-line character is encountered. Furthermore, characters are intended to be transmitted as a block to the host environment when a buffer is filled, when input is requested on an unbuffered stream, or when input is requested on a line buffered stream that requires the transmission of characters from the host environment. Support for these characteristics is implementation-defined, and may be affected via the setbuf and setvbuf functions.
4
A file may be disassociated from a controlling stream by closing the file. Output streams are flushed (any unwritten buffer contents are transmitted to the host environment) before the stream is disassociated from the file. The lifetime of a FILE object ends when the associated file is closed (including the standard text streams). Whether a file of zero length (on which no characters have been written by an output stream) actually exists is implementation-defined.
5
The file may be subsequently reopened, by the same or another program execution, and its contents reclaimed or modified (if it can be repositioned at its start). If the main function returns to its original caller, or if the exit function is called, all open files are closed (hence all output streams are flushed) before program termination. Other paths to program termination, such as calling the abort function, need not close all files properly.
6
The address of the FILE object used to control a stream may be significant; a copy of a FILE object need not serve in place of the original.
7
At program startup, three text streams are predefined and need not be opened explicitly — standard input (for reading conventional input), standard output (for writing conventional output), and standard error (for writing diagnostic output). As initially opened, the standard error stream is not fully buffered; the standard input and standard output streams are fully buffered if and only if the stream can be determined not to refer to an interactive device.
8
Functions that open additional (nontemporary) files require a file name, which is a string. The rules for composing valid file names are implementation-defined. Whether the same file can be simultaneously open multiple times is also implementation-defined.
9
Although both text and binary wide-oriented streams are conceptually sequences of wide characters, the external file associated with a wide-oriented stream is a sequence of multibyte characters, generalized as follows: — Multibyte encodings within files may contain embedded null bytes (unlike multibyte encodings valid for use internal to the program). 322
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— A file need not begin nor end in the initial shift state.330) 10
Moreover, the encodings used for multibyte characters may differ among files. Both the nature and choice of such encodings are implementation-defined.
11
The wide character input functions read multibyte characters from the stream and convert them to wide characters as if they were read by successive calls to the fgetwc function. Each conversion occurs as if by a call to the mbrtowc function, with the conversion state described by the stream’s own mbstate_t object. The byte input functions read characters from the stream as if by successive calls to the fgetc function.
12
The wide character output functions convert wide characters to multibyte characters and write them to the stream as if they were written by successive calls to the fputwc function. Each conversion occurs as if by a call to the wcrtomb function, with the conversion state described by the stream’s own mbstate_t object. The byte output functions write characters to the stream as if by successive calls to the fputc function.
13
In some cases, some of the byte input/output functions also perform conversions between multibyte characters and wide characters. These conversions also occur as if by calls to the mbrtowc and wcrtomb functions.
14
An encoding error occurs if the character sequence presented to the underlying mbrtowc function does not form a valid (generalized) multibyte character, or if the code value passed to the underlying wcrtomb does not correspond to a valid (generalized) multibyte character. The wide character input/output functions and the byte input/output functions store the value of the macro EILSEQ in errno if and only if an encoding error occurs.
15
Environmental limits The value of FOPEN_MAX shall be at least eight, including the three standard text streams. Forward references: the exit function (7.24.4.4), the fgetc function (7.23.7.1), the fopen function (7.23.5.3), the fputc function (7.23.7.3), the setbuf function (7.23.5.5), the setvbuf function (7.23.5.6), the fgetwc function (7.31.3.1), the fputwc function (7.31.3.3), conversion state (7.31.6), the mbrtowc function (7.31.6.3.2), the wcrtomb function (7.31.6.3.3).
7.23.4
Operations on files
7.23.4.1 The remove function Synopsis 1
2
3
#include <stdio.h> int remove(const char *filename);
Description The remove function causes the file whose name is the string pointed to by filename to be no longer accessible by that name. A subsequent attempt to open that file using that name will fail, unless it is created anew. If the file is open, the behavior of the remove function is implementation-defined. Returns The remove function returns zero if the operation succeeds, nonzero if it fails. 7.23.4.2 The rename function Synopsis
1
#include <stdio.h> int rename(const char *old, const char *new);
330) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has undefined behavior for a binary stream (because of possible trailing null characters) or for any stream with state-dependent encoding that does not assuredly end in the initial shift state.
§ 7.23.4.2
Library
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2
working draft — April 1, 2023
N3096
Description The rename function causes the file whose name is the string pointed to by old to be henceforth known by the name given by the string pointed to by new. The file named old is no longer accessible by that name. If a file named by the string pointed to by new exists prior to the call to the rename function, the behavior is implementation-defined. Returns
3
The rename function returns zero if the operation succeeds, nonzero if it fails,331) in which case if the file existed previously it is still known by its original name. 7.23.4.3 The tmpfile function Synopsis #include <stdio.h> FILE *tmpfile(void);
1
2
3
4
Description The tmpfile function creates a temporary binary file that is different from any other existing file and that will automatically be removed when it is closed or at program termination. If the program terminates abnormally, whether an open temporary file is removed is implementation-defined. The file is opened for update with "wb+" mode. Recommended practice It should be possible to open at least TMP_MAX temporary files during the lifetime of the program (this limit may be shared with tmpnam) and there should be no limit on the number simultaneously open other than this limit and any limit on the number of open files (FOPEN_MAX). Returns The tmpfile function returns a pointer to the stream of the file that it created. If the file cannot be created, the tmpfile function returns a null pointer. Forward references: the fopen function (7.23.5.3). 7.23.4.4 The tmpnam function Synopsis #include <stdio.h> char *tmpnam(char *s);
1
2
Description The tmpnam function generates a string that is a valid file name and that is not the same as the name of an existing file.332) The function is potentially capable of generating at least TMP_MAX different strings, but any or all of them may already be in use by existing files and thus not be suitable return values.
3
The tmpnam function generates a different string each time it is called.
4
Calls to the tmpnam function with a null pointer argument may introduce data races with each other. The implementation shall behave as if no library function calls the tmpnam function.
5
Returns If no suitable string can be generated, the tmpnam function returns a null pointer. Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an internal static object and returns a pointer to that object (subsequent calls to the tmpnam function may modify the same object). 331) Among the reasons the implementation could cause the rename function to fail are that the file is open or that it is necessary to copy its contents to effectuate its renaming. 332) Files created using strings generated by the tmpnam function are temporary only in the sense that their names are not expected to collide with those generated by conventional naming rules for the implementation. It is still necessary to use the remove function to remove such files when their use is ended, and before program termination.
324
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If the argument is not a null pointer, it is assumed to point to an array of at least L_tmpnam chars; the tmpnam function writes its result in that array and returns the argument as its value.
6
Environmental limits The value of the macro TMP_MAX shall be at least 25.
7.23.5
File access functions
7.23.5.1 The fclose function Synopsis 1
2
3
#include <stdio.h> int fclose(FILE *stream);
Description A successful call to the fclose function causes the stream pointed to by stream to be flushed and the associated file to be closed. Any unwritten buffered data for the stream are delivered to the host environment to be written to the file; any unread buffered data are discarded. Whether the call succeeds or not, the stream is disassociated from the file and any buffer set by the setbuf or setvbuf function is disassociated from the stream (and deallocated if it was automatically allocated). Returns The fclose function returns zero if the stream was successfully closed, or EOF if any errors were detected. 7.23.5.2 The fflush function Synopsis
1
2
3
4
#include <stdio.h> int fflush(FILE *stream);
Description If stream points to an output stream or an update stream in which the most recent operation was not input, the fflush function causes any unwritten data for that stream to be delivered to the host environment to be written to the file; otherwise, the behavior is undefined. If stream is a null pointer, the fflush function performs this flushing action on all streams for which the behavior is defined above. Returns The fflush function sets the error indicator for the stream and returns EOF if a write error occurs, otherwise it returns zero. Forward references: the fopen function (7.23.5.3). 7.23.5.3 The fopen function Synopsis
1
2
3
#include <stdio.h> FILE *fopen(const char * restrict filename, const char * restrict mode);
Description The fopen function opens the file whose name is the string pointed to by filename, and associates a stream with it. The argument mode points to a string. If the string is one of the following, the file is open in the indicated mode. Otherwise, the behavior is undefined.333) 333) If the string begins with one of the listed mode sequences, the implementation might choose to ignore the remaining characters, or it might use them to select different kinds of a file (some of which might not conform to the properties in 7.23.2).
§ 7.23.5.3
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r
open text file for reading
w
truncate to zero length or create text file for writing
wx
create text file for writing
a
append; open or create text file for writing at end-of-file
rb
open binary file for reading
wb
truncate to zero length or create binary file for writing
wbx
create binary file for writing
ab
append; open or create binary file for writing at end-of-file
r+
open text file for update (reading and writing)
w+
truncate to zero length or create text file for update
w+x
create text file for update
a+
append; open or create text file for update, writing at end-of-file
r+b or rb+
open binary file for update (reading and writing)
w+b or wb+
truncate to zero length or create binary file for update
w+bx or wb+x
create binary file for update
a+b or ab+
append; open or create binary file for update, writing at end-of-file
N3096
4
Opening a file with read mode (’r’ as the first character in the mode argument) fails if the file does not exist or cannot be read.
5
Opening a file with exclusive mode (’x’ as the last character in the mode argument) fails if the file already exists or cannot be created. The check for the existence of the file and the creation of the file if it does not exist is atomic with respect to other threads and other concurrent program executions. If the implementation is not capable of performing the check for the existence of the file and the creation of teh file atomically, it shall fail instead of performing a non-atomic check and creation.
6
Opening a file with append mode (’a’ as the first character in the mode argument) causes all subsequent writes to the file to be forced to the then current end-of-file at the point of buffer flush or actual write, regardless of intervening calls to the fseek, fsetpos, or rewind functions. Incrementing the current end-of-file by the amount of data written is atomic with respect to other threads writing to the same file provided the file was also opened in append mode. If the implementation is not capable of increment the current end-of-file atomically, it shall fail instead of performing non-atomic end-of-file writes. In some implementations, opening a binary file with append mode (’b’ as the second or third character in the above list of mode argument values) may initially position the file position indicator for the stream beyond the last data written, because of null character padding.
7
When a file is opened with update mode (’+’ as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file. Opening (or creating) a text file with update mode may instead open (or create) a binary stream in some implementations.
8
When opened, a stream is fully buffered if and only if it can be determined not to refer to an interactive device. The error and end-of-file indicators for the stream are cleared.
9
Returns The fopen function returns a pointer to the object controlling the stream. If the open operation fails, fopen returns a null pointer. Forward references: file positioning functions (7.23.9). 7.23.5.4 326
The freopen function Library
§ 7.23.5.4
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ISO/IEC 9899:2023 (E)
Synopsis #include <stdio.h> FILE *freopen(const char * restrict filename, const char * restrict mode, FILE * restrict stream);
1
2
Description The freopen function opens the file whose name is the string pointed to by filename and associates the stream pointed to by stream with it. The mode argument is used just as in the fopen function.334)
3
If filename is a null pointer, the freopen function attempts to change the mode of the stream to that specified by mode, as if the name of the file currently associated with the stream had been used. It is implementation-defined which changes of mode are permitted (if any), and under what circumstances.
4
The freopen function first attempts to close any file that is associated with the specified stream. Failure to close the file is ignored. The error and end-of-file indicators for the stream are cleared.
5
Returns The freopen function returns a null pointer if the open operation fails. Otherwise, freopen returns the value of stream. 7.23.5.5 The setbuf function Synopsis #include <stdio.h> void setbuf(FILE * restrict stream, char * restrict buf);
1
2
3
Description Except that it returns no value, the setbuf function is equivalent to the setvbuf function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf is a null pointer), with the value _IONBF for mode. Returns The setbuf function returns no value. Forward references: the setvbuf function (7.23.5.6). 7.23.5.6 The setvbuf function Synopsis #include <stdio.h> int setvbuf(FILE * restrict stream, char * restrict buf, int mode, size_t size);
1
2
Description The setvbuf function may be used only after the stream pointed to by stream has been associated with an open file and before any other operation (other than an unsuccessful call to setvbuf) is performed on the stream. The argument mode determines how stream will be buffered, as follows: _IOFBF
causes input/output to be fully buffered;
_IOLBF
causes input/output to be line buffered;
_IONBF
causes input/output to be unbuffered.
334) The primary use of the freopen function is to change the file associated with a standard text stream (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value returned by the fopen function could be assigned.
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If buf is not a null pointer, the array it points to may be used instead of a buffer allocated by the setvbuf function335) and the argument size specifies the size of the array; otherwise, size may determine the size of a buffer allocated by the setvbuf function. The members of the array at any time have unspecified values.
3
Returns The setvbuf function returns zero on success, or nonzero if an invalid value is given for mode or if the request cannot be honored.
7.23.6 1
Formatted input/output functions
The formatted input/output functions shall behave as if there is a sequence point after the actions associated with each specifier.336) 7.23.6.1 The fprintf function Synopsis #include <stdio.h> int fprintf(FILE * restrict stream, const char * restrict format, ...);
1
2
Description The fprintf function writes output to the stream pointed to by stream, under control of the string pointed to by format that specifies how subsequent arguments are converted for output. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated (as always) but are otherwise ignored. The fprintf function returns when the end of the format string is encountered.
3
The format shall be a multibyte character sequence, beginning and ending in its initial shift state. The format is composed of zero or more directives: ordinary multibyte characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments, converting them, if applicable, according to the corresponding conversion specifier, and then writing the result to the output stream.
4
Each conversion specification is introduced by the character %. After the %, the following appear in sequence: — Zero or more flags (in any order) that modify the meaning of the conversion specification. — An optional minimum field width. If the converted value has fewer characters than the field width, it is padded with spaces (by default) on the left (or right, if the left adjustment flag, described later, has been given) to the field width. The field width takes the form of an asterisk 337) * (described later) or a nonnegative decimal integer. — An optional precision that gives the minimum number of digits to appear for the b, d, i, o, u, x, and X conversions, the number of digits to appear after the decimal-point character for a, A, e, E, f, and F conversions, the maximum number of significant digits for the g and G conversions, or the maximum number of bytes to be written for s conversions. The precision takes the form of a period (.) followed either by an asterisk * (described later) or by an optional nonnegative decimal integer; if only the period is specified, the precision is taken as zero. If a precision appears with any other conversion specifier, the behavior is undefined. — An optional length modifier that specifies the size of the argument. — A conversion specifier character that specifies the type of conversion to be applied.
5
As noted above, a field width, or precision, or both, may be indicated by an asterisk. In this case, an int argument supplies the field width or precision. The arguments specifying field width, or 335) The buffer has to have a lifetime at least as great as the open stream, so not closing the stream before a buffer that has automatic storage duration is deallocated upon block exit results in undefined behavior. 336) The fprintf functions perform writes to memory for the %n specifier. 337) Note that 0 is taken as a flag, not as the beginning of a field width.
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ISO/IEC 9899:2023 (E)
precision, or both, shall appear (in that order) before the argument (if any) to be converted. A negative field width argument is taken as a - flag followed by a positive field width. A negative precision argument is taken as if the precision were omitted. 6
The flag characters and their meanings are: -
The result of the conversion is left-justified within the field. (It is right-justified if this flag is not specified.)
+
The result of a signed conversion always begins with a plus or minus sign. (It begins with a sign only when a value with a negative sign is converted if this flag is not specified.) 338)
space If the first character of a signed conversion is not a sign, or if a signed conversion results in no characters, a space is prefixed to the result. If the space and + flags both appear, the space flag is ignored.
7
#
The result is converted to an "alternative form". For o conversion, it increases the precision, if and only if necessary, to force the first digit of the result to be a zero (if the value and precision are both 0, a single 0 is printed). For b conversion, a nonzero result has 0b prefixed to it. For the optional B conversion as described below, a nonzero result has 0B prefixed to it. For x (or X) conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, and G conversions, the result of converting a floating-point number always contains a decimal-point character, even if no digits follow it. (Normally, a decimal-point character appears in the result of these conversions only if a digit follows it.) For g and G conversions, trailing zeros are not removed from the result. For other conversions, the behavior is undefined.
0
For b, d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros (following any indication of sign or base) are used to pad to the field width rather than performing space padding, except when converting an infinity or NaN. If the 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X conversions, if a precision is specified, the 0 flag is ignored. For other conversions, the behavior is undefined.
The length modifiers and their meanings are: hh
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a signed char or unsigned char argument (the argument will have been promoted according to the integer promotions, but its value shall be converted to signed char or unsigned char before printing); or that a following n conversion specifier applies to a pointer to a signed char argument.
h
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a short int or unsigned short int argument (the argument will have been promoted according to the integer promotions, but its value shall be converted to short int or unsigned short int before printing); or that a following n conversion specifier applies to a pointer to a short int argument.
l (ell)
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a long int or unsigned long int argument; that a following n conversion specifier applies to a pointer to a long int argument; that a following c conversion specifier applies to a wint_t argument; that a following s conversion specifier applies to a pointer to a wchar_t argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion specifier.
ll (ell-ell) Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a long long int or unsigned long long int argument; or that a following n conversion specifier applies to a pointer to a long long int argument. 338) The results of all floating conversions of a negative zero, and of negative values that round to zero, include a minus sign.
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j
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to an intmax_t or uintmax_t argument; or that a following n conversion specifier applies to a pointer to an intmax_t argument.
z
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a size_t or the corresponding signed integer type argument; or that a following n conversion specifier applies to a pointer to a signed integer type corresponding to size_t argument.
t
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a ptrdiff_t or the corresponding unsigned integer type argument; or that a following n conversion specifier applies to a pointer to a ptrdiff_t argument.
wN
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to an integer argument with a specific width where N is a positive decimal integer with no leading zeros (the argument will have been promoted according to the integer promotions, but its value shall be converted to the unpromoted type); or that a following n conversion specifier applies to a pointer to an integer type argument with a width of N bits. All minimum-width integer types (7.22.1.2) and exact-width integer types (7.22.1.1) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
wfN
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a fastest minimum-width integer argument with a specific width where N is a positive decimal integer with no leading zeros (the argument will have been promoted according to the integer promotions, but its value shall be converted to the unpromoted type); or that a following n conversion specifier applies to a pointer to a fastest minimum-width integer type argument with a width of N bits. All fastest minimum-width integer types (7.22.1.3) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
L
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument.
H
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a _Decimal32 argument.
D
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a _Decimal64 argument.
DD
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a _Decimal128 argument.
If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. 8
The conversion specifiers and their meanings are: d,i
The int argument is converted to signed decimal in the style [-]dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a zero value with a precision of zero is no characters.
b,B,o,u,x,X The unsigned int argument is converted to unsigned binary (b or B), unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the letters abcdef are used for x conversion and the letters ABCDEF for X conversion. The
precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a zero value with a precision of zero is no characters. The specifier B is optional and provides the same functionality as b, except for the # flag as specified above. The macro PRIBPTR from <inttypes.h> shall only be defined if the implementation follows the specification as given here. 330
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f,F
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ISO/IEC 9899:2023 (E)
A double argument representing a floating-point number is converted to decimal notation in the style [-]ddd.ddd, where the number of digits after the decimal-point character is equal to the precision specification. If the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point character appears. If a decimal-point character appears, at least one digit appears before it. The value is rounded to the appropriate number of digits. A double argument representing an infinity is converted in one of the styles [-]inf or [-]infinity — which style is implementation-defined. A double argument representing a NaN is converted in one of the styles [-]nan or [-]nan(n-char-sequence) — which style, and the meaning of any n-char-sequence, is implementation-defined. The F conversion specifier produces INF, INFINITY, or NAN instead of inf, infinity, or nan, respectively.339)
e,E
A double argument representing a floating-point number is converted in the style [-]d.ddde±dd, where there is one digit (which is nonzero if the argument is nonzero) before the decimal-point character and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point character appears. The value is rounded to the appropriate number of digits. The E conversion specifier produces a number with E instead of e introducing the exponent. The exponent always contains at least two digits, and only as many more digits as necessary to represent the exponent. If the value is zero, the exponent is zero. A double argument representing an infinity or NaN is converted in the style of an f or F conversion specifier.
g,G
A double argument representing a floating-point number is converted in style f or e (or in style F or E in the case of a G conversion specifier), depending on the value converted and the precision. Let P equal the precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero. Then, if a conversion with style E would have an exponent of X: if P > X ≥ −4, the conversion is with style f (or F) and precision P − (X + 1). otherwise, the conversion is with style e (or E) and precision P − 1. Finally, unless the # flag is used, any trailing zeros are removed from the fractional portion of the result and the decimal-point character is removed if there is no fractional portion remaining. A double argument representing an infinity or NaN is converted in the style of an f or F conversion specifier.
a,A
A double argument representing a floating-point number is converted in the style [-]0xh.hhhhp±d, where there is one hexadecimal digit (which is nonzero if the argument is a normalized floating-point number and is otherwise unspecified) before the decimal-point character 340) and the number of hexadecimal digits after it is equal to the precision; if the precision is missing and FLT_RADIX is a power of 2, then the precision is sufficient for an exact representation of the value; if the precision is missing and FLT_RADIX is not a power
339) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning; the # and 0 flag characters have no effect. 340) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so that subsequent digits align to nibble (4-bit) boundaries. This implementation choice affects numerical values printed with a precision P that is insufficient to represent all values exactly. Implementations with different conventions about the most significant hexadecimal digit will round at different places, affecting the numerical value of the hexadecimal result. For example, possible printed output for the code
#include <stdio.h> /* ... */ double x = 123.0; printf("%.1a", x); include "0x1.fp+6 " and "0xf.6p+3 " whose numerical values are 124 and 123, respectively. Portable code seeking identical numerical results on different platforms should avoid precisions P that require rounding.
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of 2, then the precision is sufficient to distinguish341) values of type double, except that trailing zeros may be omitted; if the precision is zero and the # flag is not specified, no decimal-point character appears. The letters abcdef are used for a conversion and the letters ABCDEF for A conversion. The A conversion specifier produces a number with X and P instead of x and p. The exponent always contains at least one digit, and only as many more digits as necessary to represent the decimal exponent of 2. If the value is zero, the exponent is zero. A double argument representing an infinity or NaN is converted in the style of an f or F conversion specifier. If an H, D, or DD modifier is present and the precision is missing, then for a decimal floating type argument represented by a triple of integers (s, c, q), where n is the number of significant digits in the coefficient c, — if −(n + 5) ≤ q ≤ 0, use style f (or style F in the case of an A conversion specifier) with formatting precision equal to −q, — otherwise, use style e (or style E in the case of an A conversion specifier) with formatting precision equal to n − 1, with the exceptions that if c = 0 then the digit-sequence in the exponent-part shall have the value q (rather than 0), and that the exponent is always expressed with the minimum number of digits required to represent its value (the exponent never contains a leading zero). If the precision P is present (in the conversion specification) and is zero or at least as large as the precision p (5.2.4.2.2) of the decimal floating type, the conversion is as if the precision were missing. If the precision P is present (and nonzero) and less than the precision p of the decimal floating type, the conversion first obtains an intermediate result as follows, where n is the number of significant digits in the coefficient: — If n ≤ P , set the intermediate result to the input. — If n > P , round the input value, according to the current rounding direction for decimal floating-point operations, to P decimal digits, with unbounded exponent range, representing the result with a P -digit integer coefficient when in the form (s, c, q). Convert the intermediate result in the manner described above for the case where the precision is missing. c
If no l length modifier is present, the int argument is converted to an unsigned char, and the resulting character is written. If an l length modifier is present, the wint_t argument is converted as if by an ls conversion specification with no precision and an argument that points to storage suitably sized for at least two wchar_t elements, the first element containing the wint_t argument to the lc conversion specification and the second a null wide character.
s
If no l length modifier is present, the argument shall be a pointer to storage of character type.342) Characters from the storage are written up to (but not including) the terminating null character. If the precision is specified, no more than that many bytes are written. If the precision is not specified or is greater than the size of the storage, the storage shall contain a null character. If an l length modifier is present, the argument shall be a pointer to storage of wchar_t type. Wide characters from the storage are converted to multibyte characters (each as if by a call to the wcrtomb function, with the conversion state described by an mbstate_t object initialized to zero before the first wide character is converted) up to and including a terminating null wide character. The resulting multibyte characters are written up to
341) The formatting precision P is sufficient to distinguish values of the source type if 16P > bp where b (not a power of 2) and p are the base and precision of the source type (5.2.4.2.2). A smaller P might suffice depending on the implementation’s scheme for determining the digit to the left of the decimal-point character. 342) No special provisions are made for multibyte characters.
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(but not including) the terminating null character (byte). If no precision is specified, the storage shall contain a null wide character. If a precision is specified, no more than that many bytes are written (including shift sequences, if any), and the storage shall contain a null wide character if, to equal the multibyte character sequence length given by the precision, the function would need to access a wide character one past the end of the array. In no case is a partial multibyte character written.343) p
The argument shall be a pointer to void or a pointer to a character type. The value of the pointer is converted to a sequence of printing characters, in an implementation-defined manner.
n
The argument shall be a pointer to signed integer whose type is specified by the length modifier, if any, for the conversion specification, or shall be int if no length modifier is specified for the conversion specification. The number of characters written to the output stream so far by this call to fprintf is stored into the integer object pointed to by the argument. No argument is converted, but one is consumed. If the conversion specification includes any flags, a field width, or a precision, the behavior is undefined.
%
A % character is written. No argument is converted. The complete conversion specification shall be %%.
9
If a conversion specification is invalid, the behavior is undefined.344) fprintf shall behave as if it uses va_arg with a type argument naming the type resulting from applying the default argument promotions to the type corresponding to the conversion specification and then converting the result of the va_arg expansion to the type corresponding to the conversion specification.345)
10
In no case does a nonexistent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.
11
For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded to a hexadecimal floating number with the given precision.
12
Recommended practice For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly representable in the given precision, the result should be one of the two adjacent numbers in hexadecimal floating style with the given precision, with the extra stipulation that the error should have a correct sign for the current rounding direction.
13
For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most the maximum value M of the T_DECIMAL_DIG macros (defined in <float.h>), then the result should be correctly rounded.346) If the number of significant decimal digits is more than M but the source value is exactly representable with M digits, then the result should be an exact representation with trailing zeros. Otherwise, the source value is bounded by two adjacent decimal strings L < U, both having M significant digits; the value of the resultant decimal string D should satisfy L ≤ D ≤ U, with the extra stipulation that the error should have a correct sign for the current rounding direction.
14
The uppercase B format specifier is made optional by the description above, because it used to be available for extensions in previous versions of this document. Implementations that did not use an uppercase B as their own extension before are encouraged to implement it similar to conversion specifier b as standardized above, with the alternative form (#B) generating 0B as prefix for nonzero values.
15
Returns The fprintf function returns the number of characters transmitted, or a negative value if an output or encoding error occurred or if the implementation does not support a specified width length modifier. 343) Redundant shift sequences can result if multibyte characters have a state-dependent encoding. 344) See "future library directions" (7.33.15). 345) The behavior is undefined when the types differ as specified for va_arg 7.16.1.1. 346) For binary-to-decimal conversion, the result format’s values are the numbers representable with the given format specifier.
The number of significant digits is determined by the format specifier, and in the case of fixed-point conversion by the source value as well.
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Environmental limits The number of characters that can be produced by any single conversion shall be at least 4095. EXAMPLE 1 To print a date and time in the form "Sunday, July 3, 10:02" followed by π to five decimal places: #include <math.h> #include <stdio.h> /* ... */ char *weekday, *month; // pointers to strings int day, hour, min; fprintf(stdout, "%s, %s %d, %.2d:%.2d\n", weekday, month, day, hour, min); fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
18
EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the members of the extended character set that consist of more than one byte each consist of exactly two bytes, the first of which is denoted here by a □ and the second by an uppercase letter.
19
Given the following wide string with length seven, static wchar_t wstr[] = L"□X□Yabc□Z□W";
the seven calls fprintf(stdout, "|1234567890123|\n"); fprintf(stdout, "|%13ls|\n", wstr); fprintf(stdout, "|%-13.9ls|\n", wstr); fprintf(stdout, "|%13.10ls|\n", wstr); fprintf(stdout, "|%13.11ls|\n", wstr); fprintf(stdout, "|%13.15ls|\n", &wstr[2]); fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);
will print the following seven lines: |1234567890123| | □X□Yabc□Z□W| |□X□Yabc□Z | | □X□Yabc□Z| | □X□Yabc□Z□W| | abc□Z□W| | □Z|
20
EXAMPLE 3 Following are representations of _Decimal64 arguments as triples (s, c, q) and the corresponding character sequences fprintf produces with "%Da": 334
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(+1, 123, 0) 123 (−1, 123, 0) -123 (+1, 123, −2) 1.23 (+1, 123, 1) 1.23e+3 (−1, 123, 1) -1.23e+3 (+1, 123, −8) 0.00000123 (+1, 123, −9) 1.23e-7 (+1, 120, −8) 0.00000120 (+1, 120, −9) 1.20e-7 (+1, 1234567890123456, 0) 1234567890123456 (+1, 1234567890123456, 1) 1.234567890123456e+16 (+1, 1234567890123456, −1) 123456789012345.6 (+1, 1234567890123456, −21) 0.000001234567890123456 (+1, 1234567890123456, −22) 1.234567890123456e-7 (+1, 0, 0) 0 (−1, 0, 0) -0 (+1, 0, −6) 0.000000 (+1, 0, −7) 0e-7 (+1, 0, 2) 0e+2 (+1, 5, −6) 0.000005 (+1, 50, −7) 0.0000050 (+1, 5, −7) 5e-7 To illustrate the effects of a precision specification, the sequence: _Decimal32 x = 6543.00DF; fprintf(stdout, "%Ha\n", x); fprintf(stdout, "%.6Ha\n", x); fprintf(stdout, "%.5Ha\n", x); fprintf(stdout, "%.4Ha\n", x); fprintf(stdout, "%.3Ha\n", x); fprintf(stdout, "%.2Ha\n", x); fprintf(stdout, "%.1Ha\n", x); fprintf(stdout, "%.0Ha\n", x);
// (+1, 654300, -2)
assuming default rounding, results in: 6543.00 6543.00 6543.0 6543 6.54e+3 6.5e+3 7e+3 6543.00
To illustrate the effects of the exponent range, the sequence: _Decimal32 x = 9543210e87DF; _Decimal32 y = 9500000e90DF;
// (+1, 9543210, 87) // (+1, 9500000, 90)
fprintf(stdout, "%.6Ha\n", x); fprintf(stdout, "%.5Ha\n", x); fprintf(stdout, "%.4Ha\n", x); fprintf(stdout, "%.3Ha\n", x); fprintf(stdout, "%.2Ha\n", x); fprintf(stdout, "%.1Ha\n", x); fprintf(stdout, "%.1Ha\n", y);
assuming default rounding, results in: § 7.23.6.1
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9.54321e+93 9.5432e+93 9.543e+93 9.54e+93 9.5e+93 1e+94 1e+97
To further illustrate the effects of the exponent range, the sequence: _Decimal32 x = 9512345e90DF; _Decimal32 y = 9512345e86DF;
// (+1, 9512345, 90) // (+1, 9512345, 86)
fprintf(stdout, "%.3Ha\n", x); fprintf(stdout, "%.2Ha\n", x); fprintf(stdout, "%.1Ha\n", x); fprintf(stdout, "%.2Ha\n", y);
assuming default rounding, results in: 9.51e+96 9.5e+96 1e+97 9.5e+92
Forward references: conversion state (7.31.6), the wcrtomb function (7.31.6.3.3). 7.23.6.2 The fscanf function Synopsis #include <stdio.h> int fscanf(FILE * restrict stream, const char * restrict format, ...);
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Description The fscanf function reads input from the stream pointed to by stream, under control of the string pointed to by format that specifies the admissible input sequences and how they are to be converted for assignment, using subsequent arguments as pointers to the objects to receive the converted input. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated (as always) but are otherwise ignored. The format shall be a multibyte character sequence, beginning and ending in its initial shift state.The format is composed of zero or more directives: one or more white-space characters, an ordinary multibyte character (neither % nor a white-space character), or a conversion specification. Each conversion specification is introduced by the character %. After the %, the following appear in sequence: — An optional assignment-suppressing character *. — An optional decimal integer greater than zero that specifies the maximum field width (in characters). — An optional length modifier that specifies the size of the receiving object. — A conversion specifier character that specifies the type of conversion to be applied.
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The fscanf function executes each directive of the format in turn. When all directives have been executed, or if a directive fails (as detailed below), the function returns. Failures are described as input failures (due to the occurrence of an encoding error or the unavailability of input characters), or matching failures (due to inappropriate input). 336
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A directive composed of white-space character(s) is executed by reading input up to the first nonwhite-space character (which remains unread), or until no more characters can be read. The directive never fails.
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A directive that is an ordinary multibyte character is executed by reading the next characters of the stream. If any of those characters differ from the ones composing the directive,the directive fails and the differing and subsequent characters remain unread. Similarly, if end-of-file, an encoding error, or a read error prevents a character from being read, the directive fails.
7
A directive that is a conversion specification defines a set of matching input sequences, as described below for each specifier. A conversion specification is executed in the following steps:
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Input white-space characters are skipped, unless the specification includes a [, c, or n specifier.347)
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An input item is read from the stream, unless the specification includes an n specifier. An input item is defined as the longest sequence of input characters which does not exceed any specified field width and which is, or is a prefix of, a matching input sequence.348) The first character, if any, after the input item remains unread. If the length of the input item is zero, the execution of the directive fails; this condition is a matching failure unless end-of-file, an encoding error, or a read error prevented input from the stream, in which case it is an input failure.
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Except in the case of a % specifier, the input item (or, in the case of a %n directive, the count of input characters) is converted to a type appropriate to the conversion specifier. If the input item is not a matching sequence, the execution of the directive fails: this condition is a matching failure. Unless assignment suppression was indicated by a *, the result of the conversion is placed in the object pointed to by the first argument following the format argument that has not already received a conversion result. If this object does not have an appropriate type, or if the result of the conversion cannot be represented in the object, the behavior is undefined.
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The length modifiers and their meanings are: hh
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to signed char or unsigned char.
h
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to short int or unsigned short int.
l (ell)
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long int or unsigned long int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to double; or that a following c, s, or [ conversion specifier applies to an argument with type pointer to wchar_t.
ll (ell-ell) Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long long int or unsigned long long int. j
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to intmax_t or uintmax_t.
z
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to size_t or the corresponding signed integer type.
t
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to ptrdiff_t or the corresponding unsigned integer type.
wN
Specifies that a following b, d, i, o, u, x, or X, or n conversion specifier applies to an argument which is a pointer to an integer with a specific width where N is a positive decimal integer with no leading zeros. All minimum-width integer types (7.22.1.2) and exact-width integer types (7.22.1.1) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
347) These white-space characters are not counted against a specified field width. 348) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.
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wfN
Specifies that a following b, d, i, o, u, x, or X, or n conversion specifier applies to an argument which is a pointer to a fastest minimum-width integer with a specific width where N is a positive decimal integer with no leading zeros. All fastest minimum-width integer types (7.22.1.3) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
L
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to long double.
H
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to _Decimal32.
D
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to _Decimal64.
DD
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to _Decimal128.
If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. 12
In the following, the type of the corresponding argument for a conversion specifier shall be a pointer to a type determined by the length modifiers, if any, or specified by the conversion specifier. The conversion specifiers and their meanings are: d
Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of the strtol function with the value 10 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to int.
b
Matches an optionally signed binary integer, whose format is the same as expected for the subject sequence of the strtol function with the value 2 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
i
Matches an optionally signed integer, whose format is the same as expected for the subject sequence of the strtol function with the value 0 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to int.
o
Matches an optionally signed octal integer, whose format is the same as expected for the subject sequence of the strtoul function with the value 8 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
u
Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of the strtoul function with the value 10 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
x
Matches an optionally signed hexadecimal integer, whose format is the same as expected for the subject sequence of the strtoul function with the value 16 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose format is the same as expected for the subject sequence of the strtod function. Unless a length modifier is specified, the corresponding argument shall be a pointer to float. c
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Matches a sequence of characters of exactly the number specified by the field width (1 if no field width is present in the directive). Library
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If no l length modifier is present, the corresponding argument shall be a pointer to char, signed char, unsigned char, or void that points to storage large enough to accept the sequence. No null character is added. If an l length modifier is present, the input shall be a sequence of multibyte characters that begins in the initial shift state. Each multibyte character in the sequence is converted to a wide character as if by a call to the mbrtowc function, with the conversion state described by an mbstate_t object initialized to zero before the first multibyte character is converted. The corresponding argument shall be a pointer to storage of wchar_t large enough to accept the resulting sequence of wide characters. No null wide character is added. s
Matches a sequence of non-white-space characters.349) If no l length modifier is present, the corresponding argument shall be a pointer to char, signed char, unsigned char, or void that points to storage large enough to accept the sequence and a terminating null character, which will be added automatically. If an l length modifier is present, the input shall be a sequence of multibyte characters that begins in the initial shift state. Each multibyte character is converted to a wide character as if by a call to the mbrtowc function, with the conversion state described by an mbstate_t object initialized to zero before the first multibyte character is converted. The corresponding argument shall be a pointer to storage of wchar_t large enough to accept the sequence and the terminating null wide character, which will be added automatically.
[
Matches a nonempty sequence of characters from a set of expected characters (the scanset).349) If no l length modifier is present, the corresponding argument shall be a pointer to char, signed char, unsigned char, or void that points to storage large enough to accept the sequence and a terminating null character, which will be added automatically. If an l length modifier is present, the input shall be a sequence of multibyte characters that begins in the initial shift state. Each multibyte character is converted to a wide character as if by a call to the mbrtowc function, with the conversion state described by an mbstate_t object initialized to zero before the first multibyte character is converted. The corresponding argument shall be a pointer that points to storage of wchar_t large enough to accept the sequence and the terminating null wide character, which will be added automatically. The conversion specifier includes all subsequent characters in the format string, up to and including the matching right bracket (]). The characters between the brackets (the scanlist) compose the scanset, unless the character after the left bracket is a circumflex (^), in which case the scanset contains all characters that do not appear in the scanlist between the circumflex and the right bracket. If the conversion specifier begins with [] or [^], the right bracket character is in the scanlist and the next following right bracket character is the matching right bracket that ends the specification; otherwise the first following right bracket character is the one that ends the specification. If a - character is in the scanlist and is not the first, nor the second where the first character is a ^, nor the last character, the behavior is implementation-defined.
p
Matches an implementation-defined set of sequences, which should be the same as the set of sequences that may be produced by the %p conversion of the fprintf function. The corresponding argument shall be a pointer to a pointer of void. The input item is converted to a pointer value in an implementation-defined manner. If the input item is a value converted earlier during the same program execution, the pointer that results shall compare equal to that value; otherwise the behavior of the %p conversion is undefined.
349) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [ conversion specifiers — the extent of the input field is determined on a byte-by-byte basis. The resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
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n
No input is consumed. The corresponding argument shall be a pointer of a signed integer type. The number of characters read from the input stream so far by this call to the fscanf function is stored into the integer object pointed to by the argument. Execution of a %n directive does not increment the assignment count returned at the completion of execution of the fscanf function. No argument is converted, but one is consumed. If the conversion specification includes an assignment-suppressing character or a field width, the behavior is undefined.
%
Matches a single % character; no conversion or assignment occurs. The complete conversion specification shall be %%.
13
If a conversion specification is invalid, the behavior is undefined.350)
14
The conversion specifiers A, E, F, G, and X are also valid and behave the same as, respectively, a, e, f, g, and x.
15
Trailing white-space characters (including new-line characters) are left unread unless matched by a directive. The success of literal matches and suppressed assignments is not directly determinable other than via the %n directive.
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17
Returns The fscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure or if the implementation does not support a specific width length modifier. EXAMPLE 1 The call: #include <stdio.h> /* ... */ int n, i; float x; char name[50]; n = fscanf(stdin, "%d%f%s", &i, &x, name);
with the input line: 25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence thompson\0. 18
EXAMPLE 2 The call: #include <stdio.h> /* ... */ int i; float x; char name[50]; fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
with input: 56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the sequence 56\0. The next character read from the input stream will be a. 19
EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name: #include <stdio.h> /* ... */ int count; float quant; char units[21], item[21]; 350) See "future library directions" (7.33.15).
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do { count = fscanf(stdin, "%f%20s of %20s", &quant, units, item); fscanf(stdin,"%*[^\n]"); } while (!feof(stdin) && !ferror(stdin)); 20
If the stdin stream contains the following lines: 2 quarts of oil -12.8degrees Celsius lots of luck 10.0LBS of dirt 100ergs of energy
the execution of the above example will be analogous to the following assignments: quant = 2; strcpy(units, "quarts"); strcpy(item, "oil"); count = 3; quant = -12.8; strcpy(units, "degrees"); count = 2; // "C" fails to match "o" count = 0; // "l" fails to match "%f" quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt"); count = 3; count = 0; // "100e" fails to match "%f" count = EOF; 21
EXAMPLE 4 In: #include <stdio.h> /* ... */ int d1, d2, n1, n2, i; i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure, the value of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i. 22
EXAMPLE 5 The call: #include <stdio.h> /* ... */ int n, i; n = sscanf("foo %bar
42", "foo%%bar%d", &i);
will assign to n the value 1 and to i the value 42 because input white-space characters are skipped for both the % and d conversion specifiers. 23
EXAMPLE 6 In these examples, multibyte characters do have a state-dependent encoding, and the members of the extended character set that consist of more than one byte each consist of exactly two bytes, the first of which is denoted here by a □ and the second by an uppercase letter, but are only recognized as such when in the alternate shift state. The shift sequences are denoted by ↑ and ↓, in which the first causes entry into the alternate shift state.
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After the call: #include <stdio.h> /* ... */ char str[50]; fscanf(stdin, "a%s", str);
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a↑□X□Y↓ bc str will contain ↑□X□Y↓\\0 assuming that none of the bytes of the shift sequences (or of the multibyte
characters, in the more general case) appears to be a single-byte white-space character. 25
In contrast, after the call: #include <stdio.h> #include <stddef.h> /* ... */ wchar_t wstr[50]; fscanf(stdin, "a%ls", wstr);
with the same input line, wstr will contain the two wide characters that correspond to □X and □Y and a terminating null wide character. 26
However, the call: #include <stdio.h> #include <stddef.h> /* ... */ wchar_t wstr[50]; fscanf(stdin, "a↑□X↓%ls", wstr);
with the same input line will return zero due to a matching failure against the ↓ sequence in the format string. 27
Assuming that the first byte of the multibyte character □X is the same as the first byte of the multibyte character □Y, after the call: #include <stdio.h> #include <stddef.h> /* ... */ wchar_t wstr[50]; fscanf(stdin, "a↑□Y↓%ls", wstr);
with the same input line, zero will again be returned, but stdin will be left with a partially consumed multibyte character. Forward references: the strtod, strtof, and strtold functions (7.24.1.5), the strtol, strtoll , strtoul, and strtoull functions (7.24.1.7), conversion state (7.31.6), the wcrtomb function (7.31.6.3.3). 7.23.6.3 The printf function Synopsis #include <stdio.h> int printf(const char * restrict format, ...);
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Description The printf function is equivalent to fprintf with the argument stdout interposed before the arguments to printf.
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Returns The printf function returns the number of characters transmitted, or a negative value if an output or encoding error occurred. 7.23.6.4 342
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Synopsis 1
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#include <stdio.h> int scanf(const char * restrict format, ...);
Description The scanf function is equivalent to fscanf with the argument stdin interposed before the arguments to scanf. Returns The scanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the scanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 7.23.6.5 The snprintf function Synopsis
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#include <stdio.h> int snprintf(char * restrict s, size_t n, const char * restrict format, ...);
Description The snprintf function is equivalent to fprintf, except that the output is written into an array (specified by argument s) rather than to a stream. If n is zero, nothing is written, and s may be a null pointer. Otherwise, output characters beyond the n-1st are discarded rather than being written to the array, and a null character is written at the end of the characters actually written into the array. If copying takes place between objects that overlap, the behavior is undefined. Returns The snprintf function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if an encoding error occurred. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. 7.23.6.6 The sprintf function Synopsis
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#include <stdio.h> int sprintf(char * restrict s, const char * restrict format, ...);
Description The sprintf function is equivalent to fprintf, except that the output is written into an array (specified by the argument s) rather than to a stream. A null character is written at the end of the characters written; it is not counted as part of the returned value. If copying takes place between objects that overlap, the behavior is undefined. Returns The sprintf function returns the number of characters written in the array, not counting the terminating null character, or a negative value if an encoding error occurred. 7.23.6.7 The sscanf function Synopsis
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#include <stdio.h> int sscanf(const char * restrict s, const char * restrict format, ...);
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Description The sscanf function is equivalent to fscanf, except that input is obtained from a string (specified by the argument s) rather than from a stream. Reaching the end of the string is equivalent to encountering end-of-file for the fscanf function. If copying takes place between objects that overlap, the behavior is undefined. Returns The sscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the sscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 7.23.6.8 The vfprintf function Synopsis #include <stdarg.h> #include <stdio.h> int vfprintf(FILE * restrict stream, const char * restrict format, va_list arg);
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Description The vfprintf function is equivalent to fprintf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vfprintf function does not invoke the va_end macro351) . Returns The vfprintf function returns the number of characters transmitted, or a negative value if an output or encoding error occurred. EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine. #include <stdarg.h> #include <stdio.h> void error(char *function_name, char *format, ...) { va_list args; va_start(args, format); // print out name of function causing error fprintf(stderr, "ERROR in %s: ", function_name); // print out remainder of message vfprintf(stderr, format, args); va_end(args); }
7.23.6.9 The vfscanf function Synopsis #include <stdarg.h> #include <stdio.h> int vfscanf(FILE * restrict stream, const char * restrict format, va_list arg);
1
2
Description The vfscanf function is equivalent to fscanf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). 351) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and vsscanf invoke the va_arg macro, arg after the return has an indeterminate representation.
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The vfscanf function does not invoke the va_end macro.351)
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Returns The vfscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the vfscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 7.23.6.10 The vprintf function Synopsis
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#include <stdarg.h> #include <stdio.h> int vprintf(const char * restrict format, va_list arg);
Description The vprintf function is equivalent to printf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vprintf function does not invoke the va_end macro.351) Returns The vprintf function returns the number of characters transmitted, or a negative value if an output or encoding error occurred. 7.23.6.11 The vscanf function Synopsis
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#include <stdarg.h> #include <stdio.h> int vscanf(const char * restrict format, va_list arg);
Description The vscanf function is equivalent to scanf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vscanf function does not invoke the va_end macro.351) Returns The vscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the vscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 7.23.6.12 The vsnprintf function Synopsis
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2
#include <stdarg.h> #include <stdio.h> int vsnprintf(char * restrict s, size_t n, const char * restrict format, va_list arg);
Description The vsnprintf function is equivalent to snprintf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vsnprintf function does not invoke the va_end macro.351) If copying takes place between objects that overlap, the behavior is undefined. § 7.23.6.12
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Returns The vsnprintf function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if an encoding error occurred. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. 7.23.6.13 The vsprintf function Synopsis #include <stdarg.h> #include <stdio.h> int vsprintf(char * restrict s, const char * restrict format, va_list arg);
1
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Description The vsprintf function is equivalent to sprintf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vsprintf function does not invoke the va_end macro.351) If copying takes place between objects that overlap, the behavior is undefined. Returns The vsprintf function returns the number of characters written in the array, not counting the terminating null character, or a negative value if an encoding error occurred. 7.23.6.14 The vsscanf function Synopsis #include <stdarg.h> #include <stdio.h> int vsscanf(const char * restrict s, const char * restrict format, va_list arg);
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Description The vsscanf function is equivalent to sscanf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vsscanf function does not invoke the va_end macro.351) Returns The vsscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the vsscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure.
7.23.7
Character input/output functions
7.23.7.1 The fgetc function Synopsis #include <stdio.h> int fgetc(FILE *stream);
1
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3
Description If the end-of-file indicator for the input stream pointed to by stream is not set and a next character is present, the fgetc function obtains that character as an unsigned char converted to an int and advances the associated file position indicator for the stream (if defined). Returns If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the fgetc function 346
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returns the next character from the input stream pointed to by stream. If a read error occurs, the error indicator for the stream is set and the fgetc function returns EOF.352) 7.23.7.2 The fgets function Synopsis 1
2
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#include <stdio.h> char *fgets(char * restrict s, int n, FILE * restrict stream);
Description The fgets function reads at most one less than the number of characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional characters are read after a new-line character (which is retained) or after end-of-file. A null character is written immediately after the last character read into the array. Returns The fgets function returns s if successful. If end-of-file is encountered and no characters have been read into the array, the contents of the array remain unchanged and a null pointer is returned. If a read error occurs during the operation, the members of the array have unspecified values and a null pointer is returned. 7.23.7.3 The fputc function Synopsis
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#include <stdio.h> int fputc(int c, FILE *stream);
Description The fputc function writes the character specified by c (converted to an unsigned char) to the output stream pointed to by stream, at the position indicated by the associated file position indicator for the stream (if defined), and advances the indicator appropriately. If the file cannot support positioning requests, or if the stream was opened with append mode, the character is appended to the output stream. Returns The fputc function returns the character written. If a write error occurs, the error indicator for the stream is set and fputc returns EOF. 7.23.7.4 The fputs function Synopsis
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#include <stdio.h> int fputs(const char * restrict s, FILE * restrict stream);
Description The fputs function writes the string pointed to by s to the stream pointed to by stream. The terminating null character is not written. Returns The fputs function returns EOF if a write error occurs; otherwise it returns a nonnegative value. 7.23.7.5 The getc function Synopsis
1
#include <stdio.h> int getc(FILE *stream); 352) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
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Description The getc function is equivalent to fgetc, except that if it is implemented as a macro, it may evaluate stream more than once, so the argument should never be an expression with side effects. Returns The getc function returns the next character from the input stream pointed to by stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and getc returns EOF. If a read error occurs, the error indicator for the stream is set and getc returns EOF. 7.23.7.6 The getchar function Synopsis #include <stdio.h> int getchar(void);
1
2
3
Description The getchar function is equivalent to getc with the argument stdin. Returns The getchar function returns the next character from the input stream pointed to by stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and getchar returns EOF. If a read error occurs, the error indicator for the stream is set and getchar returns EOF. 7.23.7.7 The putc function Synopsis #include <stdio.h> int putc(int c, FILE *stream);
1
2
Description The putc function is equivalent to fputc, except that if it is implemented as a macro, it may evaluate stream more than once, so that argument should never be an expression with side effects.
3
Returns The putc function returns the character written. If a write error occurs, the error indicator for the stream is set and putc returns EOF. 7.23.7.8 The putchar function Synopsis #include <stdio.h> int putchar(int c);
1
2
3
Description The putchar function is equivalent to putc with the second argument stdout. Returns The putchar function returns the character written. If a write error occurs, the error indicator for the stream is set and putchar returns EOF. 7.23.7.9 The puts function Synopsis #include <stdio.h> int puts(const char *s);
1
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Description The puts function writes the string pointed to by s to the stream pointed to by stdout, and appends a new-line character to the output. The terminating null character is not written. Returns The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative value. 7.23.7.10 The ungetc function Synopsis #include <stdio.h> int ungetc(int c, FILE *stream);
1
2
Description The ungetc function pushes the character specified by c (converted to an unsigned char) back onto the input stream pointed to by stream. Pushed-back characters will be returned by subsequent reads on that stream in the reverse order of their pushing. A successful intervening call (with the stream pointed to by stream) to a file positioning function (fseek, fsetpos, or rewind) discards any pushed-back characters for the stream. The external storage corresponding to the stream is unchanged.
3
One character of pushback is guaranteed. If the ungetc function is called too many times on the same stream without an intervening read or file positioning operation on that stream, the operation may fail.
4
If the value of c equals that of the macro EOF, the operation fails and the input stream is unchanged.
5
A successful call to the ungetc function clears the end-of-file indicator for the stream. The value of the file position indicator for the stream after reading or discarding all pushed-back characters shall be the same as it was before the characters were pushed back.353) For a text stream, the value of its file position indicator after a successful call to the ungetc function is unspecified until all pushed-back characters are read or discarded. For a binary stream, its file position indicator is decremented by each successful call to the ungetc function; if its value was zero before a call, it has an indeterminate representation after the call354) .
6
Returns The ungetc function returns the character pushed back after conversion, or EOF if the operation fails. Forward references: file positioning functions (7.23.9).
7.23.8
Direct input/output functions
7.23.8.1 The fread function Synopsis 1
2
#include <stdio.h> size_t fread(void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream);
Description The fread function reads, into the array pointed to by ptr, up to nmemb elements whose size is specified by size, from the stream pointed to by stream. For each object, size calls are made to the fgetc function and the results stored, in the order read, in an array of unsigned char exactly overlaying the object. The file position indicator for the stream (if defined) is advanced by the number of characters successfully read. If an error occurs, the resulting representation of the file 353) Note that a file positioning function could further modify the file position indicator after discarding any pushed-back
characters. 354) See "future library directions" (7.33.15).
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position indicator for the stream is indeterminate. If a partial element is read, its representation is indeterminate.
3
Returns The fread function returns the number of elements successfully read, which may be less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero, fread returns zero and the contents of the array and the state of the stream remain unchanged. 7.23.8.2 The fwrite function Synopsis #include <stdio.h> size_t fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream);
1
2
3
Description The fwrite function writes, from the array pointed to by ptr, up to nmemb elements whose size is specified by size, to the stream pointed to by stream. For each object, size calls are made to the fputc function, taking the values (in order) from an array of unsigned char exactly overlaying the object. The file position indicator for the stream (if defined) is advanced by the number of characters successfully written. If an error occurs, the resulting representation of the file position indicator for the stream is indeterminate. Returns The fwrite function returns the number of elements successfully written, which will be less than nmemb only if a write error is encountered. If size or nmemb is zero, fwrite returns zero and the state of the stream remains unchanged.
7.23.9
File positioning functions
7.23.9.1 The fgetpos function Synopsis #include <stdio.h> int fgetpos(FILE * restrict stream, fpos_t * restrict pos);
1
2
3
Description The fgetpos function stores the current values of the parse state (if any) and file position indicator for the stream pointed to by stream in the object pointed to by pos. The values stored contain unspecified information usable by the fsetpos function for repositioning the stream to its position at the time of the call to the fgetpos function. Returns If successful, the fgetpos function returns zero; on failure, the fgetpos function returns nonzero and stores an implementation-defined positive value in errno. Forward references: the fsetpos function (7.23.9.3). 7.23.9.2 The fseek function Synopsis #include <stdio.h> int fseek(FILE *stream, long int offset, int whence);
1
2
Description The fseek function sets the file position indicator for the stream pointed to by stream. If a read or write error occurs, the error indicator for the stream is set and fseek fails. 350
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3
For a binary stream, the new position, measured in characters from the beginning of the file, is obtained by adding offset to the position specified by whence. The specified position is the beginning of the file if whence is SEEK_SET, the current value of the file position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not meaningfully support fseek calls with a whence value of SEEK_END.
4
For a text stream, either offset shall be zero, or offset shall be a value returned by an earlier successful call to the ftell function on a stream associated with the same file and whence shall be SEEK_SET.
5
After determining the new position, a successful call to the fseek function undoes any effects of the ungetc function on the stream, clears the end-of-file indicator for the stream, and then establishes the new position. After a successful fseek call, the next operation on an update stream may be either input or output.
6
Returns The fseek function returns nonzero only for a request that cannot be satisfied. Forward references: the ftell function (7.23.9.4). 7.23.9.3 The fsetpos function Synopsis
1
2
3
4
#include <stdio.h> int fsetpos(FILE *stream, const fpos_t *pos);
Description The fsetpos function sets the mbstate_t object (if any) and file position indicator for the stream pointed to by stream according to the value of the object pointed to by pos, which shall be a value obtained from an earlier successful call to the fgetpos function on a stream associated with the same file. If a read or write error occurs, the error indicator for the stream is set and fsetpos fails. A successful call to the fsetpos function undoes any effects of the ungetc function on the stream, clears the end-of-file indicator for the stream, and then establishes the new parse state and position. After a successful fsetpos call, the next operation on an update stream may be either input or output. Returns If successful, the fsetpos function returns zero; on failure, the fsetpos function returns nonzero and stores an implementation-defined positive value in errno. 7.23.9.4 The ftell function Synopsis
1
2
3
#include <stdio.h> long int ftell(FILE *stream);
Description The ftell function obtains the current value of the file position indicator for the stream pointed to by stream. For a binary stream, the value is the number of characters from the beginning of the file. For a text stream, its file position indicator contains unspecified information, usable by the fseek function for returning the file position indicator for the stream to its position at the time of the ftell call; the difference between two such return values is not necessarily a meaningful measure of the number of characters written or read. Returns If successful, the ftell function returns the current value of the file position indicator for the stream. On failure, the ftell function returns -1L and stores an implementation-defined positive value in errno. § 7.23.9.4
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7.23.9.5 The rewind function Synopsis #include <stdio.h> void rewind(FILE *stream);
1
2
Description The rewind function sets the file position indicator for the stream pointed to by stream to the beginning of the file. It is equivalent to (void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared.
3
Returns The rewind function returns no value.
7.23.10
Error-handling functions
7.23.10.1 The clearerr function Synopsis #include <stdio.h> void clearerr(FILE *stream);
1
2
3
Description The clearerr function clears the end-of-file and error indicators for the stream pointed to by stream. Returns The clearerr function returns no value. 7.23.10.2 The feof function Synopsis #include <stdio.h> int feof(FILE *stream);
1
2
Description The feof function tests the end-of-file indicator for the stream pointed to by stream.
3
Returns The feof function returns nonzero if and only if the end-of-file indicator is set for stream.
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7.23.10.3 The ferror function Synopsis 1
#include <stdio.h> int ferror(FILE *stream);
2
Description The ferror function tests the error indicator for the stream pointed to by stream.
3
Returns The ferror function returns nonzero if and only if the error indicator is set for stream. 7.23.10.4 The perror function Synopsis
1
2
3
#include <stdio.h> void perror(const char *s);
Description The perror function maps the error number in the integer expression errno to an error message. It writes a sequence of characters to the standard error stream thus: first (if s is not a null pointer and the character pointed to by s is not the null character), the string pointed to by s followed by a colon (:) and a space; then an appropriate error message string followed by a new-line character. The contents of the error message strings are the same as those returned by the strerror function with argument errno. Returns The perror function returns no value. Forward references: the strerror function (7.26.6.3).
§ 7.23.10.4
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General utilities <stdlib.h>
1
The header <stdlib.h> declares several types and functions of general utility, and defines several macros.355)
2
The feature test macro __STDC_VERSION_STDLIB_H__ expands to the token 202311L.
3
The types declared are size_t and wchar_t (both described in 7.21), once_flag (described in 7.28), div_t
which is a structure type that is the type of the value returned by the div function, ldiv_t
which is a structure type that is the type of the value returned by the ldiv function, and lldiv_t
which is a structure type that is the type of the value returned by the lldiv function. 4
The macros defined are NULL (described in 7.21); ONCE_FLAG_INIT (described in 7.28); EXIT_FAILURE
and EXIT_SUCCESS
which expand to integer constant expressions that can be used as the argument to the exit function to return unsuccessful or successful termination status, respectively, to the host environment; RAND_MAX
which expands to an integer constant expression that is the maximum value returned by the rand function; and MB_CUR_MAX
which expands to a positive integer expression with type size_t that is the maximum number of bytes in a multibyte character for the extended character set specified by the current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX. 5
The function #include <stdlib.h> void call_once(once_flag *flag, void (*func)(void));
is described in 7.28.2.
7.24.1 1
Numeric conversion functions
The functions atof, atoi, atol, and atoll need not affect the value of the integer expression errno on an error. If the value of the result cannot be represented, the behavior is undefined. 7.24.1.1 The atof function Synopsis #include <stdlib.h> double atof(const char *nptr);
1
355) See "future library directions" (7.33.16).
354
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Description The atof function converts the initial portion of the string pointed to by nptr to double representation. Except for the behavior on error, it is equivalent to strtod(nptr, nullptr)
3
Returns The atof function returns the converted value. Forward references: the strtod, strtof, and strtold functions (7.24.1.5). 7.24.1.2 The atoi, atol, and atoll functions Synopsis #include <stdlib.h> int atoi(const char *nptr); long int atol(const char *nptr); long long int atoll(const char *nptr);
1
2
Description The atoi, atol, and atoll functions convert the initial portion of the string pointed to by nptr to int, long int, and long long int representation, respectively. Except for the behavior on error, they are equivalent to atoi: (int)strtol(nptr, nullptr, 10) atol: strtol(nptr, nullptr, 10) atoll: strtoll(nptr, nullptr, 10)
3
Returns The atoi, atol, and atoll functions return the converted value. Forward references: the strtol, strtoll, strtoul, and strtoull functions (7.24.1.7). 7.24.1.3 The strfromd, strfromf, and strfroml functions Synopsis
1
2
3
#include <stdlib.h> int strfromd(char *restrict s, size_t n, const char *restrict format, double fp); int strfromf(char *restrict s, size_t n, const char *restrict format, float fp); int strfroml(char *restrict s, size_t n, const char *restrict format, long double fp);
Description The strfromd, strfromf, and strfroml functions are equivalent to snprintf(s, n, format, fp) (7.23.6.5), except that the default argument promotions are not applied and the format string shall only contain the character %, an optional precision that does not contain an asterisk *, and one of the conversion specifiers a, A, e, E, f, F, g, or G, which applies to the type (double, float, or long double) indicated by the function suffix (rather than by a length modifier). Use of these functions with any other format string results in undefined behavior. Returns The strfromd, strfromf, and strfroml functions return the number of characters that would have been written had n been sufficiently large, not counting the terminating null character. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. 7.24.1.4 § 7.24.1.4
The strfromdN functions Library
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Synopsis 1
#include <stdlib.h> #ifdef __STDC_IEC_60559_DFP__ int strfromd32(char*restrict s, size_t n, const char*restrict format, _Decimal32 fp); int strfromd64(char*restrict s, size_t n, const char*restrict format, _Decimal64 fp); int strfromd128(char*restrict s, size_t n, const char*restrict format, _Decimal128 fp); #endif
2
3
Description The strfromdN functions are equivalent to snprintf(s, n, format, fp) (7.23.6.5), except the format string contains only the character %, an optional precision that does not contain an asterisk *, and one of the conversion specifiers a, A, e, E, f, F, g, or G, which applies to the type (_Decimal32, _Decimal64, or _Decimal128) indicated by the function suffix (rather than by a length modifier). Use of these functions with any other format string results in undefined behavior. Returns The strfromdN functions return the number of characters that would have been written had n been sufficiently large, not counting the terminating null character. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. 7.24.1.5 The strtod, strtof, and strtold functions Synopsis #include <stdlib.h> double strtod(const char *restrict nptr, char **restrict endptr); float strtof(const char *restrict nptr, char **restrict endptr); long double strtold(const char *restrict nptr, char **restrict endptr);
1
2
3
Description The strtod, strtof, and strtold functions convert the initial portion of the string pointed to by nptr to double, float, and long double representation, respectively. First, they decompose the input string into three parts: an initial, possibly empty, sequence of white-space characters, a subject sequence resembling a floating constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, they attempt to convert the subject sequence to a floating-point number, and return the result. The expected form of the subject sequence is an optional plus or minus sign, then one of the following: — a nonempty sequence of decimal digits optionally containing a decimal-point character, then an optional exponent part as defined in 6.4.4.2, excluding any digit separators (6.4.4.1); — a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a decimalpoint character, then an optional binary exponent part as defined in 6.4.4.2, excluding any digit separators; — INF or INFINITY, ignoring case — NAN or NAN(n-char-sequenceopt ), ignoring case in the NAN part, where: n-char-sequence: digit nondigit n-char-sequence digit n-char-sequence nondigit The subject sequence is defined as the longest initial subsequence of the input string, starting with the first non-white-space character, that is of the expected form. The subject sequence contains no characters if the input string is not of the expected form. 356
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4
If the subject sequence has the expected form for a floating-point number, the sequence of characters starting with the first digit or the decimal-point character (whichever occurs first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the decimal-point character is used in place of a period, and that if neither an exponent part nor a decimal-point character appears in a decimal floating-point number, or if a binary exponent part does not appear in a hexadecimal floating-point number, an exponent part of the appropriate type with value zero is assumed to follow the last digit in the string. If the subject sequence begins with a minus sign, the sequence is interpreted as negated356) .
5
A character sequence INF or INFINITY is interpreted as an infinity, if representable in the return type, else like a floating constant that is too large for the range of the return type. A character sequence NAN or NAN(n-char-sequenceopt ) is interpreted as a quiet NaN, if supported in the return type, else like a subject sequence part that does not have the expected form; the meaning of the n-char sequence is implementation-defined.357) A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
6
If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the value resulting from the conversion is correctly rounded.
7
In other than the "C" locale, additional locale-specific subject sequence forms may be accepted.
8
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
9
10
11
Recommended practice If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and the result is not exactly representable, the result should be one of the two numbers in the appropriate internal format that are adjacent to the hexadecimal floating source value, with the extra stipulation that the error should have a correct sign for the current rounding direction. If the subject sequence has the decimal form and at most M significant digits, where M is the maximum value of the T_DECIMAL_DIG macros (defined in <float.h>), the result should be correctly rounded. If the subject sequence D has the decimal form and more than M significant digits, consider the two bounding, adjacent decimal strings L and U, both having M significant digits, such that the values of L, D, and U satisfy L ≤ D ≤ U. The result should be one of the (equal or adjacent) values that would be obtained by correctly rounding L and U according to the current rounding direction, with the extra stipulation that the error with respect to D should have a correct sign for the current rounding direction.358) Returns The functions return the converted value, if any. If no conversion could be performed, positive or unsigned zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return type and sign of the value); if the integer expression math_errhandling & MATH_ERRNO is nonzero, the integer expression errno acquires the value of ERANGE; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the "overflow" floating-point exception is raised. If the result underflows (7.12.1), the functions return a value whose magnitude is no greater than the smallest normalized positive number in the return type; if the integer expression math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the value ERANGE is implementation-defined; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point exception is raised is implementation-defined. 356) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two methods could yield different results if rounding is toward positive or negative infinity. In either case, the functions honor the sign of zero if floating-point arithmetic supports signed zeros. 357) An implementation can use the n-char sequence to determine extra information to be represented in the NaN’s significand. 358) M is sufficiently large that L and U will usually correctly round to the same internal floating value, but if not will correctly round to adjacent values.
§ 7.24.1.5
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7.24.1.6 The strtodN functions Synopsis #include <stdlib.h> #ifdef __STDC_IEC_60559_DFP__ _Decimal32 strtod32(const char * restrict nptr, char ** restrict endptr); _Decimal64 strtod64(const char * restrict nptr,char ** restrict endptr); _Decimal128 strtod128(const char * restrict nptr,char ** restrict endptr); #endif
1
2
3
Description The strtodN functions convert the initial portion of the string pointed to by nptr to decimal floating type representation. First, they decompose the input string into three parts: an initial, possibly empty, sequence of white-space characters; a subject sequence resembling a floating constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, they attempt to convert the subject sequence to a floating-point number, and return the result. The expected form of the subject sequence is an optional plus or minus sign, then one of the following: — a nonempty sequence of decimal digits optionally containing a decimal-point character, then an optional exponent part as defined in 6.4.4.2, excluding any digit separators (6.4.4.1) — a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a decimalpoint character, then an optional binary exponent part as defined in 6.4.4.2, excluding any digit separators (6.4.4.1). — INF or INFINITY, ignoring case — NAN or NAN(d-char-sequenceopt ), ignoring case in the NAN part, where: d-char-sequence: digit nondigit d-char-sequence digit d-char-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input string, starting with the first non-white-space character, that is of the expected form. The subject sequence contains no characters if the input string is not of the expected form. 4
If the subject sequence has the expected form for a floating-point number, the sequence of characters starting with the first digit or the decimal-point character (whichever occurs first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the decimal-point character is used in place of a period, and that if neither an exponent part nor a decimal-point character appears in a decimal floating-point number, or if a binary exponent part does not appear in a hexadecimal floating-point number, an exponent part of the appropriate type with value zero is assumed to follow the last digit in the string. If the subject sequence begins with a minus sign, the sequence is interpreted as negated before rounding and the sign s is set to −1, else s is set to 1.
5
If the subject sequence has the expected form for a decimal floating-point number, the value resulting from the conversion is correctly rounded and the coefficient c and the quantum exponent q are determined by the rules in 6.4.4.2 for a decimal floating constant of decimal type.
6
If the subject sequence has the expected form for a hexadecimal floating-point number, the value resulting from the conversion is correctly rounded provided the subject sequence has at most 358
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M significant hexadecimal digits, where M ≥ ⌈(P − 1)/4⌉ + 1 is implementation-defined, and P is the maximum precision of the supported radix-2 floating types and binary non-arithmetic interchange formats.359) If all subject sequences of hexadecimal form are correctly rounded, M may be regarded as infinite. If the subject sequence has more than M significant hexadecimal digits, the implementation may first round to M significant hexadecimal digits according to the applicable rounding direction mode, signaling exceptions as though converting from a wider format, then correctly round the result of the shortened hexadecimal input to the result type. The preferred quantum exponent for the result is 0 if the hexadecimal number is exactly represented in the decimal type; the preferred quantum exponent for the result is the least possible if the hexadecimal number is not exactly represented in the decimal type. 7
A character sequence INF or INFINITY is interpreted as an infinity. A character sequence NAN or NAN(d-char-sequenceopt ), is interpreted as a quiet NaN; the meaning of the d-char sequence is implementation-defined.360) A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
8
In other than the "C" locale, additional locale-specific subject sequence forms may be accepted.
9
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
10
Returns The strtodN functions return the converted value, if any. If no conversion could be performed, the value of the triple (+1, 0, 0) is returned. If the correct value overflows: — the value of the macro ERANGE is stored in errno if the integer expression math_errhandling & MATH_ERRNO is nonzero; — the "overflow" floating-point exception is raised if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero. If the result underflows (7.12.1), whether errno acquires the value ERANGE if the integer expression math_errhandling & MATH_ERRNO is nonzero is implementation-defined; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point exception is raised is implementation-defined.
11
EXAMPLE Following are subject sequences of the decimal form and the resulting triples (s, c, q) produced by strtod64. Note that for _Decimal64, the precision (maximum coefficient length) is 16 and the quantum exponent range is −398 ≤ q ≤ 369. "0" "0.00" "123" "-123" "1.23E3" "1.23E+3" "12.3E+7" "12.0" "12.3" "0.00123" "-1.23E-12" "1234.5E-4" "-0" "-0.00" "0E+7" "-0E-7"
(+1, 0, 0) (+1, 0, −2) (+1, 123, 0) (−1, 123, 0) (+1, 123, 1) (+1, 123, 1) (+1, 123, 6) (+1, 120, −1) (+1, 123, −1) (+1, 123, −5) (−1, 123, −14) (+1, 12345, −5) (−1, 0, 0) (−1, 0, −2) (+1, 0, 7) (−1, 0, −7)
359) Non-arithmetic interchange formats are an optional feature in Annex H. 360) An implementation may use the d-char sequence to determine extra information to be represented in the NaN’s significand.
§ 7.24.1.6
Library
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ISO/IEC 9899:2023 (E)
"12345678901234567890" "1234E-400" "1234E-402" "1000." ".0001" "1000.e0" ".0001e0" "1000.0" "0.0001" "1000.00" "00.0001" "001000." "001000.0" "001000.00" "00.00" "00." ".00" "00.00e-5" "00.e-5" ".00e-5" "0x1.8p+4" "infinite"
working draft — April 1, 2023
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(+1, 1234567890123457, 4) or (+1, 1234567890123456, 4) depending on rounding mode (+1, 12, −398) or (+1, 13, −398) depending on rounding mode (+1, 0, −398) or (+1, 1, −398) depending on rounding mode (+1, 1000, 0) (+1, 1, −4) (+1, 1000, 0) (+1, 1, −4) (+1, 10000, −1) (+1, 1, −4) (+1, 100000, −2) (+1, 1, −4) (+1, 1000, 0) (+1, 10000, −1) (+1, 100000, −2) (+1, 0, −2) (+1, 0, 0) (+1, 0, −2) (+1, 0, −7) (+1, 0, −5) (+1, 0, −7) (+1, 24, 0) infinity, and a pointer to "inite" is stored in the object pointed to by endptr, provided endptr is not a null pointer
7.24.1.7 The strtol, strtoll, strtoul, and strtoull functions Synopsis 1
2
#include <stdlib.h> long int strtol(const char *restrict nptr, char **restrict endptr, int base); long long int strtoll(const char *restrict nptr, char **restrict endptr, int base); unsigned long int strtoul(const char *restrict nptr, char **restrict endptr, int base); unsigned long long int strtoull(const char *restrict nptr, char **restrict endptr, int base);
Description The strtol, strtoll, strtoul, and strtoull functions convert the initial portion of the string pointed to by nptr to long int, long long int, unsigned long int, and unsigned long long int representation, respectively. First, they decompose the input string into three parts: an initial, possibly empty, sequence of white-space characters, a subject sequence resembling an integer represented in some radix determined by the value of base, and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, they attempt to convert the subject sequence to an integer, and return the result.
3
If the value of base is zero, the expected form of the subject sequence is that of an integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but not including an integer suffix or any optional digit separators. If the value of base is between 2 and 36 (inclusive), the expected form of the subject sequence is a sequence of letters and digits representing an integer with the radix specified by base, optionally preceded by a plus or minus sign, but not including an integer suffix or any optional digit separators. The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only letters and digits whose ascribed values are less than that of base are permitted. If the value of base is 2, the characters 0b or 0B may optionally precede the sequence of letters and digits, following the sign if present. If the value of base is 16, the characters 0x or 0X may optionally precede the sequence of letters and digits, following the sign if present.
4
The subject sequence is defined as the longest initial subsequence of the input string, starting with the first non-white-space character, that is of the expected form. The subject sequence contains no 360
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characters if the input string is empty or consists entirely of white-space characters, or if the first non-white-space character is other than a sign or a permissible letter or digit. 5
If the subject sequence has the expected form and the value of base is zero, the sequence of characters starting with the first digit is interpreted as an integer constant according to the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value as given above. If the subject sequence begins with a minus sign, the resulting value is the negative of the converted value; for functions whose return type is an unsigned integer type this action is performed in the return type. A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
6
In other than the "C" locale, additional locale-specific subject sequence forms may be accepted.
7
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
8
Returns The strtol, strtoll, strtoul, and strtoull functions return the converted value, if any. If no conversion could be performed, zero is returned. If the correct value is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type and sign of the value, if any), and the value of the macro ERANGE is stored in errno.
7.24.2
Pseudo-random sequence generation functions
7.24.2.1 The rand function Synopsis 1
2
#include <stdlib.h> int rand(void);
Description The rand function computes a sequence of pseudo-random integers in the range 0 to RAND_MAX inclusive.
3
The rand function is not required to avoid data races with other calls to pseudo-random sequence generation functions. The implementation shall behave as if no library function calls the rand function.
4
NOTE 1 There are no guarantees as to the quality of the random sequence produced and some implementations are known to produce sequences with distressingly non-random low-order bits. Applications with particular requirements should use a generator that is known to be sufficient for their needs.
5
Returns The rand function returns a pseudo-random integer.
6
Environmental limits The value of the RAND_MAX macro shall be at least 32767. 7.24.2.2 The srand function Synopsis
1
2
#include <stdlib.h> void srand(unsigned int seed);
Description The srand function uses the argument as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls to rand. If srand is then called with the same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is called before any calls to srand have been made, the same sequence shall be generated as when srand is first called with a seed value of 1. § 7.24.2.2
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The srand function is not required to avoid data races with other calls to pseudo-random sequence generation functions. The implementation shall behave as if no library function calls the srand function.
4
Returns The srand function returns no value.
5
EXAMPLE The following functions define a portable implementation of rand and srand. static unsigned long int next = 1; int rand(void) // RAND_MAX assumed to be 32767 { next = next * 1103515245 + 12345; return (unsigned int)(next/65536) % 32768; } void srand(unsigned int seed) { next = seed; }
7.24.3
Memory management functions
1
The order and contiguity of storage allocated by successive calls to the aligned_alloc, calloc, malloc, and realloc functions is unspecified. The pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to a pointer to any type of object with a fundamental alignment requirement and size less than or equal to the size requested. It may then be used to access such an object or an array of such objects in the space allocated (until the space is explicitly deallocated). The lifetime of an allocated object extends from the allocation until the deallocation. Each such allocation shall yield a pointer to an object disjoint from any other object. The pointer returned points to the start (lowest byte address) of the allocated space. If the space cannot be allocated, a null pointer is returned. If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned to indicate an error, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.
2
For purposes of determining the existence of a data race, memory allocation functions behave as though they accessed only memory locations accessible through their arguments and not other static duration storage. These functions may, however, visibly modify the storage that they allocate or deallocate. Calls to these functions that allocate or deallocate a particular region of memory shall occur in a single total order, and each such deallocation call shall synchronize with the next allocation (if any) in this order. 7.24.3.1 The aligned_alloc function Synopsis #include <stdlib.h> void *aligned_alloc(size_t alignment, size_t size);
1
2
3
Description The aligned_alloc function allocates space for an object whose alignment is specified by alignment361) , whose size is specified by size, and whose representation is indeterminate. If the value of alignment is not a valid alignment supported by the implementation the function shall fail by returning a null pointer. Returns The aligned_alloc function returns either a null pointer or a pointer to the allocated space. 361) The alignment requirements from 7.24.3 also apply even if the requested alignment is less strict
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7.24.3.2 The calloc function Synopsis 1
#include <stdlib.h> void *calloc(size_t nmemb, size_t size);
2
Description The calloc function allocates space for an array of nmemb objects, each of whose size is size. The space is initialized to all bits zero.362)
3
Returns The calloc function returns either a pointer to the allocated space or a null pointer if the space cannot be allocated or if the product nmemb * size would wraparound size_t. 7.24.3.3 The free function Synopsis
1
2
3
#include <stdlib.h> void free(void *ptr);
Description The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined. Returns The free function returns no value. 7.24.3.4 The free_sized function Synopsis
1
2
#include <stdlib.h> void free_sized(void *ptr, size_t size);
Description If ptr is a null pointer or the result obtained from a call to malloc, realloc, or calloc, where size size is equal to the requested allocation size, this function is equivalent to free(ptr). Otherwise, the behavior is undefined.
3
NOTE 1 A conforming implementation may ignore size and call free.
4
NOTE 2 The result of an aligned_alloc call may not be passed to free_sized.
5
6
Recommended practice Implementations may provide extensions to query the usable size of an allocation, or to determine the usable size of the allocation that would result if a request for some other size were to succeed. Such implementations should allow passing the resulting usable size as the size parameter, and provide functionality equivalent to free in such cases. Returns The free_sized function returns no value. 7.24.3.5 The free_aligned_sized function Synopsis
1
#include <stdlib.h> void free_aligned_sized(void *ptr, size_t alignment, size_t size); 362) Note that this need not be the same as the representation of floating-point zero or a null pointer constant.
§ 7.24.3.5
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ISO/IEC 9899:2023 (E)
2
working draft — April 1, 2023
Description If ptr is a null pointer or the result obtained from a call to aligned_alloc, where alignment is equal to the requested allocation alignment and size is equal to the requested allocation size, this function is equivalent to free(ptr). Otherwise, the behavior is undefined.
3
NOTE 1 A conforming implementation may ignore alignment and size and call free.
4
NOTE 2 The result of an malloc, calloc, or realloc call may not be passed to free_aligned_sized.
5
6
N3096
Recommended practice Implementations may provide extensions to query the usable size of an allocation, or to determine the usable size of the allocation that would result if a request for some other size were to succeed. Such implementations should allow passing the resulting usable size as the size parameter, and provide functionality equivalent to free in such cases. Returns The free_aligned_sized function returns no value. 7.24.3.6 The malloc function Synopsis #include <stdlib.h> void *malloc(size_t size);
1
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Description The malloc function allocates space for an object whose size is specified by size and whose representation is indeterminate. Returns The malloc function returns either a null pointer or a pointer to the allocated space. 7.24.3.7 The realloc function Synopsis #include <stdlib.h> void *realloc(void *ptr, size_t size);
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Description The realloc function deallocates the old object pointed to by ptr and returns a pointer to a new object that has the size specified by size. The contents of the new object shall be the same as that of the old object prior to deallocation, up to the lesser of the new and old sizes. Any bytes in the new object beyond the size of the old object have unspecified values. If ptr is a null pointer, the realloc function behaves like the malloc function for the specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to the free or realloc function, or if the size is zero, the behavior is undefined. If memory for the new object is not allocated, the old object is not deallocated and its value is unchanged. Returns The realloc function returns a pointer to the new object (which may have the same value as a pointer to the old object), or a null pointer if the new object has not been allocated.
7.24.4
Communication with the environment
7.24.4.1 The abort function Synopsis #include <stdlib.h> [[noreturn]] void abort(void);
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Description The abort function causes abnormal program termination to occur, unless the signal SIGABRT is being caught and the signal handler does not return. Whether open streams with unwritten buffered data are flushed, open streams are closed, or temporary files are removed is implementationdefined. An implementation-defined form of the status unsuccessful termination is returned to the host environment by means of the function call raise(SIGABRT). Returns The abort function does not return to its caller. 7.24.4.2 The atexit function Synopsis
1
2
#include <stdlib.h> int atexit(void (*func)(void));
Description The atexit function registers the function pointed to by func, to be called without arguments at normal program termination.363) It is unspecified whether a call to the atexit function that does not happen before the exit function is called will succeed.
3
Environmental limits The implementation shall support the registration of at least 32 functions.
4
Returns The atexit function returns zero if the registration succeeds, nonzero if it fails. Forward references: the at_quick_exit function (7.24.4.3), the exit function (7.24.4.4). 7.24.4.3 The at_quick_exit function Synopsis
1
2
#include <stdlib.h> int at_quick_exit(void (*func)(void));
Description The at_quick_exit function registers the function pointed to by func, to be called without arguments should quick_exit be called.364) It is unspecified whether a call to the at_quick_exit function that does not happen before the quick_exit function is called will succeed.
3
Environmental limits The implementation shall support the registration of at least 32 functions.
4
Returns The at_quick_exit function returns zero if the registration succeeds, nonzero if it fails. Forward references: the quick_exit function (7.24.4.7). 7.24.4.4 The exit function Synopsis
1
#include <stdlib.h> [[noreturn]] void exit(int status);
363) The atexit function registrations are distinct from the at_quick_exit registrations, so applications might need to call both registration functions with the same argument. 364) The at_quick_exit function registrations are distinct from the atexit registrations, so applications might need to call both registration functions with the same argument.
§ 7.24.4.4
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ISO/IEC 9899:2023 (E)
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Description The exit function causes normal program termination to occur. No functions registered by the at_quick_exit function are called. If a program calls the exit function more than once, or calls the quick_exit function in addition to the exit function, the behavior is undefined.
3
First, all functions registered by the atexit function are called, in the reverse order of their registration,365) except that a function is called after any previously registered functions that had already been called at the time it was registered. If, during the call to any such function, a call to the longjmp function is made that would terminate the call to the registered function, the behavior is undefined.
4
Next, all open streams with unwritten buffered data are flushed, all open streams are closed, and all files created by the tmpfile function are removed.
5
Finally, control is returned to the host environment. If the value of status is zero or EXIT_SUCCESS, an implementation-defined form of the status successful termination is returned. If the value of status is EXIT_FAILURE, an implementation-defined form of the status unsuccessful termination is returned. Otherwise the status returned is implementation-defined.
6
Returns The exit function cannot return to its caller. 7.24.4.5 The _Exit function Synopsis #include <stdlib.h> [[noreturn]] void _Exit(int status);
1
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3
Description The _Exit function causes normal program termination to occur and control to be returned to the host environment. No functions registered by the atexit function, the at_quick_exit function, or signal handlers registered by the signal function are called. The status returned to the host environment is determined in the same way as for the exit function (7.24.4.4). Whether open streams with unwritten buffered data are flushed, open streams are closed, or temporary files are removed is implementation-defined. Returns The _Exit function cannot return to its caller. 7.24.4.6 The getenv function Synopsis #include <stdlib.h> char *getenv(const char *name);
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Description The getenv function searches an environment list, provided by the host environment, for a string that matches the string pointed to by name. The set of environment names and the method for altering the environment list are implementation-defined. The getenv function need not avoid data races with other threads of execution that modify the environment list.366) The implementation shall behave as if no library function calls the getenv function. Returns The getenv function returns a pointer to a string associated with the matched list member. The string pointed to shall not be modified by the program, but may be overwritten by a subsequent call to the getenv function. If the specified name cannot be found, a null pointer is returned. 365) Each function is called as many times as it was registered, and in the correct order with respect to other registered
functions. 366) Many implementations provide non-standard functions that modify the environment list.
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7.24.4.7 The quick_exit function Synopsis #include <stdlib.h> [[noreturn]] void quick_exit(int status);
1
2
Description The quick_exit function causes normal program termination to occur. No functions registered by the atexit function or signal handlers registered by the signal function are called. If a program calls the quick_exit function more than once, or calls the exit function in addition to the quick_exit function, the behavior is undefined. If a signal is raised while the quick_exit function is executing, the behavior is undefined.
3
The quick_exit function first calls all functions registered by the at_quick_exit function, in the reverse order of their registration,367) except that a function is called after any previously registered functions that had already been called at the time it was registered. If, during the call to any such function, a call to the longjmp function is made that would terminate the call to the registered function, the behavior is undefined.
4
Then control is returned to the host environment by means of the function call _Exit(status).
5
Returns The quick_exit function cannot return to its caller. 7.24.4.8 The system function Synopsis #include <stdlib.h> int system(const char *string);
1
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3
Description If string is a null pointer, the system function determines whether the host environment has a command processor. If string is not a null pointer, the system function passes the string pointed to by string to that command processor to be executed in a manner which the implementation shall document; this might then cause the program calling system to behave in a non-conforming manner or to terminate. Returns If the argument is a null pointer, the system function returns nonzero only if a command processor is available. If the argument is not a null pointer, and the system function does return, it returns an implementation-defined value.
7.24.5
Searching and sorting utilities
1
These utilities make use of a comparison function to search or sort arrays of unspecified type. Where an argument declared as size_t nmemb specifies the length of the array for a function, nmemb can have the value zero on a call to that function; the comparison function is not called, a search finds no matching element, and sorting performs no rearrangement. Pointer arguments on such a call shall still have valid values, as described in 7.1.4.
2
The implementation shall ensure that the second argument of the comparison function (when called from bsearch), or both arguments (when called from qsort), are pointers to elements of the array.368) 367) Each function is called as many times as it was registered, and in the correct order with respect to other registered functions. 368) That is, if the value passed is p, then the following expressions are always nonzero:
((char *)p - (char *)base) % size == 0 (char *)p >= (char *)base (char *)p < (char *)base + nmemb * size
§ 7.24.5
Library
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The first argument when called from bsearch shall equal key. 3
The comparison function shall not alter the contents of the array. The implementation may reorder elements of the array between calls to the comparison function, but shall not alter the contents of any individual element.
4
When the same objects (consisting of size bytes, irrespective of their current positions in the array) are passed more than once to the comparison function, the results shall be consistent with one another. That is, for qsort they shall define a total ordering on the array, and for bsearch the same object shall always compare the same way with the key.
5
A sequence point occurs immediately before and immediately after each call to the comparison function, and also between any call to the comparison function and any movement of the objects passed as arguments to that call. 7.24.5.1 The bsearch generic function Synopsis #include <stdlib.h> QVoid *bsearch(const void *key, QVoid *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *));
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Description The bsearch generic function searches an array of nmemb objects, the initial element of which is pointed to by base, for an element that matches the object pointed to by key. The size of each element of the array is specified by size. The comparison function pointed to by compar is called with two arguments that point to the key object and to an array element, in that order. The function shall return an integer less than, equal to, or greater than zero if the key object is considered, respectively, to be less than, to match, or to be greater than the array element. The array shall consist of: all the elements that compare less than, all the elements that compare equal to, and all the elements that compare greater than the key object, in that order.369) Returns The bsearch generic function returns a pointer to a matching element of the array, or a null pointer if no match is found. If two elements compare as equal, which element is matched is unspecified. The bsearch function is generic in the qualification of the type pointed to by the argument base. If this argument is a pointer to a const-qualified object type, the returned pointer will be a pointer to const-qualified void. Otherwise, the argument shall be a pointer to an unqualified object type or a null pointer constant370) , and the returned pointer will be a pointer to unqualified void. The external declaration of bsearch has the concrete type: void * (const void *, const void *, size_t, size_t, int (*) (const void *, const void *))
which supports all correct uses. If a macro definition of this generic function is suppressed to access an actual function, the external declaration with this concrete type is visible.371) 7.24.5.2 The qsort function Synopsis #include <stdlib.h> void qsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *));
1
369) In practice, the entire array is sorted according to the comparison function. 370) If the argument is a null pointer and the call is executed, the behavior is undefined. 371) This is an obsolescent feature.
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Description The qsort function sorts an array of nmemb objects, the initial element of which is pointed to by base. The size of each object is specified by size.
3
The contents of the array are sorted into ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared. The function shall return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.
4
If two elements compare as equal, their order in the resulting sorted array is unspecified.
5
Returns The qsort function returns no value.
7.24.6
Integer arithmetic functions
7.24.6.1 The abs, labs, and llabs functions Synopsis #include <stdlib.h> int abs(int j); long int labs(long int j); long long int llabs(long long int j);
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Description The abs, labs, and llabs functions compute the absolute value of an integer j. If the result cannot be represented, the behavior is undefined.372) Returns The abs, labs, and llabs, functions return the absolute value. 7.24.6.2 The div, ldiv, and lldiv functions Synopsis #include <stdlib.h> div_t div(int numer, int denom); ldiv_t ldiv(long int numer, long int denom); lldiv_t lldiv(long long int numer, long long int denom);
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Description The div, ldiv, and lldiv, functions compute numer/denom and numer%denom in a single operation. Returns The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and lldiv_t, respectively, comprising both the quotient and the remainder. The structures shall contain (in either order) the members quot (the quotient) and rem (the remainder), each of which has the same type as the arguments numer and denom. If either part of the result cannot be represented, the behavior is undefined.
7.24.7 1
Multibyte/wide character conversion functions
The behavior of the multibyte character functions is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, each of the mbtowc and wctomb functions is placed into its initial conversion state prior to the first call to the function and can be returned to that state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer cause the internal conversion state of the function to be altered as necessary. It is implementation-defined whether internal conversion state has thread storage duration, and whether a newly created thread has the same state as the current thread at the time of creation, or the initial 372) The absolute value of the most negative number is not representable.
§ 7.24.7
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conversion state. A call with s as a null pointer causes these functions to return a nonzero value if encodings have state dependency, and zero otherwise.373) 2
Changing the LC_CTYPE category causes the internal object describing the conversion state of the mbtowc and wctomb functions to have an indeterminate representation. It is implementation-defined whether these functions avoid data races with other calls to the same function. 7.24.7.1 The mblen function Synopsis #include <stdlib.h> int mblen(const char *s, size_t n);
1
2
Description If s is not a null pointer, the mblen function determines the number of bytes contained in the multibyte character pointed to by s. Except that the conversion state of the mbtowc function is not affected, it is equivalent to mbtowc((wchar_t *)0, (const char *)0, 0); mbtowc((wchar_t *)0, s, n);
3
Returns If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte character encodings, respectively, do or do not have state-dependent encodings. If s is not a null pointer, the mblen function either returns 0 (if s points to the null character), or returns the number of bytes that are contained in the multibyte character (if the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid multibyte character). Forward references: the mbtowc function (7.24.7.2). 7.24.7.2 The mbtowc function Synopsis #include <stdlib.h> int mbtowc(wchar_t * restrict pwc, const char * restrict s, size_t n);
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3
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Description If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with the byte pointed to by s to determine the number of bytes needed to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character is complete and valid, it determines the value of the corresponding wide character and then, if pwc is not a null pointer, stores that value in the object pointed to by pwc. If the corresponding wide character is the null wide character, the function is left in the initial conversion state. The implementation shall behave as if no library function calls the mbtowc function. Returns If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte character encodings, respectively, do or do not have state-dependent encodings. If s is not a null pointer, the mbtowc function either returns 0 (if s points to the null character), or returns the number of bytes that are contained in the converted multibyte character (if the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid multibyte character). In no case will the value returned be greater than n or the value of the MB_CUR_MAX macro. 7.24.7.3
The wctomb function
373) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide character codes, but are grouped with an adjacent multibyte character.
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Synopsis #include <stdlib.h> int wctomb(char *s, wchar_t wc);
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4
5
Description The wctomb function determines the number of bytes needed to represent the multibyte character corresponding to the wide character given by wc (including any shift sequences), and stores the multibyte character representation in the array whose first element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters are stored. If wc is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state, and the function is left in the initial conversion state. The implementation shall behave as if no library function calls the wctomb function. Returns If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte character encodings, respectively, do or do not have state-dependent encodings. If s is not a null pointer, the wctomb function returns -1 if the value of wc does not correspond to a valid multibyte character, or returns the number of bytes that are contained in the multibyte character corresponding to the value of wc. In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
7.24.8 1
Multibyte/wide string conversion functions
The behavior of the multibyte string functions is affected by the LC_CTYPE category of the current locale. 7.24.8.1 The mbstowcs function Synopsis
1
2
3
4
#include <stdlib.h> size_t mbstowcs(wchar_t * restrict pwcs, const char * restrict s, size_t n);
Description The mbstowcs function converts a sequence of multibyte characters that begins in the initial shift state from the array pointed to by s into a sequence of corresponding wide characters and stores not more than n wide characters into the array pointed to by pwcs. No multibyte characters that follow a null character (which is converted into a null wide character) will be examined or converted. Each multibyte character is converted as if by a call to the mbtowc function, except that the conversion state of the mbtowc function is not affected. No more than n elements will be modified in the array pointed to by pwcs. If copying takes place between objects that overlap, the behavior is undefined. Returns If an invalid multibyte character is encountered, the mbstowcs function returns (size_t)(-1). Otherwise, the mbstowcs function returns the number of array elements modified, not including a terminating null wide character, if any.374)
374) The array will not be null-terminated if the value returned is n.
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7.24.8.2 The wcstombs function Synopsis #include <stdlib.h> size_t wcstombs(char * restrict s, const wchar_t * restrict pwcs, size_t n);
1
2
3
4
Description The wcstombs function converts a sequence of wide characters from the array pointed to by pwcs into a sequence of corresponding multibyte characters that begins in the initial shift state, and stores these multibyte characters into the array pointed to by s, stopping if a multibyte character would exceed the limit of n total bytes or if a null character is stored. Each wide character is converted as if by a call to the wctomb function, except that the conversion state of the wctomb function is not affected. No more than n bytes will be modified in the array pointed to by s. If copying takes place between objects that overlap, the behavior is undefined. Returns If a wide character is encountered that does not correspond to a valid multibyte character, the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function returns the number of bytes modified, not including a terminating null character, if any.374)
7.24.9
Alignment of memory
7.24.9.1 The memalignment function Synopsis #include <stdlib.h> size_t memalignment(const void * p);
1
2
Description The memalignment function accepts a pointer to any object and returns the maximum alignment satisfied by its address value. The alignment may be an extended alignment and may also be beyond the range supported by the implementation for explicit use by alignas375) . If so, it will satisfy all alignments usable by the implementation. The value returned can be compared to the result of alignof, and if it is greater or equal, the alignment requirement for the type operand is satisfied.
3
Returns The alignment of the pointer p, which is a power of two. If p is a null pointer, an alignment of zero is returned.
4
NOTE 1 An alignment of zero indicates that the tested pointer cannot be used to access an object of any type.
375) The actual alignment of an object may be stricter than the alignment requested for an object by alignas or (implicitly) by an allocation function, but will always satisfy it.
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7.25 _Noreturn <stdnoreturn.h> 1
The header <stdnoreturn.h> defines the macro noreturn
which expands to _Noreturn. 2
The noreturn macro and the <stdnoreturn.h> header are obsolescent features.
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7.26 String handling <string.h> 7.26.1 String function conventions 1
The header <string.h> declares one type, several functions, several type-generic functions, and defines two macros useful for manipulating arrays of character type and other objects treated as arrays of character type.376) The type is size_t and one of the macros is NULL (both described in 7.21). Various methods are used for determining the lengths of the arrays, but in all cases a char * or void * argument points to the initial (lowest addressed) character of the array. If an array is accessed beyond the end of an object, the behavior is undefined.
2
The macro __STDC_VERSION_STRING_H__
is an integer constant expression with a value equivalent to 202311L. 3
Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters.
4
For all functions in this subclause, each character shall be interpreted as if it had the type unsigned char (and therefore every possible object representation is valid and has a different value).
7.26.2
Copying functions
7.26.2.1 The memcpy function Synopsis #include <string.h> void *memcpy(void * restrict s1, const void * restrict s2, size_t n);
1
2
3
Description The memcpy function copies n characters from the object pointed to by s2 into the object pointed to by s1. If copying takes place between objects that overlap, the behavior is undefined. Returns The memcpy function returns the value of s1. 7.26.2.2 The memccpy function Synopsis #include <string.h> void *memccpy(void * restrict s1, const void * restrict s2, int c, size_t n);
1
2
3
Description The memccpy function copies characters from the object pointed to by s2 into the object pointed to by s1, stopping after the first occurrence of character c (converted to an unsigned char) is copied, or after n characters are copied, whichever comes first. If copying takes place between objects that overlap, the behavior is undefined. Returns The memccpy function returns a pointer to the character after the copy of c in s1, or a null pointer if c was not found in the first n characters of s2. 7.26.2.3
The memmove function
376) See "future library directions" (7.33.17).
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Synopsis 1
2
3
#include <string.h> void *memmove(void *s1, const void *s2, size_t n);
Description The memmove function copies n characters from the object pointed to by s2 into the object pointed to by s1. Copying takes place as if the n characters from the object pointed to by s2 are first copied into a temporary array of n characters that does not overlap the objects pointed to by s1 and s2, and then the n characters from the temporary array are copied into the object pointed to by s1. Returns The memmove function returns the value of s1. 7.26.2.4 The strcpy function Synopsis
1
2
3
#include <string.h> char *strcpy(char * restrict s1, const char * restrict s2);
Description The strcpy function copies the string pointed to by s2 (including the terminating null character) into the array pointed to by s1. If copying takes place between objects that overlap, the behavior is undefined. Returns The strcpy function returns the value of s1. 7.26.2.5 The strncpy function Synopsis
1
2
3
4
#include <string.h> char *strncpy(char * restrict s1, const char * restrict s2, size_t n);
Description The strncpy function copies not more than n characters (characters that follow a null character are not copied) from the array pointed to by s2 to the array pointed to by s1.377) If copying takes place between objects that overlap, the behavior is undefined. If the array pointed to by s2 is a string that is shorter than n characters, null characters are appended to the copy in the array pointed to by s1, until n characters in all have been written. Returns The strncpy function returns the value of s1. 7.26.2.6 The strdup function Synopsis
1
2
#include <string.h> char *strdup(const char *s);
Description The strdup function creates a copy of the string pointed to by s in a space allocated as if by a call to malloc. 377) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will not be nullterminated.
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Returns The strdup function returns a pointer to the first character of the duplicate string. The returned pointer can be passed to free. If no space can be allocated the strdup function returns a null pointer. 7.26.2.7 The strndup function Synopsis #include <string.h> char *strndup(const char *s, size_t size);
1
2
3
Description The strndup function creates a string initialized with no more than size initial characters of the array pointed to by s and up to the first null character, whichever comes first, in a space allocated as if by a call to malloc. If the array pointed to by s does not contain a null within the first size characters, a null is appended to the copy of the array. Returns The strndup function returns a pointer to the first character of the created string. The returned pointer can be passed to free. If space cannot be allocated the strndup function returns a null pointer.
7.26.3
Concatenation functions
7.26.3.1 The strcat function Synopsis #include <string.h> char *strcat(char * restrict s1, const char * restrict s2);
1
2
3
Description The strcat function appends a copy of the string pointed to by s2 (including the terminating null character) to the end of the string pointed to by s1. The initial character of s2 overwrites the null character at the end of s1. If copying takes place between objects that overlap, the behavior is undefined. Returns The strcat function returns the value of s1. 7.26.3.2 The strncat function Synopsis #include <string.h> char *strncat(char * restrict s1, const char * restrict s2, size_t n);
1
2
3
Description The strncat function appends not more than n characters (a null character and characters that follow it are not appended) from the array pointed to by s2 to the end of the string pointed to by s1. The initial character of s2 overwrites the null character at the end of s1. A terminating null character is always appended to the result.378) If copying takes place between objects that overlap, the behavior is undefined. Returns The strncat function returns the value of s1. Forward references: the strlen function (7.26.6.4). 378) Thus, the maximum number of characters that can end up in the array pointed to by s1 is strlen(s1)+n+1.
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ISO/IEC 9899:2023 (E)
Comparison functions
The sign of a nonzero value returned by the comparison functions memcmp, strcmp, and strncmp is determined by the sign of the difference between the values of the first pair of characters (both interpreted as unsigned char) that differ in the objects being compared. 7.26.4.1 The memcmp function Synopsis
1
#include <string.h> int memcmp(const void *s1, const void *s2, size_t n);
2
Description The memcmp function compares the first n characters of the object pointed to by s1 to the first n characters of the object pointed to by s2379) .
3
Returns The memcmp function returns an integer greater than, equal to, or less than zero, accordingly as the object pointed to by s1 is greater than, equal to, or less than the object pointed to by s2. 7.26.4.2 The strcmp function Synopsis
1
2
3
#include <string.h> int strcmp(const char *s1, const char *s2);
Description The strcmp function compares the string pointed to by s1 to the string pointed to by s2. Returns The strcmp function returns an integer greater than, equal to, or less than zero, accordingly as the string pointed to by s1 is greater than, equal to, or less than the string pointed to by s2. 7.26.4.3 The strcoll function Synopsis
1
2
3
#include <string.h> int strcoll(const char *s1, const char *s2);
Description The strcoll function compares the string pointed to by s1 to the string pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the current locale. Returns The strcoll function returns an integer greater than, equal to, or less than zero, accordingly as the string pointed to by s1 is greater than, equal to, or less than the string pointed to by s2 when both are interpreted as appropriate to the current locale. 7.26.4.4 The strncmp function Synopsis
1
#include <string.h> int strncmp(const char *s1, const char *s2, size_t n);
379) The unused bytes used as padding for purposes of alignment within structure objects take on unspecified values when a value is stored in the object (see 6.2.6.1). Strings shorter than their allocated space and unions can also cause problems in comparison.
§ 7.26.4.4
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Description The strncmp function compares not more than n characters (characters that follow a null character are not compared) from the array pointed to by s1 to the array pointed to by s2. Returns The strncmp function returns an integer greater than, equal to, or less than zero, accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal to, or less than the possibly null-terminated array pointed to by s2. 7.26.4.5 The strxfrm function Synopsis #include <string.h> size_t strxfrm(char * restrict s1, const char * restrict s2, size_t n);
1
2
3
4
Description The strxfrm function transforms the string pointed to by s2 and places the resulting string into the array pointed to by s1. The transformation is such that if the strcmp function is applied to two transformed strings, it returns a value greater than, equal to, or less than zero, corresponding to the result of the strcoll function applied to the same two original strings. No more than n characters are placed into the resulting array pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to be a null pointer. If copying takes place between objects that overlap, the behavior is undefined. Returns The strxfrm function returns the length of the transformed string (not including the terminating null character). If the value returned is n or more, the members of the array pointed to by s1 have an indeterminate representation. EXAMPLE The value of the following expression is the size of the array needed to hold the transformation of the string pointed to by s. 1 + strxfrm(NULL, s, 0)
7.26.5 1
Search functions
7.26.5.1 Introduction The stateless search functions in this section (memchr, strchr, strpbrk, strrchr, strstr) are generic functions. These functions are generic in the qualification of the array to be searched and will return a result pointer to an element with the same qualification as the passed array. If the array to be searched is const-qualified, the result pointer will be to a const-qualified element. If the array to be searched is not const-qualified380) , the result pointer will be to an unqualified element.
2
The external declarations of these generic functions have a concrete function type that returns a pointer to an unqualified element (of type char when specified as QChar, and void when specified as QVoid), and accepts a pointer to a const-qualified array of the same type to search. This signature supports all correct uses. If a macro definition of any of these generic functions is suppressed to access an actual function, the external declaration with the corresponding concrete type is visible.381)
3
The volatile and restrict qualifiers are not accepted on the elements of the array to search. 7.26.5.2 The memchr generic function Synopsis #include <string.h> QVoid *memchr(QVoid *s, int c, size_t n);
1
380) The null pointer constant is not a pointer to a const-qualified type, and therefore the result expression has the type of a
pointer to an unqualified element; however, evaluating such a call is undefined. 381) This is an obsolescent feature.
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Description The memchr generic function locates the first occurrence of c (converted to an unsigned char) in the initial n characters (each interpreted as unsigned char) of the object pointed to by s. The implementation shall behave as if it reads the characters sequentially and stops as soon as a matching character is found. Returns The memchr generic function returns a pointer to the located character, or a null pointer if the character does not occur in the object. 7.26.5.3 The strchr generic function Synopsis
1
#include <string.h> QChar *strchr(QChar *s, int c);
2
Description The strchr generic function locates the first occurrence of c (converted to a char) in the string pointed to by s. The terminating null character is considered to be part of the string.
3
Returns The strchr generic function returns a pointer to the located character, or a null pointer if the character does not occur in the string. 7.26.5.4 The strcspn function Synopsis
1
2
3
#include <string.h> size_t strcspn(const char *s1, const char *s2);
Description The strcspn function computes the length of the maximum initial segment of the string pointed to by s1 which consists entirely of characters not from the string pointed to by s2. Returns The strcspn function returns the length of the segment. 7.26.5.5 The strpbrk generic function Synopsis
1
#include <string.h> QChar *strpbrk(QChar *s1, const char *s2);
2
Description The strpbrk generic function locates the first occurrence in the string pointed to by s1 of any character from the string pointed to by s2.
3
Returns The strpbrk generic function returns a pointer to the character, or a null pointer if no character from s2 occurs in s1. 7.26.5.6 The strrchr generic function Synopsis
1
#include <string.h> QChar *strrchr(QChar *s, int c);
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2
Description The strrchr generic function locates the last occurrence of c (converted to a char) in the string pointed to by s. The terminating null character is considered to be part of the string.
3
Returns The strrchr generic function returns a pointer to the character, or a null pointer if c does not occur in the string. 7.26.5.7 The strspn function Synopsis #include <string.h> size_t strspn(const char *s1, const char *s2);
1
2
3
Description The strspn function computes the length of the maximum initial segment of the string pointed to by s1 which consists entirely of characters from the string pointed to by s2. Returns The strspn function returns the length of the segment. 7.26.5.8 The strstr generic function Synopsis #include <string.h> QChar *strstr(QChar *s1, const char *s2);
1
2
Description The strstr generic function locates the first occurrence in the string pointed to by s1 of the sequence of characters (excluding the terminating null character) in the string pointed to by s2.
3
Returns The strstr generic function returns a pointer to the located string, or a null pointer if the string is not found. If s2 points to a string with zero length, the function returns s1. 7.26.5.9 The strtok function Synopsis #include <string.h> char *strtok(char * restrict s1, const char * restrict s2);
1
2
Description A sequence of calls to the strtok function breaks the string pointed to by s1 into a sequence of tokens, each of which is delimited by a character from the string pointed to by s2. The first call in the sequence has a non-null first argument; subsequent calls in the sequence have a null first argument. If any of the subsequent calls in the sequence is made by a different thread than the first, the behavior is undefined. The separator string pointed to by s2 may be different from call to call.
3
The first call in the sequence searches the string pointed to by s1 for the first character that is not contained in the current separator string pointed to by s2. If no such character is found, then there are no tokens in the string pointed to by s1 and the strtok function returns a null pointer. If such a character is found, it is the start of the first token.
4
The strtok function then searches from there for a character that is contained in the current separator string. If no such character is found, the current token extends to the end of the string pointed to by s1, and subsequent searches for a token will return a null pointer. If such a character is found, it is overwritten by a null character, which terminates the current token. The strtok function saves a pointer to the following character, from which the next search for a token will start. 380
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Each subsequent call, with a null pointer as the value of the first argument, starts searching from the saved pointer and behaves as described above.
6
The strtok function is not required to avoid data races with other calls to the strtok function.382) The implementation shall behave as if no library function calls the strtok function.
7
Returns The strtok function returns a pointer to the first character of a token, or a null pointer if there is no token.
8
EXAMPLE #include <string.h> static char str[] = "?a???b,,,#c"; char *t; t = strtok(str, "?"); // t points to the token "a" t = strtok(NULL, ","); // t points to the token "??b" t = strtok(NULL, "#,"); // t points to the token "c" t = strtok(NULL, "?"); // t is a null pointer
Forward references: The strtok_s function (K.3.7.3.1).
7.26.6
Miscellaneous functions
7.26.6.1 The memset function Synopsis 1
2
3
#include <string.h> void *memset(void *s, int c, size_t n);
Description The memset function copies the value of c (converted to an unsigned char) into each of the first n characters of the object pointed to by s. Returns The memset function returns the value of s. 7.26.6.2 The memset_explicit function Synopsis
1
2
3
#include <string.h> void *memset_explicit(void *s, int c, size_t n);
Description The memset_explicit function copies the value of c (converted to an unsigned char) into each of the first n characters of the object pointed to by s. The purpose of this function is to make sensitive information stored in the object inaccessible383) . Returns The memset_explicit function returns the value of s. 7.26.6.3 The strerror function Synopsis
1
#include <string.h> char *strerror(int errnum); 382) The strtok_s function can be used instead to avoid data races. 383) The intention is that the memory store is always performed (i.e., never elided), regardless of optimizations. This is in contrast to calls to the memset function (7.26.6.1)
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Description The strerror function maps the number in errnum to a message string. Typically, the values for errnum come from errno, but strerror shall map any value of type int to a message. The strerror function is not required to avoid data races with other calls to the strerror function.384) The implementation shall behave as if no library function calls the strerror function. Returns The strerror function returns a pointer to the string, the contents of which are locale-specific. The array pointed to shall not be modified by the program. The behavior is undefined if the returned value is used after a subsequent call to the strerror function, or after the thread which called the function to obtain the returned value has exited. Forward references: The strerror_s function (K.3.7.4.2). 7.26.6.4 The strlen function Synopsis #include <string.h> size_t strlen(const char *s);
1
2
Description The strlen function computes the length of the string pointed to by s.
3
Returns The strlen function returns the number of characters that precede the terminating null character.
384) The strerror_s function can be used instead to avoid data races.
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Type-generic math <tgmath.h>
1
The header <tgmath.h> includes the headers <math.h> and <complex.h> and defines several type-generic macros.
2
The feature test macro __STDC_VERSION_TGMATH_H__ expands to the token 202311L.
3
This clause specifies a many-to-one correspondence of functions in <math.h> and <complex.h> with type-generic macros.385) Use of a type-generic macro invokes a corresponding function whose type is determined by the types of the arguments for particular parameters called the generic parameters.386)
4
Of the <math.h> and <complex.h> functions without an f (float) or l (long double) suffix, several have one or more parameters whose corresponding real type is double. For each such function, except the functions that round result to narrower type (7.12.14) (which are covered below) and modf, there is a corresponding type-generic macro. The parameters whose corresponding real type is double in the function synopsis are generic parameters.
5
Some of the <math.h> functions for decimal floating types have no unsuffixed counterpart. Of these functions with a d64 suffix, some have one or more parameters whose type is _Decimal64. For each such function, except decodedecd64, encodedecd64, decodebind64, and encodebind64, there is a corresponding type-generic macro. The parameters whose real type is _Decimal64 in the function synopsis are generic parameters.
6
If arguments for generic parameters of a type-generic macro are such that some argument has a corresponding real type that is of standard floating type and another argument is of decimal floating type, the behavior is undefined.
7
Except for the macros for functions that round result to a narrower type (7.12.14), use of a typegeneric macro invokes a function whose generic parameters have the corresponding real type determined by the types of the arguments for the generic parameters as follows: — Arguments of integer type are regarded as having type _Decimal64 if any argument has decimal floating type, and as having type double otherwise. — If the function has exactly one generic parameter, the type determined is the corresponding real type of the argument for the generic parameter. — If the function has exactly two generic parameters, the type determined is the corresponding real type determined by the usual arithmetic conversions (6.3.1.8) applied to the arguments for the generic parameters. — If the function has more than two generic parameters, the type determined is the corresponding real type determined by repeatedly applying the usual arithmetic conversions, first to the first two arguments for generic parameters, then to that result type and the next argument for a generic parameter, and so forth until the usual arithmetic conversions have been applied to the last argument for a generic parameter. If neither <math.h> and <complex.h> define a function whose generic parameters have the determined corresponding real type, the behavior is undefined.
8
For each unsuffixed function in <math.h> for which there is a function in <complex.h> with the same name except for a c prefix, the corresponding type-generic macro (for both functions) has the same name as the function in <math.h>. The corresponding type-generic macro for fabs and cabs is fabs. 385) Like other function-like macros in standard libraries, each type-generic macro can be suppressed to make available the corresponding ordinary function. 386) If the type of the argument is not compatible with the type of the parameter for the selected function, the behavior is undefined.
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<math.h>
<complex.h>
function
function
type-generic macro
acos asin atan acosh asinh atanh cos sin tan cosh sinh tanh exp log pow sqrt fabs
cacos casin catan cacosh casinh catanh ccos csin ctan ccosh csinh ctanh cexp clog cpow csqrt cabs
acos asin atan acosh asinh atanh cos sin tan cosh sinh tanh exp log pow sqrt fabs
N3096
If at least one argument for a generic parameter is complex, then use of the macro invokes a complex function; otherwise, use of the macro invokes a real function. 9
For each unsuffixed function in <math.h> without a c-prefixed counterpart in <complex.h> (except functions that round result to narrower type, modf, and canonicalize), the corresponding typegeneric macro has the same name as the function. These type-generic macros are: acospi asinpi atan2pi atan2 atanpi cbrt ceil compoundn copysign cospi erfc erf exp10m1 exp10 exp2m1
fmod exp2 frexp expm1 fdim fromfpx floor fromfp fmax hypot fmaximum ilogb ldexp fmaximum_mag lgamma fmaximum_num fmaximum_mag_num llogb llrint fma fmin llround fminimum log10p1 fminimum_mag log10 fminimum_num log1p fminimum_mag_num log2p1
log2 logb logp1 lrint lround nearbyint nextafter nextdown nexttoward nextup pown powr remainder remquo rint
rootn roundeven round rsqrt scalbln scalbn sinpi tanpi tgamma trunc ufromfpx ufromfp
If all arguments for generic parameters are real, then use of the macro invokes a real function (provided <math.h> defines a function of the determined type); otherwise, use of the macro is undefined. 10
For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a function in <math.h>, the corresponding type-generic macro has the same name as the function. These type-generic macros are: carg
cimag
conj
cproj
creal
Use of the macro with any argument of standard floating or complex type invokes a complex function. Use of the macro with an argument of decimal floating type is undefined. 11
The functions that round result to a narrower type have type-generic macros whose names are obtained by omitting any suffix from the function names. Thus, the macros with f or d prefix are:
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fsub dsub
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fdiv ddiv
ffma dfma
fsqrt dsqrt
d32div d64div
d32fma d64fma
d32sqrt d64sqrt
and the macros with d32 or d64 prefix are: d32add d64add
d32sub d64sub
d32mul d64mul
All arguments shall be real. If the macro prefix is f or d, use of an argument of decimal floating type is undefined. If the macro prefix is d32 or d64, use of an argument of standard floating type is undefined. The function invoked is determined as follows: — If any argument has type _Decimal128, or if the macro prefix is d64, the function invoked has the name of the macro, with a d128 suffix. — Otherwise, if the macro prefix is d32, the function invoked has the name of the macro, with a d64 suffix. — Otherwise, if any argument has type long double, or if the macro prefix is d, the function invoked has the name of the macro, with an l suffix. — Otherwise, the function invoked has the name of the macro (with no suffix). 12
For each d64-suffixed function in <math.h>, except decodedecd64, encodedecd64, decodebind64, and encodebind64, that does not have an unsuffixed counterpart, the corresponding type-generic macro has the name of the function, but without the suffix. These type-generic macros are: function
type-generic macro
quantizedN samequantumdN quantumdN llquantexpdN
quantize samequantum quantum llquantexp
<math.h>
Use of the macro with an argument of standard floating or complex type or with only integer type arguments is undefined. 13
A type-generic macro corresponding to a function indicated in the table in 7.6.2 is affected by constant rounding modes (7.6.4).
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NOTE 1 The type-generic macro definition in the example in 6.5.1.1 does not conform to this specification. A conforming macro could be implemented as follows:
#define cbrt(X) \ _Generic((X), \ long double: _Roundwise_cbrtl, \ _Roundwise_cbrt, \ default: _Roundwise_cbrtf \ float: )(X) where _Roundwise_cbrtl, _Roundwise_cbrt, and _Roundwise_cbrtf are pointers to functions that are equivalent to cbrtl, cbrt, and cbrtf, respectively, but that are guaranteed to be affected by constant rounding modes (7.6.2).
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EXAMPLE With the declarations #include <tgmath.h> int n; float f; double d; long double ld; float complex fc; double complex dc; long double complex ldc; #ifdef __STDC_IEC_60559_DFP__ _Decimal32 d32; _Decimal64 d64; _Decimal128 d128; #endif
functions invoked by use of type-generic macros are shown in the following table:
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exp(n) acosh(f) sin(d) atan(ld) log(fc) sqrt(dc) pow(ldc, f) remainder(n, n) nextafter(d, f) nexttoward(f, ld) copysign(n, ld) ceil(fc) rint(dc) fmaximum(ldc, ld) carg(n) cproj(f) creal(d) cimag(ld) fabs(fc) carg(dc) cproj(ldc) fsub(f, ld) fdiv(d, n) dfma(f, d, ld) dadd(f, f) dsqrt(dc) exp(d64) sqrt(d32) fmaximum(d64, d128) pow(d32, n) remainder(d64, d) creal(d64) remquo(d32, d32, &n) llquantexp(d) quantize(dc) samequantum(n, n) d32sub(d32, d128) d32div(d64, n)
exp(n) , the function acoshf(f) sin(d) , the function atanl(ld) clogf(fc) csqrt(dc) cpowl(ldc, f) remainder(n, n) , the function nextafter(d, f) , the function nexttowardf(f, ld) copysignl(n, ld)
undefined undefined undefined carg(n) , the function cprojf(f) creal(d) , the function cimagl(ld) cabsf(fc) carg(dc) , the function cprojl(ldc) fsubl(f, ld) fdiv(d, n) , the function dfmal(f, d, ld) daddl(f, f)
undefined expd64(d64) sqrtd32(d32) fmaximumd128(d64, d128) powd64(d32, n)
undefined undefined undefined undefined undefined undefined d32subd128(d32, d128) d32divd64(d64, n)
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7.28 Threads <threads.h> 7.28.1 Introduction 1
The header <threads.h> includes the header <time.h>, defines macros, and declares types, enumeration constants, and functions that support multiple threads of execution387) .
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Implementations that define the macro __STDC_NO_THREADS__ need not provide this header nor support any of its facilities.
3
The macros are ONCE_FLAG_INIT
which expands to a value that can be used to initialize an object of type once_flag; and TSS_DTOR_ITERATIONS
which expands to an integer constant expression representing the maximum number of times that destructors will be called when a thread terminates. 4
The types are cnd_t
which is a complete object type that holds an identifier for a condition variable; thrd_t
which is a complete object type that holds an identifier for a thread; tss_t
which is a complete object type that holds an identifier for a thread-specific storage pointer; mtx_t
which is a complete object type that holds an identifier for a mutex; tss_dtor_t
which is the function pointer type void (*)(void*), used for a destructor for a thread-specific storage pointer; thrd_start_t
which is the function pointer type int (*)(void*) that is passed to thrd_create to create a new thread; and once_flag
which is a complete object type that holds a flag for use by call_once. 5
The enumeration constants are mtx_plain
which is passed to mtx_init to create a mutex object that does not support timeout; mtx_recursive 387) See "future library directions" (7.33.19).
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which is passed to mtx_init to create a mutex object that supports recursive locking; mtx_timed
which is passed to mtx_init to create a mutex object that supports timeout; thrd_timedout
which is returned by a timed wait function to indicate that the time specified in the call was reached without acquiring the requested resource; thrd_success
which is returned by a function to indicate that the requested operation succeeded; thrd_busy
which is returned by a function to indicate that the requested operation failed because a resource requested by a test and return function is already in use; thrd_error
which is returned by a function to indicate that the requested operation failed; and thrd_nomem
which is returned by a function to indicate that the requested operation failed because it was unable to allocate memory. Forward references: date and time (7.29).
7.28.2
Initialization functions
7.28.2.1 The call_once function Synopsis #include <threads.h> void call_once(once_flag *flag, void (*func)(void));
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Description The call_once function uses the once_flag pointed to by flag to ensure that func is called exactly once, the first time the call_once function is called with that value of flag. Completion of an effective call to the call_once function synchronizes with all subsequent calls to the call_once function with the same value of flag. Returns The call_once function returns no value.
7.28.3
Condition variable functions
7.28.3.1 The cnd_broadcast function Synopsis 1
#include <threads.h> int cnd_broadcast(cnd_t *cond);
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Description The cnd_broadcast function unblocks all the threads that are blocked on the condition variable pointed to by cond at the time of the call. If no threads are blocked on the condition variable pointed to by cond at the time of the call, the function does nothing. Returns The cnd_broadcast function returns thrd_success on success, or thrd_error if the request could not be honored. 7.28.3.2 The cnd_destroy function Synopsis #include <threads.h> void cnd_destroy(cnd_t *cond);
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Description The cnd_destroy function releases all resources used by the condition variable pointed to by cond. The cnd_destroy function requires that no threads be blocked waiting for the condition variable pointed to by cond. Returns The cnd_destroy function returns no value. 7.28.3.3 The cnd_init function Synopsis #include <threads.h> int cnd_init(cnd_t *cond);
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Description The cnd_init function creates a condition variable. If it succeeds it sets the object pointed to by cond to a value that uniquely identifies the newly created condition variable. A thread that calls cnd_wait on a newly created condition variable will block. Returns The cnd_init function returns thrd_success on success, or thrd_nomem if no memory could be allocated for the newly created condition, or thrd_error if the request could not be honored. 7.28.3.4 The cnd_signal function Synopsis #include <threads.h> int cnd_signal(cnd_t *cond);
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Description The cnd_signal function unblocks one of the threads that are blocked on the condition variable pointed to by cond at the time of the call. If no threads are blocked on the condition variable at the time of the call, the function does nothing and returns success. Returns The cnd_signal function returns thrd_success on success or thrd_error if the request could not be honored. 7.28.3.5 The cnd_timedwait function Synopsis #include <threads.h> int cnd_timedwait(cnd_t *restrict cond, mtx_t *restrict mtx, const struct timespec *restrict ts);
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Description The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and blocks until the condition variable pointed to by cond is signaled by a call to cnd_signal or to cnd_broadcast, or until after the TIME_UTC-based calendar time pointed to by ts, or until it is unblocked due to an unspecified reason. When the calling thread becomes unblocked it locks the object pointed to by mtx before it returns. The cnd_timedwait function requires that the mutex pointed to by mtx be locked by the calling thread. Returns The cnd_timedwait function returns thrd_success upon success, or thrd_timedout if the time specified in the call was reached without acquiring the requested resource, or thrd_error if the request could not be honored. 7.28.3.6 The cnd_wait function Synopsis #include <threads.h> int cnd_wait(cnd_t *cond, mtx_t *mtx);
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Description The cnd_wait function atomically unlocks the mutex pointed to by mtx and blocks until the condition variable pointed to by cond is signaled by a call to cnd_signal or to cnd_broadcast, or until it is unblocked due to an unspecified reason. When the calling thread becomes unblocked it locks the mutex pointed to by mtx before it returns. The cnd_wait function requires that the mutex pointed to by mtx be locked by the calling thread. Returns The cnd_wait function returns thrd_success on success or thrd_error if the request could not be honored.
7.28.4
Mutex functions
1
For purposes of determining the existence of a data race, lock and unlock operations behave as atomic operations. All lock and unlock operations on a particular mutex occur in some particular total order.
2
NOTE 1 This total order can be viewed as the modification order of the mutex.
7.28.4.1 The mtx_destroy function Synopsis 1
2
3
#include <threads.h> void mtx_destroy(mtx_t *mtx);
Description The mtx_destroy function releases any resources used by the mutex pointed to by mtx. No threads can be blocked waiting for the mutex pointed to by mtx. Returns The mtx_destroy function returns no value. 7.28.4.2 The mtx_init function Synopsis
1
#include <threads.h> int mtx_init(mtx_t *mtx, int type);
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Description The mtx_init function creates a mutex object with properties indicated by type, which shall have one of these values: mtx_plain for a simple non-recursive mutex, mtx_timed for a non-recursive mutex that supports timeout, mtx_plain | mtx_recursive for a simple recursive mutex, or mtx_timed | mtx_recursive for a recursive mutex that supports timeout.
3
4
If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that uniquely identifies the newly created mutex. Returns The mtx_init function returns thrd_success on success, or thrd_error if the request could not be honored. 7.28.4.3 The mtx_lock function Synopsis #include <threads.h> int mtx_lock(mtx_t *mtx);
1
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Description The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex is nonrecursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock on the same mutex synchronize with this operation. Returns The mtx_lock function returns thrd_success on success, or thrd_error if the request could not be honored. 7.28.4.4 The mtx_timedlock function Synopsis #include <threads.h> int mtx_timedlock(mtx_t *restrict mtx, const struct timespec *restrict ts);
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2
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Description The mtx_timedlock function endeavors to block until it locks the mutex pointed to by mtx or until after the TIME_UTC-based calendar time pointed to by ts. The specified mutex shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same mutex synchronize with this operation. Returns The mtx_timedlock function returns thrd_success on success, or thrd_timedout if the time specified was reached without acquiring the requested resource, or thrd_error if the request could not be honored. 7.28.4.5 The mtx_trylock function Synopsis #include <threads.h> int mtx_trylock(mtx_t *mtx);
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Description The mtx_trylock function endeavors to lock the mutex pointed to by mtx. If the mutex is already locked, the function returns without blocking. If the operation succeeds, prior calls to mtx_unlock on the same mutex synchronize with this operation. Returns The mtx_trylock function returns thrd_success on success, or thrd_busy if the resource requested is already in use, or thrd_error if the request could not be honored. mtx_trylock may spuriously fail to lock an unused resource, in which case it returns thrd_busy. 7.28.4.6 The mtx_unlock function Synopsis #include <threads.h> int mtx_unlock(mtx_t *mtx);
1
2
Description The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to by mtx shall be locked by the calling thread.
3
Returns The mtx_unlock function returns thrd_success on success or thrd_error if the request could not be honored.
7.28.5
Thread functions
7.28.5.1 The thrd_create function Synopsis 1
2
3
4
#include <threads.h> int thrd_create(thrd_t *thr, thrd_start_t func, void *arg);
Description The thrd_create function creates a new thread executing func(arg). If the thrd_create function succeeds, it sets the object pointed to by thr to the identifier of the newly created thread. (A thread’s identifier may be reused for a different thread once the original thread has exited and either been detached or joined to another thread.) The completion of the thrd_create function synchronizes with the beginning of the execution of the new thread. Returning from func has the same behavior as invoking thrd_exit with the value returned from func. Returns The thrd_create function returns thrd_success on success, or thrd_nomem if no memory could be allocated for the thread requested, or thrd_error if the request could not be honored. 7.28.5.2 The thrd_current function Synopsis
1
#include <threads.h> thrd_t thrd_current(void);
2
Description The thrd_current function identifies the thread that called it.
3
Returns The thrd_current function returns the identifier of the thread that called it. § 7.28.5.2
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7.28.5.3 The thrd_detach function Synopsis #include <threads.h> int thrd_detach(thrd_t thr);
1
2
3
Description The thrd_detach function tells the operating system to dispose of any resources allocated to the thread identified by thr when that thread terminates. The thread identified by thr shall not have been previously detached or joined with another thread. Returns The thrd_detach function returns thrd_success on success or thrd_error if the request could not be honored. 7.28.5.4 The thrd_equal function Synopsis #include <threads.h> int thrd_equal(thrd_t thr0, thrd_t thr1);
1
2
Description The thrd_equal function will determine whether the thread identified by thr0 refers to the thread identified by thr1.
3
Returns The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to different threads. Otherwise the thrd_equal function returns a nonzero value. 7.28.5.5 The thrd_exit function Synopsis #include <threads.h> [[noreturn]] void thrd_exit(int res);
1
2
Description For every thread-specific storage key which was created with a non-null destructor and for which the value is non-null, thrd_exit sets the value associated with the key to a null pointer value and then invokes the destructor with its previous value. The order in which destructors are invoked is unspecified.
3
If after this process there remain keys with both non-null destructors and values, the implementation repeats this process up to TSS_DTOR_ITERATIONS times.
4
Following this, the thrd_exit function terminates execution of the calling thread and sets its result code to res.
5
The program terminates normally after the last thread has been terminated. The behavior is as if the program called the exit function with the status EXIT_SUCCESS at thread termination time.
6
Returns The thrd_exit function returns no value. 7.28.5.6 The thrd_join function Synopsis #include <threads.h> int thrd_join(thrd_t thr, int *res);
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Description The thrd_join function joins the thread identified by thr with the current thread by blocking until the other thread has terminated. If the parameter res is not a null pointer, it stores the thread’s result code in the integer pointed to by res. The termination of the other thread synchronizes with the completion of the thrd_join function. The thread identified by thr shall not have been previously detached or joined with another thread. Returns The thrd_join function returns thrd_success on success or thrd_error if the request could not be honored. 7.28.5.7 The thrd_sleep function Synopsis #include <threads.h> int thrd_sleep(const struct timespec *duration, struct timespec *remaining);
1
2
3
4
Description The thrd_sleep function suspends execution of the calling thread until either the interval specified by duration has elapsed or a signal which is not being ignored is received. If interrupted by a signal and the remaining argument is not null, the amount of time remaining (the requested interval minus the time actually slept) is stored in the interval it points to. The duration and remaining arguments may point to the same object. The suspension time may be longer than requested because the interval is rounded up to an integer multiple of the sleep resolution or because of the scheduling of other activity by the system. But, except for the case of being interrupted by a signal, the suspension time will not be less than that specified, as measured by the system clock TIME_UTC. Returns The thrd_sleep function returns zero if the requested time has elapsed, −1 if it has been interrupted by a signal, or a negative value (which may also be −1) if it fails. 7.28.5.8 The thrd_yield function Synopsis #include <threads.h> void thrd_yield(void);
1
2
3
Description The thrd_yield function endeavors to permit other threads to run, even if the current thread would ordinarily continue to run. Returns The thrd_yield function returns no value.
7.28.6
Thread-specific storage functions
7.28.6.1 The tss_create function Synopsis 1
2
#include <threads.h> int tss_create(tss_t *key, tss_dtor_t dtor);
Description The tss_create function creates a thread-specific storage pointer with destructor dtor, which may be null. § 7.28.6.1
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A null pointer value is associated with the newly created key in all existing threads. Upon subsequent thread creation, the value associated with all keys is initialized to a null pointer value in the new thread.
4
Destructors associated with thread-specific storage are not invoked at program termination.
5
The tss_create function shall not be called from within a destructor.
6
Returns If the tss_create function is successful, it sets the thread-specific storage pointed to by key to a value that uniquely identifies the newly created pointer and returns thrd_success; otherwise, thrd_error is returned and the thread-specific storage pointed to by key is set to an indeterminate representation. 7.28.6.2 The tss_delete function Synopsis #include <threads.h> void tss_delete(tss_t key);
1
2
Description The tss_delete function releases any resources used by the thread-specific storage identified by key. The tss_delete function shall only be called with a value for key that was returned by a call to tss_create before the thread commenced executing destructors.
3
If tss_delete is called while another thread is executing destructors, whether this will affect the number of invocations of the destructor associated with key on that thread is unspecified.
4
Calling tss_delete will not result in the invocation of any destructors.
5
Returns The tss_delete function returns no value. 7.28.6.3 The tss_get function Synopsis #include <threads.h> void *tss_get(tss_t key);
1
2
3
Description The tss_get function returns the value for the current thread held in the thread-specific storage identified by key. The tss_get function shall only be called with a value for key that was returned by a call to tss_create before the thread commenced executing destructors. Returns The tss_get function returns the value for the current thread if successful, or zero if unsuccessful. 7.28.6.4 The tss_set function Synopsis #include <threads.h> int tss_set(tss_t key, void *val);
1
2
3
Description The tss_set function sets the value for the current thread held in the thread-specific storage identified by key to val. The tss_set function shall only be called with a value for key that was returned by a call to tss_create before the thread commenced executing destructors. This action will not invoke the destructor associated with the key on the value being replaced. 396
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Returns The tss_set function returns thrd_success on success or thrd_error if the request could not be honored.
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7.29 Date and time <time.h> 7.29.1 Components of time 1
The header <time.h> defines several macros, and declares types and functions for manipulating time. Many functions deal with a calendar time that represents the current date (according to the Gregorian calendar) and time. Some functions deal with local time, which is the calendar time expressed for some specific time zone, and with Daylight Saving Time, which is a temporary change in the algorithm for determining local time. The local time zone and Daylight Saving Time are implementation-defined.
2
The feature test macro __STDC_VERSION_TIME_H__ expands to the token 202311L. The other macros defined are NULL (described in 7.21); CLOCKS_PER_SEC
which expands to an expression with type clock_t (described below) that is the number per second of the value returned by the clock function; TIME_UTC TIME_MONOTONIC
which expand to integer constants greater than 0 designating the calendar time and monotonic time bases, respectively. Additional time base macro definitions, beginning with TIME_ and an uppercase letter, may also be specified by the implementation388) ; and, TIME_ACTIVE TIME_THREAD_ACTIVE
which, if defined, expand to integer values, designating overall execution and thread-specific active processing time bases, respectively. 3
The definition of macros for time bases other than TIME_UTC are optional. If defined, the corresponding time bases are supported by timespec_get and timespec_getres, and their values are positive. If defined, the value of the optional macro TIME_ACTIVE shall be different from the constants TIME_UTC and TIME_MONOTONIC and shall not change during the same program invocation. The optional macro TIME_THREAD_ACTIVE shall not be defined if the implementation does not support threads; its value shall be different from TIME_UTC, TIME_MONOTONIC, and TIME_ACTIVE, it shall be the same for all expansions of the macro for the same thread, and the value provided for one thread shall not be used by a different thread as the base argument of timespec_get or timespec_getres.
4
The types declared are size_t (described in 7.21); clock_t
and time_t
which are real types capable of representing times; struct timespec
which holds an interval specified in seconds and nanoseconds (which may represent a calendar time based on a particular epoch); and struct tm 388) See future library directions (7.33). Implementations can define additional time bases, but are only required to support a real time clock based on UTC.
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which holds the components of a calendar time, called the broken-down time. 5
The range and precision of times representable in clock_t and time_t are implementation-defined. The timespec structure shall contain at least the following members, in any order. The semantics of the members and their normal ranges are expressed in the comments.389) time_t tv_sec; // whole seconds -- ≥ 0 /* see below */ tv_nsec; // nanoseconds -- [0, 999999999]
The tm structure shall contain at least the following members, in any order. 390) The tv_nsec member shall be an implementation-defined signed integer type capable of representing the range [0, 999999999]. The semantics of the other member and its normal range is expressed in the comments. int tm_sec; // seconds after the minute -- [0, 60] int tm_min; // minutes after the hour -- [0, 59] int tm_hour; // hours since midnight -- [0, 23] int tm_mday; // day of the month -- [1, 31] int tm_mon; // months since January -- [0, 11] int tm_year; // years since 1900 int tm_wday; // days since Sunday -- [0, 6] int tm_yday; // days since January 1 -- [0, 365] int tm_isdst; // Daylight Saving Time flag
The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight Saving Time is not in effect, and negative if the information is not available.
7.29.2
Time manipulation functions
7.29.2.1 The clock function Synopsis 1
2
3
#include <time.h> clock_t clock(void);
Description The clock function determines the processor time used. Returns The clock function returns the implementation’s best approximation of the active processing time associated with the program execution since the beginning of an implementation-defined era related only to the program invocation. To determine the time in seconds, the value returned by the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If the processor time used is not available, the function returns the value (clock_t) (−1). If the value cannot be represented, the function returns an unspecified value391) . 7.29.2.2 The difftime function Synopsis
1
#include <time.h> double difftime(time_t time1, time_t time0);
2
Description The difftime function computes the difference between two calendar times: time1 - time0.
3
Returns The difftime function returns the difference expressed in seconds as a double. 389) The tv_sec member is a linear count of seconds and might not have the normal semantics of a time_t. 390) The range [0, 60] for tm_sec allows for a positive leap second. 391) This could be due to overflow of the clock_t type.
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7.29.2.3 The mktime function Synopsis #include <time.h> time_t mktime(struct tm *timeptr);
1
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4
Description The mktime function converts the broken-down time, expressed as local time, in the structure pointed to by timeptr into a calendar time value with the same encoding as that of the values returned by the time function. The original values of the tm_wday and tm_yday components of the structure are ignored, and the original values of the other components are not restricted to the ranges indicated above. If the local time to be used for the conversion is one that includes Daylight Saving Time adjustments, a positive or zero value for tm_isdst causes the mktime function to perform the conversion as if Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time; if it determines that Daylight Saving Time is in effect it produces the same result as an equivalent call with a positive tm_isdst value, otherwise it produces the same result as an equivalent call with a tm_isdst value of zero.392) On successful completion, the components of the structure are set to the same values that would be returned by a call to the localtime function with the calculated calendar time as its argument. Returns The mktime function returns the specified calendar time encoded as a value of type time_t. If the calendar time cannot be represented in the time_t encoding used for the return value, the function returns the value (time_t) (−1). EXAMPLE What day of the week is July 4, 2001? #include <stdio.h> #include <time.h> static const char *const wday[] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "-unknown-" }; struct tm time_str; /* ... */ time_str.tm_year = 2001 - 1900; time_str.tm_mon = 7 - 1; time_str.tm_mday = 4; time_str.tm_hour = 0; time_str.tm_min = 0; time_str.tm_sec = 1; time_str.tm_isdst = -1; if (mktime(&time_str) == (time_t)(-1)) time_str.tm_wday = 7; printf("%s\n", wday[time_str.tm_wday]);
7.29.2.4 The timegm function Synopsis #include <time.h> time_t timegm(struct tm *timeptr);
1
392) If the broken-down time specifies a time that is either skipped over or repeated when a transition to or from Daylight Saving Time occurs, it is unspecified whether the mktime function produces the same result as an equivalent call with a positive tm_isdst value or as an equivalent call with a tm_isdst value of zero.
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Description The timegm function converts the broken-down time, expressed as UTC time, in the structure pointed to by timeptr into a calendar time value with the same encoding as that of the values returned by the time function. The original values of the tm_wday and tm_yday components of the structure are ignored, and the original values of the other components are not restricted to the ranges indicated above. On successful completion, the values of the tm_wday and tm_yday components of the structure are set appropriately, and the other components are set to represent the specified calendar time, but with their values forced to the ranges indicated above; the final value of tm_mday is not set until tm_mon and tm_year are determined. Returns The timegm function returns the specified calendar time encoded as a value of type time_t. If the calendar time cannot be represented, the function returns the value (time_t)(-1). 7.29.2.5 The time function Synopsis
1
2
3
#include <time.h> time_t time(time_t *timer);
Description The time function determines the current calendar time. The encoding of the value is unspecified. Returns The time function returns the implementation’s best approximation to the current calendar time. The value (time_t) (−1) is returned if the calendar time is not available. If timer is not a null pointer, the return value is also assigned to the object it points to. 7.29.2.6 The timespec_get function Synopsis
1
2
3
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#include <time.h> int timespec_get(struct timespec *ts, int base);
Description The timespec_get function sets the interval pointed to by ts to hold the current calendar time based on the specified time base. If base is TIME_UTC, the tv_sec member is set to the number of seconds since an implementationdefined epoch, truncated to a whole value and the tv_nsec member is set to the integral number of nanoseconds, rounded to the resolution of the system clock.393) The optional time base TIME_MONOTONIC is the same, but the reference point is an implementation-defined time point; different program invocations need not refer to the same reference points.394) For the same program invocation, the results of two calls to timespec_get with TIME_MONOTONIC such that the first happens before the second shall not be decreasing. It is implementation-defined if TIME_MONOTONIC accounts for time during which the execution environment is suspended.395) For the optional time bases TIME_ACTIVE and TIME_THREAD_ACTIVE the result is similar, but the call measures the amount of active processing time associated with the whole program invocation or with the calling thread, respectively. Returns If the timespec_get function is successful it returns the nonzero value base; otherwise, it returns zero. 393) Although a struct timespec object describes times with nanosecond resolution, the available resolution is system dependent and could even be greater than 1 second. 394) Commonly, this reference point is the boot time of the execution environment or the start of the execution. 395) The execution environment may, for example, not be able to track physical time that elapsed during suspension in a low power consumption mode.
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Recommended practice It is recommended practice that timing results of calls to timespec_get with TIME_ACTIVE, if defined, and of calls to clock are as close to each other as their types, value ranges, and resolutions (obtained with timespec_getres and CLOCKS_PER_SEC, respectively) allow. Because of its wider value range and improved indications on error, timespec_get with time base TIME_ACTIVE should be used instead of clock by new code whenever possible. 7.29.2.7 The timespec_getres function Synopsis #include <time.h> int timespec_getres(struct timespec *ts, int base);
1
2
3
Description If ts is non-null and base is supported by the timespec_get function, the timespec_getres function returns the resolution of the time provided by the timespec_get function for base in the timespec structure pointed to by ts. For each supported base, multiple calls to the timespec_getres function during the same program execution shall have identical results. Returns If the value base is supported by the timespec_get function, the timespec_getres function returns the nonzero value base; otherwise, it returns zero.
7.29.3
Time conversion functions
1
Functions with a _r suffix place the result of the conversion into the buffer referred by buf and return that pointer. These functions and the function strftime shall not be subject to data races, unless the time or calendar state is changed in a multi-thread execution.396)
2
Functions gmtime and localtime are the same as their counterparts suffixed with _r. In place of the parameter buf, the following functions use a pointer to one or two broken-down time structures. Similarly, an array of char is commonly used by asctime and ctime. Execution of any of the functions that return a pointer to one of these objects may overwrite the information returned from any previous call to one of these functions that uses the same object. These functions are not reentrant and are not required to avoid data races with each other. Accessing the returned pointer after the thread that called the function that returned it has exited results in undefined behavior. The implementation shall behave as if no other library functions call these functions. 7.29.3.1 The asctime function Synopsis #include <time.h> [[deprecated]] char *asctime(const struct tm *timeptr);
1
2 3
Description This function is obsolescent and should be avoided in new code. The asctime function converts the broken-down time in the structure pointed to by timeptr into a string in the form Sun Sep 16 01:03:52 1973\n\0
using the equivalent of the following algorithm. [[deprecated]] char *asctime(const struct tm *timeptr) { 396) This does not mean that these functions may not read global state that describes the time and calendar settings of the execution, such as the LC_TIME locale or the implementation-defined specification of the local time zone. Only the setting of that state by setlocale or by means of implementation-defined functions may constitute races.
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static const char wday_name[7][3] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" }; static const char mon_name[12][3] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" }; static char result[26]; snprintf(result, 26, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n", wday_name[timeptr->tm_wday], mon_name[timeptr->tm_mon], timeptr->tm_mday, timeptr->tm_hour, timeptr->tm_min, timeptr->tm_sec, 1900 + timeptr->tm_year); return result; }
4
5
If any of the members of the broken-down time contain values that are outside their normal ranges397) , the behavior of the asctime function is undefined. Likewise, if the calculated year exceeds four digits or is less than the year 1000, the behavior is undefined. Returns The asctime function returns a pointer to the string. 7.29.3.2 The ctime function Synopsis
1
2 3
#include <time.h> [[deprecated]] char *ctime(const time_t *timer);
Description This function is obsolescent and should be avoided in new code. The ctime function converts the calendar time pointed to by timer to local time in the form of a string. They are equivalent to: asctime(localtime(timer))
4
Returns The ctime function returns the pointer returned by the asctime function with that broken-down time as argument. Forward references: the localtime functions (7.29.3.4). 7.29.3.3 The gmtime functions Synopsis
1
2
#include <time.h> struct tm *gmtime(const time_t *timer); struct tm *gmtime_r(const time_t *timer, struct tm *buf);
Description The gmtime functions convert the calendar time pointed to by timer into a broken-down time, expressed as UTC. 397) See 7.29.1.
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Returns The gmtime functions return a pointer to the broken-down time, or a null pointer if the specified time cannot be converted to UTC. 7.29.3.4 The localtime functions Synopsis #include <time.h> struct tm *localtime(const time_t *timer); struct tm *localtime_r(const time_t *timer, struct tm *buf);
1
2
Description The localtime functions convert the calendar time pointed to by timer into a broken-down time, expressed as local time.
3
Returns The localtime functions return a pointer to the broken-down time, or a null pointer if the specified time cannot be converted to local time. 7.29.3.5 The strftime function Synopsis #include <time.h> size_t strftime(char * restrict s, size_t maxsize, const char * restrict format, const struct tm * restrict timeptr);
1
2
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Description The strftime function places characters into the array pointed to by s as controlled by the string pointed to by format. The format shall be a multibyte character sequence, beginning and ending in its initial shift state. The format string consists of zero or more conversion specifiers and ordinary multibyte characters. A conversion specifier consists of a % character, possibly followed by an E or O modifier character (described below), followed by a character that determines the behavior of the conversion specifier. All ordinary multibyte characters (including the terminating null character) are copied unchanged into the array. If copying takes place between objects that overlap, the behavior is undefined. No more than maxsize characters are placed into the array. Each conversion specifier shall be replaced by appropriate characters as described in the following list. The appropriate characters shall be determined using the LC_TIME category of the current locale and by the values of zero or more members of the broken-down time structure pointed to by timeptr, as specified in brackets in the description. If any of the specified values is outside the normal range, the characters stored are unspecified. %a
is replaced by the locale’s abbreviated weekday name. [tm_wday]
%A
is replaced by the locale’s full weekday name. [tm_wday]
%b
is replaced by the locale’s abbreviated month name. [tm_mon]
%B
is replaced by the locale’s full month name. [tm_mon]
%c
is replaced by the locale’s appropriate date and time representation. [all specified in 7.29.1]
%C
is replaced by the year divided by 100 and truncated to an integer, as a decimal number (00–99). [tm_year]
%d
is replaced by the day of the month as a decimal number (01–31). [tm_mday]
%D
is equivalent to "%m/%d/%y". [tm_mon, tm_mday, tm_year]
%e
is replaced by the day of the month as a decimal number (1–31); a single digit is preceded by a space. [tm_mday]
%F
%F is equivalent to "%Y-%Pm-%d" (the ISO 8601 date format, when the year is between 1000 and 9999 inclusive). [tm_year, tm_mon, tm_mday]
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%g
is replaced by the last 2 digits of the week-based year (see below) as a decimal number (00–99). [tm_year, tm_wday, tm_yday]
%G
is replaced by the week-based year (see below) as a decimal number (e.g., 1997). [tm_year, tm_wday, tm_yday]
%h
is equivalent to "%b". [tm_mon]
%H
is replaced by the hour (24-hour clock) as a decimal number (00–23). [tm_hour]
%I
is replaced by the hour (12-hour clock) as a decimal number (01–12). [tm_hour]
%j
is replaced by the day of the year as a decimal number (001–366). [tm_yday]
%m
is replaced by the month as a decimal number (01–12). [tm_mon]
%M
is replaced by the minute as a decimal number (00–59). [tm_min]
%n
is replaced by a new-line character.
%p
is replaced by the locale’s equivalent of the AM/PM designations associated with a 12-hour clock. [tm_hour]
%r
is replaced by the locale’s 12-hour clock time. [tm_hour, tm_min, tm_sec]
%R
is equivalent to "%H:%M". [tm_hour, tm_min ]
%S
is replaced by the second as a decimal number (00–60). [tm_sec]
%t
is replaced by a horizontal-tab character.
%T
is equivalent to "%H:%M:%S" (the ISO 8601 time format). [tm_hour, tm_min, tm_sec]
%u
is replaced by the ISO 8601 weekday as a decimal number (1–7), where Monday is 1. [tm_wday]
%U
is replaced by the week number of the year (the first Sunday as the first day of week 1) as a decimal number (00–53). [tm_year, tm_wday, tm_yday]
%V
is replaced by the ISO 8601 week number (see below) as a decimal number (01–53). [tm_year, tm_wday, tm_yday]
%w
is replaced by the weekday as a decimal number (0–6), where Sunday is 0. [tm_wday]
%W
is replaced by the week number of the year (the first Monday as the first day of week 1) as a decimal number (00–53). [tm_year, tm_wday, tm_yday]
%x
is replaced by the locale’s appropriate date representation. [all specified in 7.29.1]
%X
is replaced by the locale’s appropriate time representation. [all specified in 7.29.1]
%y
is replaced by the last 2 digits of the year as a decimal number (00–99). [tm_year]
%Y
is replaced by the year as a decimal number (e.g., 1997). [tm_year]
%z
is replaced by the offset from UTC in the ISO 8601 format "-0430" (meaning 4 hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time zone is determinable. [tm_isdst]
%Z
is replaced by the locale’s time zone name or abbreviation, or by no characters if no time zone is determinable. [tm_isdst]
%%
is replaced by %.
Some conversion specifiers can be modified by the inclusion of an E or O modifier character to indicate an alternative format or specification. If the alternative format or specification does not exist for the current locale, the modifier is ignored. %Ec
is replaced by the locale’s alternative date and time representation.
%EC
is replaced by the name of the base year (period) in the locale’s alternative representation.
%Ex
is replaced by the locale’s alternative date representation.
%EX
is replaced by the locale’s alternative time representation.
%Ey
is replaced by the offset from %EC (year only) in the locale’s alternative representation.
%EY
is replaced by the locale’s full alternative year representation.
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%Ob
is replaced by the locale’s abbreviated alternative month name.
%OB
is replaced by the locale’s alternative appropriate full month name.
%Od
is replaced by the day of the month, using the locale’s alternative numeric symbols (filled as needed with leading zeros, or with leading spaces if there is no alternative symbol for zero).
%Oe
is replaced by the day of the month, using the locale’s alternative numeric symbols (filled as needed with leading spaces).
%OH
is replaced by the hour (24-hour clock), using the locale’s alternative numeric symbols.
%OI
is replaced by the hour (12-hour clock), using the locale’s alternative numeric symbols.
%Om
is replaced by the month, using the locale’s alternative numeric symbols.
%OM
is replaced by the minutes, using the locale’s alternative numeric symbols.
%OS
is replaced by the seconds, using the locale’s alternative numeric symbols.
%Ou
is replaced by the ISO 8601 weekday as a number in the locale’s alternative representation, where Monday is 1.
%OU
is replaced by the week number, using the locale’s alternative numeric symbols.
%OV
is replaced by the ISO 8601 week number, using the locale’s alternative numeric symbols.
%Ow
is replaced by the weekday as a number, using the locale’s alternative numeric symbols.
%OW
is replaced by the week number of the year, using the locale’s alternative numeric symbols.
%Oy
is replaced by the last 2 digits of the year, using the locale’s alternative numeric symbols.
%g, %G, and %V give values according to the ISO 8601 week-based year. In this system, weeks begin
on a Monday and week 1 of the year is the week that includes January 4th, which is also the week that includes the first Thursday of the year, and is also the first week that contains at least four days in the year. If the first Monday of January is the 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus, for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and %V is replaced by 01. 6
If a conversion specifier is not one of the above, the behavior is undefined.
7
In the "C" locale, the E and O modifiers are ignored and the replacement strings for the following specifiers are:
8
%a
the first three characters of %A.
%A
one of "Sunday", "Monday", . . . , "Saturday".
%b
the first three characters of %B.
%B
one of "January", "February", . . . , "December".
%c
equivalent to "%a %b %e %T %Y".
%p
one of "AM" or "PM".
%r
equivalent to "%I:%M:%S %p".
%x
equivalent to "%m/%d/%y".
%X
equivalent to %T.
%Z
implementation-defined.
Returns If the total number of resulting characters including the terminating null character is not more than maxsize, the strftime function returns the number of characters placed into the array pointed to by s not including the terminating null character. Otherwise, zero is returned and the members of the array have an indeterminate representation.
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Unicode utilities <uchar.h>
1
The header <uchar.h> declares one macro, a few types, and several functions for manipulating Unicode characters.
2
The macro __STDC_VERSION_UCHAR_H__
is an integer constant expression with a value equivalent to 202311L. 3
The types declared are mbstate_t (described in 7.31.1) and size_t (described in 7.21); char8_t
which is an unsigned integer type used for 8-bit characters and is the same type as unsigned char; char16_t
which is an unsigned integer type used for 16-bit characters and is the same type as uint_least16_t (described in 7.22.1.2); and char32_t
which is an unsigned integer type used for 32-bit characters and is the same type as uint_least32_t (also described in 7.22.1.2).
7.30.1
Restartable multibyte/wide character conversion functions
1
These functions have a parameter, ps, of type pointer to mbstate_t that points to an object that can completely describe the current conversion state of the associated multibyte character sequence, which the functions alter as necessary. If ps is a null pointer, each function uses its own internal mbstate_t object instead, which is initialized prior to the first call to the function to the initial conversion state; the functions are not required to avoid data races with other calls to the same function in this case. It is implementation-defined whether the internal mbstate_t object has thread storage duration; if it has thread storage duration, it is initialized to the initial conversion state prior to the first call to the function on the new thread. The implementation behaves as if no library function calls these functions with a null pointer for ps.
2
When used in the functions in this subclause, the encoding of char8_t, char16_t, and char32_t objects, and sequences of such objects, is UTF-8, UTF-16, and UTF-32, respectively. Similarly, the encoding of char and wchar_t, and sequences of such objects, is the execution and wide execution encodings (6.2.9), respectively. 7.30.1.1 The mbrtoc8 function Synopsis
1
2
#include <uchar.h> size_t mbrtoc8(char8_t * restrict pc8, const char * restrict s, size_t n, mbstate_t * restrict ps);
Description If s is a null pointer, the mbrtoc8 function is equivalent to the call: mbrtoc8(NULL, "", 1, ps)
In this case, the values of the parameters pc8 and n are ignored. 3
If s is not a null pointer, the mbrtoc8 function function inspects at most n bytes beginning with the byte pointed to by s to determine the number of bytes needed to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character § 7.30.1.1
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is complete and valid, it determines the values of the corresponding characters and then, if pc8 is not a null pointer, stores the value of the first (or only) such character in the object pointed to by pc8. Subsequent calls will store successive characters without consuming any additional input until all the characters have been stored. If the corresponding character is the null character, the resulting state described is the initial conversion state.
4
Returns The mbrtoc8 function returns the first of the following that applies (given the current conversion state): 0
if the next n or fewer bytes complete the multibyte character that corresponds to the null character (which is the value stored).
between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte character (which is the value stored); the value returned is the number of bytes that complete the multibyte character. (size_t)(-3) if the next character resulting from a previous call has been stored (no bytes from
the input have been consumed by this call). (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) multibyte character, and all n bytes have been processed (no value is stored).398) (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes do not contribute
to a complete and valid multibyte character (no value is stored); the value of the macro EILSEQ is stored in errno, and the conversion state is unspecified. 7.30.1.2 The c8rtomb function Synopsis #include <uchar.h> size_t c8rtomb(char * restrict s, char8_t c8, mbstate_t * restrict ps);
1
2
Description If s is a null pointer, the c8rtomb function is equivalent to the call c8rtomb(buf, u8’\0’, ps)
where buf is an internal buffer. 3
4
If s is not a null pointer, the c8rtomb function determines the number of bytes needed to represent the multibyte character that corresponds to the character given or completed by c8 (including any shift sequences), and stores the multibyte character representation in the array whose first element is pointed to by s, or stores nothing if c8 does not represent a complete character. At most MB_CUR_MAX bytes are stored. If c8 is a null character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state; the resulting state described is the initial conversion state. Returns The c8rtomb function returns the number of bytes stored in the array object (including any shift sequences). When c8 is not a valid character, an encoding error occurs: the function stores the value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion state is unspecified. 7.30.1.3
The mbrtoc16 function
398) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a sequence of redundant shift sequences (for implementations with state-dependent encodings).
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Synopsis #include <uchar.h> size_t mbrtoc16(char16_t * restrict pc16, const char * restrict s, size_t n, mbstate_t * restrict ps);
1
2
Description If s is a null pointer, the mbrtoc16 function is equivalent to the call: mbrtoc16(NULL, "", 1, ps)
In this case, the values of the parameters pc16 and n are ignored. 3
4
If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with the byte pointed to by s to determine the number of bytes needed to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character is complete and valid, it determines the values of the corresponding wide characters and then, if pc16 is not a null pointer, stores the value of the first (or only) such character in the object pointed to by pc16. Subsequent calls will store successive wide characters without consuming any additional input until all the characters have been stored. If the corresponding wide character is the null wide character, the resulting state described is the initial conversion state. Returns The mbrtoc16 function returns the first of the following that applies (given the current conversion state): if the next n or fewer bytes complete the multibyte character that corresponds to the null wide character (which is the value stored).
0
between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte character (which is the value stored); the value returned is the number of bytes that complete the multibyte character. (size_t)(-3) if the next character resulting from a previous call has been stored (no bytes from
the input have been consumed by this call). (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) multibyte character, and all n bytes have been processed (no value is stored).399) (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes do not contribute
to a complete and valid multibyte character (no value is stored); the value of the macro EILSEQ is stored in errno, and the conversion state is unspecified. 7.30.1.4 The c16rtomb function Synopsis 1
2
#include <uchar.h> size_t c16rtomb(char * restrict s, char16_t c16, mbstate_t * restrict ps);
Description If s is a null pointer, the c16rtomb function is equivalent to the call c16rtomb(buf, u’\0’, ps)
where buf is an internal buffer. 399) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a sequence of redundant shift sequences (for implementations with state-dependent encodings).
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If s is not a null pointer, the c16rtomb function determines the number of bytes needed to represent the multibyte character that corresponds to the wide character given or completed by c16 (including any shift sequences), and stores the multibyte character representation in the array whose first element is pointed to by s, or stores nothing if c16 does not represent a complete character. At most MB_CUR_MAX bytes are stored. If c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state; the resulting state described is the initial conversion state. Returns The c16rtomb function returns the number of bytes stored in the array object (including any shift sequences). When c16 is not a valid wide character, an encoding error occurs: the function stores the value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion state is unspecified. 7.30.1.5 The mbrtoc32 function Synopsis #include <uchar.h> size_t mbrtoc32(char32_t * restrict pc32, const char * restrict s, size_t n, mbstate_t * restrict ps);
1
2
Description If s is a null pointer, the mbrtoc32 function is equivalent to the call: mbrtoc32(NULL, "", 1, ps)
In this case, the values of the parameters pc32 and n are ignored. 3
4
If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with the byte pointed to by s to determine the number of bytes needed to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character is complete and valid, it determines the values of the corresponding wide characters and then, if pc32 is not a null pointer, stores the value of the first (or only) such character in the object pointed to by pc32. Subsequent calls will store successive wide characters without consuming any additional input until all the characters have been stored. If the corresponding wide character is the null wide character, the resulting state described is the initial conversion state. Returns The mbrtoc32 function returns the first of the following that applies (given the current conversion state): 0
if the next n or fewer bytes complete the multibyte character that corresponds to the null wide character (which is the value stored).
between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte character (which is the value stored); the value returned is the number of bytes that complete the multibyte character. (size_t)(-3) if the next character resulting from a previous call has been stored (no bytes from
the input have been consumed by this call). (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) multibyte character, and all n bytes have been processed (no value is stored).400) (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes do not contribute
to a complete and valid multibyte character (no value is stored); the value of the macro EILSEQ is stored in errno, and the conversion state is unspecified. 400) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a sequence of redundant shift sequences (for implementations with state-dependent encodings).
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7.30.1.6 The c32rtomb function Synopsis 1
2
#include <uchar.h> size_t c32rtomb(char * restrict s, char32_t c32, mbstate_t * restrict ps);
Description If s is a null pointer, the c32rtomb function is equivalent to the call c32rtomb(buf, U’\0’, ps)
where buf is an internal buffer. 3
4
If s is not a null pointer, the c32rtomb function determines the number of bytes needed to represent the multibyte character that corresponds to the wide character given by c32 (including any shift sequences), and stores the multibyte character representation in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state; the resulting state described is the initial conversion state. Returns The c32rtomb function returns the number of bytes stored in the array object (including any shift sequences). When c32 is not a valid wide character, an encoding error occurs: the function stores the value of the macro EILSEQ in errno and returns (size_t)(-1);the conversion state is unspecified.
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7.31 Extended multibyte and wide character utilities <wchar.h> 7.31.1 Introduction 1
The header <wchar.h> defines five macros, and declares four data types, one tag, and many functions.401)
2
The macro __STDC_VERSION_WCHAR_H__
is an integer constant expression with a value equivalent to 202311L. 3
The types declared are wchar_t and size_t (both described in 7.21); mbstate_t
which is a complete object type other than an array type that can hold the conversion state information necessary to convert between sequences of multibyte characters and wide characters; wint_t
which is an integer type unchanged by default argument promotions that can hold any value corresponding to members of the extended character set, as well as at least one value that does not correspond to any member of the extended character set (see WEOF below);402) and struct tm
which is declared as an incomplete structure type (the contents are described in 7.29.1). 4
The macros defined are NULL (described in 7.21); WCHAR_MIN, WCHAR_MAX, and WCHAR_WIDTH (described in 7.22); and WEOF
which expands to a constant expression of type wint_t whose value does not correspond to any member of the extended character set.403) It is accepted (and returned) by several functions in this subclause to indicate end-of-file, that is, no more input from a stream. It is also used as a wide character value that does not correspond to any member of the extended character set. 5
The functions declared are grouped as follows: — Functions that perform input and output of wide characters, or multibyte characters, or both; — Functions that provide wide string numeric conversion; — Functions that perform general wide string manipulation; — Functions for wide string date and time conversion; and — Functions that provide extended capabilities for conversion between multibyte and wide character sequences.
6
Arguments to the functions in this subclause may point to arrays containing wchar_t values that do not correspond to members of the extended character set. Such values shall be processed according to the specified semantics, except that it is unspecified whether an encoding error occurs if such a value appears in the format string for a function in 7.31.2 or 7.31.5 and the specified semantics do not require that value to be processed by wcrtomb.
7
Unless explicitly stated otherwise, if the execution of a function described in this subclause causes copying to take place between objects that overlap, the behavior is undefined. 401) See "future library directions" (7.33.20). 402) wchar_t and wint_t can be the same integer type. 403) The value of the macro WEOF can differ from that of EOF and need not be negative.
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Formatted wide character input/output functions
The formatted wide character input/output functions shall behave as if there is a sequence point after the actions associated with each specifier.404) 7.31.2.1 The fwprintf function Synopsis #include <stdio.h> #include <wchar.h> int fwprintf(FILE * restrict stream, const wchar_t * restrict format, ...);
1
2
Description The fwprintf function writes output to the stream pointed to by stream, under control of the wide string pointed to by format that specifies how subsequent arguments are converted for output. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated (as always) but are otherwise ignored. The fwprintf function returns when the end of the format string is encountered.
3
The format is composed of zero or more directives: ordinary wide characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments, converting them, if applicable, according to the corresponding conversion specifier, and then writing the result to the output stream.
4
Each conversion specification is introduced by the wide character %. After the %, the following appear in sequence: — Zero or more flags (in any order) that modify the meaning of the conversion specification. — An optional minimum field width. If the converted value has fewer wide characters than the field width, it is padded with spaces (by default) on the left (or right, if the left adjustment flag, described later, has been given) to the field width. The field width takes the form of an asterisk 405) * (described later) or a nonnegative decimal integer. — An optional precision that gives the minimum number of digits to appear for the b, d, i, o, u, x, and X conversions, the number of digits to appear after the decimal-point wide character for a, A, e, E, f, and F conversions, the maximum number of significant digits for the g and G conversions, or the maximum number of wide characters to be written for s conversions. The precision takes the form of a period (.) followed either by an asterisk * (described later) or by an optional nonnegative decimal integer; if only the period is specified, the precision is taken as zero. If a precision appears with any other conversion specifier, the behavior is undefined. — An optional length modifier that specifies the size of the argument. — A conversion specifier wide character that specifies the type of conversion to be applied.
5
As noted above, a field width, or precision, or both, may be indicated by an asterisk. In this case, an int argument supplies the field width or precision. The arguments specifying field width, or precision, or both, shall appear (in that order) before the argument (if any) to be converted. A negative field width argument is taken as a - flag followed by a positive field width. A negative precision argument is taken as if the precision were omitted.
6
The flag wide characters and their meanings are: -
The result of the conversion is left-justified within the field. (It is right-justified if this flag is not specified.)
+
The result of a signed conversion always begins with a plus or minus sign. (It begins with a sign only when a value with a negative sign is converted if this flag is not specified.) 406)
404) The fwprintf functions perform writes to memory for the %n specifier. 405) Note that 0 is taken as a flag, not as the beginning of a field width. 406) The results of all floating conversions of a negative zero, and of negative values that round to zero, include a minus sign.
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space If the first wide character of a signed conversion is not a sign, or if a signed conversion results in no wide characters, a space is prefixed to the result. If the space and + flags both appear, the space flag is ignored.
7
#
The result is converted to an "alternative form". For o conversion, it increases the precision, if and only if necessary, to force the first digit of the result to be a zero (if the value and precision are both 0, a single 0 is printed). For b conversion, a nonzero result has 0b prefixed to it. For the optional B conversion as described below, a nonzero result has 0B prefixed to it. For x (or X) conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, and G conversions, the result of converting a floating-point number always contains a decimal-point wide character, even if no digits follow it. (Normally, a decimal-point wide character appears in the result of these conversions only if a digit follows it.) For g and G conversions, trailing zeros are not removed from the result. For other conversions, the behavior is undefined.
0
For b, d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros (following any indication of sign or base) are used to pad to the field width rather than performing space padding, except when converting an infinity or NaN. If the 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X conversions, if a precision is specified, the 0 flag is ignored. For other conversions, the behavior is undefined.
The length modifiers and their meanings are: hh
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a signed char or unsigned char argument (the argument will have been promoted according to the integer promotions, but its value shall be converted to signed char or unsigned char before printing); or that a following n conversion specifier applies to a pointer to a signed char argument.
h
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a short int or unsigned short int argument (the argument will have been promoted according to the integer promotions, but its value shall be converted to short int or unsigned short int before printing); or that a following n conversion specifier applies to a pointer to a short int argument.
l (ell)
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a long int or unsigned long int argument; that a following n conversion specifier applies to a pointer to a long int argument; that a following c conversion specifier applies to a wint_t argument; that a following s conversion specifier applies to a pointer to a wchar_t argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion specifier.
ll (ell-ell) Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a long long int or unsigned long long int argument; or that a following n conversion specifier applies to a pointer to a long long int argument. j
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to an intmax_t or uintmax_t argument; or that a following n conversion specifier applies to a pointer to an intmax_t argument.
z
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a size_t or the corresponding signed integer type argument; or that a following n conversion specifier applies to a pointer to a signed integer type corresponding to size_t argument.
t
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a ptrdiff_t or the corresponding unsigned integer type argument; or that a following n conversion specifier applies to a pointer to a ptrdiff_t argument.
wN
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to an integer argument with a specific width where N is a positive decimal integer with no leading zeros (the argument will have been promoted according to the integer promotions, but
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its value shall be converted to the unpromoted type); or that a following n conversion specifier applies to a pointer to an integer type argument with a width of N bits. All minimum-width integer types (7.22.1.2) and exact-width integer types (7.22.1.1) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined. wfN
Specifies that a following b, d, i, o, u, x, or X conversion specifier applies to a fastest minimum-width integer argument with a specific width where N is a positive decimal integer with no leading zeros (the argument will have been promoted according to the integer promotions, but its value shall be converted to the unpromoted type); or that a following n conversion specifier applies to a pointer to a fastest minimum-width integer type argument with a width of N bits. All fastest minimum-width integer types (7.22.1.3) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
L
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument.
H
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a _Decimal32 argument.
D
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a _Decimal64 argument.
DD
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a _Decimal128 argument.
If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. 8
The conversion specifiers and their meanings are: d,i
The int argument is converted to signed decimal in the style [-]dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a zero value with a precision of zero is no wide characters.
b,B,o,u,x,X The unsigned int argument is converted to unsigned binary (b or B), unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the letters abcdef are used for x conversion and the letters ABCDEF for X conversion. The
precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a zero value with a precision of zero is no wide characters. The specifier B is optional and provides the same functionality as b, except for the # flag as specified above. The macro PRIBPTR from <inttypes.h> shall only be defined if the implementation follows the specification as given here. f,F
A double argument representing a floating-point number is converted to decimal notation in the style [-]ddd.ddd, where the number of digits after the decimal-point wide character is equal to the precision specification. If the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point wide character appears. If a decimal-point wide character appears, at least one digit appears before it. The value is rounded to the appropriate number of digits. A double argument representing an infinity is converted in one of the styles [-]inf or [-]infinity — which style is implementation-defined. A double argument representing a NaN is converted in one of the styles [-]nan or [-]nan(n-wchar-sequence) — which style, and the meaning of any n-wchar-sequence, is implementation-defined. The F conversion specifier produces INF, INFINITY, or NAN instead of inf, infinity, or nan, respectively.407)
407) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual meaning; the # and 0 flag wide characters have no effect.
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A double argument representing a floating-point number is converted in the style [-]d.ddde±dd, where there is one digit (which is nonzero if the argument is nonzero) before the decimal-point wide character and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point wide character appears. The value is rounded to the appropriate number of digits. The E conversion specifier produces a number with E instead of e introducing the exponent. The exponent always contains at least two digits, and only as many more digits as necessary to represent the exponent. If the value is zero, the exponent is zero. A double argument representing an infinity or NaN is converted in the style of an f or F conversion specifier.
g,G
A double argument representing a floating-point number is converted in style f or e (or in style F or E in the case of a G conversion specifier), depending on the value converted and the precision. Let P equal the precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero. Then, if a conversion with style E would have an exponent of X: if P > X ≥ −4, the conversion is with style f (or F) and precision P − (X + 1). otherwise, the conversion is with style e (or E) and precision P − 1. Finally, unless the # flag is used, any trailing zeros are removed from the fractional portion of the result and the decimal-point wide character is removed if there is no fractional portion remaining. A double argument representing an infinity or NaN is converted in the style of an f or F conversion specifier.
a,A
A double argument representing a floating-point number is converted in the style [-]0xh.hhhhp±d, where there is one hexadecimal digit (which is nonzero if the argument is a normalized floating-point number and is otherwise unspecified) before the decimal-point wide character 408) and the number of hexadecimal digits after it is equal to the precision; if the precision is missing and FLT_RADIX is a power of 2, then the precision is sufficient for an exact representation of the value; if the precision is missing and FLT_RADIX is not a power of 2, then the precision is sufficient to distinguish409) values of type double, except that trailing zeros may be omitted; if the precision is zero and the # flag is not specified, no decimal-point wide character appears. The letters abcdef are used for a conversion and the letters ABCDEF for A conversion. The A conversion specifier produces a number with X and P instead of x and p. The exponent always contains at least one digit, and only as many more digits as necessary to represent the decimal exponent of 2. If the value is zero, the exponent is zero. A double argument representing an infinity or NaN is converted in the style of an f or F conversion specifier. If an H, D, or DD modifier is present and the precision is missing, then for a decimal floating type argument represented by a triple of integers (s, c, q), where n is the number of significant digits in the coefficient c,
408) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide character so that subsequent digits align to nibble (4-bit) boundaries. This implementation choice affects numerical values printed with a precision P that is insufficient to represent all values exactly. Implementations with different conventions about the most significant hexadecimal digit will round at different places, affecting the numerical value of the hexadecimal result. For example, possible printed output for the code
#include <stdio.h> /* ... */ double x = 123.0; printf("%.1a", x); include "0x1.fp+6 " and "0xf.6p+3 " whose numerical values are 124 and 123, respectively. Portable code seeking identical numerical results on different platforms should avoid precisions P that require rounding. 409) The formatting precision P is sufficient to distinguish values of the source type if 16P > bp where b (not a power of 2) and p are the base and precision of the source type (5.2.4.2.2). A smaller P might suffice depending on the implementation’s scheme for determining the digit to the left of the decimal-point wide character.
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— if −(n + 5) ≤ q ≤ 0, use style f (or style F in the case of an A conversion specifier) with formatting precision equal to −q, — otherwise, use style e (or style E in the case of an A conversion specifier) with formatting precision equal to n − 1, with the exceptions that if c = 0 then the digit-sequence in the exponent-part shall have the value q (rather than 0), and that the exponent is always expressed with the minimum number of digits required to represent its value (the exponent never contains a leading zero). If the precision P is present (in the conversion specification) and is zero or at least as large as the precision p (5.2.4.2.2) of the decimal floating type, the conversion is as if the precision were missing. If the precision P is present (and nonzero) and less than the precision p of the decimal floating type, the conversion first obtains an intermediate result as follows, where n is the number of significant digits in the coefficient: — If n ≤ P , set the intermediate result to the input. — If n > P , round the input value, according to the current rounding direction for decimal floating-point operations, to P decimal digits, with unbounded exponent range, representing the result with a P -digit integer coefficient when in the form (s, c, q). Convert the intermediate result in the manner described above for the case where the precision is missing. c
If no l length modifier is present, the int argument is converted to a wide character as if by calling btowc and the resulting wide character is written. If an l length modifier is present, the wint_t argument is converted to wchar_t and written.
s
If no l length modifier is present, the argument shall be a pointer to storage of character type containing a multibyte character sequence beginning in the initial shift state. Characters from the storage are converted as if by repeated calls to the mbrtowc function, with the conversion state described by an mbstate_t object initialized to zero before the first multibyte character is converted, and written up to (but not including) the terminating null wide character. If the precision is specified, no more than that many wide characters are written. If the precision is not specified or is greater than the size of the converted storage, the converted storage shall contain a null wide character. If an l length modifier is present, the argument shall be a pointer to storage of wchar_t type. Wide characters from the storage are written up to (but not including) a terminating null wide character. If the precision is specified, no more than that many wide characters are written. If the precision is not specified or is greater than the size of the array, the storage shall contain a null wide character.
9
p
The argument shall be a pointer to void or a pointer to a character type. The value of the pointer is converted to a sequence of printing wide characters, in an implementationdefined manner.
n
The argument shall be a pointer to signed integer whose type is specified by the length modifier, if any, for the conversion specification, or shall be int if no length modifier is specified for the conversion specification. The number of wide characters written to the output stream so far by this call to fwprintf is stored into the integer object pointed to by the argument. No argument is converted, but one is consumed. If the conversion specification includes any flags, a field width, or a precision, the behavior is undefined.
%
A % wide character is written. No argument is converted. The complete conversion specification shall be %%.
If a conversion specification is invalid, the behavior is undefined.410) fwprintf shall behave as if it uses va_arg with a type argument naming the type resulting from applying the default argument 410) See "future library directions" (7.33.20).
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promotions to the type corresponding to the conversion specification and then converting the result of the va_arg expansion to the type corresponding to the conversion specification.411) 10
In no case does a nonexistent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.
11
For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded to a hexadecimal floating number with the given precision.
12
Recommended practice For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly representable in the given precision, the result should be one of the two adjacent numbers in hexadecimal floating style with the given precision, with the extra stipulation that the error should have a correct sign for the current rounding direction.
13
For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most the maximum value M of the T_DECIMAL_DIG macros (defined in <float.h>), then the result should be correctly rounded.412) If the number of significant decimal digits is more than M but the source value is exactly representable with M digits, then the result should be an exact representation with trailing zeros. Otherwise, the source value is bounded by two adjacent decimal strings L < U, both having M significant digits; the value of the resultant decimal string D should satisfy L ≤ D ≤ U, with the extra stipulation that the error should have a correct sign for the current rounding direction.
14
The uppercase B format specifier is made optional by the description above, because it used to be available for extensions in previous versions of this document. Implementations that did not use an uppercase B as their own extension before are encouraged to implement it similar to conversion specifier b as standardized above, with the alternative form (#B) generating 0B as prefix for nonzero values.
15
16 17
Returns The fwprintf function returns the number of wide characters transmitted, or a negative value if an output or encoding error occurred or if the implementation does not support a specified width length modifier. Environmental limits The number of wide characters that can be produced by any single conversion shall be at least 4095. EXAMPLE To print a date and time in the form "Sunday, July 3, 10:02" followed by π to five decimal places: #include <math.h> #include <stdio.h> #include <wchar.h> /* ... */ wchar_t *weekday, *month; // pointers to wide strings int day, hour, min; fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n", weekday, month, day, hour, min); fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
Forward references: the btowc function (7.31.6.1.1), the mbrtowc function (7.31.6.3.2). 7.31.2.2 The fwscanf function Synopsis #include <stdio.h> #include <wchar.h>
1
411) The behavior is undefined when the types differ as specified for va_arg 7.16.1.1. 412) For binary-to-decimal conversion, the result format’s values are the numbers representable with the given format specifier.
The number of significant digits is determined by the format specifier, and in the case of fixed-point conversion by the source value as well.
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int fwscanf(FILE * restrict stream, const wchar_t * restrict format, ...);
2
3
Description The fwscanf function reads input from the stream pointed to by stream, under control of the wide string pointed to by format that specifies the admissible input sequences and how they are to be converted for assignment, using subsequent arguments as pointers to the objects to receive the converted input. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated (as always) but are otherwise ignored. The format is composed of zero or more directives: one or more white-space wide characters, an ordinary wide character (neither % nor a white-space wide character), or a conversion specification. Each conversion specification is introduced by the wide character %. After the %, the following appear in sequence: — An optional assignment-suppressing wide character *. — An optional decimal integer greater than zero that specifies the maximum field width (in wide characters). — An optional length modifier that specifies the size of the receiving object. — A conversion specifier wide character that specifies the type of conversion to be applied.
4
The fwscanf function executes each directive of the format in turn. When all directives have been executed, or if a directive fails (as detailed below), the function returns. Failures are described as input failures (due to the occurrence of an encoding error or the unavailability of input characters), or matching failures (due to inappropriate input).
5
A directive composed of white-space wide character(s) is executed by reading input up to the first non-white-space wide character (which remains unread), or until no more wide characters can be read. The directive never fails.
6
A directive that is an ordinary wide character is executed by reading the next wide character of the stream. If that wide character differs from the directive,the directive fails and the differing and subsequent wide characters remain unread. Similarly, if end-of-file, an encoding error, or a read error prevents a wide character from being read, the directive fails.
7
A directive that is a conversion specification defines a set of matching input sequences, as described below for each specifier. A conversion specification is executed in the following steps:
8
Input white-space wide characters are skipped, unless the specification includes a [, c, or n specifier.413)
9
An input item is read from the stream, unless the specification includes an n specifier. An input item is defined as the longest sequence of input wide characters which does not exceed any specified field width and which is, or is a prefix of, a matching input sequence.414) The first wide character, if any, after the input item remains unread. If the length of the input item is zero, the execution of the directive fails; this condition is a matching failure unless end-of-file, an encoding error, or a read error prevented input from the stream, in which case it is an input failure.
10
Except in the case of a % specifier, the input item (or, in the case of a %n directive, the count of input wide characters) is converted to a type appropriate to the conversion specifier. If the input item is not a matching sequence, the execution of the directive fails: this condition is a matching failure. Unless assignment suppression was indicated by a *, the result of the conversion is placed in the object pointed to by the first argument following the format argument that has not already received a conversion result. If this object does not have an appropriate type, or if the result of the conversion cannot be represented in the object, the behavior is undefined. 413) These white-space wide characters are not counted against a specified field width. 414) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.
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The length modifiers and their meanings are: hh
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to signed char or unsigned char.
h
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to short int or unsigned short int.
l (ell)
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long int or unsigned long int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to double; or that a following c, s, or [ conversion specifier applies to an argument with type pointer to wchar_t.
ll (ell-ell) Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long long int or unsigned long long int. j
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to intmax_t or uintmax_t.
z
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to size_t or the corresponding signed integer type.
t
Specifies that a following b, d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to ptrdiff_t or the corresponding unsigned integer type.
wN
Specifies that a following b, d, i, o, u, x, or X, or n conversion specifier applies to an argument which is a pointer to an integer with a specific width where N is a positive decimal integer with no leading zeros. All minimum-width integer types (7.22.1.2) and exact-width integer types (7.22.1.1) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
wfN
Specifies that a following b, d, i, o, u, x, or X, or n conversion specifier applies to an argument which is a pointer to a fastest minimum-width integer with a specific width where N is a positive decimal integer with no leading zeros. All fastest minimum-width integer types (7.22.1.3) defined in the header <stdint.h> shall be supported. Other supported values of N are implementation-defined.
L
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to long double.
H
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to _Decimal32.
D
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to _Decimal64.
DD
Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to _Decimal128.
If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. 12
In the following, the type of the corresponding argument for a conversion specifier shall be a pointer to a type determined by the length modifiers, if any, or specified by the conversion specifier. The conversion specifiers and their meanings are: d
420
Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of the wcstol function with the value 10 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to int. Library
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b
Matches an optionally signed binary integer, whose format is the same as expected for the subject sequence of the wcstol function with the value 2 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
i
Matches an optionally signed integer, whose format is the same as expected for the subject sequence of the wcstol function with the value 0 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to int.
o
Matches an optionally signed octal integer, whose format is the same as expected for the subject sequence of the wcstoul function with the value 8 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
u
Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of the wcstoul function with the value 10 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
x
Matches an optionally signed hexadecimal integer, whose format is the same as expected for the subject sequence of the wcstoul function with the value 16 for the base argument. Unless a length modifier is specified, the corresponding argument shall be a pointer to unsigned int.
a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose format is the same as expected for the subject sequence of the wcstod function. Unless a length modifier is specified, the corresponding argument shall be a pointer to float. c
Matches a sequence of wide characters of exactly the number specified by the field width (1 if no field width is present in the directive). If no l length modifier is present, characters from the input field are converted as if by repeated calls to the wcrtomb function, with the conversion state described by an mbstate_t object initialized to zero before the first wide character is converted. The corresponding argument shall be a pointer to char, signed char, unsigned char, or void that points to storage large enough to accept the sequence. No null character is added. If an l length modifier is present, the corresponding argument shall be a pointer to storage of wchar_t large enough to accept the sequence. No null wide character is added.
s
Matches a sequence of non-white-space wide characters. If no l length modifier is present, characters from the input field are converted as if by repeated calls to the wcrtomb function, with the conversion state described by an mbstate_t object initialized to zero before the first wide character is converted. The corresponding argument shall be a pointer to char, signed char, unsigned char, or void that points to storage large enough to accept the sequence and a terminating null character, which will be added automatically. If an l length modifier is present, the corresponding argument shall be a pointer to storage of wchar_t large enough to accept the sequence and the terminating null wide character, which will be added automatically.
[
Matches a nonempty sequence of wide characters from a set of expected characters (the scanset). If no l length modifier is present, characters from the input field are converted as if by repeated calls to the wcrtomb function, with the conversion state described by an mbstate_t object initialized to zero before the first wide character is converted. The corresponding argument shall be a pointer to char, signed char, unsigned char, or
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void that points to storage large enough to accept the sequence and a terminating null
character, which will be added automatically. If an l length modifier is present, the corresponding argument shall be a pointer that points to storage of wchar_t large enough to accept the sequence and the terminating null wide character, which will be added automatically. The conversion specifier includes all subsequent wide characters in the format string, up to and including the matching right bracket (]). The wide characters between the brackets (the scanlist) compose the scanset, unless the wide character after the left bracket is a circumflex (^), in which case the scanset contains all wide characters that do not appear in the scanlist between the circumflex and the right bracket. If the conversion specifier begins with [] or [^], the right bracket wide character is in the scanlist and the next following right bracket wide character is the matching right bracket that ends the specification; otherwise the first following right bracket wide character is the one that ends the specification. If a - wide character is in the scanlist and is not the first, nor the second where the first wide character is a ^, nor the last character, the behavior is implementation-defined. p
Matches an implementation-defined set of sequences, which should be the same as the set of sequences that may be produced by the %p conversion of the fwprintf function. The corresponding argument shall be a pointer to a pointer of void. The input item is converted to a pointer value in an implementation-defined manner. If the input item is a value converted earlier during the same program execution, the pointer that results shall compare equal to that value; otherwise the behavior of the %p conversion is undefined.
n
No input is consumed. The corresponding argument shall be a pointer of a signed integer type. The number of wide characters read from the input stream so far by this call to the fwscanf function is stored into the integer object pointed to by the argument. Execution of a %n directive does not increment the assignment count returned at the completion of execution of the fwscanf function. No argument is converted, but one is consumed. If the conversion specification includes an assignment-suppressing wide character or a field width, the behavior is undefined.
%
Matches a single % wide character; no conversion or assignment occurs. The complete conversion specification shall be %%.
13
If a conversion specification is invalid, the behavior is undefined.415)
14
The conversion specifiers A, E, F, G, and X are also valid and behave the same as, respectively, a, e, f, g, and x.
15
Trailing white-space wide characters (including new-line wide characters) are left unread unless matched by a directive. The success of literal matches and suppressed assignments is not directly determinable other than via the %n directive.
16
17
Returns The fwscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure or if the implementation does not support a specific width length modifier. EXAMPLE 1 The call: #include <stdio.h> #include <wchar.h> /* ... */ int n, i; float x; wchar_t name[50]; n = fwscanf(stdin, L"%d%f%ls", &i, &x, name); 415) See "future library directions" (7.33.20).
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with the input line: 25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence thompson\0. 18
EXAMPLE 2 The call: #include <stdio.h> #include <wchar.h> /* ... */ int i; float x; double y; fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
with input: 56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value 56.0. The next wide character read from the input stream will be a. Forward references: the wcstod, wcstof, and wcstold functions (7.31.4.1.2), the wcstol, wcstoll, wcstoul, and wcstoull functions (7.31.4.1.4), the wcrtomb function (7.31.6.3.3). 7.31.2.3 The swprintf function Synopsis 1
2
3
#include <wchar.h> int swprintf(wchar_t * restrict s, size_t n, const wchar_t * restrict format, ...);
Description The swprintf function is equivalent to fwprintf, except that the argument s specifies an array of wide characters into which the generated output is to be written, rather than written to a stream. No more than n wide characters are written, including a terminating null wide character, which is always added (unless n is zero). Returns The swprintf function returns the number of wide characters written in the array, not counting the terminating null wide character, or a negative value if an encoding error occurred or if n or more wide characters were requested to be written. 7.31.2.4 The swscanf function Synopsis
1
2
3
#include <wchar.h> int swscanf(const wchar_t * restrict s, const wchar_t * restrict format, ...);
Description The swscanf function is equivalent to fwscanf, except that the argument s specifies a wide string from which the input is to be obtained, rather than from a stream. Reaching the end of the wide string is equivalent to encountering end-of-file for the fwscanf function. Returns The swscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the swscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. § 7.31.2.4
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7.31.2.5 The vfwprintf function Synopsis #include <stdarg.h> #include <stdio.h> #include <wchar.h> int vfwprintf(FILE * restrict stream, const wchar_t * restrict format, va_list arg);
1
2
3
4
Description The vfwprintf function is equivalent to fwprintf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vfwprintf function does not invoke the va_end macro416) . Returns The vfwprintf function returns the number of wide characters transmitted, or a negative value if an output or encoding error occurred. EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting routine. #include <stdarg.h> #include <stdio.h> #include <wchar.h> void error(char *function_name, wchar_t *format, ...) { va_list args; va_start(args, format); // print out name of function causing error fwprintf(stderr, L"ERROR in %s: ", function_name); // print out remainder of message vfwprintf(stderr, format, args); va_end(args); }
7.31.2.6 The vfwscanf function Synopsis #include <stdarg.h> #include <stdio.h> #include <wchar.h> int vfwscanf(FILE * restrict stream, const wchar_t * restrict format, va_list arg);
1
2
3
Description The vfwscanf function is equivalent to fwscanf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vfwscanf function does not invoke the va_end macro.416) Returns The vfwscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the vfwscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 416) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf invoke the va_arg macro, the representation of arg after the return is indeterminate.
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7.31.2.7 The vswprintf function Synopsis 1
2
3
#include <stdarg.h> #include <wchar.h> int vswprintf(wchar_t * restrict s, size_t n, const wchar_t * restrict format, va_list arg);
Description The vswprintf function is equivalent to swprintf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vswprintf function does not invoke the va_end macro.416) Returns The vswprintf function returns the number of wide characters written in the array, not counting the terminating null wide character, or a negative value if an encoding error occurred or if n or more wide characters were requested to be generated. 7.31.2.8 The vswscanf function Synopsis
1
2
3
#include <stdarg.h> #include <wchar.h> int vswscanf(const wchar_t * restrict s, const wchar_t * restrict format, va_list arg);
Description The vswscanf function is equivalent to swscanf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vswscanf function does not invoke the va_end macro.416) Returns The vswscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the vswscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 7.31.2.9 The vwprintf function Synopsis
1
2
3
#include <stdarg.h> #include <wchar.h> int vwprintf(const wchar_t * restrict format, va_list arg);
Description The vwprintf function is equivalent to wprintf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vwprintf function does not invoke the va_end macro.416) Returns The vwprintf function returns the number of wide characters transmitted, or a negative value if an output or encoding error occurred. 7.31.2.10 The vwscanf function Synopsis
1
#include <stdarg.h> #include <wchar.h>
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int vwscanf(const wchar_t * restrict format, va_list arg);
2
3
Description The vwscanf function is equivalent to wscanf, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vwscanf function does not invoke the va_end macro.416) Returns The vwscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the vwscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. 7.31.2.11 The wprintf function Synopsis #include <wchar.h> int wprintf(const wchar_t * restrict format, ...);
1
2
Description The wprintf function is equivalent to fwprintf with the argument stdout interposed before the arguments to wprintf.
3
Returns The wprintf function returns the number of wide characters transmitted, or a negative value if an output or encoding error occurred. 7.31.2.12 The wscanf function Synopsis #include <wchar.h> int wscanf(const wchar_t * restrict format, ...);
1
2
3
Description The wscanf function is equivalent to fwscanf with the argument stdin interposed before the arguments to wscanf. Returns The wscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the wscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure.
7.31.3
Wide character input/output functions
7.31.3.1 The fgetwc function Synopsis #include <stdio.h> #include <wchar.h> wint_t fgetwc(FILE *stream);
1
2
Description If the end-of-file indicator for the input stream pointed to by stream is not set and a next wide character is present, the fgetwc function obtains that wide character as a wchar_t converted to a wint_t and advances the associated file position indicator for the stream (if defined). 426
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Returns If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise, the fgetwc function returns the next wide character from the input stream pointed to by stream. If a read error occurs, the error indicator for the stream is set and the fgetwc function returns WEOF. If an encoding error occurs (including too few bytes), the error indicator for the stream is set and the value of the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.417) 7.31.3.2 The fgetws function Synopsis
1
2
3
#include <stdio.h> #include <wchar.h> wchar_t *fgetws(wchar_t * restrict s, int n, FILE * restrict stream);
Description The fgetws function reads at most one less than the number of wide characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional wide characters are read after a new-line wide character (which is retained) or after end-of-file. A null wide character is written immediately after the last wide character read into the array. Returns The fgetws function returns s if successful. If end-of-file is encountered and no characters have been read into the array, the contents of the array remain unchanged and a null pointer is returned. If a read or encoding error occurs during the operation, the array members have an indeterminate representation and a null pointer is returned. 7.31.3.3 The fputwc function Synopsis
1
2
3
#include <stdio.h> #include <wchar.h> wint_t fputwc(wchar_t c, FILE *stream);
Description The fputwc function writes the wide character specified by c to the output stream pointed to by stream, at the position indicated by the associated file position indicator for the stream (if defined), and advances the indicator appropriately. If the file cannot support positioning requests, or if the stream was opened with append mode, the character is appended to the output stream. Returns The fputwc function returns the wide character written. If a write error occurs, the error indicator for the stream is set and fputwc returns WEOF. If an encoding error occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF. 7.31.3.4 The fputws function Synopsis
1
2
#include <stdio.h> #include <wchar.h> int fputws(const wchar_t * restrict s, FILE * restrict stream);
Description The fputws function writes the wide string pointed to by s to the stream pointed to by stream. The terminating null wide character is not written. 417) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. Also, errno will be set to
EILSEQ by input/output functions only if an encoding error occurs.
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Returns The fputws function returns EOF if a write or encoding error occurs; otherwise, it returns a nonnegative value. 7.31.3.5 The fwide function Synopsis #include <stdio.h> #include <wchar.h> int fwide(FILE *stream, int mode);
1
2
3
Description The fwide function determines the orientation of the stream pointed to by stream. If mode is greater than zero, the function first attempts to make the stream wide oriented. If mode is less than zero, the function first attempts to make the stream byte oriented.418) Otherwise, mode is zero and the function does not alter the orientation of the stream. Returns The fwide function returns a value greater than zero if, after the call, the stream has wide orientation, a value less than zero if the stream has byte orientation, or zero if the stream has no orientation. 7.31.3.6 The getwc function Synopsis #include <stdio.h> #include <wchar.h> wint_t getwc(FILE *stream);
1
2
Description The getwc function is equivalent to fgetwc, except that if it is implemented as a macro, it may evaluate stream more than once, so the argument should never be an expression with side effects.
3
Returns The getwc function returns the next wide character from the input stream pointed to by stream, or WEOF. 7.31.3.7 The getwchar function Synopsis #include <wchar.h> wint_t getwchar(void);
1
2
3
Description The getwchar function is equivalent to getwc with the argument stdin. Returns The getwchar function returns the next wide character from the input stream pointed to by stdin, or WEOF. 7.31.3.8 The putwc function Synopsis #include <stdio.h> #include <wchar.h> wint_t putwc(wchar_t c, FILE *stream);
1
418) If the orientation of the stream has already been determined, fwide does not change it.
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Description The putwc function is equivalent to fputwc, except that if it is implemented as a macro, it may evaluate stream more than once, so that argument should never be an expression with side effects. Returns The putwc function returns the wide character written, or WEOF. 7.31.3.9 The putwchar function Synopsis #include <wchar.h> wint_t putwchar(wchar_t c);
1
2
Description The putwchar function is equivalent to putwc with the second argument stdout.
3
Returns The putwchar function returns the character written, or WEOF. 7.31.3.10 The ungetwc function Synopsis #include <stdio.h> #include <wchar.h> wint_t ungetwc(wint_t c, FILE *stream);
1
2
Description The ungetwc function pushes the wide character specified by c back onto the input stream pointed to by stream. Pushed-back wide characters will be returned by subsequent reads on that stream in the reverse order of their pushing. A successful intervening call (with the stream pointed to by stream) to a file positioning function (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the stream. The external storage corresponding to the stream is unchanged.
3
One wide character of pushback is guaranteed, even if the call to the ungetwc function follows just after a call to a formatted wide character input function fwscanf, vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times on the same stream without an intervening read or file positioning operation on that stream, the operation may fail.
4
If the value of c equals that of the macro WEOF, the operation fails and the input stream is unchanged.
5
A successful call to the ungetwc function clears the end-of-file indicator for the stream. The value of the file position indicator for the stream after reading or discarding all pushed-back wide characters is the same as it was before the wide characters were pushed back.419) For a text or binary stream, the value of its file position indicator after a successful call to the ungetwc function is unspecified until all pushed-back wide characters are read or discarded.
6
Returns The ungetwc function returns the wide character pushed back, or WEOF if the operation fails.
7.31.4
General wide string utilities
1
The header <wchar.h> declares functions for wide string manipulation. Various methods are used for determining the lengths of the arrays, but in all cases a wchar_t* argument points to the initial (lowest addressed) element of the array. If an array is accessed beyond the end of an object, the behavior is undefined.
2
Where an argument declared as size_t n determines the length of the array for a function, n can have the value zero on a call to that function. Unless explicitly stated otherwise in the description of 419) Note that a file positioning function could further modify the file position indicator after discarding any pushed-back wide characters.
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a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. On such a call, a function that locates a wide character finds no occurrence, a function that compares two wide character sequences returns zero, and a function that copies wide characters copies zero wide characters. 7.31.4.1 Wide string numeric conversion functions 7.31.4.1.1 General This subclause describes wide string analogs of the strtod family of functions (7.24.1.5, 7.24.1.6)420) . 7.31.4.1.2
The wcstod, wcstof, and wcstold functions
#include <wchar.h> double wcstod(const wchar_t * restrict nptr, wchar_t ** restrict endptr); float wcstof(const wchar_t * restrict nptr, wchar_t ** restrict endptr); long double wcstold(const wchar_t * restrict nptr, wchar_t ** restrict endptr);
1
2
Description The wcstod, wcstof, and wcstold functions convert the initial portion of the wide string pointed to by nptr to double, float, and long double representation, respectively. First, they decompose the input string into three parts: an initial, possibly empty, sequence of white-space wide characters, a subject sequence resembling a floating constant or representing an infinity or NaN; and a final wide string of one or more unrecognized wide characters, including the terminating null wide character of the input wide string. Then, they attempt to convert the subject sequence to a floating-point number, and return the result. The expected form of the subject sequence is an optional plus or minus sign, then one of the following: — a nonempty sequence of decimal digits optionally containing a decimal-point wide character, then an optional exponent part as defined for the corresponding single-byte characters in 6.4.4.2, excluding any digit separators (6.4.4.1); — a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a decimalpoint wide character, then an optional binary exponent part as defined in 6.4.4.2, excluding any digit separators (6.4.4.1); — INF or INFINITY, or any other wide string equivalent except for case — NAN or NAN(n-wchar-sequenceopt ), or any other wide string equivalent except for case in the NAN part, where: 420) Wide string analogs of the strfromd family of functions (7.24.1.5, 7.24.1.6) are not provided because those conversions can be done by using mbstowcs (7.24.8.1) to convert the result of strfromd, strfromf, and similar to wide string. For example, the following converts double d to wide string ws with at most n-1 non-null wide characters, using style g formatting, and computes the number nc of wide characters that would have been written had n been sufficiently large, not counting the terminating null wide character.
#include <stdlib.h> const size_t n = 20; double d; //... // convert d to single-byte character string s char s[n]; int nc = strfromd(s, n, "%g", d); // convert s (regarded as a multi-byte character // string) to wide string ws wchar_t ws[n]; (void)mbstowcs(ws, s, n);
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n-wchar-sequence: digit nondigit n-wchar-sequence digit n-wchar-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input wide string, starting with the first non-white-space wide character, that is of the expected form. The subject sequence contains no wide characters if the input wide string is not of the expected form. 3
If the subject sequence has the expected form for a floating-point number, the sequence of wide characters starting with the first digit or the decimal-point wide character (whichever occurs first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that if neither an exponent part nor a decimal-point wide character appears in a decimal floating-point number, or if a binary exponent part does not appear in a hexadecimal floating-point number, an exponent part of the appropriate type with value zero is assumed to follow the last digit in the string.
4
If the subject sequence begins with a minus sign, the sequence is interpreted as negated.421)
5
A wide character sequence INF or INFINITY is interpreted as an infinity, if representable in the return type, else like a floating constant that is too large for the range of the return type. A wide character sequence NAN or NAN(n-wchar-sequenceopt ) is interpreted as a quiet NaN, if supported in the return type, else like a subject sequence part that does not have the expected form; the meaning of the n-wchar sequence is implementation-defined.422) A pointer to the final wide string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
6
If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the value resulting from the conversion is correctly rounded.
7
In other than the "C" locale, additional locale-specific subject sequence forms may be accepted.
8
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
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Recommended practice If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and the result is not exactly representable, the result should be one of the two numbers in the appropriate internal format that are adjacent to the hexadecimal floating source value, with the extra stipulation that the error should have a correct sign for the current rounding direction. If the subject sequence has the decimal form and at most M significant digits, where M is the maximum value of the T_DECIMAL_DIG macros (defined in <float.h>), the result should be correctly rounded. If the subject sequence D has the decimal form and more than M significant digits, consider the two bounding, adjacent decimal strings L and U, both having M significant digits, such that the values of L, D, and U satisfy L ≤ D ≤ U. The result should be one of the (equal or adjacent) values that would be obtained by correctly rounding L and U according to the current rounding direction, with the extra stipulation that the error with respect to D should have a correct sign for the current rounding direction.423) 421) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two methods could yield different results if rounding is toward positive or negative infinity. In either case, the functions honor the sign of zero if floating-point arithmetic supports signed zeros. 422) An implementation can use the n-wchar sequence to determine extra information to be represented in the NaN’s significand. 423) M is sufficiently large that L and U will usually correctly round to the same internal floating value, but if not will correctly round to adjacent values.
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Returns The functions return the converted value, if any. If no conversion could be performed, positive or unsigned zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return type and sign of the value); if the integer expression math_errhandling & MATH_ERRNO is nonzero, the integer expression errno acquires the value of ERANGE; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the "overflow" floating-point exception is raised. If the result underflows (7.12.1), the functions return a value whose magnitude is no greater than the smallest normalized positive number in the return type; if the integer expression math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the value ERANGE is implementation-defined; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point exception is raised is implementation-defined. 7.31.4.1.3 The wcstodN functions Synopsis #include <wchar.h> #ifdef __STDC_IEC_60559_DFP__ _Decimal32 wcstod32(const wchar_t * restrict nptr, char ** restrict endptr); _Decimal64 wcstod64(const wchar_t * restrict nptr,char ** restrict endptr); _Decimal128 wcstod128(const wchar_t * restrict nptr,char ** restrict endptr); #endif
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Description The wcstodN functions convert the initial portion of the wide string pointed to by nptr to decimal floating type representation. First, they decompose the input wide string into three parts: an initial, possibly empty, sequence of white-space wide characters; a subject sequence resembling a floating constant or representing an infinity or NaN; and a final wide string of one or more unrecognized wide characters, including the terminating null wide character of the input wide string. Then, they attempt to convert the subject sequence to a floating-point number, and return the result. The expected form of the subject sequence is an optional plus or minus sign, then one of the following: — a nonempty sequence of decimal digits optionally containing a decimal-point wide character, then an optional exponent part as defined in 6.4.4.2, excluding any digit separators (6.4.4.1) — a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a decimalpoint character, then an optional binary exponent part as defined in 6.4.4.2, excluding any digit separators (6.4.4.1). — INF or INFINITY, ignoring case — NAN or NAN(d-wchar-sequenceopt ), ignoring case in the NAN part, where: d-wchar-sequence: digit nondigit d-wchar-sequence digit d-wchar-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input wide string, starting with the first non-white-space wide character, that is of the expected form. The subject sequence contains no wide characters if the input wide string is not of the expected form. 432
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If the subject sequence has the expected form for a floating-point number, the sequence of wide characters starting with the first digit or the decimal-point wide character (whichever occurs first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that if neither an exponent part nor a decimal-point wide character appears in a decimal floating-point number, or if a binary exponent part does not appear in a hexadecimal floating-point number, an exponent part of the appropriate type with value zero is assumed to follow the last digit in the wide string. If the subject sequence begins with a minus sign, the sequence is interpreted as negated before rounding and the sign s is set to −1, else s is set to 1.
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If the subject sequence has the expected form for a decimal floating-point number, the value resulting from the conversion is correctly rounded and the coefficient c and the quantum exponent q are determined by the rules in 6.4.4.2 for a decimal floating constant of decimal type.
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If the subject sequence has the expected form for a hexadecimal floating-point number, the value resulting from the conversion is correctly rounded provided the subject sequence has at most M significant hexadecimal digits, where M ≥ ⌈(P − 1)/4⌉ + 1 is implementation-defined, and P is the maximum precision of the supported radix-2 floating types and binary non-arithmetic interchange formats.424) If all subject sequences of hexadecimal form are correctly rounded, M may be regarded as infinite. If the subject sequence has more than M significant hexadecimal digits, the implementation may first round to M significant hexadecimal digits according to the applicable rounding direction mode, signaling exceptions as though converting from a wider format, then correctly round the result of the shortened hexadecimal input to the result type. The preferred quantum exponent for the result is 0 if the hexadecimal number is exactly represented in the decimal type; the preferred quantum exponent for the result is the least possible if the hexadecimal number is not exactly represented in the decimal type.
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A wide character sequence INF or INFINITY is interpreted as an infinity. A wide character sequence NAN or NAN(d-wchar-sequenceopt ), is interpreted as a quiet NaN; the meaning of the d-wchar sequence is implementation-defined.425) A pointer to the final wide string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
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In other than the "C" locale, additional locale-specific subject sequence forms may be accepted.
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If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
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Returns The wcstodN functions return the converted value, if any. If no conversion could be performed, the value of the triple (+1, 0, 0) is returned. If the correct value overflows: — the value of the macro ERANGE is stored in errno if the integer expression math_errhandling & MATH_ERRNO is nonzero; — the "overflow" floating-point exception is raised if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero. If the result underflows (7.12.1), whether errno acquires the value ERANGE if the integer expression math_errhandling & MATH_ERRNO is nonzero is implementation-defined; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point exception is raised is implementation-defined. 7.31.4.1.4 The wcstol, wcstoll, wcstoul, and wcstoull functions Synopsis
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#include <wchar.h> long int wcstol(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); 424) Non-arithmetic interchange formats are an optional feature in Annex H. 425) An implementation may use the d-wchar sequence to determine extra information to be represented in the NaN’s significand.
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long long int wcstoll(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); unsigned long int wcstoul(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); unsigned long long int wcstoull(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base);
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Description The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial portion of the wide string pointed to by nptr to long int, long long int, unsigned long int, and unsigned long long int representation, respectively. First, they decompose the input string into three parts: an initial, possibly empty, sequence of white-space wide characters, a subject sequence resembling an integer represented in some radix determined by the value of base, and a final wide string of one or more unrecognized wide characters, including the terminating null wide character of the input wide string. Then, they attempt to convert the subject sequence to an integer, and return the result.
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If the value of base is zero, the expected form of the subject sequence is that of an integer constant as described for the corresponding single-byte characters in 6.4.4.1, optionally preceded by a plus or minus sign, but not including an integer suffix or any optional digit separators (6.4.4.1). If the value of base is between 2 and 36 (inclusive), the expected form of the subject sequence is a sequence of letters and digits representing an integer with the radix specified by base, optionally preceded by a plus or minus sign, but not including an integer suffix or any optional digit separators. The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only letters and digits whose ascribed values are less than that of base are permitted. If the value of base is 2, the characters 0b or 0B may optionally precede the sequence of letters and digits, following the sign if present. If the value of base is 16, the wide characters 0x or 0X may optionally precede the sequence of letters and digits, following the sign if present.
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The subject sequence is defined as the longest initial subsequence of the input wide string, starting with the first non-white-space wide character, that is of the expected form. The subject sequence contains no wide characters if the input wide string is empty or consists entirely of white-space wide characters, or if the first non-white-space wide character is other than a sign or a permissible letter or digit.
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If the subject sequence has the expected form and the value of base is zero, the sequence of wide characters starting with the first digit is interpreted as an integer constant according to the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value as given above. If the subject sequence begins with a minus sign, the resulting value is the negative of the converted value; for functions whose return type is an unsigned integer type this action is performed in the return type. A pointer to the final wide string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
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In other than the "C" locale, additional locale-specific subject sequence forms may be accepted.
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If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
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Returns The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted value, if any. If no conversion could be performed, zero is returned. If the correct value is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type sign of the value, if any), and the value of the macro ERANGE is stored in errno. 7.31.4.2 Wide string copying functions 7.31.4.2.1 The wcscpy function Synopsis #include <wchar.h>
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wchar_t *wcscpy(wchar_t * restrict s1, const wchar_t * restrict s2);
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Description The wcscpy function copies the wide string pointed to by s2 (including the terminating null wide character) into the array pointed to by s1. Returns The wcscpy function returns the value of s1. 7.31.4.2.2 The wcsncpy function Synopsis
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#include <wchar.h> wchar_t *wcsncpy(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n);
Description The wcsncpy function copies not more than n wide characters (those that follow a null wide character are not copied) from the array pointed to by s2 to the array pointed to by s1.426) If the array pointed to by s2 is a wide string that is shorter than n wide characters, null wide characters are appended to the copy in the array pointed to by s1, until n wide characters in all have been written. Returns The wcsncpy function returns the value of s1. 7.31.4.2.3 The wmemcpy function Synopsis
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#include <wchar.h> wchar_t *wmemcpy(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n);
Description The wmemcpy function copies n wide characters from the object pointed to by s2 to the object pointed to by s1. Returns The wmemcpy function returns the value of s1. 7.31.4.2.4 The wmemmove function Synopsis
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#include <wchar.h> wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, size_t n);
Description The wmemmove function copies n wide characters from the object pointed to by s2 to the object pointed to by s1. Copying takes place as if the n wide characters from the object pointed to by s2 are first copied into a temporary array of n wide characters that does not overlap the objects pointed to by s1 or s2, and then the n wide characters from the temporary array are copied into the object pointed to by s1. Returns The wmemmove function returns the value of s1. 426) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the result will not be null-terminated.
§ 7.31.4.2.4
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7.31.4.3 Wide string concatenation functions 7.31.4.3.1 The wcscat function Synopsis #include <wchar.h> wchar_t *wcscat(wchar_t * restrict s1, const wchar_t * restrict s2);
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Description The wcscat function appends a copy of the wide string pointed to by s2 (including the terminating null wide character) to the end of the wide string pointed to by s1. The initial wide character of s2 overwrites the null wide character at the end of s1. Returns The wcscat function returns the value of s1. 7.31.4.3.2 The wcsncat function Synopsis #include <wchar.h> wchar_t *wcsncat(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n);
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Description The wcsncat function appends not more than n wide characters (a null wide character and those that follow it are not appended) from the array pointed to by s2 to the end of the wide string pointed to by s1. The initial wide character of s2 overwrites the null wide character at the end of s1. A terminating null wide character is always appended to the result.427) Returns The wcsncat function returns the value of s1. 7.31.4.4 Wide string comparison functions Unless explicitly stated otherwise, the functions described in this subclause order two wide characters the same way as two integers of the underlying integer type designated by wchar_t. 7.31.4.4.1 The wcscmp function Synopsis #include <wchar.h> int wcscmp(const wchar_t *s1, const wchar_t *s2);
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Description The wcscmp function compares the wide string pointed to by s1 to the wide string pointed to by s2. Returns The wcscmp function returns an integer greater than, equal to, or less than zero, accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the wide string pointed to by s2. 7.31.4.4.2 The wcscoll function Synopsis #include <wchar.h> int wcscoll(const wchar_t *s1, const wchar_t *s2);
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Description The wcscoll function compares the wide string pointed to by s1 to the wide string pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the current locale. 427) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is wcslen(s1)+n+1.
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Returns The wcscoll function returns an integer greater than, equal to, or less than zero, accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the wide string pointed to by s2 when both are interpreted as appropriate to the current locale. 7.31.4.4.3 The wcsncmp function Synopsis
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#include <wchar.h> int wcsncmp(const wchar_t *s1, const wchar_t *s2, size_t n);
Description The wcsncmp function compares not more than n wide characters (those that follow a null wide character are not compared) from the array pointed to by s1 to the array pointed to by s2. Returns The wcsncmp function returns an integer greater than, equal to, or less than zero, accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal to, or less than the possibly null-terminated array pointed to by s2. 7.31.4.4.4 The wcsxfrm function Synopsis
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#include <wchar.h> size_t wcsxfrm(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n);
Description The wcsxfrm function transforms the wide string pointed to by s2 and places the resulting wide string into the array pointed to by s1. The transformation is such that if the wcscmp function is applied to two transformed wide strings, it returns a value greater than, equal to, or less than zero, corresponding to the result of the wcscoll function applied to the same two original wide strings. No more than n wide characters are placed into the resulting array pointed to by s1, including the terminating null wide character. If n is zero, s1 is permitted to be a null pointer. Returns The wcsxfrm function returns the length of the transformed wide string (not including the terminating null wide character). If the value returned is n or greater, the members of the array pointed to by s1 have an indeterminate representation. EXAMPLE The value of the following expression is the length of the array needed to hold the transformation of the wide string pointed to by s: 1 + wcsxfrm(NULL, s, 0)
7.31.4.4.5 The wmemcmp function Synopsis 1
#include <wchar.h> int wmemcmp(const wchar_t *s1, const wchar_t *s2, size_t n);
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Description The wmemcmp function compares the first n wide characters of the object pointed to by s1 to the first n wide characters of the object pointed to by s2.
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Returns The wmemcmp function returns an integer greater than, equal to, or less than zero, accordingly as the object pointed to by s1 is greater than, equal to, or less than the object pointed to by s2. § 7.31.4.4.5
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7.31.4.5 Wide string search functions 7.31.4.6 Introduction The stateless search functions in this section (wcschr, wcspbrk, wcsrchr, wmemchr, wcsstr) are generic functions. These functions are generic in the qualification of the array to be searched and will return a result pointer to an element with the same qualification as the passed array. If the array to be searched is const-qualified, the result pointer will be to a const-qualified element. If the array to be searched is not const-qualified428) , the result pointer will be to an unqualified element.
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The external declarations of these generic functions have a concrete function type that returns a pointer to an unqualified element of type wchar_t (named QWchar_t), and accepts a pointer to a const-qualified array of the same type to search. This signature supports all correct uses. If a macro definition of any of these generic functions is suppressed to access an actual function, the external declaration with this concrete type is visible.429)
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The volatile and restrict qualifiers are not accepted on the elements of the array to search. 7.31.4.6.1 The wcschr generic function Synopsis #include <wchar.h> QWchar_t *wcschr(QWchar_t *s, wchar_t c);
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Description The wcschr generic function locates the first occurrence of c in the wide string pointed to by s. The terminating null wide character is considered to be part of the wide string.
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Returns The wcschr generic function returns a pointer to the located wide character, or a null pointer if the wide character does not occur in the wide string. 7.31.4.6.2 The wcscspn function Synopsis #include <wchar.h> size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
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Description The wcscspn function computes the length of the maximum initial segment of the wide string pointed to by s1 which consists entirely of wide characters not from the wide string pointed to by s2. Returns The wcscspn function returns the length of the segment. 7.31.4.6.3 The wcspbrk generic function Synopsis #include <wchar.h> QWchar_t *wcspbrk(QWchar_t *s1, const wchar_t *s2);
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Description The wcspbrk generic function locates the first occurrence in the wide string pointed to by s1 of any wide character from the wide string pointed to by s2. 428) The null pointer constant is not a pointer to a const-qualified type, and therefore the result expression has the type of a
pointer to an unqualified element; however, evaluating such a call is undefined. 429) This is an obsolescent feature.
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Returns The wcspbrk generic function returns a pointer to the wide character in s1, or a null pointer if no wide character from s2 occurs in s1. 7.31.4.6.4 The wcsrchr generic function Synopsis
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#include <wchar.h> QWchar_t *wcsrchr(QWchar_t *s, wchar_t c);
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Description The wcsrchr generic function locates the last occurrence of c in the wide string pointed to by s. The terminating null wide character is considered to be part of the wide string.
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Returns The wcsrchr generic function returns a pointer to the wide character, or a null pointer if c does not occur in the wide string. 7.31.4.6.5 The wcsspn function Synopsis
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#include <wchar.h> size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
Description The wcsspn function computes the length of the maximum initial segment of the wide string pointed to by s1 which consists entirely of wide characters from the wide string pointed to by s2. Returns The wcsspn function returns the length of the segment. 7.31.4.6.6 The wcsstr generic function Synopsis
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#include <wchar.h> QWchar_t *wcsstr(QWchar_t *s1, const wchar_t *s2);
Description The wcsstr generic function locates the first occurrence in the wide string pointed to by s1 of the sequence of wide characters (excluding the terminating null wide character) in the wide string pointed to by s2. Returns The wcsstr generic function returns a pointer to the located wide string, or a null pointer if the wide string is not found. If s2 points to a wide string with zero length, the function returns s1.
§ 7.31.4.6.6
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7.31.4.6.7 The wcstok function Synopsis #include <wchar.h> wchar_t *wcstok(wchar_t * restrict s1, const wchar_t * restrict s2, wchar_t ** restrict ptr);
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Description A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into a sequence of tokens, each of which is delimited by a wide character from the wide string pointed to by s2. The third argument points to a caller-provided wchar_t pointer into which the wcstok function stores information necessary for it to continue scanning the same wide string.
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The first call in a sequence has a non-null first argument and stores an initial value in the object pointed to by ptr. Subsequent calls in the sequence have a null first argument and the object pointed to by ptr is required to have the value stored by the previous call in the sequence, which is then updated. The separator wide string pointed to by s2 may be different from call to call.
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The first call in the sequence searches the wide string pointed to by s1 for the first wide character that is not contained in the current separator wide string pointed to by s2. If no such wide character is found, then there are no tokens in the wide string pointed to by s1 and the wcstok function returns a null pointer. If such a wide character is found, it is the start of the first token.
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The wcstok function then searches from there for a wide character that is contained in the current separator wide string. If no such wide character is found, the current token extends to the end of the wide string pointed to by s1, and subsequent searches in the same wide string for a token return a null pointer. If such a wide character is found, it is overwritten by a null wide character, which terminates the current token.
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In all cases, the wcstok function stores sufficient information in the pointer pointed to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer value for ptr, shall start searching just past the element overwritten by a null wide character (if any).
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Returns The wcstok function returns a pointer to the first wide character of a token, or a null pointer if there is no token.
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EXAMPLE #include <wchar.h> static wchar_t str1[] = L"?a???b,,,#c"; static wchar_t str2[] = L"\t \t"; wchar_t *t, *ptr1, *ptr2; t = wcstok(str1, L"?", &ptr1); t = wcstok(NULL, L",", &ptr1); t = wcstok(str2, L" \t", &ptr2); t = wcstok(NULL, L"#,", &ptr1); t = wcstok(NULL, L"?", &ptr1);
// t points to the token L"a" // t points to the token L"??b" // t is a null pointer // t points to the token L"c" // t is a null pointer
7.31.4.6.8 The wmemchr generic function Synopsis #include <wchar.h> QWchar_t *wmemchr(QWchar_t *s, wchar_t c, size_t n);
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Description The wmemchr generic function locates the first occurrence of c in the initial n wide characters of the object pointed to by s. 440
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Returns The wmemchr generic function returns a pointer to the located wide character, or a null pointer if the wide character does not occur in the object. 7.31.4.7 Miscellaneous functions 7.31.4.7.1 The wcslen function Synopsis #include <wchar.h> size_t wcslen(const wchar_t *s);
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Description The wcslen function computes the length of the wide string pointed to by s. Returns The wcslen function returns the number of wide characters that precede the terminating null wide character. 7.31.4.7.2 The wmemset function Synopsis #include <wchar.h> wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
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Description The wmemset function copies the value of c into each of the first n wide characters of the object pointed to by s. Returns The wmemset function returns the value of s.
7.31.5
Wide character time conversion functions
7.31.5.1 The wcsftime function Synopsis 1
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#include <time.h> #include <wchar.h> size_t wcsftime(wchar_t * restrict s, size_t maxsize, const wchar_t * restrict format, const struct tm * restrict timeptr);
Description The wcsftime function is equivalent to the strftime function, except that: — The argument s points to the initial element of an array of wide characters into which the generated output is to be placed. — The argument maxsize indicates the limiting number of wide characters. — The argument format is a wide string and the conversion specifiers are replaced by corresponding sequences of wide characters. — The return value indicates the number of wide characters.
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Returns If the total number of resulting wide characters including the terminating null wide character is not more than maxsize, the wcsftime function returns the number of wide characters placed into the array pointed to by s not including the terminating null wide character. Otherwise, zero is returned and the members of the array have an indeterminate representation. § 7.31.5.1
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Extended multibyte/wide character conversion utilities
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The header <wchar.h> declares an extended set of functions useful for conversion between multibyte characters and wide characters.
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Most of the following functions — those that are listed as "restartable", 7.31.6.3 and 7.31.6.4 — take as a last argument a pointer to an object of type mbstate_t that is used to describe the current conversion state from a particular multibyte character sequence to a wide character sequence (or the reverse) under the rules of a particular setting for the LC_CTYPE category of the current locale.
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The initial conversion state corresponds, for a conversion in either direction, to the beginning of a new multibyte character in the initial shift state. A zero-valued mbstate_t object is (at least) one way to describe an initial conversion state. A zero-valued mbstate_t object can be used to initiate conversion involving any multibyte character sequence, in any LC_CTYPE category setting. If an mbstate_t object has been altered by any of the functions described in this subclause, and is then used with a different multibyte character sequence, or in the other conversion direction, or with a different LC_CTYPE category setting than on earlier function calls, the behavior is undefined.430)
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On entry, each function takes the described conversion state (either internal or pointed to by an argument) as current. The conversion state described by the referenced object is altered as needed to track the shift state, and the position within a multibyte character, for the associated multibyte character sequence. 7.31.6.1 Single-byte/wide character conversion functions 7.31.6.1.1 The btowc function Synopsis #include <wchar.h> wint_t btowc(int c);
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Description The btowc function determines whether c constitutes a valid single-byte character in the initial shift state. Returns The btowc function returns WEOF if c has the value EOF or if (unsigned char)c does not constitute a valid single-byte character in the initial shift state. Otherwise, it returns the wide character representation of that character. 7.31.6.1.2 The wctob function Synopsis #include <wchar.h> int wctob(wint_t c);
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Description The wctob function determines whether c corresponds to a member of the extended character set whose multibyte character representation is a single byte when in the initial shift state. Returns The wctob function returns EOF if c does not correspond to a multibyte character with length one in the initial shift state. Otherwise, it returns the single-byte representation of that character as an unsigned char converted to an int. 7.31.6.2 Conversion state functions 7.31.6.2.1 The mbsinit function Synopsis #include <wchar.h>
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430) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and mbsrtowcs functions as long as they are used to step sequentially through the same multibyte character string.
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int mbsinit(const mbstate_t *ps);
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Description If ps is not a null pointer, the mbsinit function determines whether the referenced mbstate_t object describes an initial conversion state.
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Returns The mbsinit function returns nonzero if ps is a null pointer or if the referenced object describes an initial conversion state; otherwise, it returns zero.
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7.31.6.3 Restartable multibyte/wide character conversion functions These functions differ from the corresponding multibyte character functions of 7.24.7 (mblen, mbtowc , and wctomb) in that they have an extra parameter, ps, of type pointer to mbstate_t that points to an object that can completely describe the current conversion state of the associated multibyte character sequence. If ps is a null pointer, each function uses its own internal mbstate_t object instead, which is initialized prior to the first call to the function to the initial conversion state; the functions are not required to avoid data races with other calls to the same function in this case. It is implementation-defined whether the internal mbstate_t object has thread storage duration; if it has thread storage duration, it is initialized to the initial conversion state prior to the first call to the function on the new thread. The implementation behaves as if no library function calls these functions with a null pointer for ps. Also unlike their corresponding functions, the return value does not represent whether the encoding is state-dependent. 7.31.6.3.1 The mbrlen function Synopsis
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#include <wchar.h> size_t mbrlen(const char * restrict s, size_t n, mbstate_t * restrict ps);
Description The mbrlen function is equivalent to the call: mbrtowc(NULL, s, n, ps != NULL ? ps: &internal)
where internal is the mbstate_t object for the mbrlen function, except that the expression designated by ps is evaluated only once.
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Returns The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2), or (size_t) (-1). Forward references: the mbrtowc function (7.31.6.3.2). 7.31.6.3.2 The mbrtowc function Synopsis
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#include <wchar.h> size_t mbrtowc(wchar_t * restrict pwc, const char * restrict s, size_t n, mbstate_t * restrict ps);
Description If s is a null pointer, the mbrtowc function is equivalent to the call: mbrtowc(NULL, "", 1, ps)
In this case, the values of the parameters pwc and n are ignored. § 7.31.6.3.2
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If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with the byte pointed to by s to determine the number of bytes needed to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character is complete and valid, it determines the value of the corresponding wide character and then, if pwc is not a null pointer, stores that value in the object pointed to by pwc. If the corresponding wide character is the null wide character, the resulting state described is the initial conversion state. Returns The mbrtowc function returns the first of the following that applies (given the current conversion state): 0
if the next n or fewer bytes complete the multibyte character that corresponds to the null wide character (which is the value stored).
between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte character (which is the value stored); the value returned is the number of bytes that complete the multibyte character. (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) multibyte character, and all n bytes have been processed (no value is stored).431) (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes do not contribute
to a complete and valid multibyte character (no value is stored); the value of the macro EILSEQ is stored in errno, and the conversion state is unspecified. 7.31.6.3.3 The wcrtomb function Synopsis #include <wchar.h> size_t wcrtomb(char * restrict s, wchar_t wc, mbstate_t * restrict ps);
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Description If s is a null pointer, the wcrtomb function is equivalent to the call wcrtomb(buf, L’\0’, ps)
where buf is an internal buffer. 3
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If s is not a null pointer, the wcrtomb function determines the number of bytes needed to represent the multibyte character that corresponds to the wide character given by wc (including any shift sequences), and stores the multibyte character representation in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If wc is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state; the resulting state described is the initial conversion state. Returns The wcrtomb function returns the number of bytes stored in the array object (including any shift sequences). When wc is not a valid wide character, an encoding error occurs: the function stores the value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion state is unspecified. 7.31.6.4 Restartable multibyte/wide string conversion functions These functions differ from the corresponding multibyte string functions of 7.24.8 (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to mbstate_t that points to an object that can completely describe the current conversion state of the associated multibyte character sequence. If ps is a null pointer, each function uses its own internal mbstate_t object 431) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a sequence of redundant shift sequences (for implementations with state-dependent encodings).
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instead, which is initialized prior to the first call to the function to the initial conversion state; the functions are not required to avoid data races with other calls to the same function in this case. It is implementation-defined whether the internal mbstate_t object has thread storage duration; if it has thread storage duration, it is initialized to the initial conversion state prior to the first call to the function on the new thread. The implementation behaves as if no library function calls these functions with a null pointer for ps. 2
Also unlike their corresponding functions, the conversion source parameter, src, has a pointer-topointer type. When the function is storing the results of conversions (that is, when dst is not a null pointer), the pointer object pointed to by this parameter is updated to reflect the amount of the source processed by that invocation. 7.31.6.4.1 The mbsrtowcs function Synopsis
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#include <wchar.h> size_t mbsrtowcs(wchar_t * restrict dst, const char ** restrict src, size_t len, mbstate_t * restrict ps);
Description The mbsrtowcs function converts a sequence of multibyte characters that begins in the conversion state described by the object pointed to by ps, from the array indirectly pointed to by src into a sequence of corresponding wide characters. If dst is not a null pointer, the converted characters are stored into the array pointed to by dst. Conversion continues up to and including a terminating null character, which is also stored. Conversion stops earlier in two cases: when a sequence of bytes is encountered that does not form a valid multibyte character, or (if dst is not a null pointer) when len wide characters have been stored into the array pointed to by dst.432) Each conversion takes place as if by a call to the mbrtowc function. If dst is not a null pointer, the pointer object pointed to by src is assigned either a null pointer (if conversion stopped due to reaching a terminating null character) or the address just past the last multibyte character converted (if any). If conversion stopped due to reaching a terminating null character and if dst is not a null pointer, the resulting state described is the initial conversion state. Returns If the input conversion encounters a sequence of bytes that do not form a valid multibyte character, an encoding error occurs: the mbsrtowcs function stores the value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion state is unspecified. Otherwise, it returns the number of multibyte characters successfully converted, not including the terminating null character (if any). 7.31.6.4.2 The wcsrtombs function Synopsis
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#include <wchar.h> size_t wcsrtombs(char * restrict dst, const wchar_t ** restrict src, size_t len, mbstate_t * restrict ps);
Description The wcsrtombs function converts a sequence of wide characters from the array indirectly pointed to by src into a sequence of corresponding multibyte characters that begins in the conversion state described by the object pointed to by ps. If dst is not a null pointer, the converted characters are then stored into the array pointed to by dst. Conversion continues up to and including a terminating null wide character, which is also stored. Conversion stops earlier in two cases: when a wide character is reached that does not correspond to a valid multibyte character, or (if dst is not a null pointer) when the next multibyte character would exceed the limit of len total bytes to be stored into the 432) Thus, the value of len is ignored if dst is a null pointer.
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array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb function.433) 3
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If dst is not a null pointer, the pointer object pointed to by src is assigned either a null pointer (if conversion stopped due to reaching a terminating null wide character) or the address just past the last wide character converted (if any). If conversion stopped due to reaching a terminating null wide character, the resulting state described is the initial conversion state. Returns If conversion stops because a wide character is reached that does not correspond to a valid multibyte character, an encoding error occurs: the wcsrtombs function stores the value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte character sequence, not including the terminating null character (if any).
433) If conversion stops because a terminating null wide character has been reached, the bytes stored include those necessary to reach the initial shift state immediately before the null byte.
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7.32 Wide character classification and mapping utilities <wctype.h> 7.32.1 Introduction 1
The header <wctype.h> defines one macro, and declares three data types and many functions.434)
2
The types declared are wint_t described in 7.31.1; wctrans_t
which is a scalar type that can hold values which represent locale-specific character mappings; and wctype_t
which is a scalar type that can hold values which represent locale-specific character classifications. 3
The macro defined is WEOF (described in 7.31.1).
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The functions declared are grouped as follows: — Functions that provide wide character classification; — Extensible functions that provide wide character classification; — Functions that provide wide character case mapping; — Extensible functions that provide wide character mapping.
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For all functions described in this subclause that accept an argument of type wint_t, the value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If this argument has any other value, the behavior is undefined.
6
The behavior of these functions is affected by the LC_CTYPE category of the current locale.
7.32.2
Wide character classification utilities
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The header <wctype.h> declares several functions useful for classifying wide characters.
2
The term printing wide character refers to a member of a locale-specific set of wide characters, each of which occupies at least one printing position on a display device. The term control wide character refers to a member of a locale-specific set of wide characters that are not printing wide characters.
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7.32.2.1 Wide character classification functions The functions in this subclause return nonzero (true) if and only if the value of the argument wc conforms to that in the description of the function. Each of the following functions returns true for each wide character that corresponds (as if by a call to the wctob function) to a single-byte character for which the corresponding character classification function from 7.4.1 returns true, except that the iswgraph and iswpunct functions may differ with respect to wide characters other than L’ ’ that are both printing and white-space wide characters.435) Forward references: the wctob function (7.31.6.1.2).
434) See "future library directions" (7.33.21). 435) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true (which cannot occur for wc == L’’ of course), then either iswgraph(wc) or iswprint(wc)&& iswspace(wc) is true, but not both.
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7.32.2.1.1 The iswalnum function Synopsis #include <wctype.h> int iswalnum(wint_t wc);
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Description The iswalnum function tests for any wide character for which iswalpha or iswdigit is true. 7.32.2.1.2 The iswalpha function Synopsis #include <wctype.h> int iswalpha(wint_t wc);
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Description The iswalpha function tests for any wide character for which iswupper or iswlower is true, or any wide character that is one of a locale-specific set of alphabetic wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace is true.436) 7.32.2.1.3 The iswblank function Synopsis #include <wctype.h> int iswblank(wint_t wc);
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Description The iswblank function tests for any wide character that is a standard blank wide character or is one of a locale-specific set of wide characters for which iswspace is true and that is used to separate words within a line of text. The standard blank wide characters are the following: space (L’ ’), and horizontal tab (L’\t’). In the "C" locale, iswblank returns true only for the standard blank characters. 7.32.2.1.4 The iswcntrl function Synopsis #include <wctype.h> int iswcntrl(wint_t wc);
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Description The iswcntrl function tests for any control wide character. 7.32.2.1.5 The iswdigit function Synopsis #include <wctype.h> int iswdigit(wint_t wc);
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Description The iswdigit function tests for any wide character that corresponds to a decimal-digit character (as defined in 5.2.1).
436) The functions iswlower and iswupper test true or false separately for each of these additional wide characters; all four combinations are possible.
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7.32.2.1.6 The iswgraph function Synopsis 1
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#include <wctype.h> int iswgraph(wint_t wc);
Description The iswgraph function tests for any wide character for which iswprint is true and iswspace is false.437) 7.32.2.1.7 The iswlower function Synopsis
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#include <wctype.h> int iswlower(wint_t wc);
Description The iswlower function tests for any wide character that corresponds to a lowercase letter or is one of a locale-specific set of wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace is true. 7.32.2.1.8 The iswprint function Synopsis
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#include <wctype.h> int iswprint(wint_t wc);
Description The iswprint function tests for any printing wide character. 7.32.2.1.9 The iswpunct function Synopsis
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#include <wctype.h> int iswpunct(wint_t wc);
Description The iswpunct function tests for any printing wide character that is one of a locale-specific set of punctuation wide characters for which neither iswspace nor iswalnum is true.437) 7.32.2.1.10 Synopsis
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#include <wctype.h> int iswspace(wint_t wc);
Description The iswspace function tests for any wide character that corresponds to a locale-specific set of white-space wide characters for which none of iswalnum, iswgraph, or iswpunct is true. 7.32.2.1.11 Synopsis
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The iswspace function
The iswupper function
#include <wctype.h> int iswupper(wint_t wc); 437) Note that the behavior of the iswgraph and iswpunct functions can differ from their corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution characters other than ’ ’.
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Description The iswupper function tests for any wide character that corresponds to an uppercase letter or is one of a locale-specific set of wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace is true. 7.32.2.1.12 Synopsis
The iswxdigit function
#include <wctype.h> int iswxdigit(wint_t wc);
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Description The iswxdigit function tests for any wide character that corresponds to a hexadecimal-digit character (as defined in 6.4.4.1).
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7.32.2.2 Extensible wide character classification functions The functions wctype and iswctype provide extensible wide character classification as well as testing equivalent to that performed by the functions described in the previous subclause (7.32.2.1). 7.32.2.2.1 The iswctype function Synopsis #include <wctype.h> int iswctype(wint_t wc, wctype_t desc);
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Description The iswctype function determines whether the wide character wc has the property described by desc. The current setting of the LC_CTYPE category shall be the same as during the call to wctype that returned the value desc. Each of the following expressions has a truth-value equivalent to the call to the wide character classification function (7.32.2.1) in the comment that follows the expression: iswctype(wc, wctype("alnum")) iswctype(wc, wctype("alpha")) iswctype(wc, wctype("blank")) iswctype(wc, wctype("cntrl")) iswctype(wc, wctype("digit")) iswctype(wc, wctype("graph")) iswctype(wc, wctype("lower")) iswctype(wc, wctype("print")) iswctype(wc, wctype("punct")) iswctype(wc, wctype("space")) iswctype(wc, wctype("upper")) iswctype(wc, wctype("xdigit"))
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// iswalnum(wc) // iswalpha(wc) // iswblank(wc) // iswcntrl(wc) // iswdigit(wc) // iswgraph(wc) // iswlower(wc) // iswprint(wc) // iswpunct(wc) // iswspace(wc) // iswupper(wc) // iswxdigit(wc)
Returns The iswctype function returns nonzero (true) if and only if the value of the wide character wc has the property described by desc. If desc is zero, the iswctype function returns zero (false). Forward references: the wctype function (7.32.2.2.2). 7.32.2.2.2 The wctype function Synopsis #include <wctype.h> wctype_t wctype(const char *property);
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Description The wctype function constructs a value with type wctype_t that describes a class of wide characters identified by the string argument property. The strings listed in the description of the iswctype function shall be valid in all locales as property arguments to the wctype function. Returns If property identifies a valid class of wide characters according to the LC_CTYPE category of the current locale, the wctype function returns a nonzero value that is valid as the second argument to the iswctype function; otherwise, it returns zero.
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Wide character case mapping utilities
The header <wctype.h> declares several functions useful for mapping wide characters. 7.32.3.1 Wide character case mapping functions 7.32.3.1.1 The towlower function Synopsis
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#include <wctype.h> wint_t towlower(wint_t wc);
Description The towlower function converts an uppercase letter to a corresponding lowercase letter. Returns If the argument is a wide character for which iswupper is true and there are one or more corresponding wide characters, as specified by the current locale, for which iswlower is true, the towlower function returns one of the corresponding wide characters (always the same one for any given locale); otherwise, the argument is returned unchanged. 7.32.3.1.2 The towupper function Synopsis
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#include <wctype.h> wint_t towupper(wint_t wc);
Description The towupper function converts a lowercase letter to a corresponding uppercase letter. Returns If the argument is a wide character for which iswlower is true and there are one or more corresponding wide characters, as specified by the current locale, for which iswupper is true, the towupper function returns one of the corresponding wide characters (always the same one for any given locale); otherwise, the argument is returned unchanged. 7.32.3.2 Extensible wide character case mapping functions The functions wctrans and towctrans provide extensible wide character mapping as well as case mapping equivalent to that performed by the functions described in the previous subclause (7.32.3.1). 7.32.3.2.1 The towctrans function Synopsis
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#include <wctype.h> wint_t towctrans(wint_t wc, wctrans_t desc);
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Description The towctrans function maps the wide character wc using the mapping described by desc. The current setting of the LC_CTYPE category shall be the same as during the call to wctrans that returned the value desc. Each of the following expressions behaves the same as the call to the wide character case mapping function (7.32.3.1) in the comment that follows the expression: towctrans(wc, wctrans("tolower")) towctrans(wc, wctrans("toupper"))
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Returns The towctrans function returns the mapped value of wc using the mapping described by desc. If desc is zero, the towctrans function returns the value of wc. 7.32.3.2.2 The wctrans function Synopsis #include <wctype.h> wctrans_t wctrans(const char *property);
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Description The wctrans function constructs a value with type wctrans_t that describes a mapping between wide characters identified by the string argument property. The strings listed in the description of the towctrans function shall be valid in all locales as property arguments to the wctrans function. Returns If property identifies a valid mapping of wide characters according to the LC_CTYPE category of the current locale, the wctrans function returns a nonzero value that is valid as the second argument to the towctrans function; otherwise, it returns zero.
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7.33 1
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Future library directions
Although grouped under individual headers, all the external names identified as reserved identifiers or potentially reserved identifiers in this subclause remain so regardless of which headers are included in the program.
7.33.1 1
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Complex arithmetic <complex.h>
The function names cacospi casinpi catanpi ccompoundn ccospi cerfc cerf
cexp10m1 cexp10 cexp2m1 cexp2 cexpm1 clgamma clog10p1
clog10 clog1p clog2p1 clog2 clogp1 cpown cpowr
crootn crsqrt csinpi ctanpi ctgamma
and the same names suffixed with f or l are potentially reserved identifiers and may be added to the declarations in the <complex.h> header.
7.33.2 1
Function names that begin with either is or to, and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <ctype.h> header.
7.33.3 1
Errors <errno.h>
Macros that begin with E and a digit or E and an uppercase letter may be added to the macros defined in the <errno.h> header by a future revision of this document or by an implementation.
7.33.4 1
Character handling <ctype.h>
Floating-point environment <fenv.h>
Macros that begin with FE_ and an uppercase letter may be added to the macros defined in the <fenv.h> header by a future revision of this document or by an implementation.
7.33.5
Characteristics of floating types <float.h>
1
Macros that begin with DBL_, DEC32_, DEC64_, DEC128_, DEC_, FLT_, or LDBL_ and an uppercase letter are potentially reserved identifiers and may be added to the macros defined in the <float.h> header.
2
Use of the DECIMAL_DIG macro is an obsolescent feature. A similar type-specific macro, such as LDBL_DECIMAL_DIG, can be used instead.
3
The use of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and LDBL_HAS_SUBNORM macros is an obsolescent feature.
7.33.6
Format conversion of integer types <inttypes.h>
1
Macros that begin with either PRI or SCN, and either a lowercase letter, B, or X are potentially reserved identifiers and may be added to the macros defined in the <inttypes.h> header.
2
Function names that begin with str, or wcs and a lowercase letter are potentially reserved identifiers may be added to the declarations in the <inttypes.h> header.
7.33.7 1
Macros that begin with LC_ and an uppercase letter may be added to the macros defined in the <locale.h> header by a future revision of this document or by an implementation.
7.33.8 1
Localization <locale.h>
Mathematics <math.h>
Macros that begin with FP_ and an uppercase letter may be added to the macros defined in the <math.h> header by a future revision of this document or by an implementation. § 7.33.8
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Macros that begin with MATH_ and an uppercase letter are potentially reserved identifiers and may be added to the macros in the <math.h> header.
3
Function names that begin with is and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <math.h> header.
4
Function names that begin with cr_ are potentially reserved identifiers and may be added to the <math.h> header. The cr_ prefix is intended to indicate a correctly rounded version of the function.
5
Use of the macros INFINITY, DEC_INFINITY, NAN, and DEC_NAN in <math.h> is an obsolescent feature. Instead, use the same macros in <float.h>.
7.33.9 1
Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase letter may be added to the macros defined in the <signal.h> header by a future revision of this document or by an implementation.
7.33.10 1
Checked Arithmetic Functions <stdckdint.h>
Type and function names that begin with ckd_ are potentially reserved identifiers and may be added to the declarations in the <stdckdint.h> header.
7.33.14 1
Bit and byte utilities <stdbit.h>
Type and function names that begin with stdc_ are potentially reserved identifiers and may be added to the declarations in the <stdbit.h> header.
7.33.13 1
Boolean type and values <stdbool.h>
The macro __bool_true_false_are_defined is an obsolescent feature.
7.33.12 1
Atomics <stdatomic.h>
Macros that begin with ATOMIC_ and an uppercase letter are potentially reserved identifiers and may be added to the macros defined in the <stdatomic.h> header. Typedef names that begin with either atomic_ or memory_, and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <stdatomic.h> header. Enumeration constants that begin with memory_order_ and a lowercase letter are potentially reserved identifiers and may be added to the definition of the memory_order type in the <stdatomic.h> header. Function names that begin with atomic_ and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <stdatomic.h> header.
7.33.11 1
Signal handling <signal.h>
Integer types <stdint.h>
Typedef names beginning with int or uint and ending with _t are potentially reserved identifiers and may be added to the types defined in the <stdint.h> header. Macro names beginning with INT or UINT and ending with _MAX, _MIN, _WIDTH, or _C are potentially reserved identifiers and may be added to the macros defined in the <stdint.h> header.
7.33.15
Input/output <stdio.h>
1
Lowercase letters may be added to the conversion specifiers and length modifiers in fprintf and fscanf. Other characters may be used in extensions. The specifier B for printf may become mandatory in future versions of this document.
2
The use of ungetc on a binary stream where the file position indicator is zero prior to the call is an obsolescent feature.
7.33.16
General utilities <stdlib.h>
1
Function names that begin with str or wcs and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <stdlib.h> header.
2
Suppressing the macro definition of bsearch to access the actual function is an obsolescent feature. 454
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String handling <string.h>
1
Function names that begin with str, mem, or wcs and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <string.h> header.
2
Suppressing the macro definitions of memchr, strchr, strpbrk, strrchr, or strstr to access the corresponding actual function is an obsolescent feature.
7.33.18
Date and time <time.h>
1
Macros beginning with TIME_ and an uppercase letter may be added to the macros in the <time.h> header by a future revision of this document or by an implementation.
2
The time bases TIME_MONOTONIC, TIME_ACTIVE and TIME_THREAD_ACTIVE may become mandatory in future versions of this standard.
7.33.19 1
Threads <threads.h>
Function names, type names, and enumeration constants that begin with either cnd_, mtx_, thrd_, or tss_, and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <threads.h> header.
7.33.20
Extended multibyte and wide character utilities <wchar.h>
1
Function names that begin with wcs and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <wchar.h> header.
2
Lowercase letters may be added to the conversion specifiers and length modifiers in fwprintf and fwscanf. Other characters may be used in extensions.
3
Suppressing the macro definitions of wcschr, wcspbrk, wcsrchr, wmemchr, or wcsstr to access the corresponding actual function is an obsolescent feature.
7.33.21 1
Wide character classification and mapping utilities <wctype.h>
Function names that begin with is or to and a lowercase letter are potentially reserved identifiers and may be added to the declarations in the <wctype.h> header.
§ 7.33.21
Library
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Annex A (informative)
Language syntax summary 1
NOTE 1 The notation is described in 6.1.
A.1 Lexical grammar A.1.1 Lexical elements (6.4) token: keyword identifier constant string-literal punctuator (6.4) preprocessing-token: header-name identifier pp-number character-constant string-literal punctuator each universal-character-name that cannot be one of the above each non-white-space character that cannot be one of the above
A.1.2
Keywords
(6.4.1) keyword: one of alignas alignof auto bool break case char const constexpr continue default do double else
A.1.3
enum extern false float for goto if inline int long nullptr register restrict return
short signed sizeof static static_assert struct switch thread_local true typedef typeof typeof_unqual union unsigned
void volatile while _Atomic _BitInt _Complex _Decimal128 _Decimal32 _Decimal64 _Generic _Imaginary _Noreturn
Identifiers
(6.4.2.1) identifier: identifier-start identifier identifier-continue (6.4.2.1) identifier-start: nondigit XID_Start character universal-character-name of class XID_Start (6.4.2.1) identifier-continue: digit nondigit XID_Continue character universal-character-name of class XID_Continue 456
Language syntax summary
§ A.1.3
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(6.4.2.1) nondigit: one of _ a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
(6.4.2.1) digit: one of 0 1 2 3 4 5 6 7 8 9
A.1.4
Universal character names
(6.4.3) universal-character-name: \u hex-quad \U hex-quad hex-quad (6.4.3) hex-quad: hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
A.1.5
Constants
(6.4.4) constant: integer-constant floating-constant enumeration-constant character-constant predefined-constant (6.4.4.1) integer-constant: decimal-constant integer-suffixopt octal-constant integer-suffixopt hexadecimal-constant integer-suffixopt binary-constant integer-suffixopt (6.4.4.1) decimal-constant: nonzero-digit decimal-constant ’opt digit (6.4.4.1) octal-constant: 0
octal-constant ’opt octal-digit (6.4.4.1) hexadecimal-constant: hexadecimal-prefix hexadecimal-digit-sequence (6.4.4.1) binary-constant: binary-prefix binary-digit binary-constant ’opt binary-digit (6.4.4.1) hexadecimal-prefix: one of 0x 0X
(6.4.4.1) binary-prefix: one of 0b 0B
(6.4.4.1) nonzero-digit: one of 1 2 3 4 5 6 7 8 9
(6.4.4.1) octal-digit: one of 0 1 2 3 4 5 6 7
hexadecimal-digit-sequence: hexadecimal-digit hexadecimal-digit-sequence ’opt hexadecimal-digit § A.1.5
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(6.4.4.1) hexadecimal-digit: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
(6.4.4.1) binary-digit: one of 0 1
(6.4.4.1) integer-suffix: unsigned-suffix long-suffixopt unsigned-suffix long-long-suffix unsigned-suffix bit-precise-int-suffix long-suffix unsigned-suffixopt long-long-suffix unsigned-suffixopt bit-precise-int-suffix unsigned-suffixopt (6.4.4.1) bit-precise-int-suffix: one of wb WB
(6.4.4.1) unsigned-suffix: one of u U
(6.4.4.1) long-suffix: one of l L
(6.4.4.1) long-long-suffix: one of ll LL
(6.4.4.2) floating-constant: decimal-floating-constant hexadecimal-floating-constant (6.4.4.2) decimal-floating-constant: fractional-constant exponent-partopt floating-suffixopt digit-sequence exponent-part floating-suffixopt (6.4.4.2) hexadecimal-floating-constant: hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-part floating-suffixopt hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-suffixopt (6.4.4.2) fractional-constant: digit-sequenceopt . digit-sequence digit-sequence . (6.4.4.2) exponent-part: e signopt digit-sequence E signopt digit-sequence (6.4.4.2) sign: one of + -
(6.4.4.2) digit-sequence: digit digit-sequence ’opt digit (6.4.4.2) hexadecimal-fractional-constant: hexadecimal-digit-sequenceopt . hexadecimal-digit-sequence hexadecimal-digit-sequence . (6.4.4.2) binary-exponent-part: p signopt digit-sequence P signopt digit-sequence 458
Language syntax summary
§ A.1.5
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(6.4.4.2) floating-suffix: one of f l F L df dd dl DF DD DL
(6.4.4.3) enumeration-constant: identifier (6.4.4.4) character-constant: encoding-prefixopt ’ c-char-sequence ’ (6.4.4.4) encoding-prefix: one of u8
u
U
L
(6.4.4.4) c-char-sequence: c-char c-char-sequence c-char (6.4.4.4) c-char: any member of the source character set except the single-quote ’, backslash \, or new-line character escape-sequence (6.4.4.4) escape-sequence: simple-escape-sequence octal-escape-sequence hexadecimal-escape-sequence universal-character-name (6.4.4.4) simple-escape-sequence: one of \’ \" \? \\ \a \b \f \n \r \t \v
(6.4.4.4) octal-escape-sequence: \ octal-digit \ octal-digit octal-digit \ octal-digit octal-digit octal-digit (6.4.4.4) hexadecimal-escape-sequence: \x hexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit (6.4.4.5) predefined-constant: false true nullptr
A.1.6
String literals
(6.4.5) string-literal: encoding-prefixopt " s-char-sequenceopt " (6.4.5) s-char-sequence: s-char s-char-sequence s-char (6.4.5) s-char: any member of the source character set except the double-quote ", backslash \, or new-line character escape-sequence § A.1.6
Language syntax summary
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A.1.7
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Punctuators
(6.4.6) punctuator: one of [ ] ( ) { } . -> ++ -- & * + - ~ ! / % << >> < > <= >= ? : :: ; ... = *= /= %= += -= <<= , # ## <: :> <% %> %: %:%:
A.1.8
==
!=
>>=
&=
^
|
&&
^=
|=
||
Header names
(6.4.7) header-name: < h-char-sequence > " q-char-sequence "
(6.4.7) h-char-sequence: h-char h-char-sequence h-char (6.4.7) h-char: any member of the source character set except the new-line character and > (6.4.7) q-char-sequence: q-char q-char-sequence q-char (6.4.7) q-char: any member of the source character set except the new-line character and "
A.1.9
Preprocessing numbers
(6.4.8) pp-number: digit . digit pp-number identifier-continue pp-number ’ digit pp-number ’ nondigit pp-number e sign pp-number E sign pp-number p sign pp-number P sign pp-number .
A.2 Phrase structure grammar A.2.1 Expressions (6.5.1) primary-expression: identifier constant string-literal ( expression ) generic-selection (6.5.1.1) generic-selection: _Generic ( assignment-expression , generic-assoc-list )
(6.5.1.1) generic-assoc-list: generic-association generic-assoc-list , generic-association 460
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(6.5.1.1) generic-association: type-name : assignment-expression default : assignment-expression (6.5.2) postfix-expression: primary-expression postfix-expression [ expression ] postfix-expression ( argument-expression-listopt ) postfix-expression . identifier postfix-expression -> identifier postfix-expression ++ postfix-expression -compound-literal (6.5.2) argument-expression-list: assignment-expression argument-expression-list , assignment-expression (6.5.2.5) (6.5.2.5)
compound-literal: ( storage-class-specifiersopt type-name ) braced-initializer storage-class-specifiers: storage-class-specifier storage-class-specifiers storage-class-specifier
(6.5.3) unary-expression: postfix-expression ++ unary-expression -- unary-expression unary-operator cast-expression sizeof unary-expression sizeof ( type-name ) alignof ( type-name ) (6.5.3) unary-operator: one of &
*
+
-
~
!
(6.5.4) cast-expression: unary-expression ( type-name ) cast-expression (6.5.5) multiplicative-expression: cast-expression multiplicative-expression * cast-expression multiplicative-expression / cast-expression multiplicative-expression % cast-expression (6.5.6) additive-expression: multiplicative-expression additive-expression + multiplicative-expression additive-expression - multiplicative-expression (6.5.7) shift-expression: additive-expression shift-expression << additive-expression shift-expression >> additive-expression (6.5.8) relational-expression: shift-expression relational-expression < shift-expression relational-expression > shift-expression relational-expression <= shift-expression relational-expression >= shift-expression § A.2.1
Language syntax summary
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(6.5.9) equality-expression: relational-expression equality-expression == relational-expression equality-expression != relational-expression (6.5.10) AND-expression: equality-expression AND-expression & equality-expression (6.5.11) exclusive-OR-expression: AND-expression exclusive-OR-expression ^ AND-expression (6.5.12) inclusive-OR-expression: exclusive-OR-expression inclusive-OR-expression | exclusive-OR-expression (6.5.13) logical-AND-expression: inclusive-OR-expression logical-AND-expression && inclusive-OR-expression (6.5.14) logical-OR-expression: logical-AND-expression logical-OR-expression || logical-AND-expression (6.5.15) conditional-expression: logical-OR-expression logical-OR-expression ? expression : conditional-expression (6.5.16) assignment-expression: conditional-expression unary-expression assignment-operator assignment-expression (6.5.16) assignment-operator: one of =
*=
/=
%=
+=
-=
<<=
>>=
&=
^=
|=
(6.5.17) expression: assignment-expression expression , assignment-expression (6.6) constant-expression: conditional-expression
A.2.2
Declarations
(6.7) declaration: declaration-specifiers init-declarator-listopt ; attribute-specifier-sequence declaration-specifiers init-declarator-list ; static_assert-declaration attribute-declaration (6.7) declaration-specifiers: declaration-specifier attribute-specifier-sequenceopt declaration-specifier declaration-specifiers (6.7) declaration-specifier: storage-class-specifier type-specifier-qualifier function-specifier (6.7) init-declarator-list: init-declarator init-declarator-list , init-declarator 462
Language syntax summary
§ A.2.2
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(6.7) init-declarator: declarator declarator = initializer (6.7) attribute-declaration: attribute-specifier-sequence ; (6.7.1) storage-class-specifier: auto constexpr extern register static thread_local typedef
(6.7.2) type-specifier: void char short int long float double signed unsigned _BitInt ( constant-expression ) bool _Complex _Decimal32 _Decimal64 _Decimal128
atomic-type-specifier struct-or-union-specifier enum-specifier typedef-name typeof-specifier (6.7.2.1) struct-or-union-specifier: struct-or-union attribute-specifier-sequenceopt identifieropt { member-declaration-list } struct-or-union attribute-specifier-sequenceopt identifier (6.7.2.1) struct-or-union: struct union
(6.7.2.1) member-declaration-list: member-declaration member-declaration-list member-declaration (6.7.2.1) member-declaration: attribute-specifier-sequenceopt specifier-qualifier-list member-declarator-listopt ; static_assert-declaration (6.7.2.1) specifier-qualifier-list: type-specifier-qualifier attribute-specifier-sequenceopt type-specifier-qualifier specifier-qualifier-list (6.7.2.1) type-specifier-qualifier: type-specifier type-qualifier alignment-specifier § A.2.2
Language syntax summary
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(6.7.2.1) member-declarator-list: member-declarator member-declarator-list , member-declarator (6.7.2.1) member-declarator: declarator declaratoropt : constant-expression (6.7.2.2) enum-specifier: enum attribute-specifier-sequenceopt identifieropt enum-type-specifieropt { enumerator-list } enum attribute-specifier-sequenceopt identifieropt enum-type-specifieropt { enumerator-list , } enum identifier enum-type-specifieropt
(6.7.2.2) enumerator-list: enumerator enumerator-list , enumerator (6.7.2.2) enumerator: enumeration-constant attribute-specifier-sequenceopt enumeration-constant attribute-specifier-sequenceopt = constant-expression (6.7.2.2) enum-type-specifier: : specifier-qualifier-list (6.7.2.4) atomic-type-specifier: _Atomic ( type-name )
(6.7.2.5) typeof-specifier: typeof ( typeof-specifier-argument ) typeof_unqual ( typeof-specifier-argument )
(6.7.2.5) typeof-specifier-argument: expression type-name (6.7.3) type-qualifier: const restrict volatile _Atomic
(6.7.4) function-specifier: inline _Noreturn
(6.7.5) alignment-specifier: alignas ( type-name ) alignas ( constant-expression )
(6.7.6) declarator: pointeropt direct-declarator (6.7.6) direct-declarator: identifier attribute-specifier-sequenceopt ( declarator ) array-declarator attribute-specifier-sequenceopt function-declarator attribute-specifier-sequenceopt (6.7.6) array-declarator: direct-declarator [ type-qualifier-listopt assignment-expressionopt ] direct-declarator [ static type-qualifier-listopt assignment-expression ] direct-declarator [ type-qualifier-list static assignment-expression ] direct-declarator [ type-qualifier-listopt * ] 464
Language syntax summary
§ A.2.2
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(6.7.6) function-declarator: direct-declarator ( parameter-type-listopt ) (6.7.6) pointer: * attribute-specifier-sequenceopt type-qualifier-listopt * attribute-specifier-sequenceopt type-qualifier-listopt pointer
(6.7.6) type-qualifier-list: type-qualifier type-qualifier-list type-qualifier (6.7.6) parameter-type-list: parameter-list parameter-list , ... ...
(6.7.6) parameter-list: parameter-declaration parameter-list , parameter-declaration (6.7.6) parameter-declaration: attribute-specifier-sequenceopt declaration-specifiers declarator attribute-specifier-sequenceopt declaration-specifiers abstract-declaratoropt (6.7.7) type-name: specifier-qualifier-list abstract-declaratoropt (6.7.7) abstract-declarator: pointer pointeropt direct-abstract-declarator (6.7.7) direct-abstract-declarator: ( abstract-declarator ) array-abstract-declarator attribute-specifier-sequenceopt function-abstract-declarator attribute-specifier-sequenceopt (6.7.7) array-abstract-declarator: direct-abstract-declaratoropt [ type-qualifier-listopt assignment-expressionopt ] direct-abstract-declaratoropt [ static type-qualifier-listopt assignment-expression ] direct-abstract-declaratoropt [ type-qualifier-list static assignment-expression ] direct-abstract-declaratoropt [ * ] (6.7.7) function-abstract-declarator: direct-abstract-declaratoropt ( parameter-type-listopt ) (6.7.8) typedef-name: identifier (6.7.10) braced-initializer: { } { initializer-list } { initializer-list , }
(6.7.10) initializer: assignment-expression braced-initializer (6.7.10) initializer-list: designationopt initializer initializer-list , designationopt initializer (6.7.10) designation: designator-list = (6.7.10) designator-list: designator designator-list designator § A.2.2
Language syntax summary
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(6.7.10) designator: [ constant-expression ] . identifier
(6.7.11) static_assert-declaration: static_assert ( constant-expression , string-literal ) ; static_assert ( constant-expression ) ;
(6.7.12.1) attribute-specifier-sequence: attribute-specifier-sequenceopt attribute-specifier (6.7.12.1) attribute-specifier: [ [ attribute-list ] ] (6.7.12.1) attribute-list: attributeopt attribute-list , attributeopt (6.7.12.1) attribute: attribute-token attribute-argument-clauseopt (6.7.12.1) attribute-token: standard-attribute attribute-prefixed-token (6.7.12.1) standard-attribute: identifier (6.7.12.1) attribute-prefixed-token: attribute-prefix :: identifier (6.7.12.1) attribute-prefix: identifier (6.7.12.1) attribute-argument-clause: ( balanced-token-sequenceopt ) (6.7.12.1) balanced-token-sequence: balanced-token balanced-token-sequence balanced-token (6.7.12.1) balanced-token: ( balanced-token-sequenceopt ) [ balanced-token-sequenceopt ] { balanced-token-sequenceopt } any token other than a parenthesis, a bracket, or a brace
A.2.3
Statements
(6.8) statement: labeled-statement unlabeled-statement (6.8) unlabeled-statement: expression-statement attribute-specifier-sequenceopt primary-block attribute-specifier-sequenceopt jump-statement (6.8) primary-block: compound-statement selection-statement iteration-statement (6.8) secondary-block: statement 466
Language syntax summary
§ A.2.3
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(6.8.1) label: attribute-specifier-sequenceopt identifier : attribute-specifier-sequenceopt case constant-expression : attribute-specifier-sequenceopt default : (6.8.1) labeled-statement: label statement (6.8.2) compound-statement: { block-item-listopt } (6.8.2) block-item-list: block-item block-item-list block-item (6.8.2) block-item: declaration unlabeled-statement label (6.8.3) expression-statement: expressionopt ; attribute-specifier-sequence expression ; [-6ex] (6.8.4) selection-statement: if ( expression ) secondary-block if ( expression ) secondary-block else secondary-block switch ( expression ) secondary-block [-6ex] (6.8.5) iteration-statement: while ( expression ) secondary-block do secondary-block while ( expression ) ; for ( expressionopt ; expressionopt ; expressionopt ) secondary-block for ( declaration expressionopt ; expressionopt ) secondary-block
[-6ex] (6.8.6) jump-statement: goto identifier ; continue ; break ; return expressionopt ;
[-6ex]
A.2.4
External definitions
(6.9) translation-unit: external-declaration translation-unit external-declaration (6.9) external-declaration: function-definition declaration (6.9.1) function-definition: attribute-specifier-sequenceopt declaration-specifiers declarator function-body (6.9.1) function-body: compound-statement
A.3
Preprocessing directives
(6.10) preprocessing-file: groupopt § A.3
Language syntax summary
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(6.10) group: group-part group group-part (6.10) group-part: if-section control-line text-line # non-directive (6.10) if-section: if-group elif-groupsopt else-groupopt endif-line (6.10) if-group: # if constant-expression new-line groupopt # ifdef identifier new-line groupopt # ifndef identifier new-line groupopt
(6.10) elif-groups: elif-group elif-groups elif-group (6.10) elif-group: # elif constant-expression new-line groupopt # elifdef identifier new-line groupopt # elifndef identifier new-line groupopt
(6.10) else-group: # else new-line groupopt
(6.10) endif-line: # endif new-line
(6.10) control-line: # include pp-tokens new-line # embed pp-tokens new-line # define identifier replacement-list new-line # define identifier lparen identifier-listopt ) replacement-list new-line # define identifier lparen ... ) replacement-list new-line # define identifier lparen identifier-list , ... ) replacement-list new-line # undef identifier new-line # line pp-tokens new-line # error pp-tokensopt new-line # warning pp-tokensopt new-line # pragma pp-tokensopt new-line # new-line
(6.10) text-line: pp-tokensopt new-line (6.10) non-directive: pp-tokens new-line (6.10) lparen: a ( character not immediately preceded by white space (6.10) replacement-list: pp-tokensopt (6.10) pp-tokens: preprocessing-token pp-tokens preprocessing-token (6.10) new-line: the new-line character 468
Language syntax summary
§ A.3
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(6.10) identifier-list: identifier identifier-list , identifier (6.10) pp-parameter: pp-parameter-name pp-parameter-clauseopt (6.10) pp-parameter-name: pp-standard-parameter pp-prefixed-parameter (6.10) pp-standard-parameter: identifier (6.10) pp-prefixed-parameter: identifier :: identifier (6.10) pp-parameter-clause: ( pp-balanced-token-sequenceopt ) (6.10) pp-balanced-token-sequence: pp-balanced-token pp-balanced-token-sequence pp-balanced-token (6.10) pp-balanced-token: ( pp-balanced-token-sequenceopt ) [ pp-balanced-token-sequenceopt ] { pp-balanced-token-sequenceopt } any pp-token other than a parenthesis, a bracket, or a brace (6.10) embed-parameter-sequence: pp-parameter embed-parameter-sequence pp-parameter defined-macro-expression: defined identifier defined ( identifier )
h-preprocessing-token: any preprocessing-token other than > h-pp-tokens: h-preprocessing-token h-pp-tokens h-preprocessing-token header-name-tokens: string-literal < h-pp-tokens > has-include-expression: __has_include ( header-name ) __has_include ( header-name-tokens ) has-embed-expression: __has_embed ( header-name embed-parameter-sequenceopt ) __has_embed ( header-name-tokens pp-balanced-token-sequenceopt ) has-c-attribute-express: __has_c_attribute ( pp-tokens ) va-opt-replacement: __VA_OPT__ ( pp-tokensopt )
(6.10.7) standard-pragma: # pragma STDC FP_CONTRACT on-off-switch # pragma STDC FENV_ACCESS on-off-switch # pragma STDC FENV_DEC_ROUND dec-direction # pragma STDC FENV_ROUND direction # pragma STDC CX_LIMITED_RANGE on-off-switch
§ A.3
Language syntax summary
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(6.10.7) on-off-switch: one of ON
OFF
DEFAULT
(6.10.7) direction: one of FE_DOWNWARD FE_TOWARDZERO
FE_TONEAREST FE_UPWARD
FE_TONEARESTFROMZERO FE_DYNAMIC
(6.10.7) dec-direction: one of FE_DEC_DOWNWARD FE_DEC_TOWARDZERO
FE_DEC_TONEAREST FE_DEC_UPWARD
FE_DEC_TONEARESTFROMZERO FE_DEC_DYNAMIC
A.4 Floating-point subject sequence A.4.1 NaN char sequence (7.24.1.5)
A.4.2
n-char-sequence: digit nondigit n-char-sequence digit n-char-sequence nondigit
NaN wchar_t sequence
(7.31.4.1.2) n-wchar-sequence: digit nondigit n-wchar-sequence digit n-wchar-sequence nondigit
A.5 Decimal floating-point subject sequence A.5.1 NaN decimal char sequence (7.24.1.6) d-char-sequence: digit nondigit d-char-sequence digit d-char-sequence nondigit
A.5.2
NaN decimal wchar_t sequence
(7.31.4.1.3) d-wchar-sequence: digit nondigit d-wchar-sequence digit d-wchar-sequence nondigit
470
Language syntax summary
§ A.5.2
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Annex B (informative)
Library summary B.1
Diagnostics <assert.h>
__STDC_VERSION_ASSERT_H__ NDEBUG
void assert(scalar expression);
B.2
Complex <complex.h>
__STDC_NO_COMPLEX__ __STDC_VERSION_COMPLEX_H__ complex _Complex_I
imaginary _Imaginary_I I
#pragma STDC CX_LIMITED_RANGE on-off-switch double complex cacos(double complex z); float complex cacosf(float complex z); long double complex cacosl(long double complex z); double complex casin(double complex z); float complex casinf(float complex z); long double complex casinl(long double complex z); double complex catan(double complex z); float complex catanf(float complex z); long double complex catanl(long double complex z); double complex ccos(double complex z); float complex ccosf(float complex z); long double complex ccosl(long double complex z); double complex csin(double complex z); float complex csinf(float complex z); long double complex csinl(long double complex z); double complex ctan(double complex z); float complex ctanf(float complex z); long double complex ctanl(long double complex z); double complex cacosh(double complex z); float complex cacoshf(float complex z); long double complex cacoshl(long double complex z); double complex casinh(double complex z); float complex casinhf(float complex z); long double complex casinhl(long double complex z); double complex catanh(double complex z); float complex catanhf(float complex z); long double complex catanhl(long double complex z); double complex ccosh(double complex z); float complex ccoshf(float complex z); long double complex ccoshl(long double complex z); double complex csinh(double complex z); float complex csinhf(float complex z); long double complex csinhl(long double complex z); double complex ctanh(double complex z); float complex ctanhf(float complex z); long double complex ctanhl(long double complex z); double complex cexp(double complex z); float complex cexpf(float complex z); long double complex cexpl(long double complex z); double complex clog(double complex z); float complex clogf(float complex z);
§ B.2
Library summary
471
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
N3096
long double complex clogl(long double complex z); double cabs(double complex z); float cabsf(float complex z); long double cabsl(long double complex z); double complex cpow(double complex x, double complex y); float complex cpowf(float complex x, float complex y); long double complex cpowl(long double complex x, long double complex y); double complex csqrt(double complex z); float complex csqrtf(float complex z); long double complex csqrtl(long double complex z); double carg(double complex z); float cargf(float complex z); long double cargl(long double complex z); double cimag(double complex z); float cimagf(float complex z); long double cimagl(long double complex z); double complex CMPLX(double x, double y); float complex CMPLXF(float x, float y); long double complex CMPLXL(long double x, long double y); double complex conj(double complex z); float complex conjf(float complex z); long double complex conjl(long double complex z); double complex cproj(double complex z); float complex cprojf(float complex z); long double complex cprojl(long double complex z); double creal(double complex z); float crealf(float complex z); long double creall(long double complex z);
B.3
Character handling <ctype.h>
int isalnum(int c); int isalpha(int c); int isblank(int c); int iscntrl(int c); int isdigit(int c); int isgraph(int c); int islower(int c); int isprint(int c); int ispunct(int c); int isspace(int c); int isupper(int c); int isxdigit(int c); int tolower(int c); int toupper(int c);
B.4
Errors <errno.h>
EDOM
EILSEQ
ERANGE
errno
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <errno.h>: errno_t
B.5
472
Floating-point environment <fenv.h>
Library summary
§ B.5
N3096
working draft — April 1, 2023
fenv_t fexcept_t femode_t FE_DFL_MODE FE_DIVBYZERO FE_INEXACT
FE_INVALID FE_OVERFLOW FE_UNDERFLOW FE_ALL_EXCEPT FE_DOWNWARD FE_TONEAREST
ISO/IEC 9899:2023 (E)
FE_TONEARESTFROMZERO FE_TOWARDZERO FE_UPWARD FE_DFL_ENV
#pragma STDC FENV_ACCESS on-off-switch #pragma STDC FENV_ROUND direction #pragma STDC FENV_ROUND FE_DYNAMIC int feclearexcept(int excepts); int fegetexceptflag(fexcept_t *flagp, int excepts); int feraiseexcept(int excepts); int fesetexcept(int excepts); int fesetexceptflag(const fexcept_t *flagp, int excepts); int fetestexceptflag(const fexcept_t * flagp, int excepts); int fetestexcept(int excepts); int fegetmode(femode_t *modep); int fegetround(void); int fesetmode(const femode_t *modep); int fesetround(int rnd); int fegetenv(fenv_t *envp); int feholdexcept(fenv_t *envp); int fesetenv(const fenv_t *envp); int feupdateenv(const fenv_t *envp);
Only if the implementation defines __STDC_IEC_60559_DFP__: FE_DEC_DOWNWARD FE_DEC_TONEAREST
FE_DEC_TONEARESTFROMZERO FE_DEC_TOWARDZERO
FE_DEC_UPWARD
#pragma STDC FENV_DEC_ROUND dec-direction int fe_dec_getround(void); int fe_dec_setround(int rnd);
B.6
Characteristics of floating types <float.h>
__STDC_VERSION_FLOAT_H__ FLT_ROUNDS FLT_EVAL_METHOD FLT_HAS_SUBNORM DBL_HAS_SUBNORM LDBL_HAS_SUBNORM FLT_RADIX FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG FLT_DECIMAL_DIG DBL_DECIMAL_DIG LDBL_DECIMAL_DIG DECIMAL_DIG FLT_IS_IEC_60559 DBL_IS_IEC_60559 LDBL_IS_IEC_60559 FLT_DIG
§ B.6
DBL_DIG LDBL_DIG FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP FLT_MIN_10_EXP DBL_MIN_10_EXP LDBL_MIN_10_EXP FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP FLT_MAX_10_EXP DBL_MAX_10_EXP LDBL_MAX_10_EXP FLT_MAX DBL_MAX LDBL_MAX FLT_NORM_MAX
Library summary
DBL_NORM_MAX LDBL_NORM_MAX FLT_EPSILON DBL_EPSILON LDBL_EPSILON FLT_MIN DBL_MIN LDBL_MIN FLT_SNAN DBL_SNAN LDBL_SNAN FLT_TRUE_MIN DBL_TRUE_MIN LDBL_TRUE_MIN INFINITY NAN
473
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
N3096
The following macro is provided only if the program defines __STDC_WANT_IEC_60559_EXT__ before inclusion of the header <float.h>: CR_DECIMAL_DIG
B.6.1 1
Characteristics of decimal floating types
The following macros are provided only if the implementation defines __STDC_IEC_60559_DFP__. N is 32, 64 and 128. DEC_INFINITY DEC_NAN DECN_EPSILON
B.7
DECN_MANT_DIG DECN_MAX_EXP DECN_MAX
DECN_MIN_EXP DECN_MIN DECN_TRUE_MIN
DECN_SNAN
Format conversion of integer types <inttypes.h>
imaxdiv_t PRIdN PRIiN PRIoN PRIuN PRIxN PRIXN SCNdN SCNiN SCNoN SCNuN SCNxN
PRIdLEASTN PRIiLEASTN PRIoLEASTN PRIuLEASTN PRIxLEASTN PRIXLEASTN SCNdLEASTN SCNiLEASTN SCNoLEASTN SCNuLEASTN SCNxLEASTN
PRIdFASTN PRIiFASTN PRIoFASTN PRIuFASTN PRIxFASTN PRIXFASTN SCNdFASTN SCNiFASTN SCNoFASTN SCNuFASTN SCNxFASTN
PRIdMAX PRIiMAX PRIoMAX PRIuMAX PRIxMAX PRIXMAX SCNdMAX SCNiMAX SCNoMAX SCNuMAX SCNxMAX
PRIdPTR PRIiPTR PRIoPTR PRIuPTR PRIxPTR PRIXPTR SCNdPTR SCNiPTR SCNoPTR SCNuPTR SCNxPTR
intmax_t imaxabs(intmax_t j); imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); intmax_t strtoimax(const char * restrict nptr, char ** restrict endptr, int base); uintmax_t strtoumax(const char * restrict nptr, char ** restrict endptr, int base); intmax_t wcstoimax(const wchar_t *restrict nptr, wchar_t **restrict endptr, int base); uintmax_t wcstoumax(const wchar_t *restrict nptr, wchar_t **restrict endptr, int base);
B.8
Alternative spellings <iso646.h>
and and_eq bitand
B.9
bitor compl not
474
xor xor_eq
SCHAR_MAX UCHAR_MAX CHAR_MIN CHAR_MAX MB_LEN_MAX SHRT_MIN SHRT_MAX USHRT_MAX INT_MIN
INT_MAX UINT_MAX LONG_MIN LONG_MAX ULONG_MAX LLONG_MIN LLONG_MAX ULLONG_MAX
Sizes of integer types <limits.h>
__STDC_VERSION_LIMITS_H__ _ USHRT WIDTH INT_WIDTH BINTINT_MAXWIDTH UINT_WIDTH BOOL_WIDTH LONG_WIDTH CHAR_BIT ULONG_WIDTH CHAR_WIDTH LLONG_WIDTH SCHAR_WIDTH ULLONG_WIDTH UCHAR_WIDTH BOOL_MAX SHRT_WIDTH SCHAR_MIN
B.10
not_eq or or_eq
Localization <locale.h> Library summary
§ B.10
N3096
working draft — April 1, 2023
struct lconv NULL
LC_ALL LC_COLLATE
LC_CTYPE LC_MONETARY
ISO/IEC 9899:2023 (E)
LC_NUMERIC LC_TIME
char *setlocale(int category, const char *locale); struct lconv *localeconv(void);
B.11
Mathematics <math.h>
__STDC_VERSION_MATH_H__ float_t double_t HUGE_VAL HUGE_VALF HUGE_VALL INFINITY
NAN FP_INFINITE FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO FP_FAST_FMA
FP_FAST_FMAF FP_FAST_FMAL FP_ILOGB0 FP_ILOGBNAN MATH_ERRNO MATH_ERREXCEPT math_errhandling
#pragma STDC FP_CONTRACT on-off-switch int fpclassify(real-floating x); int iscanonical(real-floating x); int isfinite(real-floating x); int isinf(real-floating x); int isnan(real-floating x); int isnormal(real-floating x); int signbit(real-floating x); int issignaling(real-floating x); int issubnormal(real-floating x); int iszero(real-floating x); double acos(double x); float acosf(float x); long double acosl(long double x); double asin(double x); float asinf(float x); long double asinl(long double x); double atan(double x); float atanf(float x); long double atanl(long double x); double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x); double cos(double x); float cosf(float x); long double cosl(long double x); double sin(double x); float sinf(float x); long double sinl(long double x); double tan(double x); float tanf(float x); long double tanl(long double x); double acospi(double x); float acospif(float x); long double acospil(long double x); double asinpi(double x); float asinpif(float x); long double asinpil(long double x); double atanpi(double x); float atanpif(float x); long double atanpil(long double x); double atan2pi(double y, double x);
§ B.11
Library summary
475
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
float atan2pif(float y, float x); long double atan2pil(long double y, long double x); double cospi(double x); float cospif(float x); long double cospil(long double x); double sinpi(double x); float sinpif(float x); long double sinpil(long double x); double tanpi(double x); float tanpif(float x); long double tanpil(long double x); double acosh(double x); float acoshf(float x); long double acoshl(long double x); double asinh(double x); float asinhf(float x); long double asinhl(long double x); double atanh(double x); float atanhf(float x); long double atanhl(long double x); double cosh(double x); float coshf(float x); long double coshl(long double x); double sinh(double x); float sinhf(float x); long double sinhl(long double x); double tanh(double x); float tanhf(float x); long double tanhl(long double x); double exp(double x); float expf(float x); long double expl(long double x); double exp10(double x); float exp10f(float x); long double exp10l(long double x); double exp10m1(double x); float exp10m1f(float x); long double exp10m1l(long double x); double exp2(double x); float exp2f(float x); long double exp2l(long double x); double exp2m1(double x); float exp2m1f(float x); long double exp2m1l(long double x); double expm1(double x); float expm1f(float x); long double expm1l(long double x); double frexp(double value, int *p); float frexpf(float value, int *p); long double frexpl(long double value, int *p); int ilogb(double x); int ilogbf(float x); int ilogbl(long double x); double ldexp(double x, int p); float ldexpf(float x, int p); long double ldexpl(long double x, int p); long int llogb(double x); long int llogbf(float x); long int llogbl(long double x); double log(double x); float logf(float x);
476
Library summary
§ B.11
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
long double logl(long double x); double log10(double x); float log10f(float x); long double log10l(long double x); double log10p1(double x); float log10p1f(float x); long double log10p1l(long double x); double log1p(double x); float log1pf(float x); long double log1pl(long double x); double logp1(double x); float logp1f(float x); long double logp1l(long double x); double log2(double x); float log2f(float x); long double log2l(long double x); double log2p1(double x); float log2p1f(float x); long double log2p1l(long double x); double logb(double x); float logbf(float x); long double logbl(long double x); double modf(double value, double *iptr); float modff(float value, float *iptr); long double modfl(long double value, long double *iptr); double scalbn(double x, int n); float scalbnf(float x, int n); long double scalbnl(long double x, int n); double scalbln(double x, long int n); float scalblnf(float x, long int n); long double scalblnl(long double x, long int n); double cbrt(double x); float cbrtf(float x); long double cbrtl(long double x); double compoundn(double x, long long int n); float compoundnf(float x, long long int n); long double compoundnl(long double x, long long int n); double fabs(double x); float fabsf(float x); long double fabsl(long double x); double hypot(double x, double y); float hypotf(float x, float y); long double hypotl(long double x, long double y); double pow(double x, double y); float powf(float x, float y); long double powl(long double x, long double y); double pown(double x, long long int n); float pownf(float x, long long int n); long double pownl(long double x, long long int n); double powr(double y, double x); float powrf(float y, float x); long double powrl(long double y, long double x); double rootn(double x, long long int n); float rootnf(float x, long long int n); long double rootnl(long double x, long long int n); double rsqrt(double x); float rsqrtf(float x); long double rsqrtl(long double x); double sqrt(double x); float sqrtf(float x); long double sqrtl(long double x);
§ B.11
Library summary
477
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
double erf(double x); float erff(float x); long double erfl(long double x); double erfc(double x); float erfcf(float x); long double erfcl(long double x); double lgamma(double x); float lgammaf(float x); long double lgammal(long double x); double tgamma(double x); float tgammaf(float x); long double tgammal(long double x); double ceil(double x); float ceilf(float x); long double ceill(long double x); double floor(double x); float floorf(float x); long double floorl(long double x); double nearbyint(double x); float nearbyintf(float x); long double nearbyintl(long double x); double rint(double x); float rintf(float x); long double rintl(long double x); long int lrint(double x); long int lrintf(float x); long int lrintl(long double x); long long int llrint(double x); long long int llrintf(float x); long long int llrintl(long double x); double round(double x); float roundf(float x); long double roundl(long double x); long int lround(double x); long int lroundf(float x); long int lroundl(long double x); long long int llround(double x); long long int llroundf(float x); long long int llroundl(long double x); double roundeven(double x); float roundevenf(float x); long double roundevenl(long double x); double trunc(double x); float truncf(float x); long double truncl(long double x); double fromfp(double x, int rnd, unsigned int width); float fromfpf(float x, int rnd, unsigned int width); long double fromfpl(long double x, int rnd, unsigned int width); double ufromfp(double x, int rnd, unsigned int width); float ufromfpf(float x, int rnd, unsigned int width); long double ufromfpl(long double x, int rnd, unsigned int width); double fromfpx(double x, int rnd, unsigned int width); float fromfpxf(float x, int rnd, unsigned int width); long double fromfpxl(long double x, int rnd, unsigned int width); double ufromfpx(double x, int rnd, unsigned int width); float ufromfpxf(float x, int rnd, unsigned int width); long double ufromfpxl(long double x, int rnd, unsigned int width); double fmod(double x, double y); float fmodf(float x, float y); long double fmodl(long double x, long double y); double remainder(double x, double y);
478
Library summary
§ B.11
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
float remainderf(float x, float y); long double remainderl(long double x, long double y); double remquo(double x, double y, int *quo); float remquof(float x, float y, int *quo); long double remquol(long double x, long double y, int *quo); double copysign(double x, double y); float copysignf(float x, float y); long double copysignl(long double x, long double y); double nan(const char *tagp); float nanf(const char *tagp); long double nanl(const char *tagp); double nextafter(double x, double y); float nextafterf(float x, float y); long double nextafterl(long double x, long double y); double nexttoward(double x, long double y); float nexttowardf(float x, long double y); long double nexttowardl(long double x, long double y); double nextup(double x); float nextupf(float x); long double nextupl(long double x); double nextdown(double x); float nextdownf(float x); long double nextdownl(long double x); int canonicalize(double * cx, const double * x); int canonicalizef(float * cx, const float * x); int canonicalizel(long double * cx, const long double * x); double fdim(double x, double y); float fdimf(float x, float y); long double fdiml(long double x, long double y); double fmax(double x, double y); float fmaxf(float x, float y); long double fmaxl(long double x, long double y); double fmin(double x, double y); float fminf(float x, float y); long double fminl(long double x, long double y); double fmaximum(double x, double y); float fmaximumf(float x, float y); long double fmaximuml(long double x, long double y); double fminimum(double x, double y); float fminimumf(float x, float y); long double fminimuml(long double x, long double y); double fmaximum_mag(double x, double y); float fmaximum_magf(float x, float y); long double fmaximum_magl(long double x, long double y); double fminimum_mag(double x, double y); float fminimum_magf(float x, float y); long double fminimum_magl(long double x, long double y); double fmaximum_num(double x, double y); float fmaximum_numf(float x, float y); long double fmaximum_numl(long double x, long double y); double fminimum_num(double x, double y); float fminimum_numf(float x, float y); long double fminimum_numl(long double x, long double y); double fmaximum_mag_num(double x, double y); float fmaximum_mag_numf(float x, float y); long double fmaximum_mag_numl(long double x, long double y); double fminimum_mag_num(double x, double y); float fminimum_mag_numf(float x, float y); long double fminimum_mag_numl(long double x, long double y); double fma(double x, double y, double z); float fmaf(float x, float y, float z);
§ B.11
Library summary
479
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
long double fmal(long double x, long double y, long double z); float fadd(double x, double y); float faddl(long double x, long double y); double daddl(long double x, long double y); float fsub(double x, double y); float fsubl(long double x, long double y); double dsubl(long double x, long double y); float fmul(double x, double y); float fmull(long double x, long double y); double dmull(long double x, long double y); float fdiv(double x, double y); float fdivl(long double x, long double y); double ddivl(long double x, long double y); float ffma(double x, double y, double z); float ffmal(long double x, long double y, long double z); double dfmal(long double x, long double y, long double z); float fsqrt(double x); float fsqrtl(long double x); double dsqrtl(long double x); int isgreater(real-floating x, real-floating y); int isgreaterequal(real-floating x, real-floating y); int isless(real-floating x, real-floating y); int islessequal(real-floating x, real-floating y); int islessgreater(real-floating x, real-floating y); int isunordered(real-floating x, real-floating y); int iseqsig(real-floating x, real-floating y);
Only if the implementation defines __STDC_IEC_60559_DFP__: _Decimal32 acosd32(_Decimal32 x); _Decimal64 acosd64(_Decimal64 x); _Decimal128 acosd128(_Decimal128 x); _Decimal32 asind32(_Decimal32 x); _Decimal64 asind64(_Decimal64 x); _Decimal128 asind128(_Decimal128 x); _Decimal32 atand32(_Decimal32 x); _Decimal64 atand64(_Decimal64 x); _Decimal128 atand128(_Decimal128 x); _Decimal32 atan2d32(_Decimal32 y, _Decimal32 x); _Decimal64 atan2d64(_Decimal64 y, _Decimal64 x); _Decimal128 atan2d128(_Decimal128 y, _Decimal128 x); _Decimal32 cosd32(_Decimal32 x); _Decimal64 cosd64(_Decimal64 x); _Decimal128 cosd128(_Decimal128 x); _Decimal32 sind32(_Decimal32 x); _Decimal64 sind64(_Decimal64 x); _Decimal128 sind128(_Decimal128 x); _Decimal32 tand32(_Decimal32 x); _Decimal64 tand64(_Decimal64 x); _Decimal128 tand128(_Decimal128 x); _Decimal32 acospid32(_Decimal32 x); _Decimal64 acospid64(_Decimal64 x); _Decimal128 acospid128(_Decimal128 x); _Decimal32 asinpid32(_Decimal32 x); _Decimal64 asinpid64(_Decimal64 x); _Decimal128 asinpid128(_Decimal128 x); _Decimal32 atanpid32(_Decimal32 x); _Decimal64 atanpid64(_Decimal64 x); _Decimal128 atanpid128(_Decimal128 x); _Decimal32 atan2pid32(_Decimal32 y, _Decimal32 x); _Decimal64 atan2pid64(_Decimal64 y, _Decimal64 x);
480
Library summary
§ B.11
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
_Decimal128 atan2pid128(_Decimal128 y, _Decimal128 x); _Decimal32 cospid32(_Decimal32 x); _Decimal64 cospid64(_Decimal64 x); _Decimal128 cospid128(_Decimal128 x); _Decimal32 sinpid32(_Decimal32 x); _Decimal64 sinpid64(_Decimal64 x); _Decimal128 sinpid128(_Decimal128 x); _Decimal32 tanpid32(_Decimal32 x); _Decimal64 tanpid64(_Decimal64 x); _Decimal128 tanpid128(_Decimal128 x); _Decimal32 acoshd32(_Decimal32 x); _Decimal64 acoshd64(_Decimal64 x); _Decimal128 acoshd128(_Decimal128 x); _Decimal32 asinhd32(_Decimal32 x); _Decimal64 asinhd64(_Decimal64 x); _Decimal128 asinhd128(_Decimal128 x); _Decimal32 atanhd32(_Decimal32 x); _Decimal64 atanhd64(_Decimal64 x); _Decimal128 atanhd128(_Decimal128 x); _Decimal32 coshd32(_Decimal32 x); _Decimal64 coshd64(_Decimal64 x); _Decimal128 coshd128(_Decimal128 x); _Decimal32 sinhd32(_Decimal32 x); _Decimal64 sinhd64(_Decimal64 x); _Decimal128 sinhd128(_Decimal128 x); _Decimal32 tanhd32(_Decimal32 x); _Decimal64 tanhd64(_Decimal64 x); _Decimal128 tanhd128(_Decimal128 x); _Decimal32 expd32(_Decimal32 x); _Decimal64 expd64(_Decimal64 x); _Decimal128 expd128(_Decimal128 x); _Decimal32 exp10d32(_Decimal32 x); _Decimal64 exp10d64(_Decimal64 x); _Decimal128 exp10d128(_Decimal128 x); _Decimal32 exp10m1d32(_Decimal32 x); _Decimal64 exp10m1d64(_Decimal64 x); _Decimal128 exp10m1d128(_Decimal128 x); _Decimal32 exp2d32(_Decimal32 x); _Decimal64 exp2d64(_Decimal64 x); _Decimal128 exp2d128(_Decimal128 x); _Decimal32 exp2m1d32(_Decimal32 x); _Decimal64 exp2m1d64(_Decimal64 x); _Decimal128 exp2m1d128(_Decimal128 x); _Decimal32 expm1d32(_Decimal32 x); _Decimal64 expm1d64(_Decimal64 x); _Decimal128 expm1d128(_Decimal128 x); _Decimal32 frexpd32(_Decimal32 value, int *p); _Decimal64 frexpd64(_Decimal64 value, int *p); _Decimal128 frexpd128(_Decimal128 value, int *p); int ilogbd32(_Decimal32 x); int ilogbd64(_Decimal64 x); int ilogbd128(_Decimal128 x); _Decimal32 ldexpd32(_Decimal32 x, int p); _Decimal64 ldexpd64(_Decimal64 x, int p); _Decimal128 ldexpd128(_Decimal128 x, int p); long int llogbd32(_Decimal32 x); long int llogbd64(_Decimal64 x); long int llogbd128(_Decimal128 x); _Decimal32 logd32(_Decimal32 x); _Decimal64 logd64(_Decimal64 x); _Decimal128 logd128(_Decimal128 x);
§ B.11
Library summary
481
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
_Decimal32 log10d32(_Decimal32 x); _Decimal64 log10d64(_Decimal64 x); _Decimal128 log10d128(_Decimal128 x); _Decimal32 log10p1d32(_Decimal32 x); _Decimal64 log10p1d64(_Decimal64 x); _Decimal128 log10p1d128(_Decimal128 x); _Decimal32 log1pd32(_Decimal32 x); _Decimal64 log1pd64(_Decimal64 x); _Decimal128 log1pd128(_Decimal128 x); _Decimal32 logp1d32(_Decimal32 x); _Decimal64 logp1d64(_Decimal64 x); _Decimal128 logp1d128(_Decimal128 x); _Decimal32 log2d32(_Decimal32 x); _Decimal64 log2d64(_Decimal64 x); _Decimal128 log2d128(_Decimal128 x); _Decimal32 log2p1d32(_Decimal32 x); _Decimal64 log2p1d64(_Decimal64 x); _Decimal128 log2p1d128(_Decimal128 x); _Decimal32 logbd32(_Decimal32 x); _Decimal64 logbd64(_Decimal64 x); _Decimal128 logbd128(_Decimal128 x); _Decimal32 modfd32(_Decimal32 x, _Decimal32 *iptr); _Decimal64 modfd64(_Decimal64 x, _Decimal64 *iptr); _Decimal128 modfd128(_Decimal128 x, _Decimal128 *iptr); _Decimal32 scalbnd32(_Decimal32 x, int n); _Decimal64 scalbnd64(_Decimal64 x, int n); _Decimal128 scalbnd128(_Decimal128 x, int n); _Decimal32 scalblnd32(_Decimal32 x, long int n); _Decimal64 scalblnd64(_Decimal64 x, long int n); _Decimal128 scalblnd128(_Decimal128 x, long int n); _Decimal32 cbrtd32(_Decimal32 x); _Decimal64 cbrtd64(_Decimal64 x); _Decimal128 cbrtd128(_Decimal128 x); _Decimal32 compoundnd32(_Decimal32 x, long long int n); _Decimal64 compoundnd64(_Decimal64 x, long long int n); _Decimal128 compoundnd128(_Decimal128 x, long long int n); _Decimal32 fabsd32(_Decimal32 x); _Decimal64 fabsd64(_Decimal64 x); _Decimal128 fabsd128(_Decimal128 x); _Decimal32 hypotd32(_Decimal32 x, _Decimal32 y); _Decimal64 hypotd64(_Decimal64 x, _Decimal64 y); _Decimal128 hypotd128(_Decimal128 x, _Decimal128 y); _Decimal32 powd32(_Decimal32 x, _Decimal32 y); _Decimal64 powd64(_Decimal64 x, _Decimal64 y); _Decimal128 powd128(_Decimal128 x, _Decimal128 y); _Decimal32 pownd32(_Decimal32 x, long long int n); _Decimal64 pownd64(_Decimal64 x, long long int n); _Decimal128 pownd128(_Decimal128 x, long long int n); _Decimal32 powrd32(_Decimal32 y, _Decimal32 x); _Decimal64 powrd64(_Decimal64 y, _Decimal64 x); _Decimal128 powrd128(_Decimal128 y, _Decimal128 x); _Decimal32 rootnd32(_Decimal32 x, long long int n); _Decimal64 rootnd64(_Decimal64 x, long long int n); _Decimal128 rootnd128(_Decimal128 x, long long int n); _Decimal32 rsqrtd32(_Decimal32 x); _Decimal64 rsqrtd64(_Decimal64 x); _Decimal128 rsqrtd128(_Decimal128 x); _Decimal32 sqrtd32(_Decimal32 x); _Decimal64 sqrtd64(_Decimal64 x); _Decimal128 sqrtd128(_Decimal128 x); _Decimal32 erfd32(_Decimal32 x);
482
Library summary
§ B.11
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
_Decimal64 erfd64(_Decimal64 x); _Decimal128 erfd128(_Decimal128 x); _Decimal32 erfcd32(_Decimal32 x); _Decimal64 erfcd64(_Decimal64 x); _Decimal128 erfcd128(_Decimal128 x); _Decimal32 lgammad32(_Decimal32 x); _Decimal64 lgammad64(_Decimal64 x); _Decimal128 lgammad128(_Decimal128 x); _Decimal32 tgammad32(_Decimal32 x); _Decimal64 tgammad64(_Decimal64 x); _Decimal128 tgammad128(_Decimal128 x); _Decimal32 ceild32(_Decimal32 x); _Decimal64 ceild64(_Decimal64 x); _Decimal128 ceild128(_Decimal128 x); _Decimal32 floord32(_Decimal32 x); _Decimal64 floord64(_Decimal64 x); _Decimal128 floord128(_Decimal128 x); _Decimal32 nearbyintd32(_Decimal32 x); _Decimal64 nearbyintd64(_Decimal64 x); _Decimal128 nearbyintd128(_Decimal128 x); _Decimal32 rintd32(_Decimal32 x); _Decimal64 rintd64(_Decimal64 x); _Decimal128 rintd128(_Decimal128 x); long int lrintd32(_Decimal32 x); long int lrintd64(_Decimal64 x); long int lrintd128(_Decimal128 x); long long int llrintd32(_Decimal32 x); long long int llrintd64(_Decimal64 x); long long int llrintd128(_Decimal128 x); _Decimal32 roundd32(_Decimal32 x); _Decimal64 roundd64(_Decimal64 x); _Decimal128 roundd128(_Decimal128 x); long int lroundd32(_Decimal32 x); long int lroundd64(_Decimal64 x); long int lroundd128(_Decimal128 x); long long int llroundd32(_Decimal32 x); long long int llroundd64(_Decimal64 x); long long int llroundd128(_Decimal128 x); _Decimal32 roundevend32(_Decimal32 x); _Decimal64 roundevend64(_Decimal64 x); _Decimal128 roundevend128(_Decimal128 x); _Decimal32 truncd32(_Decimal32 x); _Decimal64 truncd64(_Decimal64 x); _Decimal128 truncd128(_Decimal128 x); _Decimal32 fromfpd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 fromfpd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 fromfpd128(_Decimal128 x, int rnd, unsigned int width); _Decimal32 ufromfpd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 ufromfpd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 ufromfpd128(_Decimal128 x, int rnd, unsigned int width); _Decimal32 fromfpxd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 fromfpxd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 fromfpxd128(_Decimal128 x, int rnd, unsigned int width); _Decimal32 ufromfpxd32(_Decimal32 x, int rnd, unsigned int width); _Decimal64 ufromfpxd64(_Decimal64 x, int rnd, unsigned int width); _Decimal128 ufromfpxd128(_Decimal128 x, int rnd, unsigned int width); _Decimal32 fmodd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmodd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmodd128(_Decimal128 x, _Decimal128 y); _Decimal32 remainderd32(_Decimal32 x, _Decimal32 y); _Decimal64 remainderd64(_Decimal64 x, _Decimal64 y);
§ B.11
Library summary
483
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
_Decimal128 remainderd128(_Decimal128 x, _Decimal128 y); _Decimal32 copysignd32(_Decimal32 x, _Decimal32 y); _Decimal64 copysignd64(_Decimal64 x, _Decimal64 y); _Decimal128 copysignd128(_Decimal128 x, _Decimal128 y); _Decimal32 nand32(const char *tagp); _Decimal64 nand64(const char *tagp); _Decimal128 nand128(const char *tagp); _Decimal32 nextafterd32(_Decimal32 x, _Decimal32 y); _Decimal64 nextafterd64(_Decimal64 x, _Decimal64 y); _Decimal128 nextafterd128(_Decimal128 x, _Decimal128 y); _Decimal32 nexttowardd32(_Decimal32 x, _Decimal128 y); _Decimal64 nexttowardd64(_Decimal64 x, _Decimal128 y); _Decimal128 nexttowardd128(_Decimal128 x, _Decimal128 y); _Decimal32 nextupd32(_Decimal32 x); _Decimal64 nextupd64(_Decimal64 x); _Decimal128 nextupd128(_Decimal128 x); _Decimal32 nextdownd32(_Decimal32 x); _Decimal64 nextdownd64(_Decimal64 x); _Decimal128 nextdownd128(_Decimal128 x); int canonicalized32(_Decimal32 * cx, const _Decimal32 * x); int canonicalized64(_Decimal64 * cx, const _Decimal64 * x); int canonicalized128(_Decimal128 * cx, const _Decimal128 * x); _Decimal32 fdimd32(_Decimal32 x, _Decimal32 y); _Decimal64 fdimd64(_Decimal64 x, _Decimal64 y); _Decimal128 fdimd128(_Decimal128 x, _Decimal128 y); _Decimal32 fmaxd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaxd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaxd128(_Decimal128 x, _Decimal128 y); _Decimal32 fmind32(_Decimal32 x, _Decimal32 y); _Decimal64 fmind64(_Decimal64 x, _Decimal64 y); _Decimal128 fmind128(_Decimal128 x, _Decimal128 y); _Decimal32 fmaximumd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximumd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximumd128(_Decimal128 x, _Decimal128 y); _Decimal32 fminimumd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimumd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimumd128(_Decimal128 x, _Decimal128 y); _Decimal32 fmaximum_magd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximum_magd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximum_magd128(_Decimal128 x, _Decimal128 y); _Decimal32 fminimum_magd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimum_magd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimum_magd128(_Decimal128 x, _Decimal128 y); _Decimal32 fmaximum_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximum_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximum_numd128(_Decimal128 x, _Decimal128 y); _Decimal32 fminimum_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimum_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimum_numd128(_Decimal128 x, _Decimal128 y); _Decimal32 fmaximum_mag_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fmaximum_mag_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fmaximum_mag_numd128(_Decimal128 x, _Decimal128 y); _Decimal32 fminimum_mag_numd32(_Decimal32 x, _Decimal32 y); _Decimal64 fminimum_mag_numd64(_Decimal64 x, _Decimal64 y); _Decimal128 fminimum_mag_numd128(_Decimal128 x, _Decimal128 y); _Decimal32 fmad32(_Decimal32 x, _Decimal32 y, _Decimal32 z); _Decimal64 fmad64(_Decimal64 x, _Decimal64 y, _Decimal64 z); _Decimal128 fmad128(_Decimal128 x, _Decimal128 y, _Decimal128 z); _Decimal32 d32addd64(_Decimal64 x, _Decimal64 y); _Decimal32 d32addd128(_Decimal128 x, _Decimal128 y); _Decimal64 d64addd128(_Decimal128 x, _Decimal128 y);
484
Library summary
§ B.11
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
_Decimal32 d32subd64(_Decimal64 x, _Decimal64 y); _Decimal32 d32subd128(_Decimal128 x, _Decimal128 y); _Decimal64 d64subd128(_Decimal128 x, _Decimal128 y); _Decimal32 d32muld64(_Decimal64 x, _Decimal64 y); _Decimal32 d32muld128(_Decimal128 x, _Decimal128 y); _Decimal64 d64muld128(_Decimal128 x, _Decimal128 y); _Decimal32 d32divd64(_Decimal64 x, _Decimal64 y); _Decimal32 d32divd128(_Decimal128 x, _Decimal128 y); _Decimal64 d64divd128(_Decimal128 x, _Decimal128 y); _Decimal32 d32fmad64(_Decimal64 x, _Decimal64 y, _Decimal64 z); _Decimal32 d32fmad128(_Decimal128 x, _Decimal128 y, _Decimal128 z); _Decimal64 d64fmad128(_Decimal128 x, _Decimal128 y, _Decimal128 z); _Decimal32 d32sqrtd64(_Decimal64 x); _Decimal32 d32sqrtd128(_Decimal128 x); _Decimal64 d64sqrtd128(_Decimal128 x); _Decimal32 quantized32(_Decimal32 x, _Decimal32 y); _Decimal64 quantized64(_Decimal64 x, _Decimal64 y); _Decimal128 quantized128(_Decimal128 x, _Decimal128 y); bool samequantumd32(_Decimal32 x, _Decimal32 y); bool samequantumd64(_Decimal64 x, _Decimal64 y); bool samequantumd128(_Decimal128 x, _Decimal128 y); _Decimal32 quantumd32(_Decimal32 x); _Decimal64 quantumd64(_Decimal64 x); _Decimal128 quantumd128(_Decimal128 x); long long int llquantexpd32(_Decimal32 x); long long int llquantexpd64(_Decimal64 x); long long int llquantexpd128(_Decimal128 x); void encodedecd32(unsigned char encptr[restrict static 4], const _Decimal32*restrict xptr); void encodedecd64(unsigned char encptr[restrict static 8], const _Decimal64*restrict xptr); void encodedecd128(unsigned char encptr[restrict static 16], const _Decimal128*restrict xptr); void decodedecd32(_Decimal32 * restrict xptr, const unsigned char encptr[restrict static 4]); void decodedecd64(_Decimal64 * restrict xptr, const unsigned char encptr[restrict static 8]); void decodedecd128(_Decimal128 * restrict xptr, const unsigned char encptr[restrict static 16]); void encodebind32(unsigned char encptr[restrict static 4], const _Decimal32 * restrict xptr); void encodebind64(unsigned char encptr[restrict static 8], const _Decimal64 * restrict xptr); void encodebind128(unsigned char encptr[restrict static 16], const _Decimal128 * restrict xptr); void decodebind32(_Decimal32 * restrict xptr, const unsigned char encptr[restrict static 4]); void decodebind64(_Decimal64 * restrict xptr, const unsigned char encptr[restrict static 8]); void decodebind128(_Decimal128 * restrict xptr, const unsigned char encptr[restrict static 16]);
Only if the implementation defines __STDC_IEC_60559_BFP__ or __STDC_IEC_559__ and additionally the user code defines __STDC_WANT_IEC_60559_EXT__ before any inclusion of <math.h>: int totalorder(const double *x, const double *y); int totalorderf(const float *x, const float *y); int totalorderl(const long double *x, const long double *y); int totalordermag(const double *x, const double *y); int totalordermagf(const float *x, const float *y); int totalordermagl(const long double *x, const long double *y);
§ B.11
Library summary
485
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
N3096
double getpayload(const double *x); float getpayloadf(const float *x); long double getpayloadl(const long double *x); int setpayload(double *res, double pl); int setpayloadf(float *res, float pl); int setpayloadl(long double *res, long double pl); int setpayloadsig(double *res, double pl); int setpayloadsigf(float *res, float pl); int setpayloadsigl(long double *res, long double pl);
Only if the implementation defines __STDC_IEC_60559_DFP__ and additionally the user code defines __STDC_WANT_IEC_60559_EXT__ before any inclusion of <math.h>: _Decimal32_t
_Decimal64_t
HUGE_VAL_D32
HUGE_VAL_D64
HUGE_VAL_D128
int totalorderd32(const _Decimal32 *x, const _Decimal32 *y); int totalorderd64(const _Decimal64 *x, const _Decimal64 *y); int totalorderd128(const _Decimal128 *x, const _Decimal128 *y); int totalordermagd32(const _Decimal32 *x, const _Decimal32 *y); int totalordermagd64(const _Decimal64 *x, const _Decimal64 *y); int totalordermagd128(const _Decimal128 *x, const _Decimal128 *y); _Decimal32 getpayloadd32(const _Decimal32 *x); _Decimal64 getpayloadd64(const _Decimal64 *x); _Decimal128 getpayloadd128(const _Decimal128 *x); int setpayloadd32(_Decimal32 *res, _Decimal32 pl); int setpayloadd64(_Decimal64 *res, _Decimal64 pl); int setpayloadd128(_Decimal128 *res, _Decimal128 pl); int setpayloadsigd32(_Decimal32 *res, _Decimal32 pl); int setpayloadsigd64(_Decimal64 *res, _Decimal64 pl); int setpayloadsigd128(_Decimal128 *res, _Decimal128 pl);
B.12
Non-local jumps <setjmp.h>
__STDC_VERSION_SETJMP _H__ jmp_buf
int setjmp(jmp_buf env); [[noreturn]] void longjmp(jmp_buf env, int val);
B.13
Signal handling <signal.h>
sig_atomic_t SIG_DFL SIG_ERR
SIG_IGN SIGABRT SIGFPE
SIGILL SIGINT SIGSEGV
SIGTERM
void (*signal(int sig, void (*func)(int)))(int); int raise(int sig);
B.14
Alignment <stdalign.h>
The header <stdalign.h> provides no content.
B.15
486
Variable arguments <stdarg.h>
Library summary
§ B.15
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
va_list __STDC_VERSION_STDARG_H__ type va_arg(va_list ap, type); void va_copy(va_list dest, va_list src); void va_end(va_list ap); void va_start(va_list ap, ...);
B.16
Atomics <stdatomic.h>
__STDC_NO_ATOMICS__ memory_order_acq_rel __STDC_VERSION_STDATOMIC_H__memory_order_seq_cst atomic_bool ATOMIC_BOOL_LOCK_FREE atomic_char ATOMIC_CHAR_LOCK_FREE atomic_schar ATOMIC_CHAR8_T_LOCK_FREE atomic_uchar ATOMIC_CHAR16_T_LOCK_FREE atomic_short ATOMIC_CHAR32_T_LOCK_FREE atomic_ushort ATOMIC_WCHAR_T_LOCK_FREE atomic_int ATOMIC_SHORT_LOCK_FREE atomic_uint ATOMIC_INT_LOCK_FREE atomic_long ATOMIC_LONG_LOCK_FREE atomic_ulong ATOMIC_LLONG_LOCK_FREE atomic_llong _ _ _ ATOMIC POINTER LOCK FREE atomic_ullong _ _ ATOMIC FLAG INIT atomic_char8_t _ memory order atomic_char16_t _ atomic flag atomic_char32_t _ _ memory order relaxed atomic_wchar_t _ _ memory order consume atomic_int_least8_t _ _ memory order acquire atomic_uint_least8_t _ _ memory order release atomic_int_least16_t
atomic_uint_least16_t atomic_int_least32_t atomic_uint_least32_t atomic_int_least64_t atomic_uint_least64_t atomic_int_fast8_t atomic_uint_fast8_t atomic_int_fast16_t atomic_uint_fast16_t atomic_int_fast32_t atomic_uint_fast32_t atomic_int_fast64_t atomic_uint_fast64_t atomic_intptr_t atomic_uintptr_t atomic_size_t atomic_ptrdiff_t atomic_intmax_t atomic_uintmax_t
void atomic_init(volatile A *obj, C value); type kill_dependency(type y); void atomic_thread_fence(memory_order order); void atomic_signal_fence(memory_order order); bool atomic_is_lock_free(const volatile A *obj); void atomic_store(volatile A *object, C desired); void atomic_store_explicit(volatile A *object, C desired, memory_order order); C atomic_load(const volatile A *object); C atomic_load_explicit(const volatile A *object, memory_order order); C atomic_exchange(volatile A *object, C desired); C atomic_exchange_explicit(volatile A *object, C desired, memory_order order); bool atomic_compare_exchange_strong(volatile A *object, C *expected, C desired); bool atomic_compare_exchange_strong_explicit(volatile A *object, C *expected, C desired, memory_order success, memory_order failure); bool atomic_compare_exchange_weak(volatile A *object, C *expected, C desired); bool atomic_compare_exchange_weak_explicit(volatile A *object, C *expected, C desired, memory_order success, memory_order failure); C atomic_fetch_key(volatile A *object, M operand); C atomic_fetch_key_explicit(volatile A *object, M operand, memory_order order); bool atomic_flag_test_and_set(volatile atomic_flag *object); bool atomic_flag_test_and_set_explicit(volatile atomic_flag *object, memory_order order); void atomic_flag_clear(volatile atomic_flag *object); void atomic_flag_clear_explicit(volatile atomic_flag *object, memory_order order);
§ B.16
Library summary
487
ISO/IEC 9899:2023 (E)
B.17
working draft — April 1, 2023
N3096
Bit and byte utilities <stdbit.h>
__STDC_ENDIAN_BIG__ __STDC_ENDIAN_LITTLE__
__STDC_ENDIAN_NATIVE__ __STDC_VERSION_STDBIT_H__
unsigned int stdc_leading_zeros_uc(unsigned char value); unsigned int stdc_leading_zeros_us(unsigned short value); unsigned int stdc_leading_zeros_ui(unsigned int value); unsigned int stdc_leading_zeros_ul(unsigned long value); unsigned int stdc_leading_zeros_ull(unsigned long long value); generic_return_type stdc_leading_zeros(generic_value_type value); unsigned int stdc_leading_ones_uc(unsigned char value); unsigned int stdc_leading_ones_us(unsigned short value); unsigned int stdc_leading_ones_ui(unsigned int value); unsigned int stdc_leading_ones_ul(unsigned long value); unsigned int stdc_leading_ones_ull(unsigned long long value); generic_return_type stdc_leading_ones(generic_value_type value); unsigned int stdc_trailing_zeros_uc(unsigned char value); unsigned int stdc_trailing_zeros_us(unsigned short value); unsigned int stdc_trailing_zeros_ui(unsigned int value); unsigned int stdc_trailing_zeros_ul(unsigned long value); unsigned int stdc_trailing_zeros_ull(unsigned long long value); generic_return_type stdc_trailing_zeros(generic_value_type value); unsigned int stdc_trailing_ones_uc(unsigned char value); unsigned int stdc_trailing_ones_us(unsigned short value); unsigned int stdc_trailing_ones_ui(unsigned int value); unsigned int stdc_trailing_ones_ul(unsigned long value); unsigned int stdc_trailing_ones_ull(unsigned long long value); generic_return_type stdc_trailing_ones(generic_value_type value); unsigned int stdc_first_leading_zero_uc(unsigned char value); unsigned int stdc_first_leading_zero_us(unsigned short value); unsigned int stdc_first_leading_zero_ui(unsigned int value); unsigned int stdc_first_leading_zero_ul(unsigned long value); unsigned int stdc_first_leading_zero_ull(unsigned long long value); generic_return_type stdc_first_leading_zero(generic_value_type value); unsigned int stdc_first_leading_one_uc(unsigned char value); unsigned int stdc_first_leading_one_us(unsigned short value); unsigned int stdc_first_leading_one_ui(unsigned int value); unsigned int stdc_first_leading_one_ul(unsigned long value); unsigned int stdc_first_leading_one_ull(unsigned long long value); generic_return_type stdc_first_leading_one(generic_value_type value); unsigned int stdc_first_trailing_zero_uc(unsigned char value); unsigned int stdc_first_trailing_zero_us(unsigned short value); unsigned int stdc_first_trailing_zero_ui(unsigned int value); unsigned int stdc_first_trailing_zero_ul(unsigned long value); unsigned int stdc_first_trailing_zero_ull(unsigned long long value); generic_return_type stdc_first_trailing_zero(generic_value_type value); unsigned int stdc_first_trailing_one_uc(unsigned char value); unsigned int stdc_first_trailing_one_us(unsigned short value); unsigned int stdc_first_trailing_one_ui(unsigned int value); unsigned int stdc_first_trailing_one_ul(unsigned long value); unsigned int stdc_first_trailing_one_ull(unsigned long long value); generic_return_type stdc_first_trailing_one(generic_value_type value); unsigned int stdc_count_zeros_uc(unsigned char value); unsigned int stdc_count_zeros_us(unsigned short value); unsigned int stdc_count_zeros_ui(unsigned int value); unsigned int stdc_count_zeros_ul(unsigned long value); unsigned int stdc_count_zeros_ull(unsigned long long value); generic_return_type stdc_count_zeros(generic_value_type value); unsigned int stdc_count_ones_uc(unsigned char value); unsigned int stdc_count_ones_us(unsigned short value);
488
Library summary
§ B.17
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
unsigned int stdc_count_ones_ui(unsigned int value); unsigned int stdc_count_ones_ul(unsigned long value); unsigned int stdc_count_ones_ull(unsigned long long value); generic_return_type stdc_count_ones(generic_value_type value); bool stdc_has_single_bit_uc(unsigned char value); bool stdc_has_single_bit_us(unsigned short value); bool stdc_has_single_bit_ui(unsigned int value); bool stdc_has_single_bit_ul(unsigned long value); bool stdc_has_single_bit_ull(unsigned long long value); bool stdc_has_single_bit(generic_value_type value); unsigned int stdc_bit_width_uc(unsigned char value); unsigned int stdc_bit_width_us(unsigned short value); unsigned int stdc_bit_width_ui(unsigned int value); unsigned int stdc_bit_width_ul(unsigned long value); unsigned int stdc_bit_width_ull(unsigned long long value); generic_return_type stdc_bit_width(generic_value_type value); unsigned char stdc_bit_floor_uc(unsigned char value); unsigned short stdc_bit_floor_us(unsigned short value); unsigned int stdc_bit_floor_ui(unsigned int value); unsigned long stdc_bit_floor_ul(unsigned long value); unsigned long long stdc_bit_floor_ull(unsigned long long value); generic_value_type stdc_bit_floor(generic_value_type value); unsigned char stdc_bit_ceil_uc(unsigned char value); unsigned short stdc_bit_ceil_us(unsigned short value); unsigned int stdc_bit_ceil_ui(unsigned int value); unsigned long stdc_bit_ceil_ul(unsigned long value); unsigned long long stdc_bit_ceil_ull(unsigned long long value); generic_value_type stdc_bit_ceil(generic_value_type value);
B.18
Boolean type and values <stdbool.h>
__bool_true_false_are_defined
B.19 ckd_ Checked Integer Operations <stdckdint.h> __STDC_VERSION_STDCKDINT_H__
B.20
Common definitions <stddef.h>
ptrdiff_t nullptr_t size_t
max_align_t wchar_t __STDC_VERSION_STDDEF_H__
NULL
offsetof(type, member-designator)
unreachable()
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <stddef.h>: rsize_t
B.21
§ B.21
Integer types <stdint.h>
Library summary
489
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
intN_t uintN_t int_leastN_t uint_leastN_t int_fastN_t uint_fastN_t intptr_t uintptr_t intmax_t uintmax_t __STDC_VERSION_STDINT_H__ INTN_MIN INTN_MAX INTN_WIDTH UINTN_MAX UINTN_WIDTH INT_LEASTN_MIN INT_LEASTN_MAX
INT_LEASTN_WIDTH UINT_LEASTN_MAX UINT_LEASTN_WIDTH INT_FASTN_MIN INT_FASTN_MAX INT_FASTN_WIDTH UINT_FASTN_MAX UINT_FASTN_WIDTH INTPTR_MIN INTPTR_MAX INTPTR_WIDTH UINTPTR_MAX UINTPTR_WIDTH INTMAX_MIN INTMAX_MAX INTMAX_WIDTH UINTMAX_MAX UINTMAX_WIDTH
N3096
PTRDIFF_MIN PTRDIFF_MAX SIG_ATOMIC_MIN SIG_ATOMIC_MAX SIG_ATOMIC_WIDTH SIZE_MAX SIZE_WIDTH WCHAR_MIN WCHAR_MAX WCHAR_WIDTH WINT_MIN WINT_MAX WINT_WIDTH INTN_C( value ) UINTN_C( value ) INTMAX_C( value ) UINTMAX_C( value )
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <stdint.h>: RSIZE_MAX
B.22 size_t FILE fpos_t NULL _IOFBF _IOLBF
Input/output <stdio.h> _IONBF BUFSIZ EOF FOPEN_MAX FILENAME_MAX L_tmpnam
SEEK_CUR SEEK_END SEEK_SET TMP_MAX stderr stdin
stdout _PRINTF_NAN_LEN_MAX __STDC_VERSION_STDIO_H__
int remove(const char *filename); int rename(const char *old, const char *new); FILE *tmpfile(void); char *tmpnam(char *s); int fclose(FILE *stream); int fflush(FILE *stream); FILE *fopen(const char * restrict filename, const char * restrict mode); FILE *freopen(const char * restrict filename, const char * restrict mode, FILE * restrict stream); void setbuf(FILE * restrict stream, char * restrict buf); int setvbuf(FILE * restrict stream, char * restrict buf, int mode, size_t size); int printf(const char * restrict format, ...); int scanf(const char * restrict format, ...); int snprintf(char * restrict s, size_t n, const char * restrict format, ...); int sprintf(char * restrict s, const char * restrict format, ...); int sscanf(const char * restrict s, const char * restrict format, ...); int vfprintf(FILE * restrict stream, const char * restrict format, va_list arg); int vfscanf(FILE * restrict stream, const char * restrict format, va_list arg); int vprintf(const char * restrict format, va_list arg); int vscanf(const char * restrict format, va_list arg); int vsnprintf(char * restrict s, size_t n, const char * restrict format, va_list arg); int vsprintf(char * restrict s, const char * restrict format, va_list arg); int vsscanf(const char * restrict s, const char * restrict format, va_list arg); int fgetc(FILE *stream);
490
Library summary
§ B.22
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
char *fgets(char * restrict s, int n, FILE * restrict stream); int fputc(int c, FILE *stream); int fputs(const char * restrict s, FILE * restrict stream); int getc(FILE *stream); int getchar(void); int putc(int c, FILE *stream); int putchar(int c); int puts(const char *s); int ungetc(int c, FILE *stream); size_t fread(void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream); size_t fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream); int fgetpos(FILE * restrict stream, fpos_t * restrict pos); int fseek(FILE *stream, long int offset, int whence); int fsetpos(FILE *stream, const fpos_t *pos); long int ftell(FILE *stream); void rewind(FILE *stream); void clearerr(FILE *stream); int feof(FILE *stream); int ferror(FILE *stream); void perror(const char *s); int fprintf(FILE * restrict stream, const char * restrict format, ...); int fscanf(FILE * restrict stream, const char * restrict format, ...);
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <stdio.h>: L_tmpnam_s
TMP_MAX_S
errno_t
rsize_t
errno_t tmpfile_s(FILE * restrict * restrict streamptr); errno_t tmpnam_s(char *s, rsize_t maxsize); errno_t fopen_s(FILE * restrict * restrict streamptr, const char * restrict filename, const char * restrict mode); errno_t freopen_s(FILE * restrict * restrict newstreamptr, const char * restrict filename, const char * restrict mode, FILE * restrict stream); int fprintf_s(FILE * restrict stream, const char * restrict format, ...); int fscanf_s(FILE * restrict stream, const char * restrict format, ...); int printf_s(const char * restrict format, ...); int scanf_s(const char * restrict format, ...); int snprintf_s(char * restrict s, rsize_t n, const char * restrict format, ...); int sprintf_s(char * restrict s, rsize_t n, const char * restrict format, ...); int sscanf_s(const char * restrict s, const char * restrict format, ...); int vfprintf_s(FILE *restrict stream, const char *restrict format, va_list arg); int vfscanf_s(FILE *restrict stream, const char *restrict format, va_list arg); int vprintf_s(const char * restrict format, va_list arg); int vscanf_s(const char * restrict format, va_list arg); int vsnprintf_s(char *restrict s, rsize_t n, const char *restrict format, va_list arg); int vsprintf_s(char * restrict s, rsize_t n, const char * restrict format, va_list arg); int vsscanf_s(const char *restrict s, const char *restrict format, va_list arg); char *gets_s(char *s, rsize_t n);
B.23
§ B.23
General utilities <stdlib.h>
Library summary
491
ISO/IEC 9899:2023 (E)
size_t wchar_t div_t
ldiv_t lldiv_t
working draft — April 1, 2023
__STDC_VERSION_STDLIB EXIT__FAILURE H__ EXIT_SUCCESS NULL RAND_MAX
N3096
MB_CUR_MAX
double atof(const char *nptr); int atoi(const char *nptr); long int atol(const char *nptr); long long int atoll(const char *nptr); int strfromd(char *restrict s, size_t n, const char *restrict format, double fp); int strfromf(char *restrict s, size_t n, const char *restrict format, float fp); int strfroml(char *restrict s, size_t n, const char *restrict format, long double fp); double strtod(const char *restrict nptr, char **restrict endptr); float strtof(const char *restrict nptr, char **restrict endptr); long double strtold(const char *restrict nptr, char **restrict endptr); long int strtol(const char *restrict nptr, char **restrict endptr, int base); long long int strtoll(const char *restrict nptr, char **restrict endptr, int base); unsigned long int strtoul(const char *restrict nptr, char **restrict endptr, int base); unsigned long long int strtoull(const char *restrict nptr, char **restrict endptr, int base); int rand(void); void srand(unsigned int seed); void *aligned_alloc(size_t alignment, size_t size); void *calloc(size_t nmemb, size_t size); void free(void *ptr); void free_sized(void *ptr, size_t size); void free_aligned_sized(void *ptr, size_t alignment, size_t size); void *malloc(size_t size); void *realloc(void *ptr, size_t size); [[noreturn]] void abort(void); int atexit(void (*func)(void)); int at_quick_exit(void (*func)(void)); [[noreturn]] void exit(int status); [[noreturn]] void _Exit(int status); char *getenv(const char *name); [[noreturn]] void quick_exit(int status); int system(const char *string); QVoid *bsearch(const void *key, QVoid *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)); void qsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)); int abs(int j); long int labs(long int j); long long int llabs(long long int j); div_t div(int numer, int denom); ldiv_t ldiv(long int numer, long int denom); lldiv_t lldiv(long long int numer, long long int denom); int mblen(const char *s, size_t n); int mbtowc(wchar_t * restrict pwc, const char * restrict s, size_t n); int wctomb(char *s, wchar_t wc); size_t mbstowcs(wchar_t * restrict pwcs, const char * restrict s, size_t n); size_t wcstombs(char * restrict s, const wchar_t * restrict pwcs, size_t n); size_t memalignment(const void * p);
Only if the implementation defines __STDC_IEC_60559_DFP__: int strfromd32(char*restrict s, size_t n, const char*restrict format, _Decimal32 fp); int strfromd64(char*restrict s, size_t n, const char*restrict format, _Decimal64 fp); int strfromd128(char*restrict s, size_t n, const char*restrict format, _Decimal128 fp);
492
Library summary
§ B.23
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <stdlib.h>: errno_t
rsize_t
constraint_handler_t
constraint_handler_t set_constraint_handler_s(constraint_handler_t handler); void abort_handler_s(const char * restrict msg, void * restrict ptr, errno_t error); void ignore_handler_s(const char * restrict msg, void * restrict ptr, errno_t error); errno_t getenv_s(size_t * restrict len, char * restrict value, rsize_t maxsize, const char * restrict name); QVoid *bsearch_s(const void *key, QVoid *base, rsize_t nmemb, rsize_t size, int (*compar)(const void *k, const void *y, void *context), void *context); errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, int (*compar)(const void *x, const void *y, void *context), void *context); errno_t wctomb_s(int *restrict status, char *restrict s, rsize_t smax, wchar_t wc); errno_t mbstowcs_s(size_t *restrict retval, wchar_t *restrict dst, rsize_t dstmax, const char * restrict src, rsize_t len); errno_t wcstombs_s(size_t * restrict retval, char * restrict dst, rsize_t dstmax, const wchar_t * restrict src, rsize_t len);
B.24 _Noreturn <stdnoreturn.h> noreturn bool ckd_add(type1 *result, type2 a, type3 b); bool ckd_sub(type1 *result, type2 a, type3 b); bool ckd_mul(type1 *result, type2 a, type3 b);
B.25
String handling <string.h>
size_t __STDC_VERSION_STRING_H__
NULL
void *memcpy(void * restrict s1, const void * restrict s2, size_t n); void *memccpy(void * restrict s1, const void * restrict s2, int c, size_t n); void *memmove(void *s1, const void *s2, size_t n); char *strcpy(char * restrict s1, const char * restrict s2); char *strncpy(char * restrict s1, const char * restrict s2, size_t n); char *strdup(const char *s); char *strndup(const char *s, size_t size); char *strcat(char * restrict s1, const char * restrict s2); char *strncat(char * restrict s1, const char * restrict s2, size_t n); int memcmp(const void *s1, const void *s2, size_t n); int strcmp(const char *s1, const char *s2); int strcoll(const char *s1, const char *s2); int strncmp(const char *s1, const char *s2, size_t n); size_t strxfrm(char * restrict s1, const char * restrict s2, size_t n); QVoid *memchr(QVoid *s, int c, size_t n); QChar *strchr(QChar *s, int c); size_t strcspn(const char *s1, const char *s2); QChar *strpbrk(QChar *s1, const char *s2); QChar *strrchr(QChar *s, int c); size_t strspn(const char *s1, const char *s2);
§ B.25
Library summary
493
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
QChar *strstr(QChar *s1, const char *s2); char *strtok(char * restrict s1, const char * restrict s2); void *memset(void *s, int c, size_t n); void *memset_explicit(void *s, int c, size_t n); char *strerror(int errnum); size_t strlen(const char *s);
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <string.h>: errno_t
rsize_t
errno_t memcpy_s(void * restrict s1, rsize_t s1max, const void * restrict s2, rsize_t n); errno_t memmove_s(void *s1, rsize_t s1max, const void *s2, rsize_t n); errno_t strcpy_s(char * restrict s1, rsize_t s1max, const char * restrict s2); errno_t strncpy_s(char * restrict s1, rsize_t s1max, const char * restrict s2, rsize_t n); errno_t strcat_s(char * restrict s1, rsize_t s1max, const char * restrict s2); errno_t strncat_s(char * restrict s1, rsize_t s1max, const char * restrict s2, rsize_t n); char *strtok_s(char * restrict s1, rsize_t * restrict s1max, const char * restrict s2, char ** restrict ptr); errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) errno_t strerror_s(char *s, rsize_t maxsize, errno_t errnum); size_t strerrorlen_s(errno_t errnum); size_t strnlen_s(const char *s, size_t maxsize);
B.26
Type-generic math <tgmath.h>
__STDC_VERSION_TGMATH_H__ atan2pi acos asin atan acosh asinh atanh cos sin tan cosh sinh tanh exp log pow sqrt fabs acospi asinpi
atan2 atanpi cbrt ceil compoundn copysign cospi erfc erf exp10m1 exp10 exp2m1 exp2 expm1 fdim floor fmax fmaximum fmaximum_mag fmaximum_num
fmaximum_mag_num log2p1 fma log2 fmin logb fminimum logp1 fminimum_mag lrint fminimum_num lround fminimum_mag_num nearbyint fmod nextafter frexp nextdown fromfpx nexttoward fromfp nextup hypot pown ilogb powr ldexp remainder lgamma remquo llogb rint llrint rootn llround roundeven log10p1 round log10 rsqrt log1p scalbln
scalbn sinpi tanpi tgamma trunc ufromfpx ufromfp fadd dadd fsub dsub fmul dmul fdiv ddiv ffma dfma fsqrt dsqrt
Only if the implementation does not define __STDC_NO_COMPLEX__:
494
Library summary
§ B.26
N3096
carg
working draft — April 1, 2023
cimag
conj
cproj
ISO/IEC 9899:2023 (E)
creal
Only if the implementation defines __STDC_IEC_60559_DFP__: d32add d64add d32sub
d64sub d32mul d64mul
B.27
Threads <threads.h>
__STDC_NO_THREADS__ thread_local ONCE_FLAG_INIT TSS_DTOR_ITERATIONS cnd_t thrd_t tss_t
d32div d64div d32fma
d64fma d32sqrt d64sqrt
mtx_t tss_dtor_t thrd_start_t once_flag mtx_plain mtx_recursive mtx_timed
quantize samequantum quantum
llquantexp
thrd_timedout thrd_success thrd_busy thrd_error thrd_nomem
void call_once(once_flag *flag, void (*func)(void)); int cnd_broadcast(cnd_t *cond); void cnd_destroy(cnd_t *cond); int cnd_init(cnd_t *cond); int cnd_signal(cnd_t *cond); int cnd_timedwait(cnd_t *restrict cond, mtx_t *restrict mtx, const struct timespec *restrict ts); int cnd_wait(cnd_t *cond, mtx_t *mtx); void mtx_destroy(mtx_t *mtx); int mtx_init(mtx_t *mtx, int type); int mtx_lock(mtx_t *mtx); int mtx_timedlock(mtx_t *restrict mtx, const struct timespec *restrict ts); int mtx_trylock(mtx_t *mtx); int mtx_unlock(mtx_t *mtx); int thrd_create(thrd_t *thr, thrd_start_t func, void *arg); thrd_t thrd_current(void); int thrd_detach(thrd_t thr); int thrd_equal(thrd_t thr0, thrd_t thr1); [[noreturn]] void thrd_exit(int res); int thrd_join(thrd_t thr, int *res); int thrd_sleep(const struct timespec *duration, struct timespec *remaining); void thrd_yield(void); int tss_create(tss_t *key, tss_dtor_t dtor); void tss_delete(tss_t key); void *tss_get(tss_t key); int tss_set(tss_t key, void *val);
B.28
Date and time <time.h>
__STDC_VERSION_TIME_H__ NULL CLOCKS_PER_SEC
TIME_UTC size_t clock_t
time_t struct timespec struct tm
clock_t clock(void); double difftime(time_t time1, time_t time0); time_t mktime(struct tm *timeptr); time_t timegm(struct tm *timeptr); time_t time(time_t *timer);
§ B.28
Library summary
495
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
int timespec_get(struct timespec *ts, int base); int timespec_getres(struct timespec *ts, int base); [[deprecated]] char *asctime(const struct tm *timeptr); [[deprecated]] char *ctime(const time_t *timer); struct tm *gmtime(const time_t *timer); struct tm *gmtime_r(const time_t *timer, struct tm *buf); struct tm *localtime(const time_t *timer); struct tm *localtime_r(const time_t *timer, struct tm *buf); size_t strftime(char * restrict s, size_t maxsize, const char * restrict format, const struct tm * restrict timeptr);
Only if supported by the implementation: TIME_MONOTONIC TIME_ACTIVE
Only if threads are supported and it is supported by the implementation: TIME_THREAD_ACTIVE
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <time.h>: errno_t
rsize_t
errno_t asctime_s(char *s, rsize_t maxsize, const struct tm *timeptr); errno_t ctime_s(char *s, rsize_t maxsize, const time_t *timer); struct tm *gmtime_s(const time_t * restrict timer, struct tm * restrict result); struct tm *localtime_s(const time_t *restrict timer, struct tm *restrict result);
B.29
Unicode utilities <uchar.h>
__STDC_VERSION_UCHAR_H__ mbstate_t size_t
char8_t char16_t
char32_t
size_t mbrtoc8(char8_t * restrict pc8, const char * restrict s, size_t n, mbstate_t * restrict ps); size_t c8rtomb(char * restrict s, char8_t c8, mbstate_t * restrict ps); size_t mbrtoc16(char16_t * restrict pc16, const char * restrict s, size_t n, mbstate_t * restrict ps); _ size t c16rtomb(char * restrict s, char16_t c16, mbstate_t * restrict ps); size_t mbrtoc32(char32_t * restrict pc32, const char * restrict s, size_t n, mbstate_t * restrict ps); size_t c32rtomb(char * restrict s, char32_t c32, mbstate_t * restrict ps);
B.30
Extended multibyte/wide character utilities <wchar.h>
wchar_t size_t mbstate_t wint_t
496
struct tm __STDC_VERSION_WCHAR_H__ NULL WCHAR_MAX
Library summary
WCHAR_MIN WEOF
§ B.30
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
int fwprintf(FILE * restrict stream, const wchar_t * restrict format, ...); int fwscanf(FILE * restrict stream, const wchar_t * restrict format, ...); int swprintf(wchar_t * restrict s, size_t n, const wchar_t * restrict format, ...); int swscanf(const wchar_t * restrict s, const wchar_t * restrict format, ...); int vfwprintf(FILE * restrict stream, const wchar_t * restrict format, va_list arg); int vfwscanf(FILE * restrict stream, const wchar_t * restrict format, va_list arg); int vswprintf(wchar_t * restrict s, size_t n, const wchar_t * restrict format, va_list arg); int vswscanf(const wchar_t * restrict s, const wchar_t * restrict format, va_list arg); int vwprintf(const wchar_t * restrict format, va_list arg); int vwscanf(const wchar_t * restrict format, va_list arg); int wprintf(const wchar_t * restrict format, ...); int wscanf(const wchar_t * restrict format, ...); wint_t fgetwc(FILE *stream); wchar_t *fgetws(wchar_t * restrict s, int n, FILE * restrict stream); wint_t fputwc(wchar_t c, FILE *stream); int fputws(const wchar_t * restrict s, FILE * restrict stream); int fwide(FILE *stream, int mode); wint_t getwc(FILE *stream); wint_t getwchar(void); wint_t putwc(wchar_t c, FILE *stream); wint_t putwchar(wchar_t c); wint_t ungetwc(wint_t c, FILE *stream); long int wcstol(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); long long int wcstoll(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); unsigned long int wcstoul(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); unsigned long long int wcstoull(const wchar_t * restrict nptr, wchar_t ** restrict endptr, int base); wchar_t *wcscpy(wchar_t * restrict s1, const wchar_t * restrict s2); wchar_t *wcsncpy(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n); wchar_t *wmemcpy(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n); wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, size_t n); wchar_t *wcscat(wchar_t * restrict s1, const wchar_t * restrict s2); wchar_t *wcsncat(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n); int wcscmp(const wchar_t *s1, const wchar_t *s2); int wcscoll(const wchar_t *s1, const wchar_t *s2); int wcsncmp(const wchar_t *s1, const wchar_t *s2, size_t n); size_t wcsxfrm(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n); int wmemcmp(const wchar_t *s1, const wchar_t *s2, size_t n); QWchar_t *wcschr(QWchar_t *s, wchar_t c); size_t wcscspn(const wchar_t *s1, const wchar_t *s2); QWchar_t *wcspbrk(QWchar_t *s1, const wchar_t *s2); QWchar_t *wcsrchr(QWchar_t *s, wchar_t c); size_t wcsspn(const wchar_t *s1, const wchar_t *s2); QWchar_t *wcsstr(QWchar_t *s1, const wchar_t *s2); wchar_t *wcstok(wchar_t * restrict s1, const wchar_t * restrict s2, wchar_t ** restrict ptr); QWchar_t *wmemchr(QWchar_t *s, wchar_t c, size_t n); size_t wcslen(const wchar_t *s); wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n); size_t wcsftime(wchar_t * restrict s, size_t maxsize, const wchar_t * restrict format, const struct tm * restrict timeptr); wint_t btowc(int c); int wctob(wint_t c);
§ B.30
Library summary
497
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
int mbsinit(const mbstate_t *ps); size_t mbrlen(const char * restrict s, size_t n, mbstate_t * restrict ps); size_t mbrtowc(wchar_t * restrict pwc, const char * restrict s, size_t n, mbstate_t * restrict ps); size_t wcrtomb(char * restrict s, wchar_t wc, mbstate_t * restrict ps); size_t mbsrtowcs(wchar_t * restrict dst, const char ** restrict src, size_t len, mbstate_t * restrict ps); size_t wcsrtombs(char * restrict dst, const wchar_t ** restrict src, size_t len, mbstate_t * restrict ps);
Only if the implementation defines __STDC_LIB_EXT1__ and additionally the user code defines __STDC_WANT_LIB_EXT1__ before any inclusion of <wchar.h>: errno_t
rsize_t
int fwprintf_s(FILE * restrict stream, const wchar_t * restrict format, ...); int fwscanf_s(FILE * restrict stream, const wchar_t * restrict format, ...); int snwprintf_s(wchar_t * restrict s, rsize_t n, const wchar_t * restrict format, ...); int swprintf_s(wchar_t * restrict s, rsize_t n, const wchar_t * restrict format, ...); int swscanf_s(const wchar_t * restrict s, const wchar_t * restrict format, ...); int vfwprintf_s(FILE * restrict stream, const wchar_t * restrict format, va_list arg); int vfwscanf_s(FILE * restrict stream, const wchar_t * restrict format, va_list arg); int vsnwprintf_s(wchar_t *restrict s, rsize_t n, const wchar_t *restrict format, va_list arg); int vswprintf_s(wchar_t *restrict s, rsize_t n, const wchar_t *restrict format, va_list arg); int vswscanf_s(const wchar_t * restrict s, const wchar_t * restrict format, va_list arg); int vwprintf_s(const wchar_t * restrict format, va_list arg); int vwscanf_s(const wchar_t * restrict format, va_list arg); int wprintf_s(const wchar_t * restrict format, ...); int wscanf_s(const wchar_t * restrict format, ...); errno_t wcscpy_s(wchar_t *restrict s1, rsize_t s1max, const wchar_t *restrict s2); errno_t wcsncpy_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2, rsize_t n); errno_t wmemcpy_s(wchar_t *restrict s1, rsize_t s1max, const wchar_t *restrict s2, rsize_t n); errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, const wchar_t *s2, rsize_t n); errno_t wcscat_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2); errno_t wcsncat_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2, rsize_t n); _ wchar t *wcstok_s(wchar_t * restrict s1, rsize_t * restrict s1max, const wchar_t * restrict s2, wchar_t ** restrict ptr); size_t wcsnlen_s(const wchar_t *s, size_t maxsize); errno_t wcrtomb_s(size_t * restrict retval, char * restrict s, rsize_t smax, wchar_t wc, mbstate_t * restrict ps); errno_t mbsrtowcs_s(size_t * restrict retval, wchar_t * restrict dst, rsize_t dstmax, const char ** restrict src, rsize_t len, mbstate_t * restrict ps); errno_t wcsrtombs_s(size_t * restrict retval, char * restrict dst, rsize_t dstmax, const wchar_t ** restrict src, rsize_t len, mbstate_t * restrict ps);
B.31 498
Wide character classification and mapping utilities <wctype.h> Library summary
§ B.31
N3096
wint_t
working draft — April 1, 2023
wctrans_t
wctype_t
ISO/IEC 9899:2023 (E)
WEOF
int iswalnum(wint_t wc); int iswalpha(wint_t wc); int iswblank(wint_t wc); int iswcntrl(wint_t wc); int iswdigit(wint_t wc); int iswgraph(wint_t wc); int iswlower(wint_t wc); int iswprint(wint_t wc); int iswpunct(wint_t wc); int iswspace(wint_t wc); int iswupper(wint_t wc); int iswxdigit(wint_t wc); int iswctype(wint_t wc, wctype_t desc); wctype_t wctype(const char *property); wint_t towlower(wint_t wc); wint_t towupper(wint_t wc); wint_t towctrans(wint_t wc, wctrans_t desc); wctrans_t wctrans(const char *property);
§ B.31
Library summary
499
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
Annex C (informative)
Sequence points 1
The following are the sequence points described in 5.1.2.3: — Between the evaluations of the function designator and actual arguments in a function call and the actual call. (6.5.2.2). — Between the evaluations of the first and second operands of the following operators: logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17). — Between the evaluations of the first operand of the conditional ?: operator and whichever of the second and third operands is evaluated (6.5.15). — Between the evaluation of a full expression and the next full expression to be evaluated. The following are full expressions: a full declarator for a variably modified type; an initializer that is not part of a compound literal (6.7.10); the expression in an expression statement (6.8.3); the controlling expression of a selection statement (if or switch) (6.8.4); the controlling expression of a while or do statement (6.8.5); each of the (optional) expressions of a for statement (6.8.5.3); the (optional) expression in a return statement (6.8.6.4). — Immediately before a library function returns (7.1.4). — After the actions associated with each formatted input/output function conversion specifier (7.23.6, 7.31.2). — Immediately before and immediately after each call to a comparison function, and also between any call to a comparison function and any movement of the objects passed as arguments to that call (7.24.5).
500
Sequence points
§ B.31
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Annex D (informative)
Universal character names for identifiers 1
This subclause describes the choices made in application of UAX #31 ("Unicode Identifier and Pattern Syntax") to C of the requirements from UAX #31 and how they do or do not apply to C. For UAX #31, C conforms by meeting the requirements "Default Identifiers" (D.1) and "Equivalent Normalized Identifiers" (D.1). The other requirements, also listed below, are either alternatives not taken or do not apply to C.
D.1 1
Default Identifiers
UAX #31 specifies a default syntax for identifiers based on properties from the Unicode Character Database, UAX #44. The general syntax is <Identifier> := <Start> <Continue>* (<Medial> <Continue>+)*
where <Start> has the XID_Start property, <Continue> has the XID_Continue property, and < Medial> is a list of characters permitted between continue characters. For C we add the character U+005F, LOW LINE, or _, to the set of permitted Start characters, the Medial set is empty, and the Continue characters are unmodified. In the grammar used in UAX #31, this is <Identifier> := <Start> <Continue>* <Start> := XID_Start + U+005F <Continue> := <Start> + XID_Continue
This is described in the C grammar (6.4.2.1), where identifier is formed from identifier-start or identifier followed by identifier-continue.
D.1.1
Restricted Format Characters
1
If an implementation of UAX #31 wishes to allow format characters such as ZERO WIDTH JOINER or ZERO WIDTH NON-JOINER it must define a profile allowing them, or describe precisely which combinations are permitted.
2
C does not allow format characters in identifiers, so this does not apply.
D.1.2 1
Stable Identifiers
An implementation of UAX #31 may choose to guarantee that identifiers are stable across versions of the Unicode Standard. Once a string qualifies as an identifier it does so in all future versions. C does not make this guarantee, except to the extent that UAX #31 guarantees the stability of the XID_Start and XID_Continue properties.
D.2
Immutable Identifiers
1
An implementation may choose to guarantee that the set of identifiers will never change by fixing the set of code points allowed in identifiers forever.
2
C does not choose to make this guarantee. As scripts are added to Unicode, additional characters in those scripts may become available for use in identifiers.
D.3
Pattern_White_Space and Pattern_Syntax Characters
1
UAX #31 describes how languages that use or interpret patterns of characters, such as regular expressions or number formats, may describe that syntax with Unicode properties.
2
C does not do this as part of the language, deferring to library components for such usage of patterns. This requirement does not apply to C.
D.4 1
Equivalent Normalized Identifiers
UAX #31 requires that implementations describe how identifiers are compared and considered equivalent. § D.4
Universal character names for identifiers
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2
C requires that identifiers be in Normalization Form C and therefore identifiers that compare the same under NFC are equivalent. This is described in subclause 6.4.2.
D.5 1
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Equivalent Case-Insensitive Identifiers
C considers case to be significant in identifier comparison, and does not do any case folding. This requirement does not apply to C
D.6
Filtered Normalized Identifiers
1
If any characters are excluded from normalization, UAX #31 requires a precise specification of those exclusions.
2
C does not make any such exclusions.
D.7 1
D.8 1
Filtered Case-Insensitive Identifiers
C identifiers are case sensitive, and therefore this requirement does not apply.
Hashtag Identifiers
There are no hashtags in C, so this requirement does not apply.
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ISO/IEC 9899:2023 (E)
Annex E (informative)
Implementation limits 1
The contents of the header <limits.h> are given below. The values shall all be constant expressions suitable for use in conditional expression inclusion preprocessing directives. The components are described further in 5.2.4.2.1.
2
For the following macros, the minimum values shown shall be replaced by implementation-defined values. #define BOOL_WIDTH #define CHAR_BIT #define USHRT_WIDTH #define UINT_WIDTH #define ULONG_WIDTH #define ULLONG_WIDTH #define BITINT_MAXWIDTH #define MB_LEN_MAX
3
1 // exact value 8 16 16 32 64 ULLONG_WIDTH // at minimum as large // as unsigned long long 1
For the following macros, the minimum magnitudes shown shall be replaced by implementationdefined magnitudes with the same sign that are deduced from the macros above as indicated. 438)
#define BOOL_MAX 1 #define CHAR_MAX UCHAR_MAX or SCHAR_MAX #define CHAR_MIN 0 or SCHAR_MIN #define CHAR_WIDTH 8 #define UCHAR_MAX 255 #define UCHAR_WIDTH 8 #define USHRT_MAX 65535 #define SCHAR_MAX +127 #define SCHAR_MIN -128 #define SCHAR_WIDTH 8 #define SHRT_MAX +32767 #define SHRT_MIN -32768 #define SHRT_WIDTH 16 #define INT_MAX +32767 #define INT_MIN -32768 #define INT_WIDTH 16 #define UINT_MAX 65535 #define LONG_MAX +2147483647 #define LONG_MIN -2147483648 #define LONG_WIDTH 32 #define LLONG_MAX +9223372036854775807 #define LLONG_MIN -9223372036854775808 #define LLONG_WIDTH 64 #define ULONG_MAX 4294967295 #define ULLONG_MAX 18446744073709551615
_
// 2BOOL WIDTH − 1
// CHAR_BIT _ // 2UCHAR WIDTH − 1 // CHAR_BIT _ // 2USHRT WIDTH − 1 SCHAR_WIDTH−1 // 2 −1 _ // −2SCHAR WIDTH−1 // CHAR_BIT _ // 2SHRT WIDTH−1 − 1 SHRT_WIDTH−1 // −2 // USHRT_WIDTH _ // 2INT WIDTH−1 − 1 INT_WIDTH−1 // −2 // UINT_WIDTH _ // 2UINT WIDTH − 1 LONG_WIDTH−1 // 2 −1 _ // −2LONG WIDTH−1 // ULONG_WIDTH _ // 2LLONG WIDTH−1 − 1 LLONG_WIDTH−1 // −2 // ULLONG_WIDTH _ // 2ULONG WIDTH − 1 ULLONG_WIDTH // 2 −1
4
The contents of the header <float.h> are given below. All integer values, except FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing directives; all floating values shall be arithmetic constant expressions. The components are described further in 5.2.4.2.2 and 5.2.4.2.3.
5
The values given in the following list shall be replaced by implementation-defined expressions: 438) For the minimum value of a signed integer type there is no expression consisting of a minus sign and a decimal literal of that same type. The numbers in the table are only given as indications for the values and do not represent suitable expressions to be used for these macros.
§ D.8
Implementation limits
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#define FLT_EVAL_METHOD #define FLT_ROUNDS #ifdef __STDC_IEC_60559_DFP__ #define DEC_EVAL_METHOD #endif 6
The values given in the following list shall be replaced by implementation-defined constant expressions that are greater or equal in magnitude (absolute value) to those shown, with the same sign: #define DBL_DECIMAL_DIG #define DBL_DIG #define DBL_MANT_DIG #define DBL_MAX_10_EXP #define DBL_MAX_EXP #define DBL_MIN_10_EXP #define DBL_MIN_EXP #define DECIMAL_DIG #define FLT_DECIMAL_DIG #define FLT_DIG #define FLT_MANT_DIG #define FLT_MAX_10_EXP #define FLT_MAX_EXP #define FLT_MIN_10_EXP #define FLT_MIN_EXP #define FLT_RADIX #define LDBL_DECIMAL_DIG #define LDBL_DIG #define LDBL_MANT_DIG #define LDBL_MAX_10_EXP #define LDBL_MAX_EXP #define LDBL_MIN_10_EXP #define LDBL_MIN_EXP
7
10 10 +37 -37 10 6 6 +37 -37 2 10 10 +37 -37
The values given in the following list shall be replaced by implementation-defined constant expressions with values that are greater than or equal to those shown: #define DBL_MAX #define DBL_NORM_MAX #define FLT_MAX #define FLT_NORM_MAX #define LDBL_MAX #define LDBL_NORM_MAX
8
1E+37 1E+37 1E+37 1E+37 1E+37 1E+37
The values given in the following list shall be replaced by implementation-defined constant expressions with (positive) values that are less than or equal to those shown: #define DBL_EPSILON #define DBL_MIN #define FLT_EPSILON #define FLT_MIN #define LDBL_EPSILON #define LDBL_MIN
9
1E-9 1E-37 1E-5 1E-37 1E-9 1E-37
If the implementation supports decimal floating types, the following macros provide the parameters of these types as exact values. #ifdef __STDC_IEC_60559_DFP__ #define DEC32_EPSILON 1E-6DF #define DEC32_MANT_DIG 7
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#define DEC32_MAX #define DEC32_MAX_EXP #define DEC32_MIN #define DEC32_MIN_EXP #define DEC32_TRUE_MIN #define DEC64_EPSILON #define DEC64_MANT_DIG #define DEC64_MAX #define DEC64_MAX_EXP #define DEC64_MIN #define DEC64_MIN_EXP #define DEC64_TRUE_MIN #define DEC128_EPSILON #define DEC128_MANT_DIG #define DEC128_MAX #define DEC128_MAX_EXP #define DEC128_MIN #define DEC128_MIN_EXP #define DEC128_TRUE_MIN #endif
§ D.8
ISO/IEC 9899:2023 (E)
9.999999E96DF 97 1E-95DF -94 0.000001E-95DF 1E-15DD 16 9.999999999999999E384DD 385 1E-383DD -382 0.000000000000001E-383DD 1E-33DL 34 9.999999999999999999999999999999999E6144DL 6145 1E-6143DL -6142 0.000000000000000000000000000000001E-6143DL
Implementation limits
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Annex F (normative)
IEC 60559 floating-point arithmetic F.1
Introduction
1
This annex specifies C language support for the IEC 60559 floating-point standard. The IEC 60559 floating-point standard is specifically Floating-point arithmetic (ISO/IEC 60559:2020), also designated as IEEE Standard for Floating-Point Arithmetic (IEEE 754–2019). IEC 60559 generally refers to the floating-point standard, as in IEC 60559 operation, IEC 60559 format, etc.
2
The IEC 60559 floating-point standard is a minor upgrade to IEC 60559:2011 (IEEE 754-2008). IEC 60559:2011 was a major upgrade to IEC 60559:1989 (IEEE 754–1985), specifying decimal as well as binary floating-point arithmetic.
3
An implementation that defines __STDC_IEC_60559_BFP__ to 202311L shall conform to the specifications in this annex for binary floating-point arithmetic and shall also define __STDC_IEC_559__ to 1.439)
4
An implementation that defines __STDC_IEC_60559_DFP__ to 202311L shall conform to the specifications for decimal floating-point arithmetic in the following subclauses of this annex: — — — — — — — —
F.2.1 F.3 F.4 F.6 F.7 F.8 F.9 F.10
Infinities and NaNs Operations Floating to integer conversions The return statement Contracted expressions Floating-point environment Optimization Mathematics <math.h> and <tgmath.h>
For the purpose of specifying these conformance requirements, the macros, functions, and values mentioned in the subclauses listed above are understood to refer to the corresponding macros, functions, and values for decimal floating types. Likewise, the "rounding direction mode" is understood to refer to the rounding direction mode for decimal floating-point arithmetic. 5
Where a binding between the C language and IEC 60559 is indicated, the IEC 60559-specified behavior is adopted by reference, unless stated otherwise.
F.2 1
Types
The C floating types match the IEC 60559 formats as follows: — The float type matches the IEC 60559 binary32 format. — The double type matches the IEC 60559 binary64 format. — The long double type matches the IEC 60559 binary128 format, else an IEC 60559 binary64extended format, 440) else a non-IEC 60559 extended format, else the IEC 60559 binary64 format. Any non-IEC 60559 extended format used for the long double type shall have more precision than IEC 60559 binary64 and at least the range of IEC 60559 binary64.441) The value of FLT_ROUNDS applies to all IEC 60559 types supported by the implementation, but need not apply to non-IEC 60559 types. 439) Implementations that do not define either of __STDC_IEC_60559_BFP__ and __STDC_IEC_559__ are not required to conform to these specifications. New code should not use the obsolescent macro __STDC_IEC_559__ to test for conformance to this annex. 440) IEC 60559 binary64-extended formats include the common 80-bit IEC 60559 format. 441) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include all double values.
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Recommended practice The long double type should match the IEC 60559 binary128 format, else an IEC 60559 binary64extended format.
F.2.1
Infinities and NaNs
1
Since negative and positive infinity are representable in IEC 60559 formats, all real numbers lie within the range of representable values (5.2.4.2.2).
2
The NAN and INFINITY macros in <float.h> and the nan functions in <math.h> provide designations for IEC 60559 quiet NaNs and infinities. The FLT_SNAN, DBL_SNAN, and LDBL_SNAN macros in <float.h> provide designations for IEC 60559 signaling NaNs.
3
This annex does not require the full support for signaling NaNs specified in IEC 60559. This annex uses the term NaN, unless explicitly qualified, to denote quiet NaNs. Where specification of signaling NaNs is not provided, the behavior of signaling NaNs is implementation-defined (either treated as an IEC 60559 quiet NaN or treated as an IEC 60559 signaling NaN). 442)
4
Any operator or <math.h> function that raises an "invalid" floating-point exception, if delivering a floating type result, shall return a quiet NaN, unless explicitly specified otherwise.
5
To support signaling NaNs as specified in IEC 60559, an implementation should adhere to the following recommended practice.
6
Recommended practice Any floating-point operator or <math.h> function or macro with a signaling NaN input, unless explicitly specified otherwise, raises an "invalid" floating-point exception.
7
NOTE 1 Some functions do not propagate quiet NaN arguments. For example, hypot(x, y) returns infinity if x or y is infinite and the other is a quiet NaN. The recommended practice in this subclause specifies that such functions (and others) raise the "invalid" floating-point exception if an argument is a signaling NaN, which also implies they return a quiet NaN in these cases.
8
The <fenv.h> header defines the macro FE_SNANS_ALWAYS_SIGNAL if and only if the implementation follows the recommended practice in this subclause. If defined, FE_SNANS_ALWAYS_SIGNAL expands to the integer constant 1.
F.3 1
Operations
C operators, functions, and function-like macros provide operations specified by IEC 60559 as shown in the following table. In the table, C functions are represented by the function name without a type suffix. Specifications for the C facilities are provided in the listed clauses. The C specifications are intended to match IEC 60559, unless stated otherwise. Operation binding IEC 60559 operation roundToIntegralTiesToEven roundToIntegralTiesAway roundToIntegralTowardZero roundToIntegralTowardPositive roundToIntegralTowardNegative roundToIntegralExact nextUp nextDown getPayload setPayload setPayloadSignaling quantize sameQuantum
C operation roundeven round trunc ceil floor rint nextup nextdown getpayload setpayload setpayloadsig quantize samequantum
Clause 7.12.9.8, F.10.6.8 7.12.9.6, F.10.6.6 7.12.9.9, F.10.6.9 7.12.9.1, F.10.6.1 7.12.9.2, F.10.6.2 7.12.9.4, F.10.6.4 7.12.11.5, F.10.8.5 7.12.11.6, F.10.8.6 F.10.13.1 F.10.13.2 F.10.13.3 7.12.15.1 7.12.15.2
442) Since NaNs created by IEC 60559 arithmetic operations are always quiet, quiet NaNs (along with infinities) are sufficient for closure of the arithmetic.
§ F.3
IEC 60559 floating-point arithmetic
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quantum encodeDecimal decodeDecimal encodeBinary decodeBinary remainder
quantum encodedec decodedec encodebin decodebin remainder, remquo
maximum minimum maximumMagnitude minimumMagnitude maximumNumber minimumNumber maximumMagnitudeNumber minimumMagnitudeNumber scaleB logB
fmaximum fminimum fmaximum_mag fminimum_mag fmaximum_num fminimum_num fmaximum_mag_num fminimum_mag_num
addition
+, fadd, faddl, daddl
subtraction
-, fsub, fsubl, dsubl
multiplication
*, fmul, fmull, dmull
division
/, fdiv, fdivl, ddivl
squareRoot
sqrt, fsqrt, fsqrtl, dsqrtl
fusedMultiplyAdd
fma, ffma, ffmal, dfmal
convertFromInt convertToIntegerTiesToEven convertToIntegerTowardZero convertToIntegerTowardPositive convertToIntegerTowardNegative convertToIntegerTiesToAway
cast and implicit conversion fromfp, ufromfp
7.12.15.3 7.12.16.1 7.12.16.2 7.12.16.3 7.12.16.4 7.12.10.2, F.10.7.2, 7.12.10.3, F.10.7.3 7.12.12.4, F.10.9.4 7.12.12.5, F.10.9.4 7.12.12.6, F.10.9.4 7.12.12.7, F.10.9.4 7.12.12.8, F.10.9.5 7.12.12.9, F.10.9.5 7.12.12.10, F.10.9.5 7.12.12.11, F.10.9.5 7.12.6.19, F.10.3.19 7.12.6.17, F.10.3.17, 7.12.6.8, F.10.3.8, 7.12.6.10, F.10.3.10 6.5.6, 7.12.14.1, F.10.11 6.5.6, 7.12.14.2, F.10.11 6.5.5, 7.12.14.3, F.10.11 6.5.5, 7.12.14.4, F.10.11 7.12.7.10, F.10.4.10, 7.12.14.6, F.10.11 7.12.13.1, F.10.10.1, 7.12.14.5, F.10.11 6.3.1.4, 6.5.4 7.12.9.10, F.10.6.10
fromfp, ufromfp, llround fromfpx, ufromfpx
7.12.9.10, F.10.6.10, 7.12.9.7, F.10.6.7 7.12.9.11, F.10.6.11
convertToIntegerExactTiesToEven convertToIntegerExactTowardZero convertToIntegerExactTowardPositive convertToIntegerExactTowardNegative convertToIntegerExactTiesToAway convertFormat - different formats convertFormat - same format convertFromDecimalCharacter
scalbn, scalbln logb, ilogb, llogb
lround,
cast and implicit conversions canonicalize strtod, wcstod, scanf, wscanf,
decimal floating constants convertToDecimalCharacter
printf, wprintf, strfromd
convertFromHexCharacter
strtod, wcstod, scanf, wscanf,
hexadecimal floating constants
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6.3.1.5, 6.5.4 7.12.11.7, F.10.8.7 7.24.1.5, 7.31.4.1.2, 7.23.6.4, 7.31.2.12, F.5 7.23.6.3, 7.31.2.11, 7.24.1.3, F.5 7.24.1.5, 7.31.4.1.2, 7.23.6.4, 7.31.2.12, F.5
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convertToHexCharacter
printf, wprintf, strfromd
copy negate abs copySign compareQuietEqual compareQuietNotEqual compareSignalingEqual compareSignalingGreater compareSignalingGreaterEqual compareSignalingLess compareSignalingLessEqual compareSignalingNotEqual compareSignalingNotGreater compareSignalingLessUnordered compareSignalingNotLess compareSignalingGreaterUnordered compareQuietGreater compareQuietGreaterEqual compareQuietLess compareQuietLessEqual compareQuietUnordered compareQuietNotGreater compareQuietLessUnordered compareQuietNotLess compareQuietGreaterUnordered compareQuietOrdered class
memcpy, memmove, +(x) -(x) fabs copysign == != iseqsig > >= < <= ! iseqsig(x) ! (x > y) ! (x >= y) ! (x < y) ! (x <= y) isgreater isgreaterequal isless islessequal isunordered ! isgreater(x, y) ! isgreaterequal(x, y) ! isless(x, y) ! islessequal(x, y) ! isunordered(x, y) fpclassify, signbit, issignaling signbit isnormal isfinite iszero issubnormal isinf isnan issignaling iscanonical FLT_RADIX totalorder totalordermag feclearexcept fesetexcept fetestexcept fetestexceptflag fesetexceptflag fegetexceptflag fegetround fesetround fegetmode fesetmode fesetmode(FE_DFL_MODE)
isSignMinus isNormal isFinite isZero isSubnormal isInfinite isNaN isSignaling isCanonical radix totalOrder totalOrderMag lowerFlags raiseFlags testFlags testSavedFlags restoreFlags saveAllFlags getBinaryRoundingDirection setBinaryRoundingDirection saveModes restoreModes defaultModes
§ F.3
ISO/IEC 9899:2023 (E)
IEC 60559 floating-point arithmetic
7.23.6.3, 7.31.2.11, 7.24.1.3, F.5 7.26.2.1, 7.26.2.3 6.5.3.3 7.12.7.3, F.10.4.3 7.12.11.1, F.10.8.1 6.5.9, F.9.3 6.5.9, F.9.3 7.12.17.7, F.10.14.1 6.5.8, F.9.3 6.5.8, F.9.3 6.5.8, F.9.3 6.5.8, F.9.3 7.12.17.7, F.10.14.1 6.5.8, F.9.3 6.5.8, F.9.3 6.5.8, F.9.3 6.5.8, F.9.3 7.12.17.1 7.12.17.2 7.12.17.3 7.12.17.4 7.12.17.6 7.12.17.1 7.12.17.2 7.12.17.3 7.12.17.4 7.12.17.6 7.12.3.1, 7.12.3.7, 7.12.3.8 7.12.3.7 7.12.3.6 7.12.3.3 7.12.3.10 7.12.3.9 7.12.3.4 7.12.3.5 7.12.3.8 7.12.3.2 5.2.4.2.2 F.10.12.1 F.10.12.2 7.6.4.1 7.6.4.4 7.6.4.7 7.6.4.6 7.6.4.5 7.6.4.2 7.6.5.2 7.6.5.5 7.6.5.1 7.6.5.4 7.6.5.4, 7.6
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The IEC 60559 requirement that certain of its operations be provided for operands of different formats (of the same radix) is satisfied by C’s usual arithmetic conversions (6.3.1.8) and function-call argument conversions (6.5.2.2). For example, the following operations take float f and double d inputs and produce a long double result: (long double)f * d powl(f, d)
3
The functions fmin and fmax have been superseded by fminimum_num and fmaximum_num. The fmin and fmax functions provide the minNum and maxNum operations specified in (the superseded) IEC 60559:2011.
4
Whether C assignment (6.5.16) (and conversion as if by assignment) to the same format is an IEC 60559 convertFormat or copy operation443) is implementation-defined, even if <fenv.h> defines the macro FE_SNANS_ALWAYS_SIGNAL (F.2.1). If the return expression of a return statement is evaluated to the floating-point format of the return type, it is implementation-defined whether a convertFormat operation is applied to the result of the return expression.
5
The unary + and - operators raise no floating-point exceptions, even if the operand is a signaling NaN.
6
The C classification macros fpclassify, iscanonical, isfinite, isinf, isnan, isnormal, issignaling, issubnormal, iszero, and signbit provide the IEC 60559 operations indicated in the table above provided their arguments are in the format of their semantic type. Then these macros raise no floating-point exceptions, even if an argument is a signaling NaN.
7
The signbit macro, providing the IEC 60559 isSignMinus operation, determines the sign of its argument value as the sign bit of the value’s representation. This applies to all values, including NaNs whose sign bit is not generally interpreted by IEC 60559.
8
The C nearbyint functions (7.12.9.3, F.10.6.3) provide the nearbyinteger function recommended in the Appendix to (superseded) ANSI/IEEE 854–1987.
9
The C nextafter (7.12.11.3, F.10.8.3) and nexttoward (7.12.11.4, F.10.8.4) functions provide the nextafter function recommended in the Appendix to (superseded) IEC 60559:1989 (but with a minor change to better handle signed zeros).
10
The macros (7.6) FE_DOWNWARD, FE_TONEAREST, FE_TONEARESTFROMZERO, FE_TOWARDZERO, and FE_UPWARD, which are used in conjunction with the fegetround and fesetround functions and the FENV_ROUND pragma, represent the IEC 60559 rounding-direction attributes roundTowardNegative, roundTiesToEven, roundTiesToAway, roundTowardZero, and roundTowardPositive, respectively, for binary floating-point arithmetic. Support for the roundTiesToAway attribute for binary floatingpoint arithmetic, and hence for the FE_TONEARESTFROMZERO macro, is optional.
11
The C fegetenv (7.6.6.1), feholdexcept (7.6.6.2), fesetenv (7.6.6.3) and feupdateenv (7.6.6.4) functions provide a facility to manage the dynamic floating-point environment, comprising the IEC 60559 status flags and dynamic control modes.
12
IEC 60559 requires operations with specified operand and result formats. Therefore, math functions that are bound to IEC 60559 operations (see table above) must remove any extra range and precision from arguments or results.
13
IEC 60559 requires operations that round their result to formats the same as and wider than the operands, in addition to the operations that round their result to narrower formats (see 7.12.14). Operators (+, -, *, and /) whose evaluation formats are wider than the semantic type (5.2.4.2.2) might not support some of the IEEE 60559 operations, because getting a result in a given format might require a cast that could introduce an extra rounding error. The functions that round result to narrower type (7.12.14) provide the IEC 60559 operations that round result to same and wider (as well as narrower) formats, in those cases where built-in operators and casts do not. For example, 443) Where the source and destination formats are the same, convertFormat operations differ from copy operations in that convertFormat operations raise the "invalid" floating-point exception on signaling NaN inputs and do not propagate non-canonical encodings.
510
IEC 60559 floating-point arithmetic
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ddivl(x, y) computes a correctly rounded double divide of float x by float y, regardless of
the evaluation method. 14
Decimal versions of the remquo library function are not provided. (The decimal remainder functions provide the remainder operation defined by IEC 60559.)
15
The binding for the convertFormat operation applies to all conversions among IEC 60559 formats. Therefore, for implementations that conform to Annex F, conversions between decimal floating types and standard floating types with IEC 60559 formats are correctly rounded and raise floating-point exceptions as specified in IEC 60559.
16
IEC 60559 specifies the convertFromHexCharacter and convertToHexCharacter operations only for binary floating-point arithmetic.
17
The integer constant 10 provides the radix operation defined in IEC 60559 for decimal floating-point arithmetic.
18
The fe_dec_getround (7.6.5.3) and fe_dec_setround (7.6.5.6) functions provide the getDecimalRoundingDirection and setDecimalRoundingDirection operations defined in IEC 60559 for decimal floating-point arithmetic. The macros (7.6) FE_DEC_DOWNWARD, FE_DEC_TONEAREST, FE_DEC_TONEARESTFROMZERO, FE_DEC_TOWARDZERO, and FE_DEC_UPWARD, which are used in conjunction with the fe_dec_getround and fe_dec_setround functions and the FENV_DEC_ROUND pragma, represent the IEC 60559 rounding-direction attributes roundTowardNegative, roundTiesToEven, roundTiesToAway, roundTowardZero, and roundTowardPositive, respectively, for decimal floating-point arithmetic.
19
The llquantexpdN (7.12.15.4) functions compute the (quantum) exponent q defined in IEC 60559 for decimal numbers viewed as having integer significands.
20
The C functions in the following table correspond to mathematical operations recommended by IEC 60559. However, correct rounding, which IEC 60559 specifies for its operations, is not required for the C functions in the table. 7.33.8 (potentially) reserves cr_ prefixed names for functions fully matching the IEC 60559 mathematical operations. In the table, the C functions are represented by the function name without a type suffix. IEC 60559 operation exp expm1 exp2 exp2m1 exp10 exp10m1 log log2 log10 logp1 log2p1 log10p1 hypot rSqrt compound rootn pown pow powr sin cos tan sinPi cosPi
C function exp expm1 exp2 exp2m1 exp10 exp10m1 log log2 log10
log1p, logp1 log2p1 log10p1 hypot rsqrt compoundn rootn pown pow powr sin cos tan sinpi cospi
Clause 7.12.6.1, F.10.3.1 7.12.6.6, F.10.3.6 7.12.6.4, F.10.3.4 7.12.6.5, F.10.3.5 7.12.6.2, F.10.3.2 7.12.6.3, F.10.3.3 7.12.6.11, F.10.3.11 7.12.6.15, F.10.3.15 7.12.6.12, F.10.3.12 7.12.6.14, F.10.3.14 7.12.6.16, F.10.3.16 7.12.6.13, F.10.3.13 7.12.7.4, F.10.4.4 7.12.7.9, F.10.4.9 7.12.7.2, F.10.4.2 7.12.7.8, F.10.4.8 7.12.7.6, F.10.4.6 7.12.7.5, F.10.4.5 7.12.7.7, F.10.4.7 7.12.4.6, F.10.1.6 7.12.4.5, F.10.1.5 7.12.4.7, F.10.1.7 7.12.4.13, F.10.1.13 7.12.4.12, F.10.1.12
... continued ... § F.3
IEC 60559 floating-point arithmetic
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IEC 60559 operation tanPi asinPi acosPi atanPi atan2Pi asin acos atan atan2 sinh cosh tanh asinh acosh atanh
F.4 1
... continued ... C function tanpi asinpi acospi atanpi atan2pi asin acos atan atan2 sinh cosh tanh asinh acosh atanh
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Floating to integer conversion
If the integer type is bool, 6.3.1.2 applies and the conversion raises no floating-point exceptions if the floating-point value is not a signaling NaN. Otherwise, if the floating value is infinite or NaN or if the integral part of the floating value exceeds the range of the integer type, then the "invalid" floating-point exception is raised and the resulting value is unspecified. Otherwise, the resulting value is determined by 6.3.1.4. Conversion of an integral floating value that does not exceed the range of the integer type raises no floating-point exceptions; whether conversion of a non-integral floating value raises the "inexact" floating-point exception is unspecified.444)
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Conversions between binary floating types and decimal character sequences
The <float.h> header defines the macro CR_DECIMAL_DIG
if and only if __STDC_WANT_IEC_60559_EXT__ is defined as a macro at the point in the source file where <float.h> is first included. If defined, CR_DECIMAL_DIG expands to an integer constant expression suitable for use in conditional expression inclusion preprocessing directives whose value is a number such that conversions between all supported IEC 60559 binary formats and character sequences with at most CR_DECIMAL_DIG significant decimal digits are correctly rounded. The value of CR_DECIMAL_DIG shall be at least M + 3, where M is the maximum value of the T_DECIMAL_DIG macros for IEC 60559 binary formats. If the implementation correctly rounds for all numbers of significant decimal digits, then CR_DECIMAL_DIG shall have the value of the macro UINTMAX_MAX. 2
Conversions of types with IEC 60559 binary formats to character sequences with more than CR_DECIMAL_DIG significant decimal digits shall correctly round to CR_DECIMAL_DIG significant digits and pad zeros on the right.
3
Conversions from character sequences with more than CR_DECIMAL_DIG significant decimal digits to types with IEC 60559 binary formats shall correctly round to an intermediate character sequence with CR_DECIMAL_DIG significant decimal digits, according to the applicable rounding direction, and correctly round the intermediate result (having CR_DECIMAL_DIG significant decimal digits) to the destination type. The "inexact" floating-point exception is raised (once) if either conversion is inexact.445) (The second conversion may raise the "overflow" or "underflow" floating-point 444) IEC 60559 recommends that implicit floating-to-integer conversions raise the "inexact" floating-point exception for non-integer in-range values. In those cases where it matters, library functions can be used to effect such conversions with or without raising the "inexact" floating- point exception. See fromfp, ufromfp, fromfpx, ufromfpx, rint, lrint, llrint, and nearbyint in <math.h>. 445) The intermediate conversion is exact only if all input digits after the first CR_DECIMAL_DIG digits are 0.
512
IEC 60559 floating-point arithmetic
§ F.5
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exception.) 4
The specification in this subclause assures conversion between IEC 60559 binary format and decimal character sequence follows all pertinent recommended practice. It also assures conversion from IEC 60559 format to decimal character sequence with at least T_DECIMAL_DIG digits and back, using to-nearest rounding, is the identity function, where T is the macro prefix for the format.
5
Functions such as strtod that convert character sequences to floating types honor the rounding direction. Hence, if the rounding direction might be upward or downward, the implementation cannot convert a minus-signed sequence by negating the converted unsigned sequence.
6
NOTE 1 IEC 60559 specifies that conversion to one-digit character strings using roundTiesToEven when both choices have an odd least significant digit, shall produce the value with the larger magnitude. For example, this can happen with 9.5e2 whose nearest neighbors are 9.e2 and 1.e3, both of which have a single odd digit in the significand part.
F.6
The return statement
If the return expression is evaluated in a floating-point format different from the return type, the expression is converted as if by assignment446) to the return type of the function and the resulting value is returned to the caller.
F.7 1
2
Contracted expressions
A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed zeros, subnormals, and the rounding directions in a manner consistent with the basic arithmetic operations covered by IEC 60559. Recommended practice A contracted expression should raise floating-point exceptions in a manner generally consistent with the basic arithmetic operations.
F.8
Floating-point environment
1
The floating-point environment defined in <fenv.h> includes the IEC 60559 floating-point exception status flags and rounding-direction control modes. It may also include other floating-point status or modes that the implementation provides as extensions.447)
2
This annex does not include support for IEC 60559’s optional alternate exception handling. The specification in this annex assumes IEC 60559 default exception handling: the flag is set, a default result is delivered, and execution continues. Implementations might provide alternate exception handling as an extension.
F.8.1 1
IEC 60559 requires that floating-point operations implicitly raise floating-point exception status flags, and that rounding control modes can be set explicitly to affect result values of floating-point operations. These changes to the floating-point state are treated as side effects which respect sequence points.448)
F.8.2 1
Environment management
Translation
During translation, constant rounding direction modes (7.6.2) are in effect where specified. Elsewhere, during translation the IEC 60559 default modes are in effect: — The rounding direction mode is rounding to nearest. — The rounding precision mode (if supported) is set so that results are not shortened. — Trapping or stopping (if supported) is disabled on all floating-point exceptions. 446) Assignment removes any extra range and precision. 447) Dynamic rounding precision and trap enablement modes are examples of such extensions. 448) If the state for the FENV_ACCESS pragma is "off", the implementation is free to assume the dynamic floating-point control modes will be the default ones and the floating-point status flags will not be tested, which allows certain optimizations (see F.9).
§ F.8.2
IEC 60559 floating-point arithmetic
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2
Recommended practice The implementation should produce a diagnostic message for each translation-time floating-point exception, other than "inexact";449) the implementation should then proceed with the translation of the program.
F.8.3 1
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Execution
At program startup the dynamic floating-point environment is initialized as prescribed by IEC 60559: — All floating-point exception status flags are cleared. — The dynamic rounding direction mode is rounding to nearest. — The dynamic rounding precision mode (if supported) is set so that results are not shortened. — Trapping or stopping (if supported) is disabled on all floating-point exceptions.
F.8.4
Constant expressions
1
An arithmetic constant expression of floating type, other than one in an initializer for an object that has static or thread storage duration or that is declared with storage-class specifier constexpr, is evaluated (as if) during execution; thus, it is affected by any operative floating-point control modes and raises floating-point exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma is "on").450)
2
EXAMPLE #include <fenv.h> #pragma STDC FENV_ACCESS ON void f(void) { constexpr double v = 0.0/0.0; // does not raise an exception float w[] = { 0.0/0.0 }; // raises an exception static float x = 0.0/0.0; // does not raise an exception float y = 0.0/0.0; // raises an exception double z = 0.0/0.0; // raises an exception /* ... */ }
3
For the static and constexpr initialization, the division is done at translation time, raising no (execution-time) floating-point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at execution time.
F.8.5
Initialization
1
All computation for automatic initialization is done (as if) at execution time; thus, it is affected by any operative modes and raises floating-point exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma is "on"). All computation for initialization of objects that have static or thread storage duration is done (as if) at translation time.
2
EXAMPLE #include <fenv.h> 449) As floating constants are converted to appropriate internal representations at translation time, their conversion is subject to constant or default rounding modes and raises no execution-time floating-point exceptions (even where the state of the FENV_ACCESS pragma is "on"). Library functions, for example strtod, provide execution-time conversion of numeric strings. 450) Where the state for the FENV_ACCESS pragma is "on", results of inexact expressions like 1.0/3.0 are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the efficiency of translation-time evaluation through static initialization, such as
const static double one_third = 1.0/3.0;
514
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§ F.8.5
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#pragma STDC FENV_ACCESS ON void f(void) { constexpr float t = (float)1.1e75; // does not raise exceptions float u[] = { 1.1e75 }; // raises exceptions static float v = 1.1e75; // does not raise exceptions float w = 1.1e75; // raises exceptions double x = 1.1e75; // may raise exceptions float y = 1.1e75f; // may raise exceptions long double z = 1.1e75; // does not raise exceptions /* ... */ } 3
The constexpr initialization of t and the static initialization of v raise no (execution-time) floatingpoint exceptions because their computation is done at translation time. The automatic initialization of u and w require an execution-time conversion to float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations of x and y entail execution-time conversion; however, in some expression evaluation methods, the conversions is not to a narrower format, in which case no floating-point exception is raised.451) The automatic initialization of z entails executiontime conversion, but not to a narrower format, so no floating-point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to their internal representations occur at translation time in all cases.
F.8.6
Changing the environment
1
Operations defined in 6.5 and functions and macros defined for the standard libraries change floating-point status flags and control modes just as indicated by their specifications (including conformance to IEC 60559). They do not change flags or modes (so as to be detectable by the user) in any other cases.
2
If the floating-point exceptions represented by the argument to the feraiseexcept function in <fenv.h> include both "overflow" and "inexect", then "overflow" is raised before "inexact". Similarly, if the represented exceptions include both "underflow" and "inexact", then "underflow" is raised before "inexact".
F.9 1
Optimization
This section identifies code transformations that might subvert IEC 60559-specified behavior, and others that do not.
F.9.1
Global transformations
1
Floating-point arithmetic operations and external function calls may entail side effects which optimization shall honor, at least where the state of the FENV_ACCESS pragma is "on". The flags and modes in the floating-point environment may be regarded as global variables; floating-point operations (+, *, etc.) implicitly read the modes and write the flags.
2
Concern about side effects may inhibit code motion and removal of seemingly useless code. For example, in #include <fenv.h> #pragma STDC FENV_ACCESS ON void f(double x) { /* ... */ for (i = 0; i < n; i++) x + 1; 451) Use of float_t and double_t variables increases the likelihood of translation-time computation. For example, the automatic initialization
double_t x = 1.1e75; could be done at translation time, regardless of the expression evaluation method.
§ F.9.1
IEC 60559 floating-point arithmetic
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/* ... */ }
x+1 might raise floating-point exceptions, so cannot be removed. And since the loop body might not execute (maybe 0 ≥ n), x+1 cannot be moved out of the loop. (Of course these optimizations are
valid if the implementation can rule out the nettlesome cases.) 3
This specification does not require support for trap handlers that maintain information about the order or count of floating-point exceptions. Therefore, between function calls, floating-point exceptions need not be precise: the actual order and number of occurrences of floating-point exceptions (> 1) may vary from what the source code expresses. Thus, the preceding loop could be treated as if (0
F.9.2
<
n) x + 1;
Expression transformations
1
Valid expression transformations must preserve numerical values.
2
The equivalences noted below apply to expressions of standard floating types. x/2 ↔ x × 0.5
Although similar transformations involving inexact constants generally do not yield equivalent expressions, if the constants are exact then such transformations can be made on IEC 60559 machines and others that round perfectly.
1 × x and x/1 → x The expressions 1 × x, x/1, and x may be regarded as equivalent (on IEC 60559 machines, among others).452)
3
x/x → 1.0
The expressions x/x and 1.0 are not equivalent if x can be zero, infinite, or NaN.
x − y ↔ x + (−y)
The expressions x − y, x + (−y), and (−y) + x are equivalent (on IEC 60559 machines, among others).
x − y ↔ −(y − x)
The expressions x − y and −(y − x) are not equivalent because 1 − 1 is +0 but −(1 − 1) is −0 (in the default rounding direction).453)
x − x → 0.0
The expressions x − x and 0.0 are not equivalent if x is a NaN or infinite.
0 × x → 0.0
The expressions 0 × x and 0.0 are not equivalent if x is a NaN, infinite, or −0.
x+0→x
The expressions x + 0 and x are not equivalent if x is −0, because (−0) + (+0) yields +0 (in the default rounding direction), not −0.
x−0→x
(+0) − (+0) yields −0 when rounding is downward (toward −∞), but +0 otherwise, and (−0)−(+0) always yields −0; so, if the state of the FENV_ACCESS pragma is "off", promising default rounding, then the implementation can replace x − 0 by x, even if x might be zero.
−x ↔ 0 − x
The expressions −x and 0−x are not equivalent if x is +0, because −(+0) yields −0, but 0 − (+0) yields +0 (unless rounding is downward).
For expressions of decimal floating types, transformations must preserve quantum exponents, as well as numerical values (5.2.4.2.3). 452) Implementations might have non-required features that invalidate these and other transformations that remove arithmetic operators. Examples include strict support for signaling NaNs (an optional feature) and alternate exception handling (not included in this specification). 453) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities. Examples include: 1/(1/±∞) is ±∞ and conj(csqrt(z)) is csqrt(conj(z)), for complex z.
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EXAMPLE 1. × x → x is valid for decimal floating-point expressions x, but 1.0 × x → x is not: 1. × 12.34 1.0 × 12.34
= (+1, 1, 0) × (+1, 1234, −2) yields (+1, 1234, −2) = 12.34 = (+1, 10, −1) × (+1, 1234, −2) yields (+1, 12340, −3) = 12.340
In the second case, the factor 12.34 and the result 12.340 have different quantum exponents, demonstrating that 1.0 × x and x are not equivalent expressions.
F.9.3 1
Relational operators
x ̸= x → false
The expression x ̸= x is true if x is a NaN.
x = x → true
The expression x = x is false if x is a NaN.
x < y → isless(x, y) (and similarly for ≤, >, ≥) Though equal, these expressions are not equivalent because of side effects when x or y is a NaN and the state of the FENV_ACCESS pragma is "on". This transformation, which would be desirable if extra code were required to cause the "invalid" floating-point exception for unordered cases, could be performed provided the state of the FENV_ACCESS pragma is "off". The sense of relational operators shall be maintained. This includes handling unordered cases as expressed by the source code. 2
EXAMPLE // calls g and raises "invalid" if a and b are unordered if (a < b) f(); else g();
is not equivalent to // calls f and raises "invalid" if a and b are unordered if (a >= b) g(); else f();
nor to // calls f without raising "invalid" if a and b are unordered if (isgreaterequal(a,b)) g(); else f();
nor, unless the state of the FENV_ACCESS pragma is "off", to // calls g without raising "invalid" if a and b are unordered if (isless(a,b)) f(); else g();
but is equivalent to if (!(a < g(); else f();
§ F.9.3
b))
IEC 60559 floating-point arithmetic
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The implementation shall honor floating-point exceptions raised by execution-time constant arithmetic wherever the state of the FENV_ACCESS pragma is "on". (See F.8.4 and F.8.5.) An operation on constants that raises no floating-point exception can be folded during translation, except, if the state of the FENV_ACCESS pragma is "on", a further check is required to assure that changing the rounding direction to downward does not alter the sign of the result,454) and implementations that support dynamic rounding precision modes shall assure further that the result of the operation raises no floating-point exception when converted to the semantic type of the operation.
F.10
Mathematics <math.h> and <tgmath.h>
1
This subclause contains specifications of <math.h> and <tgmath.h> facilities that are particularly suited for IEC 60559 implementations.
2
The Standard C macro HUGE_VAL and its float and long double analogs, HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive infinities.
3
For each single-argument function f in <math.h> whose mathematical counterpart is symmetric (even), f(-x) is f(x) for all rounding modes and for all x in the (valid) domain of the function. For each single-argument function f in <math.h> whose mathematical counterpart is antisymmetric (odd), f(-x) is -f(x) for the IEC 60559 rounding modes roundTiesToEven, roundTiesToAway, and roundTowardZero, and for all x in the (valid) domain of the function. The atan2 and atan2pi functions are odd in their first argument.
4
Special cases for functions in <math.h> are covered directly or indirectly by IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and (provided the state of the FENV_ACCESS pragma is "on") the floating-point status flags in a manner consistent with IEC 60559 operations.
5
The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a nonzero value.
6
The functions bound to operations in IEC 60559 (F.3) are fully specified by IEC 60559, including rounding behaviors and floating-point exceptions.
7
The "invalid" and "divide-by-zero" floating-point exceptions are raised as specified in subsequent subclauses of this annex.
8
The "overflow" floating-point exception is raised whenever an infinity — or, because of rounding direction, a maximal-magnitude finite number — is returned in lieu of a finite value whose magnitude is too large.
9
The "underflow" floating-point exception is raised whenever a computed result is tiny455) and the returned result is inexact.
10
Whether or when library functions not listed in the "Operation binding" table in F.3 raise the "inexact" floating-point exception is unspecified, unless stated otherwise.
11
Whether or when library functions not listed in the "Operation binding" table in F.3 raise a spurious "underflow" floating-point exception is not specified by this annex.456)
12
As implied by F.8.6, library functions do not raise spurious "invalid", "overflow", or "divide-by-zero" floating-point exceptions (detectable by the user).
13
Whether the functions not listed in the "Operation binding" table in F.3 honor the rounding direction mode is implementation-defined, unless explicitly specified otherwise.
14
Functions with a NaN argument return a NaN result and raise no floating-point exception, except where explicitly stated otherwise.
15
The specifications in the following subclauses append to the definitions in <math.h>. For families of functions, the specifications apply to all the functions even though only the principal function 454) 0-0 yields -0 instead of +0 just when the rounding direction is downward. 455) Tiny generally indicates having a magnitude in the subnormal range. See IEC 60559 for details about detecting tininess. 456) It is intended that spurious "underflow" and "inexact" floating-point exceptions are raised only if avoiding them would be too costly. 7.12.1 specifies that if math_errhandling & MATH_ERREXCEPT is nonzero, then an "underflow" floating-point exception shall not be raised unless an underflow range error occurs.
518
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is shown. Unless otherwise specified, where the symbol "±" occurs in both an argument and the result, the result has the same sign as the argument.
16
17
1
Recommended practice IEC 60559 specifies correct rounding for the operations in the F.3 table of operations recommended by IEC 60559, and thereby preserves useful mathematical properties such as symmetry, monotonicity, and periodicity. The corresponding functions with (potentially) reserved cr_-prefixed names (7.33.8) do the same. The C functions in the table, however, are not required to be correctly rounded, but implementations should still preserve as many of these useful mathematical properties as possible. If a function with one or more NaN arguments returns a NaN result, the result should be the same as one of the NaN arguments (after possible type conversion), except perhaps for the sign.
F.10.1
Trigonometric functions
F.10.1.1
The acos functions
— acos(1) returns +0. — acos(x) returns a NaN and raises the "invalid" floating-point exception for |x| > 1. F.10.1.2
1
The asin functions
— asin(±0) returns ±0. — asin(x) returns a NaN and raises the "invalid" floating-point exception for |x| > 1. F.10.1.3
1
The atan functions
— atan(±0) returns ±0. — atan(±∞) returns ± π2 . F.10.1.4
1
The atan2 functions
— atan2(±0, −0) returns ±π.457) — atan2(±0, +0) returns ±0. — atan2(±0, x) returns ±π for x < 0. — atan2(±0, x) returns ±0 for x > 0. — atan2(y, ±0) returns − π2 for y < 0. — atan2(y, ±0) returns π2 for y > 0. — atan2(±y, −∞) returns ±π for finite y > 0. — atan2(±y, +∞) returns ±0 for finite y > 0. — atan2(±∞, x) returns ± π2 for finite x. — atan2(±∞, −∞) returns ± 3π 4 . — atan2(±∞, +∞) returns ± π4 . F.10.1.5
1
The cos functions
— cos(±0) returns 1. — cos(±∞) returns a NaN and raises the "invalid" floating-point exception. 457) atan2(0, 0) does not raise the "invalid" floating-point exception, nor does atan2(y, 0) raise the "divide-by-zero" floatingpoint exception.
§ F.10.1.5
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— sin(±0) returns ±0. — sin(±∞) returns a NaN and raises the "invalid" floating-point exception. F.10.1.7
1
The tan functions
— tan(±0) returns ±0. — tan(±∞) returns a NaN and raises the "invalid" floating-point exception. F.10.1.8
1
The acospi functions
— acospi(+1) returns +0. — acospi(x) returns a NaN and raises the "invalid" floating-point exception for |x| > 1. F.10.1.9
1
The asinpi functions
— asinpi(±0) returns ±0. — asinpi(x) returns a NaN and raises the "invalid" floating-point exception for |x| > 1. F.10.1.10
1
The atanpi functions
— atanpi(±0) returns ±0. — atanpi(±∞) returns ± 21 . F.10.1.11
1
The atan2pi functions
— atan2pi(±0, −0) returns ±1.458) — atan2pi(±0, +0) returns ±0. — atan2pi(±0, x) returns ±1 for x < 0. — atan2pi(±0, x) returns ±0 for x > 0. — atan2pi(y, ±0) returns − 12 for y < 0. — atan2pi(y, ±0) returns + 12 for y > 0. — atan2pi(±y, −∞) returns ±1 for finite y > 0. — atan2pi(±y, +∞) returns ±0 for finite y > 0. — atan2pi(±∞, x) returns ± 21 for finite x. — atan2pi(±∞, −∞) returns ± 43 . — atan2pi(±∞, +∞) returns ± 14 . F.10.1.12
1
The cospi functions
— cospi(±0) returns 1. — cospi(n + 12 ) returns +0, for integers n. — cospi(±∞) returns a NaN and raises the "invalid" floating-point exception. 458) atan2pi(0, 0) does not raise the "invalid" floating-point exception, nor does atan2pi(y, 0) raise the "divide-by-zero" floating-point exception.
520
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The sinpi functions
— sinpi(±0) returns ±0. — sinpi(±n) returns ±0, for positive integers n. — sinpi(±∞) returns a NaN and raises the "invalid" floating-point exception. F.10.1.14
1
The tanpi functions
— tanpi(±0) returns ±0. — tanpi(n) returns +0, for positive even and negative odd integers n. — tanpi(n) returns −0, for positive odd and negative even integers n. — tanpi(n + 12 ) returns +∞ and raises the "divide-by-zero" floating-point exception, for even integers n. — tanpi(n + 12 ) returns −∞ and raises the "divide-by-zero" floating-point exception, for odd integers n. — tanpi(±∞) returns a NaN and raises the "invalid" floating-point exception.
1
F.10.2
Hyperbolic functions
F.10.2.1
The acosh functions
— acosh(1) returns +0. — acosh(x) returns a NaN and raises the "invalid" floating-point exception for x < 1. — acosh(+∞) returns +∞. F.10.2.2
1
The asinh functions
— asinh(±0) returns ±0. — asinh(±∞) returns ±∞. F.10.2.3
1
The atanh functions
— atanh(±0) returns ±0. — atanh(±1) returns ±∞ and raises the "divide-by-zero" floating-point exception. — atanh(x) returns a NaN and raises the "invalid" floating-point exception for |x| > 1. F.10.2.4
1
The cosh functions
— cosh(±0) returns 1. — cosh(±∞) returns +∞. F.10.2.5
1
The sinh functions
— sinh(±0) returns ±0. — sinh(±∞) returns ±∞. F.10.2.6
1
The tanh functions
— tanh(±0) returns ±0. — tanh(±∞) returns ±1. § F.10.2.6
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F.10.3
Exponential and logarithmic functions
F.10.3.1
The exp functions
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— exp(±0) returns 1. — exp(−∞) returns +0. — exp(+∞) returns +∞. F.10.3.2
1
The exp10 functions
— exp10(±0) returns 1. — exp10(−∞) returns +0. — exp10(+∞) returns +∞. F.10.3.3
1
The exp10m1 functions
— exp10m1(±0) returns ±0. — exp10m1(−∞) returns −1. — exp10m1(+∞) returns +∞. F.10.3.4
1
The exp2 functions
— exp2(±0) returns 1. — exp2(−∞) returns +0. — exp2(+∞) returns +∞. F.10.3.5
1
The exp2m1 functions
— exp2m1(±0) returns ±0. — exp2m1(−∞) returns −1. — exp2m1(+∞) returns +∞. F.10.3.6
1
The expm1 functions
— expm1(±0) returns ±0. — expm1(−∞) returns −1. — expm1(+∞) returns +∞. F.10.3.7
1
The frexp functions
— frexp(±0, exp) returns ±0, and stores 0 in the object pointed to by exp. — frexp(±∞, exp) returns ±∞, and stores an unspecified value in the object pointed to by exp. — frexp(NaN, exp) stores an unspecified value in the object pointed to by exp (and returns a NaN).
2
frexp raises no floating-point exceptions if value is not a signaling NaN.
3
The returned value is independent of the current rounding direction mode.
4
On a binary system, the body of the frexp function might be { *exp = (value == 0 || !isinfinite(value)) ? 0: (int)(1 + logb(value)); return scalbn(value, -(*exp)); }
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F.10.3.8 The ilogb functions When the correct result is representable in the range of the return type, the returned value is exact and is independent of the current rounding direction mode.
2
If the correct result is outside the range of the return type, the numeric result is unspecified and the "invalid" floating-point exception is raised.
3
ilogb(x), for x zero, infinite, or NaN, raises the "invalid" floating-point exception and returns the value specified in 7.12.6.8.
1
1
F.10.3.9 The ldexp functions On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp). F.10.3.10 The llogb functions The llogb functions are equivalent to the ilogb functions, except that the llogb functions determine a result in the long int type. F.10.3.11
1
The log functions
— log(±0) returns −∞ and raises the "divide-by-zero" floating-point exception. — log(1) returns +0. — log(x) returns a NaN and raises the "invalid" floating-point exception for x < 0. — log(+∞) returns +∞. F.10.3.12
1
The log10 functions
— log10(±0) returns −∞ and raises the "divide-by-zero" floating-point exception. — log10(1) returns +0. — log10(x) returns a NaN and raises the "invalid" floating-point exception for x < 0. — log10(+∞) returns +∞. F.10.3.13
1
The log10p1 functions
— log10p1(±0) returns ±0. — log10p1(−1) returns −∞ and raises the "divide-by-zero" floating-point exception. — log10p1(x) returns a NaN and raises the "invalid" floating-point exception for x < −1. — log10p1(+∞) returns +∞. F.10.3.14
1
The log1p and logp1 functions
— logp1(±0) returns ±0. — logp1(−1) returns −∞ and raises the "divide-by-zero" floating-point exception. — logp1(x) returns a NaN and raises the "invalid" floating-point exception for x < −1. — logp1(+∞) returns +∞. The log1p functions are equivalent to the logp1 functions. F.10.3.15
1
The log2 functions
— log2(±0) returns −∞ and raises the "divide-by-zero" floating-point exception. — log2(1) returns +0. — log2(x) returns a NaN and raises the "invalid" floating-point exception for x < 0. — log2(+∞) returns +∞. § F.10.3.15
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The log2p1 functions
— log2p1(±0) returns ±0. — log2p1(−1) returns −∞ and raises the "divide-by-zero" floating-point exception. — log2p1(x) returns a NaN and raises the "invalid" floating-point exception for x < −1. — log2p1(+∞) returns +∞. F.10.3.17
1
The logb functions
— logb(±0) returns −∞ and raises the "divide-by-zero" floating-point exception. — logb(±∞) returns +∞.
2
The returned value is exact and is independent of the current rounding direction mode. F.10.3.18
1
The modf functions
— modf(±x, iptr) returns a result with the same sign as x. — modf(±∞, iptr) returns ±0 and stores ±∞ in the object pointed to by iptr. — modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a NaN).
2
The returned values are exact and are independent of the current rounding direction mode.
3
modf behaves as though implemented by #include <math.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON double modf(double value, double *iptr) { int save_round = fegetround(); fesetround(FE_TOWARDZERO); *iptr = nearbyint(value); fesetround(save_round); return copysign( isinf(value) ? 0.0: value - (*iptr), value); }
F.10.3.19 1
The scalbn and scalbln functions
— scalbn(±0, n) returns ±0. — scalbn(x, 0) returns x. — scalbn(±∞, n) returns ±∞.
2
1
If the calculation does not overflow or underflow, the returned value is exact and independent of the current rounding direction mode.
F.10.4
Power and absolute value functions
F.10.4.1
The cbrt functions
— cbrt(±0) returns ±0. — cbrt(±∞) returns ±∞. 524
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F.10.4.2 The compoundn functions — compoundn(x, 0) returns 1 for x ≥ −1 or x a NaN. — compoundn(x, n) returns a NaN and raises the "invalid" floating-point exception for x < −1. — compoundn(−1, n) returns +∞ and raises the divide-by-zero floating-point exception for n < 0. — compoundn(−1, n) returns +0 for n > 0. — compoundn(±∞, n) returns +∞ for n > 0. — compoundn(±∞, n) returns +0 for n < 0.
1
F.10.4.3 The fabs functions — fabs(±0) returns +0. — fabs(±∞) returns +∞.
2
fabs(x) raises no floating-point exceptions, even if x is a signaling NaN. The returned value is
independent of the current rounding direction mode.
1
F.10.4.4 The hypot functions — hypot(x, y), hypot(y, x), and hypot(x, −y) are equivalent. — hypot(x, ±0) returns the absolute value of x, if x is not a NaN. — hypot(±∞, y) returns +∞, even if y is a NaN. — hypot(x, NaN) returns a NaN, if x is not ±∞.
1
F.10.4.5 The pow functions — pow(±0, y) returns ±∞ and raises the "divide-by-zero" floating-point exception for y an odd integer < 0. — pow(±0, y) returns +∞ and raises the "divide-by-zero" floating-point exception for y < 0, finite, and not an odd integer. — pow(±0, −∞) returns +∞. — pow(±0, y) returns ±0 for y an odd integer > 0. — pow(±0, y) returns +0 for y > 0 and not an odd integer. — pow(−1, ±∞) returns 1. — pow(+1, y) returns 1 for any y, even a NaN. — pow(x, ±0) returns 1 for any x, even a NaN. — pow(x, y) returns a NaN and raises the "invalid" floating-point exception for finite x < 0 and finite non-integer y. — pow(x, −∞) returns +∞ for |x| < 1. — pow(x, −∞) returns +0 for |x| > 1. — pow(x, +∞) returns +0 for |x| < 1. — pow(x, +∞) returns +∞ for |x| > 1. — pow(−∞, y) returns −0 for y an odd integer < 0. — pow(−∞, y) returns +0 for y < 0 and not an odd integer. — pow(−∞, y) returns −∞ for y an odd integer > 0. — pow(−∞, y) returns +∞ for y > 0 and not an odd integer. — pow(+∞, y) returns +0 for y < 0. — pow(+∞, y) returns +∞ for y > 0. § F.10.4.5
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The pown functions
— pown(x, 0) returns 1 for all x not a signalling NaN. — pown(±0, n) returns ±∞ and raises the "divide-by-zero" floating-point exception for odd n < 0. — pown(±0, n) returns +∞ and raises the "divide-by-zero" floating-point exception for even n < 0. — pown(±0, n) returns +0 for even n > 0. — pown(±0, n) returns ±0 for odd n > 0. — pown(±∞, n) is equivalent to pown(±0, −n) for n not 0, except that the "divide-by-zero" floating-point exception is not raised. F.10.4.7
1
The powr functions
— powr(x, ±0) returns 1 for finite x > 0. — powr(±0, y) returns +∞ and raises the "divide-by-zero" floating-point exception for finite y < 0. — powr(±0, −∞) returns +∞. — powr(±0, y) returns +0 for y > 0. — powr(+1, y) returns 1 for finite y. — powr(+1, ±∞) returns a NaN and raises the "invalid" floating-point exception. — powr(x, y) returns a NaN and raises the "invalid" floating-point exception for x < 0. — powr(±0, ±0) returns a NaN and raises the "invalid" floating-point exception. — powr(+∞, ±0) returns a NaN and raises the "invalid" floating-point exception. F.10.4.8
1
The rootn functions
— rootn(±0, n) returns ±∞ and raises the "divide-by-zero" floating-point exception for odd n < 0. — rootn(±0, n) returns +∞ and raises the "divide-by-zero" floating-point exception for even n < 0. — rootn(±0, n) returns +0 for even n > 0. — rootn(±0, n) returns ±0 for odd n > 0. — rootn(+∞, n) returns +∞ for n > 0. — rootn(−∞, n) returns −∞ for odd n > 0. — rootn(−∞, n) returns a NaN and raises the "invalid" floating-point exception for even n > 0. — rootn(+∞, n) returns +0 for n < 0. — rootn(−∞, n) returns −0 for odd n < 0. — rootn(−∞, n) returns a NaN and raises the "invalid" floating-point exception for even n < 0. — rootn(x, 0) returns a NaN and raises the "invalid" floating-point exception for all x (including NaN). — rootn(x, n) returns a NaN and raises the "invalid" floating-point exception for x < 0 and n even. 526
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The rsqrt functions
— rsqrt(±0) returns ±∞ and raises the "divide-by-zero" floating-point exception. — rsqrt(x) returns a NaN and raises the "invalid" floating-point exception for x < 0. — rsqrt(+∞) returns +0. F.10.4.10
1
The sqrt functions
— sqrt(±0) returns ±0. — sqrt(+∞) returns +∞. — sqrt(x) returns a NaN and raises the "invalid" floating-point exception for x < 0.
2
1
The returned value is dependent on the current rounding direction mode.
F.10.5
Error and gamma functions
F.10.5.1
The erf functions
— erf(±0) returns ±0. — erf(±∞) returns ±1. F.10.5.2
1
The erfc functions
— erfc(−∞) returns 2. — erfc(+∞) returns +0. F.10.5.3
1
The lgamma functions
— lgamma(1) returns +0. — lgamma(2) returns +0. — lgamma(x) returns +∞ and raises the "divide-by-zero" floating-point exception for x a negative integer or zero. — lgamma(−∞) returns +∞. — lgamma(+∞) returns +∞. F.10.5.4
1
The tgamma functions
— tgamma(±0) returns ±∞ and raises the "divide-by-zero" floating-point exception. — tgamma(x) returns a NaN and raises the "invalid" floating-point exception for x a negative integer. — tgamma(−∞) returns a NaN and raises the "invalid" floating-point exception. — tgamma(+∞) returns +∞.
1
F.10.6
Nearest integer functions
F.10.6.1
The ceil functions
— ceil(±0) returns ±0. — ceil(±∞) returns ±∞.
2
The returned value is exact and is independent of the current rounding direction mode.
3
The double version of ceil behaves as though implemented by § F.10.6.1
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#include <math.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON double ceil(double x) { double result; int save_round = fegetround(); fesetround(FE_UPWARD); result = nearbyint(x); fesetround(save_round); return result; }
F.10.6.2 1
The floor functions
— floor(±0) returns ±0. — floor(±∞) returns ±∞.
2
The returned value is exact and is independent of the current rounding direction mode.
3
See the sample implementation for ceil in F.10.6.1.
1
F.10.6.3 The nearbyint functions The nearbyint functions use IEC 60559 rounding according to the current rounding direction. They do not raise the "inexact" floating-point exception if the result differs in value from the argument. — nearbyint(±0) returns ±0 (for all rounding directions). — nearbyint(±∞) returns ±∞ (for all rounding directions).
1
1
F.10.6.4 The rint functions The rint functions differ from the nearbyint functions only in that they do raise the "inexact" floating-point exception if the result differs in value from the argument. F.10.6.5 The lrint and llrint functions The lrint and llrint functions provide floating-to-integer conversion as prescribed by IEC 60559. They round according to the current rounding direction. If the rounded value is outside the range of the return type, the numeric result is unspecified and the "invalid" floating-point exception is raised. When they raise no other floating-point exception and the result differs from the argument, they raise the "inexact" floating-point exception. F.10.6.6
1
The round functions
— round(±0) returns ±0. — round(±∞) returns ±∞.
2
The returned value is independent of the current rounding direction mode.
3
The double version of round behaves as though implemented by459) : #include <math.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON double round(double x) { double result; fenv_t save_env; 459) This code does not handle signaling NaNs as required of implementations that define FE_SNANS_ALWAYS_SIGNAL.
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feholdexcept(&save_env); result = rint(x); if (fetestexcept(FE_INEXACT)) { fesetround(FE_TOWARDZERO); result = rint(copysign(0.5 + fabs(x), x)); feclearexcept(FE_INEXACT); } feupdateenv(&save_env); return result; }
1
F.10.6.7 The lround and llround functions The lround and llround functions differ from the lrint and llrint functions with the default rounding direction just in that the lround and llround functions round halfway cases away from zero and need not raise the "inexact" floating-point exception for non-integer arguments that round to within the range of the return type. F.10.6.8
1
The roundeven functions roundeven returns: — ±0 for an input of ±0. — ±∞ for an input of ±∞.
2
The returned value is exact and is independent of the current rounding direction mode.
3
See the sample implementation for ceil in F.10.6.1.
1
F.10.6.9 The trunc functions The trunc functions use IEC 60559 rounding toward zero (regardless of the current rounding direction). — trunc(±0) returns ±0. — trunc(±∞) returns ±∞.
2
1
2
1
2
1
The returned value is exact and is independent of the current rounding direction mode. F.10.6.10 The fromfp and ufromfp functions The fromfp and ufromfp functions raise the "invalid" floating-point exception and return a NaN if the argument width is zero or if the floating-point argument x is infinite or NaN or rounds to an integral value that is outside the range determined by the argument width (see 7.12.9.10). These functions do not raise the "inexact" floating-point exception. F.10.6.11 The fromfpx and ufromfpx functions The fromfpx and ufromfpx functions raise the "invalid" floating-point exception and return a NaN if the argument width is zero or if the floating-point argument x is infinite or NaN or rounds to an integral value that is outside the range determined by the argument width (see 7.12.9.11). These functions raise the "inexact" floating-point exception if a valid result differs in value from the floating-point argument x.
F.10.7
Remainder functions
F.10.7.1
The fmod functions
— fmod(±0, y) returns ±0 for y not zero. — fmod(x, y) returns a NaN and raises the "invalid" floating-point exception for x infinite or y zero (and neither is a NaN). § F.10.7.1
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— fmod(x, ±∞) returns x for finite x. 2
When subnormal results are supported, the returned value is exact and is independent of the current rounding direction mode.
3
The double version of fmod behaves as though implemented by #include <math.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON double fmod(double x, double y) { double result; result = remainder(fabs(x), (y = fabs(y))); if (signbit(result)) result += y; return copysign(result, x); }
1
F.10.7.2 The remainder functions — remainder(±0, y) returns ±0 for y not zero. — remainder(x, y) returns a NaN and raises the "invalid" floating-point exception for x infinite or y zero (and neither is a NaN). — remainder(x, ±∞) returns x for finite x.
2
When subnormal results are supported, the returned value is exact and is independent of the current rounding direction mode.
1
F.10.7.3 The remquo functions The remquo functions follow the specifications for the remainder functions.
2
If a NaN is returned, the value stored in the object pointed to by quo is unspecified.
3
When subnormal results are supported, the returned value is exact and is independent of the current rounding direction mode.
F.10.8
Manipulation functions
F.10.8.1
1
The copysign functions copysign(x, y) raises no floating-point exceptions, even if x or y is a signaling NaN. The returned value is independent of the current rounding direction mode.
1
F.10.8.2 The nan functions All IEC 60559 implementations support quiet NaNs, in all floating formats.
2
The returned value is exact and is independent of the current rounding direction mode.
1
F.10.8.3 The nextafter functions — nextafter(x, y) raises the "overflow" and "inexact" floating-point exceptions for x finite and the function value infinite. — nextafter(x, y) raises the "underflow" and "inexact" floating-point exceptions for the function value subnormal or zero and x ̸= y.
2
1 2
Even though underflow or overflow can occur, the returned value is independent of the current rounding direction mode. F.10.8.4 The nexttoward functions No additional requirements beyond those on nextafter. Even though underflow or overflow can occur, the returned value is independent of the current rounding direction mode. 530
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The nextup functions
— nextup(+∞) returns +∞. — nextup(−∞) returns the largest-magnitude negative finite number in the type of the function.
2
nextup(x) raises no floating-point exceptions if x is not a signaling NaN. The returned value is
independent of the current rounding direction mode. F.10.8.6 1
The nextdown functions
— nextdown(−∞) returns −∞. — nextdown(+∞) returns the largest-magnitude positive finite number in the type of the function.
2
nextdown(x) raises no floating-point exceptions if x is not a signaling NaN. The returned value is
independent of the current rounding direction mode. F.10.8.7 1
The canonicalize functions
The canonicalize functions produce460) the canonical version of the representation in the object pointed to by the argument x. If the input *x is a signaling NaN, the "invalid" floating-point exception is raised and a (canonical) quiet NaN (which should be the canonical version of that signaling NaN made quiet) is produced. For quiet NaN, infinity, and finite inputs, the functions raise no floating-point exceptions.
F.10.9 1
Maximum, minimum, and positive difference functions
F.10.9.1 The fdim functions No additional requirements.
1
F.10.9.2 The fmax functions If just one argument is a NaN, the fmax functions return the other argument (if both arguments are NaNs, the functions return a NaN).
2
The returned value is exact and is independent of the current rounding direction mode.
3
The body of the fmax function might be461) : { double r = (isgreaterequal(x, y) || isnan(y)) ? x : y; (void) canonicalize(&r, &r); return r; }
1
F.10.9.3 The fmin functions The fmin functions are analogous to the fmax functions (see F.10.9.2).
2
The returned value is exact and is independent of the current rounding direction mode.
1
F.10.9.4 The fmaximum, fminimum, fmaximum_mag, and fminimum_mag functions These functions treat NaNs like other functions in <math.h> (see F.10). They differ from the corresponding fmaximum_num, fminimum_num, fmaximum_mag_num, and fminimum_mag_num functions only in their treatment of NaNs. 460) As if
*x * 1e0 were computed.
461) Ideally, fmax would be sensitive to the sign of zero, for example fmax(−0.0, +0.0) would return +0; however, implemen-
tation in software might be impractical. Note also that this implementation does not handle signaling NaNs as required of implementations that define FE_SNANS_ALWAYS_SIGNAL.
§ F.10.9.4
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The fmaximum_num, fminimum_num, fmaximum_mag_num, and fminimum_mag_num functions These functions return the number if one argument is a number and the other is a quiet or signaling NaN. If both arguments are NaNs, a quiet NaN is returned. If an argument is a signaling NaN, the "invalid" floating-point exception is raised (even though the function returns the number when the other argument is a number). F.10.9.5
1
1
F.10.10
Fused multiply-add
F.10.10.1
The fma functions
— fma(x, y, z) computes xy + z, correctly rounded once. — fma(x, y, z) returns a NaN and optionally raises the "invalid" floating-point exception if one of x and y is infinite, the other is zero, and z is a NaN. — fma(x, y, z) returns a NaN and raises the "invalid" floating-point exception if one of x and y is infinite, the other is zero, and z is not a NaN. — fma(x, y, z) returns a NaN and raises the "invalid" floating-point exception if x times y is an exact infinity and z is also an infinity but with the opposite sign.
F.10.11
Functions that round result to narrower type
1
The functions that round their result to narrower type (7.12.14) are fully specified in IEC 60559. The returned value is dependent on the current rounding direction mode.
2
These functions treat zero and infinite arguments like the corresponding operation or function: +, -, *, /, fma, or sqrt.
F.10.12
Total order functions
1
This subclause specifies the total order functions required by IEC 60559.
2
NOTE 1 These functions are specified only in Annex F because they depend on details of IEC 60559 formats that might not be supported if __STDC_IEC_60559_BFP__ is not defined.
F.10.12.1 The totalorder functions Synopsis #define __STDC_WANT_IEC_60559_EXT__ #include <math.h> #ifdef __STDC_IEC_60559_BFP__
1
int totalorder(const double *x, const double *y); int totalorderf(const float *x, const float *y); int totalorderl(const long double *x, const long double *y); #endif #ifdef __STDC_IEC_60559_DFP__ int totalorderd32(const _Decimal32 *x, const _Decimal32 *y); int totalorderd64(const _Decimal64 *x, const _Decimal64 *y); int totalorderd128(const _Decimal128 *x, const _Decimal128 *y); #endif
2
3
Description The totalorder functions determine whether the total order relationship, defined by IEC 60559, is true for the ordered pair of *x, *y. These functions are fully specified in IEC 60559. These functions are independent of the current rounding direction mode and raise no floating-point exceptions, even if *x or *y is a signaling NaN. Returns The totalorder functions return nonzero if and only if the total order relation is true for the ordered pair of *x, *y. 532
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F.10.12.2 The totalordermag functions Synopsis #define __STDC_WANT_IEC_60559_EXT__ #include <math.h> #ifdef __STDC_IEC_60559_BFP__
1
int totalordermag(const double *x, const double *y); int totalordermagf(const float *x, const float *y); int totalordermagl(const long double *x, const long double *y); #endif #ifdef __STDC_IEC_60559_DFP__ int totalordermagd32(const _Decimal32 *x, const _Decimal32 *y); int totalordermagd64(const _Decimal64 *x, const _Decimal64 *y); int totalordermagd128(const _Decimal128 *x, const _Decimal128 *y); #endif
2
3
Description The totalordermag functions determine whether the total order relationship, defined by IEC 60559, is true for the ordered pair of the magnitudes of *x, *y. These functions are fully specified in IEC 60559. These functions are independent of the current rounding direction mode and raise no floating-point exceptions, even if *x or *y is a signaling NaN. Returns The totalordermag functions return nonzero if and only if the total order relation is true for the ordered pair of the magnitudes of *x, *y.
F.10.13
Payload functions
1
IEC 60559 defines the payload to be information contained in a quiet or signaling NaN. The payload is intended for implementation-defined diagnostic information about the NaN, such as where or how the NaN was created. The implementation interprets the payload as a nonnegative integer suitable for use with the functions in this subclause, which get and set payloads. The implementation may restrict which payloads are admissible for the user to set.
2
NOTE 1 These functions are specified only in Annex F because they depend on details of IEC 60559 formats that might not be supported if __STDC_IEC_60559_BFP__ is not defined.
F.10.13.1 The getpayload functions Synopsis 1
2
#define __STDC_WANT_IEC_60559_EXT__ #include <math.h> #ifdef __STDC_IEC_60559_BFP__ double getpayload(const double *x); float getpayloadf(const float *x); long double getpayloadl(const long double *x); #endif #ifdef __STDC_IEC_60559_DFP__ _Decimal32 getpayloadd32(const _Decimal32 *x); _Decimal64 getpayloadd64(const _Decimal64 *x); _Decimal128 getpayloadd128(const _Decimal128 *x); #endif
Description The getpayload functions extract the payload of a quiet or signaling NaN input and return it as a positive-signed floating-point integer. If *x is not a NaN, the return result is −1. These functions raise no floating-point exceptions, even if *x is a signaling NaN. § F.10.13.1
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Returns The getpayload functions return the payload of the NaN input as a positive-signed floating-point integer. F.10.13.2 The setpayload functions Synopsis #define __STDC_WANT_IEC_60559_EXT__ #include <math.h> #ifdef __STDC_IEC_60559_BFP__
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int setpayload(double *res, double pl); int setpayloadf(float *res, float pl); int setpayloadl(long double *res, long double pl); #endif #ifdef __STDC_IEC_60559_DFP__ int setpayloadd32(_Decimal32 *res, _Decimal32 pl); int setpayloadd64(_Decimal64 *res, _Decimal64 pl); int setpayloadd128(_Decimal128 *res, _Decimal128 pl); #endif
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Description The setpayload functions create a quiet NaN with the payload specified by pl and a zero sign bit and store that NaN in the object pointed to by *res. If pl is not a floating-point integer representing an admissible payload, *res is set to +0. Returns If the setpayload functions stored the specified NaN, they return a zero value, otherwise a nonzero value (and *res is set to +0). F.10.13.3 The setpayloadsig functions Synopsis #define __STDC_WANT_IEC_60559_EXT__ #include <math.h> #ifdef __STDC_IEC_60559_BFP__ int setpayloadsig(double *res, double pl); int setpayloadsigf(float *res, float pl); int setpayloadsigl(long double *res, long double pl); #endif #ifdef __STDC_IEC_60559_DFP__ int setpayloadsigd32(_Decimal32 *res, _Decimal32 pl); int setpayloadsigd64(_Decimal64 *res, _Decimal64 pl); int setpayloadsigd128(_Decimal128 *res, _Decimal128 pl); #endif
1
2
3
Description The setpayloadsig functions create a signaling NaN with the payload specified by pl and a zero sign bit and store that NaN in the object pointed to by *res. If pl is not a floating-point integer representing an admissible payload, *res is set to +0. Returns If the setpayloadsig functions stored the specified NaN, they return a zero value, otherwise a nonzero value (and *res is set to +0).
F.10.14 1
Comparison macros
Relational operators and their corresponding comparison macros (7.12.17) produce equivalent result values, even if argument values are represented in wider formats. Thus, comparison macro arguments represented in formats wider than their semantic types are not converted to the semantic types, 534
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unless the wide evaluation method converts operands of relational operators to their semantic types. The standard wide evaluation methods characterized by FLT_EVAL_METHOD and DEC_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2, 5.2.4.2.3), do not convert operands of relational operators to their semantic types.
1
F.10.14.1 The iseqsig macro The equality operator == and the iseqsig macro produce equivalent results, except that the iseqsig macro raises the "invalid" floating-point exception if an argument is a NaN.
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Annex G (normative)
IEC 60559-compatible complex arithmetic G.1
Introduction
1
This annex supplements Annex F to specify complex arithmetic for compatibility with IEC 60559 real floating-point arithmetic. An implementation that defines __STDC_IEC_60559_COMPLEX__ or __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.462)
1
There is a new keyword _Imaginary, which is used to specify imaginary types. It is used as a type specifier within declaration specifiers in the same way as _Complex is (thus, float _Imaginary is a valid type name).
2
There are three imaginary types, designated as float _Imaginary, double _Imaginary, and long double _Imaginary. The imaginary types (along with the real floating and complex types) are floating types.
3
For imaginary types, the corresponding real type is given by deleting the keyword _Imaginary from the type name.
4
Each imaginary type has the same representation and alignment requirements as the corresponding real type. The value of an object of imaginary type is the value of the real representation times the imaginary unit.
5
The imaginary type domain comprises the imaginary types.
G.2
G.3 1
Types
Conventions
A complex or imaginary value with at least one infinite part is regarded as an infinity (even if its other part is a quiet NaN). A complex or imaginary value is a finite number if each of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is a zero if each of its parts is a zero.
G.4 Conversions G.4.1 Imaginary types 1
Conversions among imaginary types follow rules analogous to those for real floating types.
G.4.2
Real and imaginary
1
When a value of imaginary type is converted to a real type other than bool463) , the result is a positive zero.
2
When a value of real type is converted to an imaginary type, the result is a positive imaginary zero.
G.4.3
Imaginary and complex
1
When a value of imaginary type is converted to a complex type, the real part of the complex result value is a positive zero and the imaginary part of the complex result value is determined by the conversion rules for the corresponding real types.
2
When a value of complex type is converted to an imaginary type, the real part of the complex value is discarded and the value of the imaginary part is converted according to the conversion rules for the corresponding real types. 462) Implementations that do not define __STDC_IEC_60559_COMPLEX__ or __STDC_IEC_559_COMPLEX__ are not required to conform to these specifications. The use of __STDC_IEC_559_COMPLEX__ for this purpose is obsolescent and should be avoided in new code. 463) See 6.3.1.2.
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Binary operators
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The following subclauses supplement 6.5 to specify the type of the result for an operation with an imaginary operand.
2
For most operand types, the value of the result of a binary operator with an imaginary or complex operand is completely determined, with reference to real arithmetic, by the usual mathematical formula. For some operand types, the usual mathematical formula is problematic because of its treatment of infinities and because of undue overflow or underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is not completely determined.
G.5.1 1
2
Multiplicative operators
Semantics If one operand has real type and the other operand has imaginary type, then the result has imaginary type. If both operands have imaginary type, then the result has real type. (If either operand has complex type, then the result has complex type.) If the operands are not both complex, then the result and floating-point exception behavior of the * operator is defined by the usual mathematical formula: *
x iy x + iy 3
iv i(xv) (−y)v ((−y)v) + i(xv)
u + iv (xu) + i(xv) ((−y)v) + i(yu)
If the second operand is not complex, then the result and floating-point exception behavior of the / operator is defined by the usual mathematical formula: /
x iy x + iy 4
u xu i(yu) (xu) + i(yu)
u x/u i(y/u) (x/u) + i(y/u)
iv i((−x)/v) y/v (y/v) + i((−x)/v)
The * and / operators satisfy the following infinity properties for all real, imaginary, and complex operands:464) — if one operand is an infinity and the other operand is a nonzero finite number or an infinity, then the result of the * operator is an infinity; — if the first operand is an infinity and the second operand is a finite number, then the result of the / operator is an infinity; — if the first operand is a finite number and the second operand is an infinity, then the result of the / operator is a zero; — if the first operand is a nonzero finite number or an infinity and the second operand is a zero, then the result of the / operator is an infinity.
5
If both operands of the * operator are complex or if the second operand of the / operator is complex, the operator raises floating-point exceptions if appropriate for the calculation of the parts of the result, and may raise spurious floating-point exceptions.
6
EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note that the imaginary unit I has imaginary type (see G.6). #include <math.h> #include <complex.h> /* Multiply z * w ...*/ double complex _Cmultd(double complex z, double complex w) 464) These properties are already implied for those cases covered in the tables, but are required for all cases (at least where the state for CX_LIMITED_RANGE is "off").
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{ #pragma STDC FP_CONTRACT OFF double a, b, c, d, ac, bd, ad, bc, x, y; a = creal(z); b = cimag(z); c = creal(w); d = cimag(w); ac = a * c; bd = b * d; ad = a * d; bc = b * c; x = ac - bd; y = ad + bc; if (isnan(x) && isnan(y)) { /* Recover infinities that computed as NaN+iNaN ... */ int recalc = 0; if (isinf(a) || isinf(b)) { // z is infinite /* "Box" the infinity and change NaNs in the other factor to 0 */ a = copysign(isinf(a) ? 1.0: 0.0, a); b = copysign(isinf(b) ? 1.0: 0.0, b); if (isnan(c)) c = copysign(0.0, c); if (isnan(d)) d = copysign(0.0, d); recalc = 1; } if (isinf(c) || isinf(d)) { // w is infinite /* "Box" the infinity and change NaNs in the other factor to 0 */ c = copysign(isinf(c) ? 1.0: 0.0, c); d = copysign(isinf(d) ? 1.0: 0.0, d); if (isnan(a)) a = copysign(0.0, a); if (isnan(b)) b = copysign(0.0, b); recalc = 1; } if (!recalc && (isinf(ac) || isinf(bd) || isinf(ad) || isinf(bc))) { /* Recover infinities from overflow by changing NaNs to 0 ... */ if (isnan(a)) a = copysign(0.0, a); if (isnan(b)) b = copysign(0.0, b); if (isnan(c)) c = copysign(0.0, c); if (isnan(d)) d = copysign(0.0, d); recalc = 1; } if (recalc) { x = INFINITY * (a * c - b * d); y = INFINITY * (a * d + b * c); } } return x + I * y; } 7
This implementation achieves the required treatment of infinities at the cost of only one isnan test in ordinary (finite) cases. It is less than ideal in that undue overflow and underflow could occur.
8
EXAMPLE 2 Division of two double _Complex operands could be implemented as follows. #include <math.h> #include <complex.h> /* Divide z / w ... */ double complex _Cdivd(double complex z, double complex w) { #pragma STDC FP_CONTRACT OFF double a, b, c, d, logbw, denom, x, y; int ilogbw = 0; a = creal(z); b = cimag(z); c = creal(w); d = cimag(w); logbw = logb(fmaximum_num(fabs(c), fabs(d))); if (isfinite(logbw)) {
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ilogbw = (int)logbw; c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw); } denom = c * c + d * d; x = scalbn((a * c + b * d) / denom, -ilogbw); y = scalbn((b * c - a * d) / denom, -ilogbw); /* Recover infinities and zeros that computed as NaN+iNaN; */ /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ...
*/
if (isnan(x) && isnan(y)) { if ((denom == 0.0) && (!isnan(a) || !isnan(b))) { x = copysign(INFINITY, c) * a; y = copysign(INFINITY, c) * b; } else if ((isinf(a) || isinf(b)) && isfinite(c) && isfinite(d)) { a = copysign(isinf(a) ? 1.0: 0.0, a); b = copysign(isinf(b) ? 1.0: 0.0, b); x = INFINITY * (a * c + b * d); y = INFINITY * (b * c - a * d); } else if ((logbw == INFINITY) && isfinite(a) && isfinite(b)) { c = copysign(isinf(c) ? 1.0: 0.0, c); d = copysign(isinf(d) ? 1.0: 0.0, d); x = 0.0 * (a * c + b * d); y = 0.0 * (b * c - a * d); } } return x + I * y; } 9
Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than for multiplication. In the spirit of the multiplication example above, this code does not defend against overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of with division, provides better roundoff characteristics.
G.5.2 1
Additive operators
Semantics If both operands have imaginary type, then the result has imaginary type. (If one operand has real type and the other operand has imaginary type, or if either operand has complex type, then the result has complex type.)
2
In all cases the result and floating-point exception behavior of a + or - operator is defined by the usual mathematical formula: + or − u iv u + iv x x±u x±iv (x±u)±iv iy ±u + iy i(y±v) ±u + i(y±v) x + iy (x±u) + iy x + i(y±v) (x±u) + i(y±v)
1
The macros
G.6
Complex arithmetic <complex.h> imaginary
and
§ G.6
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_Imaginary_I
are defined, respectively, as _Imaginary and a constant expression of type float _Imaginary with the value of the imaginary unit. The macro I
is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro imaginary. 2
This subclause contains specifications for the <complex.h> functions that are particularly suited to IEC 60559 implementations. For families of functions, the specifications apply to all of the functions even though only the principal function is shown. Unless otherwise specified, where the symbol "±" occurs in both an argument and the result, the result has the same sign as the argument.
3
The functions are continuous onto both√sides of their branch cuts, taking into account the sign of zero. For example, csqrt(−2±i0) = ±i 2.
4
Since complex and imaginary values are composed of real values, each function may be regarded as computing real values from real values. Except as noted, the functions treat real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a manner consistent with the specifications for real functions in F.10.465)
5
In subsequent subclauses in G.6 "NaN" refers to a quiet NaN. The behavior of signaling NaNs in Annex G is implementation-defined.
6
The functions cimag, conj, cproj, and creal are fully specified for all implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating-point exceptions.
7
Each of the functions cabs and carg is specified by a formula in terms of a real function (whose special cases are covered in Annex F): cabs(x + iy ) = hypot(x, y ) carg(x + iy ) = atan2(y , x)
8
Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by a formula in terms of other complex functions (whose special cases are specified below): casin(z ) = −i casinh(iz ) catan(z ) = −i catanh(iz ) ccos(z ) = ccosh(iz ) csin(z ) = −i csinh(iz ) ctan(z ) = −i ctanh(iz )
9
For the other functions, the following subclauses specify behavior for special cases, including treatment of the "invalid" and "divide-by-zero" floating-point exceptions. For families of functions, the specifications apply to all of the functions even though only the principal function is shown. For a function f satisfying f (conj(z)) = conj(f (z)), the specifications for the upper half-plane imply the specifications for the lower half-plane; if the function f is also either even, f (−z) = f (z), or odd, f (−z) = −f (z), then the specifications for the first quadrant imply the specifications for the other three quadrants.
10
In the following subclauses, cis(y) is defined as cos(y) + i sin(y).
G.6.1 1
Trigonometric functions
G.6.1.1 The cacos functions — cacos(conj(z)) = conj(cacos(z)). — cacos(±0 + i0) returns π2 − i0. 465) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its other part is a quiet NaN.
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— cacos(±0 + iNaN) returns π2 + iNaN. — cacos(x + i∞) returns π2 − i∞, for finite x. — cacos(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for nonzero finite x. — cacos(−∞ + iy) returns π − i∞, for positive-signed finite y. — cacos(+∞ + iy) returns +0 − i∞, for positive-signed finite y. — cacos(−∞ + i∞) returns 3 π4 − i∞. — cacos(+∞ + i∞) returns π4 − i∞. — cacos(±∞ + iNaN) returns NaN±i∞ (where the sign of the imaginary part of the result is unspecified). — cacos(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite y. — cacos(NaN + i∞) returns NaN − i∞. — cacos(NaN + iNaN) returns NaN + iNaN.
1
G.6.2
Hyperbolic functions
G.6.2.1
The cacosh functions
— cacosh(conj(z)) = conj(cacosh(z)). — cacosh(±0 + i0) returns +0 + iπ 2 . — cacosh(x + i∞) returns +∞ + iπ 2 , for finite x. — cacosh(0 + iNaN) returns NaN± iπ 2 (where the sign of the imaginary part of the result is unspecified). — cacosh(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite nonzero x. — cacosh(−∞ + iy) returns +∞ + iπ, for positive-signed finite y. — cacosh(+∞ + iy) returns +∞ + i0, for positive-signed finite y. — cacosh(−∞ + i∞) returns +∞ + i 3π 4 . — cacosh(+∞ + i∞) returns +∞ + iπ 4 . — cacosh(±∞ + iNaN) returns +∞ + iNaN. — cacosh(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite y. — cacosh(NaN + i∞) returns +∞ + iNaN. — cacosh(NaN + iNaN) returns NaN + iNaN. § G.6.2.1
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— casinh(conj(z)) = conj(casinh(z)). and casinh is odd. — casinh(+0 + i0) returns 0 + i0. — casinh(x + i∞) returns +∞ + iπ 2 for positive-signed finite x. — casinh(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite x. — casinh(+∞ + iy) returns +∞ + i0 for positive-signed finite y. — casinh(+∞ + i∞) returns +∞ + iπ 4 . — casinh(+∞ + iNaN) returns +∞ + iNaN. — casinh(NaN + i0) returns NaN + i0. — casinh(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite nonzero y. — casinh(NaN + i∞) returns ±∞ + iNaN (where the sign of the real part of the result is unspecified). — casinh(NaN + iNaN) returns NaN + iNaN. G.6.2.3
1
The catanh functions
— catanh(conj(z)) = conj(catanh(z)). and catanh is odd. — catanh(+0 + i0) returns +0 + i0. — catanh(+0 + iNaN) returns +0 + iNaN. — catanh(+1 + i0) returns +∞ + i0 and raises the "divide-by-zero" floating-point exception. — catanh(x + i∞) returns +0 + iπ 2 , for finite positive-signed x. — catanh(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for nonzero finite x. — catanh(+∞ + iy) returns +0 + iπ 2 , for finite positive-signed y. — catanh(+∞ + i∞) returns +0 + iπ 2 . — catanh(+∞ + iNaN) returns +0 + iNaN. — catanh(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite y. — catanh(NaN + i∞) returns ±0 + iπ 2 (where the sign of the real part of the result is unspecified). — catanh(NaN + iNaN) returns NaN + iNaN. G.6.2.4
1
The ccosh functions
— ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even. — ccosh(+0 + i0) returns 1 + i0. — ccosh(+0 + i∞) returns NaN±i0 (where the sign of the imaginary part of the result is unspecified) and raises the "invalid" floating-point exception. — ccosh(+0 + iNaN) returns NaN±i0 (where the sign of the imaginary part of the result is unspecified). 542
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— ccosh(x + i∞) returns NaN + iNaN and raises the "invalid" floating-point exception, for finite nonzero x. — ccosh(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite nonzero x. — ccosh(+∞ + i0) returns +∞ + i0. — ccosh(+∞ + iy) returns +∞ cis(y), for finite nonzero y. — ccosh(+∞+i∞) returns ±∞+iNaN (where the sign of the real part of the result is unspecified) and raises the "invalid" floating-point exception. — ccosh(+∞ + iNaN) returns +∞ + iNaN. — ccosh(NaN + i0) returns NaN±i0 (where the sign of the imaginary part of the result is unspecified). — ccosh(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for all nonzero numbers y. — ccosh(NaN + iNaN) returns NaN + iNaN. G.6.2.5 1
The csinh functions
— csinh(conj(z)) = conj(csinh(z)). and csinh is odd. — csinh(+0 + i0) returns +0 + i0. — csinh(+0 + i∞) returns ±0 + iNaN (where the sign of the real part of the result is unspecified) and raises the "invalid" floating-point exception. — csinh(+0 + iNaN) returns ±0 + iNaN (where the sign of the real part of the result is unspecified). — csinh(x + i∞) returns NaN + iNaN and raises the "invalid" floating-point exception, for positive finite x. — csinh(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite nonzero x. — csinh(+∞ + i0) returns +∞ + i0. — csinh(+∞ + iy) returns +∞ cis(y), for positive finite y. — csinh(+∞+i∞) returns ±∞+iNaN (where the sign of the real part of the result is unspecified) and raises the "invalid" floating-point exception. — csinh(+∞ + iNaN) returns ±∞ + iNaN (where the sign of the real part of the result is unspecified). — csinh(NaN + i0) returns NaN + i0. — csinh(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for all nonzero numbers y. — csinh(NaN + iNaN) returns NaN + iNaN. § G.6.2.5
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G.6.2.6 The ctanh functions — ctanh(conj(z)) = conj(ctanh(z)) and ctanh is odd. — ctanh(+0 + i0) returns +0 + i0. — ctanh(0 + i∞) returns 0 + iNaN and raises the "invalid" floating-point exception. — ctanh(x + i∞) returns NaN + iNaN and raises the "invalid" floating-point exception, for finite nonzero x. — ctanh(0 + iNaN) returns 0 + iNaN. — ctanh(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite nonzero x. — ctanh(+∞ + iy) returns 1 + i0 sin(2y), for positive-signed finite y. — ctanh(+∞ + i∞) returns 1±i0 (where the sign of the imaginary part of the result is unspecified). — ctanh(+∞ + iNaN) returns 1±i0 (where the sign of the imaginary part of the result is unspecified). — ctanh(NaN + i0) returns NaN + i0. — ctanh(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for all nonzero numbers y. — ctanh(NaN + iNaN) returns NaN + iNaN.
G.6.3 1
Exponential and logarithmic functions
G.6.3.1 The cexp functions — cexp(conj(z)) = conj(cexp(z)). — cexp(±0 + i0) returns 1 + i0. — cexp(x + i∞) returns NaN + iNaN and raises the "invalid" floating-point exception, for finite x. — cexp(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite x. — cexp(+∞ + i0) returns +∞ + i0. — cexp(−∞ + iy) returns +0 cis(y), for finite y. — cexp(+∞ + iy) returns +∞ cis(y), for finite nonzero y. — cexp(−∞ + i∞) returns ±0±i0 (where the signs of the real and imaginary parts of the result are unspecified). — cexp(+∞ + i∞) returns ±∞ + iNaN and raises the "invalid" floating-point exception (where the sign of the real part of the result is unspecified). — cexp(−∞ + iNaN) returns ±0±i0 (where the signs of the real and imaginary parts of the result are unspecified). — cexp(+∞ + iNaN) returns ±∞ + iNaN (where the sign of the real part of the result is unspecified). — cexp(NaN + i0) returns NaN + i0. — cexp(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for all nonzero numbers y. — cexp(NaN + iNaN) returns NaN + iNaN. 544
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The clog functions
— clog(conj(z)) = conj(clog(z)). — clog(−0 + i0) returns −∞ + iπ and raises the "divide-by-zero" floating-point exception. — clog(+0 + i0) returns −∞ + i0 and raises the "divide-by-zero" floating-point exception. — clog(x + i∞) returns +∞ + iπ 2 , for finite x. — clog(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite x. — clog(−∞ + iy) returns +∞ + iπ, for finite positive-signed y. — clog(+∞ + iy) returns +∞ + i0, for finite positive-signed y. — clog(−∞ + i∞) returns +∞ + i 3π 4 . — clog(+∞ + i∞) returns +∞ + iπ 4 . — clog(±∞ + iNaN) returns +∞ + iNaN. — clog(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite y. — clog(NaN + i∞) returns +∞ + iNaN. — clog(NaN + iNaN) returns NaN + iNaN.
G.6.4 1
G.6.4.1 The cpow functions The cpow functions raise floating-point exceptions if appropriate for the calculation of the parts of the result, and may also raise spurious floating-point exceptions.466) G.6.4.2
1
Power and absolute-value functions
The csqrt functions
— csqrt(conj(z)) = conj(csqrt(z)). — csqrt(±0 + i0) returns +0 + i0. — csqrt(x + i∞) returns +∞ + i∞, for all x (including NaN). — csqrt(x + iNaN) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite x. — csqrt(−∞ + iy) returns +0 + i∞, for finite positive-signed y. — csqrt(+∞ + iy) returns +∞ + i0, for finite positive-signed y. — csqrt(−∞ + iNaN) returns NaN±i∞ (where the sign of the imaginary part of the result is unspecified). — csqrt(+∞ + iNaN) returns +∞ + iNaN. — csqrt(NaN + iy) returns NaN + iNaN and optionally raises the "invalid" floating-point exception, for finite y. — csqrt(NaN + iNaN) returns NaN + iNaN. 466) This allows cpow(z, c) to be implemented as cexp(cclog(z)) without precluding implementations that treat special cases more carefully.
§ G.6.4.2
IEC 60559-compatible complex arithmetic
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G.7
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Type-generic math <tgmath.h>
1
Type-generic macros that accept complex arguments also accept imaginary arguments. If an argument is imaginary, the macro expands to an expression whose type is real, imaginary, or complex, as appropriate for the particular function: if the argument is imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and the types of the others are complex.
2
Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh, sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real functions: cos(iy ) = cosh(y ) sin(iy ) = i sinh(y ) tan(iy ) = i tanh(y ) cosh(iy ) = cos(y ) sinh(iy ) = i sin(y ) tanh(iy ) = i tan(y ) asin(iy ) = i asinh(y ) atan(iy ) = i atanh(y ) asinh(iy ) = i asin(y ) atanh(iy ) = i atan(y )
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Annex H (normative)
IEC 60559 interchange and extended types H.1
Introduction
1
This annex specifies extension types for programming language C that have the arithmetic interchange and extended floating-point formats specified in IEC 60559. This annex also includes functions that support the non-arithmetic interchange formats in that standard. This annex was adapted from ISO/IEC TS 18661-3:2015, Floating-point extensions for C —Interchange and extended types.
2
An implementation that defines __STDC_IEC_60559_TYPES__ to 202311L shall conform to the specifications in this annex. An implementation may define __STDC_IEC_60559_TYPES__ only if it defines __STDC_IEC_60559_BFP__, indicating support for IEC 60559 binary floating-point arithmetic, or defines __STDC_IEC_60559_DFP__, indicating support for IEC 60559 decimal floatingpoint arithmetic (or defines both). Where a binding between the C language and IEC 60559 is indicated, the IEC 60559-specified behavior is adopted by reference, unless stated otherwise.
H.2 1
This clause specifies types that support IEC 60559 arithmetic interchange and extended formats. The encoding conversion functions (H.11.3) and numeric conversion functions for encodings (H.12.3, H.12.4) support the non-arithmetic interchange formats specified in IEC 60559.
H.2.1 1
Types
Interchange floating types
IEC 60559 specifies interchange formats, and their encodings, which can be used for the exchange of floating-point data between implementations. These formats are identified by their radix (binary or decimal) and their storage width N. The two tables below give the C floating-point model parameters467) (5.2.4.2.2) for the IEC 60559 interchange formats, where the function round() rounds to the nearest integer.
Parameter N , storage width in bits p, precision in bits emax , maximum exponent e emin , minimum exponent e
Binary interchange format parameters binary16 binary32 binary64 binary128 16 32 64 128 11 24 53 113 16 128 1024 16384 −13 −125 −1021 −16381
Decimal interchange format parameters Parameter decimal32 decimal64 decimal128 N , storage width in bits 32 64 128 p, precision in bits 7 16 34 emax , maximum exponent e 97 385 6145 emin , minimum exponent e −94 −382 −6142
binaryN (N ≥ 128) N, a multiple of 32 N − round(4 × log2 (N )) + 13 2(N −p−1) 3 − emax
decimalN (N ≥ 32) N, a multiple of 32 9 × (N ÷ 32) − 2 3 × 2((N ÷16)+3) + 1 3 − emax
2
EXAMPLE For the binary160 format, p = 144, emax = 32678 and emin = −32765. For the decimal160 format, p = 43, emax = 24577 and emin = −24574.
3
Types designated: _FloatN
where N is 16, 32, 64, or ≥ 128 and a multiple of 32; and, types designated 467) In IEC 60559, normal floating-point numbers are expressed with the first significant digit to the left of the radix point. Hence the exponent in the C model (shown in the tables) is 1 more than the exponent of the same number in the IEC 60559 model.
§ H.2.1
IEC 60559 interchange and extended types
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_DecimalN
where N ≥ 32 and a multiple of 32, are collectively called the interchange floating types. Each interchange floating type has the IEC 60559 interchange format corresponding to its width (N ) and radix (2 for _FloatN, 10 for _DecimalN). Each interchange floating type is not compatible with any other type. 4
An implementation that defines __STDC_IEC_60559_BFP__ and __STDC_IEC_60559_TYPES__ shall provide _Float32 and _Float64 as interchange floating types with the same representation and alignment requirements as float and double, respectively. If the implementation’s long double type supports an IEC 60559 interchange format of width N > 64, then the implementation shall also provide the type _FloatN as an interchange floating type with the same representation and alignment requirements as long double. The implementation may provide other radix-2 interchange floating types _FloatN; the set of such types supported is implementation-defined.
5
An implementation that defines __STDC_IEC_60559_DFP__ provides the decimal floating types _Decimal32, _Decimal64, and _Decimal128 (6.2.5). If the implementation also defines __STDC_IEC_60559_TYPES__, it may provide other radix-10 interchange floating types _DecimalN; the set of such types supported is implementation-defined.
H.2.2
Non-arithmetic interchange formats
1
An implementation supports IEC 60559 non-arithmetic interchange formats by providing the associated encoding-to-encoding conversion functions (H.11.3.2) in <math.h> and the string-fromencoding functions (H.12.3) and string-to-encoding functions (H.12.4) in <stdlib.h>.
2
An implementation that defines __STDC_IEC_60559_BFP__ and __STDC_IEC_60559_TYPES__ supports some IEC 60559 radix-2 interchange formats as arithmetic formats by providing types _FloatN (as well as float and double) with those formats. The implementation may support other IEC 60559 radix-2 interchange formats as non-arithmetic formats; the set of such formats supported is implementation-defined.
3
An implementation that defines __STDC_IEC_60559_DFP__ and __STDC_IEC_60559_TYPES__ supports some IEC 60559 radix-10 interchange formats as arithmetic formats by providing types _DecimalN with those formats. The implementations may support other IEC 60559 radix-10 interchange formats as non-arithmetic formats; the set of such formats supported is implementationdefined.
H.2.3 1
Extended floating types
For each of its basic formats, IEC 60559 specifies an extended format whose maximum exponent and precision exceed those of the basic format it is associated with. Extended formats are intended for arithmetic with more precision and exponent range than is available in the basic formats used for the input data. The extra precision and range often mitigate round-off error and eliminate overflow and underflow in intermediate computations. The table below gives the minimum values of these parameters, as defined for the C floating-point model (5.2.4.2.2). For all IEC 60559 extended (and interchange) formats, emin = 3 − emax . Extended format parameters for floating-point numbers Extended formats associated with: Parameter binary32 binary64 binary128 decimal64 decimal128 p digits ≥ 32 64 128 22 40 emax ≥ 1024 16384 65536 6145 24577
2
Types designated _Float32x, _Float64x, _Float128x, _Decimal64x, and _Decimal128x support the corresponding IEC 60559 extended formats and are collectively called the extended floating types. The set of values of _Float32x is a subset of the set of values of _Float64x; the set of values of _Float64x is a subset of the set of values of _Float128x. The set of values of _Decimal64x is a subset of the set of values of _Decimal128x. Each extended floating type is not compatible with any other type. An implementation that defines __STDC_IEC_60559_BFP__ 548
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and __STDC_IEC_60559_TYPES__ shall provide _Float32x, and may provide one or both of the types _Float64x and _Float128x. An implementation that defines __STDC_IEC_60559_DFP__ and __STDC_IEC_60559_TYPES__ shall provide _Decimal64x, and may provide _Decimal128x. Which (if any) of the optional extended floating types are provided is implementation-defined. 3
NOTE 1 IEC 60559 does not specify an extended format associated with the decimal32 format, nor does this annex specify an extended type associated with the _Decimal32 type.
4
NOTE 2 The _Float32x type may have the same format as double. The _Decimal64x type may have the same format as _Decimal128.
H.2.4
Classification of real floating types
1
6.2.5 defines standard floating types as a collective name for the types float, double and long double and it defines decimal floating types as a collective name for the types _Decimal32, _Decimal64, and _Decimal128.
2
H.2.1 defines interchange floating types and H.2.3 defines extended floating types.
3
The types _FloatN and _FloatNx are collectively called binary floating types.
4
This subclause broadens decimal floating types to include the types _DecimalN and _DecimalNx, introduced in this annex, as well as _Decimal32, _Decimal64, and _Decimal128.
5
This subclause broadens real floating types to include all interchange floating types and extended floating types, as well as standard floating types.
6
Thus, in this annex, real floating types are classified as follows: — standard floating types, composed of float, double, long double; — decimal floating types, composed of _DecimalN, _DecimalNx; — binary floating types, composed of _FloatN, _FloatNx; — interchange floating types, composed of _FloatN, _DecimalN; and, — extended floating types, composed of _FloatNx, _DecimalNx.
7
NOTE 1 Standard floating types (which have an implementation-defined radix) are not included in either binary floating types (which always have radix 2) or decimal floating types (which always have radix 10).
H.2.5 1
H.2.6 1
Complex types
This subclause broadens the C complex types (6.2.5) to also include similar types whose corresponding real parts have binary floating types. For the types _FloatN and _FloatNx, there are complex types designated respectively as _FloatN _Complex and _FloatNx _Complex. (Complex types are a conditional feature that implementations need not support; see 6.10.9.3.)
Imaginary types
This subclause broadens the C imaginary types (G.2) to also include similar types whose corresponding real parts have binary floating types. For the types _FloatN and _FloatNx, there are imaginary types designated respectively as _FloatN _Imaginary and _FloatNx _Imaginary. The imaginary types (along with the real floating and complex types) are floating types. (Annex G, including imaginary types, is a conditional feature that implementations need not support; see 6.10.9.3.)
H.3
Characteristics in <float.h>
1
This subclause enhances the FLT_EVAL_METHOD and DEC_EVAL_METHOD macros to apply to the types introduced in this annex.
2
If FLT_RADIX is 2, the value of FLT_EVAL_METHOD (5.2.4.2.2) characterizes the use of evaluation formats for standard floating types and for binary floating types: -1
§ H.3
indeterminable; IEC 60559 interchange and extended types
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evaluate all operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of float, to the range and precision of float; evaluate all other operations and constants to the range and precision of the semantic type;
1
evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of double, to the range and precision of double; evaluate all other operations and constants to the range and precision of the semantic type;
2
evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of long double, to the range and precision of long double; evaluate all other operations and constants to the range and precision of the semantic type;
N
where _FloatN is a supported interchange floating type, evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of _FloatN, to the range and precision of _FloatN; evaluate all other operations and constants to the range and precision of the semantic type;
N +1
where _FloatNx is a supported extended floating type, evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of _FloatNx, to the range and precision of _FloatNx; evaluate all other operations and constants to the range and precision of the semantic type.
If FLT_RADIX is not 2, the use of evaluation formats for operations and constants of binary floating types is implementation-defined. 3
4
The implementation-defined value of DEC_EVAL_METHOD (5.2.4.2.3) characterizes the use of evaluation formats for decimal floating types: -1
indeterminable;
0
evaluate all operations and constants just to the range and precision of the type;
1
evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of _Decimal64, to the range and precision of _Decimal64; evaluate all other operations and constants to the range and precision of the semantic type;
2
evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of _Decimal128, to the range and precision of _Decimal128; evaluate all other operations and constants to the range and precision of the semantic type;
N
where _DecimalN is a supported interchange floating type, evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of _DecimalN, to the range and precision of _DecimalN; evaluate all other operations and constants to the range and precision of the semantic type;
N +1
where _DecimalNx is a supported extended floating type, evaluate operations and constants, whose semantic type comprises a set of values that is a strict subset of the values of _DecimalNx, to the range and precision of _DecimalNx; evaluate all other operations and constants to the range and precision of the semantic type.
This subclause also specifies <float.h> macros, analogous to the macros for standard floating types, that characterize binary floating types in terms of the model presented in 5.2.4.2.2. This subclause generalizes the specification of characteristics in 5.2.4.2.3 to include the decimal floating types introduced in this annex. The prefix FLTN_ indicates the type _FloatN or the non-arithmetic binary interchange format of width N . The prefix FLTNX_ indicates the type _FloatNx. The prefix DECN_ indicates the type _DecimalN or the non-arithmetic decimal interchange format of width N . The prefix DECNX_ indicates the type _DecimalNx. The type parameters p, emax , and emin for 550
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extended floating types are for the extended floating type itself, not for the basic format that it extends. 5
If __STDC_WANT_IEC_60559_TYPES_EXT__ is defined (by the user) at the point in the code where <float.h> is first included, the following applies (H.8). For each interchange or extended floating type that the implementation provides, <float.h> shall define the associated macros in the following lists. Conversely, for each such type that the implementation does not provide, <float.h> shall not define the associated macros in the following list, except, the implementation shall define the macros FLTN_DECIMAL_DIG and FLTN_DIG if it supports the IEC 60559 non-arithmetic binary interchange format of width N (H.2.2).
6
The signaling NaN macros FLTN_SNAN DECN_SNAN FLTNX_SNAN DECNX_SNAN
expand to constant expressions of types _FloatN, _DecimalN, _FloatNx, and _DecimalNx respectively, representing a signaling NaN. If an optional unary + or - operator followed by a signaling NaN macro is used for initializing an object of the same type that has static or thread storage duration, the object is initialized with a signaling NaN value. 7
The integer values given in the following lists shall be replaced by integer constant expressions: — radix of exponent representation, b (2 for binary, 10 for decimal) For the standard floating types, this value is implementation-defined and is specified by the macro FLT_RADIX. For the interchange and extended floating types there is no corresponding macro; the radix is an inherent property of the types. — The number of bits in the floating-point significand, p FLTN_MANT_DIG FLTNX_MANT_DIG
— The number of digits in the coefficient, p DECN_MANT_DIG DECNX_MANT_DIG
— number of decimal digits, n, such that any floating-point number with p bits can be rounded to a floating-point number with n decimal digits and back again without change to the value, ⌈1 + p log10 (2)⌉ FLTN_DECIMAL_DIG FLTNX_DECIMAL_DIG
— number of decimal digits, q, such that any floating-point number with q decimal digits can be rounded to a floating-point number with p bits and back again without a change to the q decimal digits, ⌊(p − 1) log10 (2)⌋ FLTN_DIG FLTNX_DIG
— minimum negative integer such that the radix raised to one less than that power is a normalized floating-point number, emin § H.3
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FLTN_MIN_EXP FLTNX_MIN_EXP DECN_MIN_EXP DECNX_MIN_EXP
— minimum negative integer such that 10 raised to that power is in the range of normalized floating-point numbers, ⌈ log10 (2)emin −1 ⌉ FLTN_MIN_10_EXP FLTNX_MIN_10_EXP
— maximum positive integer such that the radix raised to one less than that power is a representable finite floating-point number, emax FLTN_MAX_EXP FLTNX_MAX_EXP DECN_MAX_EXP DECNX_MAX_EXP
— maximum integer such that 10 raised to that power is in the range of representable finite floating-point numbers, ⌊ log10 ((1 − 2−p )2emax )⌋ FLTN_MAX_10_EXP FLTNX_MAX_10_EXP
— maximum representable finite floating-pointer number, (1 − b−p )bemax FLTN_MAX FLTNX_MAX DECN_MAX DECNX_MAX
— the difference between 1 and the least normalized value greater than 1 that is representable in the given floating type, b1−p FLTN_EPSILON FLTNX_EPSILON DECN_EPSILON DECNX_EPSILON
— minimum normalized positive floating-point number, bemin −1 FLTN_MIN FLTNX_MIN DECN_MIN DECNX_MIN
— minimum positive floating-point number, bemin −p FLTN_TRUE_MIN FLTNX_TRUE_MIN DECN_TRUE_MIN DECNX_TRUE_MIN
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Conversions
1
This subclause enhances the usual arithmetic conversions (6.3.1.8) to handle interchange and extended floating types. It supports the IEC 60559 recommendation against allowing implicit conversions of operands to obtain a common type where the conversion is between types where neither is a subset of (or equivalent to) the other.
2
This subclause also broadens the operation binding in F.3 for the IEC 60559 convertFormat operation to apply to IEC 60559 arithmetic and non-arithmetic formats.
H.4.1
Real floating and integer
1
When a finite value of interchange or extended floating type is converted to an integer type other than bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the "invalid" floating-point exception shall be raised and the result of the conversion is unspecified.
2
When a value of integer type is converted to an interchange or extended floating type, if the value being converted can be represented exactly in the new type, it is unchanged. If the value being converted cannot be represented exactly, the result shall be correctly rounded with exceptions raised as specified in IEC 60559.
H.4.2 1
Usual arithmetic conversions
If either operand is of floating type, the common real type is determined as follows: — If one operand has decimal floating type, the other operand shall not have standard floating type, binary floating type, complex type, or imaginary type. — If only one operand has a floating type, the other operand is converted to the corresponding real type of the operand of floating type. — If both operands have the same corresponding real type, no further conversion is needed. — If both operands have floating types and neither of the sets of values of their corresponding real types is a subset of (or equivalent to) the other, the behavior is undefined. — Otherwise, if both operands are floating types and the sets of values of their corresponding real types are not equivalent, the operand whose set of values of its corresponding real type is a strict subset of the set of values of the corresponding real type of the other operand is converted, without change of type domain, to a type with the corresponding real type of that other operand. — Otherwise, if both operands are floating types and the sets of values of their corresponding real types are equivalent, then the following rules are applied: – If the corresponding real type of either operand is an interchange floating type, the other operand is converted, without change of type domain, to a type whose corresponding real type is that same interchange floating type. – Otherwise, if the corresponding real type of either operand is long double, the other operand is converted, without change of type domain, to a type whose corresponding real type is long double. – Otherwise, if the corresponding real type of either operand is double, the other operand is converted, without change of type domain, to a type whose corresponding real type is double468) . – Otherwise, if the corresponding real type of either operand is _Float128x or _Decimal128x, the other operand is converted, without change of type domain, to a type whose corresponding real type is _Float128x or _Decimal128x, respectively. – Otherwise, if the corresponding real type of either operand is _Float64x or _Decimal64x , the other operand is converted, without change of type domain, to a type whose corresponding real type is _Float64x or _Decimal64x, respectively. 468) All cases where float might have the same format as another type are covered above.
§ H.4.2
IEC 60559 interchange and extended types
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The operation binding in F.3 for the IEC 60559 convertFormat operation applies to IEC 60559 arithmetic and non-arithmetic formats as follows: — For conversions between arithmetic formats supported by floating types (same or different radix) – casts and implicit conversions. — For same-radix conversions between non-arithmetic interchange formats – encoding-toencoding conversion functions (H.11.3.2). — For conversions between non-arithmetic interchange formats (same or different radix) – compositions of string-from-encoding functions (H.12.3) (converting exactly) and string-to-encoding functions (H.12.4). — For same-radix conversions from interchange formats supported by interchange floating types to non-arithmetic interchange formats – compositions of encode functions (H.11.3.1.1, 7.12.16.1, 7.12.16.3) and encoding-to-encoding functions (H.11.3.2). — For same radix conversions from non-arithmetic interchange formats to interchange formats supported by interchange floating types – compositions of encoding-to-encoding conversion functions (H.11.3.2) and decode functions (H.11.3.1.2, 7.12.16.2, 7.12.16.4). See the example in H.11.3.2.1. — For conversions from non-arithmetic interchange formats to arithmetic formats supported by floating types (same or different radix) – compositions of string-from-encoding functions (H.12.3) (converting exactly) and numeric conversion functions strtod, etc. (7.24.1.5, 7.24.1.6). See the example in H.12.2. — For conversions from arithmetic formats supported by floating types to non-arithmetic interchange formats (same or different radix) – compositions of numeric conversion functions strfromd, etc. (7.24.1.3, 7.24.1.4) (converting exactly) and string-to-encoding functions (H.12.4).
H.5 Lexical Elements H.5.1 Keywords 1
This subclause expands the list of keywords (6.4.1) to also include: — _FloatN, where N is 16, 32, 64, or ≥ 128 and a multiple of 32 — _Float32x — _Float64x — _Float128x — _DecimalN, where N is 96 or > 128 and a multiple of 32 — _Decimal64x — _Decimal128x
H.5.2
Constants
1
This subclause specifies constants of interchange and extended floating types.
2
This subclause expands floating-suffix (6.4.4.2) to also include: fN, FN, fNx, FNx, dN, DN, dNx, or DNx.
3
A floating suffix dN, DN, dNx, or DNx shall not be used in a hexadecimal-floating-constant.
4
A floating suffix shall not designate a type that the implementation does not provide. 554
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If a floating constant is suffixed by fN or FN, it has type _FloatN. If suffixed by fNx or FNx, it has type _FloatNx. If suffixed by dN or DN, it has type _DecimalN. If suffixed by dNx or DNx, it has type _DecimalNx.
6
The quantum exponent of a floating constant of decimal floating type is the same as for the result value of the corresponding strtodN or strtodNx function (H.12.2) for the same numeric string.
7
NOTE 1 For N = 32, 64, and 128, the suffixes dN and DN in this subclause for constants of type _DecimalN are equivalent alternatives to the suffixes df, dd, dl, DF, DD, and DL in 6.4.4.2 for the same types.
H.6
Expressions
1
This subclause expands the specification of expressions to also cover interchange and extended floating types.
2
Operators involving operands of interchange or extended floating type are evaluated according to the semantics of IEC 60559, including production of decimal floating-point results with the preferred quantum exponent as specified in IEC 60559 (see 5.2.4.2.3).
3
For multiplicative operators (6.5.5), additive operators (6.5.6), relational operators (6.5.8), equality operators (6.5.9), and compound assignment operators (6.5.16.2), if either operand has decimal floating type, the other operand shall not have standard floating type, binary floating type, complex type, or imaginary type.
4
For conditional operators (6.5.15), if the second or third operand has decimal floating type, the other of those operands shall not have standard floating type, binary floating type, complex type, or imaginary type.
5
The equivalence of expressions noted in F.9.2 apply to expressions of binary floating types, as well as standard floating types.
H.7 1
Declarations
This subclause expands the list of type specifiers (6.7.2) to also include: — _FloatN, where N is 16, 32, 64, or ≥ 128 and a multiple of 32 — _Float32x — _Float64x — _Float128x — _DecimalN, where N is 96 or > 128 and a multiple of 32 — _Decimal64x — _Decimal128x
2
The type specifiers _FloatN (where N is 16, 32, 64, or ≥ 128 and a multiple of 32), _Float32x, _Float64x, _Float128x, _DecimalN (where N is 96 or > 128 and a multiple of 32), _Decimal64x, and _Decimal128x shall not be used if the implementation does not support the corresponding types (see 6.10.9.3 and H.2).
3
This subclause also expands the list under Constraints in 6.7.2 to also include: — _FloatN, where N is 16, 32, 64, or ≥ 128 and a multiple of 32 — _Float32x — _Float64x — _Float128x — _DecimalN, where N is 96 or > 128 and a multiple of 32 § H.7
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— _Decimal64x — _Decimal128x — _FloatN _Complex, where N is 16, 32, 64, or ≥ 128 and a multiple of 32 — _Float32x _Complex — _Float64x _Complex — _Float128x _Complex
H.8 1
Identifiers in standard headers
The identifiers added to library headers by this annex are defined or declared by their respective headers only if the macro __STDC_WANT_IEC_60559_TYPES_EXT__ is defined (by the user) at the point in the code where the appropriate header is first included.
H.9
Complex arithmetic <complex.h>
1
This subclause specifies complex functions for corresponding real types that are binary floating types.
2
Each function synopsis in 7.3 specifies a family of functions including a principal function with one or more double complex parameters and a double complex or double return value. This subclause expands the synopsis to also include other functions, with the same name as the principal function but with fN and fNx suffixes, which are corresponding functions whose parameters and return values have corresponding real types _FloatN and _FloatNx.
3
The following function prototypes are added to the synopses of the respective subclauses in 7.3. For each binary floating type that the implementation provides, <complex.h> shall declare the associated functions (see H.8). Conversely, for each such type that the implementation does not provide, <complex.h> shall not declare the associated functions. 7.3.5 Trigonometric functions _FloatN complex cacosfN(_FloatN complex z); _FloatNx complex cacosfNx(_FloatNx complex z); _FloatN complex casinfN(_FloatN complex z); _FloatNx complex casinfNx(_FloatNx complex z); _FloatN complex catanfN(_FloatN complex z); _FloatNx complex catanfNx(_FloatNx complex z); _FloatN complex ccosfN(_FloatN complex z); _FloatNx complex ccosfNx(_FloatNx complex z); _FloatN complex csinfN(_FloatN complex z); _FloatNx complex csinfNx(_FloatNx complex z); _FloatN complex ctanfN(_FloatN complex z); _FloatNx complex ctanfNx(_FloatNx complex z);
7.3.6 Hyperbolic functions _FloatN complex cacoshfN(_FloatN complex z); _FloatNx complex cacoshfNx(_FloatNx complex z); _FloatN complex casinhfN(_FloatN complex z); _FloatNx complex casinhfNx(_FloatNx complex z); _FloatN complex catanhfN(_FloatN complex z); _FloatNx complex catanhfNx(_FloatNx complex z); _FloatN complex ccoshfN(_FloatN complex z); _FloatNx complex ccoshfNx(_FloatNx complex z); _FloatN complex csinhfN(_FloatN complex z); _FloatNx complex csinhfNx(_FloatNx complex z); _FloatN complex ctanhfN(_FloatN complex z); _FloatNx complex ctanhfNx(_FloatNx complex z);
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IEC 60559 interchange and extended types
§ H.9
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working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
7.3.7 Exponential and logarithmic functions _FloatN complex cexpfN(_FloatN complex z); _FloatNx complex cexpfNx(_FloatNx complex z); _FloatN complex clogfN(_FloatN complex z); _FloatNx complex clogfNx(_FloatNx complex z);
7.3.8 Power and absolute value functions _FloatN cabsfN(_FloatN complex z); _FloatNx cabsfNx(_FloatNx complex z); _FloatN complex cpowfN(_FloatN complex x, _FloatN complex y); _FloatNx complex cpowfNx(_FloatNx complex x, _FloatNx complex y); _FloatN complex csqrtfN(_FloatN complex z); _FloatNx complex csqrtfNx(_FloatNx complex z);
7.3.9 Manipulation functions _FloatN cargfN(_FloatN complex z); _FloatNx cargfNx(_FloatNx complex z); _FloatN cimagfN(_FloatN complex z); _FloatNx cimagfNx(_FloatNx complex z); _FloatN complex CMPLXFN(_FloatN x, _FloatN y); _FloatNx complex CMPLXFNX(_FloatNx x, _FloatNx y); _FloatN complex conjfN(_FloatN complex z); _FloatNx complex conjfNx(_FloatNx complex z); _FloatN complex cprojfN(_FloatN complex z); _FloatNx complex cprojfNx(_FloatNx complex z); _FloatN crealfN(_FloatN complex z); _FloatNx crealfNx(_FloatNx complex z); 4
For the functions listed in "future library directions" for <complex.h> (7.33.1), the possible suffixes are expanded to also include fN and fNx.
H.10
Floating-point environment
1
This subclause broadens the effects of the floating-point environment (7.6) to apply to types and formats specified in this annex.
2
The same floating-point status flags are used by floating-point operations for all floating types, including those types introduced in this annex, and by conversions for IEC 60559 non-arithmetic interchange formats.
3
Both the dynamic rounding direction mode accessed by fegetround and fesetround and the FENV_ROUND rounding control pragma apply to operations for binary floating types, as well as for standard floating types, and also to conversions for radix-2 non-arithmetic interchange formats. Likewise, both the dynamic rounding direction mode accessed by fe_dec_getround and fe_dec_setround and the FENV_DEC_ROUND rounding control pragmas apply to operations for all the decimal floating types, including those decimal floating types introduced in this annex, and to conversions for radix-10 non-arithmetic interchange formats.
4
In 7.6.2, the table of functions affected by constant rounding modes for standard floating types applies also for binary floating types. Each <math.h> function family listed in the table indicates the family of functions of all standard and binary floating types (for example, the acos family includes acosf, acosl, acosfN, and acosfNx as well as acos). The fMencfN, strfromencfN, and strtoencf N functions are also affected by these constant rounding modes.
5
In 7.6.3, in the table of functions affected by constant rounding modes for decimal floating types, each <math.h> function family indicates the family of functions of all decimal floating types (for example, the acos family includes acosdN and acosdNx). The dMencbindN, dMencdecdN, strfromencbind N, strfromencdecdN, strtoencbindN, and strtoencdecdN functions are also affected by these
constant rounding modes. § H.10
IEC 60559 interchange and extended types
557
ISO/IEC 9899:2023 (E)
H.11
working draft — April 1, 2023
N3096
Mathematics <math.h>
1
This subclause specifies types, functions, and macros for interchange and extended floating types, generally corresponding to those specified in 7.12 and F.10.
2
All classification macros (7.12.3) and comparison macros (7.12.17) naturally extend to handle interchange and extended floating types. For comparison macros, if neither of the sets of values of the argument formats is a subset of (or equivalent to) the other, the behavior is undefined.
3
This subclause also specifies encoding conversion functions that are part of support for the nonarithmetic interchange formats in IEC 60559 (see H.2.2).
4
Most function synopses in 7.12 specify a family of functions including a principal function with one or more double parameters, a double return value, or both. The synopses are expanded to also include functions with the same name as the principal function but with fN, fNx, dN, and dNx suffixes, which are corresponding functions whose parameters, return values, or both are of types _FloatN, _FloatNx, _DecimalN, and _DecimalNx, respectively.
5
For each interchange or extended floating type that the implementation provides, <math.h> shall define the associated types and macros and declare the associated functions (see H.8). Conversely, for each such type that the implementation does not provide, <math.h> shall not define the associated types and macros or declare the associated functions unless explicitly specified otherwise.
6
With the types float_t double_t
in 7.12 are included the type long_double_t
and for each supported type _FloatN, the type _FloatN_t
and for each supported type _DecimalN, the type _DecimalN_t
These are floating types, such that: — each of the types has at least the range and precision of the corresponding real floating type; — long_double_t has at least the range and precision of double_t; — _FloatN_t has at least the range and precision of _FloatM_t if N > M ; — _DecimalN_t has at least the range and precision of _DecimalM_t if N > M . If FLT_RADIX is 2 and FLT_EVAL_METHOD (H.3) is nonnegative, then each of the types corresponding to a standard or binary floating type is the type whose range and precision are specified by FLT_EVAL_METHOD to be used for evaluating operations and constants of that standard or binary floating type. If DEC_EVAL_METHOD (H.3) is nonnegative, then each of the types corresponding to a decimal floating type is the type whose range and precision are specified by DEC_EVAL_METHOD to be used for evaluating operations and constants of that decimal floating type. 7
EXAMPLE If the supported standard and binary floating types are 558
IEC 60559 interchange and extended types
§ H.11
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Type _Float16 float, _Float32 double, _Float64 , _Float32x long double, _Float64x _Float128
ISO/IEC 9899:2023 (E)
IEC 60559 format binary16 binary32 binary64 80-bit binary64-extended binary128
then the following tables gives the types with _t suffixes for various values for a FLT_EVAL_METHOD of a given value m: _t type/m _Float16_t float_t _Float32_t double_t _Float64_t long_double_t _Float128_t _t type/m _Float16_t float_t _Float32_t double_t _Float64_t long_double_t _Float128_t
H.11.1
0
1
2
32
float float _Float32 double _Float64 long double _Float128
double double double double _Float64 long double _Float128
long double long double long double long double long double long double _Float128
_Float32 float _Float32 double _Float64 long double _Float128
64
128
33
65
_Float64 _Float64 _Float64
_Float128 _Float128 _Float128 _Float128 _Float128 _Float128 _Float128
_Float32x _Float32x _Float32x double _Float64
_Float64x _Float64x _Float64x _Float64x _Float64x
long double _Float128
long double _Float128
double _Float64 long double _Float128
Macros
1
This subclause adds macros in 7.12 as follows.
2
The macros HUGE_VAL_FN HUGE_VAL_DN HUGE_VAL_FNX HUGE_VAL_DNX
expand to constant expressions of types _FloatN, _DecimalN, _FloatNx, and _DecimalNx, respectively, representing positive infinity. 3
The macros FP_FAST_FMAFN FP_FAST_FMADN FP_FAST_FMAFNX FP_FAST_FMADNX
are, respectively, _FloatN, _DecimalN, _FloatNx, and _DecimalNx analogues of FP_FAST_FMA. 4
The macros in the following lists are interchange and extended floating type analogues of FP_FAST_FADD, FP_FAST_FADDL, FP_FAST_DADDL, etc.
5
For M < N , the macros FP_FAST_FMADDFN FP_FAST_FMSUBFN FP_FAST_FMMULFN FP_FAST_FMDIVFN
§ H.11.1
IEC 60559 interchange and extended types
559
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
FP_FAST_FMFMAFN FP_FAST_FMSQRTFN FP_FAST_DMADDDN FP_FAST_DMSUBDN FP_FAST_DMMULDN FP_FAST_DMDIVDN FP_FAST_DMFMADN FP_FAST_DMSQRTDN
characterize the corresponding functions whose arguments are of an interchange floating type of width N and whose return type is an interchange floating type of width M . 6
For M ≤ N , the macros FP_FAST_FMADDFNX FP_FAST_FMSUBFNX FP_FAST_FMMULFNX FP_FAST_FMDIVFNX FP_FAST_FMFMAFNX FP_FAST_FMSQRTFNX FP_FAST_DMADDDNX FP_FAST_DMSUBDNX FP_FAST_DMMULDNX FP_FAST_DMDIVDNX FP_FAST_DMFMADNX FP_FAST_DMSQRTDNX
characterize the corresponding functions whose arguments are of an extended floating type that extends a format of width N and whose return type is an interchange floating type of width M . 7
For M < N , the macros FP_FAST_FMXADDFN FP_FAST_FMXSUBFN FP_FAST_FMXMULFN FP_FAST_FMXDIVFN FP_FAST_FMXFMAFN FP_FAST_FMXSQRTFN FP_FAST_DMXADDDN FP_FAST_DMXSUBDN FP_FAST_DMXMULDN FP_FAST_DMXDIVDN FP_FAST_DMXFMADN FP_FAST_DMXSQRTDN
characterize the corresponding functions whose arguments are of an interchange floating type of width N and whose return type is an extended floating type that extends a format of width M . 8
For M < N , the macros FP_FAST_FMXADDFNX FP_FAST_FMXSUBFNX FP_FAST_FMXMULFNX FP_FAST_FMXDIVFNX FP_FAST_FMXFMAFNX FP_FAST_FMXSQRTFNX FP_FAST_DMXADDDNX FP_FAST_DMXSUBDNX FP_FAST_DMXMULDNX FP_FAST_DMXDIVDNX FP_FAST_DMXFMADNX FP_FAST_DMXSQRTDNX
560
IEC 60559 interchange and extended types
§ H.11.1
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
characterize the corresponding functions whose arguments are of an extended floating type that extends a format of width N and whose return type is an extended floating type that extends a format of width M .
H.11.2 1
Functions
This subclause adds the following functions to the synopses of the respective subclauses in 7.12. 7.12.4 Trigonometric functions _FloatN acosfN(_FloatN x); _FloatNx acosfNx(_FloatNx x); _DecimalN acosdN(_DecimalN x); _DecimalNx acosdNx(_DecimalNx x); _FloatN asinfN(_FloatN x); _FloatNx asinfNx(_FloatNx x); _DecimalN asindN(_DecimalN x); _DecimalNx asindNx(_DecimalNx x); _FloatN atanfN(_FloatN x); _FloatNx atanfNx(_FloatNx x); _DecimalN atandN(_DecimalN x); _DecimalNx atandNx(_DecimalNx x); _FloatN atan2fN(_FloatN y, _FloatN x); _FloatNx atan2fNx(_FloatNx y, _FloatNx x); _DecimalN atan2dN(_DecimalN y, _DecimalN x); _DecimalNx atan2dNx(_DecimalNx y, _DecimalNx x); _FloatN cosfN(_FloatN x); _FloatNx cosfNx(_FloatNx x); _DecimalN cosdN(_DecimalN x); _DecimalNx cosdNx(_DecimalNx x); _FloatN sinfN(_FloatN x); _FloatNx sinfNx(_FloatNx x); _DecimalN sindN(_DecimalN x); _DecimalNx sindNx(_DecimalNx x); _FloatN tanfN(_FloatN x); _FloatNx tanfNx(_FloatNx x); _DecimalN tandN(_DecimalN x); _DecimalNx tandNx(_DecimalNx x); _FloatN acospifN(_FloatN x); _FloatNx acospifNx(_FloatNx x); _DecimalN acospidN(_DecimalN x); _DecimalNx acospidNx(_DecimalNx x); _FloatN asinpifN(_FloatN x); _FloatNx asinpifNx(_FloatNx x); _DecimalN asinpidN(_DecimalN x); _DecimalNx asinpidNx(_DecimalNx x); _FloatN atanpifN(_FloatN x); _FloatNx atanpifNx(_FloatNx x); _DecimalN atanpidN(_DecimalN x); _DecimalNx atanpidNx(_DecimalNx x); _FloatN atan2pifN(_FloatN y, _FloatN x); _FloatNx atan2pifNx(_FloatNx y, _FloatNx x);
§ H.11.2
IEC 60559 interchange and extended types
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ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
_DecimalN atan2pidN(_DecimalN y, _DecimalN x); _DecimalNx atan2pidNx(_DecimalNx y, _DecimalNx x); _FloatN cospifN(_FloatN x); _FloatNx cospifNx(_FloatNx x); _DecimalN cospidN(_DecimalN x); _DecimalNx cospidNx(_DecimalNx x); _FloatN sinpifN(_FloatN x); _FloatNx sinpifNx(_FloatNx x); _DecimalN sinpidN(_DecimalN x); _DecimalNx sinpidNx(_DecimalNx x); _FloatN tanpifN(_FloatN x); _FloatNx tanpifNx(_FloatNx x); _DecimalN tanpidN(_DecimalN x); _DecimalNx tanpidNx(_DecimalNx x);
7.12.5 Hyperbolic functions _FloatN acoshfN(_FloatN x); _FloatNx acoshfNx(_FloatNx x); _DecimalN acoshdN(_DecimalN x); _DecimalNx acoshdNx(_DecimalNx x); _FloatN asinhfN(_FloatN x); _FloatNx asinhfNx(_FloatNx x); _DecimalN asinhdN(_DecimalN x); _DecimalNx asinhdNx(_DecimalNx x); _FloatN atanhfN(_FloatN x); _FloatNx atanhfNx(_FloatNx x); _DecimalN atanhdN(_DecimalN x); _DecimalNx atanhdNx(_DecimalNx x); _FloatN coshfN(_FloatN x); _FloatNx coshfNx(_FloatNx x); _DecimalN coshdN(_DecimalN x); _DecimalNx coshdNx(_DecimalNx x); _FloatN sinhfN(_FloatN x); _FloatNx sinhfNx(_FloatNx x); _DecimalN sinhdN(_DecimalN x); _DecimalNx sinhdNx(_DecimalNx x); _FloatN tanhfN(_FloatN x); _FloatNx tanhfNx(_FloatNx x); _DecimalN tanhdN(_DecimalN x); _DecimalNx tanhdNx(_DecimalNx x);
7.12.6 Exponential and logarithmic functions _FloatN expfN(_FloatN x); _FloatNx expfNx(_FloatNx x); _DecimalN expdN(_DecimalN x); _DecimalNx expdNx(_DecimalNx x); _FloatN exp10fN(_FloatN x); _FloatNx exp10fNx(_FloatNx x); _DecimalN exp10dN(_DecimalN x); _DecimalNx exp10dNx(_DecimalNx x);
562
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§ H.11.2
N3096
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ISO/IEC 9899:2023 (E)
_FloatN exp10m1fN(_FloatN x); _FloatNx exp10m1fNx(_FloatNx x); _DecimalN exp10m1dN(_DecimalN x); _DecimalNx exp10m1dNx(_DecimalNx x); _FloatN exp2fN(_FloatN x); _FloatNx exp2fNx(_FloatNx x); _DecimalN exp2dN(_DecimalN x); _DecimalNx exp2dNx(_DecimalNx x); _FloatN exp2m1fN(_FloatN x); _FloatNx exp2m1fNx(_FloatNx x); _DecimalN exp2m1dN(_DecimalN x); _DecimalNx exp2m1dNx(_DecimalNx x); _FloatN expm1fN(_FloatN x); _FloatNx expm1fNx(_FloatNx x); _DecimalN expm1dN(_DecimalN x); _DecimalNx expm1dNx(_DecimalNx x); _FloatN frexpfN(_FloatN value, int *exp); _FloatNx frexpfNx(_FloatNx value, int *exp); _DecimalN frexpdN(_DecimalN value, int *exp); _DecimalNx frexpdNx(_DecimalNx value, int *exp); int ilogbfN(_FloatN x); int ilogbfNx(_FloatNx x); int ilogbdN(_DecimalNx x); int ilogbdNx(_DecimalNx x); _FloatN ldexpfN(_FloatN value, int exp); _FloatNx ldexpfNx(_FloatNx value, int exp); _DecimalN ldexpdN(_DecimalN value, int exp); _DecimalNx ldexpdNx(_DecimalNx value, int exp); long int llogbfN(_FloatN x); long int llogbfNx(_FloatNx x); long int llogbdN(_DecimalN x); long int llogbdNx(_DecimalNx x); _FloatN logfN(_FloatN x); _FloatNx logfNx(_FloatNx x); _DecimalN logdN(_DecimalN x); _DecimalNx logdNx(_DecimalNx x); _FloatN log10fN(_FloatN x); _FloatNx log10fNx(_FloatNx x); _DecimalN log10dN(_DecimalN x); _DecimalNx log10dNx(_DecimalNx x); _FloatN log10p1fN(_FloatN x); _FloatNx log10p1fNx(_FloatNx x); _DecimalN log10p1dN(_DecimalN x); _DecimalNx log10p1dNx(_DecimalNx x); _FloatN log1pfN(_FloatN x); _FloatNx log1pfNx(_FloatNx x); _FloatN logp1fN(_FloatN x); _FloatNx logp1fNx(_FloatNx x); _DecimalN log1pdN(_DecimalN x);
§ H.11.2
IEC 60559 interchange and extended types
563
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
_DecimalNx log1pdNx(_DecimalNx x); _DecimalN logp1dN(_DecimalN x); _DecimalNx logp1dNx(_DecimalNx x); _FloatN log2fN(_FloatN x); _FloatNx log2fNx(_FloatNx x); _DecimalN log2dN(_DecimalN x); _DecimalNx log2dNx(_DecimalNx x); _FloatN log2p1fN(_FloatN x); _FloatNx log2p1fNx(_FloatNx x); _DecimalN log2p1dN(_DecimalN x); _DecimalNx log2p1dNx(_DecimalNx x); _FloatN logbfN(_FloatN x); _FloatNx logbfNx(_FloatNx x); _DecimalN logbdN(_DecimalN x); _DecimalNx logbdNx(_DecimalNx x); _FloatN modffN(_FloatN x, _FloatN *iptr); _FloatNx modffNx(_FloatNx x, _FloatNx *iptr); _DecimalN modfdN(_DecimalN x, _DecimalN *iptr); _DecimalNx modfdNx(_DecimalNx x, _DecimalNx *iptr); _FloatN scalbnfN(_FloatN value, int exp); _FloatNx scalbnfNx(_FloatNx value, int exp); _DecimalN scalbndN(_DecimalN value, int exp); _DecimalNx scalbndNx(_DecimalNx value, int exp); _FloatN scalblnfN(_FloatN value, long int exp); _FloatNx scalblnfNx(_FloatNx value, long int exp); _DecimalN scalblndN(_DecimalN value, long int exp); _DecimalNx scalblndNx(_DecimalNx value, long int exp);
7.12.7 Power and absolute-value functions _FloatN cbrtfN(_FloatN x); _FloatNx cbrtfNx(_FloatNx x); _DecimalN cbrtdN(_DecimalN x); _DecimalNx cbrtdNx(_DecimalNx x); _FloatN compoundnfN(_FloatN x, long long int n); _FloatNx compoundnfNx(_FloatNx x, long long int n); _DecimalN compoundndN(_DecimalN x, long long int n); _DecimalNx compoundndNx(_DecimalNx x, long long int n); _FloatN fabsfN(_FloatN x); _FloatNx fabsfNx(_FloatNx x); _DecimalN fabsdN(_DecimalN x); _DecimalNx fabsdNx(_DecimalNx x); _FloatN hypotfN(_FloatN x, _FloatN y); _FloatNx hypotfNx(_FloatNx x, _FloatNx y); _DecimalN hypotdN(_DecimalN x, _DecimalN y); _DecimalNx hypotdNx(_DecimalNx x, _DecimalNx y); _FloatN powfN(_FloatN x, _FloatN y); _FloatNx powfNx(_FloatNx x, _FloatNx y); _DecimalN powdN(_DecimalN x, _DecimalN y); _DecimalNx powdNx(_DecimalNx x, _DecimalNx y);
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§ H.11.2
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ISO/IEC 9899:2023 (E)
_FloatN pownfN(_FloatN x, long long int n); _FloatNx pownfNx(_FloatNx x, long long int n); _DecimalN powndN(_DecimalN x, long long int n); _DecimalNx powndNx(_DecimalNx x, long long int n); _FloatN powrfN(_FloatN x, _FloatN y); _FloatNx powrfNx(_FloatNx x, _FloatNx y); _DecimalN powrdN(_DecimalN x, _DecimalN y); _DecimalNx powrdNx(_DecimalNx x, _DecimalNx y); _FloatN rootnfN(_FloatN x, long long int n); _FloatNx rootnfNx(_FloatNx x, long long int n); _DecimalN rootndN(_DecimalN x, long long int n); _DecimalNx rootndNx(_DecimalNx x, long long int n); _FloatN rsqrtfN(_FloatN x); _FloatNx rsqrtfNx(_FloatNx x); _DecimalN rsqrtdN(_DecimalN x); _DecimalNx rsqrtdNx(_DecimalNx x); _FloatN sqrtfN(_FloatN x); _FloatNx sqrtfNx(_FloatNx x); _DecimalN sqrtdN(_DecimalN x); _DecimalNx sqrtdNx(_DecimalNx x);
7.12.8 Error and gamma functions _FloatN erffN(_FloatN x); _FloatNx erffNx(_FloatNx x); _DecimalN erfdN(_DecimalN x); _DecimalNx erfdNx(_DecimalNx x); _FloatN erfcfN(_FloatN x); _FloatNx erfcfNx(_FloatNx x); _DecimalN erfcdN(_DecimalN x); _DecimalNx erfcdNx(_DecimalNx x); _FloatN lgammafN(_FloatN x); _FloatNx lgammafNx(_FloatNx x); _DecimalN lgammadN(_DecimalN x); _DecimalNx lgammadNx(_DecimalNx x); _FloatN tgammafN(_FloatN x); _FloatNx tgammafNx(_FloatNx x); _DecimalN tgammadN(_DecimalN x); _DecimalNx tgammadNx(_DecimalNx x);
7.12.9 Nearest integer functions _FloatN ceilfN(_FloatN x); _FloatNx ceilfNx(_FloatNx x); _DecimalN ceildN(_DecimalN x); _DecimalNx ceildNx(_DecimalNx x); _FloatN floorfN(_FloatN x); _FloatNx floorfNx(_FloatNx x); _DecimalN floordN(_DecimalN x); _DecimalNx floordNx(_DecimalNx x); _FloatN nearbyintfN(_FloatN x); _FloatNx nearbyintfNx(_FloatNx x);
§ H.11.2
IEC 60559 interchange and extended types
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ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
_DecimalN nearbyintdN(_DecimalN x); _DecimalNx nearbyintdNx(_DecimalNx x); _FloatN rintfN(_FloatN x); _FloatNx rintfNx(_FloatNx x); _DecimalN rintdN(_DecimalN x); _DecimalNx rintdNx(_DecimalNx x); long int lrintfN(_FloatN x); long int lrintfNx(_FloatNx x); long int lrintdN(_DecimalN x); long int lrintdNx(_DecimalNx x); long long int llrintfN(_FloatN x); long long int llrintfNx(_FloatNx x); long long int llrintdN(_DecimalN x); long long int llrintdNx(_DecimalNx x); _FloatN roundfN(_FloatN x); _FloatNx roundfNx(_FloatNx x); _DecimalN rounddN(_DecimalN x); _DecimalNx rounddNx(_DecimalNx x); long int lroundfN(_FloatN x); long int lroundfNx(_FloatNx x); long int lrounddN(_DecimalN x); long int lrounddNx(_DecimalNx x); long long int llroundfN(_FloatN x); long long int llroundfNx(_FloatNx x); long long int llrounddN(_DecimalN x); long long int llrounddNx(_DecimalNx x); _FloatN roundevenfN(_FloatN x); _FloatNx roundevenfNx(_FloatNx x); _DecimalN roundevendN(_DecimalN x); _DecimalNx roundevendNx(_DecimalNx x); _FloatN truncfN(_FloatN x); _FloatNx truncfNx(_FloatNx x); _DecimalN truncdN(_DecimalN x); _DecimalNx truncdNx(_DecimalNx x); _FloatN fromfpfN(_FloatN x, int rnd, unsigned int width); _FloatNx fromfpfNx(_FloatNx x, int rnd, unsigned int width); _DecimalN fromfpdN(_DecimalN x, int rnd, unsigned int width); _DecimalNx fromfpdNx(_DecimalNx x, int rnd, unsigned int width); _FloatN ufromfpfN(_FloatN x, int rnd, unsigned int width); _FloatNx ufromfpfNx(_FloatNx x, int rnd, unsigned int width); _DecimalN ufromfpdN(_DecimalN x, int rnd, unsigned int width); _DecimalNx ufromfpdNx(_DecimalNx x, int rnd, unsigned int width); _FloatN fromfpxfN(_FloatN x, int rnd, unsigned int width); _FloatNx fromfpxfNx(_FloatNx x, int rnd, unsigned int width); _DecimalN fromfpxdN(_DecimalN x, int rnd, unsigned int width); _DecimalNx fromfpxdNx(_DecimalNx x, int rnd, unsigned int width); _FloatN ufromfpxfN(_FloatN x, int rnd, unsigned int width); _FloatNx ufromfpxfNx(_FloatNx x, int rnd, unsigned int width); _DecimalN ufromfpxdN(_DecimalN x, int rnd, unsigned int width); _DecimalNx ufromfpxdNx(_DecimalNx x, int rnd, unsigned int width);
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IEC 60559 interchange and extended types
§ H.11.2
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7.12.10.2 Remainder functions _FloatN fmodfN(_FloatN x, _FloatN y); _FloatNx fmodfNx(_FloatNx x, _FloatNx y); _DecimalN fmoddN(_DecimalN x, _DecimalN y); _DecimalNx fmoddNx(_DecimalNx x, _DecimalNx y); _FloatN remainderfN(_FloatN x, _FloatN y); _FloatNx remainderfNx(_FloatNx x, _FloatNx y); _DecimalN remainderdN(_DecimalN x, _DecimalN y); _DecimalNx remainderdNx(_DecimalNx x, _DecimalNx y); _FloatN remquofN(_FloatN x, _FloatN y, int *quo); _FloatNx remquofNx(_FloatNx x, _FloatNx y, int *quo);
7.12.11 Manipulation functions _FloatN copysignfN(_FloatN x, _FloatN y); _FloatNx copysignfNx(_FloatNx x, _FloatNx y); _DecimalN copysigndN(_DecimalN x, _DecimalN y); _DecimalNx copysigndNx(_DecimalNx x, _DecimalNx y); _FloatN nanfN(const char *tagp); _FloatNx nanfNx(const char *tagp); _DecimalN nandN(const char *tagp); _DecimalNx nandNx(const char *tagp); _FloatN nextafterfN(_FloatN x, _FloatN y); _FloatNx nextafterfNx(_FloatNx x, _FloatNx y); _DecimalN nextafterdN(_DecimalN x, _DecimalN y); _DecimalNx nextafterdNx(_DecimalNx x, _DecimalNx y); _FloatN nextupfN(_FloatN x); _FloatNx nextupfNx(_FloatNx x); _DecimalN nextupdN(_DecimalN x); _DecimalNx nextupdNx(_DecimalNx x); _FloatN nextdownfN(_FloatN x); _FloatNx nextdownfNx(_FloatNx x); _DecimalN nextdowndN(_DecimalN x); _DecimalNx nextdowndNx(_DecimalNx x); int canonicalizefN(_FloatN * cx, const _FloatN * x); int canonicalizefNx(_FloatNx * cx, const _FloatNx * x); int canonicalizedN(_DecimalN * cx, const _DecimalN * x); int canonicalizedNx(_DecimalNx * cx, const _DecimalNx * x);
7.12.12 Maximum, minimum, and positive difference functions _FloatN fdimfN(_FloatN x, _FloatN y); _FloatNx fdimfNx(_FloatNx x, _FloatNx y); _DecimalN fdimdN(_DecimalN x, _DecimalN y); _DecimalNx fdimdNx(_DecimalNx x, _DecimalNx y); _FloatN fmaximumfN(_FloatN x, _FloatN y); _FloatNx fmaximumfNx(_FloatNx x, _FloatNx y); _DecimalN fmaximumdN(_DecimalN x, _DecimalN y); _DecimalNx fmaximumdNx(_DecimalNx x, _DecimalNx y); _FloatN fminimumfN(_FloatN x, _FloatN y); _FloatNx fminimumfNx(_FloatNx x, _FloatNx y);
§ H.11.2
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_DecimalN fminimumdN(_DecimalN x, _DecimalN y); _DecimalNx fminimumdNx(_DecimalNx x, _DecimalNx y); _FloatN fmaximum_magfN(_FloatN x, _FloatN y); _FloatNx fmaximum_magfNx(_FloatNx x, _FloatNx y); _DecimalN fmaximum_magdN(_DecimalN x, _DecimalN y); _DecimalNx fmaximum_magdNx(_DecimalNx x, _DecimalNx y); _FloatN fminimum_magfN(_FloatN x, _FloatN y); _FloatNx fminimum_magfNx(_FloatNx x, _FloatNx y); _DecimalN fminimum_magdN(_DecimalN x, _DecimalN y); _DecimalNx fminimum_magdNx(_DecimalNx x, _DecimalNx y); _FloatN fmaximum_numfN(_FloatN x, _FloatN y); _FloatNx fmaximum_numfNx(_FloatNx x, _FloatNx y); _DecimalN fmaximum_numdN(_DecimalN x, _DecimalN y); _DecimalNx fmaximum_numdNx(_DecimalNx x, _DecimalNx y); _FloatN fminimum_numfN(_FloatN x, _FloatN y); _FloatNx fminimum_numfNx(_FloatNx x, _FloatNx y); _DecimalN fminimum_numdN(_DecimalN x, _DecimalN y); _DecimalNx fminimum_numdNx(_DecimalNx x, _DecimalNx y); _FloatN fmaximum_mag_numfN(_FloatN x, _FloatN y); _FloatNx fmaximum_mag_numfNx(_FloatNx x, _FloatNx y); _DecimalN fmaximum_mag_numdN(_DecimalN x, _DecimalN y); _DecimalNx fmaximum_mag_numdNx(_DecimalNx x, _DecimalNx y); _FloatN fminimum_mag_numfN(_FloatN x, _FloatN y); _FloatNx fminimum_mag_numfNx(_FloatNx x, _FloatNx y); _DecimalN fminimum_mag_numdN(_DecimalN x, _DecimalN y); _DecimalNx fminimum_mag_numdNx(_DecimalNx x, _DecimalNx y);
7.12.13.1 Fused multiply-add _FloatN fmafN(_FloatN x, _FloatN y, _FloatN z); _FloatNx fmafNx(_FloatNx x, _FloatNx y, _FloatNx z); _DecimalN fmadN(_DecimalN x, _DecimalN y, _DecimalN z); _DecimalNx fmadNx(_DecimalNx x, _DecimalNx y, _DecimalNx z);
7.12.14 Functions that round result to narrower type _FloatM fMaddfN(_FloatN x, _FloatN y); // M < N _FloatM fMaddfNx(_FloatNx x, _FloatNx y); // M ≤ N _FloatMx fMxaddfN(_FloatN x, _FloatN y); // M < N _FloatMx fMxaddfNx(_FloatNx x, _FloatNx y); // M < N _DecimalM dMadddN(_DecimalN x, _DecimalN y); // M < N _DecimalM dMadddNx(_DecimalNx x, _DecimalNx y); // M ≤ N _DecimalMx dMxadddN(_DecimalN x, _DecimalN y); // M < N _DecimalMx dMxadddNx(_DecimalNx x, _DecimalNx y); // M < N _FloatM fMsubfN(_FloatN x, _FloatN y); // M < N _FloatM fMsubfNx(_FloatNx x, _FloatNx y); // M ≤ N _FloatMx fMxsubfN(_FloatN x, _FloatN y); // M < N _FloatMx fMxsubfNx(_FloatNx x, _FloatNx y); // M < N _DecimalM dMsubdN(_DecimalN x, _DecimalN y); // M < N _DecimalM dMsubdNx(_DecimalNx x, _DecimalNx y); // M ≤ N _DecimalMx dMxsubdN(_DecimalN x, _DecimalN y); // M < N _DecimalMx dMxsubdNx(_DecimalNx x, _DecimalNx y); // M < N _FloatM fMmulfN(_FloatN x, _FloatN y); // M < N
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_FloatM fMmulfNx(_FloatNx x, _FloatNx y); // M ≤ N _FloatMx fMxmulfN(_FloatN x, _FloatN y); // M < N _FloatMx fMxmulfNx(_FloatNx x, _FloatNx y); // M < N _DecimalM dMmuldN(_DecimalN x, _DecimalN y); // M < N _DecimalM dMmuldNx(_DecimalNx x, _DecimalNx y); // M ≤ N _DecimalMx dMxmuldN(_DecimalN x, _DecimalN y); // M < N _DecimalMx dMxmuldNx(_DecimalNx x, _DecimalNx y); // M < N _FloatM fMdivfN(_FloatN x, _FloatN y); // M < N _FloatM fMdivfNx(_FloatNx x, _FloatNx y); // M ≤ N _FloatMx fMxdivfN(_FloatN x, _FloatN y); // M < N _FloatMx fMxdivfNx(_FloatNx x, _FloatNx y); // M < N _DecimalM dMdivdN(_DecimalN x, _DecimalN y); // M < N _DecimalM dMdivdNx(_DecimalNx x, _DecimalNx y); // M ≤ N _DecimalMx dMxdivdN(_DecimalN x, _DecimalN y); // M < N _DecimalMx dMxdivdNx(_DecimalNx x, _DecimalNx y); // M < N _FloatM fMfmafN(_FloatN x, _FloatN y, _FloatN z); // M < N _FloatM fMfmafNx(_FloatNx x, _FloatNx y, _FloatNx z); // M ≤ N _FloatMx fMxfmafN(_FloatN x, _FloatN y, _FloatN z); // M < N _FloatMx fMxfmafNx(_FloatNx x, _FloatNx y, _FloatNx z); // M < N _DecimalM dMfmadN(_DecimalN x, _DecimalN y, _DecimalN z); // M < N _DecimalM dMfmadNx(_DecimalNx x, _DecimalNx y, _DecimalNx z); // M ≤ N _DecimalMx dMxfmadN(_DecimalN x, _DecimalN y, _DecimalN z); // M < N _DecimalMx dMxfmadNx(_DecimalNx x, _DecimalNx y, _DecimalNx z); // M < N _FloatM fMsqrtfN(_FloatN x); // M < N _FloatM fMsqrtfNx(_FloatNx x); // M ≤ N _FloatMx fMxsqrtfN(_FloatN x); // M < N _FloatMx fMxsqrtfNx(_FloatNx x); // M < N _DecimalM dMsqrtdN(_DecimalN x); // M < N _DecimalM dMsqrtdNx(_DecimalNx x); // M ≤ N _DecimalMx dMxsqrtdN(_DecimalN x); // M < N _DecimalMx dMxsqrtdNx(_DecimalNx x); // M < N
7.12.15 Quantum and quantum exponent functions _DecimalN quantizedN(_DecimalN x, _DecimalN y); _DecimalNx quantizedNx(_DecimalNx x, _DecimalNx y); bool samequantumdN(_DecimalN x, _DecimalN y); bool samequantumdNx(_DecimalNx x, _DecimalNx y); _DecimalN quantumdN(_DecimalN x); _DecimalNx quantumdNx(_DecimalNx x); long long int llquantexpdN(_DecimalN x); long long int llquantexpdNx(_DecimalNx x);
7.12.16 Decimal re-encoding functions void encodedecdN(unsigned char * restrict encptr, const _DecimalN * restrict xptr); void decodedecdN(_DecimalN * restrict xptr, const unsigned char * restrict encptr); void encodebindN(unsigned char * restrict encptr, const _DecimalN * restrict xptr); void decodebindN(_DecimalN * restrict xptr, const unsigned char * restrict encptr);
F.10.12 Total order functions § H.11.2
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int totalorderfN(const _FloatN *x, const _FloatN *y); int totalorderfNx(const _FloatNx *x, const _FloatNx *y); int totalorderdN(const _DecimalN *x, const _DecimalN *y); int totalorderdNx(const _DecimalNx *x, const _DecimalNx *y); int totalordermagfN(const _FloatN *x, const _FloatN *y); int totalordermagfNx(const _FloatNx *x, const _FloatNx *y); int totalordermagdN(const _DecimalN *x, const _DecimalN *y); int totalordermagdNx(const _DecimalNx *x, const _DecimalNx *y);
F.10.13 Payload functions _FloatN getpayloadfN(const _FloatN *x); _FloatNx getpayloadfNx(const _FloatNx *x); _DecimalN getpayloaddN(const _DecimalN *x); _DecimalNx getpayloaddNx(const _DecimalNx *x); int setpayloadfN(_FloatN *res, _FloatN pl); int setpayloadfNx(_FloatNx *res, _FloatNx pl); int setpayloaddN(_DecimalN *res, _DecimalN pl); int setpayloaddNx(_DecimalNx *res, _DecimalNx pl); int setpayloadsigfN(_FloatN *res, _FloatN pl); int setpayloadsigfNx(_FloatNx *res, _FloatNx pl); int setpayloadsigdN(_DecimalN *res, _DecimalN pl); int setpayloadsigdNx(_DecimalNx *res, _DecimalNx pl); 2
The specification of the frexp functions (7.12.6.7) applies to the functions for binary floating types like those for standard floating types: the exponent is an integral power of 2 and, when applicable, value equals x × 2*exp .
3
The specification of the ldexp functions (7.12.6.9) applies to the functions for binary floating types like those for standard floating types: they return x × 2exp .
4
The specification of the logb functions (7.12.6.17) applies to binary floating types, with b = 2.
5
The specification of the scalbn and scalbln functions (7.12.6.19) applies to binary floating types, with b = 2.
1
This subclause introduces <math.h> functions that, together with the numerical conversion functions for encodings in H.12, support the non-arithmetic interchange formats specified by IEC 60559. Support for these formats is an optional feature of this annex. Implementations that do not support non-arithmetic interchange formats need not declare the functions in this subclause.
2
Non-arithmetic interchange formats are not associated with floating types. Arrays of element type unsigned char are used as parameters for conversion functions, to represent encodings in interchange formats that might be non-arithmetic formats.
H.11.3
1
Encoding conversion functions
H.11.3.1 Encode and decode functions This subclause specifies functions to map representations in binary floating types to and from encodings in unsigned char arrays. H.11.3.1.1 Synopsis
The encodefN functions
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <math.h>
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void encodefN(unsigned char encptr[restrict static N/8], const _FloatN * restrict xptr);
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Description The encodefN functions convert *xptr into an IEC 60559 binaryN encoding and store the resulting encoding as an N /8 element array, with 8 bits per array element, in the object pointed to by encptr. The order of bytes in the array follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). These functions preserve the value of *xptr and raise no floating-point exceptions. If *xptr is non-canonical, these functions may or may not produce a canonical encoding. Returns The encodefN functions return no value. H.11.3.1.2 Synopsis
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ISO/IEC 9899:2023 (E)
The decodefN functions
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <math.h> void decodefN(_FloatN * restrict xptr, const unsigned char encptr[restrict static N/8]);
2
Description The decodefN functions interpret the N /8 element array pointed to by encptr as an IEC 60559 binaryN encoding, with 8 bits per array element. The order of bytes in the array follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). These functions convert the given encoding into a representation in the type _FloatN, and store the result in the object pointed to by xptr. These functions preserve the encoded value and raise no floating-point exceptions. If the encoding is non-canonical, these functions may or may not produce a canonical representation.
3
Returns The decodefN functions return no value.
4
See EXAMPLE in H.11.3.2.1.
1
H.11.3.2 Encoding-to-encoding conversion functions An implementation shall declare an fMencfN function for each M and N equal to the width of a supported IEC 60559 arithmetic or non-arithmetic binary interchange format, M ̸= N . An implementation shall provide both dMencdecdN and dMencbindNfunctions for each M and N equal to the width of a supported IEC 60559 arithmetic or non-arithmetic decimal interchange format, M ̸= N . H.11.3.2.1 Synopsis
1
The fMencfN functions
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <math.h> void fMencfN(unsigned char encMptr[restrict static M/8], const unsigned char encNptr[restrict static N/8]);
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Description The fMencfN functions convert between IEC 60559 binary interchange formats. These functions interpret the N /8 element array pointed to by encNptr as an encoding of width N bits. They convert the encoding to an encoding of width M bits and store the resulting encoding as an M /8 element array in the object pointed to by encMptr. The conversion rounds and raises floating-point exceptions as specified in IEC 60559. The order of bytes in the arrays follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns These functions return no value. § H.11.3.2.1
IEC 60559 interchange and extended types
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EXAMPLE If the IEC 60559 binary16 format is supported as a non-arithmetic format, data in binary16 format can be converted to type float as follows: #define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <math.h> unsigned char b16[2]; // for input binary16 datum float f; // for result unsigned char b32[4]; _Float32 f32; // store input binary16 datum in array b16 ... f32encf16(b32, b16); decodef32(&f32, b32); f = f32; ...
H.11.3.2.2 Synopsis
The dMencdecdN and dMencbindN functions
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <math.h>
1
void dMencdecdN(unsigned char encMptr[restrict static M/8], const unsigned char encNptr[restrict static N/8]); void dMencbindN(unsigned char encMptr[restrict static M/8], const unsigned char encNptr[restrict static N/8]);
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Description The dMencdecdN and dMencbindN functions convert between IEC 60559 decimal interchange formats that use the same encoding scheme. The dMencdecdN functions convert between formats using the encoding scheme based on decimal encoding of the significand. The dMencbindN functions convert between formats using the encoding scheme based on binary encoding of the significand. These functions interpret the N /8 element array pointed to by encNptr as an encoding of width N bits. They convert the encoding to an encoding of width M bits and store the resulting encoding as an M /8 element array in the object pointed to by encMptr. The conversion rounds and raises floating-point exceptions as specified in IEC 60559. The order of bytes in the arrays follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns These functions return no value.
H.12
Numeric conversion functions <stdlib.h>
1
This clause expands the specification of numeric conversion functions in <stdlib.h> (7.24.1) to also include conversions of strings from and to interchange and extended floating types. The conversions from floating are provided by functions analogous to the strfromd function. The conversions to floating are provided by functions analogous to the strtod function.
2
This clause also specifies functions to convert strings from and to IEC 60559 interchange format encodings.
3
For each interchange or extended floating type that the implementation provides, <stdlib.h> shall declare the associated functions specified below in H.12.1 and H.12.2 (see H.8). Conversely, for each such type that the implementation does not provide, <stdlib.h> shall not declare the associated functions.
4
For each IEC 60559 arithmetic or non-arithmetic format that the implementation supports, <stdlib.h> shall declare the associated functions specified below in H.12.3 and H.12.4 (see H.8). Conversely, for each such format that the implementation does not provide, <stdlib.h> shall not
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declare the associated functions.
H.12.1 1
String from floating
This subclause expands 7.24.1.3 and 7.24.1.4 to also include functions for the interchange and extended floating types. It adds to the synopsis in 7.24.1.3 the prototypes int strfromfN(char * restrict s, size_t n, const char * restrict format, _FloatN fp); int strfromfNx(char * restrict s, size_t n, const char * restrict format, _FloatNx fp);
It encompasses the prototypes in 7.24.1.4 by replacing them with int strfromdN(char * restrict s, size_t n, const char * restrict format, _DecimalN fp); int strfromdNx(char * restrict s, size_t n, const char * restrict format, _DecimalNx fp); 2
The descriptions and returns for the added functions are analogous to the ones in 7.24.1.3 and 7.24.1.4.
H.12.2
String to floating
1
This subclause expands 7.24.1.5, 7.31.4.1.2, 7.24.1.6, and 7.31.4.1.3 to also include functions for the interchange and extended floating types.
2
It adds to the synopsis in 7.24.1.5 the prototypes _FloatN strtofN(const char * restrict nptr, char ** restrict endptr); _FloatNx strtofNx(const char * restrict nptr, char ** restrict endptr);
It adds to the synopsis in 7.31.4.1.2 the prototypes _FloatN wcstodN(const wchar_t * restrict nptr, wchar_t ** restrict endptr); _FloatNx wcstodNx(const wchar_t * restrict nptr, wchar_t ** restrict endptr);
It encompasses the prototypes in 7.24.1.6 by replacing them with _DecimalN strtodN(const char * restrict nptr, char ** restrict endptr); _DecimalNx strtodNx(const char * restrict nptr, char ** restrict endptr);
It encompasses the prototypes in 7.31.4.1.3 by replacing them with _DecimalN wcstodN(const wchar_t * restrict nptr, wchar_t ** restrict endptr); _DecimalNx wcstodNx(const wchar_t * restrict nptr, wchar_t ** restrict endptr); 3
The descriptions and returns for the added functions are analogous to the ones in 7.24.1.5, 7.31.4.1.2, 7.24.1.6, and 7.31.4.1.3.
4
EXAMPLE If the IEC 60559 binary128 format is supported as a non-arithmetic format, data in binary128 format can be converted to type _Decimal128 as follows:
§ H.12.2
IEC 60559 interchange and extended types
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#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <stdlib.h> #define MAXSIZE 41 // > intermediate hex string length unsigned char b128[16]; // for input binary128 datum _Decimal128 d128; // for result char s[MAXSIZE]; // store input binary128 datum in array b128 ... strfromencf128(s, MAXSIZE, "%a", b128); d128 = strtod128(s, NULL); ...
Use of "%a" for formatting assures an exact conversion of the value in binary format to character sequence. The value of that character sequence will be correctly rounded to _Decimal128, as specified above in this subclause. The array s for the output of strfromencf128 need have no greater size than 41, which is the maximum length of strings of the form [−]0xh.h . . . hp ± d where there are up to 29 hexadecimal digits h and d has 5 digits plus 1 for the null character.
H.12.3 1
String from encoding
An implementation shall declare the strfromencfN function for each N equal to the width of a supported IEC 60559 arithmetic or non-arithmetic binary interchange format. An implementation shall declare both the strfromencdecdN and strfromencbindN functions for each N equal to the width of a supported IEC 60559 arithmetic or non-arithmetic decimal interchange format. H.12.3.1 The strfromencf N functions Synopsis #define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <stdlib.h>
1
int strfromencfN(char * restrict s, size_t n, const char * restrict format, const unsigned char encptr[restrict static N/8]);
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Description The strfromencfN functions are similar to the strfromfN functions, except the input is the value of the N /8 element array pointed to by encptr, interpreted as an IEC 60559 binaryN encoding. The order of bytes in the arrays follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns The strfromencfN functions return the same values as corresponding strfromfN functions. H.12.3.2 The strfromencdecdN and strfromencbindN functions Synopsis #define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <stdlib.h>
1
int strfromencdecdN(char * restrict s, size_t n, const char * restrict format, const unsigned char encptr[restrict static N/8]); int strfromencbindN(char * restrict s, size_t n, const char * restrict format, const unsigned char encptr[restrict static N/8]);
2
Description The strfromencdecdN functions are similar to the strfromdN functions except the input is the value of the N /8 element array pointed to by encptr, interpreted as an IEC 60559 decimalN encoding in 574
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the coding scheme based on decimal encoding of the significand. The strfromencbindN functions are similar to the strfromdN functions except the input is the value of the N /8 element array pointed to by encptr, interpreted as an IEC 60559 decimalN encoding in the coding scheme based on binary encoding of the significand. The order of bytes in the arrays follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2).
3
Returns The strfromencdecdN and strfromencbindN functions return the same values as corresponding strfromdN functions.
H.12.4 1
String to encoding
An implementation shall declare the strtoencfN and wcstoencfN functions for each N equal to the width of a supported IEC 60559 arithmetic or non-arithmetic binary interchange format. An implementation shall declare both the strtoencdecdN, strtoencbindN, wcstoencdecdN, and wcstoencbindN functions for each N equal to the width of a supported IEC 60559 arithmetic or non-arithmetic decimal interchange format. H.12.4.1 The strtoencfN functions Synopsis
1
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <stdlib.h> void strtoencfN(unsigned char encptr[restrict static N/8], const char * restrict nptr, char ** restrict endptr);
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Description The strtoencfN functions are similar to the strtofN functions, except they store an IEC 60559 encoding of the result as an N /8 element array in the object pointed to by encptr. The order of bytes in the arraysfollows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns These functions return no value. H.12.4.2 The wcstoencfN functions Synopsis
1
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <wchar.h> void wcstoencfN(unsigned char encptr[restrict static N/8], const wchar_t * restrict nptr, wchar_t ** restrict endptr);
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Description The wcstoencfN functions are similar to the wcstofN functions, except they store an IEC 60559 encoding of the result as an N /8 element array in the object pointed to by encptr. The order of bytes in the array follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns These functions return no value. H.12.4.3 The strtoencdecdN and strtoencbindN functions Synopsis
1
#define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <stdlib.h> void strtoencdecdN(unsigned char encptr[restrict static N/8],
§ H.12.4.3
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const char * restrict nptr, char ** restrict endptr); void strtoencbindN(unsigned char encptr[restrict static N/8], const char * restrict nptr, char ** restrict endptr);
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Description The strtoencdecdN and strtoencbindN functions are similar to the strtodN functions, except they store an IEC 60559 encoding of the result as an N /8 element array in the object pointed to by encptr. The strtoencdecdN functions produce an encoding in the encoding scheme based on decimal encoding of the significand. The strtoencbindN functions produce an encoding in the encoding scheme based on binary encoding of the significand. The order of bytes in the arrays follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns These functions return no value. H.12.4.4 The wcstoencdecdN and wcstoencbindN functions Synopsis #define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <wchar.h>
1
void wcstoencdecdN(unsigned char encptr[restrict static N/8], const char * restrict nptr, char ** restrict endptr); void wcstoencbindN(unsigned char encptr[restrict static N/8], const char * restrict nptr, char ** restrict endptr);
2
3
Description The wcstoencdecdN and wcstoencbindN functions are similar to the wcstodN functions, except they store an IEC 60559 encoding of the result as an N /8 element array in the object pointed to by encptr. The wcstoencdecdN functions produce an encoding in the encoding scheme based on decimal encoding of the significand. The wcstoencbindN functions produce an encoding in the encoding scheme based on binary encoding of the significand. The order of bytes in the arrays follows the endianness specified with __STDC_ENDIAN_NATIVE__ (7.18.2). Returns These functions return no value.
H.13
Type-generic macros <tgmath.h>
1
This clause enhances the specification of type-generic macros in <tgmath.h> (7.27) to apply to interchange and extended floating types, as well as standard floating types.
2
If arguments for generic parameters of a type-generic macro are such that some argument has a corresponding real type that is a standard floating type or a binary floating type and another argument is of decimal floating type, the behavior is undefined.
3
The treatment of arguments of integer type in 7.27 is expanded to cases where another argument has extended type. Arguments of integer type are regarded as having type: — _Decimal64x , if any argument has a decimal extended type; otherwise — _Float32x , if any argument has a binary extended type; otherwise — _Decimal64 , if any argument has decimal type; otherwise — double
4
Use of the macros carg, cimag, conj, cproj, or creal with any argument of standard floating type, binary floating type, complex type, or imaginary type invokes a complex function. Use of the macro with an argument of a decimal floating type results in undefined behavior. 576
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The functions that round results to a narrower type have type-generic macros whose names are obtained by omitting any suffix from the function names. Thus, the macros with f or d prefix are (as in 7.27): fadd dadd fsub dsub
fmul dmul fdiv ddiv
ffma dfma fsqrt dsqrt
and the macros with fM, fMx, dM, or dMx prefix are: fMadd fMsub fMmul fMdiv fMfma fMsqrt fMxadd fMxsub
fMxmul fMxdiv fMxfma fMxsqrt dMadd dMsub dMmul dMdiv
dMfma dMsqrt dMxadd dMxsub dMxmul dMxdiv dMxfma dMxsqrt
All arguments are generic. If any argument is not real, use of the macro results in undefined behavior. The following specification uses the notation type1 ⊆ type2 to mean the values of type1 are a subset of (or the same as) the values of type2. The generic parameter type T for the function invoked by the macro is determined as follows: — First, obtain a preliminary type P for the generic parameters: if all arguments are of integer type, then P is double if the macro prefix is f, d, fN, or fNx and P is _Decimal64 if the macro prefix is dN or dNx; otherwise (if some argument is not of integer type), apply the rules (for determining the corresponding real type of the generic parameters) in 7.27 for macros that do not round result to narrower type, using the usual arithmetic conversion rules in H.4.2, to obtain P . — If there exists a corresponding function whose generic parameters have type P , then T is P . — Otherwise, T is determined from P and the macro prefix as follows: • For prefix f: if P is a standard or binary floating type, then T is the first standard floating type of either double or long double, such that P ⊆ T , if such a type T exists. Otherwise (if no such type T exists or P is a decimal floating type), the behavior is undefined. • For prefix d: if P is a standard or binary floating type, then T is long double if P ⊆ long double. Otherwise (if P ⊆ long double is false or P is a decimal floating type), the behavior is undefined. • For prefix fM: if P is a standard or binary floating type, then T is _FloatN for minimum N > M such that P ⊆ T , if such a type T is supported; otherwise T is _FloatNx for minimum N ≥ M such that P ⊆ T , if such a type T is supported. Otherwise (if no such _FloatN or _FloatNx is supported or P is a decimal floating type), the behavior is undefined. • For prefix fMx: if P is a standard or binary floating type, then T is _FloatNx for minimum N > M such that P ⊆ T , if such a type T is supported; otherwise T is _FloatN for minimum N > M such that P ⊆ T , if such a type T is supported. Otherwise (if no such _FloatNx or _FloatN is supported or P is a decimal floating type), the behavior is undefined. • For prefix dM: if P is a decimal floating type, then T is _DecimalN for minimum N > M such that P ⊆ T , if such a type T is supported; otherwise T is _DecimalNx for minimum N ≥ M such that P ⊆ T . Otherwise (P is a standard or binary floating type), the behavior is undefined. § H.13
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• For prefix dMx: if P is a decimal floating type, then T is _DecimalNx for minimum N > M such that P ⊆ T , if such a type T is supported; otherwise T is _DecimalN for minimum N > M such that P ⊆ T , if such a type T is supported. Otherwise (P is a standard or binary floating type), the behavior is undefined. 6
EXAMPLE 1 With the declarations #define __STDC_WANT_IEC_60559_TYPES_EXT__ #include <tgmath.h> int n; double d; long double ld; double complex dc; _Float32x f32x; _Float64 f64; _Float64x f64x; _Float128 f128; _Float64x complex f64xc;
functions invoked by use of type-generic macros are shown in the following tables. type1 ⊆ type2 means the values of type1 are a subset of (or the same as) the values of type2, and type1 ⊂ type2 means the values of type1 are a strict subset of the values of type2:
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macro use
invokes
cos(f64xc)
ccosf64x
pow(dc, f128)
cpowf128
pow(f64, d)
powf64
pow(d, f32x)
pow, the function, if _Float32x ⊆ double, else powf32x if double ⊂ _Float32x , else undefined
pow(f32, n)
pow, the function
pow(f32x, n)
powf32x
ISO/IEC 9899:2023 (E)
Some type-generic macros that round the result to a narrower type function behave as shown below. macro use
invokes
fsub(d, ld)
fsubl
dsub(d, f32)
dsubl
fmul(dc, d) ddiv(ld, f128)
undefined type is undefined ddivl if _Float128 ⊆ long double, else undefined
f32add(f64x, f64)
f32addf64x
f32xsqrt(n)
f32xsqrtf64x
f32mul(f128, f32x)
f32mulf128 if _Float32x ⊆ _Float128 , else f32mulf32x if _Float128 ⊂ _Float32x , else undefined
f32fma(f32x, n, f32x)
f32fmaf32x
f32add(f32, f32)
f32addf64
f32xsqrt(f32) f64div(f32x, f32x)
§ H.13
f32xsqrtf64x, as declaration above shows _Float64x is sup-
ported f64divf128 if _Float32x ⊆ _Float128 , else f64divf64x
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Annex I (informative)
Common warnings 1
2
An implementation may generate warnings in many situations, none of which are specified as part of this document. The following are a few of the more common situations. — A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3). — A block with initialization of an object that has automatic storage duration is jumped into (6.2.4). — An implicit narrowing conversion is encountered, such as the assignment of a long int or a double to an int, or a pointer to void to a pointer to any type other than a character type (6.3). — A hexadecimal floating constant cannot be represented exactly in its evaluation format (6.4.4.2). — An integer character constant includes more than one character or a wide character constant includes more than one multibyte character (6.4.4.4). — The characters /* are found in a comment (6.4.7). — An "unordered" binary operator (not comma, &&, or ||) contains a side effect to an lvalue in one operand, and a side effect to, or an access to the value of, the identical lvalue in the other operand (6.5). — An object is defined but not used (6.7). — A value is given to an object of an enumerated type other than by assignment of an enumeration constant that is a member of that type, or an enumeration object that has the same type, or the value of a function that returns the same enumerated type (6.7.2.2). — An aggregate has a partly bracketed initialization (6.7.8). — A statement cannot be reached (6.8). — A statement with no apparent effect is encountered (6.8). — A constant expression is used as the controlling expression of a selection statement (6.8.4). — An incorrectly formed preprocessing group is encountered while skipping a preprocessing group (6.10.1). — An unrecognized #pragma directive is encountered (6.10.7).
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Annex J (informative)
Portability issues 1
This annex collects some information about portability that appears in this document.
J.1 1
Unspecified behavior
The following are unspecified: (1) The manner and timing of static initialization (5.1.2). (2) The termination status returned to the hosted environment if the return type of main is not compatible with int (5.1.2.2.3). (3) The values of objects that are neither lock-free atomic objects nor of type volatile sig_atomic_t and the state of the floating-point environment, when the processing of the abstract machine is interrupted by receipt of a signal (5.1.2.3). (4) The behavior of the display device if a printing character is written when the active position is at the final position of a line (5.2.2). (5) The behavior of the display device if a backspace character is written when the active position is at the initial position of a line (5.2.2). (6) The behavior of the display device if a horizontal tab character is written when the active position is at or past the last defined horizontal tabulation position (5.2.2). (7) The behavior of the display device if a vertical tab character is written when the active position is at or past the last defined vertical tabulation position (5.2.2). (8) How an extended source character that does not correspond to a universal character name counts toward the significant initial characters in an external identifier (5.2.4.1). (9) Many aspects of the representations of types (6.2.6). (10) The value of padding bytes when storing values in structures or unions (6.2.6.1). (11) The values of bytes that correspond to union members other than the one last stored into (6.2.6.1). (12) The representation used when storing a value in an object that has more than one object representation for that value (6.2.6.1). (13) The values of any padding bits in integer representations (6.2.6.2). (14) Whether two string literals result in distinct arrays (6.4.5). (15) The order in which subexpressions are evaluated and the order in which side effects take place, except as specified for the function-call (), &&, ||, ?:, and comma operators (6.5). (16) The order in which the function designator, arguments, and subexpressions within the arguments are evaluated in a function call (6.5.2.2). (17) The order of side effects among compound literal initialization list expressions (6.5.2.5). (18) The order in which the operands of an assignment operator are evaluated (6.5.16). (19) The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1). (20) Whether a call to an inline function uses the inline definition or the external definition of the function (6.7.4). § J.1
Portability issues
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(21) Whether a size expression is evaluated when it is part of the operand of a sizeof operator and changing the value of the size expression would not affect the result of the operator (6.7.6.2). (22) The order in which any side effects occur among the initialization list expressions in an initializer (6.7.10). (23) The layout of storage for function parameters (6.9.1). (24) When a fully expanded macro replacement list contains a function-like macro name as its last preprocessing token and the next preprocessing token from the source file is a (, and the fully expanded replacement of that macro ends with the name of the first macro and the next preprocessing token from the source file is again a (, whether that is considered a nested replacement (6.10.4). (25) The order in which # and ## operations are evaluated during macro substitution (6.10.4.2, 6.10.4.3). (26) The line number of a preprocessing token, in particular __LINE__, that spans multiple physical lines (6.10.5). (27) The line number of a preprocessing directive that spans multiple physical lines (6.10.5). (28) The line number of a macro invocation that spans multiple physical or logical lines (6.10.5). (29) The line number following a directive of the form #line __LINE__ new-line (6.10.5). (30) The state of the floating-point status flags when execution passes from a part of the program translated with FENV_ACCESS "off" to a part translated with FENV_ACCESS "on" (7.6.1). (31) The order in which feraiseexcept raises floating-point exceptions, except as stated in F.8.6 (7.6.4.3). (32) Whether math_errhandling is a macro or an identifier with external linkage (7.12). (33) The results of the frexp functions when the specified value is not a floating-point number (7.12.6.7). (34) The numeric result of the ilogb functions when the correct value is outside the range of the return type (7.12.6.8, F.10.3.8). (35) The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5). (36) The value stored by the remquo functions in the object pointed to by quo when y is zero (7.12.10.3). (37) Whether a comparison macro argument that is represented in a format wider than its semantic type is converted to the semantic type (7.12.17). (38) Whether setjmp is a macro or an identifier with external linkage (7.13). (39) Whether va_copy and va_end are macros or identifiers with external linkage (7.16.1). (40) The hexadecimal digit before the decimal point when a non-normalized floating-point number is printed with an a or A conversion specifier (7.23.6.1, 7.31.2.1). (41) The value of the file position indicator after a successful call to the ungetc function for a text stream, or the ungetwc function for any stream, until all pushed-back characters are read or discarded (7.23.7.10, 7.31.3.10). (42) The details of the value stored by the fgetpos function (7.23.9.1). (43) The details of the value returned by the ftell function for a text stream (7.23.9.4). 582
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(44) Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold functions convert a minus-signed sequence to a negative number directly or by negating the value resulting from converting the corresponding unsigned sequence (7.24.1.5, 7.31.4.1.2). (45) The order and contiguity of storage allocated by successive calls to the calloc, malloc, realloc, and aligned_alloc functions (7.24.3). (46) The amount of storage allocated by a successful call to the calloc, malloc, realloc, or aligned_alloc function when 0 bytes was requested (7.24.3). (47) Whether a call to the atexit function that does not happen before the exit function is called will succeed (7.24.4.2). (48) Whether a call to the at_quick_exit function that does not happen before the quick_exit function is called will succeed (7.24.4.3). (49) Which of two elements that compare as equal is matched by the bsearch function (7.24.5.1). (50) The order of two elements that compare as equal in an array sorted by the qsort function (7.24.5.2). (51) The order in which destructors are invoked by thrd_exit (7.28.5.5). (52) Whether calling tss_delete on a key while another thread is executing destructors affects the number of invocations of the destructors associated with the key on that thread (7.28.6.2). (53) The encoding of the calendar time returned by the time function (7.29.2.5). (54) The characters stored by the strftime or wcsftime function if any of the time values being converted is outside the normal range (7.29.3.5, 7.31.5.1). (55) Whether an encoding error occurs if a wchar_t value that does not correspond to a member of the extended character set appears in the format string for a function in 7.31.2 or 7.31.5 and the specified semantics do not require that value to be processed by wcrtomb (7.31.1). (56) The conversion state after an encoding error occurs (7.31.6.3.2, 7.31.6.3.3, 7.31.6.4.1, 7.31.6.4.2, 7.30.1.1, 7.30.1.2, 7.30.1.3, 7.30.1.4, 7.30.1.5, 7.30.1.6). (57) The resulting value when the "invalid" floating-point exception is raised during IEC 60559 floating to integer conversion (F.4). (58) Whether conversion of non-integer IEC 60559 floating values to integer raises the "inexact" floating-point exception (F.4). (59) Whether or when library functions in <math.h> raise the "inexact" floating-point exception in an IEC 60559 conformant implementation (F.10). (60) Whether or when library functions in <math.h> raise an undeserved "underflow" floatingpoint exception in an IEC 60559 conformant implementation (F.10). (61) The exponent value stored by frexp for a NaN or infinity (F.10.3.7). (62) The numeric result returned by the lrint, llrint, lround, and llround functions if the rounded value is outside the range of the return type (F.10.6.5, F.10.6.7). (63) The sign of one part of the complex result of several math functions for certain special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3, G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2). § J.1
Portability issues
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Undefined behavior
The behavior is undefined in the following circumstances: (1) A "shall" or "shall not" requirement that appears outside of a constraint is violated (Clause 4). (2) A nonempty source file does not end in a new-line character which is not immediately preceded by a backslash character or ends in a partial preprocessing token or comment (5.1.1.2). (3) Token concatenation produces a character sequence matching the syntax of a universal character name (5.1.1.2). (4) A program in a hosted environment does not define a function named main using one of the specified forms (5.1.2.2.1). (5) The execution of a program contains a data race (5.1.2.4). (6) A character not in the basic source character set is encountered in a source file, except in an identifier, a character constant, a string literal, a header name, a comment, or a preprocessing token that is never converted to a token (5.2.1). (7) An identifier, comment, string literal, character constant, or header name contains an invalid multibyte character or does not begin and end in the initial shift state (5.2.1.1). (8) The same identifier has both internal and external linkage in the same translation unit (6.2.2). (9) An object is referred to outside of its lifetime (6.2.4). (10) The value of a pointer to an object whose lifetime has ended is used (6.2.4). (11) The value of an object with automatic storage duration is used while the object has an indeterminate representation (6.2.4, 6.7.10, 6.8). (12) A non-value representation is read by an lvalue expression that does not have character type (6.2.6.1). (13) A non-value representation is produced by a side effect that modifies any part of the object using an lvalue expression that does not have character type (6.2.6.1). (14) Two declarations of the same object or function specify types that are not compatible (6.2.7). (15) A program requires the formation of a composite type from a variable length array type whose size is specified by an expression that is not evaluated (6.2.7). (16) Conversion to or from an integer type produces a value outside the range that can be represented (6.3.1.4). (17) Demotion of one real floating type to another produces a value outside the range that can be represented (6.3.1.5). (18) An lvalue does not designate an object when evaluated (6.3.2.1). (19) A non-array lvalue with an incomplete type is used in a context that requires the value of the designated object (6.3.2.1). (20) An lvalue designating an object of automatic storage duration that could have been declared with the register storage class is used in a context that requires the value of the designated object, but the object is uninitialized. (6.3.2.1). (21) An lvalue having array type is converted to a pointer to the initial element of the array, and the array object has register storage class (6.3.2.1). (22) An attempt is made to use the value of a void expression, or an implicit or explicit conversion (except to void) is applied to a void expression (6.3.2.2). 584
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(23) Conversion of a pointer to an integer type produces a value outside the range that can be represented (6.3.2.3). (24) Conversion between two pointer types produces a result that is incorrectly aligned (6.3.2.3). (25) A pointer is used to call a function whose type is not compatible with the referenced type (6.3.2.3). (26) An unmatched ’ or " character is encountered on a logical source line during tokenization (6.4). (27) A reserved keyword token is used in translation phase 7 or 8 for some purpose other than as a keyword (6.4.1). (28) A universal character name in an identifier does not designate a character whose encoding falls into one of the specified ranges (6.4.2.1). (29) The initial character of an identifier is a universal character name designating a digit (6.4.2.1). (30) Two identifiers differ only in nonsignificant characters (6.4.2.1). (31) The identifier __func__ is explicitly declared (6.4.2.2). (32) The program attempts to modify a string literal (6.4.5). (33) The characters ’, \, ", //, or /* occur in the sequence between the < and > delimiters, or the characters ’, \, //, or /* occur in the sequence between the " delimiters, in a header name preprocessing token (6.4.7). (34) A side effect on a scalar object is unsequenced relative to either a different side effect on the same scalar object or a value computation using the value of the same scalar object (6.5). (35) An exceptional condition occurs during the evaluation of an expression (6.5). (36) An object has its stored value accessed other than by an lvalue of an allowable type (6.5). (37) A function is defined with a type that is not compatible with the type (of the expression) pointed to by the expression that denotes the called function (6.5.2.2). (38) A member of an atomic structure or union is accessed (6.5.2.3). (39) The operand of the unary * operator has an invalid value (6.5.3.2). (40) A pointer is converted to other than an integer or pointer type (6.5.4). (41) The value of the second operand of the / or % operator is zero (6.5.5). (42) If the quotient a/b is not representable, the behavior of both a/b and a%b (6.5.5). (43) Addition or subtraction of a pointer into, or just beyond, an array object and an integer type produces a result that does not point into, or just beyond, the same array object (6.5.6). (44) Addition or subtraction of a pointer into, or just beyond, an array object and an integer type produces a result that points just beyond the array object and is used as the operand of a unary * operator that is evaluated (6.5.6). (45) Pointers that do not point into, or just beyond, the same array object are subtracted (6.5.6). (46) An array subscript is out of range, even if an object is apparently accessible with the given subscript (as in the lvalue expression a[1][7] given the declaration int a[4][5]) (6.5.6). (47) The result of subtracting two pointers is not representable in an object of type ptrdiff_t (6.5.6). (48) An expression is shifted by a negative number or by an amount greater than or equal to the width of the promoted expression (6.5.7). § J.2
Portability issues
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(49) An expression having signed promoted type is left-shifted and either the value of the expression is negative or the result of shifting would not be representable in the promoted type (6.5.7). (50) Pointers that do not point to the same aggregate or union (nor just beyond the same array object) are compared using relational operators (6.5.8). (51) An object is assigned to an inexactly overlapping object or to an exactly overlapping object with incompatible type (6.5.16.1). (52) An expression that is required to be a an integer constant expression does not have an integer type; has operands that are not integer constants, named constants, compound literal constants, enumeration constants, character constants, predefined constants, sizeof expressions whose results are integer constants, alignof expressions, or immediately-cast floating constants; or contains casts (outside operands to sizeof and alignof operators) other than conversions of arithmetic types to integer types (6.6). (53) A constant expression in an initializer is not, or does not evaluate to, one of the following: a named constant, a compound literal constant, an arithmetic constant expression, a null pointer constant, an address constant, or an address constant for a complete object type plus or minus an integer constant expression (6.6). (54) An arithmetic constant expression does not have arithmetic type; has operands that are not integer constants, floating constants, enumeration constants, character constants, predefined constants, sizeof expressions whose results are integer constants, or alignof expressions; or contains casts (outside operands to sizeof or alignof operators) other than conversions of arithmetic types to arithmetic types (6.6). (55) The value of an object is accessed by an array-subscript [], member-access . or ->, address &, or indirection * operator or a pointer cast in creating an address constant (6.6). (56) An identifier for an object is declared with no linkage and the type of the object is incomplete after its declarator, or after its init-declarator if it has an initializer (6.7). (57) A function is declared at block scope with an explicit storage-class specifier other than extern (6.7.1). (58) A structure or union is defined without any named members (including those specified indirectly via anonymous structures and unions) (6.7.2.1). (59) An attempt is made to access, or generate a pointer to just past, a flexible array member of a structure when the referenced object provides no elements for that array (6.7.2.1). (60) When the complete type is needed, an incomplete structure or union type is not completed in the same scope by another declaration of the tag that defines the content (6.7.2.3). (61) An attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type (6.7.3). (62) An attempt is made to refer to an object defined with a volatile-qualified type through use of an lvalue with non-volatile-qualified type (6.7.3). (63) The specification of a function type includes any type qualifiers (6.7.3). (64) Two qualified types that are required to be compatible do not have the identically qualified version of a compatible type (6.7.3). (65) An object which has been modified is accessed through a restrict-qualified pointer to a constqualified type, or through a restrict-qualified pointer and another pointer that are not both based on the same object (6.7.3.1). 586
Portability issues
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ISO/IEC 9899:2023 (E)
(66) A restrict-qualified pointer is assigned a value based on another restricted pointer whose associated block neither began execution before the block associated with this pointer, nor ended before the assignment (6.7.3.1). (67) A function with external linkage is declared with an inline function specifier, but is not also defined in the same translation unit (6.7.4). (68) A function declared with a _Noreturn function specifier returns to its caller (6.7.4). (69) The definition of an object has an alignment specifier and another declaration of that object has a different alignment specifier (6.7.5). (70) Declarations of an object in different translation units have different alignment specifiers (6.7.5). (71) Two pointer types that are required to be compatible are not identically qualified, or are not pointers to compatible types (6.7.6.1). (72) The size expression in an array declaration is not a constant expression and evaluates at program execution time to a nonpositive value (6.7.6.2). (73) In a context requiring two array types to be compatible, they do not have compatible element types, or their size specifiers evaluate to unequal values (6.7.6.2). (74) A declaration of an array parameter includes the keyword static within the [ and ] and the corresponding argument does not provide access to the first element of an array with at least the specified number of elements (6.7.6.3). (75) A storage-class specifier or type qualifier modifies the keyword void as a function parameter type list (6.7.6.3). (76) In a context requiring two function types to be compatible, they do not have compatible return types, or their parameters disagree in use of the ellipsis terminator or the number and type of parameters (after default argument promotion, when there is no parameter type list) (6.7.6.3). (77) A declaration for which a type is inferred contains a pointer, array, or function declarators (6.7.9). (78) A declaration for which a type is inferred contains no or more than one declarators (6.7.9). (79) The value of an unnamed member of a structure or union is used (6.7.10). (80) The initializer for a scalar is neither a single expression nor a single expression enclosed in braces (6.7.10). (81) The initializer for an aggregate or union, other than an array initialized by a string literal, is not a brace-enclosed list of initializers for its elements or members (6.7.10). (82) A function definition that does not have the asserted property is called by a function declaration or a function pointer with a type that has the unsequenced or reproducible attribute (6.7.12.7). (83) An identifier with external linkage is used, but in the program there does not exist exactly one external definition for the identifier, or the identifier is not used and there exist multiple external definitions for the identifier (6.9). (84) A function that accepts a variable number of arguments is defined without a parameter type list that ends with the ellipsis notation (6.9.1). (85) The } that terminates a function is reached, and the value of the function call is used by the caller (6.9.1). (86) An identifier for an object with internal linkage and an incomplete type is declared with a tentative definition (6.9.2). § J.2
Portability issues
587
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
(87) A non-directive preprocessing directive is executed (6.10). (88) The token defined is generated during the expansion of a #if or #elif preprocessing directive, or the use of the defined unary operator does not match one of the two specified forms prior to macro replacement (6.10.1). (89) The #include preprocessing directive that results after expansion does not match one of the two header name forms (6.10.2). (90) The character sequence in an #include preprocessing directive does not start with a letter (6.10.2). (91) There are sequences of preprocessing tokens within the list of macro arguments that would otherwise act as preprocessing directives (6.10.4). (92) The result of the preprocessing operator # is not a valid character string literal (6.10.4.2). (93) The result of the preprocessing operator ## is not a valid preprocessing token (6.10.4.3). (94) The #line preprocessing directive that results after expansion does not match one of the two well-defined forms, or its digit sequence specifies zero or a number greater than 2147483647 (6.10.5). (95) A non-STDC #pragma preprocessing directive that is documented as causing translation failure or some other form of undefined behavior is encountered (6.10.7). (96) A #pragma STDC preprocessing directive does not match one of the well-defined forms (6.10.7). (97) The name of a predefined macro, or the identifier defined, is the subject of a #define or #undef preprocessing directive (6.10.9). (98) An attempt is made to copy an object to an overlapping object by use of a library function, other than as explicitly allowed (e.g., memmove) (Clause 7). (99) A file with the same name as one of the standard headers, not provided as part of the implementation, is placed in any of the standard places that are searched for included source files (7.1.2). (100) A header is included within an external declaration or definition (7.1.2). (101) A function, object, type, or macro that is specified as being declared or defined by some standard header is used before any header that declares or defines it is included (7.1.2). (102) A standard header is included while a macro is defined with the same name as a keyword (7.1.2). (103) The program attempts to declare a library function itself, rather than via a standard header, but the declaration does not have external linkage (7.1.2). (104) The program declares or defines a reserved identifier, other than as allowed by 7.1.4 (7.1.3). (105) The program removes the definition of a macro whose name begins with an underscore and either an uppercase letter or another underscore (7.1.3). (106) An argument to a library function has an invalid value or a type not expected by a function with a variable number of arguments (7.1.4). (107) The pointer passed to a library function array parameter does not have a value such that all address computations and object accesses are valid (7.1.4). (108) The macro definition of assert is suppressed to access an actual function (7.2). (109) The argument to the assert macro does not have a scalar type (7.2). 588
Portability issues
§ J.2
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
(110) The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in any context other than outside all external declarations or preceding all explicit declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2). (111) The value of an argument to a character handling function is neither equal to the value of EOF nor representable as an unsigned char (7.4). (112) A macro definition of errno is suppressed to access an actual object, or the program defines an identifier with the name errno (7.5). (113) Part of the program tests floating-point status flags, sets floating-point control modes, or runs under non-default mode settings, but was translated with the state for the FENV_ACCESS pragma "off" (7.6.1). (114) The exception-mask argument for one of the functions that provide access to the floating-point status flags has a nonzero value not obtained by bitwise OR of the floating-point exception macros (7.6.4). (115) The fesetexceptflag function is used to set floating-point status flags that were not specified in the call to the fegetexceptflag function that provided the value of the corresponding fexcept_t object (7.6.4.5). (116) The argument to fesetenv or feupdateenv is neither an object set by a call to fegetenv or feholdexcept, nor is it an environment macro (7.6.6.3, 7.6.6.4). (117) The value of the result of an integer arithmetic or conversion function cannot be represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.24.6.1, 7.24.6.2, 7.24.1). (118) The program modifies the string pointed to by the value returned by the setlocale function (7.11.1.1). (119) A pointer returned by the setlocale function is used after a subsequent call to the function, or after the calling thread has exited (7.11.1.1). (120) The program modifies the structure pointed to by the value returned by the localeconv function (7.11.2.1). (121) A macro definition of math_errhandling is suppressed or the program defines an identifier with the name math_errhandling (7.12). (122) An argument to a floating-point classification or comparison macro is not of real floating type (7.12.3, 7.12.17). (123) A macro definition of setjmp is suppressed to access an actual function, or the program defines an external identifier with the name setjmp (7.13). (124) An invocation of the setjmp macro occurs other than in an allowed context (7.13.2.1). (125) The longjmp function is invoked to restore a nonexistent environment (7.13.2.1). (126) After a longjmp, there is an attempt to access the value of an object of automatic storage duration that does not have volatile-qualified type, local to the function containing the invocation of the corresponding setjmp macro, that was changed between the setjmp invocation and longjmp call (7.13.2.1). (127) The program specifies an invalid pointer to a signal handler function (7.14.1.1). (128) A signal handler returns when the signal corresponded to a computational exception (7.14.1.1). (129) A signal handler called in response to SIGFPE, SIGILL, SIGSEGV, or any other implementationdefined value corresponding to a computational exception returns (7.14.1.1). (130) A signal occurs as the result of calling the abort or raise function, and the signal handler calls the raise function (7.14.1.1). § J.2
Portability issues
589
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
(131) A signal occurs other than as the result of calling the abort or raise function, and the signal handler refers to an object with static or thread storage duration that is not a lock-free atomic object other than by assigning a value to an object declared as volatile sig_atomic_t, or calls any function in the standard library other than the abort function, the _Exit function, the quick_exit function, the functions in <stdatomic.h> (except where explicitly stated otherwise) when the atomic arguments are lock-free, the atomic_is_lock_free function with any atomic argument, or the signal function (for the same signal number) (7.14.1.1). (132) The value of errno is referred to after a signal occurred other than as the result of calling the abort or raise function and the corresponding signal handler obtained a SIG_ERR return from a call to the signal function (7.14.1.1). (133) A signal is generated by an asynchronous signal handler (7.14.1.1). (134) The signal function is used in a multi-threaded program (7.14.1.1). (135) A function with a variable number of arguments attempts to access its varying arguments other than through a properly declared and initialized va_list object, or before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4). (136) The macro va_arg is invoked using the parameter ap that was passed to a function that invoked the macro va_arg with the same parameter (7.16). (137) A macro definition of va_start, va_arg, va_copy, or va_end is suppressed to access an actual function, or the program defines an external identifier with the name va_copy or va_end (7.16.1). (138) The va_start or va_copy macro is invoked without a corresponding invocation of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3, 7.16.1.4). (139) The type parameter to the va_arg macro is not such that a pointer to an object of that type can be obtained simply by postfixing a * (7.16.1.1). (140) The va_arg macro is invoked when there is no actual next argument, or with a specified type that is not compatible with the promoted type of the actual next argument, with certain exceptions (7.16.1.1). (141) Using a null pointer constant in form of an integer expression as an argument to a ... function and then interpreting it as a void* or char* (7.16.1.1). (142) The va_copy or va_start macro is called to initialize a va_list that was previously initialized by either macro without an intervening invocation of the va_end macro for the same va_list (7.16.1.2, 7.16.1.4). (143) The macro definition of a generic function is suppressed to access an actual function (7.17.1, 7.18). (144) The type parameter of an offsetof macro defines a new type (7.21). (145) When program execution reaches an unreachable() macro call (7.21.1). (146) Arbitrarily copying or changing the bytes of or copying from a non-null pointer into a nullptr_t object and then reading that object (7.21.2). (147) The member-designator parameter of an offsetof macro is an invalid right operand of the . operator for the type parameter, or designates a bit-field (7.21). (148) The argument in an instance of one of the integer-constant macros is not a decimal, octal, or hexadecimal constant, or it has a value that exceeds the limits for the corresponding type (7.22.4). (149) A byte input/output function is applied to a wide-oriented stream, or a wide character input/output function is applied to a byte-oriented stream (7.23.2). 590
Portability issues
§ J.2
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
(150) Use is made of any portion of a file beyond the most recent wide character written to a wide-oriented stream (7.23.2). (151) The value of a pointer to a FILE object is used after the associated file is closed (7.23.3). (152) The stream for the fflush function points to an input stream or to an update stream in which the most recent operation was input (7.23.5.2). (153) The string pointed to by the mode argument in a call to the fopen function does not exactly match one of the specified character sequences (7.23.5.3). (154) An output operation on an update stream is followed by an input operation without an intervening call to the fflush function or a file positioning function, or an input operation on an update stream is followed by an output operation with an intervening call to a file positioning function (7.23.5.3). (155) An attempt is made to use the contents of the array that was supplied in a call to the setvbuf function (7.23.5.6). (156) There are insufficient arguments for the format in a call to one of the formatted input/output functions, or an argument does not have an appropriate type (7.23.6.1, 7.23.6.2, 7.31.2.1, 7.31.2.2). (157) The format in a call to one of the formatted input/output functions or to the strftime or wcsftime function is not a valid multibyte character sequence that begins and ends in its initial shift state (7.23.6.1, 7.23.6.2, 7.29.3.5, 7.31.2.1, 7.31.2.2, 7.31.5.1). (158) In a call to one of the formatted output functions, a precision appears with a conversion specifier other than those described (7.23.6.1, 7.31.2.1). (159) A conversion specification for a formatted output function uses an asterisk to denote an argument-supplied field width or precision, but the corresponding argument is not provided (7.23.6.1, 7.31.2.1). (160) A conversion specification for a formatted output function uses a # or 0 flag with a conversion specifier other than those described (7.23.6.1, 7.31.2.1). (161) A conversion specification for one of the formatted input/output functions uses a length modifier with a conversion specifier other than those described (7.23.6.1, 7.23.6.2, 7.31.2.1, 7.31.2.2). (162) An s conversion specifier is encountered by one of the formatted output functions, and the argument is missing the null terminator (unless a precision is specified that does not require null termination) (7.23.6.1, 7.31.2.1). (163) An n conversion specification for one of the formatted input/output functions includes any flags, an assignment-suppressing character, a field width, or a precision (7.23.6.1, 7.23.6.2, 7.31.2.1, 7.31.2.2). (164) A % conversion specifier is encountered by one of the formatted input/output functions, but the complete conversion specification is not exactly %% (7.23.6.1, 7.23.6.2, 7.31.2.1, 7.31.2.2). (165) An invalid conversion specification is found in the format for one of the formatted input/output functions, or the strftime or wcsftime function (7.23.6.1, 7.23.6.2, 7.29.3.5, 7.31.2.1, 7.31.2.2, 7.31.5.1). (166) The number of characters or wide characters transmitted by a formatted output function (or written to an array, or that would have been written to an array) is greater than INT_MAX (7.23.6.1, 7.31.2.1). (167) The number of input items assigned by a formatted input function is greater than INT_MAX (7.23.6.2, 7.31.2.2). § J.2
Portability issues
591
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
(168) The result of a conversion by one of the formatted input functions cannot be represented in the corresponding object, or the receiving object does not have an appropriate type (7.23.6.2, 7.31.2.2). (169) A c, s, or [ conversion specifier is encountered by one of the formatted input functions, and the array pointed to by the corresponding argument is not large enough to accept the input sequence (and a null terminator if the conversion specifier is s or [) (7.23.6.2, 7.31.2.2). (170) A c, s, or [ conversion specifier with an l qualifier is encountered by one of the formatted input functions, but the input is not a valid multibyte character sequence that begins in the initial shift state (7.23.6.2, 7.31.2.2). (171) The input item for a %p conversion by one of the formatted input functions is not a value converted earlier during the same program execution (7.23.6.2, 7.31.2.2). (172) The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or vwscanf function is called with an improperly initialized va_list argument, or the argument is used (other than in an invocation of va_end) after the function returns (7.23.6.8, 7.23.6.9, 7.23.6.10, 7.23.6.11, 7.23.6.12, 7.23.6.13, 7.23.6.14, 7.31.2.5, 7.31.2.6, 7.31.2.7, 7.31.2.8, 7.31.2.9, 7.31.2.10). (173) The contents of the array supplied in a call to the fgets or fgetws function are used after a read error occurred (7.23.7.2, 7.31.3.2). (174) The file position indicator for a binary stream is used after a call to the ungetc function where its value was zero before the call (7.23.7.10). (175) The file position indicator for a stream is used after an error occurred during a call to the fread or fwrite function (7.23.8.1, 7.23.8.2). (176) A partial element read by a call to the fread function is used (7.23.8.1). (177) The fseek function is called for a text stream with a nonzero offset and either the offset was not returned by a previous successful call to the ftell function on a stream associated with the same file or whence is not SEEK_SET (7.23.9.2). (178) The fsetpos function is called to set a position that was not returned by a previous successful call to the fgetpos function on a stream associated with the same file (7.23.9.3). (179) A non-null pointer returned by a call to the calloc, malloc, realloc, or aligned_alloc function with a zero requested size is used to access an object (7.24.3). (180) The value of a pointer that refers to space deallocated by a call to the free or realloc function is used (7.24.3). (181) The pointer argument to the free or realloc function does not match a pointer earlier returned by a memory management function, or the space has been deallocated by a call to free or realloc (7.24.3.3, 7.24.3.7). (182) The value of the object allocated by the malloc function is used (7.24.3.6). (183) The values of any bytes in a new object allocated by the realloc function beyond the size of the old object are used (7.24.3.7). (184) The program calls the exit or quick_exit function more than once, or calls both functions (7.24.4.4, 7.24.4.7). (185) During the call to a function registered with the atexit or at_quick_exit function, a call is made to the longjmp function that would terminate the call to the registered function (7.24.4.4, 7.24.4.7). (186) The string set up by the getenv or strerror function is modified by the program (7.24.4.6, 7.26.6.3). 592
Portability issues
§ J.2
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
(187) A signal is raised while the quick_exit function is executing (7.24.4.7). (188) A command is executed through the system function in a way that is documented as causing termination or some other form of undefined behavior (7.24.4.8). (189) A searching or sorting utility function is called with an invalid pointer argument, even if the number of elements is zero (7.24.5). (190) The comparison function called by a searching or sorting utility function alters the contents of the array being searched or sorted, or returns ordering values inconsistently (7.24.5). (191) The array being searched by the bsearch function does not have its elements in proper order (7.24.5.1). (192) The current conversion state is used by a multibyte/wide character conversion function after changing the LC_CTYPE category (7.24.7). (193) A string or wide string utility function is instructed to access an array beyond the end of an object (7.26.1, 7.31.4). (194) A string or wide string utility function is called with an invalid pointer argument, even if the length is zero (7.26.1, 7.31.4). (195) The contents of the destination array are used after a call to the strxfrm, strftime, wcsxfrm, or wcsftime function in which the specified length was too small to hold the entire nullterminated result (7.26.4.5, 7.29.3.5, 7.31.4.4.4, 7.31.5.1). (196) A sequence of calls of the strtok function is made from different threads (7.26.5.9). (197) The first argument in the very first call to the strtok or wcstok is a null pointer (7.26.5.9, 7.31.4.6.7). (198) A pointer returned by the strerror function is used after a subsequent call to the function, or after the calling thread has exited (7.26.6.3). (199) The type of an argument to a type-generic macro is not compatible with the type of the corresponding parameter of the selected function (7.27). (200) Arguments for generic parameters of a type-generic macro are such that some argument has a corresponding real type that is of standard floating type and another argument is of decimal floating type (7.27). (201) Arguments for generic parameters of a type-generic macro are such that neither <math.h> and <complex.h> define a function whose generic parameters have the determined corresponding real type (7.27). (202) A complex argument is supplied for a generic parameter of a type-generic macro that has no corresponding complex function (7.27). (203) A decimal floating argument is supplied for a generic parameter of a type-generic macro that expects a complex argument (7.27). (204) A standard floating or complex argument is supplied for a generic parameter of a type-generic macro that expects a decimal floating type argument (7.27). (205) A non-recursive mutex passed to mtx_lock is locked by the calling thread (7.28.4.3). (206) The mutex passed to mtx_timedlock does not support timeout (7.28.4.4). (207) The mutex passed to mtx_unlock is not locked by the calling thread (7.28.4.6). (208) The thread passed to thrd_detach or thrd_join was previously detached or joined with another thread (7.28.5.3, 7.28.5.6). § J.2
Portability issues
593
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
(209) The tss_create function is called from within a destructor (7.28.6.1). (210) The key passed to tss_delete, tss_get, or tss_set was not returned by a call to tss_create before the thread commenced executing destructors (7.28.6.2, 7.28.6.3, 7.28.6.4). (211) An attempt is made to access the pointer returned by the time conversion functions after the thread that originally called the function to obtain it has exited (7.29.3). (212) At least one member of the broken-down time passed to asctime contains a value outside its normal range, or the calculated year exceeds four digits or is less than the year 1000 (7.29.3.1). (213) The argument corresponding to an s specifier without an l qualifier in a call to the fwprintf function does not point to a valid multibyte character sequence that begins in the initial shift state (7.31.2.11). (214) In a call to the wcstok function, the object pointed to by ptr does not have the value stored by the previous call for the same wide string (7.31.4.6.7). (215) An mbstate_t object is used inappropriately (7.31.6). (216) The value of an argument of type wint_t to a wide character classification or case mapping function is neither equal to the value of WEOF nor representable as a wchar_t (7.32.1). (217) The iswctype function is called using a different LC_CTYPE category from the one in effect for the call to the wctype function that returned the description (7.32.2.2.1). (218) The towctrans function is called using a different LC_CTYPE category from the one in effect for the call to the wctrans function that returned the description (7.32.3.2.1).
J.3 1
A conforming implementation is required to document its choice of behavior in each of the areas listed in this subclause. The following are implementation-defined:
J.3.1 1
Implementation-defined behavior
Translation
(1) How a diagnostic is identified (3.10, 5.1.1.3). (2) Whether each nonempty sequence of white-space characters other than new-line is retained or replaced by one space character in translation phase 3 (5.1.1.2).
J.3.2 1
Environment
(1) The mapping between physical source file multibyte characters and the source character set in translation phase 1 (5.1.1.2). (2) The name and type of the function called at program startup in a freestanding environment (5.1.2.1). (3) The effect of program termination in a freestanding environment (5.1.2.1). (4) An alternative manner in which the main function may be defined (5.1.2.2.1). (5) The values given to the strings pointed to by the argv argument to main (5.1.2.2.1). (6) What constitutes an interactive device (5.1.2.3). (7) Whether a program can have more than one thread of execution in a freestanding environment (5.1.2.4). (8) The set of signals, their semantics, and their default handling (7.14). (9) Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a computational exception (7.14.1.1). 594
Portability issues
§ J.3.2
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
(10) Signals for which the equivalent of signal(sig, SIG_IGN); is executed at program startup (7.14.1.1). (11) The set of environment names and the method for altering the environment list used by the getenv function (7.24.4.6). (12) The manner of execution of the string by the system function (7.24.4.8).
J.3.3 1
Identifiers
(1) Which additional multibyte characters may appear in identifiers and their correspondence to universal character names (6.4.2). (2) The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).
J.3.4 1
Characters
(1) The number of bits in a byte (3.6). (2) The values of the members of the execution character set (5.2.1). (3) The unique value of the member of the execution character set produced for each of the standard alphabetic escape sequences (5.2.2). (4) The value of a char object into which has been stored any character other than a member of the basic execution character set (6.2.5). (5) Which of signed char or unsigned char has the same range, representation, and behavior as "plain" char (6.2.5, 6.3.1.1). (6) The literal encoding, which maps of the characters of the execution character set to the values in a character constant or string literal (6.2.9, 6.4.4.4). (7) The wide literal encoding, of the characters of the execution character set to the values in a wchar_t character constant or wchar_t string literal (6.2.9, 6.4.4.4). (8) The mapping of members of the source character set (in character constants and string literals) to members of the execution character set (6.4.4.4, 5.1.1.2). (9) The value of an integer character constant containing more than one character or containing a character or escape sequence that does not map to a single-byte execution character (6.4.4.4). (10) The value of a wide character constant containing more than one multibyte character or a single multibyte character that maps to multiple members of the extended execution character set, or containing a multibyte character or escape sequence not represented in the extended execution character set (6.4.4.4). (11) The current locale used to convert a wide character constant consisting of a single multibyte character that maps to a member of the extended execution character set into a corresponding wide character code (6.4.4.4). (12) The current locale used to convert a wide string literal into corresponding wide character codes (6.4.5). (13) The value of a string literal containing a multibyte character or escape sequence not represented in the execution character set (6.4.5). (14) The encoding of any of wchar_t, char16_t, and char32_t where the corresponding standard encoding macro (__STDC_ISO_10646__, __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.9.2). § J.3.4
Portability issues
595
ISO/IEC 9899:2023 (E)
J.3.5 1
working draft — April 1, 2023
N3096
Integers
(1) Any extended integer types that exist in the implementation (6.2.5). (2) The rank of any extended integer type relative to another extended integer type with the same precision (6.3.1.1). (3) The result of, or the signal raised by, converting an integer to a signed integer type when the value cannot be represented in an object of that type (6.3.1.3). (4) The results of some bitwise operations on signed integers (6.5).
J.3.6 1
Floating-point
(1) The accuracy of the floating-point operations and of the library functions in <math.h> and <complex.h> that return floating-point results (5.2.4.2.2). (2) The accuracy of the conversions between floating-point internal representations and string representations performed by the library functions in <stdio.h>, <stdlib.h>, and <wchar.h> (5.2.4.2.2). (3) The rounding behaviors characterized by non-standard values of FLT_ROUNDS (5.2.4.2.2). (4) The evaluation methods characterized by non-standard negative values of FLT_EVAL_METHOD (5.2.4.2.2). (5) The evaluation methods characterized by non-standard negative values of DEC_EVAL_METHOD (5.2.4.2.3). (6) If decimal floating types are supported (6.2.5). (7) The direction of rounding when an integer is converted to a floating-point number that cannot exactly represent the original value (6.3.1.4). (8) The direction of rounding when a floating-point number is converted to a narrower floatingpoint number (6.3.1.5). (9) How the nearest representable value or the larger or smaller representable value immediately adjacent to the nearest representable value is chosen for certain floating constants (6.4.4.2). (10) Whether and how floating expressions are contracted when not disallowed by the FP_CONTRACT pragma (6.5). (11) The default state for the FENV_ACCESS pragma (7.6.1). (12) Additional floating-point exceptions, rounding modes, environments, and classifications, and their macro names (7.6, 7.12). (13) The default state for the FP_CONTRACT pragma (7.12.2).
J.3.7 1
Arrays and pointers
(1) The result of converting a pointer to an integer or vice versa (6.3.2.3). (2) The size of the result of subtracting two pointers to elements of the same array (6.5.6).
J.3.8 1
Hints
(1) The extent to which suggestions made by using the register storage-class specifier are effective (6.7.1). (2) The extent to which suggestions made by using the inline function specifier are effective (6.7.4). 596
Portability issues
§ J.3.8
N3096
J.3.9 1
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Structures, unions, enumerations, and bit-fields
(1) Whether a "plain" int bit-field is treated as a signed int bit-field or as an unsigned int bit-field (6.7.2, 6.7.2.1). (2) Allowable bit-field types other than bool, signed int, unsigned int, and bit-precise integer types (6.7.2.1). (3) Whether atomic types are permitted for bit-fields (6.7.2.1). (4) Whether a bit-field can straddle a storage-unit boundary (6.7.2.1). (5) The order of allocation of bit-fields within a unit (6.7.2.1). (6) The alignment of non-bit-field members of structures (6.7.2.1). This should present no problem unless binary data written by one implementation is read by another. (7) The integer type compatible with each enumerated type without fixed underlying type (6.7.2.2).
J.3.10 1
(1) What constitutes an access to an object that has volatile-qualified type (6.7.3).
J.3.11 1
Qualifiers
Preprocessing directives
(1) The locations within #pragma directives where header name preprocessing tokens are recognized (6.4, 6.4.7). (2) How sequences in both forms of header names are mapped to headers or external source file names (6.4.7). (3) Whether the value of a character constant in a constant expression that controls conditional inclusion matches the value of the same character constant in the execution character set (6.10.1). (4) Whether the value of a single-character character constant in a constant expression that controls conditional inclusion may have a negative value (6.10.1). (5) The places that are searched for an included < > delimited header, and how the places are specified or the header is identified (6.10.2). (6) How the named source file is searched for in an included " " delimited header (6.10.2). (7) The method by which preprocessing tokens (possibly resulting from macro expansion) in a #include directive are combined into a header name (6.10.2). (8) The nesting limit for #include processing (6.10.2). (9) Whether the # operator inserts a \ character before the \ character that begins a universal character name in a character constant or string literal (6.10.4.2). (10) The behavior on each recognized non-STDC #pragma directive(6.10.7). (11) The definitions for __DATE__ and __TIME__ when respectively, the date and time of translation are not available (6.10.9.1).
J.3.12 1
Library functions
(1) Any library facilities available to a freestanding program, other than the minimal set required by Clause 4 (5.1.2.1). (2) The format of the diagnostic printed by the assert macro (7.2.1.1). (3) The representation of the floating-point status flags stored by the fegetexceptflag function (7.6.4.2). § J.3.12
Portability issues
597
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
(4) Whether the feraiseexcept function raises the "inexact" floating-point exception in addition to the "overflow" or "underflow" floating-point exception (7.6.4.3). (5) Strings other than "C" and "" that may be passed as the second argument to the setlocale function (7.11.1.1). (6) The types defined for float_t and double_t when the value of the FLT_EVAL_METHOD macro is less than 0 (7.12). (7) The types defined for _Decimal32_t and _Decimal64_t when the value of the DEC_EVAL_METHOD macro is less than 0 (7.12). (8) Domain errors for the mathematics functions, other than those required by this document (7.12.1). (9) The values returned by the mathematics functions on domain errors or pole errors (7.12.1). (10) The values returned by the mathematics functions on underflow range errors, whether errno is set to the value of the macro ERANGE when the integer expression math_errhandling & MATH_ERRNO is nonzero, and whether the "underflow" floating-point exception is raised when the integer expression math_errhandling & MATH_ERREXCEPT is nonzero. (7.12.1). (11) Whether a domain error occurs or zero is returned when an fmod function has a second argument of zero (7.12.10.1). (12) Whether a domain error occurs or zero is returned when a remainder function has a second argument of zero (7.12.10.2). (13) The base-2 logarithm of the modulus used by the remquo functions in reducing the quotient (7.12.10.3). (14) The byte order of decimal floating type encodings (7.12.16). (15) Whether a domain error occurs or zero is returned when a remquo function has a second argument of zero (7.12.10.3). (16) Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1). (17) The value of __STDC_ENDIAN_NATIVE__ if the execution environment is not big-endian or little-endian (7.18.2) (18) The null pointer constant to which the macro NULL expands (7.21). (19) Whether the last line of a text stream requires a terminating new-line character (7.23.2). (20) Whether space characters that are written out to a text stream immediately before a new-line character appear when read in (7.23.2). (21) The number of null characters that may be appended to data written to a binary stream (7.23.2). (22) Whether the file position indicator of an append-mode stream is initially positioned at the beginning or end of the file (7.23.3). (23) Whether a write on a text stream causes the associated file to be truncated beyond that point (7.23.3). (24) The characteristics of file buffering (7.23.3). (25) Whether a zero-length file actually exists (7.23.3). (26) The rules for composing valid file names (7.23.3). (27) Whether the same file can be simultaneously open multiple times (7.23.3). 598
Portability issues
§ J.3.12
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
(28) The nature and choice of encodings used for multibyte characters in files (7.23.3). (29) The effect of the remove function on an open file (7.23.4.1). (30) The effect if a file with the new name exists prior to a call to the rename function (7.23.4.2). (31) Whether an open temporary file is removed upon abnormal program termination (7.23.4.3). (32) Which changes of mode are permitted (if any), and under what circumstances (7.23.5.4). (33) The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar sequence printed for a NaN (7.23.6.1, 7.31.2.1). (34) The output for %p conversion in the fprintf or fwprintf function (7.23.6.1, 7.31.2.1). (35) The interpretation of a - character that is neither the first nor the last character, nor the second where a ^ character is the first, in the scanlist for %[ conversion in the fscanf or fwscanf function (7.23.6.2, 7.31.2.1). (36) The set of sequences matched by a %p conversion and the interpretation of the corresponding input item in the fscanf or fwscanf function (7.23.6.2, 7.31.2.2). (37) The value to which the macro errno is set by the fgetpos, fsetpos, or ftell functions on failure (7.23.9.1, 7.23.9.3, 7.23.9.4). (38) The meaning of any n-char or n-wchar sequence in a string representing a NaN that is converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold function (7.24.1.5, 7.31.4.1.2). (39) Whether the strtod, strtof, strtold, wcstod, wcstof, or wcstold function sets errno to ERANGE when underflow occurs (7.24.1.5, 7.31.4.1.2). (40) The meaning of any d-char or d-wchar sequence in a string representing a NaN that is converted by the strtod32, strtod64, strtod128, wcstod32, wcstod64, or wcstod128 function (7.24.1.6, 7.31.4.1.3). (41) Whether the strtod32, strtod64, strtod128, wcstod32, wcstod64, or wcstod128 function sets errno to ERANGE when underflow occurs (7.24.1.6, 7.31.4.1.3). (42) Whether the calloc, malloc, realloc, and aligned_alloc functions return a null pointer or a pointer to an allocated object when the size requested is zero (7.24.3). (43) Whether open streams with unwritten buffered data are flushed, open streams are closed, or temporary files are removed when the abort or _Exit function is called (7.24.4.1, 7.24.4.5). (44) The termination status returned to the host environment by the abort, exit, _Exit, or quick_exit function (7.24.4.1, 7.24.4.4, 7.24.4.5, 7.24.4.7). (45) The value returned by the system function when its argument is not a null pointer (7.24.4.8). (46) Whether the internal state of multibyte/wide character conversion functions has thread-storage duration, and its initial value in newly created threads (7.24.7). (47) Whether the multibyte/wide character conversion functions avoid data races with other calls to the same function (7.24.7). (48) The range and precision of times representable in clock_t and time_t (7.29). (49) The local time zone and Daylight Saving Time (7.29.1). (50) Whether TIME_MONOTONIC or TIME_ACTIVE are supported time bases (7.29.1). (51) Whether TIME_THREAD_ACTIVE is a supported time bases (7.29.1, 7.28.1). (52) The era for the clock function (7.29.2.1). § J.3.12
Portability issues
599
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
(53) The TIME_UTC epoch (7.29.2.6). (54) The replacement string for the %Z specifier to the strftime, and wcsftime functions in the "C" locale (7.29.3.5, 7.31.5.1). (55) Whether internal mbstate_t objects have thread storage duration (7.30.1, 7.31.6.3, 7.31.6.4). (56) Whether the functions in <math.h> honor the rounding direction mode in an IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10).
J.3.13 1
Architecture
(1) The values or expressions assigned to the macros specified in the headers <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.22). (2) The result of attempting to indirectly access an object with automatic or thread storage duration from a thread other than the one with which it is associated (6.2.4). (3) The number, order, and encoding of bytes in any object (when not explicitly specified in this document) (6.2.6.1). (4) Whether any extended alignments are supported and the contexts in which they are supported (6.2.8). (5) Valid alignment values other than those returned by an alignof expression for fundamental types, if any (6.2.8). (6) The value of the result of the sizeof and alignof operators (6.5.3.4).
J.4 1
Locale-specific behavior
The following characteristics of a hosted environment are locale-specific and are required to be documented by the implementation: (1) Additional members of the source and execution character sets beyond the basic character set (5.2.1). (2) The presence, meaning, and representation of additional multibyte characters in the execution character set beyond the basic character set (5.2.1.1). (3) The shift states used for the encoding of multibyte characters (5.2.1.1). (4) The direction of writing of successive printing characters (5.2.2). (5) The decimal-point character (7.1.1). (6) The set of printing characters (7.4, 7.32.2). (7) The set of control characters (7.4, 7.32.2). (8) The sets of characters tested for by the isalpha, isblank, islower, ispunct, isspace , isupper, iswalpha, iswblank, iswlower, iswpunct, iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10, 7.4.1.11, 7.32.2.1.2, 7.32.2.1.3, 7.32.2.1.7, 7.32.2.1.9, 7.32.2.1.10, 7.32.2.1.11). (9) The native environment (7.11.1.1). (10) Additional subject sequences accepted by the numeric conversion functions (7.24.1, 7.31.4.1). (11) The collation sequence of the execution character set (7.26.4.3, 7.31.4.4.2). (12) The contents of the error message strings set up by the strerror function (7.26.6.3). (13) The formats for time and date (7.29.3.5, 7.31.5.1). (14) Character mappings that are supported by the towctrans function (7.32.1). (15) Character classifications that are supported by the iswctype function (7.32.1). 600
Portability issues
§ J.4
N3096
J.5 1
The following extensions are widely used in many systems, but are not portable to all implementations. The inclusion of any extension that may cause a strictly conforming program to become invalid renders an implementation nonconforming. Examples of such extensions are new keywords, extra library functions declared in standard headers, or predefined macros with names that do not begin with an underscore.
Writable string literals
String literals are modifiable (in which case, identical string literals should denote distinct objects) (6.4.5).
J.5.6 1
Scopes of identifiers
A function identifier, or the identifier of an object the declaration of which contains the keyword extern, has file scope (6.2.1).
J.5.5 1
Lengths and cases of identifiers
All characters in identifiers (with or without external linkage) are significant (6.4.2).
J.5.4 1
Specialized identifiers
Characters other than the underscore _, letters, and digits, that are not part of the basic source character set (such as the dollar sign $, or characters in national character sets) may appear in an identifier (6.4.2).
J.5.3 1
Environment arguments
In a hosted environment, the main function receives a third argument, char *envp[], that points to a null-terminated array of pointers to char, each of which points to a string that provides information about the environment for this execution of the program (5.1.2.2.1).
J.5.2 1
ISO/IEC 9899:2023 (E)
Common extensions
J.5.1 1
working draft — April 1, 2023
Other arithmetic types
Additional arithmetic types, such as __int128 or double double, and their appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have more range or precision than long double, may be used for evaluating expressions of other floating types, and may be used to define float_t or double_t. Additional floating types may also have less range or precision than float.
J.5.7
Function pointer casts
1
A pointer to an object or to void may be cast to a pointer to a function, allowing data to be invoked as a function (6.5.4).
2
A pointer to a function may be cast to a pointer to an object or to void, allowing a function to be inspected or modified (for example, by a debugger) (6.5.4).
J.5.8 1
A bit-field may be declared with a type other than bool, unsigned int, signed int, or a bit-precise integer type, with an appropriate maximum width (6.7.2.1).
J.5.9 1
The fortran keyword
The fortran function specifier may be used in a function declaration to indicate that calls suitable for FORTRAN should be generated, or that a different representation for the external name is to be generated (6.7.4).
J.5.10 1
Extended bit-field types
The asm keyword
The asm keyword may be used to insert assembly language directly into the translator output (6.8). The most common implementation is via a statement of the form: asm (character-string-literal);
§ J.5.10
Portability issues
601
ISO/IEC 9899:2023 (E)
J.5.11 1
Predefined macro names
Floating-point status flags
If any floating-point status flags are set on normal termination after all calls to functions registered by the atexit function have been made (see 7.24.4.4), the implementation writes some diagnostics indicating the fact to the stderr stream, if it is still open,
J.5.15 1
Multiple external definitions
Macro names that do not begin with an underscore, describing the translation and execution environments, are defined by the implementation before translation begins (6.10.9).
J.5.14 1
Type inference
There may be more than one external definition for the identifier of an object, with or without the explicit use of the keyword extern; if the definitions disagree, or more than one is initialized, the behavior is undefined (6.9.2).
J.5.13 1
N3096
A declaration for which a type is inferred (6.7.9) may additionally accept pointer declarators, function declarators, and may have more than one declarator.
J.5.12 1
working draft — April 1, 2023
Extra arguments for signal handlers
Handlers for specific signals are called with extra arguments in addition to the signal number (7.14.1.1).
J.5.16
Additional stream types and file-opening modes
1
Additional mappings from files to streams are supported (7.23.2).
2
Additional file-opening modes may be specified by characters appended to the mode argument of the fopen function (7.23.5.3).
J.5.17 1
The file position indicator is decremented by each successful call to the ungetc or ungetwc function for a text stream, except if its value was zero before a call (7.23.7.10, 7.31.3.10).
J.5.18 1
Reserved identifiers and keywords
A lot of identifier preprocessing tokens are used for specific purposes in regular clauses or appendices from translation phase 3 onwards. Using any of these for a purpose different from their description in this document, even if the use is in a context where they are normatively permitted, may have an impact on the portability of code and should thus be avoided.
J.6.1 1
Math error reporting
Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors instead of, or in addition to, setting errno or raising floating-point exceptions (7.3, 7.12).
J.6 1
Defined file position indicator
Rule based identifiers
The following 53 regular expressions characterize identifiers that are systematically reserved by some clause in this document. ATOMIC_[A-Z][a-zA-Z0-9_]* DBL_[A-Z][a-zA-Z0-9_]* DEC128_[A-Z][a-zA-Z0-9_]* DEC32_[A-Z][a-zA-Z0-9_]* DEC64_[A-Z][a-zA-Z0-9_]* DEC_[A-Z][a-zA-Z0-9_]* E[0-9A-Z][a-zA-Z0-9_]* FE_[A-Z][a-zA-Z0-9_]* FLT_[A-Z][a-zA-Z0-9_]* FP_[A-Z][a-zA-Z0-9_]*
602
INT[a-zA-Z0-9_]*_C INT[a-zA-Z0-9_]*_MAX INT[a-zA-Z0-9_]*_MIN INT[a-zA-Z0-9_]*_WIDTH LC_[A-Z][a-zA-Z0-9_]* LDBL_[A-Z][a-zA-Z0-9_]* MATH_[A-Z][a-zA-Z0-9_]* PRI[a-zX][a-zA-Z0-9_]* SCN[a-zX][a-zA-Z0-9_]* SIG[A-Z][a-zA-Z0-9_]*
Portability issues
§ J.6.1
N3096
working draft — April 1, 2023
SIG_[A-Z][a-zA-Z0-9_]* TIME_[A-Z][a-zA-Z0-9_]* UINT[a-zA-Z0-9_]*_C UINT[a-zA-Z0-9_]*_MAX UINT[a-zA-Z0-9_]*_WIDTH [a-zA-Z0-9_]*_DECIMAL_DIG [a-zA-Z0-9_]*_DIG [a-zA-Z0-9_]*_EPSILON [a-zA-Z0-9_]*_MANT_DIG [a-zA-Z0-9_]*_MAX_10_EXP [a-zA-Z0-9_]*_MAX_EXP [a-zA-Z0-9_]*_MAX [a-zA-Z0-9_]*_MIN_10_EXP [a-zA-Z0-9_]*_MIN_EXP [a-zA-Z0-9_]*_MIN [a-zA-Z0-9_]*_SNAN [a-zA-Z0-9_]*_TRUE_MIN 2
ISO/IEC 9899:2023 (E)
_[a-zA-Z_][a-zA-Z0-9_]* atomic_[a-z][a-zA-Z0-9_]* ckd_[a-zA-Z0-9_]* cnd_[a-z][a-zA-Z0-9_]* cr_[a-z][a-zA-Z0-9_]* int[a-zA-Z0-9_]*_t is[a-z][a-zA-Z0-9_]* mem[a-z][a-zA-Z0-9_]* mtx_[a-z][a-zA-Z0-9_]* stdc_[a-zA-Z0-9_]* str[a-z][a-zA-Z0-9_]* thrd_[a-z][a-zA-Z0-9_]* to[a-z][a-zA-Z0-9_]* tss_[a-z][a-zA-Z0-9_]* uint[a-zA-Z0-9_]*_t wcs[a-z][a-zA-Z0-9_]*
The following 835 identifiers or keywords match these patterns and have particular semantics provided by this document. atomic_bool ATOMIC_BOOL_LOCK_FREE atomic_char atomic_char16_t ATOMIC_CHAR16_T_LOCK_FREE atomic_char32_t ATOMIC_CHAR32_T_LOCK_FREE atomic_char8_t ATOMIC_CHAR8_T_LOCK_FREE ATOMIC_CHAR_LOCK_FREE atomic_compare_exchange_strong atomic_compare_exchange_strong_explicit atomic_compare_exchange_weak atomic_compare_exchange_weak_explicit atomic_exchange atomic_exchange_explicit atomic_fetch_ atomic_fetch_add atomic_fetch_add_explicit atomic_fetch_and atomic_fetch_and_explicit atomic_fetch_or atomic_fetch_or_explicit atomic_fetch_sub atomic_fetch_sub_explicit atomic_fetch_xor atomic_fetch_xor_explicit atomic_flag atomic_flag_clear atomic_flag_clear_explicit ATOMIC_FLAG_INIT atomic_flag_test_and_set atomic_flag_test_and_set_explicit atomic_init atomic_int
§ J.6.1
atomic_intmax_t atomic_intptr_t atomic_int_fast16_t atomic_int_fast32_t atomic_int_fast64_t atomic_int_fast8_t atomic_int_least16_t atomic_int_least32_t atomic_int_least64_t atomic_int_least8_t ATOMIC_INT_LOCK_FREE atomic_is_lock_free atomic_llong ATOMIC_LLONG_LOCK_FREE atomic_load atomic_load_explicit atomic_long ATOMIC_LONG_LOCK_FREE ATOMIC_POINTER_LOCK_FREE atomic_ptrdiff_t atomic_schar atomic_short ATOMIC_SHORT_LOCK_FREE atomic_signal_fence atomic_size_t atomic_store atomic_store_explicit atomic_thread_fence atomic_uchar atomic_uint atomic_uintmax_t atomic_uintptr_t atomic_uint_fast16_t atomic_uint_fast32_t atomic_uint_fast64_t
Portability issues
603
ISO/IEC 9899:2023 (E)
atomic_uint_fast8_t atomic_uint_least16_t atomic_uint_least32_t atomic_uint_least64_t atomic_uint_least8_t atomic_ullong atomic_ulong atomic_ushort atomic_wchar_t ATOMIC_WCHAR_T_LOCK_FREE BOOL_MAX CHAR_MAX CHAR_MIN ckd_ ckd_add ckd_div ckd_mul ckd_sub cnd_broadcast cnd_destroy cnd_init cnd_signal cnd_t cnd_timedwait cnd_wait CR_DECIMAL_DIG DBL_DECIMAL_DIG DBL_DIG DBL_EPSILON DBL_HAS_SUBNORM DBL_IS_IEC_60559 DBL_MANT_DIG DBL_MAX DBL_MAX_10_EXP DBL_MAX_EXP DBL_MIN DBL_MIN_10_EXP DBL_MIN_EXP DBL_NORM_MAX DBL_SNAN DBL_TRUE_MIN DEC128_EPSILON DEC128_MANT_DIG DEC128_MAX DEC128_MAX_EXP DEC128_MIN DEC128_MIN_EXP DEC128_SNAN DEC128_TRUE_MIN DEC32_EPSILON DEC32_MANT_DIG DEC32_MAX DEC32_MAX_EXP DEC32_MIN DEC32_MIN_EXP DEC32_SNAN
604
working draft — April 1, 2023
N3096
DEC32_TRUE_MIN DEC64_EPSILON DEC64_MANT_DIG DEC64_MAX DEC64_MAX_EXP DEC64_MIN DEC64_MIN_EXP DEC64_SNAN DEC64_TRUE_MIN DECIMAL_DIG DEC_EVAL_METHOD DEC_INFINITY DEC_NAN EDOM EILSEQ EOF EOL ERANGE EXIT_FAILURE EXIT_SUCCESS FE_ALL_EXCEPT FE_DEC_DOWNWARD FE_DEC_DYNAMIC FE_DEC_TONEAREST FE_DEC_TONEARESTFROMZERO FE_DEC_TOWARDZERO FE_DEC_UPWARD FE_DFL_ENV FE_DFL_MODE FE_DIVBYZERO FE_DOWNWARD FE_DYNAMIC FE_INEXACT FE_INVALID FE_OVERFLOW FE_SNANS_ALWAYS_SIGNAL FE_TONEAREST FE_TONEARESTFROMZERO FE_TOWARDZERO FE_UNDERFLOW FE_UPWARD FILENAME_MAX FLT_DECIMAL_DIG FLT_DIG FLT_EPSILON FLT_EVAL_METHOD FLT_HAS_SUBNORM FLT_IS_IEC_60559 FLT_MANT_DIG FLT_MAX FLT_MAX_10_EXP FLT_MAX_EXP FLT_MIN FLT_MIN_10_EXP FLT_MIN_EXP FLT_NORM_MAX
Portability issues
§ J.6.1
N3096
FLT_RADIX FLT_ROUNDS FLT_SNAN FLT_TRUE_MIN FOPEN_MAX FP_CONTRACT FP_FAST_D FP_FAST_D32ADDD128 FP_FAST_D32ADDD64 FP_FAST_D32DIVD128 FP_FAST_D32DIVD64 FP_FAST_D32FMAD128 FP_FAST_D32FMAD64 FP_FAST_D32MULD128 FP_FAST_D32MULD64 FP_FAST_D32SQRTD128 FP_FAST_D32SQRTD64 FP_FAST_D32SUBD128 FP_FAST_D32SUBD64 FP_FAST_D64ADDD128 FP_FAST_D64DIVD128 FP_FAST_D64FMAD128 FP_FAST_D64MULD128 FP_FAST_D64SQRTD128 FP_FAST_D64SUBD128 FP_FAST_DADDL FP_FAST_DDIVL FP_FAST_DFMAL FP_FAST_DMULL FP_FAST_DSQRTL FP_FAST_DSUBL FP_FAST_F FP_FAST_FADD FP_FAST_FADDL FP_FAST_FDIV FP_FAST_FDIVL FP_FAST_FFMA FP_FAST_FFMAL FP_FAST_FMA FP_FAST_FMAD FP_FAST_FMAD128 FP_FAST_FMAD32 FP_FAST_FMAD64 FP_FAST_FMAF FP_FAST_FMAL FP_FAST_FMUL FP_FAST_FMULL FP_FAST_FSQRT FP_FAST_FSQRTL FP_FAST_FSUB FP_FAST_FSUBL FP_ILOGB0 FP_ILOGBNAN FP_INFINITE FP_INT_DOWNWARD FP_INT_TONEAREST
§ J.6.1
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
FP_INT_TONEARESTFROMZERO FP_INT_TOWARDZERO FP_INT_UPWARD FP_LLOGB0 FP_LLOGBNAN FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO INT16_C INT16_MAX INT16_MIN int16_t INT16_WIDTH INT32_C INT32_MAX INT32_MIN int32_t INT32_WIDTH INT64_C INT64_MAX INT64_MIN int64_t INT64_WIDTH INT8_C INT8_MAX INT8_MIN int8_t INT8_WIDTH INTMAX_C INTMAX_MAX INTMAX_MIN intmax_t INTMAX_WIDTH INTPTR_MAX INTPTR_MIN intptr_t INTPTR_WIDTH int_fast16_t int_fast32_t int_fast64_t int_fast8_t int_least16_t int_least32_t int_least64_t int_least8_t INT_MAX INT_MIN INT_WIDTH isalnum isalpha isblank iscanonical iscntrl isdigit iseqsig
Portability issues
605
ISO/IEC 9899:2023 (E)
isfinite isgraph isgreater isgreaterequal isinf isless islessequal islessgreater islower isnan isnormal isprint ispunct issignaling isspace issubnormal isunordered isupper iswalnum iswalpha iswblank iswcntrl iswctype iswdigit iswgraph iswlower iswprint iswpunct iswspace iswupper iswxdigit isxdigit iszero LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME LDBL_DECIMAL_DIG LDBL_DIG LDBL_EPSILON LDBL_HAS_SUBNORM LDBL_IS_IEC_60559 LDBL_MANT_DIG LDBL_MAX LDBL_MAX_10_EXP LDBL_MAX_EXP LDBL_MIN LDBL_MIN_10_EXP LDBL_MIN_EXP LDBL_NORM_MAX LDBL_SNAN LDBL_TRUE_MIN LLONG_MAX LLONG_MIN
606
working draft — April 1, 2023
N3096
LONG_MAX LONG_MIN MATH_ERREXCEPT MATH_ERRNO MB_CUR_MAX MB_LEN_MAX memalignment memccpy memchr memcmp memcpy memcpy_s memmove memmove_s memory_order memory_order_acquire memory_order_acq_rel memory_order_consume memory_order_relaxed memory_order_release memory_order_seq_cst memset memset_explicit memset_s mtx_destroy mtx_init mtx_lock mtx_plain mtx_recursive mtx_t mtx_timed mtx_timedlock mtx_trylock mtx_unlock PRId32 PRId64 PRIdFAST32 PRIdFAST64 PRIdLEAST32 PRIdLEAST64 PRIdMAX PRIdPTR PRIi32 PRIi64 PRIiFAST32 PRIiFAST64 PRIiLEAST32 PRIiLEAST64 PRIiMAX PRIiPTR PRIo32 PRIo64 PRIoFAST32 PRIoFAST64 PRIoLEAST32 PRIoLEAST64
Portability issues
§ J.6.1
N3096
PRIoMAX PRIoPTR PRIu32 PRIu64 PRIuFAST32 PRIuFAST64 PRIuLEAST32 PRIuLEAST64 PRIuMAX PRIuPTR PRIX32 PRIX64 PRIXFAST32 PRIXFAST64 PRIXLEAST32 PRIXLEAST64 PRIXMAX PRIXPTR PTRDIFF_MAX PTRDIFF_MIN RAND_MAX RSIZE_MAX SCHAR_MAX SCHAR_MIN SCNdMAX SCNdPTR SCNiMAX SCNiPTR SCNoMAX SCNoPTR SCNuMAX SCNuPTR SCNxMAX SCNxPTR SHRT_MAX SHRT_MIN SIGABRT SIGFPE SIGILL SIGINT SIGSEGV SIGTERM SIG_ATOMIC_MAX SIG_ATOMIC_MIN SIG_ATOMIC_WIDTH SIG_DFL SIG_ERR SIG_IGN SIZE_MAX stdc_ stdc_bit_ceil stdc_bit_ceiluc stdc_bit_ceilui stdc_bit_ceilul stdc_bit_ceilull stdc_bit_ceilus
§ J.6.1
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
stdc_bit_floor stdc_bit_flooruc stdc_bit_floorui stdc_bit_floorul stdc_bit_floorull stdc_bit_floorus stdc_bit_width stdc_bit_widthuc stdc_bit_widthui stdc_bit_widthul stdc_bit_widthull stdc_bit_widthus stdc_count_ones stdc_count_onesuc stdc_count_onesui stdc_count_onesul stdc_count_onesull stdc_count_onesus stdc_count_zeros stdc_count_zerosuc stdc_count_zerosui stdc_count_zerosul stdc_count_zerosull stdc_count_zerosus stdc_first_leading_one stdc_first_leading_oneuc stdc_first_leading_oneui stdc_first_leading_oneul stdc_first_leading_oneull stdc_first_leading_oneus stdc_first_leading_zero stdc_first_leading_zerouc stdc_first_leading_zeroui stdc_first_leading_zeroul stdc_first_leading_zeroull stdc_first_leading_zerous stdc_first_trailing_one stdc_first_trailing_oneuc stdc_first_trailing_oneui stdc_first_trailing_oneul stdc_first_trailing_oneull stdc_first_trailing_oneus stdc_first_trailing_zero stdc_first_trailing_zerouc stdc_first_trailing_zeroui stdc_first_trailing_zeroul stdc_first_trailing_zeroull stdc_first_trailing_zerous stdc_has_single_bit stdc_has_single_bituc stdc_has_single_bitui stdc_has_single_bitul stdc_has_single_bitull stdc_has_single_bitus stdc_leading_ones stdc_leading_onesuc
Portability issues
607
ISO/IEC 9899:2023 (E)
stdc_leading_onesui stdc_leading_onesul stdc_leading_onesull stdc_leading_onesus stdc_leading_zeros stdc_leading_zerosuc stdc_leading_zerosui stdc_leading_zerosul stdc_leading_zerosull stdc_leading_zerosus stdc_trailing_ones stdc_trailing_onesuc stdc_trailing_onesui stdc_trailing_onesul stdc_trailing_onesull stdc_trailing_onesus stdc_trailing_zeros stdc_trailing_zerosuc stdc_trailing_zerosui stdc_trailing_zerosul stdc_trailing_zerosull stdc_trailing_zerosus strcat strcat_s strchr strcmp strcoll strcpy strcpy_s strcspn strdup strerror strerrorlen_s strerror_s strfromd strfromd128 strfromd32 strfromd64 strfromencbind strfromencdecd strfromencf strfromencf128 strfromf strfroml strftime strlen strncat strncat_s strncmp strncpy strncpy_s strndup strnlen_s strpbrk strrchr strspn
608
working draft — April 1, 2023
N3096
strstr strto strtod strtod128 strtod32 strtod64 strtoencbind strtoencdecd strtoencf strtof strtoimax strtok strtok_s strtol strtold strtoll strtoul strtoull strtoumax struct strxfrm thrd_busy thrd_create thrd_current thrd_detach thrd_equal thrd_error thrd_exit thrd_join thrd_nomem thrd_sleep thrd_start_t thrd_success thrd_t thrd_timedout thrd_yield TIME_ACTIVE TIME_MONOTONIC TIME_THREAD_ACTIVE TIME_UTC TMP_MAX tolower totalorder totalorderd totalorderd128 totalorderd32 totalorderd64 totalorderf totalorderl totalordermag totalordermagd totalordermagd128 totalordermagd32 totalordermagd64 totalordermagf totalordermagl
Portability issues
§ J.6.1
N3096
toupper towctrans towlower towupper tss_create tss_delete tss_dtor_t tss_get tss_set tss_t UCHAR_MAX UINT16_C UINT16_MAX uint16_t UINT16_WIDTH UINT32_C UINT32_MAX uint32_t UINT32_WIDTH UINT64_C UINT64_MAX uint64_t UINT64_WIDTH UINT8_C UINT8_MAX uint8_t UINT8_WIDTH UINTMAX_C UINTMAX_MAX uintmax_t UINTMAX_WIDTH UINTPTR_MAX uintptr_t UINTPTR_WIDTH uint_fast16_t uint_fast32_t uint_fast64_t uint_fast8_t uint_least16_t uint_least32_t uint_least64_t uint_least8_t UINT_MAX UINT_WIDTH ULLONG_MAX ULONG_MAX USHRT_MAX WCHAR_MAX WCHAR_MIN wcscat wcscat_s wcschr wcscmp wcscoll wcscpy wcscpy_s
§ J.6.1
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
wcscspn wcsftime wcslen wcsncat wcsncat_s wcsncmp wcsncpy wcsncpy_s wcsnlen_s wcspbrk wcsrchr wcsrtombs wcsrtombs_s wcsspn wcsstr wcsto wcstod wcstod128 wcstod32 wcstod64 wcstof wcstoimax wcstok wcstok_s wcstol wcstold wcstoll wcstombs wcstombs_s wcstoul wcstoull wcstoumax wcsxfrm WINT_MAX WINT_MIN _Alignas _Alignof _Atomic _BitInt _Bool _Complex _Complex_I _Decimal _Decimal128 _Decimal128x _Decimal32 _Decimal32_t _Decimal64 _Decimal64x _Decimal64_t _Exit _EXT__ _Float _Float128 _Float128x _Float128_t
Portability issues
609
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
_Float16 _Float16_t _Float32 _Float32x _Float32_t _Float64 _Float64x _Float64_t _Generic _Imaginary _Imaginary_I _IOFBF _IOLBF _IONBF _Noreturn _Pragma _PRINTF_NAN_LEN_MAX _Static_assert _Thread_local __alignas_is_defined __alignof_is_defined __bool_true_false_are_defined __cplusplus __DATE__ __deprecated__ __fallthrough__ __FILE__ __func__ __has_c_attribute __has_embed __has_include __if_empty__ __limit__ __LINE__ __maybe_unused__ __nodiscard__ __noreturn__ __pp_param__ __prefix__ __reproducible__ __STDC_ANALYZABLE__ __STDC_EMBED_EMPTY__ __STDC_EMBED_FOUND__ __STDC_EMBED_NOT_FOUND__ __STDC_ENDIAN_BIG__ __STDC_ENDIAN_LITTLE__ __STDC_ENDIAN_NATIVE__
J.6.2 1
N3096
__STDC_HOSTED__ __STDC_IEC_559_COMPLEX__ __STDC_IEC_559__ __STDC_IEC_60559_BFP__ __STDC_IEC_60559_COMPLEX__ __STDC_IEC_60559_DFP__ __STDC_IEC_60559_TYPES__ __STDC_ISO_10646__ __STDC_LIB_EXT1__ __STDC_MB_MIGHT_NEQ_WC__ __STDC_NO_ATOMICS__ __STDC_NO_COMPLEX__ __STDC_NO_THREADS__ __STDC_NO_VLA__ __STDC_UTF_16__ __STDC_UTF_32__ __STDC_VERSION_ASSERT_H__ __STDC_VERSION_COMPLEX_H__ __STDC_VERSION_FENV_H__ __STDC_VERSION_FLOAT_H__ __STDC_VERSION_MATH_H__ __STDC_VERSION_SETJMP_H__ __STDC_VERSION_STDARG_H__ __STDC_VERSION_STDATOMIC_H__ __STDC_VERSION_STDBIT_H__ __STDC_VERSION_STDCKDINT_H__ __STDC_VERSION_STDDEF_H__ __STDC_VERSION_STDINT_H__ __STDC_VERSION_STDIO_H__ __STDC_VERSION_STDLIB_H__ __STDC_VERSION_STRING_H__ __STDC_VERSION_TGMATH_H__ __STDC_VERSION_TIME_H__ __STDC_VERSION_UCHAR_H__ __STDC_VERSION_WCHAR_H__ __STDC_VERSION__ __STDC_WANT_IEC_60559_EXT__ __STDC_WANT_IEC_60559_TYPES_EXT__ __STDC_WANT_LIB_EXT1__ __STDC__ __suffix__ __TIME__ __unsequenced__ __VA_ARGS__ __VA_OPT__ ___Noreturn__
Particular identifiers or keywords
The following 1320 identifiers or keywords are not covered by the above and have particular semantics provided by this document. abort_handler_s abort abs acosd128
610
acosd32 acosd64 acosd acosf
Portability issues
acoshd128 acoshd32 acoshd64 acoshd
§ J.6.2
N3096
working draft — April 1, 2023
acoshf acoshl acosh acosl acospid128 acospid32 acospid64 acospid acospif acospil acospi acos addd addf alignas aligned_alloc alignof and_eq and asctime_s asctime asind128 asind32 asind64 asind asinf asinhd128 asinhd32 asinhd64 asinhd asinhf asinhl asinh asinl asinpid128 asinpid32 asinpid64 asinpid asinpif asinpil asinpi asin assert atan2d128 atan2d32 atan2d64 atan2d atan2f atan2l atan2pid128 atan2pid32 atan2pid64 atan2pid atan2pif atan2pil atan2pi
atan2 atand128 atand32 atand64 atand atanf atanhd128 atanhd32 atanhd64 atanhd atanhf atanhl atanh atanl atanpid128 atanpid32 atanpid64 atanpid atanpif atanpil atanpi atan atexit atof atoi atoll atol at_quick_exit auto bitand BITINT_MAXWIDTH bitor BOOL_WIDTH bool break bsearch_s bsearch btowc BUFSIZ c16rtomb c32rtomb c8rtomb cabsf cabsl cabs cacosf cacoshf cacoshl cacosh cacosl cacospi cacos calloc call_once canonicalized128 canonicalized32
§ J.6.2
Portability issues
ISO/IEC 9899:2023 (E)
canonicalized64 canonicalized canonicalizef canonicalizel canonicalize cargf cargl carg case casinf casinhf casinhl casinh casinl casinpi casin catanf catanhf catanhl catanh catanl catanpi catan cbrtd128 cbrtd32 cbrtd64 cbrtd cbrtf cbrtl cbrt ccompoundn ccosf ccoshf ccoshl ccosh ccosl ccospi ccos ceild128 ceild32 ceild64 ceild ceilf ceill ceil cerfc cerf cexp10m1 cexp10 cexp2m1 cexp2 cexpf cexpl cexpm1 cexp char16_t
611
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
char32_t char8_t CHAR_BIT CHAR_WIDTH char cimagf cimagl cimag clearerr clgamma CLOCKS_PER_SEC clock_t
coshd coshf coshl cosh cosl cospid128 cospid32 cospid64 cospid cospif cospil cospi cos cpowf cpowl cpown cpowr cpow cprojf cprojl cproj crealf creall creal crootn crsqrt csinf csinhf csinhl csinh csinl csinpi csin csqrtf csqrtl csqrt ctanf ctanhf ctanhl ctanh ctanl ctanpi ctan ctgamma ctime_s ctime currency_symbol CX_LIMITED_RANGE d32addd128 d32addd64 d32add d32divd128 d32divd64 d32div d32fmad128 d32fmad64
clock clog10p1 clog10 clog1p clog2p1 clog2 clogf clogl clogp1 clog CMPLXF CMPLXL CMPLX complex compl compoundnd128 compoundnd32 compoundnd64 compoundnd compoundnf compoundnl compoundn conjf conjl conj constexpr constraint_handler_t const continue copysignd128 copysignd32 copysignd64 copysignd copysignf copysignl copysign cosd128 cosd32 cosd64 cosd cosf coshd128 coshd32 coshd64
612
Portability issues
N3096
d32fma d32muld128 d32muld64 d32mul d32sqrtd128 d32sqrtd64 d32sqrt d32subd128 d32subd64 d32sub d64addd128 d64add d64divd128 d64div d64fmad128 d64fma d64muld128 d64mul d64sqrtd128 d64sqrt d64subd128 d64sub daddl dadd ddivl ddiv decimal_point Decimal DECN_ DECN decodebind128 decodebind32 decodebind64 decodebind decodebin decodedecd128 decodedecd32 decodedecd64 decodedecd decodedec decodef DEC DEFAULT defined define deprecated dfmal dfma difftime divd divf div_t div dmull dmul double_t
§ J.6.2
N3096
working draft — April 1, 2023
double do dsqrtl dsqrt dsubl dsub elifdef elifndef elif else embed encbind encdecd encf encodebind128 encodebind32 encodebind64 encodebind encodebin encodedecd128 encodedecd32 encodedecd64 encodedecd encodedec encodef endif enum erfcd128 erfcd32 erfcd64 erfcd erfcf erfcl erfc erfd128 erfd32 erfd64 erfd erff erfl erf errno_t errno error exit exp10d128 exp10d32 exp10d64 exp10d exp10f exp10l exp10m1d128 exp10m1d32 exp10m1d64 exp10m1d exp10m1f
exp10m1l exp10m1 exp10 exp2d128 exp2d32 exp2d64 exp2d exp2f exp2l exp2m1d128 exp2m1d32 exp2m1d64 exp2m1d exp2m1f exp2m1l exp2m1 exp2 expd128 expd32 expd64 expd expf expl expm1d128 expm1d32 expm1d64 expm1d expm1f expm1l expm1 exp extern fabsd128 fabsd32 fabsd64 fabsd fabsf fabsl fabs faddl fadd fallthrough false fclose fdimd128 fdimd32 fdimd64 fdimd fdimf fdiml fdim fdivl fdiv feclearexcept fegetenv fegetexceptflag
§ J.6.2
Portability issues
ISO/IEC 9899:2023 (E)
fegetmode fegetround feholdexcept femode_t FENV_ACCESS FENV_DEC_ROUND FENV_ROUND fenv_t feof feraiseexcept ferror fesetenv fesetexceptflag fesetexcept fesetmode fesetround fetestexceptflag fetestexcept feupdateenv fexcept_t fe_dec_getround fe_dec_setround fflush ffmal ffma fgetc fgetpos fgets fgetwc fgetws FILE float_t Float floord128 floord32 floord64 floord floorf floorl floor FLTN_ FLTN FLT fmad128 fmad32 fmad64 fmad fmaf fmal fmaxd128 fmaxd32 fmaxd64 fmaxd fmaxf fmaximumd128 fmaximumd32
613
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
fmaximumd64 fmaximumd fmaximumf fmaximuml fmaximum_magd128 fmaximum_magd32 fmaximum_magd64 fmaximum_magd fmaximum_magf fmaximum_magl fmaximum_mag_numd128 fmaximum_mag_numd32 fmaximum_mag_numd64 fmaximum_mag_numd fmaximum_mag_numf fmaximum_mag_numl fmaximum_mag_num fmaximum_mag fmaximum_numd128 fmaximum_numd32 fmaximum_numd64 fmaximum_numd fmaximum_numf fmaximum_numl fmaximum_num fmaximum fmaxl fmax fma fmind128 fmind32 fmind64 fmind fminf fminimumd128 fminimumd32 fminimumd64 fminimumd fminimumf fminimuml fminimum_magd128 fminimum_magd32 fminimum_magd64 fminimum_magd fminimum_magf fminimum_magl fminimum_mag_numd128 fminimum_mag_numd32 fminimum_mag_numd64 fminimum_mag_numd fminimum_mag_numf fminimum_mag_numl fminimum_mag_num fminimum_mag fminimum_numd128 fminimum_numd32
fminimum_numd64 fminimum_numd fminimum_numf fminimum_numl fminimum_num fminimum fminl fmin fmodd128 fmodd32 fmodd64 fmodd fmodf fmodl fmod fmull fmul fopen_s fopen for fpclassify fpos_t fprintf_s fprintf fputc fputs fputwc fputws frac_digits fread free_aligned_sized free_sized free freopen_s freopen frexpd128 frexpd32 frexpd64 frexpd frexpf frexpl frexp fromfpd128 fromfpd32 fromfpd64 fromfpd fromfpf fromfpl fromfpxd128 fromfpxd32 fromfpxd64 fromfpxd fromfpxf fromfpxl fromfpx fromfp
614
Portability issues
N3096
frompfpd frompfpf frompfpl frompfpxd frompfpxf frompfpxl frompfpx frompfp fscanf_s fscanf fseek fsetpos fsqrtl fsqrt fsubl fsub ftell fwide fwprintf_s fwprintf fwrite fwscanf_s fwscanf generic_count_type generic_return_type generic_value_type getchar getc getenv_s getenv getpayloadd128 getpayloadd32 getpayloadd64 getpayloadd getpayloadf getpayloadl getpayload gets_s gets getwchar getwc gmtime_r gmtime_s gmtime goto grouping HUGE_VALF HUGE_VALL HUGE_VAL_D128 HUGE_VAL_D32 HUGE_VAL_D64 HUGE_VAL_D HUGE_VAL_F HUGE_VAL hypotd128 hypotd32
§ J.6.2
N3096
working draft — April 1, 2023
hypotd64 hypotd hypotf hypotl hypot ifdef ifndef if_empty if ignore_handler_s ilogbd128 ilogbd32 ilogbd64 ilogbd ilogbf ilogbl ilogb imaginary imaxabs imaxdiv_t imaxdiv include INFINITY inline int_curr_symbol int_frac_digits int_n_cs_precedes int_n_sep_by_space int_n_sign_posn int_p_cs_precedes int_p_sep_by_space int_p_sign_posn I jmp_buf kill_dependency labs lconv ldexpd128 ldexpd32 ldexpd64 ldexpd ldexpf ldexpl ldexp ldiv_t ldiv lgammad128 lgammad32 lgammad64 lgammad lgammaf lgammal lgamma limit line llabs
lldiv_t lldiv llogbd128 llogbd32 llogbd64 llogbd llogbf llogbl llogb LLONG_WIDTH llquantexpd128 llquantexpd32 llquantexpd64 llquantexpd llquantexp llrintd128 llrintd32 llrintd64 llrintd llrintf llrintl llrint llroundd128 llroundd32 llroundd64 llroundd llroundf llroundl llround localeconv localtime_r localtime_s localtime log10d128 log10d32 log10d64 log10d log10f log10l log10p1d128 log10p1d32 log10p1d64 log10p1d log10p1f log10p1l log10p1 log10 log1pd128 log1pd32 log1pd64 log1pd log1pf log1pl log1p log2d128 log2d32
§ J.6.2
Portability issues
ISO/IEC 9899:2023 (E)
log2d64 log2d log2f log2l log2p1d128 log2p1d32 log2p1d64 log2p1d log2p1f log2p1l log2p1 log2 logbd128 logbd32 logbd64 logbd logbf logbl logb logd128 logd32 logd64 logd logf logl logp1d128 logp1d32 logp1d64 logp1d logp1f logp1l logp1 log longjmp long_double_t LONG_WIDTH long lrintd128 lrintd32 lrintd64 lrintd lrintf lrintl lrint lroundd128 lroundd32 lroundd64 lroundd lroundf lroundl lround L_tmpnam_s L_tmpnam main malloc math_errhandling
615
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
max_align_t maybe_unused
nextdownl nextdown nexttowardd128 nexttowardd32 nexttowardd64 nexttowardf nexttowardl nexttoward nextupd128 nextupd32 nextupd64 nextupd nextupf nextupl nextup nodiscard noreturn not_eq not nullptr_t nullptr NULL n_cs_precedes n_sep_by_space n_sign_posn offsetof OFF ONCE_FLAG_INIT once_flag ON or_eq or perror positive_sign powd128 powd32 powd64 powd powf powl pownd128 pownd32 pownd64 pownd pownf pownl pown powrd128 powrd32 powrd64 powrd powrf powrl powr pow pp_param
mblen mbrlen mbrtoc16 mbrtoc32 mbrtoc8 mbrtowc mbsinit mbsrtowcs_s mbsrtowcs mbstate_t mbstowcs_s mbstowcs mbtowc mktime modfd128 modfd32 modfd64 modfd modff modfl modf mon_decimal_point mon_grouping mon_thousands_sep muld mulf nand128 nand32 nand64 nand nanf nanl nan NDEBUG nearbyintd128 nearbyintd32 nearbyintd64 nearbyintd nearbyintf nearbyintl nearbyint negative_sign nextafterd128 nextafterd32 nextafterd64 nextafterd nextafterf nextafterl nextafter nextdownd128 nextdownd32 nextdownd64 nextdownd nextdownf
616
Portability issues
N3096
pragma prefix printf_s printf ptrdiff_t PTRDIFF_WIDTH putchar putc puts putwchar putwc p_cs_precedes p_sep_by_space p_sign_posn QChar qsort_s qsort quantized128 quantized32 quantized64 quantized quantize quantumd128 quantumd32 quantumd64 quantumd quantum quick_exit QVoid QWchar_t raise rand realloc register remainderd128 remainderd32 remainderd64 remainderd remainderf remainderl remainder remove remquof remquol remquo rename reproducible restrict return rewind rintd128 rintd32 rintd64 rintd rintf rintl
§ J.6.2
N3096
working draft — April 1, 2023
rint rootnd128 rootnd32 rootnd64 rootnd rootnf rootnl rootn roundd128 roundd32 roundd64 roundd roundevend128 roundevend32 roundevend64 roundevend roundevenf roundevenl roundeven roundf roundl round rsize_t rsqrtd128 rsqrtd32 rsqrtd64 rsqrtd rsqrtf rsqrtl rsqrt samequantumd128 samequantumd32 samequantumd64 samequantumd samequantum scalblnd128 scalblnd32 scalblnd64 scalblnd scalblnf scalblnl scalbln scalbnd128 scalbnd32 scalbnd64 scalbnd scalbnf scalbnl scalbn scanf_s scanf SCHAR_WIDTH SEEK_CUR SEEK_END SEEK_SET setbuf
setjmp setlocale setpayloadd128 setpayloadd32 setpayloadd64 setpayloadd setpayloadf setpayloadl setpayloadsigd128 setpayloadsigd32 setpayloadsigd64 setpayloadsigd setpayloadsigf setpayloadsigl setpayloadsig setpayload setvbuf set_constraint_handler_s short SHRT_WIDTH signal signbit signed sig_atomic_t sind128 sind32 sind64 sind sinf sinhd128 sinhd32 sinhd64 sinhd sinhf sinhl sinh sinl sinpid128 sinpid32 sinpid64 sinpid sinpif sinpil sinpi sin sizeof size_t SIZE_WIDTH snprintf_s snprintf snwprintf_s sprintf_s sprintf sqrtd128 sqrtd32 sqrtd64
§ J.6.2
Portability issues
ISO/IEC 9899:2023 (E)
sqrtd sqrtf sqrtl sqrt srand sscanf_s sscanf static_assert static STDC stderr stdin stdout subd subf suffix switch swprintf_s swprintf swscanf_s swscanf system tand128 tand32 tand64 tand tanf tanhd128 tanhd32 tanhd64 tanhd tanhf tanhl tanh tanl tanpid128 tanpid32 tanpid64 tanpid tanpif tanpil tanpi tan tgammad128 tgammad32 tgammad64 tgammad tgammaf tgammal tgamma thousands_sep thread_local timegm timespec_getres timespec_get timespec
617
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
time_t time tmpfile_s tmpfile tmpnam_s tmpnam TMP_MAX_S tm_hour tm_isdst tm_mday tm_min tm_mon tm_sec tm_wday tm_yday tm_year tm true truncd128 truncd32 truncd64 truncd truncf truncl trunc TSS_DTOR_ITERATIONS tv_nsec tv_sec typedef typeof_unqual typeof UCHAR_WIDTH ufromfpd128 ufromfpd32 ufromfpd64 ufromfpd ufromfpf ufromfpl ufromfpxd128 ufromfpxd32 ufromfpxd64 ufromfpxd ufromfpxf ufromfpxl
ufromfpx ufromfp ULLONG_WIDTH ULONG_WIDTH undef ungetc ungetwc union unreachable unsequenced unsigned USHRT_WIDTH va_arg va_copy va_end va_list va_start vfprintf_s vfprintf vfscanf_s vfscanf vfwprintf_s vfwprintf vfwscanf_s vfwscanf void volatile vprintf_s vprintf vscanf_s vscanf vsnprintf_s vsnprintf vsnwprintf_s vsprintf_s vsprintf vsscanf_s vsscanf vswprintf_s vswprintf vswscanf_s vswscanf vwprintf_s vwprintf
618
Portability issues
N3096
vwscanf_s vwscanf warning wchar_t WCHAR_WIDTH wcrtomb_s wcrtomb wctob wctomb_s wctomb wctrans_t wctrans wctype_t wctype WEOF while wint_t WINT_WIDTH wmemchr wmemcmp wmemcpy_s wmemcpy wmemmove_s wmemmove wmemset wprintf_s wprintf wscanf_s wscanf xaddd xaddf xdivd xdivf xfmad xfmaf xmuld xmulf xor_eq xor xsqrtd xsqrtf xsubd xsubf X_
§ J.6.2
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Annex K (normative)
Bounds-checking interfaces K.1
Background
1
Traditionally, the C Library has contained many functions that trust the programmer to provide output character arrays big enough to hold the result being produced. Not only do these functions not check that the arrays are big enough, they frequently lack the information needed to perform such checks. While it is possible to write safe, robust, and error-free code using the existing library, the library tends to promote programming styles that lead to mysterious failures if a result is too big for the provided array.
2
A common programming style is to declare character arrays large enough to handle most practical cases. However, if these arrays are not large enough to handle the resulting strings, data can be written past the end of the array overwriting other data and program structures. The program never gets any indication that a problem exists, and so never has a chance to recover or to fail gracefully.
3
Worse, this style of programming has compromised the security of computers and networks. Buffer overflows can often be exploited to run arbitrary code with the permissions of the vulnerable (defective) program.
4
If the programmer writes runtime checks to verify lengths before calling library functions, then those runtime checks frequently duplicate work done inside the library functions, which discover string lengths as a side effect of doing their job.
5
This annex provides alternative library functions that promote safer, more secure programming. The alternative functions verify that output buffers are large enough for the intended result and return a failure indicator if they are not. Data is never written past the end of an array. All string results are null terminated.
6
This annex also addresses another problem that complicates writing robust code: functions that are not reentrant because they return pointers to static objects owned by the function. Such functions can be troublesome since a previously returned result can change if the function is called again, perhaps by another thread.
K.2
Scope
1
This annex specifies a series of optional extensions that can be useful in the mitigation of security vulnerabilities in programs, and comprise new functions, macros, and types declared or defined in existing standard headers.
2
An implementation that defines __STDC_LIB_EXT1__ shall conform to the specifications in this annex.469)
3
Subclause K.3 should be read as if it were merged into the parallel structure of named subclauses of Clause 7.
K.3 Library K.3.1 Introduction 1
2
K.3.1.1 Standard headers The functions, macros, and types declared or defined in K.3 and its subclauses are not declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is defined as a macro which expands to the integer constant 0 at the point in the source file where the appropriate header is first included. The functions, macros, and types declared or defined in K.3 and its subclauses are declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is defined as a macro which expands to the integer constant 1 at the point in the source file where the appropriate header is first 469) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these specifications.
§ K.3.1.1
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included.470) 3
It is implementation-defined whether the functions, macros, and types declared or defined in K.3 and its subclauses are declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file where the appropriate header is first included.471)
4
Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be defined identically for all inclusions of any headers from Subclause K.3. If __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the implementation shall issue a diagnostic as if a preprocessor error directive were used.
1
K.3.1.2 Reserved identifiers Each macro name in any of the following subclauses is reserved for use as specified if it is defined by any of its associated headers when included; unless explicitly stated otherwise (see 7.1.4).
2
All identifiers with external linkage in any of the following subclauses are reserved for use as identifiers with external linkage if any of them are used by the program. None of them are reserved if none of them are used.
3
Each identifier with file scope listed in any of the following subclauses is reserved for use as a macro name and as an identifier with file scope in the same name space if it is defined by any of its associated headers when included.
1
1
K.3.1.3 Use of errno An implementation may set errno for the functions defined in this annex, but is not required to. K.3.1.4 Runtime-constraint violations Most functions in this annex include as part of their specification a list of runtime-constraints. These runtime-constraints are requirements on the program using the library.472)
2
Implementations shall verify that the runtime-constraints for a function are not violated by the program. If a runtime-constraint is violated, the implementation shall call the currently registered runtime-constraint handler (see set_constraint_handler_s in <stdlib.h>). Multiple runtimeconstraint violations in the same call to a library function result in only one call to the runtimeconstraint handler. It is unspecified which one of the multiple runtime-constraint violations cause the handler to be called.
3
If the runtime-constraints section for a function states an action to be performed when a runtimeconstraint violation occurs, the function shall perform the action before calling the runtime-constraint handler. If the runtime-constraints section lists actions that are prohibited when a runtime-constraint violation occurs, then such actions are prohibited to the function both before calling the handler and after the handler returns.
4
The runtime-constraint handler might not return. If the handler does return, the library function whose runtime-constraint was violated shall return some indication of failure as given by the returns section in the function’s specification.
K.3.2
Errors <errno.h>
1
The header <errno.h> defines a type.
2
The type is errno_t
470) Future revisions of this document might define meanings for other values of __STDC_WANT_LIB_EXT1__. 471) Subclause 7.1.3 reserves certain names and patterns of names that an implementation can use in headers. All other names are not reserved, and a conforming implementation is not permitted to use them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the implementation is not conforming. 472) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a runtime-constraint violation by calling the runtime-constraint handler. This license comes directly from the definition of undefined behavior.
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which is type int.473)
K.3.3
Common definitions <stddef.h>
1
The header <stddef.h> defines a type.
2
The type is rsize_t
which is the type size_t.474)
K.3.4
Integer types <stdint.h>
1
The header <stdint.h> defines a macro.
2
The macro is RSIZE_MAX
which expands to a value475) of type size_t. Functions that have parameters of type rsize_t consider it a runtime-constraint violation if the values of those parameters are greater than RSIZE_MAX.
3
4
Recommended practice Extremely large object sizes are frequently a sign that an object’s size was calculated incorrectly. For example, negative numbers appear as very large positive numbers when converted to an unsigned type like size_t. Also, some implementations do not support objects as large as the maximum value that can be represented by type size_t. For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect programming errors. For implementations targeting machines with large address spaces, it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of some legitimate, but very large, objects. Implementations targeting machines with small address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there is no object size that is considered a runtime-constraint violation.
K.3.5
Input/output <stdio.h>
1
The header <stdio.h> defines several macros and two types.
2
The macros are L_tmpnam_s
which expands to an integer constant expression that is the size needed for an array of char large enough to hold a temporary file name string generated by the tmpnam_s function; TMP_MAX_S
which expands to an integer constant expression that is the maximum number of unique file names that can be generated by the tmpnam_s function. 3
The types are errno_t
which is type int; and 473) As a matter of programming style, errno_t can be used as the type of something that deals only with the values that might be found in errno. For example, a function which returns the value of errno could be declared as having the return type errno_t. 474) See the description of the RSIZE_MAX macro in <stdint.h>. 475) The macro RSIZE_MAX need not expand to a constant expression.
§ K.3.5
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rsize_t
which is the type size_t. K.3.5.1 Operations on files K.3.5.1.1 The tmpfile_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> errno_t tmpfile_s(FILE * restrict * restrict streamptr);
1
2
Runtime-constraints streamptr shall not be a null pointer.
3
If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file.
4
5
Description The tmpfile_s function creates a temporary binary file that is different from any other existing file and that will automatically be removed when it is closed or at program termination. If the program terminates abnormally, whether an open temporary file is removed is implementation-defined. The file is opened for update with "wb+" mode with the meaning that mode has in the fopen_s function (including the mode’s effect on exclusive access and file permissions). If the file was created successfully, then the pointer to FILE pointed to by streamptr will be set to the pointer to the object controlling the opened file. Otherwise, the pointer to FILE pointed to by streamptr will be set to a null pointer. Recommended practice It should be possible to open at least TMP_MAX_S temporary files during the lifetime of the program (this limit may be shared with tmpnam_s) and there should be no limit on the number simultaneously open other than this limit and any limit on the number of open files (FOPEN_MAX).
6
Returns The tmpfile_s function returns zero if it created the file. If it did not create the file or there was a runtime-constraint violation, tmpfile_s returns a nonzero value. K.3.5.1.2 The tmpnam_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> errno_t tmpnam_s(char *s, rsize_t maxsize);
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3
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Runtime-constraints s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX. maxsize shall be greater than the length of the generated file name string. Description The tmpnam_s function generates a string that is a valid file name and that is not the same as the name of an existing file.476) The function is potentially capable of generating TMP_MAX_S different strings, but any or all of them may already be in use by existing files and thus not be suitable return values. The lengths of these strings shall be less than the value of the L_tmpnam_s macro. The tmpnam_s function generates a different string each time it is called. 476) Files created using strings generated by the tmpnam_s function are temporary only in the sense that their names are not expected to collide with those generated by conventional naming rules for the implementation. It is still necessary to use the remove function to remove such files when their use is ended, and before program termination.
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It is assumed that s points to an array of at least maxsize characters. This array will be set to generated string, as specified below.
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The implementation shall behave as if no library function except tmpnam calls the tmpnam_s function.477)
7
8
9
Recommended practice After a program obtains a file name using the tmpnam_s function and before the program creates a file with that name, the possibility exists that someone else may create a file with that same name. To avoid this race condition, the tmpfile_s function should be used instead of tmpnam_s when possible. One situation that requires the use of the tmpnam_s function is when the program needs to create a temporary directory rather than a temporary file. Implementations should take care in choosing the patterns used for names returned by tmpnam_s. For example, making a thread ID part of the names avoids the race condition and possible conflict when multiple programs run simultaneously by the same user generate the same temporary file names. Returns If no suitable string can be generated, or if there is a runtime-constraint violation, the tmpnam_s function: — if s is not null and maxsize is both greater than zero and not greater than RSIZE_MAX, writes a null character to s[0] — returns a nonzero value.
10
Otherwise, the tmpnam_s function writes the string in the array pointed to by s and returns zero.
11
Environmental limits The value of the macro TMP_MAX_S shall be at least 25. K.3.5.2 File access functions K.3.5.2.1 The fopen_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> errno_t fopen_s(FILE * restrict * restrict streamptr, const char * restrict filename, const char * restrict mode);
1
2 3
4
5
Runtime-constraints None of streamptr, filename, or mode shall be a null pointer. If there is a runtime-constraint violation, fopen_s does not attempt to open a file. Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the null pointer. Description The fopen_s function opens the file whose name is the string pointed to by filename, and associates a stream with it. The mode string shall be as described for fopen, with the addition that modes starting with the character ’w’ or ’a’ may be preceded by the character ’u’, see below: uw
truncate to zero length or create text file for writing, default permissions
uwx
create text file for writing, default permissions
ua
append; open or create text file for writing at end-of-file, default permissions
477) An implementation can have tmpnam call tmpnam_s (perhaps so there is only one naming convention for temporary files), but this is not required.
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uwb
truncate to zero length or create binary file for writing, default permissions
uwbx
create binary file for writing, default permissions
uab
append; open or create binary file for writing at end-of-file, default permissions
uw+
truncate to zero length or create text file for update, default permissions
uw+x
create text file for update, default permissions
ua+
append; open or create text file for update, writing at end-of-file, default permissions
uw+b or uwb+
truncate to zero length or create binary file for update, default permissions
uw+bx or uwb+x create binary file for update, default permissions ua+b or uab+
append; open or create binary file for update, writing at end-of-file, default permissions
6
Opening a file with exclusive mode (’x’ as the last character in the mode argument) fails if the file already exists or cannot be created.
7
If the file was opened successfully, then the pointer to FILE pointed to by streamptr will be set to the pointer to the object controlling the opened file. Otherwise, the pointer to FILE pointed to by streamptr will be set to a null pointer.
8
Returns The fopen_s function returns zero if it opened the file. If it did not open the file or if there was a runtime-constraint violation, fopen_s returns a nonzero value. K.3.5.2.2 The freopen_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> errno_t freopen_s(FILE * restrict * restrict newstreamptr, const char * restrict filename, const char * restrict mode, FILE * restrict stream);
1
2 3
4
Runtime-constraints None of newstreamptr, mode, and stream shall be a null pointer. If there is a runtime-constraint violation, freopen_s neither attempts to close any file associated with stream nor attempts to open a file. Furthermore, if newstreamptr is not a null pointer, fopen_s sets *newstreamptr to the null pointer. Description The freopen_s function opens the file whose name is the string pointed to by filename and associates the stream pointed to by stream with it. The mode argument has the same meaning as in the fopen_s function (including the mode’s effect on exclusive access and file permissions).
5
If filename is a null pointer, the freopen_s function attempts to change the mode of the stream to that specified by mode, as if the name of the file currently associated with the stream had been used. It is implementation-defined which changes of mode are permitted (if any), and under what circumstances.
6
The freopen_s function first attempts to close any file that is associated with stream. Failure to close the file is ignored. The error and end-of-file indicators for the stream are cleared.
7
If the file was opened successfully, then the pointer to FILE pointed to by newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE pointed to by newstreamptr will be set to a null pointer. 624
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Returns The freopen_s function returns zero if it opened the file. If it did not open the file or there was a runtime-constraint violation, freopen_s returns a nonzero value.
1
K.3.5.3 Formatted input/output functions Unless explicitly stated otherwise, if the execution of a function described in this subclause causes copying to take place between objects that overlap, the objects take on unspecified values. K.3.5.3.1 The fprintf_s function Synopsis
1
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int fprintf_s(FILE * restrict stream, const char * restrict format, ...);
Runtime-constraints 2
Neither stream nor format shall be a null pointer. The %n specifier478) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to fprintf_s corresponding to a %s specifier shall not be a null pointer.
3
If there is a runtime-constraint violation, the479) fprintf_s function does not attempt to produce further output, and it is unspecified to what extent fprintf_s produced output before discovering the runtime-constraint violation.
4
Description The fprintf_s function is equivalent to the fprintf function except for the explicit runtimeconstraints listed above.
5
Returns The fprintf_s function returns the number of characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. K.3.5.3.2 The fscanf_s function Synopsis
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3
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int fscanf_s(FILE * restrict stream, const char * restrict format, ...);
Runtime-constraints Neither stream nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the480) fscanf_s function does not attempt to perform further input, and it is unspecified to what extent fscanf_s performed input before discovering the runtime-constraint violation. Description The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion specifiers apply to a pair of arguments (unless assignment suppression is indicated by a *). The first of these arguments is the same as for fscanf. That argument is immediately followed in the argument list by the second argument, which has type rsize_t and gives the number of elements in the array pointed to by the first argument of the pair. If the first argument points to a scalar object, it is 478) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n. 479) Because an implementation can treat any undefined behavior as a runtime-constraint violation, an implementation can treat any unsupported specifiers in the string pointed to by format as a runtime-constraint violation. 480) Because an implementation can treat any undefined behavior as a runtime-constraint violation, an implementation can treat any unsupported specifiers in the string pointed to by format as a runtime-constraint violation.
§ K.3.5.3.2
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considered to be an array of one element.481) 5
6
7
A matching failure occurs if the number of elements in a receiving object is insufficient to hold the converted input (including any trailing null character). Returns The fscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the fscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. EXAMPLE 1 The call: #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> /* ... */ int n, i; float x; char name[50]; n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50);
with the input line: 25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence thompson\0. 8
EXAMPLE 2 The call: #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> /* ... */ int n; char s[5]; n = fscanf_s(stdin, "%s", s, sizeof s);
with the input line: hello
will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an array of six characters to store it. K.3.5.3.3 The printf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int printf_s(const char * restrict format, ...);
1
Runtime-constraints 2
format shall not be a null pointer. The %n specifier482) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to printf_s 481) If the format is known at translation time, an implementation can issue a diagnostic for any argument used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an argument of a type compatible with rsize_t. A limited amount of checking can be done if even if the format is not known at translation time. For example, an implementation could issue a diagnostic for each argument after format that has of type pointer to one of char, signed char, unsigned char, or void that is not followed by an argument of a type compatible with rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier using the hh length modifier, a length argument is expected to follow the pointer argument. Another useful diagnostic could flag any non-pointer argument following format that did not have a type compatible with rsize_t. 482) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n.
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corresponding to a %s specifier shall not be a null pointer. 3
If there is a runtime-constraint violation, the printf_s function does not attempt to produce further output, and it is unspecified to what extent printf_s produced output before discovering the runtime-constraint violation.
4
Description The printf_s function is equivalent to the printf function except for the explicit runtimeconstraints listed above.
5
Returns The printf_s function returns the number of characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. K.3.5.3.4 The scanf_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int scanf_s(const char * restrict format, ...);
Runtime-constraints format shall not be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the scanf_s function does not attempt to perform further input, and it is unspecified to what extent scanf_s performed input before discovering the runtimeconstraint violation. Description The scanf_s function is equivalent to fscanf_s with the argument stdin interposed before the arguments to scanf_s. Returns The scanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the scanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.5.3.5 The snprintf_s function Synopsis
1
2
3
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int snprintf_s(char * restrict s, rsize_t n, const char * restrict format, ...);
Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX. The %n specifier483) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX, then the snprintf_s function sets s[0] to the null character. 483) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n.
§ K.3.5.3.5
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Description The snprintf_s function is equivalent to the snprintf function except for the explicit runtimeconstraints listed above. The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the array pointed to by s. Returns The snprintf_s function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if a runtimeconstraint violation occurred. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. K.3.5.3.6 The sprintf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int sprintf_s(char * restrict s, rsize_t n, const char * restrict format, ...);
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Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX. The number of characters (including the trailing null) required for the result to be written to the array pointed to by s shall not be greater than n. The %n specifier484) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to sprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX, then the sprintf_s function sets s[0] to the null character. Description The sprintf_s function is equivalent to the sprintf function except for the parameter n and the explicit runtime-constraints listed above. The sprintf_s function, unlike snprintf_s, treats a result too big for the array pointed to by s as a runtime-constraint violation. Returns If no runtime-constraint violation occurred, the sprintf_s function returns the number of characters written in the array, not counting the terminating null character. If an encoding error occurred, sprintf_s returns a negative value. If any other runtime-constraint violation occurred, sprintf_s returns zero.
484) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n.
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K.3.5.3.7 The sscanf_s function Synopsis 1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> int sscanf_s(const char * restrict s, const char * restrict format, ...);
Runtime-constraints Neither s nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the sscanf_s function does not attempt to perform further input, and it is unspecified to what extent sscanf_s performed input before discovering the runtimeconstraint violation. Description The sscanf_s function is equivalent to fscanf_s, except that input is obtained from a string (specified by the argument s) rather than from a stream. Reaching the end of the string is equivalent to encountering end-of-file for the fscanf_s function. If copying takes place between objects that overlap, the objects take on unspecified values. Returns The sscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the sscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.5.3.8 The vfprintf_s function Synopsis
1
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vfprintf_s(FILE *restrict stream, const char *restrict format, va_list arg);
Runtime-constraints 2
Neither stream nor format shall be a null pointer. The %n specifier485) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a null pointer.
3
If there is a runtime-constraint violation, the vfprintf_s function does not attempt to produce further output, and it is unspecified to what extent vfprintf_s produced output before discovering the runtime-constraint violation.
4
Description The vfprintf_s function is equivalent to the vfprintf function except for the explicit runtimeconstraints listed above.
5
Returns The vfprintf_s function returns the number of characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred.
485) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n.
§ K.3.5.3.8
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K.3.5.3.9 The vfscanf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vfscanf_s(FILE *restrict stream, const char *restrict format, va_list arg);
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Runtime-constraints Neither stream nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the vfscanf_s function does not attempt to perform further input, and it is unspecified to what extent vfscanf_s performed input before discovering the runtime-constraint violation. Description The vfscanf_s function is equivalent to fscanf_s, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vfscanf_s function does not invoke the va_end macro.486) Returns The vfscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the vfscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.5.3.10 Synopsis
The vprintf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vprintf_s(const char * restrict format, va_list arg);
1
Runtime-constraints 2
format shall not be a null pointer. The %n specifier487) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to vprintf_s corresponding to a %s specifier shall not be a null pointer.
3
If there is a runtime-constraint violation, the vprintf_s function does not attempt to produce further output, and it is unspecified to what extent vprintf_s produced output before discovering the runtime-constraint violation.
4
Description The vprintf_s function is equivalent to the vprintf function except for the explicit runtimeconstraints listed above.
5
Returns The vprintf_s function returns the number of characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. K.3.5.3.11
The vscanf_s function
486) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, vsprintf_s, and vsscanf_s invoke the va_arg macro, the representation of arg after the return is indeterminate. 487) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n.
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§ K.3.5.3.11
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Synopsis 1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vscanf_s(const char * restrict format, va_list arg);
Runtime-constraints format shall not be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the vscanf_s function does not attempt to perform further input, and it is unspecified to what extent vscanf_s performed input before discovering the runtimeconstraint violation. Description The vscanf_s function is equivalent to scanf_s, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vscanf_s function does not invoke the va_end macro.488) Returns The vscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the vscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.5.3.12 Synopsis
1
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The vsnprintf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vsnprintf_s(char *restrict s, rsize_t n, const char *restrict format, va_list arg);
Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX. The %n specifier489) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the null character. Description The vsnprintf_s function is equivalent to the vsnprintf function except for the explicit runtimeconstraints listed above. The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within the array pointed to by s. Returns The vsnprintf_s function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if a runtimeconstraint violation occurred. Thus, the null-terminated output has been completely written if and 488) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, vsprintf_s, and vsscanf_s invoke the va_arg macro, the representation of arg after the return is indeterminate. 489) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n.
§ K.3.5.3.12
Bounds-checking interfaces
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only if the returned value is both nonnegative and less than n. K.3.5.3.13 Synopsis
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vsprintf_s(char * restrict s, rsize_t n, const char * restrict format, va_list arg);
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Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX. The number of characters (including the trailing null) required for the result to be written to the array pointed to by s shall not be greater than n. The %n specifier490) (modified or not by flags, field width, or precision) shall not appear in the string pointed to by format. Any argument to vsprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX, then the vsprintf_s function sets s[0] to the null character. Description The vsprintf_s function is equivalent to the vsprintf function except for the parameter n and the explicit runtime-constraints listed above. The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array pointed to by s as a runtime-constraint violation. Returns If no runtime-constraint violation occurred, the vsprintf_s function returns the number of characters written in the array, not counting the terminating null character. If an encoding error occurred, vsprintf_s returns a negative value. If any other runtime-constraint violation occurred, vsprintf_s returns zero. K.3.5.3.14 Synopsis
3
4
The vsscanf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> int vsscanf_s(const char *restrict s, const char *restrict format, va_list arg);
1
2
The vsprintf_s function
Runtime-constraints Neither s nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the vsscanf_s function does not attempt to perform further input, and it is unspecified to what extent vsscanf_s performed input before discovering the runtime-constraint violation. Description The vsscanf_s function is equivalent to sscanf_s, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vsscanf_s function does not invoke the va_end macro.491) 490) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed at by format when those characters are not a interpreted as a %n specifier. For example, if the entire format string was %%n. 491) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is indeterminate.
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§ K.3.5.3.14
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Returns The vsscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the vscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.5.4 Character input/output functions K.3.5.4.1 The gets_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> char *gets_s(char *s, rsize_t n);
Runtime-constraints s shall not be a null pointer. n shall neither be equal to zero nor be greater than RSIZE_MAX. A newline character, end-of-file, or read error shall occur within reading n-1 characters from stdin.492) If there is a runtime-constraint violation, characters are read and discarded from stdin until a new-line character is read, or end-of-file or a read error occurs, and if s is not a null pointer, s[0] is set to the null character. Description The gets_s function reads at most one less than the number of characters specified by n from the stream pointed to by stdin, into the array pointed to by s. No additional characters are read after a new-line character (which is discarded) or after end-of-file. The discarded new-line character does not count towards number of characters read. A null character is written immediately after the last character read into the array. If end-of-file is encountered and no characters have been read into the array, or if a read error occurs during the operation, then s[0] is set to the null character, and the other elements of s take unspecified values. Recommended practice The fgets function allows properly-written programs to safely process input lines too long to store in the result array. In general this requires that callers of fgets pay attention to the presence or absence of a new-line character in the result array. Consider using fgets (along with any needed processing based on new-line characters) instead of gets_s. Returns The gets_s function returns s if successful. If there was a runtime-constraint violation, or if end-offile is encountered and no characters have been read into the array, or if a read error occurs during the operation, then a null pointer is returned.
492) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets expect such a relationship.
§ K.3.5.4.1
Bounds-checking interfaces
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K.3.6
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General utilities <stdlib.h>
1
The header <stdlib.h> defines three types.
2
The types are errno_t
which is type int; and rsize_t
which is the type size_t; and constraint_handler_t
which has the following definition typedef void (*constraint_handler_t)( const char * restrict msg, void * restrict ptr, errno_t error);
K.3.6.1 Runtime-constraint handling K.3.6.1.1 The set_constraint_handler_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> constraint_handler_t set_constraint_handler_s(constraint_handler_t handler);
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Description The set_constraint_handler_s function sets the runtime-constraint handler to be handler. The runtime-constraint handler is the function to be called when a library function detects a runtimeconstraint violation. Only the most recent handler registered with set_constraint_handler_s is called when a runtime-constraint violation occurs. When the handler is called, it is passed the following arguments in the following order: 1. A pointer to a character string describing the runtime-constraint violation. 2. A null pointer or a pointer to an implementation-defined object. 3. If the function calling the handler has a return type declared as errno_t, the return value of the function is passed. Otherwise, a positive value of type errno_t is passed.
4
The implementation has a default constraint handler that is used if no calls to the set_constraint_handler_s function have been made. The behavior of the default handler is implementation-defined, and it may cause the program to exit or abort.
5
If the handler argument to set_constraint_handler_s is a null pointer, the implementation default handler becomes the current constraint handler. Returns
6
The set_constraint_handler_s function returns a pointer to the previously registered handler.493)
493) If the previous handler was registered by calling set_constraint_handler_s with a null pointer argument, a pointer to the implementation default handler is returned (not NULL).
634
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K.3.6.1.2 The abort_handler_s function Synopsis 1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> void abort_handler_s(const char * restrict msg, void * restrict ptr, errno_t error);
Description A pointer to the abort_handler_s function shall be a suitable argument to the set_constraint_handler_s function. The abort_handler_s function writes a message on the standard error stream in an implementationdefined format. The message shall include the string pointed to by msg. The abort_handler_s function then calls the abort function.494) Returns The abort_handler_s function does not return to its caller. K.3.6.1.3 The ignore_handler_s function Synopsis
1
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> void ignore_handler_s(const char * restrict msg, void * restrict ptr, errno_t error);
2
Description A pointer to the ignore_handler_s function shall be a suitable argument to the set_constraint_handler_s function.
3
The ignore_handler_s function simply returns to its caller.495)
4
Returns The ignore_handler_s function returns no value. K.3.6.2 Communication with the environment K.3.6.2.1 The getenv_s function Synopsis
1
2
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> errno_t getenv_s(size_t * restrict len, char * restrict value, rsize_t maxsize, const char * restrict name);
Runtime-constraints name shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer.
494) Many implementations invoke a debugger when the abort function is called. 495) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in which a runtime-
constraint violation occurs will return to its caller. The caller can determine whether a runtime-constraint violation occurred based on the library function’s specification (usually, the library function returns a nonzero errno_t).
§ K.3.6.2.1
Bounds-checking interfaces
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ISO/IEC 9899:2023 (E)
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If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len is not null), and the environment list is not searched. Description The getenv_s function searches an environment list, provided by the host environment, for a string that matches the string pointed to by name.
5
If that name is found then getenv_s performs the following actions. If len is not a null pointer, the length of the string associated with the matched list member is stored in the integer pointed to by len. If the length of the associated string is less than maxsize, then the associated string is copied to the array pointed to by value.
6
If that name is not found then getenv_s performs the following actions. If len is not a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than zero, then value[0] is set to the null character.
7
The set of environment names and the method for altering the environment list are implementationdefined. The getenv_s function need not avoid data races with other threads of execution that modify the environment list.496)
8
1
Returns The getenv_s function returns zero if the specified name is found and the associated string was successfully stored in value. Otherwise, a nonzero value is returned. K.3.6.3 Searching and sorting utilities These utilities make use of a comparison function to search or sort arrays of unspecified type. Where an argument declared as size_t nmemb specifies the length of the array for a function, if nmemb has the value zero on a call to that function, then the comparison function is not called, a search finds no matching element, sorting performs no rearrangement, and the pointer to the array may be null.
2
The implementation shall ensure that the second argument of the comparison function (when called from bsearch_s), or both arguments (when called from qsort_s), are pointers to elements of the array.497) The first argument when called from bsearch_s shall equal key.
3
The comparison function shall not alter the contents of either the array or search key. The implementation may reorder elements of the array between calls to the comparison function, but shall not otherwise alter the contents of any individual element.
4
When the same objects (consisting of size bytes, irrespective of their current positions in the array) are passed more than once to the comparison function, the results shall be consistent with one another. That is, for qsort_s they shall define a total ordering on the array, and for bsearch_s the same object shall always compare the same way with the key.
5
A sequence point occurs immediately before and immediately after each call to the comparison function, and also between any call to the comparison function and any movement of the objects passed as arguments to that call. K.3.6.3.1 The bsearch_s generic function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> QVoid *bsearch_s(const void *key, QVoid *base, rsize_t nmemb, rsize_t size, int (*compar)(const void *k, const void *y, void *context), void *context);
1
496) Many implementations provide non-standard functions that modify the environment list. 497) That is, if the value passed is p, then the following expressions are always valid and nonzero:
((char *)p - (char *)base) % size == 0 (char *)p >= (char *)base (char *)p < (char *)base + nmemb * size
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Runtime-constraints Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to zero, then none of key, base, or compar shall be a null pointer.
3
If there is a runtime-constraint violation, the bsearch_s generic function does not search the array.
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Description The bsearch_s generic function searches an array of nmemb objects, the initial element of which is pointed to by base, for an element that matches the object pointed to by key. The size of each element of the array is specified by size. The comparison function pointed to by compar is called with three arguments. The first two point to the key object and to an array element, in that order. The function shall return an integer less than, equal to, or greater than zero if the key object is considered, respectively, to be less than, to match, or to be greater than the array element. The array shall consist of: all the elements that compare less than, all the elements that compare equal to, and all the elements that compare greater than the key object, in that order.498) The third argument to the comparison function is the context argument passed to bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison function.499) Returns The bsearch_s generic function returns a pointer to a matching element of the array, or a null pointer if no match is found or there is a runtime-constraint violation. If two elements compare as equal, which element is matched is unspecified.
7
The bsearch_s generic function is generic in the qualification of the type pointed to by the argument base. If this argument is a pointer to a const-qualified object type, the returned pointer will be a pointer to const-qualified void. Otherwise, the argument shall be a pointer to an unqualified object type or a null pointer constant.500) , and the returned pointer will be a pointer to unqualified void
8
The external declaration of bsearch_s has the concrete type: void * (const void *, const void *, rsize_t, rsize_t, int (*) (const void *, const void *), void *)
which supports all correct uses. If a macro definition of the generic function is suppressed to access an actual function, the external declaration with this concrete type is visible.501) K.3.6.3.2 The qsort_s function Synopsis 1
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, int (*compar)(const void *x, const void *y, void *context), void *context);
2
Runtime-constraints Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to zero, then neither base nor compar shall be a null pointer.
3
If there is a runtime-constraint violation, the qsort_s function does not sort the array. 498) In practice, this means that the entire array has been sorted according to the comparison function. 499) The context argument is for the use of the comparison function in performing its duties. For example, it might specify a collating sequence used by the comparison function. 500) If the argument is a null pointer and the call is executed, the behavior is undefined. 501) This is an obsolescent feature.
§ K.3.6.3.2
Bounds-checking interfaces
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Description The qsort_s function sorts an array of nmemb objects, the initial element of which is pointed to by base. The size of each object is specified by size.
5
The contents of the array are sorted into ascending order according to a comparison function pointed to by compar, which is called with three arguments. The first two point to the objects being compared. The function shall return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second. The third argument to the comparison function is the context argument passed to qsort_s. The sole use of context by qsort_s is to pass it to the comparison function.502)
6
If two elements compare as equal, their relative order in the resulting sorted array is unspecified.
7
Returns The qsort_s function returns zero if there was no runtime-constraint violation. Otherwise, a nonzero value is returned.
1
K.3.6.4 Multibyte/wide character conversion functions The behavior of the multibyte character functions is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, each function is placed into its initial conversion state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer cause the internal conversion state of the function to be altered as necessary. A call with s as a null pointer causes these functions to set the int pointed to by their status argument to a nonzero value if encodings have state dependency, and zero otherwise. 503) Changing the LC_CTYPE category causes the internal object describing the conversion state of these functions to have an indeterminate representation. K.3.6.4.1 The wctomb_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdlib.h> errno_t wctomb_s(int *restrict status, char *restrict s, rsize_t smax, wchar_t wc);
1
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Runtime-constraints Let n denote the number of bytes needed to represent the multibyte character corresponding to the wide character given by wc (including any shift sequences).
3
If s is not a null pointer, then smax shall not be less than n, and smax shall not be greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero.
4
If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to by status, and if s is not a null pointer, no more than smax elements in the array pointed to by s will be accessed.
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Description The wctomb_s function determines n and stores the multibyte character representation of wc in the array whose first element is pointed to by s (if s is not a null pointer). The number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state, and the function is left in the initial conversion state.
6
The implementation shall behave as if no library function calls the wctomb_s function.
7
If s is a null pointer, the wctomb_s function stores into the int pointed to by status a nonzero 502) The context argument is for the use of the comparison function in performing its duties. For example, it might specify a collating sequence used by the comparison function. 503) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide character codes, but are grouped with an adjacent multibyte character.
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Bounds-checking interfaces
§ K.3.6.4.1
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or zero value, if multibyte character encodings, respectively, do or do not have state-dependent encodings. 8
If s is not a null pointer, the wctomb_s function stores into the int pointed to by status either n or −1 if wc, respectively, does or does not correspond to a valid multibyte character.
9
In no case will the int pointed to by status be set to a value greater than the MB_CUR_MAX macro.
10
Returns The wctomb_s function returns zero if successful, and a nonzero value if there was a runtimeconstraint violation or wc did not correspond to a valid multibyte character.
1
K.3.6.5 Multibyte/wide string conversion functions The behavior of the multibyte string functions is affected by the LC_CTYPE category of the current locale. K.3.6.5.1 The mbstowcs_s function Synopsis
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#include <stdlib.h> errno_t mbstowcs_s(size_t *restrict retval, wchar_t *restrict dst, rsize_t dstmax, const char * restrict src, rsize_t len);
Runtime-constraints Neither retval nor src shall be a null pointer. If dst is not a null pointer, then neither len nor dstmax shall be greater than RSIZE_MAX/sizeof(wchar_t). If dst is a null pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null character shall occur within the first dstmax multibyte characters of the array pointed to by src. If there is a runtime-constraint violation, then mbstowcs_s does the following. If retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If dst is not a null pointer and dstmax is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then mbstowcs_s sets dst[0] to the null wide character. Description The mbstowcs_s function converts a sequence of multibyte characters that begins in the initial shift state from the array pointed to by src into a sequence of corresponding wide characters. If dst is not a null pointer, the converted characters are stored into the array pointed to by dst. Conversion continues up to and including a terminating null character, which is also stored. Conversion stops earlier in two cases: when a sequence of bytes is encountered that does not form a valid multibyte character, or (if dst is not a null pointer) when len wide characters have been stored into the array pointed to by dst.504) If dst is not a null pointer and no null wide character was stored into the array pointed to by dst, then dst[len] is set to the null wide character. Each conversion takes place as if by a call to the mbrtowc function.
5
Regardless of whether dst is or is not a null pointer, if the input conversion encounters a sequence of bytes that do not form a valid multibyte character, an encoding error occurs: the mbstowcs_s function stores the value (size_t)(-1) into *retval. Otherwise, the mbstowcs_s function stores into *retval the number of multibyte characters successfully converted, not including the terminating null character (if any).
6
All elements following the terminating null wide character (if any) written by mbstowcs_s in the array of dstmax wide characters pointed to by dst take unspecified values when mbstowcs_s returns.505) 504) Thus, the value of len is ignored if dst is a null pointer. 505) This allows an implementation to attempt converting the multibyte string before discovering a terminating null character
did not occur where required.
§ K.3.6.5.1
Bounds-checking interfaces
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7
If copying takes place between objects that overlap, the objects take on unspecified values.
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Returns The mbstowcs_s function returns zero if no runtime-constraint violation and no encoding error occurred. Otherwise, a nonzero value is returned. K.3.6.5.2 The wcstombs_s function Synopsis #include <stdlib.h> errno_t wcstombs_s(size_t * restrict retval, char * restrict dst, rsize_t dstmax, const wchar_t * restrict src, rsize_t len);
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Runtime-constraints Neither retval nor src shall be a null pointer. If dst is not a null pointer, then len shall not be greater than RSIZE_MAX/sizeof(wchar_t) and dstmax shall be nonzero and not greater than RSIZE_MAX. If dst is a null pointer, then dstmax shall equal zero. If dst is not a null pointer and len is not less than dstmax, then the conversion shall have been stopped (see below) because a terminating null wide character was reached or because an encoding error occurred. If there is a runtime-constraint violation, then wcstombs_s does the following. If retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If dst is not a null pointer and dstmax is greater than zero and not greater than RSIZE_MAX, then wcstombs_s sets dst[0] to the null character. Description The wcstombs_s function converts a sequence of wide characters from the array pointed to by src into a sequence of corresponding multibyte characters that begins in the initial shift state. If dst is not a null pointer, the converted characters are then stored into the array pointed to by dst. Conversion continues up to and including a terminating null wide character, which is also stored. Conversion stops earlier in two cases: — when a wide character is reached that does not correspond to a valid multibyte character; — (if dst is not a null pointer) when the next multibyte character would exceed the limit of n total bytes to be stored into the array pointed to by dst. If the wide character being converted is the null wide character, then n is the lesser of len or dstmax. Otherwise, n is the lesser of len or dstmax-1. If the conversion stops without converting a null wide character and dst is not a null pointer, then a null character is stored into the array pointed to by dst immediately following any multibyte characters already stored. Each conversion takes place as if by a call to the wcrtomb function.506)
5
Regardless of whether dst is or is not a null pointer, if the input conversion encounters a wide character that does not correspond to a valid multibyte character, an encoding error occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval. Otherwise, the wcstombs_s function stores into *retval the number of bytes in the resulting multibyte character sequence, not including the terminating null character (if any).
6
All elements following the terminating null character (if any) written by wcstombs_s in the array of dstmax elements pointed to by dst take unspecified values when wcstombs_s returns.507)
7
If copying takes place between objects that overlap, the objects take on unspecified values. 506) If conversion stops because a terminating null wide character has been reached, the bytes stored include those necessary to reach the initial shift state immediately before the null byte. However, if the conversion stops before a terminating null wide character has been reached, the result will be null terminated, but might not end in the initial shift state. 507) When len is not less than dstmax, the implementation might fill the array before discovering a runtime-constraint violation.
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Returns The wcstombs_s function returns zero if no runtime-constraint violation and no encoding error occurred. Otherwise, a nonzero value is returned.
K.3.7
String handling <string.h>
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The header <string.h> defines two types.
2
The types are errno_t
which is type int; and rsize_t
which is the type size_t. K.3.7.1 Copying functions K.3.7.1.1 The memcpy_s function Synopsis 1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t memcpy_s(void * restrict s1, rsize_t s1max, const void * restrict s2, rsize_t n);
Runtime-constraints Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between objects that overlap. If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is not greater than RSIZE_MAX.
4
Description The memcpy_s function copies n characters from the object pointed to by s2 into the object pointed to by s1.
5
Returns The memcpy_s function returns zero if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.7.1.2 The memmove_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t memmove_s(void *s1, rsize_t s1max, const void *s2, rsize_t n);
Runtime-constraints Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX. n shall not be greater than s1max. If there is a runtime-constraint violation, the memmove_s function stores zeros in the first s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is not greater than RSIZE_MAX. § K.3.7.1.2
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Description The memmove_s function copies n characters from the object pointed to by s2 into the object pointed to by s1. This copying takes place as if the n characters from the object pointed to by s2 are first copied into a temporary array of n characters that does not overlap the objects pointed to by s1 or s2, and then the n characters from the temporary array are copied into the object pointed to by s1. Returns The memmove_s function returns zero if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.7.1.3 The strcpy_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t strcpy_s(char * restrict s1, rsize_t s1max, const char * restrict s2);
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Runtime-constraints Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max). Copying shall not take place between objects that overlap. If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the null character. Description The strcpy_s function copies the string pointed to by s2 (including the terminating null character) into the array pointed to by s1. All elements following the terminating null character (if any) written by strcpy_s in the array of s1max characters pointed to by s1 take unspecified values when strcpy_s returns.508) Returns
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The strcpy_s function returns zero509) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.7.1.4 The strncpy_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t strncpy_s(char * restrict s1, rsize_t s1max, const char * restrict s2, rsize_t n);
1
2
3
Runtime-constraints Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max shall be greater than strnlen_s( s2, s1max). Copying shall not take place between objects that overlap. If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the null character. 508) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if any of those characters are null. Such an approach might write a character to every element of s1 before discovering that the first element was set to the null character. 509) A zero return value implies that all the requested characters from the string pointed to by s2 fit within the array pointed to by s1 and that the result in s1 is null terminated.
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Description The strncpy_s function copies not more than n successive characters (characters that follow a null character are not copied) from the array pointed to by s2 to the array pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null character. All elements following the terminating null character (if any) written by strncpy_s in the array of s1max characters pointed to by s1 take unspecified values when strncpy_s returns a nonzero value.510) Returns
6
The strncpy_s function returns zero511) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned.
7
EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result will not be null terminated or that characters will be written past the end of the destination array. #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> /* ... */ char src1[100] = "hello"; char src2[7] = {’g’, ’o’, ’o’, ’d’, ’b’, ’y’, ’e’}; char dst1[6], dst2[5], dst3[5]; int r1, r2, r3; r1 = strncpy_s(dst1, 6, src1, 100); r2 = strncpy_s(dst2, 5, src2, 7); r3 = strncpy_s(dst3, 5, src2, 4);
The first call will assign to r1 the value zero and to dst1 the sequence hello\0. The second call will assign to r2 a nonzero value and to dst2 the sequence \0. The third call will assign to r3 the value zero and to dst3 the sequence good\0. K.3.7.2 Concatenation functions K.3.7.2.1 The strcat_s function Synopsis 1
2
#define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t strcat_s(char * restrict s1, rsize_t s1max, const char * restrict s2);
Runtime-constraints Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to strcat_s.
3
Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.512) m shall be greater than strnlen_s(s2, m). Copying shall not take place between objects that overlap.
4
If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the null character.
5
Description The strcat_s function appends a copy of the string pointed to by s2 (including the terminating null character) to the end of the string pointed to by s1. The initial character from s2 overwrites the 510) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if any of those characters are null. Such an approach might write a character to every element of s1 before discovering that the first element was set to the null character. 511) A zero return value implies that all of he requested characters from the string pointed to by s2 fit within the array pointed to by s1 and that the result in s1 is null terminated. 512) Zero means that s1 was not null terminated upon entry to strcat_s.
§ K.3.7.2.1
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null character at the end of s1. 6
All elements following the terminating null character (if any) written by strcat_s in the array of s1max characters pointed to by s1 take unspecified values when strcat_s returns.513) Returns
7
The strcat_s function returns zero514) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.7.2.2 The strncat_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t strncat_s(char * restrict s1, rsize_t s1max, const char * restrict s2, rsize_t n);
1
2
Runtime-constraints Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to strncat_s.
3
Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.515) If n is not less than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take place between objects that overlap.
4
If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the null character.
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Description The strncat_s function appends not more than n successive characters (characters that follow a null character are not copied) from the array pointed to by s2 to the end of the string pointed to by s1. The initial character from s2 overwrites the null character at the end of s1. If no null character was copied from s2, then s1[s1max- m +n] is set to a null character. All elements following the terminating null character (if any) written by strncat_s in the array of s1max characters pointed to by s1 take unspecified values when strncat_s returns.516) Returns
7
The strncat_s function returns zero517) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned.
8
EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result will not be null terminated or that characters will be written past the end of the destination array. #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> /* ... */ char s1[100] = "good"; char s2[6] = "hello"; char s3[6] = "hello"; char s4[7] = "abc"; 513) This allows an implementation to append characters from s2 to s1 while simultaneously checking if any of those characters are null. Such an approach might write a character to every element of s1 before discovering that the first element was set to the null character. 514) A zero return value implies that all the requested characters from the string pointed to by s2 were appended to the string pointed to by s1 and that the result in s1 is null terminated. 515) Zero means that s1 was not null terminated upon entry to strncat_s. 516) This allows an implementation to append characters from s2 to s1 while simultaneously checking if any of those characters are null. Such an approach might write a character to every element of s1 before discovering that the first element was set to the null character. 517) A zero return value implies that all the requested characters from the string pointed to by s2 were appended to the string pointed to by s1 and that the result in s1 is null terminated.
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char s5[1000] = "bye"; int r1, r2, r3, r4; r1 = strncat_s(s1, 100, s5, 1000); r2 = strncat_s(s2, 6, "", 1); r3 = strncat_s(s3, 6, "X", 2); r4 = strncat_s(s4, 7, "defghijklmn", 3);
After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0. After the second call r2 will have the value zero and s2 will contain the sequence hello\0. After the third call r3 will have a nonzero value and s3 will contain the sequence \0. After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0. K.3.7.3 Search functions K.3.7.3.1 The strtok_s function Synopsis 1
2
3
4
#define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> char *strtok_s(char * restrict s1, rsize_t * restrict s1max, const char * restrict s2, char ** restrict ptr);
Runtime-constraints None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. The end of the token found shall occur within the first *s1max characters of s1 for the first call, and shall occur within the first *s1max characters of where searching resumes on subsequent calls. If there is a runtime-constraint violation, the strtok_s function does not indirect through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. Description A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a sequence of tokens, each of which is delimited by a character from the string pointed to by s2. The fourth argument points to a caller-provided char pointer into which the strtok_s function stores information necessary for it to continue scanning the same string.
5
The first call in a sequence has a non-null first argument and s1max points to an object whose value is the number of elements in the character array pointed to by the first argument. The first call stores an initial value in the object pointed to by ptr and updates the value pointed to by s1max to reflect the number of elements that remain in relation to ptr. Subsequent calls in the sequence have a null first argument and the objects pointed to by s1max and ptr are required to have the values stored by the previous call in the sequence, which are then updated. The separator string pointed to by s2 may be different from call to call.
6
The first call in the sequence searches the string pointed to by s1 for the first character that is not contained in the current separator string pointed to by s2. If no such character is found, then there are no tokens in the string pointed to by s1 and the strtok_s function returns a null pointer. If such a character is found, it is the start of the first token.
7
The strtok_s function then searches from there for the first character in s1 that is contained in the current separator string. If no such character is found, the current token extends to the end of the string pointed to by s1, and subsequent searches in the same string for a token return a null pointer. If such a character is found, it is overwritten by a null character, which terminates the current token.
8
In all cases, the strtok_s function stores sufficient information in the pointer pointed to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer value for ptr, shall start searching just past the element overwritten by a null character (if any). § K.3.7.3.1
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Returns The strtok_s function returns a pointer to the first character of a token, or a null pointer if there is no token or there is a runtime-constraint violation.
10
EXAMPLE #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> static char str1[] = "?a???b,,,#c"; static char str2[] = "\t \t"; char *t, *ptr1, *ptr2; rsize_t max1 = sizeof(str1); rsize_t max2 = sizeof(str2); t = strtok_s(str1, &max1, "?", &ptr1); t = strtok_s(NULL, &max1, ",", &ptr1); t = strtok_s(str2, &max2, " \t", &ptr2); t = strtok_s(NULL, &max1, "#,", &ptr1); t = strtok_s(NULL, &max1, "?", &ptr1);
// t points to the token "a" // t points to the token "??b" // t is a null pointer // t points to the token "c" // t is a null pointer
K.3.7.4 Miscellaneous functions K.3.7.4.1 The memset_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
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Runtime-constraints s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n shall not be greater than smax. If there is a runtime-constraint violation, then if s is not a null pointer and smax is not greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an unsigned char) into each of the first smax characters of the object pointed to by s. Description The memset_s function copies the value of c (converted to an unsigned char) into each of the first n characters of the object pointed to by s. Unlike memset, any call to the memset_s function shall be evaluated strictly according to the rules of the abstract machine as described in (5.1.2.3). That is, any call to the memset_s function shall assume that the memory indicated by s and n may be accessible in the future and thus contains the values indicated by c. Returns The memset_s function returns zero if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.7.4.2 The strerror_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> errno_t strerror_s(char *s, rsize_t maxsize, errno_t errnum);
1
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Runtime-constraints s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX. maxsize shall not equal zero.
3
If there is a runtime-constraint violation, then the array (if any) pointed to by s is not modified. 646
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Description The strerror_s function maps the number in errnum to a locale-specific message string. Typically, the values for errnum come from errno, but strerror_s shall map any value of type int to a message.
5
If the length of the desired string is less than maxsize, then the string is copied to the array pointed to by s.
6
Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied from the string to the array pointed to by s and then s[maxsize-1] is set to the null character. Then, if maxsize is greater than 3, then s[maxsize-2], s[maxsize-3], and s[maxsize-4] are set to the character period (.).
7
Returns The strerror_s function returns zero if the length of the desired string was less than maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s function returns a nonzero value. K.3.7.4.3 The strerrorlen_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> size_t strerrorlen_s(errno_t errnum);
1
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Description The strerrorlen_s function calculates the length of the (untruncated) locale-specific message string that the strerror_s function maps to errnum.
3
Returns The strerrorlen_s function returns the number of characters (not including the null character) in the full message string. K.3.7.4.4 The strnlen_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> size_t strnlen_s(const char *s, size_t maxsize);
1
2
Description The strnlen_s function computes the length of the string pointed to by s. Returns
3
If s is a null pointer,518) then the strnlen_s function returns zero.
4
Otherwise, the strnlen_s function returns the number of characters that precede the terminating null character. If there is no null character in the first maxsize characters of s then strnlen_s returns maxsize. At most the first maxsize characters of s shall be accessed by strnlen_s.
K.3.8
Date and time <time.h>
1
The header <time.h> defines two types.
2
The types are errno_t 518) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints along with the values returned for a null pointer or an unterminated string argument make strnlen_s useful in algorithms that gracefully handle such exceptional data.
§ K.3.8
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which is type int; and rsize_t
which is the type size_t.
1
K.3.8.1 Components of time A broken-down time is normalized if the values of the members of the tm structure are in their normal rages.519)
1
K.3.8.2 Time conversion functions Like the strftime function, the asctime_s and ctime_s functions do not return a pointer to a static object, and other library functions are permitted to call them. K.3.8.2.1 The asctime_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <time.h> errno_t asctime_s(char *s, rsize_t maxsize, const struct tm *timeptr);
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Runtime-constraints Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr shall be normalized. The calendar year represented by the broken-down time pointed to by timeptr shall not be less than calendar year 0 and shall not be greater than calendar year 9999. If there is a runtime-constraint violation, there is no attempt to convert the time, and s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is not greater than RSIZE_MAX. Description The asctime_s function converts the normalized broken-down time in the structure pointed to by timeptr into a 26 character (including the null character) string in the form Sun Sep 16 01:03:52 1973\n\0
The fields making up this string are (in order): 1. The name of the day of the week represented by timeptr->tm_wday using the following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat. 2. The character space. 3. The name of the month represented by timeptr->tm_mon using the following three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, and Dec. 4. The character space. 5. The value of timeptr->tm_mday as if printed using the fprintf format "%2d". 6. The character space. 7. The value of timeptr->tm_hour as if printed using the fprintf format "%.2d". 8. The character colon. 9. The value of timeptr->tm_min as if printed using the fprintf format "%.2d". 10. The character colon. 519) The normal ranges are defined in 7.29.1.
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11. The value of timeptr->tm_sec as if printed using the fprintf format "%.2d". 12. The character space. 13. The value of timeptr->tm_year + 1900 as if printed using the fprintf format "%4d". 14. The character new line. 15. The null character. Recommended practice The strftime function allows more flexible formatting and supports locale-specific behavior. If you do not require the exact form of the result string produced by the asctime_s function, consider using the strftime function instead.
5
Returns The asctime_s function returns zero if the time was successfully converted and stored into the array pointed to by s. Otherwise, it returns a nonzero value. K.3.8.2.2 The ctime_s function Synopsis
1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <time.h> errno_t ctime_s(char *s, rsize_t maxsize, const time_t *timer);
Runtime-constraints Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and shall not be greater than RSIZE_MAX. If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null pointer and maxsize is not equal zero and is not greater than RSIZE_MAX. Description The ctime_s function converts the calendar time pointed to by timer to local time in the form of a string. It is equivalent to asctime_s(s, maxsize, localtime_s(timer, &(struct tm){ 0 }))
Recommended practice The strftime function allows more flexible formatting and supports locale-specific behavior. If you do not require the exact form of the result string produced by the ctime_s function, consider using the strftime function instead.
5
Returns The ctime_s function returns zero if the time was successfully converted and stored into the array pointed to by s. Otherwise, it returns a nonzero value. K.3.8.2.3 The gmtime_s function Synopsis
1
#define __STDC_WANT_LIB_EXT1__ 1 #include <time.h> struct tm *gmtime_s(const time_t * restrict timer, struct tm * restrict result);
2
Runtime-constraints Neither timer nor result shall be a null pointer.
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If there is a runtime-constraint violation, there is no attempt to convert the time. § K.3.8.2.3
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Description The gmtime_s function converts the calendar time pointed to by timer into a broken-down time, expressed as UTC. The broken-down time is stored in the structure pointed to by result.
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Returns The gmtime_s function returns result, or a null pointer if the specified time cannot be converted to UTC or there is a runtime-constraint violation. K.3.8.2.4 The localtime_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <time.h> struct tm *localtime_s(const time_t *restrict timer, struct tm *restrict result);
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Runtime-constraints Neither timer nor result shall be a null pointer.
3
If there is a runtime-constraint violation, there is no attempt to convert the time.
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Description The localtime_s function converts the calendar time pointed to by timer into a broken-down time, expressed as local time. The broken-down time is stored in the structure pointed to by result.
5
Returns The localtime_s function returns result, or a null pointer if the specified time cannot be converted to local time or there is a runtime-constraint violation.
1
The header <wchar.h> defines two types.
2
The types are
K.3.9
Extended multibyte and wide character utilities <wchar.h>
errno_t
which is type int; and rsize_t
which is the type size_t. 3
Unless explicitly stated otherwise, if the execution of a function described in this subclause causes copying to take place between objects that overlap, the objects take on unspecified values. K.3.9.1 Formatted wide character input/output functions K.3.9.1.1 The fwprintf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> int fwprintf_s(FILE * restrict stream, const wchar_t * restrict format, ...);
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Runtime-constraints 2
Neither stream nor format shall be a null pointer. The %n specifier520) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a null pointer. 520) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
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If there is a runtime-constraint violation, the fwprintf_s function does not attempt to produce further output, and it is unspecified to what extent fwprintf_s produced output before discovering the runtime-constraint violation.
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Description The fwprintf_s function is equivalent to the fwprintf function except for the explicit runtimeconstraints listed above.
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Returns The fwprintf_s function returns the number of wide characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. K.3.9.1.2 The fwscanf_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdio.h> #include <wchar.h> int fwscanf_s(FILE * restrict stream, const wchar_t * restrict format, ...);
Runtime-constraints Neither stream nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the fwscanf_s function does not attempt to perform further input, and it is unspecified to what extent fwscanf_s performed input before discovering the runtime-constraint violation. Description The fwscanf_s function is equivalent to fwscanf except that the c, s, and [ conversion specifiers apply to a pair of arguments (unless assignment suppression is indicated by a *). The first of these arguments is the same as for fwscanf. That argument is immediately followed in the argument list by the second argument, which has type size_t and gives the number of elements in the array pointed to by the first argument of the pair. If the first argument points to a scalar object, it is considered to be an array of one element.521) A matching failure occurs if the number of elements in a receiving object is insufficient to hold the converted input (including any trailing null character). Returns The fwscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the fwscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.9.1.3 The snwprintf_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> int snwprintf_s(wchar_t * restrict s, rsize_t n, const wchar_t * restrict format, ...); 521) If the format is known at translation time, an implementation can issue a diagnostic for any argument used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an argument of a type compatible with rsize_t. A limited amount of checking can be done if even if the format is not known at translation time. For example, an implementation could issue a diagnostic for each argument after format that has of type pointer to one of char, signed char, unsigned char, or void that is not followed by an argument of a type compatible with rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier using the hh length modifier, a length argument is expected to follow the pointer argument. Another useful diagnostic could flag any non-pointer argument following format that did not have a type compatible with rsize_t.
§ K.3.9.1.3
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Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX /sizeof(wchar_t). The %n specifier522) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then the snwprintf_s function sets s[0] to the null wide character. Description The snwprintf_s function is equivalent to the swprintf function except for the explicit runtimeconstraints listed above. The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within the array pointed to by s. Returns The snwprintf_s function returns the number of wide characters that would have been written had n been sufficiently large, not counting the terminating wide null character, or a negative value if a runtime-constraint violation occurred. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. K.3.9.1.4 The swprintf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> int swprintf_s(wchar_t * restrict s, rsize_t n, const wchar_t * restrict format, ...);
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Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX /sizeof(wchar_t). The number of wide characters (including the trailing null) required for the result to be written to the array pointed to by s shall not be greater than n. The %n specifier523) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to swprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then the swprintf_s function sets s[0] to the null wide character. Description The swprintf_s function is equivalent to the swprintf function except for the explicit runtimeconstraints listed above. The swprintf_s function, unlike snwprintf_s, treats a result too big for the array pointed to by s as a runtime-constraint violation. Returns If no runtime-constraint violation occurred, the swprintf_s function returns the number of wide characters written in the array, not counting the terminating null wide character. If an encoding 522) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n". 523) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
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error occurred or if n or more wide characters are requested to be written, swprintf_s returns a negative value. If any other runtime-constraint violation occurred, swprintf_s returns zero. K.3.9.1.5 The swscanf_s function Synopsis 1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> int swscanf_s(const wchar_t * restrict s, const wchar_t * restrict format, ...);
Runtime-constraints Neither s nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the swscanf_s function does not attempt to perform further input, and it is unspecified to what extent swscanf_s performed input before discovering the runtime-constraint violation. Description The swscanf_s function is equivalent to fwscanf_s, except that the argument s specifies a wide string from which the input is to be obtained, rather than from a stream. Reaching the end of the wide string is equivalent to encountering end-of-file for the fwscanf_s function. Returns The swscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the swscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.9.1.6 The vfwprintf_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> #include <wchar.h> int vfwprintf_s(FILE * restrict stream, const wchar_t * restrict format, va_list arg);
Runtime-constraints 2
Neither stream nor format shall be a null pointer. The %n specifier524) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be a null pointer.
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If there is a runtime-constraint violation, the vfwprintf_s function does not attempt to produce further output, and it is unspecified to what extent vfwprintf_s produced output before discovering the runtime-constraint violation.
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Description The vfwprintf_s function is equivalent to the vfwprintf function except for the explicit runtimeconstraints listed above.
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Returns The vfwprintf_s function returns the number of wide characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. 524) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
§ K.3.9.1.6
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K.3.9.1.7 The vfwscanf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <stdio.h> #include <wchar.h> int vfwscanf_s(FILE * restrict stream, const wchar_t * restrict format, va_list arg);
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Runtime-constraints Neither stream nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to perform further input, and it is unspecified to what extent vfwscanf_s performed input before discovering the runtime-constraint violation. Description The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the va_end macro.525) Returns The vfwscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the vfwscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.9.1.8 The vsnwprintf_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <wchar.h> int vsnwprintf_s(wchar_t *restrict s, rsize_t n, const wchar_t *restrict format, va_list arg);
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Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX /sizeof(wchar_t). The %n specifier526) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then the vsnwprintf_s function sets s[0] to the null wide character. Description The vsnwprintf_s function is equivalent to the vswprintf function except for the explicit runtimeconstraints listed above. The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit within the array pointed to by s. 525) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the representation of arg after the return is indeterminate. 526) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
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§ K.3.9.1.8
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Returns The vsnwprintf_s function returns the number of wide characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if a runtime-constraint violation occurred. Thus, the null-terminated output has been completely written if and only if the returned value is both nonnegative and less than n. K.3.9.1.9 The vswprintf_s function Synopsis
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#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <wchar.h> int vswprintf_s(wchar_t *restrict s, rsize_t n, const wchar_t *restrict format, va_list arg);
Runtime-constraints Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater than RSIZE_MAX /sizeof(wchar_t). The number of wide characters (including the trailing null) required for the result to be written to the array pointed to by s shall not be greater than n. The %n specifier527) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to vswprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding error shall occur. If there is a runtime-constraint violation, then if s is not a null pointer and n is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then the vswprintf_s function sets s[0] to the null wide character. Description The vswprintf_s function is equivalent to the vswprintf function except for the explicit runtimeconstraints listed above. The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the array pointed to by s as a runtime-constraint violation. Returns If no runtime-constraint violation occurred, the vswprintf_s function returns the number of wide characters written in the array, not counting the terminating null wide character. If an encoding error occurred or if n or more wide characters are requested to be written, vswprintf_s returns a negative value. If any other runtime-constraint violation occurred, vswprintf_s returns zero. K.3.9.1.10 Synopsis
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The vswscanf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <wchar.h> int vswscanf_s(const wchar_t * restrict s, const wchar_t * restrict format, va_list arg);
Runtime-constraints Neither s nor format shall be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the vswscanf_s function does not attempt to perform further input, and it is unspecified to what extent vswscanf_s performed input before discovering the runtime-constraint violation. 527) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
§ K.3.9.1.10
Bounds-checking interfaces
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Description The vswscanf_s function is equivalent to swscanf_s, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vswscanf_s function does not invoke the va_end macro.528) Returns The vswscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the vswscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.9.1.11 Synopsis
The vwprintf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <wchar.h> int vwprintf_s(const wchar_t * restrict format, va_list arg);
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Runtime-constraints 2
format shall not be a null pointer. The %n specifier529) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer.
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If there is a runtime-constraint violation, the vwprintf_s function does not attempt to produce further output, and it is unspecified to what extent vwprintf_s produced output before discovering the runtime-constraint violation.
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Description The vwprintf_s function is equivalent to the vwprintf function except for the explicit runtimeconstraints listed above.
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Returns The vwprintf_s function returns the number of wide characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. K.3.9.1.12 Synopsis
#define __STDC_WANT_LIB_EXT1__ 1 #include <stdarg.h> #include <wchar.h> int vwscanf_s(const wchar_t * restrict format, va_list arg);
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The vwscanf_s function
Runtime-constraints format shall not be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the vwscanf_s function does not attempt to perform further input, and it is unspecified to what extent vwscanf_s performed input before discovering the runtime-constraint violation. 528) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the representation of arg after the return is indeterminate. 529) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
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§ K.3.9.1.12
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Description The vwscanf_s function is equivalent to wscanf_s, with the variable argument list replaced by arg, which shall have been initialized by the va_start macro (and possibly subsequent va_arg calls). The vwscanf_s function does not invoke the va_end macro.530) Returns The vwscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the vwscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.9.1.13 Synopsis
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ISO/IEC 9899:2023 (E)
The wprintf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> int wprintf_s(const wchar_t * restrict format, ...);
Runtime-constraints 2
format shall not be a null pointer. The %n specifier531) (modified or not by flags, field width, or precision) shall not appear in the wide string pointed to by format. Any argument to wprintf_s corresponding to a %s specifier shall not be a null pointer.
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If there is a runtime-constraint violation, the wprintf_s function does not attempt to produce further output, and it is unspecified to what extent wprintf_s produced output before discovering the runtime-constraint violation.
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Description The wprintf_s function is equivalent to the wprintf function except for the explicit runtimeconstraints listed above.
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Returns The wprintf_s function returns the number of wide characters transmitted, or a negative value if an output error, encoding error, or runtime-constraint violation occurred. K.3.9.1.14 Synopsis
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The wscanf_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> int wscanf_s(const wchar_t * restrict format, ...);
Runtime-constraints format shall not be a null pointer. Any argument indirected though to store converted input shall not be a null pointer. If there is a runtime-constraint violation, the wscanf_s function does not attempt to perform further input, and it is unspecified to what extent wscanf_s performed input before discovering the runtimeconstraint violation. Description The wscanf_s function is equivalent to fwscanf_s with the argument stdin interposed before the arguments to wscanf_s. 530) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the representation of arg after the return is indeterminate. 531) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide string pointed at by format when those wide characters are not a interpreted as a %n specifier. For example, if the entire format string was L"%%n".
§ K.3.9.1.14
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Returns The wscanf_s function returns the value of the macro EOF if an input failure occurs before any conversion or if there is a runtime-constraint violation. Otherwise, the wscanf_s function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure. K.3.9.2 General wide string utilities K.3.9.2.1 Wide string copying functions K.3.9.2.1.1 The wcscpy_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> errno_t wcscpy_s(wchar_t *restrict s1, rsize_t s1max, const wchar_t *restrict s2);
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Runtime-constraints Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX/sizeof( wchar_t). s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between objects that overlap. If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then wcscpy_s sets s1[0] to the null wide character. Description The wcscpy_s function copies the wide string pointed to by s2 (including the terminating null wide character) into the array pointed to by s1. All elements following the terminating null wide character (if any) written by wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified values when wcscpy_s returns.532) Returns
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The wcscpy_s function returns zero533) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.9.2.1.2 Synopsis
#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> errno_t wcsncpy_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2, rsize_t n);
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Runtime-constraints Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX /sizeof(wchar_t). s1max shall not equal zero. If n is not less than s1max, then s1max shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between objects that overlap. If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then wcsncpy_s sets s1[0] to the null wide character. 532) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking if any of those wide characters are null. Such an approach might write a wide character to every element of s1 before discovering that the first element was set to the null wide character. 533) A zero return value implies that all the requested wide characters from the string pointed to by s2 fit within the array pointed to by s1 and that the result in s1 is null terminated.
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§ K.3.9.2.1
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ISO/IEC 9899:2023 (E)
Description The wcsncpy_s function copies not more than n successive wide characters (wide characters that follow a null wide character are not copied) from the array pointed to by s2 to the array pointed to by s1. If no null wide character was copied from s2, then s1[n] is set to a null wide character. All elements following the terminating null wide character (if any) written by wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified values when wcsncpy_s returns.534) Returns
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The wcsncpy_s function returns zero535) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned.
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EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the result will not be null terminated or that wide characters will be written past the end of the destination array. #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> /* ... */ wchar_t src1[100] = L"hello"; wchar_t src2[7] = {L’g’, L’o’, L’o’, L’d’, L’b’, L’y’, L’e’}; wchar_t dst1[6], dst2[5], dst3[5]; int r1, r2, r3; r1 = wcsncpy_s(dst1, 6, src1, 100); r2 = wcsncpy_s(dst2, 5, src2, 7); r3 = wcsncpy_s(dst3, 5, src2, 4);
The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0. The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0. The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0. K.3.9.2.1.3 Synopsis 1
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#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> errno_t wmemcpy_s(wchar_t *restrict s1, rsize_t s1max, const wchar_t *restrict s2, rsize_t n);
Runtime-constraints Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX/ sizeof(wchar_t). n shall not be greater than s1max. Copying shall not take place between objects that overlap. If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and s1max is not greater than RSIZE_MAX/sizeof(wchar_t). Description The wmemcpy_s function copies n successive wide characters from the object pointed to by s2 into the object pointed to by s1. 534) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking if any of those wide characters are null. Such an approach might write a wide character to every element of s1 before discovering that the first element was set to the null wide character. 535) A zero return value implies that all the requested wide characters from the string pointed to by s2 fit within the array pointed to by s1 and that the result in s1 is null terminated.
§ K.3.9.2.1
Bounds-checking interfaces
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ISO/IEC 9899:2023 (E)
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The wmemmove_s function
#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, const wchar_t *s2, rsize_t n);
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Returns The wmemcpy_s function returns zero if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.9.2.1.4 Synopsis
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Runtime-constraints Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX/ sizeof(wchar_t). n shall not be greater than s1max. If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and s1max is not greater than RSIZE_MAX/sizeof(wchar_t). Description The wmemmove_s function copies n successive wide characters from the object pointed to by s2 into the object pointed to by s1. This copying takes place as if the n wide characters from the object pointed to by s2 are first copied into a temporary array of n wide characters that does not overlap the objects pointed to by s1 or s2, and then the n wide characters from the temporary array are copied into the object pointed to by s1. Returns The wmemmove_s function returns zero if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.9.2.2 Wide string concatenation functions K.3.9.2.2.1 The wcscat_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> errno_t wcscat_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2);
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Runtime-constraints Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to wcscat_s.
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If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then wcscat_s sets s1[0] to the null wide character.
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Description The wcscat_s function appends a copy of the wide string pointed to by s2 (including the terminating null wide character) to the end of the wide string pointed to by s1. The initial wide character from s2 overwrites the null wide character at the end of s1. All elements following the terminating null wide character (if any) written by wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified values when wcscat_s returns.537) 536) Zero means that s1 was not null terminated upon entry to wcscat_s. 537) This allows an implementation to append wide characters from s2 to s1 while simultaneously checking if any of those
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Bounds-checking interfaces
§ K.3.9.2.2
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Returns 7
The wcscat_s function returns zero538) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned. K.3.9.2.2.2 Synopsis
#define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> errno_t wcsncat_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2, rsize_t n);
1
2
The wcsncat_s function
Runtime-constraints Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to wcsncat_s.
3
Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than RSIZE_MAX/ sizeof(wchar_t). s1max shall not equal zero. m shall not equal zero.539) If n is not less than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take place between objects that overlap.
4
If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then wcsncat_s sets s1[0] to the null wide character.
5
6
Description The wcsncat_s function appends not more than n successive wide characters (wide characters that follow a null wide character are not copied) from the array pointed to by s2 to the end of the wide string pointed to by s1. The initial wide character from s2 overwrites the null wide character at the end of s1. If no null wide character was copied from s2, then s1[s1max- m +n] is set to a null wide character. All elements following the terminating null wide character (if any) written by wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified values when wcsncat_s returns.540) Returns
7
The wcsncat_s function returns zero541) if there was no runtime-constraint violation. Otherwise, a nonzero value is returned.
8
EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the result will not be null terminated or that wide characters will be written past the end of the destination array. #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> /* ... */ wchar_t s1[100] = L"good"; wchar_t s2[6] = L"hello"; wchar_t s3[6] = L"hello"; wchar_t s4[7] = L"abc"; wchar_t s5[1000] = L"bye"; int r1, r2, r3, r4; wide characters are null. Such an approach might write a wide character to every element of s1 before discovering that the first element was set to the null wide character. 538) A zero return value implies that all the requested wide characters from the wide string pointed to by s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. 539) Zero means that s1 was not null terminated upon entry to wcsncat_s. 540) This allows an implementation to append wide characters from s2 to s1 while simultaneously checking if any of those wide characters are null. Such an approach might write a wide character to every element of s1 before discovering that the first element was set to the null wide character. 541) A zero return value implies that all the requested wide characters from the wide string pointed to by s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
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r1 = wcsncat_s(s1, 100, s5, 1000); r2 = wcsncat_s(s2, 6, L"", 1); r3 = wcsncat_s(s3, 6, L"X", 2); r4 = wcsncat_s(s4, 7, L"defghijklmn", 3);
After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0. After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0. After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0. After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0. K.3.9.2.3 Wide string search functions K.3.9.2.3.1 The wcstok_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> wchar_t *wcstok_s(wchar_t * restrict s1, rsize_t * restrict s1max, const wchar_t * restrict s2, wchar_t ** restrict ptr);
1
2
3
4
Runtime-constraints None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX/sizeof(wchar_t). The end of the token found shall occur within the first *s1max wide characters of s1 for the first call, and shall occur within the first *s1max wide characters of where searching resumes on subsequent calls. If there is a runtime-constraint violation, the wcstok_s function does not indirect through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. Description A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1 into a sequence of tokens, each of which is delimited by a wide character from the wide string pointed to by s2. The fourth argument points to a caller-provided wchar_t pointer into which the wcstok_s function stores information necessary for it to continue scanning the same wide string.
5
The first call in a sequence has a non-null first argument and s1max points to an object whose value is the number of elements in the wide character array pointed to by the first argument. The first call stores an initial value in the object pointed to by ptr and updates the value pointed to by s1max to reflect the number of elements that remain in relation to ptr. Subsequent calls in the sequence have a null first argument and the objects pointed to by s1max and ptr are required to have the values stored by the previous call in the sequence, which are then updated. The separator wide string pointed to by s2 may be different from call to call.
6
The first call in the sequence searches the wide string pointed to by s1 for the first wide character that is not contained in the current separator wide string pointed to by s2. If no such wide character is found, then there are no tokens in the wide string pointed to by s1 and the wcstok_s function returns a null pointer. If such a wide character is found, it is the start of the first token.
7
The wcstok_s function then searches from there for the first wide character in s1 that is contained in the current separator wide string. If no such wide character is found, the current token extends to the end of the wide string pointed to by s1, and subsequent searches in the same wide string for a token return a null pointer. If such a wide character is found, it is overwritten by a null wide character, which terminates the current token.
8
In all cases, the wcstok_s function stores sufficient information in the pointer pointed to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer value for ptr, shall start searching just past the element overwritten by a null wide character (if any). 662
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9
Returns The wcstok_s function returns a pointer to the first wide character of a token, or a null pointer if there is no token or there is a runtime-constraint violation.
10
EXAMPLE #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> static wchar_t str1[] = L"?a???b,,,#c"; static wchar_t str2[] = L"\t \t"; wchar_t *t, *ptr1, *ptr2; rsize_t max1 = wcslen(str1)+1; rsize_t max2 = wcslen(str2)+1; t = wcstok_s(str1, &max1, "?", &ptr1); t = wcstok_s(NULL, &max1, ",", &ptr1); t = wcstok_s(str2, &max2, " \t", &ptr2); t = wcstok_s(NULL, &max1, "#,", &ptr1); t = wcstok_s(NULL, &max1, "?", &ptr1);
// t points to the token "a" // t points to the token "??b" // t is a null pointer // t points to the token "c" // t is a null pointer
K.3.9.2.4 Miscellaneous functions K.3.9.2.4.1 The wcsnlen_s function Synopsis #define __STDC_WANT_LIB_EXT1__ 1 #include <wchar.h> size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
1
2
Description The wcsnlen_s function computes the length of the wide string pointed to by s. Returns
3
If s is a null pointer,542) then the wcsnlen_s function returns zero.
4
Otherwise, the wcsnlen_s function returns the number of wide characters that precede the terminating null wide character. If there is no null wide character in the first maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first maxsize wide characters of s shall be accessed by wcsnlen_s.
1
K.3.9.3 Extended multibyte/wide character conversion utilities K.3.9.3.1 Restartable multibyte/wide character conversion functions Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the conversion state) to be a null pointer. K.3.9.3.1.1 Synopsis
1
2
The wcrtomb_s function
#include <wchar.h> errno_t wcrtomb_s(size_t * restrict retval, char * restrict s, rsize_t smax, wchar_t wc, mbstate_t * restrict ps);
Runtime-constraints Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer, then smax shall be not be less 542) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints along with the values returned for a null pointer or an unterminated wide string argument make wcsnlen_s useful in algorithms that gracefully handle such exceptional data.
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than the number of bytes to be stored in the array pointed to by s. If s is a null pointer, then smax shall equal zero. 3
4
If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then wcrtomb_s sets *retval to (size_t)(-1). Description If s is a null pointer, the wcrtomb_s function is equivalent to the call wcrtomb_s(&retval, buf, sizeof buf, L’\0’, ps)
where retval and buf are internal objects of the appropriate types, and the size of buf is greater than MB_CUR_MAX. 5
If s is not a null pointer, the wcrtomb_s function determines the number of bytes needed to represent the multibyte character that corresponds to the wide character given by wc (including any shift sequences), and stores the multibyte character representation in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If wc is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state; the resulting state described is the initial conversion state.
6
If wc does not correspond to a valid multibyte character, an encoding error occurs: the wcrtomb_s function stores the value (size_t)(-1) into *retval and the conversion state is unspecified. Otherwise, the wcrtomb_s function stores into *retval the number of bytes (including any shift sequences) stored in the array pointed to by s.
7
Returns The wcrtomb_s function returns zero if no runtime-constraint violation and no encoding error occurred. Otherwise, a nonzero value is returned.
1
K.3.9.3.2 Restartable multibyte/wide string conversion functions Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not permit the ps parameter (the pointer to the conversion state) to be a null pointer. K.3.9.3.2.1 Synopsis
#include <wchar.h> errno_t mbsrtowcs_s(size_t * restrict retval, wchar_t * restrict dst, rsize_t dstmax, const char ** restrict src, rsize_t len, mbstate_t * restrict ps);
1
2
3
4
The mbsrtowcs_s function
Runtime-constraints None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, then neither len nor dstmax shall be greater than RSIZE_MAX/sizeof(wchar_t). If dst is a null pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null character shall occur within the first dstmax multibyte characters of the array pointed to by *src. If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1). If dst is not a null pointer and dstmax is greater than zero and not greater than RSIZE_MAX/sizeof(wchar_t), then mbsrtowcs_s sets dst[0] to the null wide character. Description The mbsrtowcs_s function converts a sequence of multibyte characters that begins in the conversion state described by the object pointed to by ps, from the array indirectly pointed to by src into a sequence of corresponding wide characters. If dst is not a null pointer, the converted characters are stored into the array pointed to by dst. Conversion continues up to and including a terminating null 664
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character, which is also stored. Conversion stops earlier in two cases: when a sequence of bytes is encountered that does not form a valid multibyte character, or (if dst is not a null pointer) when len wide characters have been stored into the array pointed to by dst.543) If dst is not a null pointer and no null wide character was stored into the array pointed to by dst, then dst[len] is set to the null wide character. Each conversion takes place as if by a call to the mbrtowc function. 5
If dst is not a null pointer, the pointer object pointed to by src is assigned either a null pointer (if conversion stopped due to reaching a terminating null character) or the address just past the last multibyte character converted (if any). If conversion stopped due to reaching a terminating null character and if dst is not a null pointer, the resulting state described is the initial conversion state.
6
Regardless of whether dst is or is not a null pointer, if the input conversion encounters a sequence of bytes that do not form a valid multibyte character, an encoding error occurs: the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into *retval the number of multibyte characters successfully converted, not including the terminating null character (if any).
7
All elements following the terminating null wide character (if any) written by mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take unspecified values when mbsrtowcs_s returns.544)
8
If copying takes place between objects that overlap, the objects take on unspecified values.
9
Returns The mbsrtowcs_s function returns zero if no runtime-constraint violation and no encoding error occurred. Otherwise, a nonzero value is returned. K.3.9.3.2.2 Synopsis
1
2
3
4
The wcsrtombs_s function
#include <wchar.h> errno_t wcsrtombs_s(size_t * restrict retval, char * restrict dst, rsize_t dstmax, const wchar_t ** restrict src, rsize_t len, mbstate_t * restrict ps);
Runtime-constraints None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, then neither len shall be greater than RSIZE_MAX/sizeof(wchar_t) nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal zero. If dst is not a null pointer and len is not less than dstmax, then the conversion shall have been stopped (see below) because a terminating null wide character was reached or because an encoding error occurred. If there is a runtime-constraint violation, then wcsrtombs_s does the following. If retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1). If dst is not a null pointer and dstmax is greater than zero and not greater than RSIZE_MAX, then wcsrtombs_s sets dst[0] to the null character. Description The wcsrtombs_s function converts a sequence of wide characters from the array indirectly pointed to by src into a sequence of corresponding multibyte characters that begins in the conversion state described by the object pointed to by ps. If dst is not a null pointer, the converted characters are then stored into the array pointed to by dst. Conversion continues up to and including a terminating null wide character, which is also stored. Conversion stops earlier in two cases: — when a wide character is reached that does not correspond to a valid multibyte character; 543) Thus, the value of len is ignored if dst is a null pointer. 544) This allows an implementation to attempt converting the multibyte string before discovering a terminating null character
did not occur where required.
§ K.3.9.3.2
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— (if dst is not a null pointer) when the next multibyte character would exceed the limit of n total bytes to be stored into the array pointed to by dst. If the wide character being converted is the null wide character, then n is the lesser of len or dstmax. Otherwise, n is the lesser of len or dstmax-1. If the conversion stops without converting a null wide character and dst is not a null pointer, then a null character is stored into the array pointed to by dst immediately following any multibyte characters already stored. Each conversion takes place as if by a call to the wcrtomb function.545) 5
If dst is not a null pointer, the pointer object pointed to by src is assigned either a null pointer (if conversion stopped due to reaching a terminating null wide character) or the address just past the last wide character converted (if any). If conversion stopped due to reaching a terminating null wide character, the resulting state described is the initial conversion state.
6
Regardless of whether dst is or is not a null pointer, if the input conversion encounters a wide character that does not correspond to a valid multibyte character, an encoding error occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores into *retval the number of bytes in the resulting multibyte character sequence, not including the terminating null character (if any).
7
All elements following the terminating null character (if any) written by wcsrtombs_s in the array of dstmax elements pointed to by dst take unspecified values when wcsrtombs_s returns.546)
8
If copying takes place between objects that overlap, the objects take on unspecified values.
9
Returns The wcsrtombs_s function returns zero if no runtime-constraint violation and no encoding error occurred. Otherwise, a nonzero value is returned.
545) If conversion stops because a terminating null wide character has been reached, the bytes stored include those necessary to reach the initial shift state immediately before the null byte. However, if the conversion stops before a terminating null wide character has been reached, the result will be null terminated, but might not end in the initial shift state. 546) When len is not less than dstmax, the implementation might fill the array before discovering a runtime-constraint violation.
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Annex L (normative)
Analyzability L.1
Scope
1
This annex specifies optional behavior that can aid in the analyzability of C programs.
2
An implementation that defines __STDC_ANALYZABLE__ shall conform to the specifications in this annex.547)
L.2 Definitions L.2.1 1
out-of-bounds store an (attempted) access (3.1) that, at run time, for a given computational state, would modify (or, for an object declared volatile, fetch) one or more bytes that lie outside the bounds permitted by this document.
L.2.2 1
bounded undefined behavior undefined behavior (3.4.3) that does not perform an out-of-bounds store.
2
Note 1 to entry: The behavior might perform a trap.
3
Note 2 to entry: Any values produced might be unspecified values, and the representation of objects that are written to might become indeterminate.
L.2.3 1
critical undefined behavior undefined behavior that is not bounded undefined behavior.
2
Note 1 to entry: The behavior might perform an out-of-bounds store or perform a trap.
L.3
Requirements
1
If the program performs a trap (3.19.5), the implementation is permitted to invoke a runtimeconstraint handler. Any such semantics are implementation-defined.
2
All undefined behavior shall be limited to bounded undefined behavior, except for the following which are permitted to result in critical undefined behavior: — An object is referred to outside of its lifetime (6.2.4). — A store is performed to an object that has two incompatible declarations (6.2.7), — A pointer is used to call a function whose type is not compatible with the referenced type (6.2.7, 6.3.2.3, 6.5.2.2). — An lvalue does not designate an object when evaluated (6.3.2.1). — The program attempts to modify a string literal (6.4.5). — The operand of the unary * operator has an invalid value (6.5.3.2). — Addition or subtraction of a pointer into, or just beyond, an array object and an integer type produces a result that points just beyond the array object and is used as the operand of a unary * operator that is evaluated (6.5.6). — An attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type (6.7.3). 547) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these specifications.
§ L.3
Analyzability
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— An argument to a function or macro defined in the standard library has an invalid value or a type not expected by a function with variable number of arguments (7.1.4). — The longjmp function is called with a jmp_buf argument where the most recent invocation of the setjmp macro in the same invocation of the program with the corresponding jmp_buf argument is nonexistent, or the invocation was from another thread of execution, or the function containing the invocation has terminated execution in the interim, or the invocation was within the scope of an identifier with variably modified type and execution has left that scope in the interim (7.13.2.1). — The value of a pointer that refers to space deallocated by a call to the free or realloc function is used (7.24.3). — A string or wide string utility function accesses an array beyond the end of an object (7.26.1, 7.31.4).
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Analyzability
§ L.3
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Annex M (informative)
Change History M.1
Attribute Changes
1
The attribute feature was introduced in the fifth edition of this document, as detailed in the change list below (M.2). The following table illustrates what usage of the __has_c_attribute preprocessor conditional expression should return in the latest revision, previous values, and the change associated with that value.
2
Programs and implementations may use this table know what values were being used at any specific point in time, leading up to the publication of this document. The value at the bottom of a particular row in a table is the latest value and corresponds with the behavior for the given attribute described in this document. Table Annex M.1: __has_c_attribute values and associated changes. attribute tokens
value
deprecated
201904L 202311L 201904L
fallthrough
201910L maybe_unused
nodiscard
202311L 201904L 202106L 202311L 201904L 202003L
noreturn reproducible unsequenced
M.2 1
202311L 202002L 202311L 202207L 202311L 202207L 202311L
semantic and/or syntactic changes Initial introduction. Harmonized for fifth edition. Initial introduction. Expanded locations where fallthrough provides diagnostics due to improvements in specification of blocks. Harmonized for fifth edition. Initial introduction. maybe_unused may appertain to labels. Harmonized for fifth edition. Initial introduction. Added a form which accepts a string literal for diagnostic purposes, e.g. nodiscard("should have a reason"). Harmonized for fifth edition. Initial introduction. Harmonized for fifth edition. Initial introduction. Harmonized for fifth edition. Initial introduction. Harmonized for fifth edition.
Fifth Edition
Major changes in this fifth edition (__STDC_VERSION__ 202311L) include: — add new keywords such as bool, static_assert, true, false, thread_local and others, and allowed implementations to provide macros for the older spelling with a leading underscore followed by a capital letter as well as defining old and new keywords as macros to enable transition of programs easily; — removed integer width constraints and obsolete sign representations (so-called "1’s complement" and "sign-magnitude"); — added a one-argument version of static_assert; — removed support for function definitions with identifier lists; § M.2
Change History
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— mandated function declarations whose parameter list is empty be treated the same as a parameter list which only contain a single void; — harmonization with ISO/IEC 9945 (POSIX): • extended month name formats for strftime • integration of functions: gmtime_r, localtime_r, memccpy, strdup, strndup — harmonization with floating point standard IEC 60559: • integration of binary floating-point technical specification TS 18661-1 • integration of decimal floating-point technical specification TS 18661-2 • integration of mathematical functions technical specification TS 18661-4a — made the DECIMAL_DIG macro obsolescent; — added version test macros to library headers that contained changes to aid in upgrading and portability to be used alongside the __STDC_VERSION__ macro; — allowed placement of labels in front of declarations and at the end of compound statement; — added the attributes feature, which includes the attributes: • deprecated, for marking entities as discouraged for future use; • fallthrough, for explicitly marking cases where falling through in switches or labels is intended rather than accidental; • maybe_unused, for marking entities which may end up not being used; • nodiscard, for marking entities which, when used, should have their value handled in some way by a program; • noreturn, for indicating a function shall never return; • reproducible, for marking function types for which inputs may always produce predictable output if given the same input (e.g., cached data) but for which the order of such calls still matter; and, • unsequenced, for marking function types which always produce predictable output and have no dependencies upon other data (and other relevant caveats); — added the u8 character prefix to match the u8 string prefix; — mandated all u8, u, and U strings be UTF-8, UTF-16, and UTF-32, respectively, as defined by ISO/IEC 10646; — separated the literal, wide literal, and UTF-8 literal, UTF-16 literal, and UTF-32 literal encodings for strings and characters and now have a solely execution-based version of these, particularly execution and wide execution encodings; — added mbrtoc8 and c8rtomb functions missing from <uchar.h>; — compound literals may also include storage-class specifiers as part of the type to change the lifetime of the compound literal (and possibly turn it into a constant expression) — added the constexpr specifier for object definitions and improved what is recognized as a constant expression in conjunction with the constexpr storage-class specifier; — added the typeof and typeof_unqual operations for deducing the type of an expression; — improved tag compatibility rules, enabling more types to be compatible with other types; — added bit-precise integer types _BitInt( N) and unsigned _BitInt( N), where N can be an integer constant expression whose value is from one to BITINT_MAXWIDTH, inclusive. 670
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— improved rules for handling enumerations without underlying types, in particular allowing for enumerations without fixed underlying type to have value representations that have a greater range than int; — added a new colon-delimited type specifier for enumerations to specify a fixed underlying type (and which, subject to an implementation’s definitions governing such constructs, adopt the fixed underlying type’s rules for padding, alignment, and sizing within structures and unions as well as with bit-fields); — added a new header <stdbit.h> and a suite of bit and byte-handling utilities for portable access to many implementations’ most efficient functionality; — modified existing functions to preserve the const-ness of the type placed into the function; — added a feature to embed binary data as faithfully as possible with a new preprocessor directive #embed; — added a nullptr constant and a nullptr_t type with a well-defined underlying representation identical to a pointer to void; — added the __VA_OPT__ specifier and clarified language in the handling of macro invocation and arguments; — mandated support for variably-modified types (but not variable-length arrays themselves); — ellipses on functions may appear without a preceding parameter in the parameter list of functions and va_start no longer requires such an argument to be passed to it; — Unicode identifiers allowed in syntax following Unicode Standard Annex, UAX #31; — added the memset_explicit function for making sensitive information inaccessible; — certain type definitions (i.e., exact-width integer types such as int128_t), bit-precise integer types, and extended integer types may exceed the normal boundaries of intmax_t and uintmax_t for signed and unsigned integer types, respectively; — names of functions, macros, and variables in this document, where clarified, are potentially reserved rather than reserved to avoid undefined behavior for a large class of identifiers used by programs existing and to be created; — mandated support for call_once; — allowed ptrdiff_t to be an integer type with a width of at least 16, rather than requiring an integer type with a width of at least 17; — added the __has_include feature for conditional inclusion expression preprocessor directives to check if a header is available for inclusion; — changed the type qualifiers of the _Imaginary_I and _Complex_I macros; — added @ (U+0040 Commercial At), $ (U+0024 Dollar Sign), and ‘ (U+0060 Grave Accent, "Backtick") into the source and execution character set; — enhanced the auto type specifier for single object definitions using type inference; — added the #elifdef and #elifndef conditional inclusion preprocessor directives; — added the #warning preprocessing directive; — binary integer literals and appropriate formatting for input/output of binary integer numbers; — digit separators with ’ (single quotation mark); — removed conditional support for mixed wide and narrow string literal concatenation; § M.2
Change History
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— added support for additional time bases, as well as timespec_getres, in <time.h>; — added support for new interface timegm to retrieve the broken-down time, in <time.h>; — zero-sized reallocations with realloc are undefined behavior; — added an unreachable feature which has undefined behavior if reached during program execution.
M.3 1
There were no major changes in the fourth edition (__STDC_VERSION__ 201710L), only technical corrections and clarifications.
M.4 1
Fourth Edition
Third Edition
Major changes in the third edition (__STDC_VERSION__ 201112L) included: — conditional (optional) features (including some that were previously mandatory) — support for multiple threads of execution including an improved memory sequencing model, atomic objects, and thread storage (<stdatomic.h> and <threads.h>) — additional floating-point characteristic macros (<float.h>) — querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>) — Unicode characters and strings (<uchar.h>) (originally specified in ISO/IEC TR 19769:2004) — type-generic expressions — static assertions — anonymous structures and unions — no-return functions — macros to create complex numbers (<complex.h>) — support for opening files for exclusive access — removed the gets function (<stdio.h>) — added the aligned_alloc, at_quick_exit, and quick_exit functions (<stdlib.h>) — (conditional) support for bounds-checking interfaces (originally specified in ISO/IEC TR 24731– 1:2007) — (conditional) support for analyzability
M.5 1
Second Edition
Major changes in the second edition (__STDC_VERSION__ 199901L) included: — restricted character set support via digraphs and <iso646.h> (originally specified in ISO/IEC 9899:1990/Amd 1:1995) — wide character library support in <wchar.h> and <wctype.h> (originally specified in ISO/IEC 9899:1990/Amd 1:1995) — more precise aliasing rules via effective type — restricted pointers — variable length arrays 672
Change History
§ M.5
N3096
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ISO/IEC 9899:2023 (E)
— flexible array members — static and type qualifiers in parameter array declarators — complex (and imaginary) support in <complex.h> — type-generic math macros in <tgmath.h> — the long long int type and library functions — extended integer types — increased minimum translation limits — additional floating-point characteristics in <float.h> — remove implicit int — reliable integer division — universal character names (\u and \U) — extended identifiers — hexadecimal floating constants and %a and %A printf/scanf conversion specifiers — compound literals — designated initializers — // comments — specified width integer types and corresponding library functions in <inttypes.h> and <stdint.h>
— remove implicit function declaration — preprocessor arithmetic done in intmax_t/uintmax_t — mixed declarations and statements — new block scopes for selection and iteration statements — integer constant type rules — integer promotion rules — macros with a variable number of arguments (__VA_ARGS__) — the vscanf family of functions in <stdio.h> and <wchar.h> — additional math library functions in <math.h> — treatment of error conditions by math library functions (math_errhandling) — floating-point environment access in <fenv.h> — IEC 60559 (also known as IEC 559 or IEEE 754 arithmetic) support — trailing comma allowed in enum declaration — %lf conversion specifier allowed in printf — inline functions — the snprintf family of functions in <stdio.h> — boolean type in <stdbool.h> § M.5
Change History
673
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
— idempotent type qualifiers — empty macro arguments — new structure type compatibility rules (tag compatibility) — additional predefined macro names — _Pragma preprocessing operator — standard pragmas — __func__ predefined identifier — va_copy macro — additional strftime conversion specifiers — LIA compatibility annex — deprecate ungetc at the beginning of a binary file — remove deprecation of aliased array parameters — conversion of array to pointer not limited to lvalues — relaxed constraints on aggregate and union initialization — relaxed restrictions on portable header names — return without expression not permitted in function that returns a value (and vice versa)
M.6 1
First Edition, Amendment 1
Major changes in the amendment to the first edition (__STDC_VERSION__ 199409L) included: — addition of the predefined __STDC_VERSION__ macro — restricted character set support via digraphs and <iso646.h> — wide character library support in <wchar.h> and <wctype.h>
674
Change History
§ M.6
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
Bibliography [1] ISO/IEC 14882 Programming languages — C++. [2] ISO/IEC 646:1991, Information technology — ISO 7-bit coded character set for information interchange. [3] ISO/IEC 9945–2:1993, Information technology — Portable Operating System Interface (POSIX) — Part 2: Shell and Utilities. [4] ISO/IEC TR 10176:2003, Information technology — Guidelines for the preparation of programming language standards. [5] ISO/IEC 10967–1:2012, Information technology — Language independent arithmetic — Part 1: Integer and floating point arithmetic. [6] ISO/IEC TR 19769:2004, Information technology — Programming languages, their environments and system software interfaces — Extensions for the programming language C to support new character data types. [7] ISO/IEC TR 24731–1:2007, Information technology — Programming languages, their environments and system software interfaces — Extensions to the C library — Part 1: Bounds-checking interfaces. [8] IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems. [9] ISO/IEC 60559:2011, Floating-point arithmetic. [10] IEEE 754–1985 IEEE Standard for Binary Floating-Point Arithmetic. [11] IEEE 754–2019 IEEE Standard for Floating-Point Arithmetic. [12] ANSI/IEEE 854–1987, American National Standard for Radix-Independent Floating-Point Arithmetic. [13] ANSI X3/TR–1–82 (1982), American National Dictionary for Information Processing Systems, Information Processing Systems Technical Report. [14] "The C Reference Manual" by Dennis M. Ritchie, a version of which was published in The C Programming Language by Brian W. Kernighan and Dennis M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T. [15] 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara, California, USA, November 1984. [16] The Unicode Consortium. Unicode Standard Annex, UAX #31, Unicode Identifier and Pattern Syntax [online]. Edited by Mark Davis. Revision 33; issued for Unicode 13.0.0. 2020-0213 [viewed 2020-05-27]. Available at https://www.unicode.org/reports/tr31/tr31-33. html.
Bibliography
675
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
N3096
Index - (minus punctuator), 68 - (subtraction operator), 84, 539 - (unary minus operator), 81, 510 - format flag, 329, 413 -- (minus-minus punctuator), 68 -- (postfix decrement operator), 48, 77 -- (prefix decrement operator), 48, 80 -= (minus-equal punctuator), 68 -= (subtraction assignment operator), 92 -> (minus-greater punctuator), 68 -> (structure/union pointer operator), 75 . (dot punctuator), 68, 135 . (structure/union member operator), 48, 75 ... (ellipsis punctuator), 68, 128, 178 / (division operator), 83, 537 / (slash punctuator), 68 /* */ (comment delimiters), 70 // (comment delimiter), 70 /= (division assignment operator), 92 /= (slash-equal punctuator), 68 : (colon punctuator), 68, 103 :> (alternative spelling of ]), 68 :> (colon greater punctuator), 68 ; (semicolon punctuator), 68, 96, 103, 152, 154,
! (exclamation-mark punctuator), 68 ! (logical negation operator), 81 != (inequality operator), 87 != (not-equal punctuator), 68 # (hash punctuator), 68 # preprocessing directive, 186 # punctuator, 162 ## (hash-hash punctuator), 68 #define preprocessing directive, 177 #elif preprocessing directive, 166 #elifdef preprocessing directive, 167 #elifndef preprocessing directive, 167 #else preprocessing directive, 167 #embed preprocessing directive, 170 #endif preprocessing directive, 167 #error preprocessing directive, 8, 185 #if preprocessing directive, 166 #ifdef preprocessing directive, 167 #ifndef preprocessing directive, 167 #include preprocessing directive, 10, 169 #line preprocessing directive, 184 #pragma preprocessing directive, 185 #undef preprocessing directive, 182, 192
⌈x⌉, 7 ⌊x⌋, 7 & (bitwise AND operator), 87 && (logical AND operator), 16, 88 &= (bitwise AND assignment operator), 92 ’ ’ (space character), 10, 19, 51, 204, 206, 448 ( (opening parenthesis punctuator), 68 () (cast operator), 83 () (function-call operator), 74 () (parentheses punctuator), 128, 153, 154 (){} (compound-literal operator), 78 ) (closing parenthesis punctuator), 68 * (asterisk punctuator), 68, 125, 126 * (indirection operator), 74, 81 * (multiplication operator), 83, 537 *= (asterisk-equal punctuator), 68 *= (multiplication assignment operator), 92 + (addition operator), 74, 81, 84, 539 + (plus punctuator), 68 + (unary plus operator), 81 + format flag, 329, 413 ++ (plus-plus punctuator), 68 ++ (postfix increment operator), 48, 77 ++ (prefix increment operator), 48, 80 += (addition assignment operator), 92 += (plus-equal punctuator), 68 , (comma operator), 16, 93 , (comma punctuator), 68, 73, 96, 103, 107, 114, 135 676
155 < (less punctuator), 68 < (less-than operator), 86 <: (alternative spelling of [), 68 <: (less-colon punctuator), 68 << (left-shift operator), 85 << (less-less punctuator), 68 <<= (left-shift assignment operator), 92 <<= (less-less equal punctuator), 68 <= (less-equal punctuator), 68 <= (less-than-or-equal-to operator), 86 <% (alternative spelling of {), 68 <% (less-percent punctuator), 68 <assert.h> header, 173–175, 191, 194, 218,
471 <complex.h> header, 24, 29, 137, 188, 190, 191,
195–202, 383, 384, 453, 471, 537, 538, 539, 540, 556, 557, 593, 596, 602, 672, 673 <ctype.h> header, 191, 204, 205, 206, 453, 472 <errno.h> header, 148, 191, 208, 453, 472, 620 <fenv.h> header, 8, 13, 15, 24, 29, 33, 92, 148, 191, 209, 211–213, 215–220, 236, 453, 472, 507, 510, 513–515, 524, 528, 530, 673 <float.h> header, vi, 8, 9, 21, 23, 24, 28, 29, 191, 221, 234, 333, 357, 418, 431, 453, 454, 473, 474, 503, 507, 512, 549, 550, Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
<uchar.h> header, 65, 66, 68, 191, 407, 408–
551, 600, 672, 673
411, 496, 670, 672
<inttypes.h> header, 191, 222, 223, 224, 330,
<wchar.h> header, 24, 29, 33, 148, 191, 213,
415, 453, 474, 673 <iso646.h> header, 8, 9, 191, 225, 474, 672, 674 <limits.h> header, vi, 8, 9, 21, 22, 38, 39, 191, 226, 474, 503, 600 <locale.h> header, 148, 191, 227, 228, 453, 474 <math.h> header, 8, 24, 29, 33, 72, 148, 191, 213, 214, 233, 234, 236–239, 240–273, 274, 275–280, 334, 383–385, 418, 453, 454, 475, 485, 486, 506, 507, 512, 518, 524, 528, 530–534, 537, 538, 548, 557, 558, 570–572, 583, 593, 596, 600, 602, 673 <setjmp.h> header, 191, 282, 283, 486 <signal.h> header, 191, 284, 286, 454, 486 <stdalign.h> header, 8, 9, 191, 287, 486, 672 <stdarg.h> header, 8, 9, 128, 191, 288, 289– 291, 344–346, 424, 425, 486, 629–632, 653–656 <stdatomic.h> header, 187, 190, 191, 285, 292, 293, 295–301, 454, 487, 590, 672 <stdbit.h> header, 8, 191, 302, 303–309, 454, 488, 671 <stdbool.h> header, 8, 9, 191, 310, 454, 489, 673 <stdckdint.h> header, 191, 311, 454, 489 <stddef.h> header, 8, 9, 49, 66, 68, 82, 84, 85, 140, 171, 172, 191, 224, 312, 313, 342, 489, 621 <stdint.h> header, 8, 9, 21, 22, 166, 191, 222, 255–257, 263, 315, 317, 318, 330, 337, 338, 415, 420, 454, 489, 490, 600, 621, 673 <stdio.h> header, 15, 24, 29, 33, 55, 148, 169, 172, 191, 213, 214, 319, 323–325, 327, 328, 334, 336, 340–353, 400, 413, 418, 422–424, 426–429, 454, 490, 491, 596, 621, 622–633, 651, 653, 654, 672, 673 <stdlib.h> header, 8, 24, 29, 33, 191, 193, 213, 214, 354, 355, 356, 358, 360–372, 454, 491, 493, 548, 572, 574, 575, 596, 620, 634, 635–640, 672 <stdnoreturn.h> header, 8, 9, 146, 191, 373, 493 <string.h> header, vii, 8, 172, 175, 176, 191, 374, 375–382, 455, 493, 494, 641, 642– 647 <tgmath.h> header, 33, 191, 383, 386, 494, 506, 518, 546, 576, 578, 673 <threads.h> header, 148, 188, 190, 191, 388, 389–396, 455, 495, 672 <time.h> header, 191, 388, 398, 399–404, 441, 455, 495, 496, 647, 648–650, 672
214, 223, 320, 412, 413, 418, 422–430, 432–445, 455, 496, 498, 575, 576, 596, 650, 651–665, 672–674 <wctype.h> header, 191, 447, 448–452, 455, 498, 672, 674 = (equal-sign punctuator), 68, 96, 107, 135 = (simple assignment operator), 91 == (equal-equal punctuator), 68 == (equality operator), 87 > (greater punctuator), 68 > (greater-than operator), 86 >= (greater-equal punctuator), 68 >= (greater-than-or-equal-to operator), 86 >> (greater greater punctuator), 68 >> (right-shift operator), 85 >>= (greater-greater-equal punctuator), 68 >>= (right-shift assignment operator), 92 ? (question-mark punctuator), 68 ?: (conditional operator), 16, 89 [ (opening bracket punctuator), 68 [ ] (array subscript operator), 74, 81 [ ] (brackets punctuator), 126, 135 # format flag, 329, 414 % (percent punctuator), 68 % (remainder operator), 83 %: (alternative spelling of #), 68 %: (percent-colon punctuator), 68 %:%: (alternative spelling of ##), 68 %:%: (percent-percent punctuator), 68 %= (percent-equal punctuator), 68 %= (remainder assignment operator), 92 %> (alternative spelling of }), 68 %> (percent-greater punctuator), 68 %A conversion specifier, 331, 404, 416 %B conversion specifier, 330, 404, 415 %C conversion specifier, 404 %D conversion specifier, 404 %E conversion specifier, 331, 416 %F conversion specifier, 331, 404, 415 %G conversion specifier, 331, 405, 416 %H conversion specifier, 405 %I conversion specifier, 405 %M conversion specifier, 405 %R conversion specifier, 405 %S conversion specifier, 405 %T conversion specifier, 405 %U conversion specifier, 405 %V conversion specifier, 405 %W conversion specifier, 405 %X conversion specifier, 330, 405, 415 %Y conversion specifier, 405 %Z conversion specifier, 405 %[ conversion specifier, 339, 421 Index
677
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
_C identifier suffix, 318, 454, 490, 602, 603 _Complex type, 101, 195 _Complex types, 25, 38, 39, 47, 53, 101, 102,
%% conversion specifier, 333, 340, 417, 422 %a conversion specifier, 331, 338, 404, 416, 421 %b conversion specifier, 330, 404, 415 %c conversion specifier, 332, 338, 404, 417, 421 %d conversion specifier, 330, 338, 404, 415, 420 %e conversion specifier, 331, 338, 404, 416, 421 %f conversion specifier, 331, 338, 415, 421 %g conversion specifier, 331, 338, 405, 416, 421 %h conversion specifier, 405 %i conversion specifier, 330, 415 %j conversion specifier, 405 %m conversion specifier, 405 %n conversion specifier, 333, 340, 405, 417, 422 %o conversion specifier, 330, 338, 415, 421 %p conversion specifier, 333, 339, 405, 417, 422 %r conversion specifier, 405 %s conversion specifier, 332, 339, 417, 421 %t conversion specifier, 405 %u conversion specifier, 330, 338, 405, 415, 421 %w conversion specifier, 405 %x conversion specifier, 330, 338, 405, 415, 421 %y conversion specifier, 405 %z conversion specifier, 405 & (address operator), 48, 80 & (ampersand punctuator), 68 &= (ampersand-equal punctuator), 68 && (ampersand-ampersand punctuator), 68 \ (backslash character), 10, 18, 64 \ (backslash escape sequence), 64, 188 \" (double-quote escape sequence), 64, 67, 188 \’ (single-quote escape sequence), 64, 67 \0 (null character), 18, 66, 67
195, 456, 463, 536, 537, 538, 549, 556, 609 _Complex_I macro, iv, 195, 471, 540, 609, 671 _DECIMAL_DIG identifier prefix, 28, 333, 357, 418, 431, 512, 513 _Decimal32_t type, 233, 486, 598, 609 _Decimal64_t type, 233, 486, 598, 609 _EXT__ identifier suffix, 609 _Exit function, 285, 366, 367, 492, 590, 599, 609 _Float128_t type, 559, 609 _Float16_t type, 559, 610 _Float32_t type, 559, 610 _Float64_t type, 559, 610 _Generic , 53, 72, 73, 110, 111, 119, 134, 314, 385, 456, 460, 610 _H__ identifier prefix, 191 _IOFBF macro, 319, 327, 490, 610 _IOLBF macro, 319, 327, 490, 610 _IONBF macro, 319, 327, 490, 610 _Imaginary type, 195 _Imaginary types, 536 _Imaginary_I macro, iv, 195, 202, 471, 539, 540, 610, 671 _MAX identifier suffix, 22, 46, 317, 318, 454, 474, 490, 552, 602, 603 _MIN identifier suffix, 22, 317, 318, 454, 474, 490, 552, 602, 603 _Noreturn , 122 _PRINTF_NAN_LEN_MAX macro, 320, 490, 610 _Pragma operator, 188 _Static_assert , 53, 610 _Thread_local storage-class specifier, 53, 610 _WIDTH identifier suffix, 22, 317, 318, 454, 490, 602, 603 __STDC_ identifier prefix, 189 __STDC_VERSION_ identifier prefix, 191 __DATE__ macro, 186, 597, 610 __FILE__ macro, 168, 186, 194, 610 __LINE__ macro, 184, 185, 186, 194, 582, 610 __STDC_ANALYZABLE__ macro, 187, 610, 667 __STDC_EMBED_EMPTY__ macro, 166, 186, 610 __STDC_EMBED_FOUND__ macro, 165, 186, 610 __STDC_EMBED_NOT_FOUND__ macro, 165, 186, 610 __STDC_ENDIAN_BIG__ macro, 302, 303, 488, 610 __STDC_ENDIAN_LITTLE__ macro, 302, 303, 488, 610 __STDC_ENDIAN_NATIVE__ macro, 277, 278, 302, 488, 571, 572, 574–576, 598, 610 __STDC_HOSTED__ macro, 186, 610 __STDC_IEC_559_COMPLEX__ (obsolete), 23,
padding of binary stream, 321 \? (question-mark escape sequence), 64 \U (universal character names), 56 \a (alert escape sequence), 20, 65 \b (backspace escape sequence), 20, 65 \ (escape character), 64 \f (form-feed escape sequence), 20, 65, 206 \n (new-line escape sequence), 20, 65, 206 \octal digits (octal-character escape sequence),
64 \r (carriage-return escape sequence), 20, 65,
206 \t (horizontal-tab escape sequence), 20, 65,
204, 206, 448 \u (universal character names), 56 \v (vertical-tab escape sequence), 20, 65, 206 _Alignas , 53, 609 _Alignof operator, 53, 609 _Atomic type qualifier, 118 _Atomic type specifier, 115 _BitInt , vi, 22, 38, 45, 48, 53, 59, 60, 101, 102,
456, 463, 609, 670 _BitInt type, 101 _Bool type, ii, 53, 609
678
N3096
Index
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working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
610
187, 188–190, 536, 610
__STDC_VERSION_WCHAR_H__ macro, 412, 496,
__STDC_IEC_559_COMPLEX__ macro, 23 __STDC_IEC_559_COMPLEX__ macro, 536 __STDC_IEC_559__ (obsolete), 23, 187, 189,
610 __STDC_VERSION__ macro, 187, 610, 669, 670,
672, 674
190, 485, 506, 610
__STDC_WANT_IEC_60559_EXT__ macro, 233,
__STDC_IEC_559__ macro, 23 __STDC_IEC_60559_BFP__ macro, 8, 23, 187,
474, 485, 486, 512, 532–534, 610 __STDC_WANT_IEC_60559_TYPES_EXT__
188, 190, 485, 506, 532–534, 547, 548, 610 __STDC_IEC_60559_COMPLEX__ macro, 23, 187, 188, 190, 536, 610 __STDC_IEC_60559_DFP__ macro, 8, 29, 187, 188, 190, 214, 217, 219, 233, 240–267, 268, 269–273, 274, 275–278, 356, 358, 386, 432, 473, 474, 480, 486, 492, 504, 506, 532–534, 547–549, 610 __STDC_IEC_60559_TYPES__ macro, 187, 188, 190, 547–549, 610 __STDC_ISO_10646__ macro, 187, 595, 610 __STDC_LIB_EXT1__ macro, 187, 188, 190, 472, 489–491, 493, 494, 496, 498, 610, 619 __STDC_MB_MIGHT_NEQ_WC__ macro, 44, 187, 312, 610 __STDC_NO_ATOMICS__ macro, 187, 292, 487, 610 __STDC_NO_COMPLEX__ macro, 188, 195, 471, 610 __STDC_NO_THREADS__ macro, 15, 188, 388, 495, 610 __STDC_NO_VLA__ macro, 188, 610 __STDC_UTF_16__ macro, 186, 595, 610 __STDC_UTF_32__ macro, 186, 595, 610 __STDC_VERSION_ASSERT_H__ macro, 194, 471, 610 __STDC_VERSION_COMPLEX_H__ macro, 195, 471, 610 __STDC_VERSION_FENV_H__ macro, 209, 610 __STDC_VERSION_FLOAT_H__ macro, 221, 473, 610 __STDC_VERSION_MATH_H__ macro, 233, 475, 610 __STDC_VERSION_SETJMP_H__ macro, 282, 486, 610 __STDC_VERSION_STDARG_H__ macro, 288, 487, 610 __STDC_VERSION_STDIO_H__ macro, 319, 490, 610 __STDC_VERSION_STDLIB_H__ macro, 354, 492, 610 __STDC_VERSION_STRING_H__ macro, 374, 493, 610 __STDC_VERSION_TGMATH_H__ macro, 383, 610 __STDC_VERSION_TIME_H__ macro, 398, 495, 610 __STDC_VERSION_UCHAR_H__ macro, 407, 496,
macro, 551, 556, 570–572, 574–576, 578, 610 __STDC_WANT_LIB_EXT1__ macro, 472, 489– 491, 493, 494, 496, 498, 610, 619, 620, 622–638, 641–663 __STDC__ macro, 167, 186, 610 __TIME__ macro, 187, 597, 610 __VA_ARGS__ identifier, 177, 178, 179, 184, 610, 673 __VA_OPT__ identifier, vi, 177, 178–180, 469, 610, 671 ___Noreturn__ pragma, 610 __alignas_is_defined macro, 610 __alignof_is_defined macro, 610 __bool_true_false_are_defined (obsolete), 310, 454, 489, 610 __cplusplus macro, 167, 186, 610 __deprecated__ attribute, 142, 610 __fallthrough__ attribute, 610 __func__ identifier, 55, 194, 585, 610, 674 __has_c_attribute macro, 141–146, 148, 166, 167, 186, 610, 669 __has_c_attribute operator, 186 __has_embed macro, 51, 69, 166, 168, 186, 610 __has_embed operator, 186 __has_include macro, iv, 51, 69, 166, 167, 186, 610, 671 __has_include operator, 186 __if_empty__ embed parameter, 610 __limit__ embed parameter, 164 __maybe_unused__ attribute, 610 __noreturn__ attribute, 610 __pp_param__ pragma, 164, 610 __prefix__ embed parameter, 175 __prefix__ embed parameter, 610 __reproducible__ attribute, 610 __suffix__ embed parameter, 175 __suffix__ embed parameter, 610 __unsequenced__ attribute, 610 _explicit identifier suffix, 292, 300, 487 _r identifier prefix, 402 _t type, 315, 316, 318, 454, 490, 558, 559, 603 wchar_t character constant, 64 wchar_t string literal, 67 {} (braces punctuator), 107, 114, 135, 152 {} (compound-literal operator), 78 { (opening brace punctuator), 68 } (closing brace punctuator), 68 Index
679
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
] (closing bracket punctuator), 68 ^ (bitwise exclusive OR operator), 88 ^ (caret punctuator), 68 ^= (bitwise exclusive OR assignment opera-
active position, 19 add and round to narrower type, 273 addd function, 568, 611 ADDD macro, 560 addf function, 568, 611 ADDF macro, 559, 560 addition assignment operator (+=), 92 addition operator (+), 74, 81, 84, 539 additive expressions, 83, 539 address constant, 95 address operator (&), 48, 80 address-free, 297 aggregate initialization, 136 aggregate types, 40 alert, 20 alert escape sequence (\a), 20, 65 aliasing, 71 alignas, 123 aligned_alloc function, 362, 363, 364, 492, 583, 592, 599, 611, 672 alignment, 3, 43, 362 pointer, 40, 49 structure/union member, 104 alignment header, 287 alignment of memory, 372 alignment specifier, 123 alignof operator, 80, 81 allocated storage, order and contiguity, 362 alternative spellings header, 225 and macro, 225, 474, 611 AND operators bitwise (&), 87 bitwise assignment (&=), 92 logical (&&), 88 AND operators logical (&&), 16 and_eq macro, 225, 474, 611 anonymous structure, 104 anonymous union, 104 argc (main function parameter), 12 argument, 3 array, 159 default promotions, 75 function, 74, 159 macro, substitution, 178 argument, complex, 201 argv (main function parameter), 12 arithmetic constant expression, 95 arithmetic conversions, usual, see usual arithmetic conversions arithmetic operators additive, 83, 539 bitwise, 81, 87, 88 increment and decrement, 77, 80 multiplicative, 83, 537 shift, 85
tor), 92 ^= (caret-equal punctuator), 68 | (bitwise inclusive OR operator), 88 | (vertical-line punctuator), 68 |= (bitwise inclusive OR assignment operator),
92 |= (vertical-line-equal punctuator), 68 || (logical OR operator), 16, 88 || (vertical-vertical punctuator), 68 ~ (bitwise complement operator), 81 ~ (tilde punctuator), 68 0 format flag, 329, 414 abort function, 146, 194, 284, 285, 293, 322,
364, 365, 492, 589, 590, 599, 610, 635 abort_handler_s function, 493, 610, 635 abs function, 192, 369, 492, 610 abs macro, 192
absolute-value functions complex, 200, 545 integer, 223, 369 real, 255, 524 abstract declarator, 130 abstract machine, 12 access, 119, 667 access (verb), 3 acos function, 213, 240, 241, 384, 475, 512, 519, 557, 611 acos type-generic macro, 384 acosd function, 557, 561, 610 acosd128 function, 214, 240, 480, 610 acosd32 function, 214, 240, 480, 610 acosd64 function, 214, 240, 480, 610 acosf function, 213, 240, 475, 557, 561, 610 acosh function, 245, 384, 476, 512, 521, 611 acosh type-generic macro, 384 acoshd function, 562, 610 acoshd128 function, 245, 481, 610 acoshd32 function, 245, 481, 610 acoshd64 function, 245, 481, 610 acoshf function, 245, 386, 476, 562, 611 acoshl function, 245, 476, 611 acosl function, 213, 240, 475, 557, 611 acospi function, 243, 475, 512, 520, 611 acospi type-generic macro, 384 acospid function, 561, 611 acospid128 function, 243, 480, 611 acospid32 function, 243, 480, 611 acospid64 function, 243, 480, 611 acospif function, 243, 475, 561, 611 acospil function, 243, 475, 611 acquire fence, 296 acquire operation, 16 680
N3096
Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
at_quick_exit function, 365, 366, 367, 492,
unary, 81 arithmetic types, 39 arithmetic, pointer, 84 array argument, 159 declarator, 126 initialization, 136 multidimensional, 74 parameter, 159 storage order, 74 subscript operator ([ ]), 74, 81 subscripting, 74 type, 39 type conversion, 48 variable length, 125, 126, 188 arrow operator (->), 75 as–if rule, 13 asctime function, 186, 187, 402, 403, 496, 594, 611 asctime_s function, 496, 611, 648, 649 asin function, 241, 384, 475, 512, 519, 546, 611 asin type-generic macro, 384, 546 asind function, 561, 611 asind128 function, 241, 480, 611 asind32 function, 241, 480, 611 asind64 function, 241, 480, 611 asinf function, 241, 475, 561, 611 asinh function, 245, 246, 384, 476, 512, 521, 546, 611 asinh type-generic macro, 384, 546 asinhd function, 562, 611 asinhd128 function, 246, 481, 611 asinhd32 function, 246, 481, 611 asinhd64 function, 246, 481, 611 asinhf function, 246, 476, 562, 611 asinhl function, 246, 476, 611 asinl function, 241, 475, 611 asinpi function, 243, 475, 512, 520, 611 asinpi type-generic macro, 384 asinpid function, 561, 611 asinpid128 function, 243, 480, 611 asinpid32 function, 243, 480, 611 asinpid64 function, 243, 480, 611 asinpif function, 243, 475, 561, 611 asinpil function, 243, 475, 611 assert macro, v, 143, 174, 176, 194, 218, 471, 588, 597, 611 assignment compound, 92 conversion, 91 expression, 90 operators, 48, 90 simple, 91 associativity of operators, 71 asterisk punctuator (*), 125, 126
583, 592, 611, 672 atan function, 241, 334, 384, 418, 475, 512, 519,
546, 611 atan type-generic macro, 384, 546 atan2 function, 241, 242, 475, 512, 518, 519,
540, 611 atan2 type-generic macro, 384 atan2d function, 561, 611 atan2d128 function, 241, 480, 611 atan2d32 function, 241, 480, 611 atan2d64 function, 241, 480, 611 atan2f function, 241, 475, 561, 611 atan2l function, 241, 475, 611 atan2pi function, 244, 475, 512, 518, 520, 611 atan2pi type-generic macro, 384 atan2pid function, 562, 611 atan2pid128 function, 244, 481, 611 atan2pid32 function, 244, 480, 611 atan2pid64 function, 244, 480, 611 atan2pif function, 244, 476, 561, 611 atan2pil function, 244, 476, 611 atand function, 561, 611 atand128 function, 241, 480, 611 atand32 function, 241, 480, 611 atand64 function, 241, 480, 611 atanf function, 241, 475, 561, 611 atanh function, 246, 384, 476, 512, 521, 546,
611 atanh type-generic macro, 384, 546 atanhd function, 562, 611 atanhd128 function, 246, 481, 611 atanhd32 function, 246, 481, 611 atanhd64 function, 246, 481, 611 atanhf function, 246, 476, 562, 611 atanhl function, 246, 476, 611 atanl function, 241, 386, 475, 611 atanpi function, 243, 244, 475, 512, 520, 611 atanpi type-generic macro, 384 atanpid function, 561, 611 atanpid128 function, 244, 480, 611 atanpid32 function, 243, 480, 611 atanpid64 function, 243, 480, 611 atanpif function, 243, 475, 561, 611 atanpil function, 243, 475, 611 atexit function, 365, 366, 367, 492, 583, 592,
602, 611 atof function, 213, 354, 355, 492, 611 atoi function, 193, 354, 355, 492, 611 atol function, 354, 355, 492, 611 atoll function, 354, 355, 492, 611
atomic lock-free macros, 292, 297 atomic operations, 16 atomic types, 13, 40, 41, 48, 75, 77, 92, 115, 187, 297 ATOMIC_ identifier prefix, 454, 602 Index
681
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
atomic_ identifier prefix, 454, 603 atomic_bool type, 297, 298, 487, 603 ATOMIC_BOOL_LOCK_FREE macro, 292, 487,
atomic_int_least64_t type, 298, 487, 603 atomic_int_least8_t type, 298, 487, 603 ATOMIC_INT_LOCK_FREE macro, 292, 487, 603 atomic_intmax_t type, 298, 487, 603 atomic_intptr_t type, 298, 487, 603 atomic_is_lock_free function, 285, 297,
603 atomic_char type, 297, 487, 603 atomic_char16_t type, 298, 487, 603 ATOMIC_CHAR16_T_LOCK_FREE macro,
292,
487, 590, 603 atomic_llong type, 297, 487, 603 ATOMIC_LLONG_LOCK_FREE macro, 292, 487,
487, 603 atomic_char32_t type, 298, 487, 603 ATOMIC_CHAR32_T_LOCK_FREE macro,
292,
603 atomic_load function, 298, 299, 300, 487, 603 atomic_load_explicit function, 295, 299,
487, 603 atomic_char8_t type, 297, 487, 603 ATOMIC_CHAR8_T_LOCK_FREE macro, 292, 487,
487, 603
603
atomic_long type, 297, 487, 603 ATOMIC_LONG_LOCK_FREE macro, 292, 487,
ATOMIC_CHAR_LOCK_FREE macro, 292, 487,
603 atomic_compare_exchange_strong
603 func-
ATOMIC_POINTER_LOCK_FREE macro, 292, 487,
tion, 77, 92, 299, 487, 603
atomic_compare_exchange_strong_explicit
function, 299, 487, 603 atomic_compare_exchange_weak function,
299, 300, 487, 603
603 atomic_ptrdiff_t type, 298, 487, 603 atomic_schar type, 297, 487, 603 atomic_short type, 297, 487, 603 ATOMIC_SHORT_LOCK_FREE macro, 292, 487,
603
atomic_compare_exchange_weak_explicit
atomic_signal_fence function, 296, 297,
487, 603
function, 299, 487, 603 atomic_exchange function, 299, 487, 603 atomic_exchange_explicit function, 299, 487, 603 atomic_fetch_ function, 300, 487, 603 atomic_fetch_add function, 603 atomic_fetch_add_explicit function, 603 atomic_fetch_and function, 603 atomic_fetch_and_explicit function, 603 atomic_fetch_or function, 603 atomic_fetch_or_explicit function, 603 atomic_fetch_sub function, 603 atomic_fetch_sub_explicit function, 603 atomic_fetch_xor function, 603 atomic_fetch_xor_explicit function, 603 atomic_flag type, 292, 293, 300, 301, 487, 603 atomic_flag_clear function, 301, 487, 603 atomic_flag_clear_explicit function, 301, 487, 603 ATOMIC_FLAG_INIT macro, 292, 300, 487, 603 atomic_flag_test_and_set function, 301, 487, 603
atomic_size_t type, 298, 487, 603 atomic_store function, 298, 487, 603 atomic_store_explicit function, 295, 298,
487, 603 atomic_thread_fence function, 148, 296,
297, 487, 603 atomic_uchar type, 297, 487, 603 atomic_uint type, 297, 487, 603 atomic_uint_fast16_t type, 298, 487, 603 atomic_uint_fast32_t type, 298, 487, 603 atomic_uint_fast64_t type, 298, 487, 603 atomic_uint_fast8_t type, 298, 487, 604 atomic_uint_least16_t type, 298, 487, 604 atomic_uint_least32_t type, 298, 487, 604 atomic_uint_least64_t type, 298, 487, 604 atomic_uint_least8_t type, 298, 487, 604 atomic_uintmax_t type, 298, 487, 603 atomic_uintptr_t type, 298, 487, 603 atomic_ullong type, 297, 487, 604 atomic_ulong type, 297, 487, 604 atomic_ushort type, 297, 487, 604 atomic_wchar_t type, 298, 487, 604 ATOMIC_WCHAR_T_LOCK_FREE macro, 292, 487,
atomic_flag_test_and_set_explicit
function, 301, 487, 603 atomic_init function, 293, 487, 603 atomic_int type, 293, 297, 487, 603 atomic_int_fast16_t type, 298, 487, 603 atomic_int_fast32_t type, 298, 487, 603 atomic_int_fast64_t type, 298, 487, 603 atomic_int_fast8_t type, 298, 487, 603 atomic_int_least16_t type, 298, 487, 603 atomic_int_least32_t type, 298, 487, 603
682
N3096
604 atomics header, 292, 454 attribute __deprecated__ , 142, 610 __fallthrough__ , 610 __maybe_unused__ , 610 __noreturn__ , 610 __reproducible__ , 610 Index
N3096
working draft — April 1, 2023
__unsequenced__ , 610
ISO/IEC 9899:2023 (E)
exclusive OR, 88 exclusive OR assignment (^=), 92 inclusive OR, 88 inclusive OR assignment (|=), 92 shift, 85 blank character, 204 block, 151, 152 primary, 151 secondary, 151 block scope, 34 block structure, 34 bold type convention, 34 bool macro, 611 bool type, 45, 101 bool type conversions, 45 BOOL_MAX macro, 474, 503, 604 BOOL_WIDTH macro, 21, 474, 503, 611 boolean type, 45 boolean type and values header, 310, 454 boolean type conversion, 44, 45 bounded undefined behavior, 667 braces punctuator ({}), 107, 114, 135, 152 brackets operator ([ ]), 74, 81 brackets punctuator ([ ]), 126, 135 branch cuts, 196 broken-down time, 399, 400–404, 648, 650 bsearch macro, 367, 368, 454, 492, 583, 593, 611 bsearch_s macro, 493, 611, 636, 637 btowc function, 417, 418, 442, 497, 611 BUFSIZ macro, 319, 322, 327, 490, 611 byte, 4, 81 byte input/output functions, 320 byte-oriented stream, 321
deprecated, ii, 97, 105, 141, 142, 144, 402,
403, 496, 612, 669, 670 fallthrough, ii, 141, 145, 167, 613, 669,
670 for function types, 146 maybe_unused, ii, iv, 141, 143, 616, 669, 670 nodiscard, ii, 140, 141, 142, 143, 616, 669, 670 noreturn, 123, 141, 146, 283, 364–367, 373, 394, 486, 492, 493, 495, 616, 669, 670 reproducible, 141, 146, 148, 149, 587, 616, 669, 670 unsequenced, 141, 146, 148, 149, 150, 587, 618, 669, 670 attribute declaration, 96 attribute prefixed token, 140 attribute token, 140 attributes, 140 auto storage-class specifier, 53, 97, 98, 99, 127, 128, 133, 134, 158, 456, 463, 611, 671 automatic storage duration, 20, 37 backslash character (\), 10, 18, 64 backslash escape sequence (\), 64, 188 backspace, 20 backspace escape sequence (\b), 20, 65 basic character set, 4, 18 basic types, 39 behavior, 3 big-endian, 302 binary constant, 57 binary digit, 58 binary floating types, 549 binary prefix, 57 binary resource inclusion, 170 binary streams, 321, 349, 351 bit, 4 high order, 4 low order, 4 bit and byte utilities, 302 bit and byte utilities header, 454 bit-field, 104 bit-precise integer suffix, wb or WB, 59 bit-precise integer types, 38 bit-precise signed integer type, 38 bit-precise unsigned integer types, 38 bitand macro, 225, 474, 611 BITINT_MAXWIDTH macro, 22, 102, 503, 611, 670 bitor macro, 225, 474, 611 bitwise operators, 71 AND, 87 AND assignment (&=), 92 complement (~), 81
c identifier prefix, 383, 384
C program, 10 c16rtomb function, i, 409, 410, 496, 611 c32rtomb function, 411, 496, 611 c8rtomb function, 408, 496, 611, 670 cabs function, 200, 383, 384, 472, 540, 611 cabs functions, 540 type-generic macro for, 384 cabsf function, 200, 386, 472, 557, 611 cabsl function, 200, 472, 611 cacos function, 196, 197, 384, 471, 540, 541, 611 cacos functions type-generic macro for, 384 cacosf function, 196, 471, 556, 611 cacosh function, 198, 384, 471, 541, 611 cacosh functions type-generic macro for, 384 cacoshf function, 198, 471, 556, 611 cacoshl function, 198, 471, 611 cacosl function, 196, 471, 611 cacospi function, 453, 611 Index
683
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
calendar time, 398, 399–401, 403, 404, 649, 650 call by value, 74 call_once function, v, 354, 388, 389, 495, 611, 671 calloc function, v, 362, 363, 364, 492, 583, 592, 599, 611 canonical representation, 24 canonicalize family, 32, 268 canonicalize function, 24, 268, 384, 479, 508, 531, 611 canonicalized function, 567, 611 canonicalized128 function, 268, 484, 611 canonicalized32 function, 268, 484, 611 canonicalized64 function, 268, 484, 611 canonicalizef function, 268, 479, 567, 611 canonicalizel function, 268, 479, 611 carg function, 201, 386, 472, 540, 546, 576, 611 carg functions, 540 carg type-generic macro, 384, 546 cargf function, 201, 472, 557, 611 cargl function, 201, 472, 611 carriage return, 20 carriage-return escape sequence (\r), 20, 65, 206 carries a dependency, 16 case label, 152, 153 case mapping functions character, 206 wide character, 451 extensible, 451 casin function, 197, 384, 471, 540, 611 casin functions, 540 type-generic macro for, 384 casinf function, 197, 471, 556, 611 casinh function, 198, 384, 471, 540, 542, 611 casinh functions type-generic macro for, 384 casinhf function, 198, 471, 556, 611 casinhl function, 198, 471, 611 casinl function, 197, 471, 611 casinpi function, 453, 611 cast, 83 cast expression, 82 cast operator (()), 83 catan function, 197, 384, 471, 540, 611 catan functions, 540 type-generic macro for, 384 catanf function, 197, 471, 556, 611 catanh function, 198, 199, 384, 471, 540, 542, 611 catanh functions type-generic macro for, 384 catanhf function, 199, 471, 556, 611 catanhl function, 199, 471, 611 catanl function, 197, 471, 611 catanpi function, 453, 611 684
N3096
cbrt function, i, 73, 255, 385, 477, 524, 611 cbrt type-generic macro, 384 cbrtd function, 564, 611 cbrtd128 function, 255, 482, 611 cbrtd32 function, 255, 482, 611 cbrtd64 function, 255, 482, 611 cbrtf function, 73, 255, 385, 477, 564, 611 cbrtl function, 73, 255, 385, 477, 611 ccompoundn function, 453, 611 ccos function, 197, 384, 471, 540, 611 ccos functions, 540
type-generic macro for, 384 ccosf function, 197, 471, 556, 611 ccosh function, 199, 384, 471, 540, 542, 543,
611 ccosh functions
type-generic macro for, 384 ccoshf function, 199, 471, 556, 611 ccoshl function, 199, 471, 611 ccosl function, 197, 471, 611 ccospi function, 453, 611 ceil function, 234, 260, 478, 507, 527, 528, 529,
611 ceil type-generic macro, 384 ceild function, 565, 611 ceild128 function, 32, 260, 483, 611 ceild32 function, 32, 260, 483, 611 ceild64 function, 32, 260, 483, 611 ceilf function, 260, 478, 565, 611 ceill function, 260, 264, 478, 611 cerf function, 453, 611 cerfc function, 453, 611 cexp function, 199, 200, 384, 471, 544, 545, 611 cexp functions
type-generic macro for, 384 cexp10 function, 453, 611 cexp10m1 function, 453, 611 cexp2 function, 453, 611 cexp2m1 function, 453, 611 cexpf function, 200, 471, 557, 611 cexpl function, 200, 471, 611 cexpm1 function, 453, 611
change history, 669 char type, 101 char type conversion, 45–47 char16_t type, i, iv, 65, 67, 136, 186, 298, 407, 409, 496, 595, 611 char32_t type, iv, 65, 67, 136, 186, 298, 407, 410, 411, 496, 595, 612 char8_t type, v, 65, 67, 99, 297, 407, 408, 496, 612 CHAR_BIT macro, 21, 41, 103, 170–172, 174, 474, 503, 612 CHAR_MAX macro, 22, 229, 230, 474, 503, 604 CHAR_MIN macro, 22, 39, 474, 503, 604 CHAR_WIDTH macro, 21, 474, 503, 612 Index
N3096
working draft — April 1, 2023
character, 4 character array initialization, 136 character case mapping functions, 206 wide character, 451 extensible, 451 character classification functions, 204 wide character, 447 extensible, 450 character constant, 11, 18, 63 character display semantics, 19 character handling header, 204, 228, 453 character input/output functions, 346, 633 wide character, 426 character sets, 18 character string literal, see string literal character type conversion, 44 character types, 39, 136 characteristics of floating types header, 221, 453 characteristics of integer types header, 226 checked arithmetic functions, 454 checked integer arithmetic header, 311 cimag function, 201, 202, 203, 472, 538, 540, 546, 576, 612 cimag functions, 540 cimag type-generic macro, 384, 546 cimagf function, 201, 472, 557, 612 cimagl function, 201, 386, 472, 612 cis function, 540 ckd_ macro, iv, xiv, 311, 454, 489, 603, 604 ckd_add macro, 311, 493, 604 ckd_div macro, 604 ckd_mul macro, 311, 493, 604 ckd_sub macro, 311, 493, 604 classification functions character, 204 floating-point, 237 wide character, 447 extensible, 450 clearerr function, 352, 491, 612 clgamma function, 453, 612 clock function, 398, 399, 402, 495, 599, 612 clock_t type, 398, 399, 495, 599, 612 CLOCKS_PER_SEC macro, 398, 399, 402, 495, 612 clog function, 200, 384, 471, 545, 612 clog functions type-generic macro for, 384 clog10 function, 453, 612 clog10p1 function, 453, 612 clog1p function, 453, 612 clog2 function, 453, 612 clog2p1 function, 453, 612 clogf function, 200, 386, 471, 557, 612 clogl function, 200, 472, 612 clogp1 function, 453, 612
ISO/IEC 9899:2023 (E)
closing, 322 CMPLX macro, 195, 201, 202, 472, 612 CMPLXF macro, 201, 202, 472, 557, 612 CMPLXL macro, 202, 472, 612 cnd_ identifier prefix, 455, 603 cnd_broadcast function, 389, 390, 391, 495, 604 cnd_destroy function, 390, 495, 604 cnd_init function, 390, 495, 604 cnd_signal function, 390, 391, 495, 604 cnd_t type, 388, 389–391, 495, 604 cnd_timedwait function, 390, 391, 495, 604 cnd_wait function, 390, 391, 495, 604 code point, 501 coefficient, 31 collating sequences, 18 colon punctuator (:), 103 comma operator (,), 16, 93 comma punctuator (,), 73, 96, 103, 107, 114, 135 command processor, 367 comment delimiters (/* */ and //), 70 comments, 10, 51, 70 common definitions header, 312 common extensions, 601 common initial sequence, 76 common real type, 47 common warnings, 11, 580 comparison functions, 367, 368, 369, 636, 637, 638 string, 377 wide string, 436 comparison macros, 279 comparison, pointer, 86 compatible type, 102, 119, 125 compatible types, 42 compl macro, 225, 474, 612 complement operator (~), 81 complete, 37 complete type, 37 complex arithmetic header, 195, 453 complex macro, 137, 195–203, 386, 471, 472, 537, 538, 556, 557, 578, 583, 612 complex numbers, 38, 536 complex type conversion, 46, 47 complex type domain, 39 complex types, 38, 101, 188, 536 components of time, 398, 648 composite type, 43 compound assignment, 92 compound literal, 78 compound literal constant, 94 compound literals, 77 compound statement, 152 compound-literal operator ((){}), 78 compoundn function, 255, 477, 511, 525, 612 Index
685
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
compoundn type-generic macro, 384 compoundnd function, 564, 612 compoundnd128 function, 255, 482, 612 compoundnd32 function, 255, 482, 612 compoundnd64 function, 255, 482, 612 compoundnf function, 255, 477, 564, 612 compoundnl function, 255, 477, 612
arithmetic operands, 44 array argument, 159 array parameter, 159 arrays, 48 boolean, 45 boolean, characters, and integers, 44 by assignment, 91 by return statement, 157 complex types, 46 explicit, 44 function, 49 function argument, 75, 159 function designators, 48 function parameter, 159 imaginary, 536 imaginary and complex, 536 implicit, 44 lvalues, 48 nullptr_t, 50 pointer, 48, 49 real and complex, 47 real and imaginary, 536 real floating and integer, 46, 512 real floating types, 46 signed and unsigned integers, 46 usual arithmetic, see usual arithmetic conversions void type, 49 conversion functions multibyte/wide character, 369, 638 extended, 442, 663 restartable, 407, 443, 663 multibyte/wide string, 371, 639 restartable, 444, 664 numeric, 223, 354 wide string, 224, 430 single byte/wide character, 442 time, 402, 648 wide character, 441 conversion specifier, 328, 336, 413, 419 %A, 331, 404, 416 %B, 330, 404, 415 %C, 404 %D, 404 %E, 331, 416 %F, 331, 404, 415 %G, 331, 405, 416 %H, 405 %I, 405 %M, 405 %R, 405 %S, 405 %T, 405 %U, 405 %V, 405 %W, 405
concatenation functions string, 376, 643 wide string, 436, 660 conceptual models, 10 conditional expression inclusion preprocessing directives, 21, 24, 165, 192 conditional features, 8, 38–40, 126, 187, 190, 506, 536, 619, 667 conditional inclusion, 164 conditional inclusion preprocessing directives, 165 conditional operator (?:), 16, 89 conflict, 16 conformance, 8 conforming freestanding implementation, 8 conforming hosted implementation, 8 conforming implementation, 8 conforming program, 8 conj function, 202, 472, 540–545, 576, 612 conj functions, 540 conj type-generic macro, 384 conjf function, 202, 472, 557, 612 conjl function, 202, 472, 612 const type qualifier, 118 const-qualified type, 40, 48, 119 constant expression, 94, 514 constants, 57 as primary expression, 72 binary, 57 character, 63 enumeration, 34, 63 floating, 60 hexadecimal, 57 integer, 57 octal, 57 constexpr storage-class specifier, 35, 37, 53, 78, 94, 95, 97–100, 135, 189, 285, 456, 463, 514, 515, 612, 670 constraint, 5, 8 constraint_handler_t type, 493, 612, 634 consume operation, 16 content of structure/union/enumeration, 114 contiguity of allocated storage, 362 continue, 53, 155, 156, 456, 467, 612 contracted, 72 contracted expression, 72, 237, 513 control character, 19, 204 control wide character, 447 conversion, 44 686
N3096
Index
N3096
working draft — April 1, 2023
%X, 330, 405, 415 %Y, 405 %Z, 405 %[, 339, 421 %%, 333, 340, 417, 422 %a, 331, 338, 404, 416, 421 %b, 330, 404, 415 %c, 332, 338, 404, 417, 421 %d, 330, 338, 404, 415, 420 %e, 331, 338, 404, 416, 421 %f, 331, 338, 415, 421 %g, 331, 338, 405, 416, 421 %h, 405 %i, 330, 415 %j, 405 %m, 405 %n, 333, 340, 405, 417, 422 %o, 330, 338, 415, 421 %p, 333, 339, 405, 417, 422 %r, 405 %s, 332, 339, 417, 421 %t, 405 %u, 330, 338, 405, 415, 421 %w, 405 %x, 330, 338, 405, 415, 421 %y, 405 %z, 405
ISO/IEC 9899:2023 (E)
coshd128 function, 246, 481, 612 coshd32 function, 246, 481, 612 coshd64 function, 246, 481, 612 coshf function, 246, 476, 562, 612 coshl function, 246, 476, 612 cosl function, 242, 475, 612 cospi function, 244, 476, 511, 520, 612 cospi type-generic macro, 384 cospid function, 562, 612 cospid128 function, 244, 481, 612 cospid32 function, 244, 481, 612 cospid64 function, 244, 481, 612 cospif function, 244, 476, 562, 612 cospil function, 244, 476, 612 cpow function, 200, 201, 384, 472, 545, 612 cpow functions
type-generic macro for, 384 cpowf function, 200, 472, 557, 612 cpowl function, 200, 386, 472, 612 cpown function, 453, 612 cpowr function, 453, 612 cproj function, 202, 472, 540, 576, 612 cproj functions, 540 cproj type-generic macro, 384 cprojf function, 202, 386, 472, 557, 612 cprojl function, 202, 386, 472, 612 cr_ identifier prefix, 454 CR_DECIMAL_DIG macro, 24, 474, 512, 604
conversion state, 369, 407–411, 442, 443–445, 638, 663–666 conversion state functions, 442 copying functions string, 374, 641 wide string, 434, 658 copysign function, iv, 202, 265, 266, 479, 509, 524, 529, 530, 538, 539, 612 copysign type-generic macro, 384 copysignd function, 567, 612 copysignd128 function, 266, 484, 612 copysignd32 function, 266, 484, 612 copysignd64 function, 266, 484, 612 copysignf function, 266, 479, 567, 612 copysignl function, 266, 386, 479, 612 correctly rounded result, 5 corresponding real type, 39 corresponding unsigned integer type, 38 cos function, 134, 242, 384, 475, 511, 519, 546, 579, 612 cos type-generic macro, 384, 546 cosd function, 561, 612 cosd128 function, 242, 480, 612 cosd32 function, 242, 480, 612 cosd64 function, 242, 480, 612 cosf function, 242, 475, 561, 612 cosh function, 246, 384, 476, 512, 521, 546, 612 cosh type-generic macro, 384, 546 coshd function, 562, 612
creal function, 201, 202, 203, 386, 472, 538,
540, 546, 576, 612 creal functions, 540 creal type-generic macro, 384, 546 crealf function, 203, 472, 557, 612 creall function, 203, 472, 612
creating, 322 critical undefined behavior, 667 crootn function, 453, 612 crsqrt function, 453, 612 csin function, 197, 198, 384, 471, 540, 612 csin functions, 540 type-generic macro for, 384 csinf function, 197, 471, 556, 612 csinh function, 199, 384, 471, 540, 543, 612 csinh functions type-generic macro for, 384 csinhf function, 199, 471, 556, 612 csinhl function, 199, 471, 612 csinl function, 197, 471, 612 csinpi function, 453, 612 csqrt function, 201, 384, 386, 472, 540, 545, 612 csqrt functions type-generic macro for, 384 csqrtf function, 201, 472, 557, 612 csqrtl function, 201, 472, 612 ctan function, 198, 384, 471, 540, 612 Index
687
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
d64fmad128 function, 275, 387, 485, 612 d64mul macro, 32, 214, 385, 612 d64mul type-generic macro, 385 d64muld128 function, 274, 485, 612 d64sqrt macro, 32, 214, 385, 612 d64sqrt type-generic macro, 385 d64sqrtd128 function, 275, 485, 612 d64sub macro, 32, 214, 385, 612 d64sub type-generic macro, 385 d64subd128 function, 274, 485, 612 dadd macro, 385, 577, 612 dadd type-generic macro, 385 daddl function, 273, 386, 480, 508, 612
ctan functions, 540
type-generic macro for, 384 ctanf function, 198, 471, 556, 612 ctanh function, 199, 384, 471, 540, 544, 612 ctanh functions type-generic macro for, 384 ctanhf function, 199, 471, 556, 612 ctanhl function, 199, 471, 612 ctanl function, 198, 471, 612 ctanpi function, 453, 612 ctgamma function, 453, 612 ctime function, 402, 403, 496, 612 ctime_s function, 496, 612, 648, 649 currency_symbol structure member, 227, 229, 231, 612 current object, 136 CX_LIMITED_RANGE pragma, xii, 185, 186, 196, 469, 471, 537, 589, 612
data race, 18, 193, 361, 362, 366, 381, 382, 402, 407, 443, 445, 636 date and time header, 388, 398, 455, 647 Daylight Saving Time, 398 DBL_ identifier prefix, 453, 602 DBL_DECIMAL_DIG macro, 26, 28, 473, 504, 604 DBL_DIG macro, 26, 29, 473, 504, 604 DBL_EPSILON macro, 27, 28, 473, 504, 604 DBL_HAS_SUBNORM macro, 25, 29, 453, 473, 604 DBL_IS_IEC_60559 macro, 24, 28, 473, 604 DBL_MANT_DIG macro, 26, 28, 100, 473, 504, 604 DBL_MAX macro, 27, 29, 473, 504, 604 DBL_MAX_10_EXP macro, 27, 29, 473, 504, 604 DBL_MAX_EXP macro, 27, 29, 473, 504, 604 DBL_MIN macro, 27, 29, 473, 504, 604 DBL_MIN_10_EXP macro, 26, 27, 29, 473, 504, 604 DBL_MIN_EXP macro, 26, 29, 473, 504, 604 DBL_NORM_MAX macro, ii, 27, 473, 504, 604 DBL_SNAN macro, 25, 473, 507, 604 DBL_TRUE_MIN macro, 27, 29, 473, 604 DD format modifier, 330, 338, 415, 420 ddiv macro, 385, 577, 579, 612 ddiv type-generic macro, 385 ddivl function, 274, 480, 508, 511, 579, 612 DEC identifier prefix, 474, 550, 551, 552, 612 DEC128_ identifier prefix, 29, 453, 602 DEC128_EPSILON macro, 30, 505, 604 DEC128_MANT_DIG macro, 30, 505, 604 DEC128_MAX macro, 30, 505, 604 DEC128_MAX_EXP macro, 30, 505, 604 DEC128_MIN macro, 30, 505, 604 DEC128_MIN_EXP macro, 30, 505, 604 DEC128_SNAN macro, 29, 604 DEC128_TRUE_MIN macro, 30, 505, 604 DEC32_ identifier prefix, 29, 453, 602 DEC32_EPSILON macro, 30, 504, 604 DEC32_MANT_DIG macro, 30, 504, 604 DEC32_MAX macro, 30, 505, 604 DEC32_MAX_EXP macro, 30, 505, 604 DEC32_MIN macro, 30, 505, 604 DEC32_MIN_EXP macro, 30, 505, 604 DEC32_SNAN macro, 29, 604
D format modifier, 330, 338, 415, 420 d identifier prefix, 384, 385
d-wchar sequence, 358, 432 d128 identifier prefix, 385 d32 identifier prefix, 385 d32add macro, 32, 214, 385, 612 d32add type-generic macro, 385 d32addd128 function, 273, 484, 612 d32addd64 function, 273, 484, 612 d32div macro, 32, 214, 385, 612 d32div type-generic macro, 385 d32divd128 function, 274, 485, 612 d32divd64 function, 274, 386, 485, 612 d32fma macro, 32, 214, 385, 612 d32fma type-generic macro, 385 d32fmad128 function, 275, 485, 612 d32fmad64 function, 275, 485, 612 d32mul macro, 32, 214, 385, 612 d32mul type-generic macro, 385 d32muld128 function, 274, 485, 612 d32muld64 function, 274, 485, 612 d32sqrt macro, 32, 214, 385, 612 d32sqrt type-generic macro, 385 d32sqrtd128 function, 275, 485, 612 d32sqrtd64 function, 275, 485, 612 d32sub macro, 32, 214, 385, 612 d32sub type-generic macro, 385 d32subd128 function, 274, 386, 485, 612 d32subd64 function, 274, 485, 612 d64 identifier prefix, 383, 385 d64add macro, 32, 214, 385, 612 d64add type-generic macro, 385 d64addd128 function, 273, 387, 484, 612 d64div macro, 32, 214, 385, 612 d64div type-generic macro, 385 d64divd128 function, 274, 485, 612 d64fma macro, 32, 214, 385, 612 d64fma type-generic macro, 385
688
N3096
Index
N3096
working draft — April 1, 2023
DEC32_TRUE_MIN macro, 30, 505, 604 DEC64_ identifier prefix, 29, 453, 602 DEC64_EPSILON macro, 30, 505, 604 DEC64_MANT_DIG macro, 30, 505, 604 DEC64_MAX macro, 30, 505, 604 DEC64_MAX_EXP macro, 30, 505, 604 DEC64_MIN macro, 30, 505, 604 DEC64_MIN_EXP macro, 30, 505, 604 DEC64_SNAN macro, 29, 604 DEC64_TRUE_MIN macro, 30, 99, 505, 604 DEC_ identifier prefix, 453, 602 DEC_EVAL_METHOD macro, iii, 24, 29, 62, 94,
ISO/IEC 9899:2023 (E)
decodedecd64 function, 277, 383, 385, 485,
612 decodef function, 571, 612
default argument promotions, 75 default initialization, 135 default label, 152, 153 DEFAULT pragma, 612 define preprocessing directive, 177 defined operator, 166, 167, 173, 186, 588, 612 definition, 96 function, 158 dependency-ordered before, 16 deprecated attribute, ii, 97, 105, 141, 142, 144, 402, 403, 496, 612, 669, 670 derived declarator types, 40 derived types, 39 designated initializer, 136 destringizing, 188 device input/output, 13 dfma macro, 385, 577, 612 dfma type-generic macro, 385 dfmal function, 275, 386, 480, 508, 612 diagnostic message, 5, 11 diagnostics, 11 diagnostics header, 194 difftime function, 399, 495, 612 digit, 204 digits, 19 digraphs, 68 direct input/output functions, 349 display device, 19 div function, 134, 354, 369, 492, 577, 612 div_t type, 139, 354, 369, 492, 612 divd function, 569, 612 DIVD macro, 560 divf function, 569, 612 DIVF macro, 559, 560 divide and round to narrower type, 274 division assignment operator (/=), 92 division operator (/), 83, 537 dmul macro, 385, 577, 612 dmul type-generic macro, 385 dmull function, 274, 480, 508, 612 documentation of implementation, 9 domain error, 236, 241–246, 250–259, 261, 262, 265 dot operator (.), 75 double _Complex type, 38 double _Complex type conversion, 46, 47 double _Imaginary type, 536 double type, 38, 101 double type conversion, 46, 47 double-precision arithmetic, 14 double-quote escape sequence (\"), 64, 67, 188 double_t type, 233, 475, 515, 558, 559, 598, 601, 612
233, 504, 535, 549, 550, 558, 596, 598, 604 DEC_INFINITY macro, 29, 234, 276, 454, 474, 604 DEC_NAN macro, 29, 234, 454, 474, 604 decimal constant, 57 decimal digit, 19 decimal floating types, 38, 549 decimal re-encoding functions, 277 decimal rounding control pragma, 213 decimal-point character, 190, 229 decimal128 suffix, dl or DL, 61 decimal32 suffix, df or DF, 61 decimal64 suffix, dd or DD, 61 DECIMAL_DIG macro, i, 24, 26, 453, 473, 504, 604, 670 decimal_point structure member, 227, 229, 612 declaration specifier, 96 declaration specifiers, 96 declarations, 96 function, 128 pointer, 125 structure/union, 102 typedef, 131 declarator, 124 abstract, 130 declarator type derivation, 40, 125 DECN identifier prefix, 612 DECN_ identifier prefix, 612 decodebin family, 32, 278 decodebin function, 508, 612 decodebind family, 278, 279 decodebind function, 569, 612 decodebind128 function, 278, 485, 612 decodebind32 function, 278, 485, 612 decodebind64 function, 278, 383, 385, 485, 612 decodedec family, 32, 277 decodedec function, 508, 612 decodedecd family, 277, 278 decodedecd function, 569, 612 decodedecd128 function, 277, 485, 612 decodedecd32 function, 277, 485, 612 Index
689
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
dsqrt macro, 385, 577, 613 dsqrt type-generic macro, 385 dsqrtl function, 275, 480, 508, 613 dsub macro, 385, 577, 579, 613 dsub type-generic macro, 385 dsubl function, 273, 480, 508, 579, 613
encodedecd128 function, 277, 485, 613 encodedecd32 function, 277, 485, 613 encodedecd64 function, 277, 383, 385, 485,
613 encodef function, 570, 571, 613
encoding error, 323, 333, 336, 337, 342–346, 408–412, 418, 419, 423–428, 444–446, 639, 640, 664–666 encodings, 44 end-of-file, 412 end-of-file indicator, 319, 326, 346, 348, 349, 351, 352, 426, 429 end-of-line indicator, 19 endif preprocessing directive, 167 enum type, 39, 101, 107 enumerated type, 39 enumeration, 39, 107 enumeration constant, 34, 63 enumeration content, 114 enumeration member type, 108 enumeration members, 107 enumeration specifiers, 107 enumeration tag, 36, 114 enumerator, 107 environment, 10 environment functions, 364, 635 environment list, 366, 636 environmental considerations, 18 environmental limits, 20, 282, 322, 323, 325, 334, 361, 365, 418, 623 EOF macro, 204, 319, 325, 340, 341, 343–349, 412, 422–426, 428, 442, 490, 589, 604, 626, 627, 629–631, 633, 651, 653, 654, 656–658 EOL macro, 604 epoch, 401 equal-sign punctuator (=), 96, 107, 135 equality expressions, 86 equality operator (==), 87 ERANGE macro, 208, 224, 236, 237, 357, 359, 361, 432–434, 472, 598, 599, 604 erf function, 258, 478, 527, 613 erf type-generic macro, 384 erfc function, 259, 478, 527, 613 erfc type-generic macro, 384 erfcd function, 565, 613 erfcd128 function, 259, 483, 613 erfcd32 function, 259, 483, 613 erfcd64 function, 259, 483, 613 erfcf function, 259, 478, 565, 613 erfcl function, 259, 478, 613 erfd function, 565, 613 erfd128 function, 258, 483, 613 erfd32 function, 258, 482, 613 erfd64 function, 258, 483, 613 erff function, 258, 478, 565, 613
during, 147 dynamic floating-point environment, 209 E format modifier, 405 E identifier prefix, 208, 453, 602 EDOM macro, 208, 236, 472, 604
effective type, 71 effectless, 147 EILSEQ macro, 208, 323, 408–411, 427, 444–446, 472, 604 element type, 39 elif preprocessing directive, 166 elifdef preprocessing directive, 167 elifndef preprocessing directive, 167 ellipsis punctuator (...), 128, 178 else preprocessing directive, 167 else statement, 153 embed element width, 170 embed parameter, 170 __if_empty__ , 610 __prefix__ , 610 __suffix__ , 610 if_empty, 176 if_empty, 171, 176, 177, 615 limit, 164, 173 limit, 164, 168, 170, 171, 173, 174–177, 615 prefix, 175 prefix, 171, 175, 176, 616 suffix, 175 suffix, 171, 175, 176, 617 embed parameter sequence, 170 empty initialization, 135 empty initializer, 135 empty resource, 170 empty statement, 152 encbind function, 557, 571, 572, 613 encdecd function, 557, 571, 572, 613 encf function, 557, 571, 613 encodebin family, 32, 278 encodebin function, 508, 613 encodebind family, 278 encodebind function, 569, 613 encodebind128 function, 278, 485, 613 encodebind32 function, 278, 485, 613 encodebind64 function, 278, 383, 385, 485, 613 encodedec family, 32, 277 encodedec function, 508, 613 encodedecd family, 277 encodedecd function, 569, 613 690
N3096
Index
N3096
working draft — April 1, 2023
erfl function, 258, 478, 613 errno identifier, 147, 148, 192, 195, 208, 224,
ISO/IEC 9899:2023 (E)
exp2d function, 563, 613 exp2d128 function, 248, 481, 613 exp2d32 function, 248, 481, 613 exp2d64 function, 248, 481, 613 exp2f function, 248, 476, 563, 613 exp2l function, 248, 476, 613 exp2m1 function, 249, 476, 511, 522, 613 exp2m1 type-generic macro, 384 exp2m1d function, 563, 613 exp2m1d128 function, 249, 481, 613 exp2m1d32 function, 249, 481, 613 exp2m1d64 function, 249, 481, 613 exp2m1f function, 249, 476, 563, 613 exp2m1l function, 249, 476, 613 expd function, 562, 613 expd128 function, 247, 481, 613 expd32 function, 247, 481, 613 expd64 function, 247, 386, 481, 613 expf function, 247, 476, 562, 613 expl function, 247, 476, 613
236, 237, 285, 323, 350, 351, 353, 354, 357, 359, 361, 382, 408–411, 427, 432– 434, 444–446, 472, 589, 590, 598, 599, 602, 613, 620, 621, 647 errno_t type, 472, 491, 493, 494, 496, 498, 613, 620, 621, 622–624, 634, 635, 637–640, 641, 642–644, 646, 647, 648, 649, 650, 658–661, 663–665 error conditions, 236 error functions, 258, 527 error indicator, 319, 326, 347, 348, 350, 352, 353, 427 error preprocessing directive, 8, 185 error-handling functions, 352, 381, 646, 647 errors header, 208, 453 escape character (\), 64 escape sequences, 18, 20, 64, 189 escapes, 147 evaluation format, 25, 63, 233 evaluation method, 25, 72, 515 evaluation of expression, 13 exceptional condition, 71 excess precision, 25, 48, 157 excess range, 25, 48, 157 exclusive OR operators bitwise (^), 88 bitwise assignment (^=), 92 executable program, 10 execution character set, 18 execution environment, 10, 11 execution sequence, 12, 151 EXIT_FAILURE macro, 354, 366, 492, 604 EXIT_SUCCESS macro, 354, 366, 394, 492, 604 exp function, 247, 248, 249, 300, 384, 386, 476, 511, 522, 563, 564, 570, 613 exp type-generic macro, 384 exp10 function, 248, 476, 511, 522, 613 exp10 type-generic macro, 384 exp10d function, 562, 613 exp10d128 function, 248, 481, 613 exp10d32 function, 248, 481, 613 exp10d64 function, 248, 481, 613 exp10f function, 248, 476, 562, 613 exp10l function, 248, 476, 613 exp10m1 function, 248, 476, 511, 522, 613 exp10m1 type-generic macro, 384 exp10m1d function, 563, 613 exp10m1d128 function, 248, 481, 613 exp10m1d32 function, 248, 481, 613 exp10m1d64 function, 248, 481, 613 exp10m1f function, 248, 476, 563, 613 exp10m1l function, 248, 476, 613 exp2 function, 248, 249, 476, 511, 522, 613 exp2 type-generic macro, 384
explicit conversion, 44 expm1 function, 249, 476, 511, 522, 613 expm1 type-generic macro, 384 expm1d function, 563, 613 expm1d128 function, 249, 481, 613 expm1d32 function, 249, 481, 613 expm1d64 function, 249, 481, 613 expm1f function, 249, 476, 563, 613 expm1l function, 249, 476, 613 exponent part, 61 exponential functions complex, 199, 544 real, 247, 522 expression, 71, 116 assignment, 90 cast, 82 constant, 94 evaluation, 13 full, 151 parenthesized, 72 primary, 72 unary, 80 void, 49 expression statement, 152 extended alignment, 44 extended character set, 4, 18, 19 extended characters, 18 extended floating types, 548 extended integer types, 38, 45, 59, 315 extended multibyte and wide character utilities header, 412, 455 extended multibyte/wide character conversion utilities, 442, 663 extended signed integer types, 38 extended unsigned integer types, 38 Index
691
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
fe_dec_getround function, 211, 217, 218, 473,
extensible wide character case mapping functions, 451 extensible wide character classification functions, 450 extern storage-class specifier, 35, 36, 53, 82, 97, 98, 99, 111, 112, 118–121, 123, 127, 128, 131, 149, 150, 159–161, 175, 176, 193, 456, 463, 586, 601, 602, 613 external definition, 158 external identifiers, underscore, 191 external linkage, 35 external name, 55 external object definitions, 160
511, 557, 613 fe_dec_setround function, 211, 214, 219, 473,
511, 557, 613 FE_DEC_TONEAREST macro, 210, 211, 214, 473,
511, 604 FE_DEC_TONEAREST pragma, 186 FE_DEC_TONEARESTFROMZERO macro, 210, 214,
473, 511, 604 FE_DEC_TONEARESTFROMZERO pragma, 186 FE_DEC_TOWARDZERO macro, 210, 214, 473, 511,
604 FE_DEC_TOWARDZERO pragma, 186 FE_DEC_UPWARD macro, 210, 214, 473, 511, 604 FE_DEC_UPWARD pragma, 186 FE_DFL_ENV macro, 211, 473, 604 FE_DFL_MODE macro, 210, 218, 473, 509, 604 FE_DIVBYZERO macro, 210, 236, 473, 604 FE_DOWNWARD macro, 210, 473, 510, 604 FE_DOWNWARD pragma, 186 FE_DYNAMIC pragma, 186, 212, 213, 473, 604 FE_INEXACT macro, 210, 214, 473, 529, 604 FE_INVALID macro, 210, 217, 236, 473, 604 FE_OVERFLOW macro, 210, 214, 217, 236, 473,
f identifier suffix, 195, 233, 383–385, 453 fabs function, iv, 255, 256, 383, 384, 477, 509,
525, 529, 530, 538, 546, 613 fabs type-generic macro, 384, 546 fabsd function, 564, 613 fabsd128 function, 255, 482, 613 fabsd32 function, 255, 482, 613 fabsd64 function, 255, 482, 613 fabsf function, 255, 477, 564, 613 fabsl function, 255, 477, 613 fadd function, 273, 480, 508, 577, 613 fadd type-generic macro, 385 faddl function, 273, 480, 508, 613 fallthrough attribute, ii, 141, 145, 167, 613,
604 FE_SNANS_ALWAYS_SIGNAL macro, 507, 510,
528, 531, 604 FE_TONEAREST macro, 149, 210, 473, 510, 604 FE_TONEAREST pragma, 186 FE_TONEARESTFROMZERO macro, i, 210, 473,
669, 670 fallthrough declaration, 145 family canonicalize, 32, 268 decodebin, 32, 278 decodedec, 32, 277 encodebin, 32, 278 encodedec, 32, 277 modf, 32, 254, 383 strto, 32, 358 wcsto, 32, 432 fclose function, 173, 325, 490, 613 fdim function, 268, 269, 479, 531, 613 fdim type-generic macro, 384 fdimd function, 567, 613 fdimd128 function, 269, 484, 613 fdimd32 function, 269, 484, 613 fdimd64 function, 269, 484, 613 fdimf function, 269, 479, 567, 613 fdiml function, 269, 479, 613 fdiv function, 274, 386, 480, 508, 577, 613 fdiv type-generic macro, 385 fdivl function, 274, 480, 508, 613 FE_ identifier prefix, 210, 211, 453, 602 FE_ALL_EXCEPT macro, 92, 210, 473, 604 FE_DEC_DOWNWARD macro, 210, 214, 473, 511, 604 FE_DEC_DOWNWARD pragma, 186 FE_DEC_DYNAMIC pragma, 186, 214, 604 692
N3096
510, 604 FE_TONEARESTFROMZERO pragma, 186 FE_TOWARDZERO macro, 210, 473, 510, 524, 529,
604 FE_TOWARDZERO pragma, 186 FE_UNDERFLOW macro, 210, 220, 473, 604 FE_UPWARD macro, 8, 210, 473, 510, 528, 604 FE_UPWARD pragma, 186
feature test macro, 191, 209, 233, 315, 354, 383, 398 feclearexcept function, 92, 214, 215, 217, 220, 473, 509, 529, 613 fegetenv function, 219, 220, 473, 510, 589, 613 fegetexceptflag function, 214, 215, 216, 473, 509, 589, 597, 613 fegetmode function, 217, 218, 473, 509, 613 fegetround function, 210, 213, 217, 218, 473, 509, 510, 524, 528, 557, 613 feholdexcept function, 92, 219, 220, 473, 510, 528, 589, 613 femode_t type, 209, 210, 217, 218, 473, 613 fence, 16, 296 acquire, 296 release, 296 FENV_ACCESS pragma, xii, 8, 92, 185, 186, 211, 212, 217, 218, 220, 469, 473, 513–518, Index
N3096
working draft — April 1, 2023
524, 528, 530, 582, 589, 596, 613
ISO/IEC 9899:2023 (E)
fixed underlying type, 107 flags, 328, 413 flexible array member, 105 float _Complex type, 38 float _Complex type conversion, 46, 47 float _Imaginary type, 536 float type, 38, 101 float type conversion, 46, 47 float_t type, 233, 475, 515, 558, 559, 598, 601, 613 floating constant, 60 floating suffix, f or F, 61 floating type conversion, 46, 47, 512 floating types, 39, 189 floating-point accuracy, 24, 63, 72, 357, 512 floating-point arithmetic functions, 233, 518 floating-point classification functions, 237 floating-point control mode, 209, 515 floating-point environment, 209, 513, 515 dynamic, 209 floating-point environment header, 209, 453 floating-point exception, 209, 214, 518 floating-point number, 23, 38 floating-point rounding mode, 24 floating-point status flag, 209, 515 floor function, 234, 260, 478, 507, 528, 613 floor type-generic macro, 384 floord function, 565, 613 floord128 function, 260, 483, 613 floord32 function, 260, 483, 613 floord64 function, 260, 483, 613 floorf function, 260, 478, 565, 613 floorl function, 260, 478, 613 FLT identifier prefix, 550, 551, 552, 613 FLT_ identifier prefix, 453, 602 FLT_DECIMAL_DIG macro, 26, 28, 473, 504, 604 FLT_DIG macro, 26, 28, 473, 504, 604 FLT_EPSILON macro, 27, 28, 473, 504, 604 FLT_EVAL_METHOD macro, i, 24, 25, 29, 92, 94, 100, 233, 473, 504, 535, 549, 558, 559, 596, 598, 604 FLT_HAS_SUBNORM macro, 25, 28, 453, 473, 604 FLT_IS_IEC_60559 macro, 24, 28, 473, 604 FLT_MANT_DIG macro, 26, 28, 100, 473, 504, 604 FLT_MAX macro, 27, 28, 473, 504, 604 FLT_MAX_10_EXP macro, 27, 28, 473, 504, 604 FLT_MAX_EXP macro, 27, 28, 473, 504, 604 FLT_MIN macro, 27, 28, 473, 504, 604 FLT_MIN_10_EXP macro, 26, 27, 28, 473, 504, 604 FLT_MIN_EXP macro, 26, 28, 473, 504, 604 FLT_NORM_MAX macro, 27, 473, 504, 604 FLT_RADIX macro, 24, 26, 27, 28, 30, 61, 214, 219, 254, 331, 333, 357, 416, 418, 431, 473, 504, 509, 549–551, 558, 605 FLT_ROUNDS macro, 24, 210, 473, 503, 504, 506,
FENV_DEC_ROUND pragma, xii, 63, 185, 186,
213, 214, 469, 473, 511, 557, 613 FENV_ROUND pragma, xii, 149, 185, 186, 211,
212, 213, 214, 469, 473, 510, 557, 613 fenv_t type, 92, 209, 211, 219, 220, 473, 528,
613 feof function, 341, 347, 352, 427, 491, 613 feraiseexcept function, 214, 215, 473, 515,
582, 598, 613 ferror function, 341, 347, 353, 427, 491, 613 fesetenv function, 212, 220, 473, 510, 589, 613 fesetexcept function, 215, 216, 473, 509, 613 fesetexceptflag function, 214, 216, 473, 509,
589, 613 fesetmode function, 212, 217, 218, 473, 509,
613 fesetround function, 8, 24, 98, 210, 212, 213,
217, 218, 219, 473, 509, 510, 524, 528, 529, 557, 613 fetestexcept function, 214, 216, 217, 473, 509, 529, 613 fetestexceptflag function, 216, 473, 509, 613 feupdateenv function, 92, 212, 219, 220, 473, 510, 529, 589, 613 fexcept_t type, 209, 215, 216, 473, 589, 613 fflush function, 325, 326, 490, 591, 613 ffma function, 275, 480, 508, 577, 613 ffma type-generic macro, 385 ffmal function, 275, 480, 508, 613 fgetc function, 320, 323, 346, 347–349, 490, 613 fgetpos function, 321, 322, 350, 351, 491, 582, 592, 599, 613 fgets function, 320, 347, 491, 592, 613, 633 fgetwc function, ii, 320, 323, 426, 427, 428, 497, 613 fgetws function, 320, 427, 497, 592, 613 field width, 328, 413 file, 322 access functions, 325, 623 name, 322 operations, 323, 622 position indicator, 319, 321, 322, 326, 346, 347, 349–352, 426, 427, 429 positioning functions, 350 file name, 322 file position indicator, 322 file scope, 34, 158 FILE type, 173, 319, 320, 322, 324, 325, 327, 328, 336, 344, 346–353, 413, 419, 424, 426–429, 490, 491, 497, 498, 591, 613, 622–625, 629, 630, 650, 651, 653, 654 FILENAME_MAX macro, 319, 490, 604 finite number, 536 Index
693
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
596, 605
fmaximumd32 function, 270, 484, 613 fmaximumd64 function, 270, 484, 614 fmaximumf function, 270, 479, 567, 614 fmaximuml function, 270, 479, 614 fmaxl function, 269, 479, 614 fmin function, iv, vii, 269, 270, 479, 510, 531,
FLT_SNAN macro, 25, 473, 507, 605 FLT_TRUE_MIN macro, 27, 28, 473, 605 FLTN identifier prefix, 613 FLTN_ identifier prefix, 613 fma function, 235, 273, 479, 508, 532, 577, 614 fma type-generic macro, 384 fmad function, 568, 569, 613 FMAD macro, 560 fmad128 function, 273, 484, 613 fmad32 function, 273, 484, 613 fmad64 function, 273, 484, 613 fmaf function, 273, 479, 568, 569, 613 FMAF macro, 560 fmal function, 235, 273, 480, 613 fmax function, iv, vii, 269, 270, 479, 510, 531,
614 fmin type-generic macro, 384 fmind function, 614 fmind128 function, 269, 484, 614 fmind32 function, 269, 484, 614 fmind64 function, 269, 484, 614 fminf function, 269, 479, 614 fminimum function, 270, 271, 272, 479, 508, 531,
614 fminimum type-generic macro, 384 fminimum_mag type-generic macro, 384 fminimum_mag_num type-generic macro, 384 fminimum_num type-generic macro, 384 fminimum_mag function, 271, 272, 479, 508,
614 fmax type-generic macro, 384 fmaxd function, 613 fmaxd128 function, 269, 484, 613 fmaxd32 function, 269, 484, 613 fmaxd64 function, 269, 484, 613 fmaxf function, 269, 479, 613 fmaximum function, 270, 271, 479, 508, 531, 614 fmaximum type-generic macro, 384 fmaximum_mag type-generic macro, 384 fmaximum_mag_num type-generic macro, 384 fmaximum_num type-generic macro, 384 fmaximum_mag function, 270, 271, 272, 479,
531, 614 fminimum_mag_num function, 271, 272, 479,
508, 531, 532, 614 fminimum_mag_numd function, 568, 614 fminimum_mag_numd128 function, 272, 484,
614 fminimum_mag_numd32 function, 272, 484, 614 fminimum_mag_numd64 function, 272, 484, 614 fminimum_mag_numf function, 272, 479, 568,
614
508, 531, 614
fminimum_mag_numl function, 272, 479, 614 fminimum_magd function, 568, 614 fminimum_magd128 function, 271, 484, 614 fminimum_magd32 function, 271, 484, 614 fminimum_magd64 function, 271, 484, 614 fminimum_magf function, 271, 479, 568, 614 fminimum_magl function, 271, 479, 614 fminimum_num function, 270, 271, 272, 479,
fmaximum_mag_num function, 271, 272, 479,
508, 531, 532, 614 fmaximum_mag_numd function, 568, 614 fmaximum_mag_numd128 function, 272, 484,
614 fmaximum_mag_numd32 function, 272, 484, 614 fmaximum_mag_numd64 function, 272, 484, 614 fmaximum_mag_numf function, 272, 479, 568,
508, 510, 531, 532, 614
614
fminimum_numd function, 568, 614 fminimum_numd128 function, 272, 484, 614 fminimum_numd32 function, 272, 484, 614 fminimum_numd64 function, 272, 484, 614 fminimum_numf function, 271, 479, 568, 614 fminimum_numl function, 272, 479, 614 fminimumd function, 568, 614 fminimumd128 function, 270, 484, 614 fminimumd32 function, 270, 484, 614 fminimumd64 function, 270, 484, 614 fminimumf function, 270, 479, 567, 614 fminimuml function, 270, 479, 614 fminl function, 269, 479, 614 fmod function, 264, 265, 478, 529, 530, 598, 614 fmod type-generic macro, 384 fmodd function, 567, 614 fmodd128 function, 264, 483, 614
fmaximum_mag_numl function, 272, 479, 614 fmaximum_magd function, 568, 614 fmaximum_magd128 function, 270, 484, 614 fmaximum_magd32 function, 270, 484, 614 fmaximum_magd64 function, 270, 484, 614 fmaximum_magf function, 270, 479, 568, 614 fmaximum_magl function, 270, 479, 614 fmaximum_num function, 270, 271, 479, 508,
510, 531, 532, 538, 614 fmaximum_numd function, 568, 614 fmaximum_numd128 function, 271, 484, 614 fmaximum_numd32 function, 271, 484, 614 fmaximum_numd64 function, 271, 484, 614 fmaximum_numf function, 271, 479, 568, 614 fmaximum_numl function, 271, 479, 614 fmaximumd function, 567, 614 fmaximumd128 function, 270, 386, 484, 613
694
N3096
Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
FP_FAST_D32SUBD64 macro, 235, 605 FP_FAST_D64ADDD128 macro, 235, 605 FP_FAST_D64DIVD128 macro, 235, 605 FP_FAST_D64FMAD128 macro, 235, 605 FP_FAST_D64MULD128 macro, 235, 605 FP_FAST_D64SQRTD128 macro, 235, 605 FP_FAST_D64SUBD128 macro, 235, 605 FP_FAST_DADDL macro, 235, 559, 605 FP_FAST_DDIVL macro, 235, 605 FP_FAST_DFMAL macro, 235, 605 FP_FAST_DMULL macro, 235, 605 FP_FAST_DSQRTL macro, 235, 605 FP_FAST_DSUBL macro, 235, 605 FP_FAST_F macro, 559, 560, 605 FP_FAST_FADD macro, 235, 559, 605 FP_FAST_FADDL macro, 235, 559, 605 FP_FAST_FDIV macro, 235, 605 FP_FAST_FDIVL macro, 235, 605 FP_FAST_FFMA macro, 235, 605 FP_FAST_FFMAL macro, 235, 605 FP_FAST_FMA macro, 235, 475, 559, 605 FP_FAST_FMAD macro, 559, 605 FP_FAST_FMAD128 macro, 235, 605 FP_FAST_FMAD32 macro, 235, 605 FP_FAST_FMAD64 macro, 235, 605 FP_FAST_FMAF macro, 235, 475, 559, 605 FP_FAST_FMAL macro, 235, 475, 605 FP_FAST_FMUL macro, 235, 605 FP_FAST_FMULL macro, 235, 605 FP_FAST_FSQRT macro, 235, 605 FP_FAST_FSQRTL macro, 235, 605 FP_FAST_FSUB macro, 235, 605 FP_FAST_FSUBL macro, 235, 605 FP_ILOGB0 macro, 235, 236, 250, 475, 605 FP_ILOGBNAN macro, 235, 236, 250, 475, 605 FP_INFINITE macro, 234, 475, 605 FP_INT_DOWNWARD macro, 234, 605 FP_INT_TONEAREST macro, 234, 605 FP_INT_TONEARESTFROMZERO macro, 234, 605 FP_INT_TOWARDZERO macro, 234, 605 FP_INT_UPWARD macro, 234, 264, 605 FP_LLOGB0 macro, 236, 251, 605 FP_LLOGBNAN macro, 236, 251, 605 FP_NAN macro, 234, 475, 605 FP_NORMAL macro, 234, 475, 605 FP_SUBNORMAL macro, 234, 475, 605 FP_ZERO macro, 234, 475, 605
fmodd32 function, 264, 483, 614 fmodd64 function, 264, 483, 614 fmodf function, 264, 478, 567, 614 fmodl function, 264, 478, 614 fmul function, 274, 480, 508, 577, 579, 614 fmul type-generic macro, 385 fmull function, 274, 480, 508, 614 fopen function, 173, 323, 324, 325, 326, 327,
490, 591, 602, 614, 623 FOPEN_MAX macro, 319, 323, 324, 490, 605, 622 fopen_s function, 491, 614, 622, 623, 624
form feed, 20 form-feed character, 19, 51 form-feed escape sequence (\f), 20, 65, 206 format conversion of integer types header, 453 format flag +, 329, 413 -, 329, 413 #, 329, 414 0, 329, 414 space, 329, 414 format modifier D, 330, 338, 415, 420 DD, 330, 338, 415, 420 E, 405 H, 330, 338, 415, 420 h, 329, 337, 414, 420 hh, 329, 337, 414, 420 j, 330, 337, 414, 420 L, 330, 338, 415, 420 l, 329, 337, 414, 420 ll, 329, 337, 414, 420 O, 405 t, 330, 337, 414, 420 wfN, 330, 338, 415, 420 wN, 330, 337, 414, 420 z, 330, 337, 414, 420 formatted input/output functions, 228, 328, 625 wide character, 413, 650 forward reference, 5 FP_ identifier prefix, 234, 453, 602 FP_CONTRACT pragma, xii, 72, 149, 185, 186, 237, 469, 475, 538, 589, 596, 605 FP_FAST_D macro, 560, 605 FP_FAST_D32ADDD128 macro, 235, 605 FP_FAST_D32ADDD64 macro, 235, 605 FP_FAST_D32DIVD128 macro, 235, 605 FP_FAST_D32DIVD64 macro, 235, 605 FP_FAST_D32FMAD128 macro, 235, 605 FP_FAST_D32FMAD64 macro, 235, 605 FP_FAST_D32MULD128 macro, 235, 605 FP_FAST_D32MULD64 macro, 235, 605 FP_FAST_D32SQRTD128 macro, 235, 605 FP_FAST_D32SQRTD64 macro, 235, 605 FP_FAST_D32SUBD128 macro, 235, 605
fpclassify macro, 238, 475, 509, 510, 614 fpos_t type, 319, 321, 350, 351, 490, 491, 614 fprintf_s function, 491, 614, 625 fputc function, 19, 20, 320, 323, 347, 348, 350,
491, 614 fputs function, 183, 320, 347, 491, 614 fputwc function, 320, 323, 427, 429, 497, 614 fputws function, 320, 427, 428, 497, 614
Index
695
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
frac_digits structure member, 227, 229, 231,
fsqrt function, 275, 480, 508, 577, 614 fsqrt type-generic macro, 385 fsqrtl function, 275, 480, 508, 614 fsub function, 273, 480, 508, 577, 579, 614 fsub type-generic macro, 385 fsubl function, 273, 386, 480, 508, 579, 614 ftell function, 351, 491, 582, 592, 599, 614
614 fread function, 171, 173, 320, 349, 350, 491, 592, 614 free function, 363, 364, 376, 492, 592, 614, 668 free_aligned_sized function, 363, 364, 492, 614 free_sized function, 363, 492, 614 freestanding execution environment, 8, 11 freopen function, 321, 322, 326, 327, 490, 614 freopen_s function, 491, 614, 624, 625 frexp function, 249, 250, 476, 522, 570, 582, 583, 614 frexp type-generic macro, 384 frexpd function, 563, 614 frexpd128 function, 249, 481, 614 frexpd32 function, 249, 481, 614 frexpd64 function, 249, 481, 614 frexpf function, 249, 476, 563, 614 frexpl function, 249, 476, 614 fromfp function, 234, 263, 264, 478, 508, 512, 529, 614 frompfp functions, 263 fromfp type-generic macro, 384 fromfpd function, 566, 614 fromfpd128 function, 263, 483, 614 fromfpd32 function, 263, 483, 614 fromfpd64 function, 263, 483, 614 fromfpf function, 263, 478, 566, 614 fromfpl function, 263, 478, 614 fromfpx function, 234, 264, 478, 508, 512, 529, 614 frompfpx functions, 264 fromfpx type-generic macro, 384 fromfpxd function, 566, 614 fromfpxd128 function, 264, 483, 614 fromfpxd32 function, 264, 483, 614 fromfpxd64 function, 264, 483, 614 fromfpxf function, 264, 478, 566, 614 fromfpxl function, 264, 478, 614 frompfp function, 614 frompfpd function, 614 frompfpf function, 614 frompfpl function, 614 frompfpx function, 614 frompfpxd function, 614 frompfpxf function, 614 frompfpxl function, 614 fscanf function, 222, 320, 336, 340–344, 454, 491, 599, 614, 625 fscanf_s function, 491, 614, 625, 626, 627, 629, 630 fseek function, 320, 323, 326, 349, 350, 351, 352, 429, 491, 592, 614 fsetpos function, 321, 322, 326, 349, 350, 351, 429, 491, 592, 599, 614 696
N3096
full declarator, 125 full expression, 151 fully buffered, 322 fully buffered stream, 322 function argument, 74, 159 body, 158 call, 74 library, 192 declarator, 128 definition, 128, 158 designator, 49 image, 20 inline, 122 library, 10, 192 name length, 21, 55, 189 no-return, 123 parameter, 12, 74, 97, 159 prototype, 12, 34, 128, 159, 233 prototype scope, 34, 126, 127 recursive call, 75 return, 157, 513 scope, 34 type, 39 type conversion, 49 function prototype, 34 function prototype scope, 34 function scope, 34 function specifiers, 122 function type, 37 function type attributes, 146 function-call operator (()), 74 function-like macro, 178 fundamental alignment, 43 Fused multiply-add and round to narrower type, 275 future directions language, 189 library, 453 fwide function, 321, 322, 428, 497, 614 fwprintf function, 222, 320, 413, 418, 422–424, 426, 455, 497, 594, 599, 614, 651 fwprintf_s function, 498, 614, 650, 651 fwrite function, 320, 350, 491, 592, 614 fwscanf function, 222, 320, 418, 419, 422–424, 426, 429, 455, 497, 599, 614, 651 fwscanf_s function, 498, 614, 651, 653, 654, 657 gamma functions, 258, 527 Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
HUGE_VAL macro, 233, 237, 357, 432, 475, 518,
general utilities, 634 wide string, 429, 658 general utilities header, 354, 454 general wide string utilities, 429, 658 generic association, 73 generic parameters, 383 generic selection, 72 generic_count_type type, 614 generic_return_type type, 303–308, 488, 489, 614 generic_value_type type, 303–309, 488, 489, 614 getc function, 320, 347, 348, 491, 614 getchar function, 15, 320, 348, 491, 614 getenv function, 366, 492, 592, 595, 614 getenv_s function, 493, 614, 635, 636 getpayload function, 486, 507, 533, 534, 614 getpayloadd function, 570, 614 getpayloadd128 function, 486, 533, 614 getpayloadd32 function, 486, 533, 614 getpayloadd64 function, 486, 533, 614 getpayloadf function, 486, 533, 570, 614 getpayloadl function, 486, 533, 614 gets (obsolete), 614, 633, 672 gets_s function, 491, 614, 633 getwc function, 320, 428, 497, 614 getwchar function, 320, 428, 497, 614 gmtime function, 402, 403, 404, 496, 614 gmtime_r function, 403, 496, 614, 670 gmtime_s function, 496, 614, 649, 650 goto statement, 34, 152 graphic characters, 19 greater-than operator (>), 86 greater-than-or-equal-to operator (>=), 86 grouping structure member, 227, 229, 230, 614
614 HUGE_VAL_D macro, 559, 614 HUGE_VAL_D128 macro, 234, 486, 614 HUGE_VAL_D32 macro, 233, 234, 486, 614 HUGE_VAL_D64 macro, 234, 486, 614 HUGE_VAL_F macro, 559, 614 HUGE_VALF macro, 233, 237, 357, 432, 475, 518,
614 HUGE_VALL macro, 233, 237, 357, 432, 475, 518,
614 hyperbolic functions complex, 198, 541 real, 245, 521 hypot function, iv, 256, 477, 507, 511, 525, 540, 615 hypot type-generic macro, 384 hypotd function, 564, 615 hypotd128 function, 256, 482, 614 hypotd32 function, 256, 482, 614 hypotd64 function, 256, 482, 615 hypotf function, 256, 477, 564, 615 hypotl function, 256, 477, 615 I macro, 202, 540 I macro, 615
idempotent, 147 identifier, 53, 72 continue, 53, 501 maximum length, 54 name spaces, 36 reserved, 53, 191, 602, 610, 620 rules, 602 scope, 34 start, 53, 501 type, 37 identifier continue, 53, 501 identifier list, 163 identifier start, 53, 501 IEC 60559, 13, 23, 209, 219, 237, 279 IEC 60559, 2, 23, 187, 196, 265, 506, 536, 547 if preprocessing directive, 166 if_empty embed parameter, 171, 176, 177, 615 ifdef, 8, 162, 165–167, 214, 217, 219, 240–267, 268, 269–273, 274, 275–278, 356, 358, 386, 432, 468, 504, 532–534, 615 ifdef preprocessing directive, 167 ifndef preprocessing directive, 167 ignore_handler_s function, 493, 615, 635 ilogb function, 235, 250, 476, 508, 523, 582, 615 ilogb type-generic macro, 384 ilogbd function, 563, 615 ilogbd128 function, 250, 481, 615 ilogbd32 function, 250, 481, 615 ilogbd64 function, 250, 481, 615 ilogbf function, 250, 476, 563, 615
H format modifier, 330, 338, 415, 420 h format modifier, 329, 337, 414, 420
happens before, 17 header, 10, 190 header names, 51, 69, 169 hexadecimal constant, 57 hexadecimal digit, 58, 61, 65 hexadecimal digit sequence, 58 \xhexadecimal digits (hexadecimal-character escape sequence), 64 hexadecimal prefix, 57 hexadecimal-character escape sequence (\x hexadecimal digits), 64 hh format modifier, 329, 337, 414, 420 hidden, 35 high-order bit, 4 horizontal tab, 20 horizontal-tab character, 19, 51 horizontal-tab escape sequence (\t), 20, 65, 204, 206, 448 hosted execution environment, 8, 11 Index
697
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
ilogbl function, 250, 476, 615 imaginary macro, 195, 471, 539, 540, 615
int type, 37, 46, 59, 101 int type conversion, 45–47 intN_t types, 315 INTN_C macros, 318 INTN_MAX macros, 317 INTN_MIN macros, 317, 318 INT16_C macro, 605 INT16_MAX macro, 605 INT16_MIN macro, 605 int16_t type, 605 INT16_WIDTH macro, 605 INT32_C macro, 605 INT32_MAX macro, 605 INT32_MIN macro, 605 int32_t type, 605 INT32_WIDTH macro, 605 INT64_C macro, 605 INT64_MAX macro, 605 INT64_MIN macro, 605 int64_t type, 605 INT64_WIDTH macro, 605 INT8_C macro, 605 INT8_MAX macro, 605 INT8_MIN macro, 605 int8_t type, 315, 605 INT8_WIDTH macro, 605 INT_FAST identifier prefix, 317, 490 int_fast identifier prefix, 316, 490 INT_LEAST identifier prefix, 317, 490 int_least identifier prefix, 315, 318, 490 int_curr_symbol structure member, 227, 230,
imaginary numbers, 536 imaginary type domain, 536 imaginary types, 536 imaxabs function, 223, 474, 615 imaxdiv function, 222, 223, 474, 615 imaxdiv_t type, 222, 223, 474, 615 implementation, 5 implementation limit, 5, 8, 21, 55, 125, 154, 503 implementation resource width, 170 implementation-defined behavior, 3, 8, 594 implementation-defined value, 6 implicit conversion, 44 implicit initialization, 135 include preprocessing directive, 10, 169 inclusive OR operators bitwise (|), 88 bitwise assignment (|=), 92 incomplete, 37 incomplete type, 37 independent, 147 indeterminate representation, 6 indeterminately sequenced, 13, 75, 77, 92 indirection operator (*), 74, 81 inequality operator (!=), 87 infinitary, 236 infinity, 536 INFINITY macro, 25, 202, 234, 331, 356–359, 415, 430–433, 454, 473, 475, 507, 538, 539, 615 initial position, 20 initial shift state, 19 initialization, 11, 36, 48, 78, 134, 514 in blocks, 151 initialized, 11 initializer, 135 permitted form, 94 string literal, 48 inline, 122 inline definition, 123 inline function, 122 inner scope, 35 input failure, 424–426, 626, 627, 629–631, 633, 651, 653, 654, 656–658 input/output functions character, 346, 633 direct, 349 formatted, 328, 625 wide character, 413, 650 wide character, 426 formatted, 413, 650 input/output header, 319, 454, 621 input/output, device, 13 INT identifier prefix, 317, 318, 454, 490, 602 int identifier prefix, 315, 454, 490, 603 698
N3096
231, 615 INT_FASTN_MAX macros, 317 INT_FASTN_MIN macros, 317, 318 int_fast16_t type, 298, 316, 605 int_fast32_t type, 222, 298, 316, 605 int_fast64_t type, 298, 316, 605 int_fast8_t type, 298, 316, 605 int_fastN_t types, 316 int_frac_digits structure member, 227, 230,
231, 615 INT_LEASTN_MAX macros, 317 INT_LEASTN_MIN macros, 317, 318 int_leastN_t types, 315 int_least16_t type, 298, 316, 605 int_least32_t type, 298, 315, 316, 605 int_least64_t type, 298, 316, 605 int_least8_t type, 298, 316, 605 INT_MAX macro, 22, 38, 100, 166, 235, 236, 250,
474, 503, 591, 605 INT_MIN macro, 22, 38, 235, 236, 474, 503, 605 int_n_cs_precedes structure member, 227,
230, 231, 615 int_n_sep_by_space structure member, 227,
230, 231, 615 Index
N3096
working draft — April 1, 2023
int_n_sign_posn structure member, 227, 230,
ISO/IEC 9899:2023 (E)
islessgreater macro, 280, 480, 606 islower function, 4, 204, 205, 206, 207, 472,
231, 615 int_p_cs_precedes structure member, 227,
600, 606 isnan macro, 239, 475, 509, 510, 531, 538, 539,
230, 231, 615 int_p_sep_by_space structure member, 227,
606 isnormal macro, 239, 475, 509, 510, 606
230, 231, 615 int_p_sign_posn structure member, 227, 230, 231, 615 INT_WIDTH macro, 22, 264, 474, 503, 605 integer arithmetic functions, 223, 369 integer character constant, 64 integer constant, 57 integer constant expression, 49, 94, 103, 107, 126, 135, 140, 153, 165, 192 integer conversion rank, 44 integer promotions, 14, 45, 81, 85, 153, 329, 414 integer suffix, 59 integer type conversion, 44, 46, 512 integer types, 39, 315 extended, 38, 45, 59, 315 integer types header, 315, 454 inter-thread happens before, 17 interactive device, 13, 322, 326 interchange floating types, 548 internal linkage, 35 internal name, 55 interrupt, 20 INTMAX_C macro, 318, 490, 605 INTMAX_MAX macro, 224, 317, 490, 605 INTMAX_MIN macro, 224, 317, 318, 490, 605 intmax_t type, iii, 22, 166, 223, 224, 298, 316, 318, 330, 337, 414, 420, 474, 490, 605, 671, 673 INTMAX_WIDTH macro, 317, 490, 605 INTPTR_MAX macro, 317, 490, 605 INTPTR_MIN macro, 317, 318, 490, 605 intptr_t type, 298, 316, 490, 605 INTPTR_WIDTH macro, 317, 490, 605 is identifier prefix, 453–455, 603 isalnum function, 204, 205, 206, 472, 605 isalpha function, 204, 447, 472, 600, 605 isblank function, 204, 472, 600, 605 iscanonical macro, 24, 238, 475, 509, 510, 605 iscntrl function, 204, 205, 206, 472, 605 isdigit function, 204, 205, 206, 228, 472, 605 iseqsig macro, 280, 281, 480, 509, 535, 605 isfinite macro, 238, 475, 509, 510, 538, 539, 606 isgraph function, 205, 447, 472, 606 isgreater macro, 279, 480, 509, 606 isgreaterequal macro, 279, 480, 509, 517, 531, 606 isinf macro, 238, 239, 475, 509, 510, 524, 538, 539, 606 isless macro, 279, 280, 480, 509, 517, 606 islessequal macro, 280, 480, 509, 606
ISO/IEC 9945–2, 227 ISO/IEC 10646, 2, 56, 187 ISO/IEC 2382, 2, 3 ISO 4217, 2, 230 ISO 80000–2, 2, 3 ISO 80000–3, 2 ISO 8601, 2, 404 isprint function, 19, 20, 205, 472, 606 ispunct function, 204, 205, 206, 472, 600, 606 issignaling macro, 239, 240, 475, 509, 510, 606 isspace function, 190, 204, 205, 206, 472, 600, 606 issubnormal macro, 240, 475, 509, 510, 606 isunordered macro, 280, 480, 509, 606 isupper function, 204, 206, 207, 472, 600, 606 iswalnum function, 448, 449, 450, 499, 606 iswalpha function, 447, 448, 450, 499, 600, 606 iswblank function, 448, 450, 499, 600, 606 iswcntrl function, 448, 449, 450, 499, 606 iswctype function, 450, 451, 499, 594, 600, 606 iswdigit function, 448, 449, 450, 499, 606 iswgraph function, 447, 449, 450, 499, 606 iswlower function, 448, 449, 450, 451, 499, 600, 606 iswprint function, 447, 449, 450, 499, 606 iswpunct function, 447, 448, 449, 450, 499, 600, 606 iswspace function, 190, 447, 448, 449, 450, 499, 600, 606 iswupper function, 448, 449, 450, 451, 499, 600, 606 iswxdigit function, 450, 499, 606 isxdigit function, 206, 228, 472, 606 iszero macro, 240, 475, 509, 510, 606 italic type convention, 3, 34 iteration statements, 154 j format modifier, 330, 337, 414, 420 jmp_buf type, 282, 283, 486, 615, 668
jump statements, 155 keyword _Alignas , 53, 609 _Alignof operator, 53, 609 _BitInt , vi, 22, 38, 45, 48, 53, 59, 60, 101,
102, 456, 463, 609, 670 _Bool type, ii, 53, 609 _Complex types, 25, 38, 39, 47, 53, 101,
102, 195, 456, 463, 536–538, 549, 556, 609 Index
699
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
_Generic , 53, 72, 73, 110, 111, 119, 134,
639 LC_MONETARY macro, 227, 228, 231, 475, 606 LC_NUMERIC macro, 227, 228, 231, 475, 606 LC_TIME macro, 227, 228, 402, 404, 475, 606 lconv structure type, 227, 228, 475, 615 LDBL_ identifier prefix, 453, 602 LDBL_DECIMAL_DIG macro, 26, 453, 473, 504,
314, 385, 456, 460, 610 _Static_assert , 53, 610 _Thread_local storage-class specifier, 53, 610 auto storage-class specifier, 53, 97–99, 127, 128, 133, 134, 158, 456, 463, 611, 671 constexpr storage-class specifier, 35, 37, 53, 78, 94, 95, 97–100, 135, 189, 285, 456, 463, 514, 515, 612, 670 continue, 53, 155, 156, 456, 467, 612 defined operator, 166, 167, 173, 186, 588, 612 extern storage-class specifier, 35, 36, 53, 82, 97–99, 111, 112, 118–121, 123, 127, 128, 131, 149, 150, 159–161, 175, 176, 193, 456, 463, 586, 601, 602, 613 ifdef, 8, 162, 165–167, 214, 217, 219, 240– 267, 268, 269–273, 274, 275–278, 356, 358, 386, 432, 468, 504, 532–534, 615 pragma preprocessing directive, 51, 69, 92, 149, 162, 185, 188, 196, 211–214, 217, 218, 220, 237, 468, 469, 471, 473, 475, 514, 515, 524, 528, 530, 538, 580, 588, 597, 616 static_assert, 140 undef, 55, 162, 165, 182, 186, 192, 193, 468, 588, 618 keywords, 53, 536, 601 kill_dependency macro, 16, 295, 296, 487, 615 known constant size, 40
606 LDBL_DIG macro, 26, 473, 504, 606 LDBL_EPSILON macro, 27, 473, 504, 606 LDBL_HAS_SUBNORM macro, 25, 453, 473, 606 LDBL_IS_IEC_60559 macro, 24, 473, 606 LDBL_MANT_DIG macro, 26, 473, 504, 606 LDBL_MAX macro, 27, 473, 504, 606 LDBL_MAX_10_EXP macro, 27, 473, 504, 606 LDBL_MAX_EXP macro, 27, 473, 504, 606 LDBL_MIN macro, 27, 473, 504, 606 LDBL_MIN_10_EXP macro, 26, 27, 473, 504, 606 LDBL_MIN_EXP macro, 26, 473, 504, 606 LDBL_NORM_MAX macro, 27, 473, 504, 606 LDBL_SNAN macro, 25, 473, 507, 606 LDBL_TRUE_MIN macro, 27, 473, 606 ldexp function, 250, 251, 476, 523, 570, 615 ldexp type-generic macro, 384 ldexpd function, 563, 615 ldexpd128 function, 250, 481, 615 ldexpd32 function, 250, 481, 615 ldexpd64 function, 250, 481, 615 ldexpf function, 250, 476, 563, 615 ldexpl function, 250, 476, 615 ldiv function, 134, 354, 369, 492, 615 ldiv_t type, 354, 369, 492, 615
leading underscore in identifiers, 191 least significant index, 302 left-shift assignment operator (<<=), 92 left-shift operator (<<), 85 length external name, 21, 55, 189 function name, 21, 55, 189 identifier, 54 internal name, 21, 55 length function, 370, 382, 441, 443, 647, 663 length modifier, 328, 336, 413, 419 length of a string, 190 length of a wide string, 190 less-than operator (<), 86 less-than-or-equal-to operator (<=), 86 letter, 19, 204 lexical elements, 10, 51 lgamma function, 259, 478, 527, 615 lgamma type-generic macro, 384 lgammad function, 565, 615 lgammad128 function, 259, 483, 615 lgammad32 function, 259, 483, 615 lgammad64 function, 259, 483, 615 lgammaf function, 259, 478, 565, 615
L encoding prefix, 64, 65, 67, 459 L format modifier, 330, 338, 415, 420 l format modifier, 329, 337, 414, 420 l identifier suffix, 195, 233, 383, 385, 453 L_tmpnam macro, 320, 325, 490, 615 L_tmpnam_s macro, 491, 615, 621, 622
label name, 34, 36 labeled statement, 151 labs function, 369, 492, 615 language, 34 encoding prefix L, 64, 65, 67, 459 U, 64, 65, 67, 459 u, 64, 65, 67, 459 u8, 64, 65, 67, 459 future directions, 189 syntax summary, 456 Latin alphabet, 18 LC_ identifier prefix, 227, 453, 602 LC_ALL macro, 227, 228, 231, 475, 606 LC_COLLATE macro, 227, 228, 377, 436, 475, 606 LC_CTYPE macro, 227, 228, 354, 369–371, 442, 447, 450–452, 475, 593, 594, 606, 638, 700
N3096
Index
N3096
working draft — April 1, 2023
lgammal function, 259, 478, 615
ISO/IEC 9899:2023 (E)
acoshf, 245, 386, 476, 562, 611 acoshl, 245, 476, 611 acosl, 213, 240, 475, 557, 611 acospi, 243, 475, 512, 520, 611 acospid, 561, 611 acospid128, 243, 480, 611 acospid32, 243, 480, 611 acospid64, 243, 480, 611 acospif, 243, 475, 561, 611 acospil, 243, 475, 611 addd, 568, 611 addf, 568, 611 aligned_alloc, 362, 363, 364, 492, 583,
library, 10, 190, 619 constant memory_order_acq_rel, 294, 295, 296,
298, 299, 301, 487, 606 memory_order_acquire, 294, 296, 298,
301, 487, 606 memory_order_consume, 294, 296, 298,
487, 606 memory_order_relaxed, 148, 294, 295,
296, 487, 606 memory_order_release, 294, 296, 299,
487, 606 memory_order_seq_cst, 18, 41, 77, 91,
592, 599, 611, 672
92, 292, 294, 296, 487, 606 mtx_plain, 388, 392, 495, 606 mtx_recursive, 388, 392, 495, 606 mtx_timed, 389, 392, 495, 606 thrd_busy, 389, 393, 495, 608 thrd_error, 389, 390–397, 495, 608 thrd_nomem, 389, 390, 393, 495, 608 thrd_success, 389, 390–397, 495, 608 thrd_timedout, 389, 391, 392, 495, 608 family canonicalize, 32 decodebin, 32 decodebind, 278, 279 decodedec, 32 decodedecd, 277, 278 encodebin, 32 encodebind, 278 encodedec, 32 encodedecd, 277 modf, 32 strto, 8, 32, 63, 213, 214, 608 strtod, 358, 359 wcsto, 32, 213, 214, 609 wcstod, 432, 433 function _Exit , 285, 366, 367, 492, 590, 599, 609 abort, 146, 194, 284, 285, 293, 322, 364, 365, 492, 589, 590, 599, 610, 635 abort_handler_s, 493, 610, 635 abs, 192, 369, 492, 610 acos, 213, 240, 241, 384, 475, 512, 519, 557, 611 acosd, 557, 561, 610 acosd128, 214, 240, 480, 610 acosd32, 214, 240, 480, 610 acosd64, 214, 240, 480, 610 acosf, 213, 240, 475, 557, 561, 610 acosh, 245, 384, 476, 512, 521, 611 acoshd, 562, 610 acoshd128, 245, 481, 610 acoshd32, 245, 481, 610 acoshd64, 245, 481, 610
asctime, 186, 187, 402, 403, 496, 594,
611 asctime_s, 496, 611, 648, 649 asin, 241, 384, 475, 512, 519, 546, 611 asind, 561, 611 asind128, 241, 480, 611 asind32, 241, 480, 611 asind64, 241, 480, 611 asinf, 241, 475, 561, 611 asinh, 245, 246, 384, 476, 512, 521, 546,
611 asinhd, 562, 611 asinhd128, 246, 481, 611 asinhd32, 246, 481, 611 asinhd64, 246, 481, 611 asinhf, 246, 476, 562, 611 asinhl, 246, 476, 611 asinl, 241, 475, 611 asinpi, 243, 475, 512, 520, 611 asinpid, 561, 611 asinpid128, 243, 480, 611 asinpid32, 243, 480, 611 asinpid64, 243, 480, 611 asinpif, 243, 475, 561, 611 asinpil, 243, 475, 611 at_quick_exit, 365, 366, 367, 492, 583,
592, 611, 672 atan, 241, 334, 384, 418, 475, 512, 519,
546, 611 atan2, 241, 242, 475, 512, 518, 519, 540,
611 atan2d, 561, 611 atan2d128, 241, 480, 611 atan2d32, 241, 480, 611 atan2d64, 241, 480, 611 atan2f, 241, 475, 561, 611 atan2l, 241, 475, 611 atan2pi, 244, 475, 512, 518, 520, 611 atan2pid, 562, 611 atan2pid128, 244, 481, 611 atan2pid32, 244, 480, 611 atan2pid64, 244, 480, 611
Index
701
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
atomic_flag_test_and_set_explicit,
atan2pif, 244, 476, 561, 611 atan2pil, 244, 476, 611 atand, 561, 611 atand128, 241, 480, 611 atand32, 241, 480, 611 atand64, 241, 480, 611 atanf, 241, 475, 561, 611 atanh, 246, 384, 476, 512, 521, 546, 611 atanhd, 562, 611 atanhd128, 246, 481, 611 atanhd32, 246, 481, 611 atanhd64, 246, 481, 611 atanhf, 246, 476, 562, 611 atanhl, 246, 476, 611 atanl, 241, 386, 475, 611 atanpi, 243, 244, 475, 512, 520, 611 atanpid, 561, 611 atanpid128, 244, 480, 611 atanpid32, 243, 480, 611 atanpid64, 243, 480, 611 atanpif, 243, 475, 561, 611 atanpil, 243, 475, 611 atexit, 365, 366, 367, 492, 583, 592, 602,
301, 487, 603 atomic_init, 293, 487, 603 atomic_is_lock_free, 285, 297, 487,
590, 603 atomic_load, 298, 299, 300, 487, 603 atomic_load_explicit, 295, 299, 487,
603 atomic_signal_fence, 296, 297, 487,
603 atomic_store, 298, 487, 603 atomic_store_explicit, 295,
atomic_thread_fence, 148, 296, 297,
611
77, 92, 299, 487, 603
atomic_compare_exchange_strong_explicit
, 299, 487, 603 atomic_compare_exchange_weak,
299, 300, 487, 603
atomic_compare_exchange_weak_explicit
, 299, 487, 603 299,
487, 603 atomic_fetch_, 300, 487, 603 atomic_fetch_add, 603 atomic_fetch_add_explicit, 603 atomic_fetch_and, 603 atomic_fetch_and_explicit, 603 atomic_fetch_or, 603 atomic_fetch_or_explicit, 603 atomic_fetch_sub, 603 atomic_fetch_sub_explicit, 603 atomic_fetch_xor, 603 atomic_fetch_xor_explicit, 603 atomic_flag_clear, 301, 487, 603 atomic_flag_clear_explicit, 301,
487, 603 atomic_flag_test_and_set,
301,
487, 603 702
298,
487, 603
atof, 213, 354, 355, 492, 611 atoi, 193, 354, 355, 492, 611 atol, 354, 355, 492, 611 atoll, 354, 355, 492, 611 atomic_compare_exchange_strong,
atomic_exchange, 299, 487, 603 atomic_exchange_explicit,
N3096
Index
487, 603 btowc, 417, 418, 442, 497, 611 c16rtomb, i, 409, 410, 496, 611 c32rtomb, 411, 496, 611 c8rtomb, 408, 496, 611, 670 cabs, 200, 383, 384, 472, 540, 611 cabsf, 200, 386, 472, 557, 611 cabsl, 200, 472, 611 cacos, 196, 197, 384, 471, 540, 541, 611 cacosf, 196, 471, 556, 611 cacosh, 198, 384, 471, 541, 611 cacoshf, 198, 471, 556, 611 cacoshl, 198, 471, 611 cacosl, 196, 471, 611 cacospi, 453, 611 call_once, v, 354, 388, 389, 495, 611, 671 calloc, v, 362, 363, 364, 492, 583, 592, 599, 611 canonicalize, 24, 268, 384, 479, 508, 531, 611 canonicalized, 567, 611 canonicalized128, 268, 484, 611 canonicalized32, 268, 484, 611 canonicalized64, 268, 484, 611 canonicalizef, 268, 479, 567, 611 canonicalizel, 268, 479, 611 carg, 201, 386, 472, 540, 546, 576, 611 cargf, 201, 472, 557, 611 cargl, 201, 472, 611 casin, 197, 384, 471, 540, 611 casinf, 197, 471, 556, 611 casinh, 198, 384, 471, 540, 542, 611 casinhf, 198, 471, 556, 611 casinhl, 198, 471, 611 casinl, 197, 471, 611 casinpi, 453, 611 catan, 197, 384, 471, 540, 611 catanf, 197, 471, 556, 611 catanh, 198, 199, 384, 471, 540, 542, 611 catanhf, 199, 471, 556, 611 catanhl, 199, 471, 611
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
cnd_wait, 390, 391, 495, 604 compoundn, 255, 477, 511, 525, 612 compoundnd, 564, 612 compoundnd128, 255, 482, 612 compoundnd32, 255, 482, 612 compoundnd64, 255, 482, 612 compoundnf, 255, 477, 564, 612 compoundnl, 255, 477, 612 conj, 202, 472, 540–545, 576, 612 conjf, 202, 472, 557, 612 conjl, 202, 472, 612 copysign, iv, 202, 265, 266, 479, 509,
catanl, 197, 471, 611 catanpi, 453, 611 cbrt, i, 73, 255, 385, 477, 524, 611 cbrtd, 564, 611 cbrtd128, 255, 482, 611 cbrtd32, 255, 482, 611 cbrtd64, 255, 482, 611 cbrtf, 73, 255, 385, 477, 564, 611 cbrtl, 73, 255, 385, 477, 611 ccompoundn, 453, 611 ccos, 197, 384, 471, 540, 611 ccosf, 197, 471, 556, 611 ccosh, 199, 384, 471, 540, 542, 543, 611 ccoshf, 199, 471, 556, 611 ccoshl, 199, 471, 611 ccosl, 197, 471, 611 ccospi, 453, 611 ceil, 234, 260, 478, 507, 527, 528, 529,
524, 529, 530, 538, 539, 612 copysignd, 567, 612 copysignd128, 266, 484, 612 copysignd32, 266, 484, 612 copysignd64, 266, 484, 612 copysignf, 266, 479, 567, 612 copysignl, 266, 386, 479, 612 cos, 134, 242, 384, 475, 511, 519, 546,
611 ceild, 565, 611 ceild128, 32, 260, 483, 611 ceild32, 32, 260, 483, 611 ceild64, 32, 260, 483, 611 ceilf, 260, 478, 565, 611 ceill, 260, 264, 478, 611 cerf, 453, 611 cerfc, 453, 611 cexp, 199, 200, 384, 471, 544, 545, 611 cexp10, 453, 611 cexp10m1, 453, 611 cexp2, 453, 611 cexp2m1, 453, 611 cexpf, 200, 471, 557, 611 cexpl, 200, 471, 611 cexpm1, 453, 611 cimag, 201, 202, 203, 472, 538, 540, 546,
579, 612 cosd, 561, 612 cosd128, 242, 480, 612 cosd32, 242, 480, 612 cosd64, 242, 480, 612 cosf, 242, 475, 561, 612 cosh, 246, 384, 476, 512, 521, 546, 612 coshd, 562, 612 coshd128, 246, 481, 612 coshd32, 246, 481, 612 coshd64, 246, 481, 612 coshf, 246, 476, 562, 612 coshl, 246, 476, 612 cosl, 242, 475, 612 cospi, 244, 476, 511, 520, 612 cospid, 562, 612 cospid128, 244, 481, 612 cospid32, 244, 481, 612 cospid64, 244, 481, 612 cospif, 244, 476, 562, 612 cospil, 244, 476, 612 cpow, 200, 201, 384, 472, 545, 612 cpowf, 200, 472, 557, 612 cpowl, 200, 386, 472, 612 cpown, 453, 612 cpowr, 453, 612 cproj, 202, 472, 540, 576, 612 cprojf, 202, 386, 472, 557, 612 cprojl, 202, 386, 472, 612 creal, 201, 202, 203, 386, 472, 538, 540,
576, 612 cimagf, 201, 472, 557, 612 cimagl, 201, 386, 472, 612 clearerr, 352, 491, 612 clgamma, 453, 612 clock, 398, 399, 402, 495, 599, 612 clog, 200, 384, 471, 545, 612 clog10, 453, 612 clog10p1, 453, 612 clog1p, 453, 612 clog2, 453, 612 clog2p1, 453, 612 clogf, 200, 386, 471, 557, 612 clogl, 200, 472, 612 clogp1, 453, 612 cnd_broadcast, 389, 390, 391, 495, 604 cnd_destroy, 390, 495, 604 cnd_init, 390, 495, 604 cnd_signal, 390, 391, 495, 604 cnd_timedwait, 390, 391, 495, 604
546, 576, 612 crealf, 203, 472, 557, 612 creall, 203, 472, 612 crootn, 453, 612 crsqrt, 453, 612 csin, 197, 198, 384, 471, 540, 612
Index
703
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
csinf, 197, 471, 556, 612 csinh, 199, 384, 471, 540, 543, 612 csinhf, 199, 471, 556, 612 csinhl, 199, 471, 612 csinl, 197, 471, 612 csinpi, 453, 612 csqrt, 201, 384, 386, 472, 540, 545, 612 csqrtf, 201, 472, 557, 612 csqrtl, 201, 472, 612 ctan, 198, 384, 471, 540, 612 ctanf, 198, 471, 556, 612 ctanh, 199, 384, 471, 540, 544, 612 ctanhf, 199, 471, 556, 612 ctanhl, 199, 471, 612 ctanl, 198, 471, 612 ctanpi, 453, 612 ctgamma, 453, 612 ctime, 402, 403, 496, 612 ctime_s, 496, 612, 648, 649 d32addd128, 273, 484, 612 d32addd64, 273, 484, 612 d32divd128, 274, 485, 612 d32divd64, 274, 386, 485, 612 d32fmad128, 275, 485, 612 d32fmad64, 275, 485, 612 d32muld128, 274, 485, 612 d32muld64, 274, 485, 612 d32sqrtd128, 275, 485, 612 d32sqrtd64, 275, 485, 612 d32subd128, 274, 386, 485, 612 d32subd64, 274, 485, 612 d64addd128, 273, 387, 484, 612 d64divd128, 274, 485, 612 d64fmad128, 275, 387, 485, 612 d64muld128, 274, 485, 612 d64sqrtd128, 275, 485, 612 d64subd128, 274, 485, 612 daddl, 273, 386, 480, 508, 612 ddivl, 274, 480, 508, 511, 579, 612 decodebin, 508, 612 decodebind, 569, 612 decodebind128, 278, 485, 612 decodebind32, 278, 485, 612 decodebind64, 278, 383, 385, 485, 612 decodedec, 508, 612 decodedecd, 569, 612 decodedecd128, 277, 485, 612 decodedecd32, 277, 485, 612 decodedecd64, 277, 383, 385, 485, 612 decodef, 571, 612 dfmal, 275, 386, 480, 508, 612 difftime, 399, 495, 612 div, 134, 354, 369, 492, 577, 612 divd, 569, 612 divf, 569, 612 dmull, 274, 480, 508, 612
704
N3096
dsqrtl, 275, 480, 508, 613 dsubl, 273, 480, 508, 579, 613 encbind, 557, 571, 572, 613 encdecd, 557, 571, 572, 613 encf, 557, 571, 613 encodebin, 508, 613 encodebind, 569, 613 encodebind128, 278, 485, 613 encodebind32, 278, 485, 613 encodebind64, 278, 383, 385, 485, 613 encodedec, 508, 613 encodedecd, 569, 613 encodedecd128, 277, 485, 613 encodedecd32, 277, 485, 613 encodedecd64, 277, 383, 385, 485, 613 encodef, 570, 571, 613 erf, 258, 478, 527, 613 erfc, 259, 478, 527, 613 erfcd, 565, 613 erfcd128, 259, 483, 613 erfcd32, 259, 483, 613 erfcd64, 259, 483, 613 erfcf, 259, 478, 565, 613 erfcl, 259, 478, 613 erfd, 565, 613 erfd128, 258, 483, 613 erfd32, 258, 482, 613 erfd64, 258, 483, 613 erff, 258, 478, 565, 613 erfl, 258, 478, 613 exp, 247, 248, 249, 300, 384, 386, 476,
511, 522, 563, 564, 570, 613 exp10, 248, 476, 511, 522, 613 exp10d, 562, 613 exp10d128, 248, 481, 613 exp10d32, 248, 481, 613 exp10d64, 248, 481, 613 exp10f, 248, 476, 562, 613 exp10l, 248, 476, 613 exp10m1, 248, 476, 511, 522, 613 exp10m1d, 563, 613 exp10m1d128, 248, 481, 613 exp10m1d32, 248, 481, 613 exp10m1d64, 248, 481, 613 exp10m1f, 248, 476, 563, 613 exp10m1l, 248, 476, 613 exp2, 248, 249, 476, 511, 522, 613 exp2d, 563, 613 exp2d128, 248, 481, 613 exp2d32, 248, 481, 613 exp2d64, 248, 481, 613 exp2f, 248, 476, 563, 613 exp2l, 248, 476, 613 exp2m1, 249, 476, 511, 522, 613 exp2m1d, 563, 613 exp2m1d128, 249, 481, 613
Index
N3096
working draft — April 1, 2023
exp2m1d32, 249, 481, 613 exp2m1d64, 249, 481, 613 exp2m1f, 249, 476, 563, 613 exp2m1l, 249, 476, 613 expd, 562, 613 expd128, 247, 481, 613 expd32, 247, 481, 613 expd64, 247, 386, 481, 613 expf, 247, 476, 562, 613 expl, 247, 476, 613 expm1, 249, 476, 511, 522, 613 expm1d, 563, 613 expm1d128, 249, 481, 613 expm1d32, 249, 481, 613 expm1d64, 249, 481, 613 expm1f, 249, 476, 563, 613 expm1l, 249, 476, 613 fabs, iv, 255, 256, 383, 384, 477, 509,
ISO/IEC 9899:2023 (E)
fesetexcept, 215, 216, 473, 509, 613 fesetexceptflag, 214, 216, 473, 509,
589, 613 fesetmode, 212, 217, 218, 473, 509, 613 fesetround, 8, 24, 98, 210, 212, 213,
217, 218, 219, 473, 509, 510, 524, 528, 529, 557, 613 fetestexcept, 214, 216, 217, 473, 509, 529, 613 fetestexceptflag, 216, 473, 509, 613 feupdateenv, 92, 212, 219, 220, 473, 510, 529, 589, 613 fflush, 325, 326, 490, 591, 613 ffma, 275, 480, 508, 577, 613 ffmal, 275, 480, 508, 613 fgetc, 320, 323, 346, 347–349, 490, 613 fgetpos, 321, 322, 350, 351, 491, 582, 592, 599, 613 fgets, 320, 347, 491, 592, 613, 633 fgetwc, ii, 320, 323, 426, 427, 428, 497, 613 fgetws, 320, 427, 497, 592, 613 floor, 234, 260, 478, 507, 528, 613 floord, 565, 613 floord128, 260, 483, 613 floord32, 260, 483, 613 floord64, 260, 483, 613 floorf, 260, 478, 565, 613 floorl, 260, 478, 613 fma, 235, 273, 479, 508, 532, 577, 614 fmad, 568, 569, 613 fmad128, 273, 484, 613 fmad32, 273, 484, 613 fmad64, 273, 484, 613 fmaf, 273, 479, 568, 569, 613 fmal, 235, 273, 480, 613 fmax, iv, vii, 269, 270, 479, 510, 531, 614 fmaxd, 613 fmaxd128, 269, 484, 613 fmaxd32, 269, 484, 613 fmaxd64, 269, 484, 613 fmaxf, 269, 479, 613 fmaximum, 270, 271, 479, 508, 531, 614 fmaximum_mag, 270, 271, 272, 479, 508, 531, 614 fmaximum_mag_num, 271, 272, 479, 508, 531, 532, 614 fmaximum_mag_numd, 568, 614 fmaximum_mag_numd128, 272, 484, 614 fmaximum_mag_numd32, 272, 484, 614 fmaximum_mag_numd64, 272, 484, 614 fmaximum_mag_numf, 272, 479, 568, 614 fmaximum_mag_numl, 272, 479, 614 fmaximum_magd, 568, 614 fmaximum_magd128, 270, 484, 614 fmaximum_magd32, 270, 484, 614
525, 529, 530, 538, 546, 613 fabsd, 564, 613 fabsd128, 255, 482, 613 fabsd32, 255, 482, 613 fabsd64, 255, 482, 613 fabsf, 255, 477, 564, 613 fabsl, 255, 477, 613 fadd, 273, 480, 508, 577, 613 faddl, 273, 480, 508, 613 fclose, 173, 325, 490, 613 fdim, 268, 269, 479, 531, 613 fdimd, 567, 613 fdimd128, 269, 484, 613 fdimd32, 269, 484, 613 fdimd64, 269, 484, 613 fdimf, 269, 479, 567, 613 fdiml, 269, 479, 613 fdiv, 274, 386, 480, 508, 577, 613 fdivl, 274, 480, 508, 613 fe_dec_getround, 211, 217, 218, 473,
511, 557, 613 fe_dec_setround, 211, 214, 219, 473,
511, 557, 613 feclearexcept, 92, 214, 215, 217, 220,
473, 509, 529, 613 fegetenv, 219, 220, 473, 510, 589, 613 fegetexceptflag, 214, 215, 216, 473,
509, 589, 597, 613 fegetmode, 217, 218, 473, 509, 613 fegetround, 210, 213, 217, 218, 473,
509, 510, 524, 528, 557, 613 feholdexcept, 92, 219, 220, 473, 510,
528, 589, 613 feof, 341, 347, 352, 427, 491, 613 feraiseexcept, 214, 215, 473, 515, 582,
598, 613 ferror, 341, 347, 353, 427, 491, 613 fesetenv, 212, 220, 473, 510, 589, 613
Index
705
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
fmaximum_magd64, 270, 484, 614 fmaximum_magf, 270, 479, 568, 614 fmaximum_magl, 270, 479, 614 fmaximum_num, 270, 271, 479, 508, 510,
fminl, 269, 479, 614 fmod, 264, 265, 478, 529, 530, 598, 614 fmodd, 567, 614 fmodd128, 264, 483, 614 fmodd32, 264, 483, 614 fmodd64, 264, 483, 614 fmodf, 264, 478, 567, 614 fmodl, 264, 478, 614 fmul, 274, 480, 508, 577, 579, 614 fmull, 274, 480, 508, 614 fopen, 173, 323, 324, 325, 326, 327, 490,
531, 532, 538, 614 fmaximum_numd, 568, 614 fmaximum_numd128, 271, 484, 614 fmaximum_numd32, 271, 484, 614 fmaximum_numd64, 271, 484, 614 fmaximum_numf, 271, 479, 568, 614 fmaximum_numl, 271, 479, 614 fmaximumd, 567, 614 fmaximumd128, 270, 386, 484, 613 fmaximumd32, 270, 484, 613 fmaximumd64, 270, 484, 614 fmaximumf, 270, 479, 567, 614 fmaximuml, 270, 479, 614 fmaxl, 269, 479, 614 fmin, iv, vii, 269, 270, 479, 510, 531, 614 fmind, 614 fmind128, 269, 484, 614 fmind32, 269, 484, 614 fmind64, 269, 484, 614 fminf, 269, 479, 614 fminimum, 270, 271, 272, 479, 508, 531,
591, 602, 614, 623 fopen_s, 491, 614, 622, 623, 624 fprintf_s, 491, 614, 625 fputc, 19, 20, 320, 323, 347, 348, 350,
491, 614 fputs, 183, 320, 347, 491, 614 fputwc, 320, 323, 427, 429, 497, 614 fputws, 320, 427, 428, 497, 614 fread, 171, 173, 320, 349, 350, 491, 592,
614 free, 363, 364, 376, 492, 592, 614, 668 free_aligned_sized, 363, 364, 492,
614 free_sized, 363, 492, 614 freopen, 321, 322, 326, 327, 490, 614 freopen_s, 491, 614, 624, 625 frexp, 249, 250, 476, 522, 570, 582, 583,
614 fminimum_mag, 271, 272, 479, 508, 531,
614 fminimum_mag_num, 271, 272, 479, 508,
614 frexpd, 563, 614 frexpd128, 249, 481, 614 frexpd32, 249, 481, 614 frexpd64, 249, 481, 614 frexpf, 249, 476, 563, 614 frexpl, 249, 476, 614 fromfp, 234, 263, 264, 478, 508, 512, 529,
531, 532, 614 fminimum_mag_numd, 568, 614 fminimum_mag_numd128, 272, 484, 614 fminimum_mag_numd32, 272, 484, 614 fminimum_mag_numd64, 272, 484, 614 fminimum_mag_numf, 272, 479, 568, 614 fminimum_mag_numl, 272, 479, 614 fminimum_magd, 568, 614 fminimum_magd128, 271, 484, 614 fminimum_magd32, 271, 484, 614 fminimum_magd64, 271, 484, 614 fminimum_magf, 271, 479, 568, 614 fminimum_magl, 271, 479, 614 fminimum_num, 270, 271, 272, 479, 508,
614 fromfpd, 566, 614 fromfpd128, 263, 483, 614 fromfpd32, 263, 483, 614 fromfpd64, 263, 483, 614 fromfpf, 263, 478, 566, 614 fromfpl, 263, 478, 614 fromfpx, 234, 264, 478, 508, 512, 529,
510, 531, 532, 614 fminimum_numd, 568, 614 fminimum_numd128, 272, 484, 614 fminimum_numd32, 272, 484, 614 fminimum_numd64, 272, 484, 614 fminimum_numf, 271, 479, 568, 614 fminimum_numl, 272, 479, 614 fminimumd, 568, 614 fminimumd128, 270, 484, 614 fminimumd32, 270, 484, 614 fminimumd64, 270, 484, 614 fminimumf, 270, 479, 567, 614 fminimuml, 270, 479, 614
706
N3096
614 fromfpxd, 566, 614 fromfpxd128, 264, 483, 614 fromfpxd32, 264, 483, 614 fromfpxd64, 264, 483, 614 fromfpxf, 264, 478, 566, 614 fromfpxl, 264, 478, 614 frompfp, 614 frompfpd, 614 frompfpf, 614 frompfpl, 614 frompfpx, 614
Index
N3096
working draft — April 1, 2023
frompfpxd, 614 frompfpxf, 614 frompfpxl, 614 fscanf, 222, 320, 336, 340–344, 454, 491,
ISO/IEC 9899:2023 (E)
ilogbl, 250, 476, 615 imaxabs, 223, 474, 615 imaxdiv, 222, 223, 474, 615 isalnum, 204, 205, 206, 472, 605 isalpha, 204, 447, 472, 600, 605 isblank, 204, 472, 600, 605 iscntrl, 204, 205, 206, 472, 605 isdigit, 204, 205, 206, 228, 472, 605 isgraph, 205, 447, 472, 606 islower, 4, 204, 205, 206, 207, 472, 600,
599, 614, 625 fscanf_s, 491, 614, 625, 626, 627, 629,
630 fseek, 320, 323, 326, 349, 350, 351, 352,
429, 491, 592, 614 fsetpos, 321, 322, 326, 349, 350, 351,
429, 491, 592, 599, 614
606
fsqrt, 275, 480, 508, 577, 614 fsqrtl, 275, 480, 508, 614 fsub, 273, 480, 508, 577, 579, 614 fsubl, 273, 386, 480, 508, 579, 614 ftell, 351, 491, 582, 592, 599, 614 fwide, 321, 322, 428, 497, 614 fwprintf, 222, 320, 413, 418, 422–424,
isprint, 19, 20, 205, 472, 606 ispunct, 204, 205, 206, 472, 600, 606 isspace, 190, 204, 205, 206, 472, 600,
606 isupper, 204, 206, 207, 472, 600, 606 iswalnum, 448, 449, 450, 499, 606 iswalpha, 447, 448, 450, 499, 600, 606 iswblank, 448, 450, 499, 600, 606 iswcntrl, 448, 449, 450, 499, 606 iswctype, 450, 451, 499, 594, 600, 606 iswdigit, 448, 449, 450, 499, 606 iswgraph, 447, 449, 450, 499, 606 iswlower, 448, 449, 450, 451, 499, 600,
426, 455, 497, 594, 599, 614, 651 fwprintf_s, 498, 614, 650, 651 fwrite, 320, 350, 491, 592, 614 fwscanf, 222, 320, 418, 419, 422–424,
426, 429, 455, 497, 599, 614, 651 fwscanf_s, 498, 614, 651, 653, 654, 657 getc, 320, 347, 348, 491, 614 getchar, 15, 320, 348, 491, 614 getenv, 366, 492, 592, 595, 614 getenv_s, 493, 614, 635, 636 getpayload, 486, 507, 533, 534, 614 getpayloadd, 570, 614 getpayloadd128, 486, 533, 614 getpayloadd32, 486, 533, 614 getpayloadd64, 486, 533, 614 getpayloadf, 486, 533, 570, 614 getpayloadl, 486, 533, 614 gets_s, 491, 614, 633 getwc, 320, 428, 497, 614 getwchar, 320, 428, 497, 614 gmtime, 402, 403, 404, 496, 614 gmtime_r, 403, 496, 614, 670 gmtime_s, 496, 614, 649, 650 hypot, iv, 256, 477, 507, 511, 525, 540,
606 iswprint, 447, 449, 450, 499, 606 iswpunct, 447, 448, 449, 450, 499, 600,
606 iswspace, 190, 447, 448, 449, 450, 499,
600, 606 iswupper, 448, 449, 450, 451, 499, 600,
606 iswxdigit, 450, 499, 606 isxdigit, 206, 228, 472, 606 labs, 369, 492, 615 ldexp, 250, 251, 476, 523, 570, 615 ldexpd, 563, 615 ldexpd128, 250, 481, 615 ldexpd32, 250, 481, 615 ldexpd64, 250, 481, 615 ldexpf, 250, 476, 563, 615 ldexpl, 250, 476, 615 ldiv, 134, 354, 369, 492, 615 lgamma, 259, 478, 527, 615 lgammad, 565, 615 lgammad128, 259, 483, 615 lgammad32, 259, 483, 615 lgammad64, 259, 483, 615 lgammaf, 259, 478, 565, 615 lgammal, 259, 478, 615 llabs, 369, 492, 615 lldiv, 134, 354, 369, 492, 615 llogb, 236, 251, 476, 508, 523, 615 llogbd, 563, 615 llogbd128, 251, 481, 615 llogbd32, 251, 481, 615
615 hypotd, 564, 615 hypotd128, 256, 482, 614 hypotd32, 256, 482, 614 hypotd64, 256, 482, 615 hypotf, 256, 477, 564, 615 hypotl, 256, 477, 615 ignore_handler_s, 493, 615, 635 ilogb, 235, 250, 476, 508, 523, 582, 615 ilogbd, 563, 615 ilogbd128, 250, 481, 615 ilogbd32, 250, 481, 615 ilogbd64, 250, 481, 615 ilogbf, 250, 476, 563, 615
Index
707
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
llogbd64, 251, 481, 615 llogbf, 251, 476, 563, 615 llogbl, 251, 476, 615 llquantexpd, 511, 569, 615 llquantexpd128, 277, 485, 615 llquantexpd32, 277, 485, 615 llquantexpd64, 277, 485, 615 llrint, 261, 478, 512, 528, 529, 583, 615 llrintd, 566, 615 llrintd128, 261, 483, 615 llrintd32, 261, 483, 615 llrintd64, 261, 483, 615 llrintf, 261, 478, 566, 615 llrintl, 261, 478, 615 llround, 262, 478, 508, 529, 583, 615 llroundd, 566, 615 llroundd128, 262, 483, 615 llroundd32, 262, 483, 615 llroundd64, 262, 483, 615 llroundf, 262, 478, 566, 615 llroundl, 262, 478, 615 localeconv, 228, 231, 475, 589, 615 localtime, 400, 402, 403, 404, 496, 615 localtime_r, 404, 496, 615, 670 localtime_s, 496, 615, 649, 650 log, 236, 251, 252, 384, 476, 511, 523,
log2p1d, 564, 615 log2p1d128, 253, 482, 615 log2p1d32, 253, 482, 615 log2p1d64, 253, 482, 615 log2p1f, 253, 477, 564, 615 log2p1l, 253, 477, 615 logb, 250, 251, 253, 254, 477, 508, 522,
524, 538, 570, 615 logbd, 564, 615 logbd128, 253, 482, 615 logbd32, 253, 482, 615 logbd64, 253, 482, 615 logbf, 253, 477, 564, 615 logbl, 253, 477, 615 logd, 563, 615 logd128, 251, 481, 615 logd32, 251, 481, 615 logd64, 251, 481, 615 logf, 251, 476, 563, 615 logl, 251, 477, 615 logp1, ii, 252, 253, 477, 511, 523, 615 logp1d, 564, 615 logp1d128, 252, 482, 615 logp1d32, 252, 482, 615 logp1d64, 252, 482, 615 logp1f, 252, 477, 563, 615 logp1l, 252, 477, 615 longjmp, 282, 283, 366, 367, 486, 589,
615 log10, 251, 252, 477, 511, 523, 615 log10d, 563, 615 log10d128, 252, 482, 615 log10d32, 251, 482, 615 log10d64, 251, 482, 615 log10f, 251, 477, 563, 615 log10l, 251, 477, 615 log10p1, 252, 477, 511, 523, 615 log10p1d, 563, 615 log10p1d128, 252, 482, 615 log10p1d32, 252, 482, 615 log10p1d64, 252, 482, 615 log10p1f, 252, 477, 563, 615 log10p1l, 252, 477, 615 log1p, 252, 253, 477, 511, 523, 615 log1pd, 563, 564, 615 log1pd128, 252, 482, 615 log1pd32, 252, 482, 615 log1pd64, 252, 482, 615 log1pf, 252, 477, 563, 615 log1pl, 252, 477, 615 log2, 253, 477, 511, 523, 615 log2d, 564, 615 log2d128, 253, 482, 615 log2d32, 253, 482, 615 log2d64, 253, 482, 615 log2f, 253, 477, 564, 615 log2l, 253, 477, 615 log2p1, 252, 253, 477, 511, 524, 615
708
N3096
592, 615, 668 lrint, 261, 478, 512, 528, 529, 583, 615 lrintd, 566, 615 lrintd128, 261, 483, 615 lrintd32, 261, 483, 615 lrintd64, 261, 483, 615 lrintf, 261, 478, 566, 615 lrintl, 261, 478, 615 lround, 262, 478, 508, 529, 583, 615 lroundd, 566, 615 lroundd128, 262, 483, 615 lroundd32, 262, 483, 615 lroundd64, 262, 483, 615 lroundf, 262, 478, 566, 615 lroundl, 262, 478, 615 mblen, ii, 370, 443, 492, 616 mbrlen, 443, 498, 616 mbrtoc16, 408, 409, 496, 616 mbrtoc32, 410, 496, 616 mbrtoc8, 407, 408, 496, 616, 670 mbrtowc, 323, 339, 417, 418, 442, 443,
444, 445, 498, 616, 639, 665 mbsinit, 442, 443, 498, 616 mbsrtowcs, 442, 445, 498, 616, 664 mbsrtowcs_s, 498, 616, 664, 665 mbstowcs, 68, 371, 430, 444, 492, 616 mbstowcs_s, 493, 616, 639, 640 mbtowc, 66, 369, 370, 371, 443, 492, 616
Index
N3096
working draft — April 1, 2023
memalignment, 8, 372, 492, 606 memccpy, ii, 374, 493, 606, 670 memcmp, 41, 173, 299, 377, 493, 606 memcpy, vii, 41, 71, 170, 193, 293, 299,
ISO/IEC 9899:2023 (E)
nextdownl, 268, 479, 616 nexttoward, 267, 479, 510, 530, 616 nexttowardd128, 267, 484, 616 nexttowardd32, 267, 484, 616 nexttowardd64, 267, 484, 616 nexttowardf, 267, 386, 479, 616 nexttowardl, 267, 479, 616 nextup, 267, 479, 507, 531, 616 nextupd, 567, 616 nextupd128, 267, 484, 616 nextupd32, 267, 484, 616 nextupd64, 267, 484, 616 nextupf, 267, 479, 567, 616 nextupl, 267, 479, 616 perror, 353, 491, 616 pow, ii, 256, 384, 477, 511, 525, 579, 616 powd, 564, 616 powd128, 256, 482, 616 powd32, 256, 482, 616 powd64, 256, 386, 482, 616 powf, 256, 477, 564, 616 powl, 256, 477, 510, 616 pown, 256, 257, 477, 511, 526, 616 pownd, 565, 616 pownd128, 256, 482, 616 pownd32, 256, 482, 616 pownd64, 256, 482, 616 pownf, 256, 477, 565, 616 pownl, 256, 477, 616 powr, iii, 257, 477, 511, 526, 616 powrd, 565, 616 powrd128, 257, 482, 616 powrd32, 257, 482, 616 powrd64, 257, 482, 616 powrf, 257, 477, 565, 616 powrl, 257, 477, 616 printf_s, 491, 616, 626, 627 puts, 184, 313, 320, 348, 349, 491, 616 putwc, 320, 428, 429, 497, 616 putwchar, 320, 429, 497, 616 qsort, 367, 368, 369, 492, 583, 616 qsort_s, 493, 616, 636, 637, 638 quantize, 32, 214, 385, 507, 616 quantized, 569, 616 quantized128, 275, 485, 616 quantized32, 275, 485, 616 quantized64, 275, 485, 616 quantum, 32, 385, 508, 616 quantumd, 569, 616 quantumd128, 276, 485, 616 quantumd32, 276, 485, 616 quantumd64, 276, 485, 616 quick_exit, 285, 365, 366, 367, 492,
374, 493, 509, 606 memcpy_s, 494, 606, 641 memmove, 71, 374, 375, 493, 509, 588, 606 memmove_s, 494, 606, 641, 642 memset, vii, 293, 381, 494, 606, 646 memset_explicit, v, 381, 494, 606, 671 memset_s, 494, 606, 646 mktime, 400, 495, 616 modf, 254, 383, 384, 477, 524, 616 modfd, 564, 616 modfd128, 254, 482, 616 modfd32, 254, 482, 616 modfd64, 254, 482, 616 modff, 254, 477, 564, 616 modfl, 254, 477, 616 mtx_destroy, 391, 495, 606 mtx_init, 388, 389, 391, 392, 495, 606 mtx_lock, 392, 495, 593, 606 mtx_timedlock, 392, 495, 593, 606 mtx_trylock, 392, 393, 495, 606 mtx_unlock, 392, 393, 495, 593, 606 muld, 569, 616 mulf, 568, 569, 616 nan, 266, 331, 415, 479, 507, 530, 616 nand, 567, 616 nand128, 266, 484, 616 nand32, 266, 484, 616 nand64, 266, 484, 616 nanf, 266, 479, 567, 616 nanl, 266, 479, 616 nearbyint, 260, 261, 478, 510, 512, 524,
528, 616 nearbyintd, 566, 616 nearbyintd128, 260, 483, 616 nearbyintd32, 260, 483, 616 nearbyintd64, 260, 483, 616 nearbyintf, 260, 478, 565, 616 nearbyintl, 260, 478, 616 nextafter, 266, 267, 386, 479, 510, 530,
616 nextafterd, 567, 616 nextafterd128, 266, 484, 616 nextafterd32, 266, 484, 616 nextafterd64, 266, 484, 616 nextafterf, 266, 479, 567, 616 nextafterl, 266, 479, 616 nextdown, 268, 479, 507, 531, 616 nextdownd, 567, 616 nextdownd128, 268, 484, 616 nextdownd32, 268, 484, 616 nextdownd64, 268, 484, 616 nextdownf, 268, 479, 567, 616
583, 590, 592, 593, 599, 616, 672 raise, 284, 285, 286, 293, 365, 486, 589,
590, 616 Index
709
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
rand, 354, 361, 362, 492, 616 realloc, 362, 363, 364, 492, 583, 592,
samequantumd128, 276, 485, 617 samequantumd32, 276, 485, 617 samequantumd64, 276, 485, 617 scalbln, 254, 477, 508, 524, 570, 617 scalblnd, 564, 617 scalblnd128, 254, 482, 617 scalblnd32, 254, 482, 617 scalblnd64, 254, 482, 617 scalblnf, 254, 477, 564, 617 scalblnl, 254, 477, 617 scalbn, 254, 477, 508, 522, 523, 524, 539,
599, 616, 668, 672 remainder, i, 265, 386, 478, 508, 511,
530, 598, 616 remainderd, 567, 616 remainderd128, 265, 484, 616 remainderd32, 265, 483, 616 remainderd64, 265, 483, 616 remainderf, 265, 479, 567, 616 remainderl, 265, 479, 616 remove, 323, 324, 490, 599, 616, 622 remquo, 265, 479, 508, 511, 530, 582, 598,
570, 617 scalbnd, 564, 617 scalbnd128, 254, 482, 617 scalbnd32, 254, 482, 617 scalbnd64, 254, 482, 617 scalbnf, 254, 477, 564, 617 scalbnl, 254, 477, 617 scanf, 32, 213, 214, 320, 342, 343, 345,
616 remquof, 265, 479, 567, 616 remquol, 265, 479, 616 rename, 323, 324, 490, 599, 616 rewind, 326, 349, 352, 429, 491, 616 rint, 261, 478, 507, 512, 528, 529, 617 rintd, 566, 616 rintd128, 261, 483, 616 rintd32, 261, 483, 616 rintd64, 261, 483, 616 rintf, 261, 478, 566, 616 rintl, 261, 478, 616 rootn, 257, 477, 511, 526, 617 rootnd, 565, 617 rootnd128, 257, 482, 617 rootnd32, 257, 482, 617 rootnd64, 257, 482, 617 rootnf, 257, 477, 565, 617 rootnl, 257, 477, 617 round, 234, 261, 262, 478, 507, 528, 617 roundd, 566, 617 roundd128, 262, 483, 617 roundd32, 261, 483, 617 roundd64, 262, 483, 617 roundeven, 234, 262, 263, 478, 507, 529,
490, 508, 617, 673 scanf_s, 491, 617, 627, 631 set_constraint_handler_s,
493, 617, 620, 634, 635 setbuf, 319, 322, 323, 325, 327, 490, 617 setjmp, 192, 282, 283, 486, 582, 589, 617, 668 setlocale, 190, 227, 228, 231, 402, 475, 589, 598, 617 setpayload, 486, 507, 534, 617 setpayloadd, 570, 617 setpayloadd128, 486, 534, 617 setpayloadd32, 486, 534, 617 setpayloadd64, 486, 534, 617 setpayloadf, 486, 534, 570, 617 setpayloadl, 486, 534, 617 setpayloadsig, 486, 507, 534, 617 setpayloadsigd, 570, 617 setpayloadsigd128, 486, 534, 617 setpayloadsigd32, 486, 534, 617 setpayloadsigd64, 486, 534, 617 setpayloadsigf, 486, 534, 570, 617 setpayloadsigl, 486, 534, 617 setvbuf, 319, 322, 323, 325, 327, 328, 490, 591, 617 signal, 14, 15, 132, 284, 285, 366, 367, 486, 590, 595, 598, 617 sin, 76, 242, 384, 386, 475, 511, 520, 546, 617 sind, 561, 617 sind128, 242, 480, 617 sind32, 242, 480, 617 sind64, 242, 480, 617 sinf, 242, 475, 561, 617 sinh, 247, 384, 476, 512, 521, 546, 617 sinhd, 562, 617 sinhd128, 247, 481, 617
617 roundevend, 566, 617 roundevend128, 262, 483, 617 roundevend32, 262, 483, 617 roundevend64, 262, 483, 617 roundevenf, 262, 478, 566, 617 roundevenl, 262, 478, 617 roundf, 261, 478, 566, 617 roundl, 261, 478, 617 rsqrt, 257, 258, 477, 511, 527, 617 rsqrtd, 565, 617 rsqrtd128, 258, 482, 617 rsqrtd32, 258, 482, 617 rsqrtd64, 258, 482, 617 rsqrtf, 258, 477, 565, 617 rsqrtl, 258, 477, 617 samequantum, 385, 507, 617 samequantumd, 569, 617
710
N3096
Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
stdc_first_leading_oneui, 607 stdc_first_leading_oneul, 607 stdc_first_leading_oneull, 607 stdc_first_leading_oneus, 607 stdc_first_leading_zerouc, 607 stdc_first_leading_zeroui, 607 stdc_first_leading_zeroul, 607 stdc_first_leading_zeroull, 607 stdc_first_leading_zerous, 607 stdc_first_trailing_oneuc, 607 stdc_first_trailing_oneui, 607 stdc_first_trailing_oneul, 607 stdc_first_trailing_oneull, 607 stdc_first_trailing_oneus, 607 stdc_first_trailing_zerouc, 607 stdc_first_trailing_zeroui, 607 stdc_first_trailing_zeroul, 607 stdc_first_trailing_zeroull, 607 stdc_first_trailing_zerous, 607 stdc_has_single_bituc, 607 stdc_has_single_bitui, 607 stdc_has_single_bitul, 607 stdc_has_single_bitull, 607 stdc_has_single_bitus, 607 stdc_leading_onesuc, 607 stdc_leading_onesui, 608 stdc_leading_onesul, 608 stdc_leading_onesull, 608 stdc_leading_onesus, 608 stdc_leading_zerosuc, 608 stdc_leading_zerosui, 608 stdc_leading_zerosul, 608 stdc_leading_zerosull, 608 stdc_leading_zerosus, 608 stdc_trailing_onesuc, 608 stdc_trailing_onesui, 608 stdc_trailing_onesul, 608 stdc_trailing_onesull, 608 stdc_trailing_onesus, 608 stdc_trailing_zerosuc, 608 stdc_trailing_zerosui, 608 stdc_trailing_zerosul, 608 stdc_trailing_zerosull, 608 stdc_trailing_zerosus, 608 strcat, 376, 493, 608 strcat_s, 494, 608, 643, 644 strcmp, 377, 378, 493, 608 strcoll, 8, 228, 377, 378, 493, 608 strcpy, 175–177, 341, 375, 493, 608 strcpy_s, 494, 608, 642 strcspn, 379, 493, 608 strdup, ii, 8, 375, 376, 493, 608, 670 strerror, 8, 353, 381, 382, 494, 592, 593,
sinhd32, 247, 481, 617 sinhd64, 247, 481, 617 sinhf, 247, 476, 562, 617 sinhl, 247, 476, 617 sinl, 242, 475, 617 sinpi, 244, 245, 476, 511, 521, 617 sinpid, 562, 617 sinpid128, 245, 481, 617 sinpid32, 245, 481, 617 sinpid64, 245, 481, 617 sinpif, 244, 476, 562, 617 sinpil, 245, 476, 617 snprintf, iii, 343, 345, 355, 356, 403,
490, 617, 628, 673 snprintf_s, 491, 617, 627, 628 snwprintf_s, 498, 617, 651, 652 sprintf, 343, 346, 490, 617, 628 sprintf_s, 491, 617, 628 sqrt, 149, 258, 384, 477, 508, 527, 532,
577, 617 sqrtd, 565, 569, 617 sqrtd128, 258, 482, 617 sqrtd32, 258, 386, 482, 617 sqrtd64, 258, 482, 617 sqrtf, 258, 477, 565, 569, 617 sqrtl, 258, 477, 617 srand, 361, 362, 492, 617 sscanf, 341, 343, 344, 346, 490, 617 sscanf_s, 491, 617, 629, 632 stdc_, 454, 603, 607 stdc_bit_ceiluc, 607 stdc_bit_ceilui, 607 stdc_bit_ceilul, 607 stdc_bit_ceilull, 607 stdc_bit_ceilus, 607 stdc_bit_flooruc, 607 stdc_bit_floorui, 607 stdc_bit_floorul, 607 stdc_bit_floorull, 607 stdc_bit_floorus, 607 stdc_bit_widthuc, 607 stdc_bit_widthui, 607 stdc_bit_widthul, 607 stdc_bit_widthull, 607 stdc_bit_widthus, 607 stdc_count_onesuc, 607 stdc_count_onesui, 607 stdc_count_onesul, 607 stdc_count_onesull, 607 stdc_count_onesus, 607 stdc_count_zerosuc, 607 stdc_count_zerosui, 607 stdc_count_zerosul, 607 stdc_count_zerosull, 607 stdc_count_zerosus, 607 stdc_first_leading_oneuc, 607
600, 608 strerror_s, 382, 494, 608, 646, 647 strerrorlen_s, 494, 608, 647
Index
711
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
strfromd, 355, 430, 492, 508, 509, 554,
tan, 242, 243, 384, 475, 511, 520, 546,
572, 573, 574, 575, 608 strfromd128, 355, 356, 492, 608 strfromd32, 355, 356, 492, 608 strfromd64, 355, 356, 492, 608 strfromencbind, 557, 574, 575, 608 strfromencdecd, 557, 574, 575, 608 strfromencf, 557, 574, 608 strfromencf128, 574, 608 strfromf, 355, 430, 492, 573, 574, 608 strfroml, 355, 492, 608 strftime, ii, 228, 402, 404, 406, 441, 496, 583, 591, 593, 600, 608, 648, 649, 670, 674 strlen, 376, 382, 494, 608 strncat, 376, 493, 608 strncat_s, 494, 608, 644, 645 strncmp, 183, 377, 378, 493, 608 strncpy, 375, 493, 608 strncpy_s, 494, 608, 642, 643 strndup, ii, 8, 376, 493, 608, 670 strnlen_s, 494, 608, 642–644, 647 strspn, 380, 493, 608 strtod, 63, 266, 337, 338, 342, 355, 356, 430, 492, 508, 513, 514, 554, 555, 572, 573, 576, 583, 599, 608 strtod128, 358, 574, 599, 608 strtod32, 358, 599, 608 strtod64, 358, 359, 599, 608 strtoencbind, 557, 575, 576, 608 strtoencdecd, 557, 575, 576, 608 strtoencf, 557, 575, 608 strtof, 266, 342, 355, 356, 492, 573, 575, 583, 599, 608 strtoimax, 223, 474, 608 strtok, 380, 381, 494, 593, 608 strtok_s, 381, 494, 608, 645, 646 strtol, 223, 224, 337, 338, 342, 355, 360, 361, 492, 608 strtold, 266, 342, 355, 356, 492, 583, 599, 608 strtoll, 223, 224, 342, 355, 360, 361, 492, 608 strtoul, 223, 224, 338, 342, 355, 360, 361, 492, 608 strtoull, 223, 224, 342, 355, 360, 361, 492, 608 strtoumax, 223, 474, 608 strxfrm, 8, 228, 378, 493, 593, 608 subd, 568, 617 subf, 568, 617 swprintf, 423, 425, 497, 617, 652 swprintf_s, 498, 617, 652, 653 swscanf, 423, 425, 497, 617 swscanf_s, 498, 617, 653, 656 system, 367, 492, 593, 595, 599, 617 712
N3096
617 tand, 561, 617 tand128, 242, 480, 617 tand32, 242, 480, 617 tand64, 242, 480, 617 tanf, 242, 475, 561, 617 tanh, 247, 384, 476, 512, 521, 546, 617 tanhd, 562, 617 tanhd128, 247, 481, 617 tanhd32, 247, 481, 617 tanhd64, 247, 481, 617 tanhf, 247, 476, 562, 617 tanhl, 247, 476, 617 tanl, 242, 475, 617 tanpi, 245, 476, 512, 521, 617 tanpid, 562, 617 tanpid128, 245, 481, 617 tanpid32, 245, 481, 617 tanpid64, 245, 481, 617 tanpif, 245, 476, 562, 617 tanpil, 245, 476, 617 tgamma, 259, 260, 478, 527, 617 tgammad, 565, 617 tgammad128, 259, 483, 617 tgammad32, 259, 483, 617 tgammad64, 259, 483, 617 tgammaf, 259, 478, 565, 617 tgammal, 259, 478, 617 thrd_create, 388, 393, 495, 608 thrd_current, 393, 495, 608 thrd_detach, 394, 495, 593, 608 thrd_equal, 394, 495, 608 thrd_exit, 393, 394, 495, 583, 608 thrd_join, 394, 395, 495, 593, 608 thrd_sleep, 395, 495, 608 thrd_yield, 395, 495, 608 time, 400, 401, 495, 583, 618 timegm, 400, 401, 495, 617, 672 timespec_get, 398, 401, 402, 496, 617 timespec_getres, 398, 402, 496, 617,
672 tmpfile, 324, 366, 490, 618 tmpfile_s, 491, 618, 622, 623 tmpnam, 320, 324, 325, 490, 618, 623 tmpnam_s, 491, 618, 621, 622, 623 tolower, 206, 472, 608 totalorder, i, 485, 509, 532, 608 totalorderd, 570, 608 totalorderd128, 486, 532, 608 totalorderd32, 486, 532, 608 totalorderd64, 486, 532, 608 totalorderf, 485, 532, 570, 608 totalorderl, 485, 532, 608 totalordermag, 485, 509, 533, 608 totalordermagd, 570, 608
Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
totalordermagd128, 486, 533, 608 totalordermagd32, 486, 533, 608 totalordermagd64, 486, 533, 608 totalordermagf, 485, 533, 570, 608 totalordermagl, 485, 533, 608 toupper, 206, 207, 472, 609 towctrans, 451, 452, 499, 594, 600, 609 towlower, 451, 452, 499, 609 towupper, 451, 452, 499, 609 trunc, 234, 263, 478, 507, 529, 618 truncd, 566, 618 truncd128, 263, 483, 618 truncd32, 263, 483, 618 truncd64, 263, 483, 618 truncf, 263, 478, 566, 618 truncl, 263, 478, 618 tss_create, 395, 396, 495, 594, 609 tss_delete, 396, 495, 583, 594, 609 tss_get, 396, 495, 594, 609 tss_set, 396, 397, 495, 594, 609 ufromfp, 234, 263, 264, 478, 508, 512,
vfwscanf , 320, 424, 429, 497, 592, 618 vfwscanf_s, 498, 618, 654, 656, 657 vprintf , 320, 344, 345, 490, 592, 618,
529, 618 ufromfpd, 566, 618 ufromfpd128, 263, 483, 618 ufromfpd32, 263, 483, 618 ufromfpd64, 263, 483, 618 ufromfpf, 263, 478, 566, 618 ufromfpl, 263, 478, 618 ufromfpx, 234, 264, 478, 508, 512, 529, 618 ufromfpxd, 566, 618 ufromfpxd128, 264, 483, 618 ufromfpxd32, 264, 483, 618 ufromfpxd64, 264, 483, 618 ufromfpxf, 264, 478, 566, 618 ufromfpxl, 264, 478, 618 ungetc, 320, 349, 351, 454, 491, 582, 592, 602, 618, 674 ungetwc, 320, 429, 497, 582, 602, 618 va_arg, 288, 289–291, 333, 344–346, 417, 418, 424–426, 487, 590, 618, 630–632, 654, 656, 657 va_copy , 192, 288, 289, 291, 487, 582, 590, 618, 674 va_end, 192, 288, 289, 290, 291, 344–346, 424–426, 487, 582, 590, 592, 618, 630– 632, 654, 656, 657 va_start, vi, 288, 289, 290, 291, 344– 346, 424–426, 487, 590, 618, 630–632, 654, 656, 657, 671 vfprintf, 320, 344, 490, 592, 618, 629 vfprintf_s , 491, 618, 629, 630–632 vfscanf , 320, 344, 345, 490, 592, 618 vfscanf_s , 491, 618, 630, 631, 632 vfwprintf, 320, 424, 497, 592, 618, 653 vfwprintf_s , 498, 618, 653
vwprintf , 320, 424, 425, 497, 592, 618,
630 vprintf_s , 491, 618, 630, 631, 632 vscanf , 320, 344, 345, 490, 592, 618, 673 vscanf_s , 491, 618, 630, 631–633 vsnprintf , 344, 345, 346, 490, 592, 618,
631 vsnprintf_s , 491, 618, 630, 631, 632 vsnwprintf_s , 498, 618, 654, 655 vsprintf , 344, 346, 490, 592, 618, 632 vsprintf_s, 491, 618, 630, 631, 632 vsscanf , 344, 346, 490, 592, 618 vsscanf_s , 491, 618, 630, 631, 632, 633 vswprintf , 424, 425, 497, 592, 618, 654,
655 vswprintf_s , 498, 618, 654, 655 vswscanf , 424, 425, 497, 592, 618 vswscanf_s, 498, 618, 654, 655, 656,
657 656 vwprintf_s, 498, 618, 656 vwscanf , 320, 424, 425, 426, 429, 497,
592, 618 vwscanf_s , 498, 618, 654, 656, 657 wcrtomb , 323, 332, 336, 342, 412, 421,
423, 444, 446, 498, 583, 618, 640, 663, 666 wcrtomb_s , 498, 618, 663, 664 wcscat , 436, 497, 609 wcscat_s , 498, 609, 660, 661 wcscmp , 436, 437, 497, 609 wcscoll , 436, 437, 497, 609 wcscpy , 434, 435, 497, 609 wcscpy_s , 498, 609, 658 wcscspn , 438, 497, 609 wcsftime , 228, 441, 497, 583, 591, 593, 600, 609 wcslen , 436, 441, 497, 609, 663 wcsncat , 436, 497, 609 wcsncat_s , 498, 609, 661, 662 wcsncmp , 437, 497, 609 wcsncpy , 435, 497, 609 wcsncpy_s , 498, 609, 658, 659 wcsnlen_s , 498, 609, 658, 660, 661, 663 wcsrtombs , 445, 446, 498, 609, 664 wcsrtombs_s , 498, 609, 664, 665, 666 wcsspn , 439, 497, 609 wcstod , 419, 421, 423, 430, 508, 573, 576, 583, 599, 609 wcstod128 , 430, 432, 599, 609 wcstod32 , 430, 432, 599, 609 wcstod64 , 430, 432, 599, 609 wcstof , 423, 430, 575, 583, 599, 609 Index
713
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
_DECIMAL_DIG, 28, 333, 357, 418, 431,
wcstoimax, 224, 474, 609 wcstok, 440, 497, 593, 594, 609 wcstok_s, 498, 609, 662, 663 wcstol, 224, 419–421, 423, 433, 434, 497,
512, 513 _H__, 191 __STDC_VERSION_, 191 _r, 402 __STDC_, 189 ATOMIC_, 454, 602 atomic_, 454, 603
609 wcstold , 423, 430, 583, 599, 609 wcstoll , 224, 423, 433, 434, 497, 609 wcstombs, 372, 444, 492, 609 wcstombs_s , 493, 609, 640, 641 wcstoul , 224, 421, 423, 433, 434, 497,
c, 383, 384 cnd_, 455, 603 cr_, 454
609
d, 384, 385 d128, 385 d32, 385 d64, 383, 385 DBL_, 453, 602 DEC, 474, 550, 551, 552, 612 DEC128_, 29, 453, 602 DEC32_, 29, 453, 602 DEC64_, 29, 453, 602 DEC_, 453, 602 DECN, 612 DECN_, 612 E, 208, 453, 602 FE_, 210, 211, 453, 602 FLT, 550, 551, 552, 613 FLT_, 453, 602
wcstoull, 224, 423, 433, 434, 497, 609 wcstoumax, 224, 474, 609 wcsxfrm , 437, 497, 593, 609 wctob, 442, 447, 497, 618 wctomb, 369, 370, 371, 372, 443, 492, 618 wctomb_s, 493, 618, 638, 639 wctrans , 451, 452, 499, 594, 618 wctype, 450, 451, 499, 594, 618 wmemcmp , 437, 497, 618 wmemcpy , 435, 497, 618 wmemcpy_s , 498, 618, 659, 660 wmemmove, 435, 497, 618 wmemmove_s , 498, 618, 660 wmemset , 441, 497, 618 wprintf , 213, 214, 223, 320, 425, 426,
497, 508, 509, 618, 657 wprintf_s , 498, 618, 657 wscanf, 213, 214, 320, 426, 429, 497, 508,
FLTN, 613 FLTN_, 613 FP_, 234, 453, 602
618 wscanf_s, 498, 618, 657, 658 xaddd, 568, 618 xaddf, 568, 618 xdivd, 569, 618 xdivf, 569, 618 xfmad, 569, 618 xfmaf, 569, 618 xmuld, 569, 618 xmulf, 569, 618 xsqrtd, 569, 618 xsqrtf, 569, 618 xsubd, 568, 618 xsubf, 568, 618
INT, 317, 318, 454, 490, 602 int, 315, 454, 490, 603 INT_FAST, 317, 490 int_fast, 316, 490 INT_LEAST, 317, 490 int_least, 315, 318, 490 is, 453–455, 603 LC_, 227, 453, 602 LDBL_, 453, 602 llquantexpd, 276, 277, 385 MATH_, 454, 602 mem, 455, 603 memory_, 454 memory_order_, 454 mtx_, 455, 603 PRI, 222, 453, 602 PRId, 222, 474 PRIdFAST, 222, 474 PRIdLEAST, 222, 474 PRIi, 222, 474 PRIiFAST, 222, 474 PRIiLEAST, 222, 474 PRIo, 222, 474 PRIoFAST, 222, 474 PRIoLEAST, 222, 474 PRIu, 222, 474
future directions, 453 identifier __VA_ARGS__ , 177, 178, 179, 184, 610, 673 __VA_OPT__ , vi, 177, 178–180, 469, 610, 671 __func__ , 55, 194, 585, 610, 674 errno, 147, 148, 192, 195, 208, 224, 236, 237, 285, 323, 350, 351, 353, 354, 357, 359, 361, 382, 408–411, 427, 432–434, 444–446, 472, 589, 590, 598, 599, 602, 613, 620, 621, 647 identifier prefix 714
N3096
Index
N3096
working draft — April 1, 2023
PRIuFAST, 222, 474 PRIuLEAST, 222, 474 PRIX, 222, 474 PRIx, 222, 474 PRIXFAST, 222, 474 PRIxFAST, 222, 474 PRIXLEAST, 222, 474 PRIxLEAST, 222, 474 quantized, 275, 276, 385 quantumd, 276, 385 samequantumd, 276, 385 SCN, 222, 453, 602 SCNd, 222, 474 SCNdFAST, 222, 474 SCNdLEAST, 222, 474 SCNi, 222, 474 SCNiFAST, 222, 474 SCNiLEAST, 222, 474 SCNo, 222, 474 SCNoFAST, 222, 474 SCNoLEAST, 222, 474 SCNu, 222, 474 SCNuFAST, 222, 474 SCNuLEAST, 222, 474 SCNx, 222, 474 SCNxFAST, 222, 474 SCNxLEAST, 222, 474 SIG, 284, 454, 602 SIG_, 284, 454, 603
ISO/IEC 9899:2023 (E)
macro _Complex_I , iv, 195, 471, 540, 609, 671 _IOFBF , 319, 327, 490, 610 _IOLBF , 319, 327, 490, 610 _IONBF , 319, 327, 490, 610 _Imaginary_I , iv, 195, 202, 471, 539,
540, 610, 671 _PRINTF_NAN_LEN_MAX , 320, 490, 610 __DATE__ , 186, 597, 610 __FILE__ , 168, 186, 194, 610 __LINE__ , 184, 185, 186, 194, 582, 610 __STDC_ANALYZABLE__ , 187, 610, 667 __STDC_EMBED_EMPTY__ , 166, 186, 610 __STDC_EMBED_FOUND__ , 165, 186, 610 __STDC_EMBED_NOT_FOUND__ , 165,
186, 610 __STDC_ENDIAN_BIG__ , 302, 303, 488,
610 __STDC_ENDIAN_LITTLE__ , 302, 303,
488, 610 __STDC_ENDIAN_NATIVE__ , 277, 278,
302, 488, 571, 572, 574–576, 598, 610 __STDC_HOSTED__ , 186, 610 __STDC_IEC_60559_BFP__ , 8, 23, 187,
188, 190, 485, 506, 532–534, 547, 548, 610 __STDC_IEC_60559_COMPLEX__ , 23, 187, 188, 190, 536, 610 __STDC_IEC_60559_DFP__ , 8, 29, 187, 188, 190, 214, 217, 219, 233, 240–267, 268, 269–273, 274, 275–278, 356, 358, 386, 432, 473, 474, 480, 486, 492, 504, 506, 532–534, 547–549, 610 __STDC_IEC_60559_TYPES__ , 187, 188, 190, 547–549, 610 __STDC_ISO_10646__ , 187, 595, 610 __STDC_LIB_EXT1__ , 187, 188, 190, 472, 489–491, 493, 494, 496, 498, 610, 619 __STDC_MB_MIGHT_NEQ_WC__ , 44, 187, 312, 610 __STDC_NO_ATOMICS__ , 187, 292, 487, 610 __STDC_NO_COMPLEX__ , 188, 195, 471, 610 __STDC_NO_THREADS__ , 15, 188, 388, 495, 610 __STDC_NO_VLA__ , 188, 610 __STDC_UTF_16__ , 186, 595, 610 __STDC_UTF_32__ , 186, 595, 610 __STDC_VERSION_ASSERT_H__ , 194, 471, 610 __STDC_VERSION_COMPLEX_H__ , 195, 471, 610 __STDC_VERSION_FENV_H__ , 209, 610 __STDC_VERSION_FLOAT_H__ , 221,
str, 453–455, 603 strfrom, 213, 214 strfromd, 355, 356 thrd_, 455, 603 TIME_, 398, 455, 603 to, 453, 455, 603 tss_, 455, 603 UINT, 317, 318, 454, 490, 603 uint, 315, 454, 490, 603 UINT_FAST, 317, 490 uint_fast, 316, 490 UINT_LEAST, 317, 490 uint_least, 315, 318, 490 wcs, 453–455, 603 X_, 550, 618
identifier suffix _C, 318, 454, 490, 602, 603 _EXT__, 609 _MAX, 22, 46, 317, 318, 454, 474, 490, 552, 602, 603 _MIN, 22, 317, 318, 454, 474, 490, 552, 602, 603 _WIDTH, 22, 317, 318, 454, 490, 602, 603 _explicit, 292, 300, 487 f, 195, 233, 383–385, 453 l, 195, 233, 383, 385, 453 MAX, 140 Index
715
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
ATOMIC_FLAG_INIT , 292, 300, 487, 603 ATOMIC_INT_LOCK_FREE , 292, 487, 603 ATOMIC_LLONG_LOCK_FREE , 292, 487,
473, 610 __STDC_VERSION_MATH_H__ , 233, 475,
610 __STDC_VERSION_SETJMP_H__ ,
603
282,
ATOMIC_LONG_LOCK_FREE ,
486, 610 __STDC_VERSION_STDARG_H__ ,
ATOMIC_POINTER_LOCK_FREE,
ATOMIC_SHORT_LOCK_FREE , 292, 487,
603
354,
ATOMIC_WCHAR_T_LOCK_FREE,
492, 610 __STDC_VERSION_STRING_H__ ,
374,
493, 610 __STDC_VERSION_TGMATH_H__ ,
383,
610 __STDC_VERSION_TIME_H__ , 398, 495,
610 __STDC_VERSION_UCHAR_H__ ,
407,
496, 610 __STDC_VERSION_WCHAR_H__ ,
412,
496, 610 __STDC_VERSION__ , 187, 610, 669, 670,
672, 674 __STDC_WANT_IEC_60559_EXT__ , 233,
474, 485, 486, 512, 532–534, 610 __STDC_WANT_IEC_60559_TYPES_EXT__ ,
551, 556, 570–572, 574–576, 578, 610 __STDC_WANT_LIB_EXT1__ , 472, 489–
491, 493, 494, 496, 498, 610, 619, 620, 622–638, 641–663 __STDC__ , 167, 186, 610 __TIME__ , 187, 597, 610 __alignas_is_defined , 610 __alignof_is_defined , 610 __cplusplus , 167, 186, 610 __has_c_attribute , 141–146, 148, 166, 167, 186, 610, 669 __has_embed , 51, 69, 166, 168, 186, 610 __has_include , iv, 51, 69, 166, 167, 186, 610, 671 ADDD , 560 ADDF , 559, 560 and, 225, 474, 611 and_eq, 225, 474, 611 assert, v, 143, 174, 176, 194, 218, 471, 588, 597, 611 ATOMIC_BOOL_LOCK_FREE , 292, 487, 603 292, ATOMIC_CHAR16_T_LOCK_FREE , 487, 603 ATOMIC_CHAR32_T_LOCK_FREE , 292, 487, 603 ATOMIC_CHAR8_T_LOCK_FREE , 292, 487, 603 ATOMIC_CHAR_LOCK_FREE , 292, 487, 603 716
292,
487, 603
319,
490, 610 __STDC_VERSION_STDLIB_H__ ,
292, 487,
603
288,
487, 610 __STDC_VERSION_STDIO_H__ ,
N3096
Index
292, 487, 604 bitand, 225, 474, 611 BITINT_MAXWIDTH, 22, 102, 503, 611, 670 bitor, 225, 474, 611 bool, 611 BOOL_MAX, 474, 503, 604 BOOL_WIDTH, 21, 474, 503, 611 bsearch, 367, 368, 454, 492, 583, 593, 611 bsearch_s, 493, 611, 636, 637 BUFSIZ, 319, 322, 327, 490, 611 CHAR_BIT, 21, 41, 103, 170–172, 174, 474, 503, 612 CHAR_MAX, 22, 229, 230, 474, 503, 604 CHAR_MIN, 22, 39, 474, 503, 604 CHAR_WIDTH, 21, 474, 503, 612 ckd_, iv, xiv, 311, 454, 489, 603, 604 ckd_add, 311, 493, 604 ckd_div, 604 ckd_mul, 311, 493, 604 ckd_sub, 311, 493, 604 CLOCKS_PER_SEC, 398, 399, 402, 495, 612 CMPLX, 195, 201, 202, 472, 612 CMPLXF, 201, 202, 472, 557, 612 CMPLXL, 202, 472, 612 compl, 225, 474, 612 complex, 137, 195–203, 386, 471, 472, 537, 538, 556, 557, 578, 583, 612 CR_DECIMAL_DIG, 24, 474, 512, 604 d32add, 32, 214, 385, 612 d32div, 32, 214, 385, 612 d32fma, 32, 214, 385, 612 d32mul, 32, 214, 385, 612 d32sqrt, 32, 214, 385, 612 d32sub, 32, 214, 385, 612 d64add, 32, 214, 385, 612 d64div, 32, 214, 385, 612 d64fma, 32, 214, 385, 612 d64mul, 32, 214, 385, 612 d64sqrt, 32, 214, 385, 612 d64sub, 32, 214, 385, 612 dadd, 385, 577, 612 DBL_DECIMAL_DIG, 26, 28, 473, 504, 604
N3096
working draft — April 1, 2023
DBL_DIG, 26, 29, 473, 504, 604 DBL_EPSILON, 27, 28, 473, 504, 604 DBL_HAS_SUBNORM, 25, 29, 453, 473, 604 DBL_IS_IEC_60559, 24, 28, 473, 604 DBL_MANT_DIG, 26, 28, 100, 473, 504,
ISO/IEC 9899:2023 (E)
EILSEQ, 208, 323, 408–411, 427, 444–446,
472, 604 EOF, 204, 319, 325, 340, 341, 343–349,
412, 422–426, 428, 442, 490, 589, 604, 626, 627, 629–631, 633, 651, 653, 654, 656–658 EOL, 604 ERANGE, 208, 224, 236, 237, 357, 359, 361, 432–434, 472, 598, 599, 604 EXIT_FAILURE, 354, 366, 492, 604 EXIT_SUCCESS, 354, 366, 394, 492, 604 FE_ALL_EXCEPT, 92, 210, 473, 604 FE_DEC_DOWNWARD, 210, 214, 473, 511, 604 FE_DEC_TONEAREST, 210, 211, 214, 473, 511, 604 FE_DEC_TONEARESTFROMZERO, 210, 214, 473, 511, 604 FE_DEC_TOWARDZERO, 210, 214, 473, 511, 604 FE_DEC_UPWARD, 210, 214, 473, 511, 604 FE_DFL_ENV, 211, 473, 604 FE_DFL_MODE, 210, 218, 473, 509, 604 FE_DIVBYZERO, 210, 236, 473, 604 FE_DOWNWARD, 210, 473, 510, 604 FE_INEXACT, 210, 214, 473, 529, 604 FE_INVALID, 210, 217, 236, 473, 604 FE_OVERFLOW, 210, 214, 217, 236, 473, 604 FE_SNANS_ALWAYS_SIGNAL, 507, 510, 528, 531, 604 FE_TONEAREST, 149, 210, 473, 510, 604 FE_TONEARESTFROMZERO, i, 210, 473, 510, 604 FE_TOWARDZERO, 210, 473, 510, 524, 529, 604 FE_UNDERFLOW, 210, 220, 473, 604 FE_UPWARD, 8, 210, 473, 510, 528, 604 FILENAME_MAX, 319, 490, 604 FLT_DECIMAL_DIG, 26, 28, 473, 504, 604 FLT_DIG, 26, 28, 473, 504, 604 FLT_EPSILON, 27, 28, 473, 504, 604 FLT_EVAL_METHOD, i, 24, 25, 29, 92, 94, 100, 233, 473, 504, 535, 549, 558, 559, 596, 598, 604 FLT_HAS_SUBNORM, 25, 28, 453, 473, 604 FLT_IS_IEC_60559, 24, 28, 473, 604 FLT_MANT_DIG, 26, 28, 100, 473, 504, 604 FLT_MAX, 27, 28, 473, 504, 604 FLT_MAX_10_EXP, 27, 28, 473, 504, 604 FLT_MAX_EXP, 27, 28, 473, 504, 604 FLT_MIN, 27, 28, 473, 504, 604 FLT_MIN_10_EXP, 26, 27, 28, 473, 504, 604 FLT_MIN_EXP, 26, 28, 473, 504, 604
604 DBL_MAX, 27, 29, 473, 504, 604 DBL_MAX_10_EXP, 27, 29, 473, 504, 604 DBL_MAX_EXP, 27, 29, 473, 504, 604 DBL_MIN, 27, 29, 473, 504, 604 DBL_MIN_10_EXP, 26, 27, 29, 473, 504,
604 DBL_MIN_EXP, 26, 29, 473, 504, 604 DBL_NORM_MAX, ii, 27, 473, 504, 604 DBL_SNAN, 25, 473, 507, 604 DBL_TRUE_MIN, 27, 29, 473, 604 ddiv, 385, 577, 579, 612 DEC128_EPSILON, 30, 505, 604 DEC128_MANT_DIG, 30, 505, 604 DEC128_MAX, 30, 505, 604 DEC128_MAX_EXP, 30, 505, 604 DEC128_MIN, 30, 505, 604 DEC128_MIN_EXP, 30, 505, 604 DEC128_SNAN, 29, 604 DEC128_TRUE_MIN, 30, 505, 604 DEC32_EPSILON, 30, 504, 604 DEC32_MANT_DIG, 30, 504, 604 DEC32_MAX, 30, 505, 604 DEC32_MAX_EXP, 30, 505, 604 DEC32_MIN, 30, 505, 604 DEC32_MIN_EXP, 30, 505, 604 DEC32_SNAN, 29, 604 DEC32_TRUE_MIN, 30, 505, 604 DEC64_EPSILON, 30, 505, 604 DEC64_MANT_DIG, 30, 505, 604 DEC64_MAX, 30, 505, 604 DEC64_MAX_EXP, 30, 505, 604 DEC64_MIN, 30, 505, 604 DEC64_MIN_EXP, 30, 505, 604 DEC64_SNAN, 29, 604 DEC64_TRUE_MIN, 30, 99, 505, 604 DEC_EVAL_METHOD, iii, 24, 29, 62, 94,
233, 504, 535, 549, 550, 558, 596, 598, 604 DEC_INFINITY, 29, 234, 276, 454, 474, 604 DEC_NAN, 29, 234, 454, 474, 604 DECIMAL_DIG, i, 24, 26, 453, 473, 504, 604, 670 dfma, 385, 577, 612 DIVD, 560 DIVF, 559, 560 dmul, 385, 577, 612 dsqrt, 385, 577, 613 dsub, 385, 577, 579, 613 EDOM, 208, 236, 472, 604 Index
717
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
FP_ILOGB0, 235, 236, 250, 475, 605 FP_ILOGBNAN, 235, 236, 250, 475, 605 FP_INFINITE, 234, 475, 605 FP_INT_DOWNWARD, 234, 605 FP_INT_TONEAREST, 234, 605 FP_INT_TONEARESTFROMZERO, 234, 605 FP_INT_TOWARDZERO, 234, 605 FP_INT_UPWARD, 234, 264, 605 FP_LLOGB0, 236, 251, 605 FP_LLOGBNAN, 236, 251, 605 FP_NAN, 234, 475, 605 FP_NORMAL, 234, 475, 605 FP_SUBNORMAL, 234, 475, 605 FP_ZERO, 234, 475, 605
FLT_NORM_MAX, 27, 473, 504, 604 FLT_RADIX, 24, 26, 27, 28, 30, 61, 214,
219, 254, 331, 333, 357, 416, 418, 431, 473, 504, 509, 549–551, 558, 605 FLT_ROUNDS, 24, 210, 473, 503, 504, 506, 596, 605 FLT_SNAN, 25, 473, 507, 605 FLT_TRUE_MIN, 27, 28, 473, 605 FMAD, 560 FMAF, 560 FOPEN_MAX, 319, 323, 324, 490, 605, 622 FP_FAST_D, 560, 605 FP_FAST_D32ADDD128, 235, 605 FP_FAST_D32ADDD64, 235, 605 FP_FAST_D32DIVD128, 235, 605 FP_FAST_D32DIVD64, 235, 605 FP_FAST_D32FMAD128, 235, 605 FP_FAST_D32FMAD64, 235, 605 FP_FAST_D32MULD128, 235, 605 FP_FAST_D32MULD64, 235, 605 FP_FAST_D32SQRTD128, 235, 605 FP_FAST_D32SQRTD64, 235, 605 FP_FAST_D32SUBD128, 235, 605 FP_FAST_D32SUBD64, 235, 605 FP_FAST_D64ADDD128, 235, 605 FP_FAST_D64DIVD128, 235, 605 FP_FAST_D64FMAD128, 235, 605 FP_FAST_D64MULD128, 235, 605 FP_FAST_D64SQRTD128, 235, 605 FP_FAST_D64SUBD128, 235, 605 FP_FAST_DADDL, 235, 559, 605 FP_FAST_DDIVL, 235, 605 FP_FAST_DFMAL, 235, 605 FP_FAST_DMULL, 235, 605 FP_FAST_DSQRTL, 235, 605 FP_FAST_DSUBL, 235, 605 FP_FAST_F, 559, 560, 605 FP_FAST_FADD, 235, 559, 605 FP_FAST_FADDL, 235, 559, 605 FP_FAST_FDIV, 235, 605 FP_FAST_FDIVL, 235, 605 FP_FAST_FFMA, 235, 605 FP_FAST_FFMAL, 235, 605 FP_FAST_FMA, 235, 475, 559, 605 FP_FAST_FMAD, 559, 605 FP_FAST_FMAD128, 235, 605 FP_FAST_FMAD32, 235, 605 FP_FAST_FMAD64, 235, 605 FP_FAST_FMAF, 235, 475, 559, 605 FP_FAST_FMAL, 235, 475, 605 FP_FAST_FMUL, 235, 605 FP_FAST_FMULL, 235, 605 FP_FAST_FSQRT, 235, 605 FP_FAST_FSQRTL, 235, 605 FP_FAST_FSUB, 235, 605 FP_FAST_FSUBL, 235, 605 718
N3096
fpclassify, 238, 475, 509, 510, 614 HUGE_VAL, 233, 237, 357, 432, 475, 518,
614 HUGE_VAL_D, 559, 614 HUGE_VAL_D128, 234, 486, 614 HUGE_VAL_D32, 233, 234, 486, 614 HUGE_VAL_D64, 234, 486, 614 HUGE_VAL_F, 559, 614 HUGE_VALF, 233, 237, 357, 432, 475, 518,
614 HUGE_VALL, 233, 237, 357, 432, 475, 518,
614 I, 615 imaginary, 195, 471, 539, 540, 615 INFINITY, 25, 202, 234, 331, 356–359,
415, 430–433, 454, 473, 475, 507, 538, 539, 615 INT16_C, 605 INT16_MAX, 605 INT16_MIN, 605 INT16_WIDTH, 605 INT32_C, 605 INT32_MAX, 605 INT32_MIN, 605 INT32_WIDTH, 605 INT64_C, 605 INT64_MAX, 605 INT64_MIN, 605 INT64_WIDTH, 605 INT8_C, 605 INT8_MAX, 605 INT8_MIN, 605 INT8_WIDTH, 605 INT_MAX, 22, 38, 100, 166, 235, 236, 250, 474, 503, 591, 605 INT_MIN, 22, 38, 235, 236, 474, 503, 605 INT_WIDTH, 22, 264, 474, 503, 605 INTMAX_C, 318, 490, 605 INTMAX_MAX, 224, 317, 490, 605 INTMAX_MIN, 224, 317, 490, 605 INTMAX_WIDTH, 317, 490, 605 INTPTR_MAX, 317, 490, 605 Index
N3096
working draft — April 1, 2023
INTPTR_MIN, 317, 490, 605 INTPTR_WIDTH, 317, 490, 605 iscanonical, 24, 238, 475, 509, 510,
ISO/IEC 9899:2023 (E)
llquantexp, i, 385, 615 LONG_MAX, 22, 236, 251, 361, 434, 474,
503, 606 LONG_MIN, 22, 236, 361, 434, 474, 503,
605
606
iseqsig, 280, 281, 480, 509, 535, 605 isfinite, 238, 475, 509, 510, 538, 539,
LONG_WIDTH, 22, 474, 503, 615 MATH_ERREXCEPT, 236, 237, 357, 359,
606
432, 433, 475, 518, 598, 606
isgreater, 279, 480, 509, 606 isgreaterequal, 279, 480, 509, 517,
math_errhandling, 192, 236, 237, 357,
359, 432, 433, 475, 518, 582, 589, 598, 615, 673 MATH_ERRNO, 236, 237, 357, 359, 432, 433, 475, 598, 606 MB_CUR_MAX, 190, 354, 370, 371, 408– 411, 444, 492, 606, 638, 639, 664 MB_LEN_MAX, 22, 190, 354, 474, 503, 606 memchr, 378, 379, 455, 493, 606 MULD, 560 MULF, 559, 560 NAN, ii, 25, 234, 331, 356–359, 415, 430– 433, 454, 473, 475, 507 NDEBUG, 143, 191, 194, 471, 616 not, 225, 474, 616 not_eq, 225, 474, 616 NULL, 49, 118, 173, 227, 312, 319, 354, 374, 378, 381, 398, 407, 409, 410, 412, 437, 440, 443, 475, 489, 490, 492, 493, 495, 496, 574, 598, 616, 646, 663 offsetof, i, ii, 106, 312, 489, 590, 616 ONCE_FLAG_INIT, 354, 388, 495, 616 or, 225, 474, 616 or_eq, 225, 474, 616 PRIcMAX, 222 PRIcPTR, 222 PRId32, 606 PRId64, 606 PRIdFAST32, 222, 606 PRIdFAST64, 606 PRIdLEAST32, 606 PRIdLEAST64, 606 PRIdMAX, 222, 474, 606 PRIdPTR, 222, 474, 606 PRIi32, 606 PRIi64, 606 PRIiFAST32, 606 PRIiFAST64, 606 PRIiLEAST32, 606 PRIiLEAST64, 606 PRIiMAX, 222, 474, 606 PRIiPTR, 222, 474, 606 PRIo32, 606 PRIo64, 606 PRIoFAST32, 606 PRIoFAST64, 606 PRIoLEAST32, 606 PRIoLEAST64, 606
531, 606 isinf, 238, 239, 475, 509, 510, 524, 538,
539, 606 isless, 279, 280, 480, 509, 517, 606 islessequal, 280, 480, 509, 606 islessgreater, 280, 480, 606 isnan, 239, 475, 509, 510, 531, 538, 539, 606 isnormal, 239, 475, 509, 510, 606 issignaling, 239, 240, 475, 509, 510, 606 issubnormal, 240, 475, 509, 510, 606 isunordered, 280, 480, 509, 606 iszero, 240, 475, 509, 510, 606 kill_dependency, 16, 295, 296, 487, 615 L_tmpnam, 320, 325, 490, 615 L_tmpnam_s, 491, 615, 621, 622 LC_ALL, 227, 228, 231, 475, 606 LC_COLLATE, 227, 228, 377, 436, 475, 606 LC_CTYPE, 227, 228, 354, 369–371, 442, 447, 450–452, 475, 593, 594, 606, 638, 639 LC_MONETARY, 227, 228, 231, 475, 606 LC_NUMERIC, 227, 228, 231, 475, 606 LC_TIME, 227, 228, 402, 404, 475, 606 LDBL_DECIMAL_DIG, 26, 453, 473, 504, 606 LDBL_DIG, 26, 473, 504, 606 LDBL_EPSILON, 27, 473, 504, 606 LDBL_HAS_SUBNORM, 25, 453, 473, 606 LDBL_IS_IEC_60559, 24, 473, 606 LDBL_MANT_DIG, 26, 473, 504, 606 LDBL_MAX, 27, 473, 504, 606 LDBL_MAX_10_EXP, 27, 473, 504, 606 LDBL_MAX_EXP, 27, 473, 504, 606 LDBL_MIN, 27, 473, 504, 606 LDBL_MIN_10_EXP, 26, 27, 473, 504, 606 LDBL_MIN_EXP, 26, 473, 504, 606 LDBL_NORM_MAX, 27, 473, 504, 606 LDBL_SNAN, 25, 473, 507, 606 LDBL_TRUE_MIN, 27, 473, 606 LLONG_MAX, 22, 361, 434, 474, 503, 606 LLONG_MIN, 22, 277, 361, 434, 474, 503, 606 LLONG_WIDTH, 22, 474, 503, 615 Index
719
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
SIGABRT, 284, 365, 486, 607 SIGFPE, 236, 284, 285, 486, 589, 594, 602,
PRIoMAX, 222, 474, 607 PRIoPTR, 222, 474, 607 PRIu32, 607 PRIu64, 607 PRIuFAST32, 607 PRIuFAST64, 607 PRIuLEAST32, 607 PRIuLEAST64, 607 PRIuMAX, 222, 474, 607 PRIuPTR, 222, 474, 607 PRIX32, 607 PRIX64, 607 PRIXFAST32, 607 PRIXFAST64, 607 PRIXLEAST32, 607 PRIXLEAST64, 607 PRIXMAX, 222, 474, 607 PRIxMAX, 222, 223, 474 PRIXPTR, 222, 474, 607 PRIxPTR, 222, 474 PTRDIFF_MAX, 490, 607 PTRDIFF_MIN, 490, 607 PTRDIFF_WIDTH, 317, 616 putc, 320, 348, 491, 616 putchar, 320, 348, 491, 616 RAND_MAX, 354, 361, 362, 492, 607 RSIZE_MAX, 490, 607, 621, 622, 623, 627,
607 SIGILL, 284, 285, 486, 589, 594, 607 SIGINT, 284, 486, 607 signbit, iv, 239, 475, 509, 510, 530, 617 SIGSEGV, 284, 285, 486, 589, 594, 607 SIGTERM, 284, 486, 607 SIZE_MAX, 40, 490, 607, 621 SIZE_WIDTH, 318, 490, 617 SQRTD, 560 SQRTF, 560 stdc_bit_ceil, 309, 489, 607 stdc_bit_floor, 308, 489, 607 stdc_bit_width, 308, 489, 607 stdc_count_ones, 307, 489, 607 stdc_count_zeros, 306, 488, 607 stdc_first_leading_one, 305, 488,
607 stdc_first_leading_zero, 305, 488,
607 stdc_first_trailing_one, 306, 488,
607 stdc_first_trailing_zero,
305,
488, 607 stdc_has_single_bit, 307, 489, 607 stdc_leading_ones, 303, 488, 607 stdc_leading_zeros, 303, 488, 608 stdc_trailing_ones, 304, 488, 608 stdc_trailing_zeros, 304, 488, 608 strchr, 378, 379, 455, 493, 608 strpbrk, 378, 379, 455, 493, 608 strrchr, 378, 379, 380, 455, 493, 608 strstr, 378, 380, 455, 494, 608 SUBD, 560 SUBF, 559, 560 TIME_ACTIVE, 398, 401, 402, 455, 496,
628, 631–633, 635, 637–646, 648, 649, 652, 654, 655, 658–665 SCHAR_MAX, 22, 474, 503, 607 SCHAR_MIN, 22, 39, 474, 503, 607 SCHAR_WIDTH, 21, 474, 503, 617 SCNcMAX, 222 SCNcPTR, 222 SCNdMAX, 222, 474, 607 SCNdPTR, 222, 474, 607 SCNiMAX, 222, 474, 607 SCNiPTR, 222, 474, 607 SCNoMAX, 222, 474, 607 SCNoPTR, 222, 474, 607 SCNuMAX, 222, 474, 607 SCNuPTR, 222, 474, 607 SCNxMAX, 222, 474, 607 SCNxPTR, 222, 474, 607 SEEK_CUR, 320, 351, 490, 617 SEEK_END, 320, 323, 351, 490, 617 SEEK_SET, 320, 351, 352, 490, 592, 617 SHRT_MAX, 22, 474, 503, 607 SHRT_MIN, 22, 474, 503, 607 SHRT_WIDTH, 22, 474, 503, 617 SIG_ATOMIC_MAX, 490, 607 SIG_ATOMIC_MIN, 490, 607 SIG_ATOMIC_WIDTH, 317, 490, 607 SIG_DFL, 284, 285, 486, 598, 607 SIG_ERR, 284, 285, 486, 590, 607 SIG_IGN, 284, 285, 486, 595, 607 720
N3096
599, 608 TIME_MONOTONIC, 398, 401, 455, 496,
599, 608 TIME_THREAD_ACTIVE, 398, 401, 455,
496, 599, 608 TIME_UTC, 391, 392, 395, 398, 401, 495,
600, 608 TMP_MAX, 320, 324, 325, 490, 608 TMP_MAX_S , 491, 618, 621, 622, 623 TSS_DTOR_ITERATIONS, 388, 394, 495,
618 UCHAR_MAX, 22, 474, 503, 609 UCHAR_WIDTH, 21, 474, 503, 618 UINT16_C, 609 UINT16_MAX, 609 UINT16_WIDTH, 609 UINT32_C, 609 UINT32_MAX, 609 UINT32_WIDTH, 609
Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
__bool_true_false_are_defined ,
UINT64_C, 318, 609 UINT64_MAX, 609 UINT64_WIDTH, 609 UINT8_C, 609 UINT8_MAX, 609 UINT8_WIDTH, 609 UINT_MAX, 22, 100, 109, 110, 166, 474,
310, 454, 489, 610 gets, 614, 633, 672
stream stderr, 184, 320, 321, 322, 327, 344, 424,
490, 602, 617 stdin, 320, 321, 322, 327, 340–343, 348,
422, 423, 426, 428, 490, 617, 626, 627, 633, 657 stdout, 320, 321, 322, 327, 334–336, 342, 348, 349, 418, 426, 429, 490, 617 structure member currency_symbol, 227, 229, 231, 612 decimal_point, 227, 229, 612 frac_digits, 227, 229, 231, 614 grouping, 227, 229, 230, 614 int_curr_symbol, 227, 230, 231, 615 int_frac_digits, 227, 230, 231, 615 int_n_cs_precedes, 227, 230, 231, 615 int_n_sep_by_space, 227, 230, 231, 615 int_n_sign_posn, 227, 230, 231, 615 int_p_cs_precedes, 227, 230, 231, 615 int_p_sep_by_space, 227, 230, 231, 615 int_p_sign_posn, 227, 230, 231, 615 mon_decimal_point, 227, 229, 231, 616 mon_grouping, 227, 229–231, 616 mon_thousands_sep, 227, 229, 231, 616 n_cs_precedes, 227, 229, 231, 616 n_sep_by_space, 227, 229–231, 616 n_sign_posn, 227, 230, 231, 616 negative_sign, 227, 229–231, 616 p_cs_precedes, 227, 229, 231, 232, 616 p_sep_by_space, 227, 229–232, 616 p_sign_posn, 227, 229, 231, 232, 616 positive_sign, 227, 229–231, 616 thousands_sep, 227, 229, 617 tm_hour, 399, 400, 403, 405, 618, 648 tm_isdst, 399, 400, 405, 618 tm_mday, 399, 400, 401, 403, 404, 618, 648 tm_min, 399, 400, 403, 405, 618, 648 tm_mon, 399, 400, 401, 403–405, 618, 648 tm_sec, 399, 400, 403, 405, 618, 649 tm_wday, 399, 400, 401, 403–405, 618, 648 tm_yday, 399, 400, 401, 405, 618 tm_year, 399, 400, 401, 403–405, 618, 649 tv_nsec, 399, 401, 618 tv_sec, 399, 401, 618 structure type lconv, 227, 228, 475, 615 timespec, 390, 392, 395, 398, 399, 401, 402, 495, 496, 617
503, 609 UINT_WIDTH, 22, 264, 474, 503, 609 UINTMAX_C, 318, 490, 609 UINTMAX_MAX, 223, 224, 317, 490, 512,
609 UINTMAX_WIDTH, 317, 490, 609 UINTPTR_MAX, 317, 490, 609 UINTPTR_WIDTH, 317, 490, 609 ULLONG_MAX, 22, 100, 110, 361, 434, 474,
503, 609 ULLONG_WIDTH, 22, 474, 503, 618 ULONG_MAX, 22, 361, 434, 474, 503, 609 ULONG_WIDTH, 22, 474, 503, 618 unreachable, v, xiv, 312, 313, 489, 590,
618, 672 USHRT_MAX, 22, 109, 474, 503, 609 USHRT_WIDTH, 22, 474, 503, 618 WCHAR_MAX, 412, 490, 496, 609 WCHAR_MIN, 412, 490, 496, 609 WCHAR_WIDTH, 318, 412, 490, 618 wcschr, 438, 455, 497, 609 wcspbrk , 438, 439, 455, 497, 609 wcsrchr , 438, 439, 455, 497, 609 wcsstr, 438, 439, 455, 497, 609 WEOF , 412, 427–429, 442, 447, 496, 499,
594, 618 WINT_MAX, 490, 609 WINT_MIN, 490, 609 WINT_WIDTH , 318, 490, 618 wmemchr , 438, 440, 441, 455, 497, 618 XADDD, 560 XADDF, 560 XDIVD, 560 XDIVF, 560 XFMAD, 560 XFMAF, 560 XMULD, 560 XMULF, 560 xor, 225, 474, 618 xor_eq, 225, 474, 618 XSQRTD, 560 XSQRTF, 560 XSUBD, 560 XSUBF, 560
obsolete __STDC_IEC_559_COMPLEX__ , 23, 187,
188–190, 536, 610 __STDC_IEC_559__ , 23, 187, 189, 190,
485, 506, 610 Index
721
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
atomic_ushort, 297, 487, 604 atomic_wchar_t, 298, 487, 604 bool, 45, 101 char, 101 char16_t, i, iv, 65, 67, 136, 186, 298,
tm, 398, 399, 400, 402–404, 412, 441, 495–
497, 618, 648, 649, 650 summary, 471 terms, 190 type _BitInt , 101 _Complex types, 101, 195 _Decimal32_t , 233, 486, 598, 609 _Decimal64_t , 233, 486, 598, 609 _Float128_t , 559, 609 _Float16_t , 559, 610 _Float32_t , 559, 610 _Float64_t , 559, 610 _Imaginary types, 195 _t , 315, 316, 318, 454, 490, 558, 559, 603 atomic_bool, 297, 298, 487, 603 atomic_char, 297, 487, 603 atomic_char16_t, 298, 487, 603 atomic_char32_t, 298, 487, 603 atomic_char8_t, 297, 487, 603 atomic_flag, 292, 293, 300, 301, 487, 603 atomic_int, 293, 297, 487, 603 atomic_int_fast16_t, 298, 487, 603 atomic_int_fast32_t, 298, 487, 603 atomic_int_fast64_t, 298, 487, 603 atomic_int_fast8_t, 298, 487, 603 atomic_int_least16_t, 298, 487, 603 atomic_int_least32_t, 298, 487, 603 atomic_int_least64_t, 298, 487, 603 atomic_int_least8_t, 298, 487, 603 atomic_intmax_t, 298, 487, 603 atomic_intptr_t, 298, 487, 603 atomic_llong, 297, 487, 603 atomic_long, 297, 487, 603 atomic_ptrdiff_t, 298, 487, 603 atomic_schar, 297, 487, 603 atomic_short, 297, 487, 603 atomic_size_t, 298, 487, 603 atomic_uchar, 297, 487, 603 atomic_uint, 297, 487, 603 atomic_uint_fast16_t, 298, 487, 603 atomic_uint_fast32_t, 298, 487, 603 atomic_uint_fast64_t, 298, 487, 603 atomic_uint_fast8_t, 298, 487, 604 atomic_uint_least16_t, 298, 487, 604 atomic_uint_least32_t, 298, 487, 604 atomic_uint_least64_t, 298, 487, 604 atomic_uint_least8_t, 298, 487, 604 atomic_uintmax_t, 298, 487, 603 atomic_uintptr_t, 298, 487, 603 atomic_ullong, 297, 487, 604 atomic_ulong, 297, 487, 604 722
N3096
407, 409, 496, 595, 611 char32_t, iv, 65, 67, 136, 186, 298, 407,
410, 411, 496, 595, 612 char8_t, v, 65, 67, 99, 297, 407, 408, 496,
612 clock_t, 398, 399, 495, 599, 612 cnd_t, 388, 389–391, 495, 604 constraint_handler_t, 493, 612, 634 div_t, 139, 354, 369, 492, 612 double, 101 double_t, 233, 475, 515, 558, 559, 598,
601, 612 enum, 101 errno_t, 472, 491, 493, 494, 496, 498,
613, 620, 621, 622–624, 634, 635, 637– 640, 641, 642–644, 646, 647, 648, 649, 650, 658–661, 663–665 femode_t, 209, 210, 217, 218, 473, 613 fenv_t, 92, 209, 211, 219, 220, 473, 528, 613 fexcept_t, 209, 215, 216, 473, 589, 613 FILE, 173, 319, 320, 322, 324, 325, 327, 328, 336, 344, 346–353, 413, 419, 424, 426–429, 490, 491, 497, 498, 591, 613, 622–625, 629, 630, 650, 651, 653, 654 float, 101 float_t, 233, 475, 515, 558, 559, 598, 601, 613 fpos_t, 319, 321, 350, 351, 490, 491, 614 generic_count_type, 614 generic_return_type, 303–308, 488, 489, 614 generic_value_type, 303–309, 488, 489, 614 imaxdiv_t, 222, 223, 474, 615 int, 46, 59, 101 int16_t, 605 int32_t, 605 int64_t, 605 int8_t, 315, 605 int_fast16_t, 298, 316, 605 int_fast32_t, 222, 298, 316, 605 int_fast64_t, 298, 316, 605 int_fast8_t, 298, 316, 605 int_least16_t, 298, 316, 605 int_least32_t, 298, 315, 316, 605 int_least64_t, 298, 316, 605 int_least8_t, 298, 316, 605 intmax_t, iii, 22, 166, 223, 224, 298, 316, 318, 330, 337, 414, 420, 474, 490, 605, 671, 673 Index
N3096
working draft — April 1, 2023
intptr_t, 298, 316, 490, 605 jmp_buf, 282, 283, 486, 615, 668 ldiv_t, 354, 369, 492, 615 lldiv_t, 354, 369, 492, 615 long_double_t, 558, 559, 615 max_align_t, 43, 44, 312, 489, 616 mbstate_t, 321–323, 332, 339, 351, 407,
ISO/IEC 9899:2023 (E)
void , 49, 101 wchar_t, 5, 44, 64–67, 136, 187, 224, 298,
312, 318, 329, 332, 334, 337, 339, 342, 354, 370–372, 407, 412, 413, 414, 417– 430, 432–441, 443–445, 447, 470, 474, 489, 492, 493, 496–498, 573, 575, 583, 594, 595, 618, 638–640, 650–665 wctrans_t , 447, 451, 452, 499, 618 wctype_t , 447, 450, 451, 499, 618 wint_t , 318, 329, 332, 334, 412, 414, 417, 426–429, 442, 447, 448–451, 496, 497, 499, 594, 618 use of functions, 192 lifetime, 36 limit embed parameter, 164 limit embed parameter, 164, 168, 170, 171, 173, 174–177, 615 line buffered, 322 line buffered stream, 322 line number, 184, 186 line preprocessing directive, 184 lines, 10, 321 preprocessing directive, 163 linkage, 35, 96, 122, 126, 158, 160, 189 literal encoding, 44 little-endian, 302 ll format modifier, 329, 337, 414, 420 llabs function, 369, 492, 615 lldiv function, 134, 354, 369, 492, 615 lldiv_t type, 354, 369, 492, 615 llogb function, 236, 251, 476, 508, 523, 615 llogb type-generic macro, 384 llogbd function, 563, 615 llogbd128 function, 251, 481, 615 llogbd32 function, 251, 481, 615 llogbd64 function, 251, 481, 615 llogbf function, 251, 476, 563, 615 llogbl function, 251, 476, 615 LLONG_MAX macro, 22, 361, 434, 474, 503, 606 LLONG_MIN macro, 22, 277, 361, 434, 474, 503, 606 LLONG_WIDTH macro, 22, 474, 503, 615 llquantexp macro, i, 385, 615 llquantexpd function, 511, 569, 615 llquantexpd identifier prefix, 276, 277, 385 llquantexpd128 function, 277, 485, 615 llquantexpd32 function, 277, 485, 615 llquantexpd64 function, 277, 485, 615 llrint function, 261, 478, 512, 528, 529, 583, 615 llrint type-generic macro, 384 llrintd function, 566, 615 llrintd128 function, 261, 483, 615 llrintd32 function, 261, 483, 615 llrintd64 function, 261, 483, 615 llrintf function, 261, 478, 566, 615
408–411, 412, 417, 421, 442–445, 496, 498, 594, 600, 616, 663–665 memory_order, 292, 293, 296, 298–301, 454, 487, 606 mtx_t, 388, 390–393, 495, 606 nullptr_t, vi, xiv, 40, 45, 49, 50, 82, 83, 86, 87, 89, 91, 289, 312, 313, 314, 489, 590, 616, 671 once_flag, 354, 388, 389, 495, 616 ptrdiff_t, iv, 84, 292, 298, 312, 313, 317, 330, 337, 414, 420, 489, 585, 616, 671 QChar, 378, 616 QVoid, 378, 616 QWchar_t, 438, 616 rsize_t, 489, 491, 493, 494, 496, 498, 617, 621, 622, 625–628, 631–633, 634, 635–640, 641, 642–646, 648, 649, 650, 651, 652, 654, 655, 658–665 sig_atomic_t, 13, 284, 285, 317, 486, 581, 590, 617 signed, 101 thrd_start_t, 388, 393, 495, 608 thrd_t, 388, 393, 394, 495, 608 time_t, 398, 399, 400, 401, 403, 404, 495, 496, 599, 618, 649, 650 tss_dtor_t, 388, 395, 495, 609 tss_t, 388, 395, 396, 495, 609 uint16_t, 609 uint32_t, 609 uint64_t, 264, 609 uint8_t, 609 uint_fast16_t, 298, 316, 609 uint_fast32_t, 298, 316, 609 uint_fast64_t, 298, 316, 609 uint_fast8_t, 298, 316, 609 uint_least16_t, 298, 315, 316, 407, 609 uint_least32_t, 298, 316, 407, 609 uint_least64_t, 298, 316, 318, 609 uint_least8_t, 298, 316, 609 uintmax_t, 22, 166, 223, 224, 298, 316, 318, 330, 337, 414, 420, 474, 490, 609, 671, 673 uintptr_t, 298, 316, 490, 609 unsigned, 101, 329, 337, 414, 420 va_list , 288, 289–291, 344–346, 424– 426, 487, 490, 491, 497, 498, 590, 592, 618, 629–632, 653–656 Index
723
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
log2p1 type-generic macro, 384 log2p1d function, 564, 615 log2p1d128 function, 253, 482, 615 log2p1d32 function, 253, 482, 615 log2p1d64 function, 253, 482, 615 log2p1f function, 253, 477, 564, 615 log2p1l function, 253, 477, 615
llrintl function, 261, 478, 615 llround function, 262, 478, 508, 529, 583, 615 llround functions, 262 llround type-generic macro, 384 llroundd function, 566, 615 llroundd128 function, 262, 483, 615 llroundd32 function, 262, 483, 615 llroundd64 function, 262, 483, 615 llroundf function, 262, 478, 566, 615 llroundl function, 262, 478, 615
logarithmic functions complex, 199, 544 real, 247, 522 logb function, 250, 251, 253, 254, 477, 508, 522, 524, 538, 570, 615 logb type-generic macro, 384 logbd function, 564, 615 logbd128 function, 253, 482, 615 logbd32 function, 253, 482, 615 logbd64 function, 253, 482, 615 logbf function, 253, 477, 564, 615 logbl function, 253, 477, 615 logd function, 563, 615 logd128 function, 251, 481, 615 logd32 function, 251, 481, 615 logd64 function, 251, 481, 615 logf function, 251, 476, 563, 615 logical operators AND (&&), 16, 88 negation (!), 81 OR (||), 88 OR (||), 16 logical source lines, 10 logl function, 251, 477, 615 logp1 function, ii, 252, 253, 477, 511, 523, 615 logp1 type-generic macro, 384 logp1d function, 564, 615 logp1d128 function, 252, 482, 615 logp1d32 function, 252, 482, 615 logp1d64 function, 252, 482, 615 logp1f function, 252, 477, 563, 615 logp1l function, 252, 477, 615 long double _Complex type, 39 long double _Complex type conversion, 46, 47 long double _Imaginary type, 536 long double suffix, l or L, 61 long double type, 38, 101 long double type conversion, 46, 47 long int type, 37, 101 long int type conversion, 45–47 long integer suffix, l or L, 59 long long int type, 37, 101 long long int type conversion, 45–47 long long integer suffix, ll or LL, 59 long_double_t type, 558, 559, 615 LONG_MAX macro, 22, 236, 251, 361, 434, 474, 503, 606
local, 147 local time, 398 locale, 3 locale-specific behavior, 3, 600 localeconv function, 228, 231, 475, 589, 615 localization header, 227, 453 localtime function, 400, 402, 403, 404, 496, 615 localtime_r function, 404, 496, 615, 670 localtime_s function, 496, 615, 649, 650 log function, 236, 251, 252, 384, 476, 511, 523, 615 log type-generic macro, 384 log10 function, 251, 252, 477, 511, 523, 615 log10 type-generic macro, 384 log10d function, 563, 615 log10d128 function, 252, 482, 615 log10d32 function, 251, 482, 615 log10d64 function, 251, 482, 615 log10f function, 251, 477, 563, 615 log10l function, 251, 477, 615 log10p1 function, 252, 477, 511, 523, 615 log10p1 type-generic macro, 384 log10p1d function, 563, 615 log10p1d128 function, 252, 482, 615 log10p1d32 function, 252, 482, 615 log10p1d64 function, 252, 482, 615 log10p1f function, 252, 477, 563, 615 log10p1l function, 252, 477, 615 log1p function, 252, 253, 477, 511, 523, 615 log1p type-generic macro, 384 log1pd function, 563, 564, 615 log1pd128 function, 252, 482, 615 log1pd32 function, 252, 482, 615 log1pd64 function, 252, 482, 615 log1pf function, 252, 477, 563, 615 log1pl function, 252, 477, 615 log2 function, 253, 477, 511, 523, 615 log2 type-generic macro, 384 log2d function, 564, 615 log2d128 function, 253, 482, 615 log2d32 function, 253, 482, 615 log2d64 function, 253, 482, 615 log2f function, 253, 477, 564, 615 log2l function, 253, 477, 615 log2p1 function, 252, 253, 477, 511, 524, 615 724
N3096
Index
N3096
working draft — April 1, 2023
LONG_MIN macro, 22, 236, 361, 434, 474, 503,
ISO/IEC 9899:2023 (E)
max_align_t type, 43, 44, 312, 489, 616
606
maximal munch, 51 maximum functions, 268, 531 maybe_unused attribute, ii, iv, 141, 143, 616, 669, 670 MB_CUR_MAX macro, 190, 354, 370, 371, 408– 411, 444, 492, 606, 638, 639, 664 MB_LEN_MAX macro, 22, 190, 354, 474, 503, 606 mblen function, ii, 370, 443, 492, 616 mbrlen function, 443, 498, 616 mbrtoc16 function, 408, 409, 496, 616 mbrtoc32 function, 410, 496, 616 mbrtoc8 function, 407, 408, 496, 616, 670 mbrtowc function, 323, 339, 417, 418, 442, 443, 444, 445, 498, 616, 639, 665 mbsinit function, 442, 443, 498, 616 mbsrtowcs function, 442, 445, 498, 616, 664 mbsrtowcs_s function, 498, 616, 664, 665 mbstate_t type, 321–323, 332, 339, 351, 407, 408–411, 412, 417, 421, 442–445, 496, 498, 594, 600, 616, 663–665 mbstowcs function, 68, 371, 430, 444, 492, 616 mbstowcs_s function, 493, 616, 639, 640 mbtowc function, 66, 369, 370, 371, 443, 492, 616 mem identifier prefix, 455, 603 memalignment function, 8, 372, 492, 606 member access operators (. and-> ), 75 member alignment, 104 members, 36 memccpy function, ii, 374, 493, 606, 670 memchr macro, 378, 379, 455, 493, 606 memcmp function, 41, 173, 299, 377, 493, 606 memcpy function, vii, 41, 71, 170, 193, 293, 299, 374, 493, 509, 606 memcpy_s function, 494, 606, 641 memmove function, 71, 374, 375, 493, 509, 588, 606 memmove_s function, 494, 606, 641, 642 memory location, 5 memory management functions, 362 memory_ identifier prefix, 454 memory_order_ identifier prefix, 454 memory_order type, 292, 293, 296, 298–301, 454, 487, 606 memory_order_acq_rel constant, 294, 295, 296, 298, 299, 301, 487, 606 memory_order_acquire constant, 294, 296, 298, 301, 487, 606 memory_order_consume constant, 294, 296, 298, 487, 606 memory_order_relaxed constant, 148, 294, 295, 296, 487, 606 memory_order_release constant, 294, 296, 299, 487, 606 memory_order_seq_cst constant, 18, 41, 77,
LONG_WIDTH macro, 22, 474, 503, 615 longjmp function, 282, 283, 366, 367, 486, 589,
592, 615, 668 loop body, 154 low-order bit, 4 lowercase letters, 18 lrint function, 261, 478, 512, 528, 529, 583, 615 lrint type-generic macro, 384 lrintd function, 566, 615 lrintd128 function, 261, 483, 615 lrintd32 function, 261, 483, 615 lrintd64 function, 261, 483, 615 lrintf function, 261, 478, 566, 615 lrintl function, 261, 478, 615 lround function, 262, 478, 508, 529, 583, 615 lround functions, 262 lround type-generic macro, 384 lroundd function, 566, 615 lroundd128 function, 262, 483, 615 lroundd32 function, 262, 483, 615 lroundd64 function, 262, 483, 615 lroundf function, 262, 478, 566, 615 lroundl function, 262, 478, 615 lvalue, 48, 77, 80, 90, 115 lvalue conversion, 48, 90, 92 macro argument substitution, 178 macro definition library function, 192 macro invocation, 178 macro name, 177 length, 21 predefined, 186, 189 redefinition, 177 scope, 182 macro parameter, 178 macro preprocessor, 162 macro replacement, 177 magnitude, complex, 200 manipulation functions complex, 201 real, 265, 530 matching failure, 424–426, 654, 656, 657 math rounding direction macros, 234 MATH_ identifier prefix, 454, 602 MATH_ERREXCEPT macro, 236, 237, 357, 359, 432, 433, 475, 518, 598, 606 math_errhandling macro, 192, 236, 237, 357, 359, 432, 433, 475, 518, 582, 589, 598, 615, 673 MATH_ERRNO macro, 236, 237, 357, 359, 432, 433, 475, 598, 606 mathematics header, 233, 453 MAX identifier suffix, 140 Index
725
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
multibyte/wide character conversion functions, 369, 638 extended, 442, 663 restartable, 407, 443, 663 multibyte/wide string conversion functions, 371, 639 restartable, 444, 664 multidimensional array, 74 multiplication assignment operator (*=), 92 multiplication operator (*), 83, 537 multiplicative expressions, 83, 537 multiply and round to narrower type, 274
91, 92, 292, 294, 296, 487, 606 memset explicit, 381 memset function, vii, 293, 381, 494, 606, 646 memset_explicit function, v, 381, 494, 606, 671 memset_s function, 494, 606, 646 minimum functions, 268, 531 minus operator, unary, 81, 510 miscellaneous functions string, 381, 646 wide string, 441, 663 mktime function, 400, 495, 616 modf family, 32, 254, 383 modf function, 254, 383, 384, 477, 524, 616 modfd function, 564, 616 modfd128 function, 254, 482, 616 modfd32 function, 254, 482, 616 modfd64 function, 254, 482, 616 modff function, 254, 477, 564, 616 modfl function, 254, 477, 616 modifiable lvalue, 48 modification order, 16 modulus functions, 254 modulus, complex, 200 mon_decimal_point structure member, 227, 229, 231, 616 mon_grouping structure member, 227, 229– 231, 616 mon_thousands_sep structure member, 227, 229, 231, 616 most significant index, 302 mtx_ identifier prefix, 455, 603 mtx_destroy function, 391, 495, 606 mtx_init function, 388, 389, 391, 392, 495, 606 mtx_lock function, 392, 495, 593, 606 mtx_plain constant, 388, 392, 495, 606 mtx_recursive constant, 388, 392, 495, 606 mtx_t type, 388, 390–393, 495, 606 mtx_timed constant, 389, 392, 495, 606 mtx_timedlock function, 392, 495, 593, 606 mtx_trylock function, 392, 393, 495, 606 mtx_unlock function, 392, 393, 495, 593, 606 muld function, 569, 616 MULD macro, 560 mulf function, 568, 569, 616 MULF macro, 559, 560 multibyte character, 4, 19, 64 multibyte conversion functions wide character, 369, 638 extended, 442, 663 restartable, 407, 443, 663 wide string, 371, 639 restartable, 444, 664 multibyte string, 190 726
N3096
n-char sequence, 356 n-wchar sequence, 431 n_cs_precedes structure member, 227, 229, 231, 616 n_sep_by_space structure member, 227, 229– 231, 616 n_sign_posn structure member, 227, 230, 231, 616 name external, 21, 55, 189 file, 322 internal, 21, 55 label, 36 structure/union member, 36 name spaces, 36 named constant, 94 named label, 152 NaN, 23 nan function, 266, 331, 415, 479, 507, 530, 616 NAN macro, ii, 25, 234, 331, 356–359, 415, 430– 433, 454, 473, 475, 507 nand function, 567, 616 nand128 function, 266, 484, 616 nand32 function, 266, 484, 616 nand64 function, 266, 484, 616 nanf function, 266, 479, 567, 616 nanl function, 266, 479, 616 NDEBUG macro, 143, 191, 194, 471, 616 nearbyint function, 260, 261, 478, 510, 512, 524, 528, 616 nearbyint type-generic macro, 384 nearbyintd function, 566, 616 nearbyintd128 function, 260, 483, 616 nearbyintd32 function, 260, 483, 616 nearbyintd64 function, 260, 483, 616 nearbyintf function, 260, 478, 565, 616 nearbyintl function, 260, 478, 616 nearest integer functions, 260, 527 negation operator (!), 81 negative zero, 266 negative_sign structure member, 227, 229– 231, 616 new line, 20 new-line character, 10, 19, 51, 163, 184 Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
437, 440, 443, 475, 489, 490, 492, 493, 495, 496, 574, 598, 616, 646, 663 null pointer, 49 null pointer constant, 49 null preprocessing directive, 186 null statement, 152 null wide character, 190 nullptr_t type, vi, xiv, 40, 45, 49, 50, 82, 83, 86, 87, 89, 91, 289, 312, 313, 314, 489, 590, 616, 671 nullptr_t type conversions, 50 number classification macros, 234, 238 numeric conversion functions, 223, 354 wide string, 224, 430 numerical limits, 21
new-line escape sequence (\n), 20, 65, 206 nextafter function, 266, 267, 386, 479, 510, 530, 616 nextafter type-generic macro, 384 nextafterd function, 567, 616 nextafterd128 function, 266, 484, 616 nextafterd32 function, 266, 484, 616 nextafterd64 function, 266, 484, 616 nextafterf function, 266, 479, 567, 616 nextafterl function, 266, 479, 616 nextdown function, 268, 479, 507, 531, 616 nextdown type-generic macro, 384 nextdownd function, 567, 616 nextdownd128 function, 268, 484, 616 nextdownd32 function, 268, 484, 616 nextdownd64 function, 268, 484, 616 nextdownf function, 268, 479, 567, 616 nextdownl function, 268, 479, 616 nexttoward function, 267, 479, 510, 530, 616 nexttoward type-generic macro, 384 nexttowardd128 function, 267, 484, 616 nexttowardd32 function, 267, 484, 616 nexttowardd64 function, 267, 484, 616 nexttowardf function, 267, 386, 479, 616 nexttowardl function, 267, 479, 616 nextup function, 267, 479, 507, 531, 616 nextup type-generic macro, 384 nextupd function, 567, 616 nextupd128 function, 267, 484, 616 nextupd32 function, 267, 484, 616 nextupd64 function, 267, 484, 616 nextupf function, 267, 479, 567, 616 nextupl function, 267, 479, 616 no linkage, 35 no-return function, 123 nodiscard attribute, ii, 140, 141, 142, 143, 616, 669, 670 non-canonical, 24 non-canonical representation, 24 non-graphic characters, 20, 65 non-local jumps header, 282 non-stop floating-point control mode, 219 non-value representation, 7, 41, 49, 75 noreturn attribute, 123, 141, 146, 283, 364– 367, 373, 394, 486, 492, 493, 495, 616, 669, 670 norm, complex, 200 normalized, 648 normalized broken-down time, 648 normalized floating-point numbers, 23 not macro, 225, 474, 616 not_eq macro, 225, 474, 616 null character (\0), 18, 66, 67 padding of binary stream, 321 NULL macro, 49, 118, 173, 227, 312, 319, 354, 374, 378, 381, 398, 407, 409, 410, 412,
O format modifier, 405
object, 6 object representation, 41 object type, 37 object types, 37 object-like macro, 178 observable, 147 observable behavior, 13 observed, 147 obsolescence, xix, 189, 453 octal constant, 57 octal digit, 58, 65 octal-character escape sequence (\octal digits), 64 OFF pragma, 149, 538, 616 offsetof macro, i, ii, 106, 312, 489, 590, 616 ON pragma, 92, 212, 217, 218, 220, 514, 515, 524, 528, 530, 616 on-off switch, 185 once_flag type, 354, 388, 389, 495, 616 ONCE_FLAG_INIT macro, 354, 388, 495, 616 opening, 322 operand, 68, 71 operating system, 11, 367 operations on files, 323, 622 operator, 68 operators, 71 additive, 83 alignof, 81 assignment, 90 associativity, 71 equality, 86 multiplicative, 83, 537 postfix, 73 precedence, 71 preprocessing, 180, 188 relational, 85 shift, 85 sizeof operator, 81 unary, 80 unary arithmetic, 81 Index
727
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
or macro, 225, 474, 616
pole error, 236, 245, 246, 251–259 portability, 8, 581 positive difference, 269 positive difference functions, 268, 531 positive_sign structure member, 227, 229– 231, 616 postfix decrement operator (--), 48, 77 postfix expressions, 73 postfix increment operator (++), 48, 77 pow function, ii, 256, 384, 477, 511, 525, 579, 616 pow type-generic macro, 384 powd function, 564, 616 powd128 function, 256, 482, 616 powd32 function, 256, 482, 616 powd64 function, 256, 386, 482, 616 power functions complex, 200, 545 real, 255, 524 powf function, 256, 477, 564, 616 powl function, 256, 477, 510, 616 pown function, 256, 257, 477, 511, 526, 616 pown type-generic macro, 384 pownd function, 565, 616 pownd128 function, 256, 482, 616 pownd32 function, 256, 482, 616 pownd64 function, 256, 482, 616 pownf function, 256, 477, 565, 616 pownl function, 256, 477, 616 powr function, iii, 257, 477, 511, 526, 616 powr type-generic macro, 384 powrd function, 565, 616 powrd128 function, 257, 482, 616 powrd32 function, 257, 482, 616 powrd64 function, 257, 482, 616 powrf function, 257, 477, 565, 616 powrl function, 257, 477, 616 pp-number, 70 pp_param pragma, 164, 616 pragma ___Noreturn__ , 610 __pp_param__ , 164, 610 CX_LIMITED_RANGE, xii, 185, 186, 196, 469, 471, 537, 589, 612 DEFAULT, 612 FE_DEC_DOWNWARD, 186 FE_DEC_DYNAMIC, 186, 214, 604 FE_DEC_TONEAREST, 186 FE_DEC_TONEARESTFROMZERO, 186 FE_DEC_TOWARDZERO, 186 FE_DEC_UPWARD, 186 FE_DOWNWARD, 186 FE_DYNAMIC, 186, 212, 213, 473, 604 FE_TONEAREST, 186 FE_TONEARESTFROMZERO, 186 FE_TOWARDZERO, 186
OR operators bitwise exclusive (^), 88 bitwise exclusive assignment (^=), 92 bitwise inclusive (|), 88 bitwise inclusive assignment (|=), 92 logical (||), 88 logical (||), 16 or_eq macro, 225, 474, 616 order of allocated storage, 362 order of evaluation, 71, 90, 180 ordinary identifier name space, 36 orientation, 321 orientation of stream, 321, 428 out-of-bounds store, 667 outer scope, 35 over-aligned, 44 p_cs_precedes structure member, 227, 229,
231, 232, 616 p_sep_by_space structure member, 227, 229–
232, 616 p_sign_posn structure member, 227, 229, 231,
232, 616 padding binary stream, 321 bits, 41, 315 structure/union, 41, 104 parameter, 6 array, 159 ellipsis, 128, 178 embed, 170 function, 74, 97, 159 macro, 178 main function, 12 program, 12 parameter type list, 128 parentheses punctuator (()), 128, 153, 154 parenthesized expression, 72 parse state, 321 perform a trap, 7 permitted form of initializer, 94 perror function, 353, 491, 616 phase angle, complex, 201 physical source lines, 10 placemarker, 180 plus operator, unary, 81 pointer arithmetic, 84 pointer comparison, 86 pointer declarator, 125 pointer operator (->), 75 pointer to a string, 190 pointer to a wide string, 190 pointer to function, 74 pointer type, 39 pointer type conversion, 48, 49 pointer, null, 49 728
N3096
Index
N3096
working draft — April 1, 2023
FE_UPWARD, 186 FENV_ACCESS, xii, 8, 92, 185, 186, 211, 212,
ISO/IEC 9899:2023 (E)
PRIcMAX macro, 222 PRIcN macros, 222 PRIcPTR macro, 222 PRId identifier prefix, 222, 474 PRId32 macro, 606 PRId64 macro, 606 PRIdFAST identifier prefix, 222, 474 PRIdFAST32 macro, 222, 606 PRIdFAST64 macro, 606 PRIdLEAST identifier prefix, 222, 474 PRIdLEAST32 macro, 606 PRIdLEAST64 macro, 606 PRIdMAX macro, 222, 474, 606 PRIdPTR macro, 222, 474, 606 PRIi identifier prefix, 222, 474 PRIi32 macro, 606 PRIi64 macro, 606 PRIiFAST identifier prefix, 222, 474 PRIiFAST32 macro, 606 PRIiFAST64 macro, 606 PRIiLEAST identifier prefix, 222, 474 PRIiLEAST32 macro, 606 PRIiLEAST64 macro, 606 PRIiMAX macro, 222, 474, 606 PRIiPTR macro, 222, 474, 606
217, 218, 220, 469, 473, 513–518, 524, 528, 530, 582, 589, 596, 613 FENV_DEC_ROUND, xii, 63, 185, 186, 213, 214, 469, 473, 511, 557, 613 FENV_ROUND, xii, 149, 185, 186, 211, 212, 213, 214, 469, 473, 510, 557, 613 FP_CONTRACT, xii, 72, 149, 185, 186, 237, 469, 475, 538, 589, 596, 605 OFF, 149, 538, 616 ON, 92, 212, 217, 218, 220, 514, 515, 524, 528, 530, 616 pp_param, 164, 616 STDC, 92, 185, 189, 196, 211–214, 217, 218, 220, 237, 469, 471, 473, 475, 514, 515, 524, 528, 530, 538, 588, 597, 617 pragma operator, 188 pragma preprocessing directive, 51, 69, 92, 149, 162, 185, 188, 189, 196, 211–214, 217, 218, 220, 237, 468, 469, 471, 473, 475, 514, 515, 524, 528, 530, 538, 580, 588, 597, 616 precedence of operators, 71 precedence of syntax rules, 10 precision, 42, 45, 328, 413 excess, 25, 48, 157 predefined macro names, 186, 189 preferred quantum exponent, 31 prefix decrement operator (--), 48, 80 prefix embed parameter, 175 prefix embed parameter, 171, 175, 176, 616 prefix increment operator (++), 48, 80 preprocessing, 164 preprocessing concatenation, 180 preprocessing directive, 163 preprocessing directives, 10, 162 preprocessing file, 10, 162 preprocessing files, 10 preprocessing numbers, 51, 70 preprocessing operators #, 180 ##, 180 _Pragma operator, 188 preprocessing parameter, 164 preprocessing tokens, 10, 51, 163 preprocessing translation unit, 10 preprocessor, 162 preprocessor parameter, 164 prefixed, 164 standard, 164 preprocessor prefixed parameter, 164 preprocessor standard parameter, 164 PRI identifier prefix, 222, 453, 602 PRIcFASTN macros, 222 PRIcLEASTN macros, 222
primary block, 151 primary expression, 72 printf_s function, 491, 616, 626, 627 printing character, 19, 204, 205 printing wide character, 447 PRIo identifier prefix, 222, 474 PRIo32 macro, 606 PRIo64 macro, 606 PRIoFAST identifier prefix, 222, 474 PRIoFAST32 macro, 606 PRIoFAST64 macro, 606 PRIoLEAST identifier prefix, 222, 474 PRIoLEAST32 macro, 606 PRIoLEAST64 macro, 606 PRIoMAX macro, 222, 474, 607 PRIoPTR macro, 222, 474, 607 PRIu identifier prefix, 222, 474 PRIu32 macro, 607 PRIu64 macro, 607 PRIuFAST identifier prefix, 222, 474 PRIuFAST32 macro, 607 PRIuFAST64 macro, 607 PRIuLEAST identifier prefix, 222, 474 PRIuLEAST32 macro, 607 PRIuLEAST64 macro, 607 PRIuMAX macro, 222, 474, 607 PRIuPTR macro, 222, 474, 607 PRIX identifier prefix, 222, 474 PRIx identifier prefix, 222, 474 PRIX32 macro, 607 PRIX64 macro, 607 Index
729
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
PRIXFAST identifier prefix, 222, 474 PRIxFAST identifier prefix, 222, 474 PRIXFAST32 macro, 607 PRIXFAST64 macro, 607 PRIXLEAST identifier prefix, 222, 474 PRIxLEAST identifier prefix, 222, 474 PRIXLEAST32 macro, 607 PRIXLEAST64 macro, 607 PRIXMAX macro, 222, 474, 607 PRIxMAX macro, 222, 223, 474 PRIXPTR macro, 222, 474, 607 PRIxPTR macro, 222, 474
quantumd identifier prefix, 276, 385 quantumd128 function, 276, 485, 616 quantumd32 function, 276, 485, 616 quantumd64 function, 276, 485, 616 question-mark escape sequence (\?), 64 quick_exit function, 285, 365, 366, 367, 492,
583, 590, 592, 593, 599, 616, 672 quiet NaN, 23 QVoid type, 378, 616 QWchar_t type, 438, 616 raise function, 284, 285, 286, 293, 365, 486,
program diagnostics, 194 program execution, 12 program file, 10 program image, 11 program name, 12 program name (argv[0]), 12 program parameters, 12 program startup, 11, 12 program structure, 10 program termination, 11, 12, 13 program, conforming, 8 program, strictly conforming, 8 promotions default argument, 75 integer, 14, 45 pseudo-random sequence functions, 361 PTRDIFF_MAX macro, 317, 490, 607 PTRDIFF_MIN macro, 317, 318, 490, 607 ptrdiff_t type, iv, 84, 292, 298, 312, 313, 317, 330, 337, 414, 420, 489, 585, 616, 671 PTRDIFF_WIDTH macro, 317, 616 punctuators, 68 putc macro, 320, 348, 491, 616 putchar macro, 320, 348, 491, 616 puts function, 184, 313, 320, 348, 349, 491, 616 putwc function, 320, 428, 429, 497, 616 putwchar function, 320, 429, 497, 616
589, 590, 616 rand function, 354, 361, 362, 492, 616 RAND_MAX macro, 354, 361, 362, 492, 607
range excess, 25, 48, 157 range error, 236, 241–250, 252–259, 261, 262, 267, 269, 273 read-modify-write operations, 16 read-read coherence, 17 read-write coherence, 17 real floating type conversion, 46, 47, 512 real floating types, 38, 549 real type domain, 39 real types, 39 real-floating, 238 realloc function, 362, 363, 364, 492, 583, 592, 599, 616, 668, 672 recommended practice, 6 recursion, 75 recursive function call, 75 redefinition of macro, 177 reentrancy, 13, 20 library functions, 193 referenced type, 39 register storage-class specifier, 97, 158 relational expressions, 85 relaxed atomic operations, 16 release fence, 296 release operation, 16 release sequence, 16 reliability of data, interrupted, 13 remainder assignment operator (%=), 92 remainder function, i, 265, 386, 478, 508, 511, 530, 598, 616 remainder functions, 264, 529 remainder operator (%), 83 remainder type-generic macro, 384 remainderd function, 567, 616 remainderd128 function, 265, 484, 616 remainderd32 function, 265, 483, 616 remainderd64 function, 265, 483, 616 remainderf function, 265, 479, 567, 616 remainderl function, 265, 479, 616 remove function, 323, 324, 490, 599, 616, 622
QChar type, 378, 616 qsort function, 367, 368, 369, 492, 583, 616 qsort_s function, 493, 616, 636, 637, 638
qualified types, 40 qualified version of type, 40 quantize function, 32, 214, 385, 507, 616 quantized function, 569, 616 quantized identifier prefix, 275, 276, 385 quantized128 function, 275, 485, 616 quantized32 function, 275, 485, 616 quantized64 function, 275, 485, 616 quantum, 31 quantum exponent, 31 quantum exponent functions, 275 quantum function, 32, 385, 508, 616 quantum functions, 275 quantumd function, 569, 616 730
N3096
Index
N3096
working draft — April 1, 2023
remquo function, 265, 479, 508, 511, 530, 582,
ISO/IEC 9899:2023 (E)
roundeven function, 234, 262, 263, 478, 507,
598, 616 remquo type-generic macro, 384 remquof function, 265, 479, 567, 616 remquol function, 265, 479, 616 rename function, 323, 324, 490, 599, 616 representation canonical, 24 non-canonical, 24 representations of types, 41 pointer, 40 reproducible, 148 reproducible attribute, 141, 146, 148, 149, 587, 616, 669, 670 rescanning and replacement, 181 reserved identifier, 602, 610 reserved identifiers, 53, 191, 620 resource, 165, 170 #embed preprocessing directive, 170 empty, 170 resource width, 170 restartable multibyte/wide character conversion functions, 407, 443, 663 restartable multibyte/wide string conversion functions, 444, 664 restore calling environment function, 282 restrict type qualifier, 118, 120 restrict-qualified type, 40, 119 rewind function, 326, 349, 352, 429, 491, 616 right-shift assignment operator (>>=), 92 right-shift operator (>>), 85 rint function, 261, 478, 507, 512, 528, 529, 617 rint type-generic macro, 384 rintd function, 566, 616 rintd128 function, 261, 483, 616 rintd32 function, 261, 483, 616 rintd64 function, 261, 483, 616 rintf function, 261, 478, 566, 616 rintl function, 261, 478, 616 rootn function, 257, 477, 511, 526, 617 rootn type-generic macro, 384 rootnd function, 565, 617 rootnd128 function, 257, 482, 617 rootnd32 function, 257, 482, 617 rootnd64 function, 257, 482, 617 rootnf function, 257, 477, 565, 617 rootnl function, 257, 477, 617 round function, 234, 261, 262, 478, 507, 528, 617 round to narrower type, 273 round type-generic macro, 384 roundd function, 566, 617 roundd128 function, 262, 483, 617 roundd32 function, 261, 483, 617 roundd64 function, 262, 483, 617
529, 617 roundeven type-generic macro, 384 roundevend function, 566, 617 roundevend128 function, 262, 483, 617 roundevend32 function, 262, 483, 617 roundevend64 function, 262, 483, 617 roundevenf function, 262, 478, 566, 617 roundevenl function, 262, 478, 617 roundf function, 261, 478, 566, 617
rounding, 262 rounding control pragma, 212 rounding directions, 234 rounding mode, floating-point, 24 roundl function, 261, 478, 617 RSIZE_MAX macro, 490, 607, 621, 622, 623, 627, 628, 631–633, 635, 637–646, 648, 649, 652, 654, 655, 658–665 rsize_t type, 489, 491, 493, 494, 496, 498, 617, 621, 622, 625–628, 631–633, 634, 635– 640, 641, 642–646, 648, 649, 650, 651, 652, 654, 655, 658–665 rsqrt function, 257, 258, 477, 511, 527, 617 rsqrt type-generic macro, 384 rsqrtd function, 565, 617 rsqrtd128 function, 258, 482, 617 rsqrtd32 function, 258, 482, 617 rsqrtd64 function, 258, 482, 617 rsqrtf function, 258, 477, 565, 617 rsqrtl function, 258, 477, 617 runtime-constraint, 6 Runtime-constraint handling functions, 634 rvalue, 48 same scope, 35 samequantum function, 385, 507, 617 samequantumd function, 569, 617 samequantumd identifier prefix, 276, 385 samequantumd128 function, 276, 485, 617 samequantumd32 function, 276, 485, 617 samequantumd64 function, 276, 485, 617 save calling environment function, 282 scalar types, 40 scalbln function, 254, 477, 508, 524, 570, 617 scalbln type-generic macro, 384 scalblnd function, 564, 617 scalblnd128 function, 254, 482, 617 scalblnd32 function, 254, 482, 617 scalblnd64 function, 254, 482, 617 scalblnf function, 254, 477, 564, 617 scalblnl function, 254, 477, 617 scalbn function, 254, 477, 508, 522, 523, 524, 539, 570, 617 scalbn type-generic macro, 384 scalbnd function, 564, 617 scalbnd128 function, 254, 482, 617 scalbnd32 function, 254, 482, 617 Index
731
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
scalbnd64 function, 254, 482, 617 scalbnf function, 254, 477, 564, 617 scalbnl function, 254, 477, 617 scanf function, 32, 213, 214, 320, 342, 343, 345,
separate compilation, 10 separate translation, 10 sequence points, 13, 75, 88, 89, 93, 119, 120, 151, 192, 193, 328, 368, 413, 500, 636 sequenced before, 13, 71, 75, 77, 90 sequencing of statements, 151 sequential consistency, 18 set_constraint_handler_s function, 493, 617, 620, 634, 635 setbuf function, 319, 322, 323, 325, 327, 490, 617 setjmp function, 192, 282, 283, 486, 582, 589, 617, 668 setlocale function, 190, 227, 228, 231, 402, 475, 589, 598, 617 setpayload function, 486, 507, 534, 617 setpayloadd function, 570, 617 setpayloadd128 function, 486, 534, 617 setpayloadd32 function, 486, 534, 617 setpayloadd64 function, 486, 534, 617 setpayloadf function, 486, 534, 570, 617 setpayloadl function, 486, 534, 617 setpayloadsig function, 486, 507, 534, 617 setpayloadsigd function, 570, 617 setpayloadsigd128 function, 486, 534, 617 setpayloadsigd32 function, 486, 534, 617 setpayloadsigd64 function, 486, 534, 617 setpayloadsigf function, 486, 534, 570, 617 setpayloadsigl function, 486, 534, 617 setvbuf function, 319, 322, 323, 325, 327, 328, 490, 591, 617 shall, 8 shift expressions, 85 shift sequence, 190 shift states, 19 short identifier, character, 21 short int type, 37, 101 short int type conversion, 45–47 SHRT_MAX macro, 22, 474, 503, 607 SHRT_MIN macro, 22, 474, 503, 607 SHRT_WIDTH macro, 22, 474, 503, 617 side effects, 13, 41, 49, 71, 77, 90, 137, 152, 209, 212, 348, 428, 429, 513, 515, 517 SIG identifier prefix, 284, 454, 602 SIG_ identifier prefix, 284, 454, 603 SIG_ATOMIC_MAX macro, 317, 490, 607 SIG_ATOMIC_MIN macro, 318, 490, 607 sig_atomic_t type, 13, 284, 285, 317, 486, 581, 590, 617 SIG_ATOMIC_WIDTH macro, 317, 490, 607 SIG_DFL macro, 284, 285, 486, 598, 607 SIG_ERR macro, 284, 285, 486, 590, 607 SIG_IGN macro, 284, 285, 486, 595, 607 SIGABRT macro, 284, 365, 486, 607 SIGFPE macro, 236, 284, 285, 486, 589, 594, 602, 607
490, 508, 617, 673 scanf_s function, 491, 617, 627, 631
scanlist, 339, 422 scanset, 339, 421 SCHAR_MAX macro, 22, 474, 503, 607 SCHAR_MIN macro, 22, 39, 474, 503, 607 SCHAR_WIDTH macro, 21, 474, 503, 617 SCN identifier prefix, 222, 453, 602 SCNcFASTN macros, 222 SCNcLEASTN macros, 222 SCNcMAX macro, 222 SCNcN macros, 222 SCNcPTR macro, 222 SCNd identifier prefix, 222, 474 SCNdFAST identifier prefix, 222, 474 SCNdLEAST identifier prefix, 222, 474 SCNdMAX macro, 222, 474, 607 SCNdPTR macro, 222, 474, 607 SCNi identifier prefix, 222, 474 SCNiFAST identifier prefix, 222, 474 SCNiLEAST identifier prefix, 222, 474 SCNiMAX macro, 222, 474, 607 SCNiPTR macro, 222, 474, 607 SCNo identifier prefix, 222, 474 SCNoFAST identifier prefix, 222, 474 SCNoLEAST identifier prefix, 222, 474 SCNoMAX macro, 222, 474, 607 SCNoPTR macro, 222, 474, 607 SCNu identifier prefix, 222, 474 SCNuFAST identifier prefix, 222, 474 SCNuLEAST identifier prefix, 222, 474 SCNuMAX macro, 222, 474, 607 SCNuPTR macro, 222, 474, 607 SCNx identifier prefix, 222, 474 SCNxFAST identifier prefix, 222, 474 SCNxLEAST identifier prefix, 222, 474 SCNxMAX macro, 222, 474, 607 SCNxPTR macro, 222, 474, 607 scope, 34 scope of identifier, 34, 160 search functions string, 378, 645 utility, 367, 636 wide string, 438, 662 secondary block, 151 SEEK_CUR macro, 320, 351, 490, 617 SEEK_END macro, 320, 323, 351, 490, 617 SEEK_SET macro, 320, 351, 352, 490, 592, 617 selection statements, 153 self-referential structure, 114 semicolon punctuator (;), 96, 103, 152, 154, 155 732
N3096
Index
N3096
working draft — April 1, 2023
ISO/IEC 9899:2023 (E)
SIGILL macro, 284, 285, 486, 589, 594, 607 SIGINT macro, 284, 486, 607
snprintf function, iii, 343, 345, 355, 356, 403,
sign bit, 42 signal function, 14, 15, 132, 284, 285, 366, 367, 486, 590, 595, 598, 617 signal handler, 13, 20, 284, 286 signal handling functions, 284 signal handling header, 284, 454 signaling NaN, 23, 507 signals, 13, 20, 284 signbit macro, iv, 239, 475, 509, 510, 530, 617 signed char type, 37 signed character, 45 signed integer types, 37, 38, 46, 59 signed type, 101 signed type conversion, 45–47 signed types, 37 significand part, 61 SIGSEGV macro, 284, 285, 486, 589, 594, 607 SIGTERM macro, 284, 486, 607 simple assignment, 91 simple assignment operator (=), 91 sin function, 76, 242, 384, 386, 475, 511, 520, 546, 617 sin type-generic macro, 384, 546 sind function, 561, 617 sind128 function, 242, 480, 617 sind32 function, 242, 480, 617 sind64 function, 242, 480, 617 sinf function, 242, 475, 561, 617 single-byte character, 19 single-byte/wide character conversion functions, 442 single-precision arithmetic, 14 single-quote escape sequence (\’), 64, 67 singularity, 236 sinh function, 247, 384, 476, 512, 521, 546, 617 sinh type-generic macro, 384, 546 sinhd function, 562, 617 sinhd128 function, 247, 481, 617 sinhd32 function, 247, 481, 617 sinhd64 function, 247, 481, 617 sinhf function, 247, 476, 562, 617 sinhl function, 247, 476, 617 sinl function, 242, 475, 617 sinpi function, 244, 245, 476, 511, 521, 617 sinpi type-generic macro, 384 sinpid function, 562, 617 sinpid128 function, 245, 481, 617 sinpid32 function, 245, 481, 617 sinpid64 function, 245, 481, 617 sinpif function, 244, 476, 562, 617 sinpil function, 245, 476, 617 SIZE_MAX macro, 40, 490, 607, 621 SIZE_WIDTH macro, 318, 490, 617 sizeof operator, 48, 80, 81
snprintf_s function, 491, 617, 627, 628 snwprintf_s function, 498, 617, 651, 652
490, 617, 628, 673
sorting utility functions, 367, 636 source character set, 10, 18 source file, 10 name, 184, 186 source file inclusion, 168 source lines, 10 source text, 10 space character (’ ’), 10, 19, 51, 204, 206, 448 space format flag, 329, 414 spilling, 14 sprintf function, 343, 346, 490, 617, 628 sprintf_s function, 491, 617, 628 sqrt function, 149, 258, 384, 477, 508, 527, 532, 577, 617 sqrt type-generic macro, 384 sqrtd function, 565, 569, 617 SQRTD macro, 560 sqrtd128 function, 258, 482, 617 sqrtd32 function, 258, 386, 482, 617 sqrtd64 function, 258, 482, 617 sqrtf function, 258, 477, 565, 569, 617 SQRTF macro, 560 sqrtl function, 258, 477, 617 square root rounded to narrower type, 275 srand function, 361, 362, 492, 617 sscanf function, 341, 343, 344, 346, 490, 617 sscanf_s function, 491, 617, 629, 632 standard attribute, 140 standard embed parameter, 171 standard error stream, 320, 322, 353 standard floating types, 38 standard headers, 8, 190 <assert.h>, 173–175, 191, 194, 218, 471 <complex.h>, 24, 29, 137, 188, 190, 191, 195–202, 383, 384, 453, 471, 537, 538, 539, 540, 556, 557, 593, 596, 602, 672, 673 <ctype.h>, 191, 204, 205, 206, 453, 472 <errno.h>, 148, 191, 208, 453, 472, 620 <fenv.h>, 8, 13, 15, 24, 29, 33, 92, 148, 191, 209, 211–213, 215–220, 236, 453, 472, 507, 510, 513–515, 524, 528, 530, 673 <float.h>, vi, 8, 9, 21, 23, 24, 28, 29, 191, 221, 234, 333, 357, 418, 431, 453, 454, 473, 474, 503, 507, 512, 549, 550, 551, 600, 672, 673 <inttypes.h>, 191, 222, 223, 224, 330, 415, 453, 474, 673 <iso646.h>, 8, 9, 191, 225, 474, 672, 674 <limits.h>, vi, 8, 9, 21, 22, 38, 39, 191, 226, 474, 503, 600 <locale.h>, 148, 191, 227, 228, 453, 474 Index
733
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
<math.h>, 8, 24, 29, 33, 72, 148, 191, 213,
state-dependent encoding, 19, 369, 638 stateless, 147 statement, 151 statements, 151 break, 156 compound, 152 continue, 156 do, 155 else, 153 expression, 152 for, 155 goto, 155 if, 153 iteration, 154 jump, 155 labeled, 151 null, 152 return, 157, 513 selection, 153 sequencing, 151 switch, 153 while, 154 static assertions, 140 static storage duration, 36 static storage-class specifier, 35, 36, 97 static, in array declarators, 126, 128 static_assert, 140 STDC pragma, 92, 185, 189, 196, 211–214, 217, 218, 220, 237, 469, 471, 473, 475, 514, 515, 524, 528, 530, 538, 588, 597, 617 stdc_ function, 454, 603, 607 stdc_bit_ceil macro, 309, 489, 607 stdc_bit_ceiluc function, 607 stdc_bit_ceilui function, 607 stdc_bit_ceilul function, 607 stdc_bit_ceilull function, 607 stdc_bit_ceilus function, 607 stdc_bit_floor macro, 308, 489, 607 stdc_bit_flooruc function, 607 stdc_bit_floorui function, 607 stdc_bit_floorul function, 607 stdc_bit_floorull function, 607 stdc_bit_floorus function, 607 stdc_bit_width macro, 308, 489, 607 stdc_bit_widthuc function, 607 stdc_bit_widthui function, 607 stdc_bit_widthul function, 607 stdc_bit_widthull function, 607 stdc_bit_widthus function, 607 stdc_count_ones macro, 307, 489, 607 stdc_count_onesuc function, 607 stdc_count_onesui function, 607 stdc_count_onesul function, 607 stdc_count_onesull function, 607 stdc_count_onesus function, 607 stdc_count_zeros macro, 306, 488, 607
214, 233, 234, 236–239, 240–273, 274, 275–280, 334, 383–385, 418, 453, 454, 475, 485, 486, 506, 507, 512, 518, 524, 528, 530–534, 537, 538, 548, 557, 558, 570–572, 583, 593, 596, 600, 602, 673 <setjmp.h>, 191, 282, 283, 486 <signal.h>, 191, 284, 286, 454, 486 <stdalign.h>, 8, 9, 191, 287, 486, 672 <stdarg.h>, 8, 9, 128, 191, 288, 289–291, 344–346, 424, 425, 486, 629–632, 653– 656 <stdatomic.h>, 187, 190, 191, 285, 292, 293, 295–301, 454, 487, 590, 672 <stdbit.h>, 8, 191, 302, 303–309, 454, 488, 671 <stdbool.h>, 8, 9, 191, 310, 454, 489, 673 <stdckdint.h>, 191, 311, 454, 489 <stddef.h>, 8, 9, 49, 66, 68, 82, 84, 85, 140, 171, 172, 191, 224, 312, 313, 342, 489, 621 <stdint.h>, 8, 9, 21, 22, 166, 191, 222, 255–257, 263, 315, 317, 318, 330, 337, 338, 415, 420, 454, 489, 490, 600, 621, 673 <stdio.h>, 15, 24, 29, 33, 55, 148, 169, 172, 191, 213, 214, 319, 323–325, 327, 328, 334, 336, 340–353, 400, 413, 418, 422– 424, 426–429, 454, 490, 491, 596, 621, 622–633, 651, 653, 654, 672, 673 <stdlib.h>, 8, 24, 29, 33, 191, 193, 213, 214, 354, 355, 356, 358, 360–372, 454, 491, 493, 548, 572, 574, 575, 596, 620, 634, 635–640, 672 <stdnoreturn.h>, 8, 9, 146, 191, 373, 493 <string.h>, vii, 8, 172, 175, 176, 191, 374, 375–382, 455, 493, 494, 641, 642–647 <tgmath.h>, 33, 191, 383, 386, 494, 506, 518, 546, 576, 578, 673 <threads.h>, 148, 188, 190, 191, 388, 389– 396, 455, 495, 672 <time.h>, 191, 388, 398, 399–404, 441, 455, 495, 496, 647, 648–650, 672 <uchar.h>, 65, 66, 68, 191, 407, 408–411, 496, 670, 672 <wchar.h>, 24, 29, 33, 148, 191, 213, 214, 223, 320, 412, 413, 418, 422–430, 432– 445, 455, 496, 498, 575, 576, 596, 650, 651–665, 672–674 <wctype.h>, 191, 447, 448–452, 455, 498, 672, 674 standard input stream, 320, 322 standard integer types, 38 standard output stream, 320, 322 standard signed integer types, 37 standard unsigned integer types, 38 734
N3096
Index
N3096
working draft — April 1, 2023
stdc_count_zerosuc function, 607 stdc_count_zerosui function, 607 stdc_count_zerosul function, 607 stdc_count_zerosull function, 607 stdc_count_zerosus function, 607 stdc_first_leading_one macro, 305, 488,
ISO/IEC 9899:2023 (E)
stdc_trailing_onesull function, 608 stdc_trailing_onesus function, 608 stdc_trailing_zeros macro, 304, 488, 608 stdc_trailing_zerosuc function, 608 stdc_trailing_zerosui function, 608 stdc_trailing_zerosul function, 608 stdc_trailing_zerosull function, 608 stdc_trailing_zerosus function, 608 stderr stream, 184, 320, 321, 322, 327, 344,
607 stdc_first_leading_oneuc function, 607 stdc_first_leading_oneui function, 607 stdc_first_leading_oneul function, 607 stdc_first_leading_oneull function, 607 stdc_first_leading_oneus function, 607 stdc_first_leading_zero macro, 305, 488,
424, 490, 602, 617 stdin stream, 320, 321, 322, 327, 340–343, 348, 422, 423, 426, 428, 490, 617, 626, 627, 633, 657 stdout stream, 320, 321, 322, 327, 334–336, 342, 348, 349, 418, 426, 429, 490, 617 storage duration, 36 storage order of array, 74 storage unit (bit-field), 41, 104 storage-class specifiers, 97, 189 store and load, 14 str identifier prefix, 453–455, 603 strcat function, 376, 493, 608 strcat_s function, 494, 608, 643, 644 strchr macro, 378, 379, 455, 493, 608 strcmp function, 377, 378, 493, 608 strcoll function, 8, 228, 377, 378, 493, 608 strcpy function, 175–177, 341, 375, 493, 608 strcpy_s function, 494, 608, 642 strcspn function, 379, 493, 608 strdup function, ii, 8, 375, 376, 493, 608, 670 streams, 321, 366 fully buffered, 322 line buffered, 322 orientation, 321 standard error, 320, 322 standard input, 320, 322 standard output, 320, 322 unbuffered, 322 strerror function, 8, 353, 381, 382, 494, 592, 593, 600, 608 strerror_s function, 382, 494, 608, 646, 647 strerrorlen_s function, 494, 608, 647 strfrom identifier prefix, 213, 214 strfromd function, 355, 430, 492, 508, 509, 554, 572, 573, 574, 575, 608 strfromd identifier prefix, 355, 356 strfromd128 function, 355, 356, 492, 608 strfromd32 function, 355, 356, 492, 608 strfromd64 function, 355, 356, 492, 608 strfromencbind function, 557, 574, 575, 608 strfromencdecd function, 557, 574, 575, 608 strfromencf function, 557, 574, 608 strfromencf128 function, 574, 608 strfromf function, 355, 430, 492, 573, 574, 608 strfroml function, 355, 492, 608 strftime function, ii, 228, 402, 404, 406, 441,
607 stdc_first_leading_zerouc function, 607 stdc_first_leading_zeroui function, 607 stdc_first_leading_zeroul function, 607 stdc_first_leading_zeroull function, 607 stdc_first_leading_zerous function, 607 stdc_first_trailing_one macro, 306, 488,
607 stdc_first_trailing_oneuc function, 607 stdc_first_trailing_oneui function, 607 stdc_first_trailing_oneul function, 607 stdc_first_trailing_oneull function, 607 stdc_first_trailing_oneus function, 607 stdc_first_trailing_zero macro, 305, 488,
607 stdc_first_trailing_zerouc function, 607 stdc_first_trailing_zeroui function, 607 stdc_first_trailing_zeroul function, 607 stdc_first_trailing_zeroull function,
607 stdc_first_trailing_zerous function, 607 stdc_has_single_bit macro, 307, 489, 607 stdc_has_single_bituc function, 607 stdc_has_single_bitui function, 607 stdc_has_single_bitul function, 607 stdc_has_single_bitull function, 607 stdc_has_single_bitus function, 607 stdc_leading_ones macro, 303, 488, 607 stdc_leading_onesuc function, 607 stdc_leading_onesui function, 608 stdc_leading_onesul function, 608 stdc_leading_onesull function, 608 stdc_leading_onesus function, 608 stdc_leading_zeros macro, 303, 488, 608 stdc_leading_zerosuc function, 608 stdc_leading_zerosui function, 608 stdc_leading_zerosul function, 608 stdc_leading_zerosull function, 608 stdc_leading_zerosus function, 608 stdc_trailing_ones macro, 304, 488, 608 stdc_trailing_onesuc function, 608 stdc_trailing_onesui function, 608 stdc_trailing_onesul function, 608
Index
735
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
496, 583, 591, 593, 600, 608, 648, 649, 670, 674 stricter, 44 strictly conforming program, 8 string, 190 comparison functions, 377 concatenation functions, 376, 643 conversion functions, 228 copying functions, 374, 641 library function conventions, 374 literal, 11, 18, 48, 66, 72, 136 miscellaneous functions, 381, 646 numeric conversion functions, 223, 354 search functions, 378, 645 string duplicate function, 375, 376 string handling header, 374, 455, 641 stringizing, 180, 188 stringizing argument, 180 strlen function, 376, 382, 494, 608 strncat function, 376, 493, 608 strncat_s function, 494, 608, 644, 645 strncmp function, 183, 377, 378, 493, 608 strncpy function, 375, 493, 608 strncpy_s function, 494, 608, 642, 643 strndup function, ii, 8, 376, 493, 608, 670 strnlen_s function, 494, 608, 642–644, 647 stronger, 44 strpbrk macro, 378, 379, 455, 493, 608 strrchr macro, 378, 379, 380, 455, 493, 608 strspn function, 380, 493, 608 strstr macro, 378, 380, 455, 494, 608 strto family, 8, 32, 63, 213, 214, 358, 608 strtod family, 358, 359 strtod function, 63, 266, 337, 338, 342, 355, 356, 430, 492, 508, 513, 514, 554, 555, 572, 573, 576, 583, 599, 608 strtod128 function, 358, 574, 599, 608 strtod32 function, 358, 599, 608 strtod64 function, 358, 359, 599, 608 strtoencbind function, 557, 575, 576, 608 strtoencdecd function, 557, 575, 576, 608 strtoencf function, 557, 575, 608 strtof function, 266, 342, 355, 356, 492, 573, 575, 583, 599, 608 strtoimax function, 223, 474, 608 strtok function, 380, 381, 494, 593, 608 strtok_s function, 381, 494, 608, 645, 646 strtol function, 223, 224, 337, 338, 342, 355, 360, 361, 492, 608 strtold function, 266, 342, 355, 356, 492, 583, 599, 608 strtoll function, 223, 224, 342, 355, 360, 361, 492, 608 strtoul function, 223, 224, 338, 342, 355, 360, 361, 492, 608 strtoull function, 223, 224, 342, 355, 360, 361, 736
N3096
492, 608 strtoumax function, 223, 474, 608
structure arrow operator (->), 75 content, 114 dot operator (.), 75 initialization, 136 member alignment, 104 member name space, 36 member operator (.), 48, 75 pointer operator (->), 75 specifier, 102 tag, 36, 114 type, 39, 102 structure content, 114 structure or union constant, 95 strxfrm function, 8, 228, 378, 493, 593, 608 subd function, 568, 617 SUBD macro, 560 subf function, 568, 617 SUBF macro, 559, 560 subnormal floating-point numbers, 23 subscripting, 74 subtract and round to narrower type, 273 subtraction assignment operator (-=), 92 subtraction operator (-), 84, 539 successful termination, 366 suffix floating constant, 61 integer constant, 59 suffix embed parameter, 175 suffix embed parameter, 171, 175, 176, 617 switch body, 153 switch case label, 152, 153 switch default label, 152, 153 switch statement, 152 swprintf function, 423, 425, 497, 617, 652 swprintf_s function, 498, 617, 652, 653 swscanf function, 423, 425, 497, 617 swscanf_s function, 498, 617, 653, 656 symbols, 3 synchronization operation, 16 synchronize, 147 synchronize with, 16 syntactic categories, 34 syntax notation, 34 syntax rule precedence, 10 syntax summary, language, 456 system function, 367, 492, 593, 595, 599, 617 t format modifier, 330, 337, 414, 420
tab characters, 19, 51 tag compatibility, 42 tag name space, 36 tags, 36, 112 tan function, 242, 243, 384, 475, 511, 520, 546, 617 Index
N3096
working draft — April 1, 2023
tan type-generic macro, 384, 546 tand function, 561, 617 tand128 function, 242, 480, 617 tand32 function, 242, 480, 617 tand64 function, 242, 480, 617 tanf function, 242, 475, 561, 617 tanh function, 247, 384, 476, 512, 521, 546, 617 tanh type-generic macro, 384, 546 tanhd function, 562, 617 tanhd128 function, 247, 481, 617 tanhd32 function, 247, 481, 617 tanhd64 function, 247, 481, 617 tanhf function, 247, 476, 562, 617 tanhl function, 247, 476, 617 tanl function, 242, 475, 617 tanpi function, 245, 476, 512, 521, 617 tanpi type-generic macro, 384 tanpid function, 562, 617 tanpid128 function, 245, 481, 617 tanpid32 function, 245, 481, 617 tanpid64 function, 245, 481, 617 tanpif function, 245, 476, 562, 617 tanpil function, 245, 476, 617
ISO/IEC 9899:2023 (E)
thread of execution, 15, 193, 209, 366, 636 thread storage duration, 36, 209 thread_local storage-class specifier, 36, 97 threads header, 388, 455 time broken down, 399, 400–404, 648, 650 calendar, 398, 399–401, 403, 404, 649, 650 components, 398, 648 conversion functions, 402, 648 wide character, 441 local, 398 manipulation functions, 399 normalized broken down, 648 time base, 398, 401 time function, 400, 401, 495, 583, 618 TIME_ identifier prefix, 398, 455, 603 TIME_ACTIVE macro, 398, 401, 402, 455, 496, 599, 608 TIME_MONOTONIC macro, 398, 401, 455, 496, 599, 608 time_t type, 398, 399, 400, 401, 403, 404, 495, 496, 599, 618, 649, 650 TIME_THREAD_ACTIVE macro, 398, 401, 455, 496, 599, 608 TIME_UTC macro, 391, 392, 395, 398, 401, 495, 600, 608 timegm function, 400, 401, 495, 617, 672 timespec structure type, 390, 392, 395, 398, 399, 401, 402, 495, 496, 617 timespec_get function, 398, 401, 402, 496, 617 timespec_getres function, 398, 402, 496, 617, 672 tm structure type, 398, 399, 400, 402–404, 412, 441, 495–497, 618, 648, 649, 650 tm_hour structure member, 399, 400, 403, 405, 618, 648 _ tm isdst structure member, 399, 400, 405, 618 tm_mday structure member, 399, 400, 401, 403, 404, 618, 648 tm_min structure member, 399, 400, 403, 405, 618, 648 tm_mon structure member, 399, 400, 401, 403– 405, 618, 648 tm_sec structure member, 399, 400, 403, 405, 618, 649 tm_wday structure member, 399, 400, 401, 403– 405, 618, 648 tm_yday structure member, 399, 400, 401, 405, 618 tm_year structure member, 399, 400, 401, 403– 405, 618, 649 TMP_MAX macro, 320, 324, 325, 490, 608 TMP_MAX_S macro, 491, 618, 621, 622, 623 tmpfile function, 324, 366, 490, 618 tmpfile_s function, 491, 618, 622, 623
temporary lifetime, 37 tentative definition, 160 terms, 3 text streams, 321, 349, 351 tgamma function, 259, 260, 478, 527, 617 tgamma type-generic macro, 384 tgammad function, 565, 617 tgammad128 function, 259, 483, 617 tgammad32 function, 259, 483, 617 tgammad64 function, 259, 483, 617 tgammaf function, 259, 478, 565, 617 tgammal function, 259, 478, 617 thousands_sep structure member, 227, 229, 617 thrd_ identifier prefix, 455, 603 thrd_busy constant, 389, 393, 495, 608 thrd_create function, 388, 393, 495, 608 thrd_current function, 393, 495, 608 thrd_detach function, 394, 495, 593, 608 thrd_equal function, 394, 495, 608 thrd_error constant, 389, 390–397, 495, 608 thrd_exit function, 393, 394, 495, 583, 608 thrd_join function, 394, 395, 495, 593, 608 thrd_nomem constant, 389, 390, 393, 495, 608 thrd_sleep function, 395, 495, 608 thrd_start_t type, 388, 393, 495, 608 thrd_success constant, 389, 390–397, 495, 608 thrd_t type, 388, 393, 394, 495, 608 thrd_timedout constant, 389, 391, 392, 495, 608 thrd_yield function, 395, 495, 608 thread, 15 Index
737
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
tmpnam function, 320, 324, 325, 490, 618, 623 tmpnam_s function, 491, 618, 621, 622, 623
type category, 40 type conversion, 44 type definitions, 131 type domain, 39, 536 type inference, 133, 602 type name, 130 type names, 130 type punning, 75 type qualifiers, 118 type specifiers, 101 type-generic macro, 546 type-generic macros, 383 type-generic math header, 383 typedef declaration, 131 typedef storage-class specifier, 97, 131 typeof operators, 48, 115 typeof specifiers, 115 types, 37 atomic, 13, 40, 41, 48, 75, 77, 92, 115, 187, 297 character, 136 compatible, 42, 102, 119, 125 complex, 38, 536 composite, 43 const qualified, 119 conversions, 44 imaginary, 536 restrict qualified, 119 typeof, 115 volatile qualified, 119
to identifier prefix, 453, 455, 603
token, 11, 51 token concatenation, 180 token pasting, 180 tolower function, 206, 472, 608 totalorder function, i, 485, 509, 532, 608 totalorderd function, 570, 608 totalorderd128 function, 486, 532, 608 totalorderd32 function, 486, 532, 608 totalorderd64 function, 486, 532, 608 totalorderf function, 485, 532, 570, 608 totalorderl function, 485, 532, 608 totalordermag function, 485, 509, 533, 608 totalordermagd function, 570, 608 totalordermagd128 function, 486, 533, 608 totalordermagd32 function, 486, 533, 608 totalordermagd64 function, 486, 533, 608 totalordermagf function, 485, 533, 570, 608 totalordermagl function, 485, 533, 608 toupper function, 206, 207, 472, 609 towctrans function, 451, 452, 499, 594, 600, 609 towlower function, 451, 452, 499, 609 towupper function, 451, 452, 499, 609 translation environment, 10 translation limits, 20 translation phases, 10 translation unit, 10, 158 trigonometric functions complex, 196, 540 real, 240, 519 trunc function, 234, 263, 478, 507, 529, 618 trunc type-generic macro, 384 truncation, 46, 263, 322, 326 truncation toward zero, 83 truncd function, 566, 618 truncd128 function, 263, 483, 618 truncd32 function, 263, 483, 618 truncd64 function, 263, 483, 618 truncf function, 263, 478, 566, 618 truncl function, 263, 478, 618 tss_ identifier prefix, 455, 603 tss_create function, 395, 396, 495, 594, 609 tss_delete function, 396, 495, 583, 594, 609 TSS_DTOR_ITERATIONS macro, 388, 394, 495, 618 tss_dtor_t type, 388, 395, 495, 609 tss_get function, 396, 495, 594, 609 tss_set function, 396, 397, 495, 594, 609 tss_t type, 388, 395, 396, 495, 609 tv_nsec structure member, 399, 401, 618 tv_sec structure member, 399, 401, 618 two’s complement, 42 type, 37 738
N3096
U encoding prefix, 64, 65, 67, 459 u encoding prefix, 64, 65, 67, 459 u8 encoding prefix, 64, 65, 67, 459 UCHAR_MAX macro, 22, 474, 503, 609 UCHAR_WIDTH macro, 21, 474, 503, 618 ufromfp function, 234, 263, 264, 478, 508, 512,
529, 618 ufromfp functions, 263 ufromfp type-generic macro, 384 ufromfpd function, 566, 618 ufromfpd128 function, 263, 483, 618 ufromfpd32 function, 263, 483, 618 ufromfpd64 function, 263, 483, 618 ufromfpf function, 263, 478, 566, 618 ufromfpl function, 263, 478, 618 ufromfpx function, 234, 264, 478, 508, 512, 529,
618 ufromfpx functions, 264 ufromfpx type-generic macro, 384 ufromfpxd function, 566, 618 ufromfpxd128 function, 264, 483, 618 ufromfpxd32 function, 264, 483, 618 ufromfpxd64 function, 264, 483, 618 ufromfpxf function, 264, 478, 566, 618 ufromfpxl function, 264, 478, 618 UINT identifier prefix, 317, 318, 454, 490, 603
Index
N3096
working draft — April 1, 2023
uint identifier prefix, 315, 454, 490, 603 UINTN_C macros, 318 UINTN_MAX macros, 317 uintN_t types, 315 UINT16_C macro, 609 UINT16_MAX macro, 609 uint16_t type, 609 UINT16_WIDTH macro, 609 UINT32_C macro, 609 UINT32_MAX macro, 609 uint32_t type, 609 UINT32_WIDTH macro, 609 UINT64_C macro, 318, 609 UINT64_MAX macro, 609 uint64_t type, 264, 609 UINT64_WIDTH macro, 609 UINT8_C macro, 609 UINT8_MAX macro, 609 uint8_t type, 609 UINT8_WIDTH macro, 609 UINT_FAST identifier prefix, 317, 490 uint_fast identifier prefix, 316, 490 UINT_LEAST identifier prefix, 317, 490 uint_least identifier prefix, 315, 318, 490 UINT_FASTN_MAX macros, 317 uint_fast16_t type, 298, 316, 609 uint_fast32_t type, 298, 316, 609 uint_fast64_t type, 298, 316, 609 uint_fast8_t type, 298, 316, 609 uint_fastN_t types, 316 UINT_LEASTN_MAX macros, 317 uint_leastN_t types, 315 uint_least16_t type, 298, 315, 316, 407, 609 uint_least32_t type, 298, 316, 407, 609 uint_least64_t type, 298, 316, 318, 609 uint_least8_t type, 298, 316, 609 UINT_MAX macro, 22, 100, 109, 110, 166, 474,
ISO/IEC 9899:2023 (E)
unary minus operator (-), 81, 510 unary operators, 80 unary plus operator (+), 81 unbuffered, 322 unbuffered stream, 322 undef, 55, 162, 165, 182, 186, 192, 193, 468, 588, 618 undef preprocessing directive, 182, 192 undefined behavior, 4, 8, 584 underlying type, 107 underscore, leading, in identifier, 191 underspecified, 97 ungetc function, 320, 349, 351, 454, 491, 582, 592, 602, 618, 674 ungetwc function, 320, 429, 497, 582, 602, 618 Unicode, 407 Unicode required set, 187 Unicode Standard Annex, UAX #31, 2 Annex, UAX #44, 2 Derived Core Properties, 2 Unicode utilities header, 407 union arrow operator (->), 75 content, 114 dot operator (.), 75 initialization, 136 member alignment, 104 member name space, 36 member operator (.), 48, 75 pointer operator (->), 75 specifier, 102 tag, 36, 114 type, 39, 102 union content, 114 universal character name, 56 universl character name, 501 unnormalized floating-point numbers, 23 unqualified type, 40 unqualified version of type, 40 unreachable, 313 unreachable macro, v, xiv, 312, 313, 489, 590, 618, 672 unsequenced, 13, 71, 90, 148 unsequenced attribute, 141, 146, 148, 149, 150, 587, 618, 669, 670 unsigned bit-precise integer suffix, uwb or UWB, 59 unsigned integer suffix, u or U, 59 unsigned integer types, 38, 46, 59 unsigned type, 101, 329, 337, 414, 420 unsigned type conversion, 45–47 unsigned types, 38 unspecified behavior, 4, 8, 581 unspecified value, 6 unsuccessful termination, 365, 366
503, 609 UINT_WIDTH macro, 22, 264, 474, 503, 609 UINTMAX_C macro, 318, 490, 609 UINTMAX_MAX macro, 223, 224, 317, 490, 512,
609 uintmax_t type, 22, 166, 223, 224, 298, 316,
318, 330, 337, 414, 420, 474, 490, 609, 671, 673 UINTMAX_WIDTH macro, 317, 490, 609 UINTPTR_MAX macro, 317, 490, 609 uintptr_t type, 298, 316, 490, 609 UINTPTR_WIDTH macro, 317, 490, 609 ULLONG_MAX macro, 22, 100, 110, 361, 434, 474, 503, 609 ULLONG_WIDTH macro, 22, 474, 503, 618 ULONG_MAX macro, 22, 361, 434, 474, 503, 609 ULONG_WIDTH macro, 22, 474, 503, 618 unary arithmetic operators, 81 unary expression, 80 Index
739
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
uppercase letters, 18 use of library functions, 192 USHRT_MAX macro, 22, 109, 474, 503, 609 USHRT_WIDTH macro, 22, 474, 503, 618 usual arithmetic conversions, 47, 83, 84, 86–89 UTF–8 string literal, see string literal UTF-16 character constant, 64 UTF-16 string literal, 67 UTF-32 character constant, 64 UTF-32 string literal, 67 UTF-8 character constant, 64 UTF-8 string literal, 67 utilities, bit and byte, 302 utilities, general, 354, 454, 634 wide string, 429, 658 utilities, Unicode, 407
void type, 49, 101 void type conversion, 49
volatile access, 12, 13 volatile type qualifier, 118 volatile-qualified type, 40, 119 vprintf function, 320, 344, 345, 490, 592, 618, 630 vprintf_s function, 491, 618, 630, 631, 632 vscanf function, 320, 344, 345, 490, 592, 618, 673 _ vscanf s function, 491, 618, 630, 631–633 vsnprintf function, 344, 345, 346, 490, 592, 618, 631 vsnprintf_s function, 491, 618, 630, 631, 632 vsnwprintf_s function, 498, 618, 654, 655 vsprintf function, 344, 346, 490, 592, 618, 632 vsprintf_s function, 491, 618, 630, 631, 632 vsscanf function, 344, 346, 490, 592, 618 vsscanf_s function, 491, 618, 630, 631, 632, 633 vswprintf function, 424, 425, 497, 592, 618, 654, 655 vswprintf_s function, 498, 618, 654, 655 vswscanf function, 424, 425, 497, 592, 618 vswscanf_s function, 498, 618, 654, 655, 656, 657 vwprintf function, 320, 424, 425, 497, 592, 618, 656 vwprintf_s function, 498, 618, 656 vwscanf function, 320, 424, 425, 426, 429, 497, 592, 618 vwscanf_s function, 498, 618, 654, 656, 657
va_arg function, 288, 289–291, 333, 344–346,
417, 418, 424–426, 487, 590, 618, 630– 632, 654, 656, 657 va_copy function, 192, 288, 289, 291, 487, 582, 590, 618, 674 va_end function, 192, 288, 289, 290, 291, 344– 346, 424–426, 487, 582, 590, 592, 618, 630–632, 654, 656, 657 va_list type, 288, 289–291, 344–346, 424–426, 487, 490, 491, 497, 498, 590, 592, 618, 629–632, 653–656 va_start function, vi, 288, 289, 290, 291, 344– 346, 424–426, 487, 590, 618, 630–632, 654, 656, 657, 671 value, 6 value bits, 41 value of a string, 190 value of a wide string, 190 variable arguments, 178 variable arguments header, 288 variable length array, 125, 126, 188 variably modified, 125 variably modified type, 125, 126, 188 vertical tab, 20 vertical-tab character, 19, 51 vertical-tab escape sequence (\v), 20, 65, 206 vfprintf function, 320, 344, 490, 592, 618, 629 vfprintf_s function, 491, 618, 629, 630–632 vfscanf function, 320, 344, 345, 490, 592, 618 vfscanf_s function, 491, 618, 630, 631, 632 vfwprintf function, 320, 424, 497, 592, 618, 653 vfwprintf_s function, 498, 618, 653 vfwscanf function, 320, 424, 429, 497, 592, 618 vfwscanf_s function, 498, 618, 654, 656, 657 visibility of identifier, 34 visible, 34 visible side effect, 17 void expression, 49 void function parameter, 128 740
N3096
warnings, 11, 580 WCHAR_MAX macro, 412, 490, 496, 609 WCHAR_MIN macro, 318, 412, 490, 496, 609 wchar_t type, 5, 44, 64–67, 136, 187, 224, 298, 312, 318, 329, 332, 334, 337, 339, 342, 354, 370–372, 407, 412, 413, 414, 417– 430, 432–441, 443–445, 447, 470, 474, 489, 492, 493, 496–498, 573, 575, 583, 594, 595, 618, 638–640, 650–665 WCHAR_WIDTH macro, 318, 412, 490, 618 wcrtomb function, 323, 332, 336, 342, 412, 421, 423, 444, 446, 498, 583, 618, 640, 663, 666 wcrtomb_s function, 498, 618, 663, 664 wcs identifier prefix, 453–455, 603 wcscat function, 436, 497, 609 wcscat_s function, 498, 609, 660, 661 wcschr macro, 438, 455, 497, 609 wcscmp function, 436, 437, 497, 609 wcscoll function, 436, 437, 497, 609 wcscpy function, 434, 435, 497, 609 wcscpy_s function, 498, 609, 658 wcscspn function, 438, 497, 609 Index
N3096
working draft — April 1, 2023
wcsftime function, 228, 441, 497, 583, 591, 593,
ISO/IEC 9899:2023 (E)
extensible, 451 classification functions, 447 extensible, 450 constant, 64 formatted input/output functions, 413, 650 input functions, 320 input/output functions, 320, 426 output functions, 320 single-byte conversion functions, 442 wide character classification and mapping utilities header, 447, 455 wide character constants, 64 wide character input functions, 320 wide character input/output functions, 320 wide character output functions, 320 wide literal encoding, 44 wide string, 190 wide string comparison functions, 436 wide string concatenation functions, 436, 660 wide string copying functions, 434, 658 wide string literal, see string literal wide string literals, 67 wide string miscellaneous functions, 441, 663 wide string numeric conversion functions, 224, 430 wide string search functions, 438, 662 wide-oriented stream, 321 width, 41, 42 WINT_MAX macro, 490, 609 WINT_MIN macro, 318, 490, 609 wint_t type, 318, 329, 332, 334, 412, 414, 417, 426–429, 442, 447, 448–451, 496, 497, 499, 594, 618 WINT_WIDTH macro, 318, 490, 618 wmemchr macro, 438, 440, 441, 455, 497, 618 wmemcmp function, 437, 497, 618 wmemcpy function, 435, 497, 618 wmemcpy_s function, 498, 618, 659, 660 wmemmove function, 435, 497, 618 wmemmove_s function, 498, 618, 660 wmemset function, 441, 497, 618 wN format modifier, 330, 337, 414, 420 wprintf function, 213, 214, 223, 320, 425, 426, 497, 508, 509, 618, 657 wprintf_s function, 498, 618, 657 wraparound, 7 write-read coherence, 18 write-write coherence, 17 wscanf function, 213, 214, 320, 426, 429, 497, 508, 618 wscanf_s function, 498, 618, 657, 658
600, 609 wcslen function, 436, 441, 497, 609, 663 wcsncat function, 436, 497, 609 wcsncat_s function, 498, 609, 661, 662 wcsncmp function, 437, 497, 609 wcsncpy function, 435, 497, 609 wcsncpy_s function, 498, 609, 658, 659 wcsnlen_s function, 498, 609, 658, 660, 661, 663 wcspbrk macro, 438, 439, 455, 497, 609 wcsrchr macro, 438, 439, 455, 497, 609 wcsrtombs function, 445, 446, 498, 609, 664 wcsrtombs_s function, 498, 609, 664, 665, 666 wcsspn function, 439, 497, 609 wcsstr macro, 438, 439, 455, 497, 609 wcsto family, 32, 213, 214, 432, 609 wcstod family, 432, 433 wcstod function, 419, 421, 423, 430, 508, 573, 576, 583, 599, 609 wcstod128 function, 430, 432, 599, 609 wcstod32 function, 430, 432, 599, 609 wcstod64 function, 430, 432, 599, 609 wcstof function, 423, 430, 575, 583, 599, 609 wcstoimax function, 224, 474, 609 wcstok function, 440, 497, 593, 594, 609 wcstok_s function, 498, 609, 662, 663 wcstol function, 224, 419–421, 423, 433, 434, 497, 609 wcstold function, 423, 430, 583, 599, 609 wcstoll function, 224, 423, 433, 434, 497, 609 wcstombs function, 372, 444, 492, 609 wcstombs_s function, 493, 609, 640, 641 wcstoul function, 224, 421, 423, 433, 434, 497, 609 wcstoull function, 224, 423, 433, 434, 497, 609 wcstoumax function, 224, 474, 609 wcsxfrm function, 437, 497, 593, 609 wctob function, 442, 447, 497, 618 wctomb function, 369, 370, 371, 372, 443, 492, 618 _ wctomb s function, 493, 618, 638, 639 wctrans function, 451, 452, 499, 594, 618 wctrans_t type, 447, 451, 452, 499, 618 wctype function, 450, 451, 499, 594, 618 wctype_t type, 447, 450, 451, 499, 618 weaker, 44 WEOF macro, 412, 427–429, 442, 447, 496, 499, 594, 618 wfN format modifier, 330, 338, 415, 420 white space, 10, 51, 163, 164, 206, 449 white-space character, 190 white-space characters, 51 White-space wide character, 190 wide character, 5 case mapping functions, 451
X_ identifier prefix, 550, 618 xaddd function, 568, 618 XADDD macro, 560 xaddf function, 568, 618
Index
741
ISO/IEC 9899:2023 (E)
working draft — April 1, 2023
XADDF macro, 560 xdivd function, 569, 618 XDIVD macro, 560 xdivf function, 569, 618 XDIVF macro, 560 xfmad function, 569, 618 XFMAD macro, 560 xfmaf function, 569, 618 XFMAF macro, 560
XMULF macro, 560 xor macro, 225, 474, 618 xor_eq macro, 225, 474, 618 xsqrtd function, 569, 618 XSQRTD macro, 560 xsqrtf function, 569, 618 XSQRTF macro, 560 xsubd function, 568, 618 XSUBD macro, 560 xsubf function, 568, 618 XSUBF macro, 560
XID_Continue, 54 XID_Start, 54 xmuld function, 569, 618 XMULD macro, 560 xmulf function, 569, 618
742
z format modifier, 330, 337, 414, 420
zero, 536
Index
N3096