View source for C2x

{{Short description|C programming language standard, future revision}}

'''C2x''' is an informal name for the next (after [[C17 (C standard revision)|C17]]) major C language standard revision.<ref name="HistoryOfC">{{cite web |title=History of C |url=https://en.cppreference.com/w/c/language/history |website=cppreference.com  |archive-url=https://web.archive.org/web/20221019191546/https://en.cppreference.com/w/c/language/history |archive-date=October 19, 2022 |date=2022-06-27 |url-status=live}}</ref><ref name="C2xCharter">{{cite web |title=WG14-N2086 : C2x Charter |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2086.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221222213708/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2086.htm |archive-date=December 22, 2022 |date=2016-09-20 |url-status=live}}</ref>  It is expected to be voted on in 2023 and would therefore become '''C23'''.<ref name="N2984">{{cite web |title=WG14-N2984 : Revised C23 Schedule |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2984.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221025071157/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2984.pdf |archive-date=October 25, 2022 |date=2022-05-05 |url-status=live}}</ref>  The most recent publicly available draft of C23 was released on January 24, 2023.<ref name="N3088"/>

The first WG14 meeting for the C2x draft was held in October 2019, then virtual remote meetings were held due to COVID-19 pandemic in March/April 2020, October/November 2020, March/April 2021, August/September 2021, November/December 2021, January/February 2022, May 2022, July 2022, January 2023.<ref name="N2984"/><ref name="N3088"/>

==Features==
Changes integrated into the latest C23 draft are:<ref name="N3088">{{cite web |title=WG14-N3088 : Draft for ISO/IEC 9899:2023 |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3088.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20230125062238/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3088.pdf |archive-date=January 25, 2023 |date=January 24, 2023 |url-status=live}}</ref>

;Standard Library (new functions)
:* add <code>memset_explicit()</code> function in <code><string.h></code> to erase sensitive data, where memory store must always be performed regardless of optimizations.<ref name="N2897">{{cite web |title=WG14-N2897 : memset_explicit() |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2897.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221025074215/https://open-std.org/jtc1/sc22/wg14/www/docs/n2897.htm |archive-date=October 25, 2022 |date=2021-12-27 |url-status=live}}</ref>
:* add <code>memccpy()</code> function in <code><string.h></code> to efficiently concatenate strings - similar to [[POSIX]] and [[System V Interface Definition|SVID]] C extensions.<ref name="N2349">{{cite web |title=WG14-N2349 : Toward more efficient string copying and concatenation |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2349.htm |website=open-std.org |archive-url=https://web.archive.org/web/20220930092258/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2349.htm |archive-date=September 30, 2022 |date=2019-03-18 |url-status=live}}</ref>
:* add <code>strdup()</code> and <code>strndup()</code> functions in <code><string.h></code> to allocate a copy of a string – similar to [[POSIX]] and [[System V Interface Definition|SVID]] C extensions.<ref name="N2353">{{cite web |title=WG14-N2353 : strdup() and strndup() |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2353.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224063709/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2353.htm |archive-date=December 24, 2022 |date=2019-03-18 |url-status=live}}</ref>
:* add <code>memalignment()</code> function in <code><stdlib.h></code> to determine the byte alignment of a pointer.<ref name="N2974">{{cite web |title=WG14-N2974 : Queryable pointer alignment |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2974.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221013182240/https://www.open-std.org/jtc1/sc22/WG14/www/docs/n2974.pdf |archive-date=October 13, 2022 |date=2022-04-15 |url-status=live}}</ref>
:* add bit utility functions / macros / types in new header <code><stdbit.h></code> to examine many integer types.  All start with <code>stdc_</code> to minimize conflict with legacy code and 3rd party libraries.<ref name="N3022">{{cite web |title=WG14-N3022 : Modern Bit Utilities |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3022.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224194734/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3022.htm |archive-date=December 24, 2022 |date=2022-07-06 |url-status=live}}</ref>
:** In the following, replace <code>*</code> with <code>uc</code>, <code>us</code>, <code>ui</code>, <code>ul</code>, <code>ull</code> for five function names, or blank for a type-generic macro.<ref name="N3022"/>
:** add <code>stdc_count_ones*()</code> and <code>stdc_count_zeros*()</code> to count number of 1 or 0 bits in value.<ref name="N3022"/>
:** add <code>stdc_leading_ones*()</code> and <code>stdc_leading_zeros*()</code> to count leading 1 or 0 bits in value.<ref name="N3022"/>
:** add <code>stdc_trailing_ones*()</code> and <code>stdc_trailing_zeros*()</code> to count trailing 1 or 0 bits in value.<ref name="N3022"/>
:** add <code>stdc_first_leading_one*()</code> and <code>stdc_first_leading_zero*()</code> to find first leading bit with 1 or 0 in value.<ref name="N3022"/>
:** add <code>stdc_first_trailing_one*()</code> and <code>stdc_first_trailing_zero*()</code> to find first trailing bit with 1 or 0 in value.<ref name="N3022"/>
:** add <code>stdc_has_single_bit*()</code> to determine if value an exact power of 2 (return true if and only if there is a single 1 bit).<ref name="N3022"/>
:** add <code>stdc_bit_floor*()</code> to determine the largest integral power of 2 that is not greater than value.<ref name="N3022"/>
:** add <code>stdc_bit_ceil*()</code> to determine the smallest integral power of 2 that is not less than value.<ref name="N3022"/>
:** add <code>stdc_bit_width*()</code> to determine number of bits to represent a value.<ref name="N3022"/>

;Standard Library (existing functions)
:* add <code>%b</code> binary conversion specifier to <code>printf()</code> function family, prepending non-zero values with <code>0b</code>, similar to how <code>%x</code> works.  Implementations that previously didn't use <code>%B</code> as their own extension are encouraged to implement and prepend non-zero values with <code>0B</code>, similar to how <code>%X</code> works.<ref name="N2630">{{cite web |title=WG14-N2630 : formatted input/output of binary integer numbers |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2630.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221214154315/https://open-std.org/JTC1/SC22/WG14/www/docs/n2630.pdf |archive-date=December 14, 2022 |date=2021-01-01 |url-status=live}}</ref>
:* add <code>%b</code> binary conversion specifier to <code>scanf()</code> function family.<ref name="N2630"/>
:* add <code>0b</code> and <code>0B</code> binary conversion support to <code>strtol()</code> and <code>wcstol()</code> function families.<ref name="N2630"/>
:* make the functions <code>bsearch()</code>, <code>bsearch s()</code>, <code>memchr()</code>, <code>strchr()</code>, <code>strpbrk()</code>, <code>strrchr()</code>, <code>strstr()</code>, and their wide counterparts <code>wmemchr()</code>, <code>wcschr()</code>, <code>wcspbrk()</code>, <code>wcsrchr()</code>, <code>wcsstr()</code> return a const qualified object if one was passed to them.<ref name="N3020">{{cite web |title=WG14-N3020 : Qualifier-preserving standard library functions |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3020.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221013190826/https://www.open-std.org/jtc1/sc22/WG14/www/docs/n3020.pdf |archive-date=October 13, 2022 |date=2022-06-13 |url-status=live}}</ref>

;Preprocessor
:* add {{code|#elifdef|c}} and {{code|#elifndef|c}} directives<ref name="N2645">{{cite web |title=WG14-N2645 : Add support for preprocessing directives #elifdef and #elifndef |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2645.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221128133337/https://open-std.org/JTC1/SC22/WG14/www/docs/n2645.pdf |archive-date=November 28, 2022 |date=2020-01-25 |url-status=live}}</ref> are essentially equivalent to {{code|#elif defined|c}} and {{code|#elif !defined|c}}.  Both directives were added to [[C++23]] and [[Software:GNU Compiler Collection|GCC]] 12 too.<ref>{{cite web |title=GCC 12 Adds Support For New #elifdef #elifndef Directives |url=https://www.phoronix.com/news/GCC-12-elifdef-elifndef |website=phoronix |archive-url=https://web.archive.org/web/20221227050002/https://www.phoronix.com/news/GCC-12-elifdef-elifndef |archive-date=December 27, 2022 |date=May 12, 2021 |url-status=live}}</ref>
:* add {{code|#embed|c}} directive for binary resource inclusion.<ref name="N3017">{{cite web |title=WG14-N3017 : #embed - a scannable, tooling-friendly binary resource inclusion mechanism |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224045304/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm |archive-date=December 24, 2022 |date=2022-06-27 |url-status=live}}</ref>
:* add {{code|#warning|c}} directive for diagnostics.<ref name="N2686">{{cite web |title=WG14-N2686 : #warning |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2686.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221128133337/https://open-std.org/JTC1/SC22/WG14/www/docs/n2686.pdf |archive-date=November 28, 2022 |date=2022-07-22 |url-status=live}}</ref>
:* add {{code|__has_include|c}} allowing the availability of a header to be checked by preprocessor directives.<ref name="N2799">{{cite web |title=WG14-N2799 : __has_include for C |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2799.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221224103617/https://open-std.org/JTC1/SC22/WG14/www/docs/n2799.pdf |archive-date=December 24, 2022 |date=2021-08-30 |url-status=live}}</ref>
:* add {{code|__has_c_attribute|c}} allowing the availability of an attribute to be checked by preprocessor directives.<ref name="N2553">{{cite web |title=WG14-N2553 : Querying attribute support |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2553.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221014221314/https://open-std.org/JTC1/SC22/WG14/www/docs/n2553.pdf |archive-date=October 14, 2022 |date=2020-08-04 |url-status=live}}</ref>  (see C++ compatibility group below for new attribute feature)
:* add {{code|__VA_OPT__|c}} functional macro for [[Variadic macro|variadic macro]]s which expands to its argument only if a variadic argument has been passed to the containing macro.<ref name="N3033">{{cite web |title=WG14-N3033 : Comma omission and comma deletion |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3033.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221227031727/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3033.htm |archive-date=December 27, 2022 |date=2022-07-20 |url-status=live}}</ref>

;Types
:* add {{code|nullptr_t|c}} type.<ref name="N3042"/>
:* add {{code|_BitInt(N)|c}} and {{code|unsigned _BitInt(N)|c}} types for bit-precise integers. Add {{code|BITINT_MAXWIDTH|c}} macro for maximum bit width.<ref name="N2763">{{cite web |title=WG14-N2763 : Adding a Fundamental Type for N-bit integers |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2763.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221227055250/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2763.pdf |archive-date=December 27, 2022 |date=2021-06-21 |url-status=live}}</ref><ref name="N3035">{{cite web |title=WG14-N3035 : _BitInt Fixes |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3035.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221013182206/https://www.open-std.org/jtc1/sc22/WG14/www/docs/n3035.pdf |archive-date=October 13, 2022 |date=2022-07-21 |url-status=live}}</ref>  Add <code>ckd_add()</code>, <code>ckd_sub()</code>, <code>ckd_mul()</code> macros for checked integer operations.<ref name="N2867">{{cite web |title=WG14-N2867 : Checked N-Bit Integers |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2867.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221214154907/https://open-std.org/JTC1/SC22/WG14/www/docs/n2867.pdf |archive-date=December 14, 2022 |date=2021-11-28 |url-status=live}}</ref>
:* Variably-modified types (but not [[Variable-length array|VLAs]] which are [[Automatic variable|automatic variables]] allocated on the stack) become a mandatory feature.<ref name="N2778">{{cite web |title=WG14-N2778 : Variably-Modified Types |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2778.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221222053411/https://open-std.org/jtc1/sc22/wg14/www/docs/n2778.pdf |archive-date=December 22, 2022 |date=2021-07-11 |url-status=live}}</ref>
:* Standardization of the <code>[[Typeof|typeof]](...)</code> operator.<ref name="N2899">{{cite web |title=WG14-N2899 : Not-so-magic - typeof for C |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2899.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224044528/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2899.htm |archive-date=December 24, 2022 |date=2022-01-21 |url-status=live}}</ref>
:* the meaning of the {{code|auto|c}} keyword was changed to cause [[Type inference|type inference]] while also retaining its old meaning of a [[Storage class specifier|storage class specifier]] if used alongside a type.<ref name="N3007">{{cite web |title=WG14-N3007 : Type inference for object definitions |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3007.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224105654/https://open-std.org/JTC1/SC22/WG14/www/docs/n3007.htm |archive-date=December 24, 2022 |date=2022-06-10 |url-status=live}}</ref>

;Constants
:* add {{code|nullptr|c}} constant for <code>nullptr_t</code> type.<ref name="N3042">{{cite web |title=WR14-N3042 : Introduce the nullptr constant |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n3042.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224043228/https://open-std.org/JTC1/SC22/WG14/www/docs/n3042.htm |archive-date=December 24, 2022 |date=2022-07-22 |url-status=live}}</ref>
:* add <code>wb</code> and <code>uwb</code> integer literal suffixes for {{code|_BitInt(N)|c}} and {{code|unsigned _BitInt(N)|c}} types,<ref name="N2775">{{cite web |title=WG14-N2775 : Literal suffixes for bit-precise integers |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2775.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221227014728/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2775.pdf |archive-date=December 27, 2022 |date=2021-07-13 |url-status=live}}</ref> such as {{code|6uwb|c}} yields an <code>unsigned _BitInt(3)</code>, and {{code|-6wb|c}} yields a <code>signed _BitInt(4)</code> which has three value bits and one sign bit.
:* add <code>0b</code> and <code>0B</code> [[Integer literal|binary literal constant]] prefixes,<ref name="N2549">{{cite web |title=WG14-N2549 : Allow for binary integer constants |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2549.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221222192818/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2549.pdf |archive-date=December 22, 2022 |date=2020-07-30 |url-status=live}}</ref> such as {{code|0b10101010|c}} (equating to 0xAA).
:* add <code>'</code> digit separator to literal constants,<ref name="N2626">{{cite web |title=WG14-N2626 : Digit separators |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2626.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221219215425/https://open-std.org/JTC1/SC22/WG14/www/docs/n2626.pdf |archive-date=December 19, 2022 |date=2020-12-15 |url-status=live}}</ref> such as {{code|0xFE'DC'BA'98|c}} (equating to 0xFEDCBA98), {{code|299'792'458|c}} (equating to [[Physics:Speed of light|299792458]]), {{code|1.414'213'562|c}} (equating to [[Square root of 2|1.414213562]]).
:* add the ability to specify the underlying type of an <code>[[Enumerated type|enum]]</code>.<ref name="N3030">{{cite web |title=WG14-N3030 : Enhancements to Enumerations |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n3030.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221126132709/https://open-std.org/JTC1/SC22/WG14/www/docs/n3030.htm |archive-date=November 26, 2022 |date=2022-07-19 |url-status=live}}</ref>
:* allow {{code|enum|c}}s with no fixed underlying type to store values that aren't representable by {{code|int|c}}.<ref name="N3029">{{cite web |title=WG14-N3029 : Improved Normal Enumerations |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n3029.htm |website=open-std.org |archive-url=https://web.archive.org/web/20230129180341/https://open-std.org/JTC1/SC22/WG14/www/docs/n3029.htm |archive-date=January 29, 2023 |date=2022-07-19 |url-status=live}}</ref>

;C++ compatibility
:* add [[C++11]] style [[C++11#Attributes|attribute]] syntax<ref name="N2335">{{cite web |title=WG14-N2335 : Attributes in C |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2335.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221026060722/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2335.pdf |archive-date=October 26, 2022 |date=2019-03-09 |url-status=live}}</ref> using double square brackets {{code|<nowiki>[[]]</nowiki>|c}}.  Add attributes <ref name="N2554">{{cite web |title=WG14-N2554 : Minor attribute wording cleanups |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2554.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221128133337/https://open-std.org/JTC1/SC22/WG14/www/docs/n2554.pdf |archive-date=November 28, 2022 |date=2020-08-04 |url-status=live}}</ref> {{code|<nowiki>deprecated</nowiki>|c}},<ref name="N2334">{{cite web |title=WG14-N2334 : The deprecated attribute |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2334.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221019131835/https://open-std.org/JTC1/SC22/WG14/www/docs/n2334.pdf |archive-date=October 19, 2022 |date=2019-01-22 |url-status=live}}</ref> {{code|<nowiki>fallthrough</nowiki>|c}},<ref name="N2408">{{cite web |title=WG14-N2408 : The fallthrough attribute |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2408.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221225070709/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2408.pdf |archive-date=December 25, 2022 |date=2019-08-11 |url-status=live}}</ref> {{code|<nowiki>maybe unused</nowiki>|c}},<ref name="N2270">{{cite web |title=WG14-N2270 : The maybe_unused attribute |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2270.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221225070836/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2270.pdf |archive-date=December 25, 2022 |date=2018-07-06 |url-status=live}}</ref> {{code|<nowiki>nodiscard</nowiki>,|c}}<ref name="N2267">{{cite web |title=WG14-N2267 : The nodiscard attribute |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2267.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221019131846/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2267.pdf |archive-date=October 19, 2022 |date=2018-07-06 |url-status=live}}</ref> and {{code|<nowiki>noreturn</nowiki>|c}} attribute for compatibility with [[C++11]], then deprecate {{code|_Noreturn|c}}, {{code|noreturn|c}}, header <code><stdnoreturn.h></code> features introduced in [[C11 (C standard revision)|C11]].<ref name="N2764">{{cite web |title=WG14-N2764 : The noreturn attribute |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n2764.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221225063437/https://open-std.org/JTC1/SC22/WG14/www/docs/n2764.pdf |archive-date=December 25, 2022 |date=2021-06-21 |url-status=live}}</ref>  Duplicate attributes are allowed for compatibility with [[C++23]].<ref name="N2557">{{cite web |title=WG14-N2557 : Allow Duplicate Attributes |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2557.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221128133337/https://open-std.org/JTC1/SC22/WG14/www/docs/n2557.pdf |archive-date=November 28, 2022 |date=2020-09-01 |url-status=live}}</ref>
:* add <code>u8</code> prefix for [[Character literal|character literal]]s to represent [[UTF-8]] encoding for compatibility with [[C++17]].<ref name="N2418">{{cite web |title=WG14-N2418 : Adding the u8 character prefix |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2418.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20230113210023/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2418.pdf |archive-date=January 13, 2023 |date=2019-09-02 |url-status=live}}</ref><ref>[https://stackoverflow.com/questions/31970111/what-is-the-point-of-the-utf-8-character-literals-proposed-for-c17#31970297 What is the point of the UTF-8 character literals proposed for C++17?; Stack Overflow.]</ref>
:* add {{code|#elifdef|c}} and {{code|#elifndef|c}} preprocessing directives for compatibility with [[C++23]].<ref name="N2645"/> (see preprocessor group above)

;Other
:* Support for the ISO/IEC 60559:2020, the current version of the [[IEEE 754|IEEE 754 standard]] for floating-point arithmetic, with extended binary floating-point arithmetic and (optional) decimal floating-point arithmetic.<ref name="N2341">{{cite web |title=WG14-N2341 : ISO/IEC TS 18661-2 - Floating-point extensions for C - Part 2: Decimal floating-point arithmetic |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2341.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221121122559/https://open-std.org/JTC1/SC22/WG14/www/docs/n2341.pdf |archive-date=December 27, 2022 |date=February 26, 2019 |url-status=live}}</ref><ref name="N2601">{{cite web |title=WG14-N2601 : Annex X - IEC 60559 interchange and extended types |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2601.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221014221322/https://open-std.org/JTC1/SC22/WG14/www/docs/n2601.pdf |archive-date=December 27, 2022 |date=October 15, 2020 |url-status=live}}</ref>
:* Single-argument <code>[[Assert.h#Static assert|Static assert]]</code>.<ref>{{Cite web|url=https://open-std.org/JTC1/SC22/WG14/www/docs/n2265.pdf|title=Harmonizing static_assert with C++}}</ref>
:* [[Label (computer science)|Labels]] can appear before [[Declaration (computer programming)|declaration]]s and at the end of [[Statement (computer science)#Compound statements|compound statements]].<ref name="N2508">{{cite web |title=WG14-N2508 : Free Positioning of Labels Inside Compound Statements |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2508.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221227183107/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2508.pdf |archive-date=December 27, 2022 |date=2020-03-28 |url-status=live}}</ref>
:* Unnamed parameters in function definitions.<ref name="N2510">{{cite web |title=WG14-N2510 : Allowing unnamed parameters in a function definition |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2510.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221224075948/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2510.pdf |archive-date=December 24, 2022 |date=2020-04-09 |url-status=live}}</ref>
:* Better support for using <code>[[Const (computer programming)|const]]</code> with arrays.<ref name="N2607">{{cite web |title=WG14-N2607 : Compatibility of Pointers to Arrays with Qualifiers |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2607.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221013182946/https://www.open-std.org/jtc1/sc22/WG14/www/docs/n2607.pdf |archive-date=October 13, 2022 |date=2020-10-31 |url-status=live}}</ref>
:* Zero initialization with <code>{}</code> (including initialization of VLAs).<ref name="N2900">{{cite web |title=WG14-N2900 : Consistent, Warningless, and Intuitive Initialization with {} |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2900.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221227181452/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2900.htm |archive-date=December 27, 2022 |date=2022-01-01 |url-status=live}}</ref>
:* {{code|alignas|c}}, {{code|alignof|c}}, {{code|bool|c}}, {{code|true|c}}, {{code|false|c}}, {{code|static_assert|c}}, [[Thread-local storage|{{code|thread local|c}}]] become keywords.<ref name="N2935">{{cite web |title=WG14-N2935 : Make false and true first-class language features |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2935.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221121123457/https://open-std.org/JTC1/SC22/WG14/www/docs/n2935.pdf |archive-date=November 21, 2022 |date=2022-02-15 |url-status=live}}</ref><ref name="N2934">{{cite web |title=WG14-N2934 : Revise spelling of keywords |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2934.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221224132455/https://open-std.org/JTC1/SC22/WG14/www/docs/n2934.pdf |archive-date=December 24, 2022 |date=2022-02-15 |url-status=live}}</ref>
:* The <code>constexpr</code> specifier for objects but not functions, unlike C++'s equivalent.<ref name="N3018">{{cite web |title=WG14-N3018 : The constexpr specifier for object definitions |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3018.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224074302/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3018.htm |archive-date=December 24, 2022 |date=2022-07-06 |url-status=live}}</ref>
:* variadic functions no longer need a named argument before the ellipsis and the {{code|va_start|c}} macro no longer needs a second argument nor does it evaluate any argument after the first one if present.<ref name="N2975">{{cite web |title=WG14-N2975 : Relax requirements for variadic parameter lists |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2975.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221128133337/https://open-std.org/JTC1/SC22/WG14/www/docs/n2975.pdf |archive-date=November 28, 2022 |date=2022-04-15 |url-status=live}}</ref>
:* add the {{code|char8_t|c}} type for storing [[UTF-8]] encoded data and change the type of u8 character constants and string literals to {{code|char8_t|c}}. Also, the functions <code>mbrtoc8()</code> and <code>c8rtomb()</code> to convert a narrow multibyte character to UTF-8 encoding and a single code point from UTF-8 to a narrow multibyte character representation respectively.<ref>{{cite web|url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm|title=char8_t: A type for UTF-8 characters and strings (Revision 1)}}</ref>
:* allow [[Storage class specifier|storage class specifier]]s to appear in compound literal definition.<ref name="N3038">{{cite web |title=WG14-N3038 : Introduce storage-class specifiers for compound literals |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n3038.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221126130057/https://open-std.org/JTC1/SC22/WG14/www/docs/n3038.htm |archive-date=November 26, 2022 |date=2022-07-21 |url-status=live}}</ref>
<!-- hide the following until references can be added!!
:* Type generic functions for performing checked integer arithmetic ([[Integer overflow]]).{{Citation needed|date=December 2022}} https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2683.pdf ?
:* Pragmas for rounding direction: <code>STDC FENV_ROUND</code> and <code>STDC FENV_DEC_ROUND</code>.{{Citation needed|date=December 2022}}
-->
<!--
atomic_char8_t type alias
ATOMIC_CHAR8_T_LOCK_FREE test macro
-->
<!-- Seems regular binary floating point (IEEE-754), is actually optional! Not just for newer decimal:
Feature test macros for optional features
__STDC_IEC_60559_BFP__
Indicates IEEE-754 binary floating-point arithmetic and required math functions are supported.
This macro supersedes __STDC_IEC_559__.
__STDC_IEC_60559_DFP__
Indicates IEEE-754 decimal floating-point arithmetic and required math functions are supported.
__STDC_IEC_60559_COMPLEX__
Indicates IEEE-754 complex arithmetic and required math functions are supported.
This macro supersedes __STDC_IEC_55
-->

==Obsolete features==
Some old obsolete features are either removed or deprecated:
:* Remove [[Digraphs and trigraphs#C|Trigraphs]].<ref name="N2940">{{cite web |title=WG14-N2940 : Removing trigraphs??! |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2940.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221026005747/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2940.pdf |archive-date=October 26, 2022 |date=2022-03-02 |url-status=live}}</ref>
:* Remove [[C (programming language)#K&R C|K&R]] function definitions/declarations.<ref name="N2432">{{cite web |title=WG14-N2432 : Remove support for function definitions with identifier lists proposal |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2432.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221227012244/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2432.pdf |archive-date=December 27, 2022 |date=September 25, 2019 |url-status=live}}</ref><ref name="N2841">{{cite web |title=WG14-N2841 : No function declarators without prototypes |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2841.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221112154740/https://www9.open-std.org/jtc1/sc22/wg14/www/docs/n2841.htm |archive-date=November 12, 2022 |date=2021-10-10 |url-status=live}}</ref>
:* Remove representations for signed integers other than two's complement. [[Two's complement]] signed integer representation will be required.<ref name="N2412">{{cite web |title=WG14-N2412 : Two’s complement sign representation |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2412.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20221227174224/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2412.pdf |archive-date=December 27, 2022 |date=August 11, 2019 |url-status=live}}</ref>
:* The {{code|*_HAS_SUBNORM|c}} macros in <code><float.h></code> are obsolescent features.<ref name="N2993">{{cite web |title=WG14-N2993 : Make *_HAS_SUBNORM be obsolescent |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2993.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221205194635/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2993.htm |archive-date=December 5, 2022 |date=2022-06-06 |url-status=live}}</ref>

==Compiler support==
The [[Software:GNU Compiler Collection|GCC]] 9,<ref>{{cite web |title=GCC 9 Release Notes |url=https://gcc.gnu.org/gcc-9/changes.html#c |website=GNU Project |archive-url=https://web.archive.org/web/20221227032646/https://gcc.gnu.org/gcc-9/changes.html |archive-date=December 27, 2022 |url-status=live}}</ref> [[Software:Clang|Clang]] 9.0,<ref>{{cite web |title=Clang 9.0 - add new language mode for C2x |url=https://github.com/llvm/llvm-project/commit/d06f3917913d2558b771ccc48d838f8cd8993c01 |website=LLVM Project Repository |archive-url=https://web.archive.org/web/20221227032640/https://github.com/llvm/llvm-project/commit/d06f3917913d2558b771ccc48d838f8cd8993c01 |archive-date=December 27, 2022 |date=May 14, 2019 |url-status=live}}</ref> and [[Software:LCC (compiler)#Pelles C|Pelles C]] 11.00<ref>{{cite web |title=Pelles C - major changes between 10.00 and 11.00 |url=http://www.smorgasbordet.com/pellesc/changes_1000_1100.htm |website=smorgasbordet.com |archive-url=https://web.archive.org/web/20221227032644/http://www.smorgasbordet.com/pellesc/changes_1000_1100.htm |archive-date=December 27, 2022 |url-status=live}}</ref> compilers implement an experimental compiler flag to support this standard.
<!--
Obsolete 
Removed
Old-style function declarations and definitions
Representations for signed integers other than two's complement
Permission that u/U-prefixed character constants and string literals may be not UTF-16/32
Mixed wide string literal concatenation
Support for calling realloc() with zero size (the behavior becomes undefined)
__alignof_is_defined and __alignas_is_defined

Deprecated
Old feature-test macros
__STDC_IEC_559__
__STDC_IEC_559_COMPLEX__
_Noreturn function specifier
_Noreturn attribute token
asctime()
ctime()
DECIMAL_DIG
Definition of following numeric limit macros in <math.h> (they should be used via <limits.h>)
INFINITY
DEC_INFINITY
NAN
DEC_NAN
__bool_true_false_are_defined

New language features 
Decimal floating-point types (_Decimal32, _Decimal64, and _Decimal128)
Bit-precise integers (_BitInt(N))
Binary integer constants
u8 character constants
Type change of u8 string literals
Digit separator '
Empty initializer = {}
Attributes
deprecated
fallthrough
maybe unused
nodiscard
noreturn
Unnamed parameters in function definitions
Identical cvr-qualifications for array types and their element types
Single-argument _Static_assert
Labels followed by declarations and }
nullptr constant and the associated nullptr_t type
true and false become keywords (may be predefined macros for compatibility reasons)

New preprocessor directives
 #elifdef
 #elifndef
 #warning
 #embed

Pragmas for rounding direction
 STDC FENV_ROUND
 STDC FENV_DEC_ROUND

New library features 
 Extended binary floating-point math functions

This section is incomplete
Reason: List TBD
Decimal floating-point math functions
-dN variants for existing and new floating-point math functions
quantizedN()
samequantumdN()
quantumdN()
llquantexpdN()
encodedecdN()
decodedecdN()
encodebindN()
decodebindN()
Floating-point formatting functions

POSIX functions
memccpy()
strdup()
strndup()
gmtime_r()
localtime_r()
Extensions for strftime() and wcsftime()
Extensions for fscanf() and fprintf() function families
wN and wfN length modifiers for [u]intN_t and [u]int_fastN_t respectively
H, D, and DD length modifiers for _Decimal32, _Decimal64, and _Decimal128 respectively
b conversion specifier for unsigned integer types
timespec_getres()
Macro constants for width of integer types
Additional numeric limit macros for floating-point types
Library version-test macros
__STDC_VERSION_FENV_H__
__STDC_VERSION_MATH_H__
__STDC_VERSION_STDINT_H__
__STDC_VERSION_STDLIB_H__
__STDC_VERSION_TGMATH_H__
__STDC_VERSION_TIME_H__ Obsolete 

Removed
Old-style function declarations and definitions
Representations for signed integers other than two's complement
Permission that u/U-prefixed character constants and string literals may be not UTF-16/32
Mixed wide string literal concatenation
Support for calling realloc() with zero size (the behavior becomes undefined)
__alignof_is_defined and __alignas_is_defined

Deprecated
Old feature-test macros
__STDC_IEC_559__
__STDC_IEC_559_COMPLEX__
_Noreturn function specifier
_Noreturn attribute token
asctime()
ctime()
DECIMAL_DIG
Definition of following numeric limit macros in <math.h> (they should be used via <limits.h>)
INFINITY
DEC_INFINITY
NAN
DEC_NAN
__bool_true_false_are_defined

New language features 
Decimal floating-point types (_Decimal32, _Decimal64, and _Decimal128)
Bit-precise integers (_BitInt(N))
Binary integer constants
u8 character constants
Type change of u8 string literals
Digit separator '
Empty initializer = {}
Attributes
deprecated
fallthrough
maybe unused
nodiscard
noreturn
Unnamed parameters in function definitions
Identical cvr-qualifications for array types and their element types
Single-argument _Static_assert
Labels followed by declarations and }
nullptr constant and the associated nullptr_t type
true and false become keywords (may be predefined macros for compatibility reasons)

New library features 
 Extended binary floating-point math functions

This section is incomplete
Reason: List TBD
Decimal floating-point math functions
-dN variants for existing and new floating-point math functions
quantizedN()
samequantumdN()
quantumdN()
llquantexpdN()
encodedecdN()
decodedecdN()
encodebindN()
decodebindN()
Floating-point formatting functions
Library support for UTF-8
char8_t type alias
mbrtoc8()
c8rtomb()
atomic_char8_t type alias
ATOMIC_CHAR8_T_LOCK_FREE test macro
POSIX functions
memccpy()
strdup()
strndup()
gmtime_r()
localtime_r()
Extensions for strftime() and wcsftime()
Extensions for fscanf() and fprintf() function families
wN and wfN length modifiers for [u]intN_t and [u]int_fastN_t respectively
H, D, and DD length modifiers for _Decimal32, _Decimal64, and _Decimal128 respectively
b conversion specifier for unsigned integer types
timespec_getres()
Macro constants for width of integer types
Additional numeric limit macros for floating-point types
Library version-test macros
__STDC_VERSION_FENV_H__
__STDC_VERSION_MATH_H__
__STDC_VERSION_STDINT_H__
__STDC_VERSION_STDLIB_H__
__STDC_VERSION_TGMATH_H__
__STDC_VERSION_TIME_H__

-->

== See also ==
* [[C++23]], [[C++20]], [[C++17]], [[C++14]], [[C++11]], [[C++03]], C++98, versions of the C++ programming language standard
* [[Compatibility of C and C++]]

==References==
{{Reflist}}

==External links==
* [https://www.open-std.org/jtc1/sc22/wg14/www/wg14_document_log.htm C Working Group WG14 Documents]
* [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3088.pdf N3088, draft of C23 standard (January 2023)]

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{{S-ttl| title=[[C (programming language)|C language]] standards}}
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{{C programming language}}

[[Category:C (programming language)]]
[[Category:Programming language standards]]

{{Sourceattribution|C2x|1}}