View source for C23 (C standard revision)

{{Short description|C programming language standard, current revision}}
{{C language revisions}}
'''C23''', formally '''ISO/IEC 9899:2024''', is the current [[open standard]] for the [[C (programming language)|C]] programming language, which supersedes [[C17 (C standard revision)|C17]] (standard ISO/IEC 9899:2018).<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>  It was started in 2016 informally as C2x,<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> and was published on October 31, 2024.<ref>{{cite web |title=ISO/IEC PRF 9899 |url=https://www.iso.org/standard/82075.html |website=iso.org |archive-url=http://web.archive.org/web/20240919185914/https://www.iso.org/standard/82075.html |archive-date=September 19, 2024 |url-status=live}}</ref>  The freely available draft most similar to the one published is document N3220<ref name="N3220"></ref> (see [[#Available texts|Available texts]], below).  The first WG14 meeting for the C2x draft was held in October 2019,<ref name="N2437">{{cite web |title=WG14-N2437: Agenda for October 2019 |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2437.htm |website=open-std.org |archive-url=https://web.archive.org/web/20210305073426/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2437.htm |archive-date=March 5, 2021 |date=2019-10-21 |url-status=live}}</ref> virtual remote meetings were held in 2020 due to the [[COVID-19 pandemic]], then various teleconference meetings continued to occur through 2024.

In C23, the value of __STDC_VERSION__ changes from 201710L to 202311L. The common names "C17" and "C23" reflect these values, which are frozen prior to final adoption, rather than the years in the ISO standards identifiers (9899:2018 and 9899:2024).

==Features==
Changes integrated into the latest working draft of C23 are listed below.<ref name="N3096">{{cite web |title=WG14-N3096: Draft for ISO/IEC 9899:2024 |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20230402172459/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf |archive-date=April 2, 2023 |date=April 1, 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 is 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"/>
* Add <code>timegm()</code> function in <code><[[time.h]]></code> to convert time structure into calendar time value - similar to function in [[glibc]] and [[musl]] libraries.<ref name="N2833">{{cite web |title=WG14-N2833: Add timegm() as non-optional part of time.h |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2833.htm |website=open-std.org |archive-url=https://web.archive.org/web/20211201062452/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2833.htm |archive-date=December 1, 2021 |date=2021-10-07 |url-status=live}}</ref>
* New <code><[[math.h]]></code> functions based on IEEE 754-2019 recommendations, such as trigonometry functions operating on units of <math>\pi x</math> and <code>exp10</code>.<ref>See N3096 § B.11 for a useful overview. The functions were added in separate documents: N2488, its updated versions, and its refs.</ref>

====Existing functions====
* Add <code>%b</code> binary conversion specifier to <code>printf()</code> function family.<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|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 {{C-lang|#elifdef}} and {{C-lang|#elifndef}} [[preprocessor directive|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> which are essentially equivalent to {{C-lang|#elif defined}} and {{C-lang|#elif !defined}}.  Both directives were added to {{nowrap|[[C++23]]}} standard and [[GNU Compiler Collection|GCC]] 12.<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 {{C-lang|#embed}} directive for binary resource inclusion and {{C-lang|__has_embed}} allowing the availability of a resource to be checked by preprocessor directives.<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 {{C-lang|#warning}} 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 {{C-lang|__has_include}} 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 {{C-lang|__has_c_attribute}} 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 "{{nowrap|C++}} compatibility" group for new attribute feature)
* Add {{C-lang|__VA_OPT__}} functional macro for [[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 [[nullptr_t|{{Code|nullptr_t|c}}]], a [[null pointer]] type.<ref name="N3042"/>
* Add {{C-lang|_BitInt(N)}} and {{C-lang|unsigned _BitInt(N)}} types for bit-precise integers. Add {{C-lang|BITINT_MAXWIDTH}} 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>
* 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>
* Standardization of the <code>[[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 {{C-lang|auto}} keyword was changed to cause [[type inference]] while also retaining its old meaning of a [[storage class specifier]] if used alongside a type. Unlike [[C++]], C23 allows type inference only for object definitions (no inferring function return type or function parameter 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>
* Compatibility rules for structure, union, and enumerated types were changed to allow a redeclaration of a compatible type with the same tag.<ref name="N3037">{{cite web |title=WG14-N3037: Improved Rules for Tag Compatibility (updates N3032) |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3037.pdf}}</ref>
* Exact-width integer may now exceed {{code|intmax_t}} (N2888).<ref name=shep2207>{{cite web |title=C23 is Finished: Here is What is on the Menu |url=https://thephd.dev/c23-is-coming-here-is-what-is-on-the-menu |website=The Pasture |language=en |date=31 July 2022}}<!-- The author is a member of WG14, the working group responsible for C. They do not use a traditional-sounding name in dealing with the WG, so there is no name to cite; in N2900, one of their papers, the name is listed as "Shepherd (Shepherd's Oasis LLC)". --></ref>

===Constants===
* Add [[nullptr|{{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 {{C-lang|_BitInt(N)}} and {{C-lang|unsigned _BitInt(N)}} 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 {{C-lang|6uwb}} yields an <code>unsigned _BitInt(3)</code>, and {{C-lang|-6wb}} 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 {{C-lang|0b10101010}} (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 {{C-lang|0xFE'DC'BA'98}} (equating to 0xFEDCBA98), {{C-lang|299'792'458}} (equating to [[Speed of light|299792458]]), {{C-lang|1.414'213'562}} (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 {{C-lang|enum}}s with no fixed underlying type to store values that are not representable by {{C-lang|int}}.<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>

===Keywords===
* Add {{C-lang|true}} and {{C-lang|false}} 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>
* Add {{C-lang|alignas}}, {{C-lang|alignof}}, {{C-lang|bool}}, {{C-lang|static_assert}}, [[thread-local storage|{{Code|thread_local|c}}]] keywords.  Previously defined keywords become alternative spellings: {{C-lang|_Alignas}}, {{C-lang|_Alignof}}, {{C-lang|_Bool}}, {{C-lang|_Static_assert}}, {{C-lang|_Thread_local}}.<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>
* Add {{C-lang|_BitInt}} keyword (see "types" group)
* Add {{C-lang|typeof}} and {{C-lang|typeof_unqual}} keywords (see "types" group)
* Add {{C-lang|nullptr}} keyword (see "constants" group)
* Add {{C-lang|constexpr}} keyword (see "other" group)
* Add {{C-lang|_Decimal32}}, {{C-lang|_Decimal64}}, {{C-lang|_Decimal128}} keywords for (optional) [[decimal floating point|decimal floating-point]] arithmetic (see "other" group)

===Syntax===
* [[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>
* 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>
* [[Variadic functions]] no longer need a named argument before the ellipsis and the {{C-lang|va_start}} 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 [[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 {{C-lang|1=[[]]}}. In addition to [[C++11]] attributes listed below, add new attributes:
** <code><nowiki>[[unsequenced]]</nowiki></code><ref name=":0">{{Cite web |title=Unsequenced functions |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n2956.htm |access-date=2024-07-18 |website=open-std.org}}</ref> allows compiler optimizations for functions producing repeatable outputs only based on their parameters
** <code><nowiki>[[reproducible]]</nowiki></code>,<ref name=":0" /> similar to <code><nowiki>[[unsequenced]]</nowiki></code>, but for functions whose call order also matters
* Add single-argument <code>[[Assert.h#static assert|_Static_assert]]</code> for compatibility with [[C++17]].<ref name="N2265">{{cite web |title=WG14-N2265: Harmonizing static_assert with C++ |url=https://open-std.org/JTC1/SC22/WG14/www/docs/n2265.pdf |website=open-std.org |archive-url=https://web.archive.org/web/20230328064918/https://open-std.org/JTC1/SC22/WG14/www/docs/n2265.pdf |archive-date=March 28, 2023 |date=2018-07-06 |url-status=live}}</ref>
* Functions with no arguments listed in the prototype (e.g. <code>void foo()</code>) are understood as taking no arguments (see removal of K&R function declarations)

===C++ compatibility===
* Various syntax changes improve compatibility with C++, such as [[label (computer science)|label]]s before declarations, unnamed function arguments, zero initialization with <code>{}</code>, variadic functions without named argument, [[C++11]] style attributes, <code>[[Assert.h#static assert|_Static_assert]]</code> (see Syntax). For [[label (computer science)|label]]s at the end of compound statements a corresponding change was made to [[C++23]].<ref>{{cite web|url=https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2324r2.pdf|title=Labels at the end of compound statements (C compatibility)|date=2022-01-13}}</ref>
* Add C++-style attributes (see Syntax). 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> {{C-lang|1=[[deprecated]]}},<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> {{C-lang|1=[[fallthrough]]}},<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> {{C-lang|1=[[maybe_unused]]}},<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> {{C-lang|1=[[nodiscard]]}},<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 {{C-lang|1=[[noreturn]]}} attribute for compatibility with [[C++11]], then deprecate {{C-lang|_Noreturn}}, {{C-lang|noreturn}}, 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> All standard attributes can also be surrounded by double underscores (e.g. {{C-lang|1=[[__deprecated__]]}} is equivalent to {{C-lang|1=[[deprecated]]}}).
* Add <code>u8</code> prefix for [[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 {{C-lang|#elifdef}} and {{C-lang|#elifndef}} preprocessing directives for compatibility with [[C++23]].<ref name="N2645"/> (see "preprocessor" group)

===Other features===
* 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=November 21, 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=October 14, 2022 |date=October 15, 2020 |url-status=live}}</ref>

* The <code>[[constexpr]]</code> specifier for objects but not functions, unlike [[constexpr (C++)|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>
* Add {{C-lang|char8_t}} type for storing [[UTF-8]] encoded data and change the type of u8 character constants and string literals to {{C-lang|char8_t}}. 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 name="N2653">{{cite web |title=WG14-N2653: char8_t: A type for UTF-8 characters and strings (Revision 1) |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm |website=open-std.org |archive-url=https://web.archive.org/web/20230527110842/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm |archive-date=May 27, 2023 |date=2021-06-04 |url-status=live}}</ref>
* Clarify that all {{C-lang|char16_t}} strings and literals shall be [[UTF-16]] encoded, and all {{C-lang|char32_t}} strings and literals shall be [[UTF-32]] encoded, unless otherwise explicitly specified.<ref name="N2728">{{cite web |title=WG14-N2728: char16_t & char32_t string literals shall be UTF-16 & UTF-32 |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2728.htm |website=open-std.org |archive-url=https://web.archive.org/web/20230527110756/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2728.htm |archive-date=May 27, 2023 |date=2021-05-15 |url-status=live}}</ref>
* Allow [[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>

==Obsolete features==
Some old obsolete features are either removed or deprecated from the working draft of C23:
:* Remove [[Digraphs and trigraphs (programming)#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 (with no information about the function arguments).<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 {{C-lang|*_HAS_SUBNORM}} 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 following compilers implement an experimental compiler flag to support this standard: 

* [[GNU Compiler Collection|GCC]] 9,<ref>{{cite web |title=GCC 9 Release Notes |url=https://gcc.gnu.org/gcc-9/changes.html#c |url-status=live |archive-url=https://web.archive.org/web/20221227032646/https://gcc.gnu.org/gcc-9/changes.html |archive-date=December 27, 2022 |website=GNU Project}}</ref> 
* [[Clang]] 9.0,<ref>{{cite web |date=May 14, 2019 |title=Clang 9.0 - add new language mode for C2x |url=https://github.com/llvm/llvm-project/commit/d06f3917913d2558b771ccc48d838f8cd8993c01 |url-status=live |archive-url=https://web.archive.org/web/20221227032640/https://github.com/llvm/llvm-project/commit/d06f3917913d2558b771ccc48d838f8cd8993c01 |archive-date=December 27, 2022 |website=LLVM Project Repository}}</ref> 
* [[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 |url-status=live |archive-url=https://web.archive.org/web/20221227032644/http://www.smorgasbordet.com/pellesc/changes_1000_1100.htm |archive-date=December 27, 2022 |website=smorgasbordet.com}}</ref> 

== Available texts ==

Like other editions of the C standard, the official ISO text of the standard is not freely available.

The latest working draft pre-C23 that was made public was N3096,<ref name="N3096"/> dated 2023-04-01. In the months that followed this draft, hundreds of changes<ref name="N3150">{{cite web |title=N3150 - Editor's Report, Post January-February 2023 Meeting |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3150.htm |website=open-std.org |date=2023-07-08}}</ref> were made before producing the working draft N3149 dated 2023-07-09 and the official draft standard N3219 dated 2024-02-22.<ref name="N3150" /><ref name="N3221">{{cite web |title=N3221 - Editor's Report, Post January 2024 Meeting |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3221.htm |website=open-std.org |date=2024-02-15}}</ref> Neither of these later drafts is public.<ref name="N3150"/><ref name="N3221"/>

On the same date that the draft standard N3219 was announced, a new working draft N3220<ref name="N3220">{{cite web |title=ISO/IEC 9899:2024 (en) — N3220 working draft |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf |website=open-std.org |date=2024-02-22}}</ref> was made public. While this document is officially described<ref name="N3221"/> as a draft of the future version "C2Y" of the standard, the accompanying "Editor's Report" specifies that N3220 differs from the draft C23 standard N3219 only by a fix to one footnote in Annex K.<ref name="N3221"/>

== See also ==
{{Portal|Computer programming}}
* [[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}}

==Further reading==
* [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf N3096] (last freely-available working draft before C23); WG14; April 2023. ''(free download)''
* N3149 (working draft of C23 standard); WG14; July 2023. ''(not available to public)''
* N3219 ([https://www.iso.org/standard/82075.html ISO/IEC 9899:2023 DIS Draft]); WG14; February 2024. ''(ISO draft available but not free)''
* ISO/IEC 9899:2024 (official C23 standard); [[International Organization for Standardization|ISO]]; 2024. ''(planning for release in 2024)''
* [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf N3220] (first working draft after C23; differs from draft standard N3219 only in one footnote); WG14; February 2024. ''(free download)''

==External links==
* [https://www.open-std.org/jtc1/sc22/wg14/ C Language WG14 (Working Group 14)]
:* [https://www.open-std.org/jtc1/sc22/wg14/www/wg14_document_log.htm WG14 Document Repository]
:* [https://www.open-std.org/jtc1/sc22/wg14/www/meetings WG14 Meetings] - agenda and minutes
:* WG14 Charters: [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2021.htm C2x Charter], [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2611.htm C23 Charter], [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2986.htm Interpreting the C23 Charter], [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3223.pdf C Standard Charter]

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