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====Existing functions====

====Existing functions====

* For functions <code>strtol()</code>, <code>strtoll()</code>, <code>strtoul()</code>, <code>strtoull()</code>, and their wide counterparts <code>wcstol()</code>, <code>wcstoll()</code>, <code>wcstoul()</code>, <code>wcstoull()</code>; if the value of base is 8 (octal), the characters <code>0o</code> or <code>0O</code> may optionally precede the sequence of letters and digits. If a sign is present, the <code>0o</code> or <code>0O</code> follows the sign.<ref name=”N3353″/>

* For functions <code>strtol()</code>, <code>strtoll()</code>, <code>strtoul()</code>, <code>strtoull()</code>, and their wide counterparts <code>wcstol()</code>, <code>wcstoll()</code>, <code>wcstoul()</code>, <code>wcstoull()</code> if the value of base is 8 (octal), the characters <code>0o</code> or <code>0O</code> may optionally precede the sequence of letters and digits. If a sign is present, the <code>0o</code> or <code>0O</code> follows the sign.<ref name=”N3353″/>

===Constants===

===Constants===

Revision as of 18:21, 27 October 2025

C programming language standard draft, next revision

C2Y is an informal name for the next revision of the C programming language after C23. The first “C Language Working Group 14” (WG14) meeting primarily about the C2Y draft was held in February 2025.[1] Changes have already started to be integrated in popular C/C++ compilers: GCC 15 and Clang 19.[2][3][4]

Features

The following are changes integrated into the latest working draft of C2Y.[5][6] Note: This section is not complete. Changes listed in the History section will be incrementally migrated into section.

Standard Library

New functions

Existing functions

  • For functions strtol(), strtoll(), strtoul(), strtoull(), and their wide counterparts wcstol(), wcstoll(), wcstoul(), wcstoull(), if the value of base is 8 (octal), the characters 0o or 0O may optionally precede the sequence of letters and digits. If a sign is present, the 0o or 0O follows the sign.[7]

Constants

  • Add new style of octal literals that start with 0o and 0O; such as 0o137 and 0O247.[7]
  • Add delimited escape sequences \u{} for universal character name (using hexadecimal), \x{} for hexadecimal escape sequence, \o{} for octal escape sequence; such as \u{123}, \x{123}, \o{123}. This was previously added to the C++23 standard.[7]

Obsolete features

Obsolete C programming language features removed or deprecated from the working draft of C2Y:[5][6]

  • Remove _Imaginary from the list of keywords.[8]
  • Octal literals, such as 052 with a leading zero, will be retained but marked as obsolescent to avoid breaking existing code. Compilers should output a warning that will hopefully encourage rewrites. As of N3353, there will be no changes to printf(), but WG14 would like to see a future paper that propose changes.[7]

Compiler support

The following compilers implement an experimental compiler flag to support C2Y:

History

January 2024

The following changes were made after the January 2024 WG14 meeting:[5][6]

  • N3192 – “Sequential hexdigits”.
  • Editorial – Adjusted a footnote in Annex K from “reserved” to “potentially reserved”.

June 2024

The following changes were made after the June 2024 WG14 meeting:[5][6]

  • N3064 – “Writing to multibyte character files”.
  • N3232 – “Round-trip rounding”.
  • N3233 – “Recommendation for printf rounding”.
  • N3239 – “Some constants are literally literals, v2”.
  • N3242 – “Problematic use of “correctly rounded”.
  • N3244 – “Slay Some Earthly Demons I”.
  • N3247 – “fopen “p” and bring fopen’s mode closer to POSIX 202x”.
  • N3254 – “Accessing byte arrays, v4”.
  • N3259 – “Support ++ and — on complex values”.
  • N3260 – “_Generic selection expression with a type operand”.
  • N3273 – “alignof of an incomplete array type”.
  • N3274 – “Remove imaginary types, v3”.
  • Editorial – “may” -> “can” for alignment with ISO/IEC directives.
  • Editorial – Table headings changed to match ISO/IEC directives.

September 2024

The following changes were made after the September/October 2024 WG14 meeting:[5][6]

  • N3272 – “strftime broken-down structure usage (Option 1 – “Undefined Behavior)”.
  • N3286 – “Floating-point exception for Macro Replacements”.
  • N3287 – “Nonsensical Parenthetical in Mathematics Specification”.
  • N3291 – “Decimal Floating-Point Number Term Misuse”.
  • N3298 – “Introduce Complex Literals”.
  • N3303 – “HUGE_VAL Corrections”.
  • N3305 – “Leftover WANT_… Macros for <math.h> and Decimal Floating-Point”.
  • N3312 – “Relax Atomic Alignment Requirements”.
  • N3322 – “Allow Zero Length operations on Null Pointers (Including in the Library)”.
  • N3323 – “How Do You Add One To Something? (By Using The Proper Type)”.
  • N3324 – “‘pole-error’ Wording Fix”.
  • N3326 – “Standardize strnlen and wcsnlen”.
  • N3340 – “Slay Some Earthly Demons II”.
  • N3341 – “Slay Some Earthly Demons III”.
  • N3342 – “Slay Some Earthly Demons IV”.
  • N3344 – “Slay Some Earthly Demons VI”.
  • N3345 – “Slay Some Earthly Demons VII”.
  • N3346 – “Slay Some Earthly Demons VIII”.
  • N3349 – “abs Without Undefined Behavior”.
  • N3353 – “Obsolete Octal and Provide New, Proper Escape Sequences”.
  • N3355 – “Named/Labeled Loops”.
  • N3356 – “if Declarations”.
  • N3364 – “SNAN Initialization”.
  • N3366 – “Restartable Functions for Efficient Character Conversions”.
  • N3367 – “More Modern Bit Utilities”.
  • N3369 – “The _Lengthof Operator”.
  • N3370 – “Case Ranges in switch Statements”.
  • N3461 – “range error definition followup”.

February 2025

The following changes were made after the February 2025 WG14 meeting:[5][6]

  • N3363 – “<stdarg.h> Wording”.
  • N3401 – “SIGFPE and I/O (v2)”.
  • N3405 – “Improved Wording for Treatment of Error Conditions in <math.h>”.
  • N3409 – “Slay Some Earthly Demons X”.
  • N3410 – “Slay Some Earthly Demons XI”.
  • N3411 – “Slay Some Earthly Demons XII”.
  • N3418 – “Slay Some Earthly Demons XIV”.
  • N3447 – “Chasing Ghost I – “Constant Expressions”.
  • N3448 – “Chasing Ghosts II – “Accessing Allocated Storage”.
  • N3451 – “Initialization of Anonymous Structures and Unions (v2)”.
  • N3452 – “Complex Literals Warning”.
  • N3459 – “Integer and Arithmetic Constant Expressions”.
  • N3460 – “Complex Operators”.
  • N3466 – “Clarifications on Null Pointers in the Library”.
  • N3469 – “Big Array Size Survey (_Lengthof -> _Countof, and <stdcountof.h> header)”.
  • N3478 – “Slay Some Earthly Demons XIII”.
  • N3481 – “Slay Some Earthly Demons XVI”.
  • N3482 – “Slay Some Earthly Demons XVII”.
  • N3492 – “Improved treatment of error conditions for functions that round result”.
  • N3496 – “Clarify the Specification of the Width Macros”.
  • N3505 – “Preprocessor integer expressions, II”.

See also

References

  1. ^ “WG14-N3583: Draft Minutes for 24–28 February, 2025”. open-std.org. February 28, 2025. Archived from the original on September 20, 2025.
  2. ^ a b “GCC 15 Release Series”. GNU.org. Archived from the original on October 27, 2025.
  3. ^ a b “LLVM Clang 19 Adds Initial “-std=c2y” Support For The Next C Standard”. Phoronix.com. July 2, 2024. Archived from the original on October 27, 2025.
  4. ^ a b “C Support in Clang – C2Y implementation status”. LLVM.org. Archived from the original on October 27, 2025.
  5. ^ a b c d e f “WG14-N3550: Working Draft for ISO/IEC 9899:202Y” (PDF). open-std.org. May 4, 2025. Archived (PDF) from the original on October 11, 2025.
  6. ^ a b c d e f “WG14 Document Repository”. open-std.org. Archived from the original on September 30, 2025.
  7. ^ a b c d “WG14-N3353: Obsolete implicitly octal literals and add delimited escape sequences”. open-std.org. October 18, 2024. Archived from the original on October 3, 2025.
  8. ^ “WG14-N3274: Remove imaginary types” (PDF). open-std.org. June 14, 2024. Archived (PDF) from the original on August 24, 2025.

Further reading

  • N3550 (first working draft with C2Y changes); WG14; May 2025. (free download)
  • N3220 (first working draft after C23; differs from final C23 draft N3219 only in one footnote); WG14; February 2024. (free download)

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