C++23

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C++23 is the name for the version of the International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC) 14882 standard for the C++ programming language that follows C++20. The final draft of this version is N4950.[1][2]

In February 2020, at the final meeting for C++20 in Prague, an overall plan for C++23 was adopted:[3][4] planned features for C++23 were library support for coroutines, a modular standard library, executors, and networking.

The first WG21 meeting focused on C++23 was intended to take place in Varna in early June 2020, but was cancelled due to the COVID-19 pandemic,[5][6] as was the November 2020 meeting in New York[7][6] and the February 2021 meeting in Kona, Hawaii.[7] All meetings until November 2022 were virtual while the November 2022 meeting until the final meeting in February 2023 was hybrid.[7] The standard was technically finalized by WG21 at the hybrid meeting in Issaquah in February 2023.[8]

Modern "Hello, world" Example

After many library changes applied to the working draft, the new "Hello, world" program will be: [1]

<syntaxhighlight lang="cpp">

  1. include <print>

int main() { 

   std::println("Hello, world!");

} </syntaxhighlight>

Features

Changes that have been accepted into C++23 include:

Language

  • explicit this object parameter[9]
  • if consteval[10]
  • multidimensional subscript operator[11]
  • static call and subscript operators and static lambdas[12][13]
  • simplifying implicit move[14]
  • auto(x) and auto{x}[15]
  • new preprocessor directives:
  • extending the lifetime of some temporaries in range-based for loop[18]
  • new standard attribute [[assume(expression)]][19]
  • class template argument deduction from inherited constructors[20]
  • labels at the end of the compound statement[21]
  • alias declarations in init-statements[22]
  • literal suffixes for std::size_t and the corresponding signed type[23]
  • extended floating-point types with literals (conditionally supported)[24]
  • optional () from nullary lambda expressions[25]
  • attributes on lambda expressions[26]
  • constexpr changes:
    • non-literal variables, labels, and gotos in constexpr functions[27]
    • allowing static and thread_local variables that are usable in constant expressions in constexpr functions[28]
    • constexpr function does not need its return type and parameter types to be literal type
    • it is now possible to write a constexpr function for which no invocation satisfies the requirements of a core constant expression[29]
  • narrowing contextual conversions to bool in static_assert and if constexpr[30]
  • trimming whitespaces before line splicing[31]
  • make declaration order layout mandated[32]
  • delimited escape sequences[33]
  • named universal character escapes[34]
  • text encoding changes:
    • support for UTF-8 as a portable source file encoding[35]
    • consistent character literal encoding[36]
    • character sets and encodings[37]

Library

Standard Library Module Support

  • standard library modules std and std.compat[38]

Coroutine Library Support

  • synchronous coroutine std::generator for ranges[39]

General Utilities Support

  • result type std::expected[40]
  • monadic operations for std::optional[41] and std::expected[42]
  • utility function std::to_underlying to get the underlying value of enum[43]
  • move-only callable wrapper std::move_only_function[44]
  • std::forward_like[45]
  • std::invoke_r[46]
  • std::bind_back[47]
  • std::byteswap[48]
  • std::unreachable: a function to mark unreachable code[49]
  • made std::tuple compatible with other tuple-like objects[50]
  • std::basic_common_reference specialization for std::reference_wrapper yielding reference types[51]
  • adding default arguments for std::pair's forwarding constructor[52]

Compile-time Support

  • constexpr support for:
    • std::type_info::operator==[53]
    • std::bitset[54]
    • std::unique_ptr[55]
    • for some <cmath> functions[56]
    • for integral overloads of std::to_chars and std::from_chars[57]
  • metaprogramming utilities:
    • type traits std::is_scoped_enum,[58] std::is_implicit_lifetime,[59] std::reference_constructs_from_temporary, and std::reference_converts_from_temporary.[60]
  • adding move-only types support for comparison concepts[61]

Iterators, Ranges, and Algorithm Support

  • new range conversion function std::ranges::to[62]
  • new constrained ranges algorithm:
    • std::ranges::starts_with
    • std::ranges::ends_with[63]
    • std::ranges::contains
    • std::ranges::contains_subrange[64]
    • std::ranges::find_last and other variants[65]
    • rangified versions of iota, shift_left, and shift_right[66]
    • range fold algorithms[67]
  • new std::ranges::range_adaptor_closure, a helper for defining user-defined range adaptor closures[47]
  • new range adaptors:
    • std::views::zip and other variants
    • std::views::adjacent and other variants[68]
    • std::views::join_with[69]
    • std::views::slide
    • std::views::chunk[70]
    • std::views::chunk_by[71]
    • std::views::as_rvalue[72]
    • std::views::as_const[73]
    • std::views::repeat[74]
    • std::views::stride[75]
    • std::views::cartesian_product[76]
    • std::views::enumerate[77]
  • rectifying constant iterators, sentinels, and ranges, that is, std::ranges::cbegin and other similar utilities returning constant iterators should be fully guaranteed even for shallow-const views (such as std::span)[73]
  • ranges iterators as inputs to non-ranges algorithms[78]
  • relaxing range adaptors to allow for move only types[79]
  • making multi-param constructors of some views explicit[80]

Memory Management Support

  • std::out_ptr and std::inout_ptr for C interoperability[81]
  • std::allocate_at_least and std::allocator::allocate_at_least[82]
  • explicit lifetime management function std::start_lifetime_as for implicit-lifetime types[83]
  • disallowing user specialization of std::allocator_traits[84]

String and Text Processing Support

  • new member functions and changes in string types:
    • std::basic_string_view::contains and std::basic_string::contains[85]
    • disabling construction from nullptr for std::basic_string and std::basic_string_view[86]
    • explicit range constructor for std::basic_string_view[87]
    • std::basic_string::resize_and_overwrite[88]
    • rvalue reference overload of std::basic_string::substr for efficient slicing[89]
  • formatting ranges, tuples, escaped presentation of characters and strings, std::thread::id, and stacktraces.[90][91][92]

Diagnostic Support

  • stacktrace library[93]

I/O Support

  • formatted output functions std::print and std::println from new header <print>[94]
  • spanstream library (std::span-based string stream) from new header <spanstream>[95]
  • a support for exclusive mode in std::fstreams[96]
  • std::basic_ostream::operator<<(const volatile void*)[97]

Containers Support

  • multidimensional-span std::mdspan[98][99][100][101]
  • constructability and assignability of containers from other compatible ranges[62]
  • flat set and flat map container adapters[102][103]
  • non-deduction context for allocators in container deduction guides[104]
  • heterogeneous erasure overloads for associative containers[105]
  • allowing iterator pair construction in stack and queue[106]
  • requiring std::span and std::basic_string_view to be trivially copyable[107]

C-Compatibility Support

  • new header <stdatomic.h>[108]

Language defect reports

  • C++ identifier syntax using Unicode Standard Annex 31[109]
  • allowing duplicate attributes[110]
  • changing scope of lambda trailing return type[111]
  • making overloaded comparison operators less breaking change[112]
  • undeprecating volatile compound assignments[113][114]
  • fixing the compatibility and portability of char8_t[115]
  • relaxing requirements on wchar_t to match existing practices[116]
  • allowing some pointers and references of this or unknown origin in constant expressions[117]
  • introduction of immediate-escalating functions promoted to immediate functions[118]
  • allowing static_assert(false) in uninstantiated template contexts

Library defect reports

  • changes in ranges library:
    • conditionally borrowed ranges[119]
    • repairing input range adaptors and std::counted_iterator[120]
    • relaxing the constraint on std::ranges::join_view[121]
    • renamed std::ranges::split_view to std::ranges::lazy_split_view and new split_view[122]
    • removed std::default_initializable constraint from concept std::ranges::view[123]
    • view with ownership and new std::ranges::owning_view[124]
    • fixed std::ranges::istream_view[125]
  • changes in text formatting library:
    • std::basic_format_string[126]
    • compile-time format string checks
    • reducing binary code size of std::format_to[127]
    • fixing locale handling in chrono formatters[128]
    • improving width estimation[129] and fill character allowances of std::format[130]
    • use of forwarding references in format arguments to allow non-const-formattable types[131]
  • fully constexpr std::variant and std::optional[132]
  • supporting types derived from std::variant in std::visit[133]

Removed features and deprecation

Removed features:

  • Garbage Collection Support and Reachability-Based Leak Detection. It was added to the standard since C++11 but no compilers support this feature until C++23.[134]
  • Mixed wide string literal concatenation.[135]
  • Non-encodable wide character literals and multicharacter wide character literals.[136]

Deprecated features:

  • std::aligned_storage and std::aligned_union[137]
  • std::numeric_limits::has_denorm[138]

Reverted deprecated features:

  • Use of comma operator in subscript expressions was no longer deprecated but the semantics has been changed to support overloadable n-adic operator[].
  • C headers (The corresponding <*.h> headers for compatibility with C)

Published as Technical Specifications

Compiler support

  • Clang progressively added partial C++23 support from 2021 in version 13 through to version 18 in 2024, available through the option -std=c++23 . [140]
  • GCC added partial, experimental C++23 support in 2021 in version 11 through the option -std=c++2b or -std=c++23 It also has an option to enable GNU extensions in addition to the experimental C++23 support, -std=gnu++2b. [141]

History

In the absence of face-to-face WG21 meetings, the following changes were applied after several virtual WG21 meetings, where they were approved by straw polls.

The following were added after the virtual WG21 meeting of 9 November 2020, where they were approved by straw polls:[142]

  • Literal suffixes for std::size_t and the corresponding signed type
  • A member function <syntaxhighlight lang="cpp" inline="1">contains</syntaxhighlight> for <syntaxhighlight lang="cpp" inline="1">std::basic_string</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">std::basic_string_view</syntaxhighlight>, to check whether or not the string contains a given substring or character
  • A stacktrace library (<syntaxhighlight lang="cpp" inline="1"><stacktrace></syntaxhighlight>), based on Boost.Stacktrace
  • A type trait <syntaxhighlight lang="cpp" inline="1">std::is_scoped_enum</syntaxhighlight>
  • The header <syntaxhighlight lang="cpp" inline="1"><stdatomic.h></syntaxhighlight>, for interoperability with C atomics

After the virtual WG21 meeting of 22 February 2021, following features are added where they were approved by straw polls:[143]

  • Removing unnecessary empty parameter list <syntaxhighlight lang="cpp" inline="1">()</syntaxhighlight> from lambda expressions.
  • Repairing input range adaptors and <syntaxhighlight lang="cpp" inline="1">counted_iterator</syntaxhighlight>.
  • Relax the requirements for <syntaxhighlight lang="cpp" inline="1">time_point::clock</syntaxhighlight>.[144]
  • <syntaxhighlight lang="cpp" inline="1">std::visit</syntaxhighlight> for classes that are derived from <syntaxhighlight lang="cpp" inline="1">std::variant</syntaxhighlight>.
  • Locks lock lockables.[145]
  • Conditionally borrowed ranges.
  • <syntaxhighlight lang="cpp" inline="1">std::to_underlying</syntaxhighlight>.

After the summer 2021 ISO C++ standards plenary virtual meeting of June 2021, new features and defect reports were approved by straw polls:[146]

  • Consteval if (<syntaxhighlight lang="cpp" inline="1">if consteval</syntaxhighlight>).
  • Narrowing contextual conversions to <syntaxhighlight lang="cpp" inline="1">bool</syntaxhighlight>.
  • Allowing duplicate attributes.
  • <syntaxhighlight lang="cpp" inline="1">std::span</syntaxhighlight>-based string-stream (<syntaxhighlight lang="cpp" inline="1"><spanstream></syntaxhighlight>).
  • <syntaxhighlight lang="cpp" inline="1">std::out_ptr()</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">std::inout_ptr()</syntaxhighlight>.
  • <syntaxhighlight lang="cpp" class="" style="" inline="1">constexpr</syntaxhighlight> for <syntaxhighlight lang="cpp" inline="1">std::optional</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">std::variant</syntaxhighlight>, and <syntaxhighlight lang="cpp" inline="1">std::type_info::operator==</syntaxhighlight>.
  • Iterators pair constructors for <syntaxhighlight lang="cpp" inline="1">std::stack</syntaxhighlight> (stack) and <syntaxhighlight lang="cpp" inline="1">std::queue</syntaxhighlight> (queue).
  • Few changes of the ranges library:
    • Generalized <syntaxhighlight lang="cpp" inline="1">starts_with</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">ends_with</syntaxhighlight> for arbitrary ranges.
    • Renamed <syntaxhighlight lang="cpp" inline="1">split_view</syntaxhighlight> to <syntaxhighlight lang="cpp" inline="1">lazy_split_view</syntaxhighlight> and new <syntaxhighlight lang="cpp" inline="1">split_view</syntaxhighlight>.
    • Relaxing the constraint on <syntaxhighlight lang="cpp" inline="1">join_view</syntaxhighlight>.
    • Removing <syntaxhighlight lang="cpp" inline="1">default_initializable</syntaxhighlight> constraint from concept <syntaxhighlight lang="cpp" inline="1">view</syntaxhighlight>.
    • Range constructor for <syntaxhighlight lang="cpp" inline="1">std::basic_string_view</syntaxhighlight>.
  • Prohibiting <syntaxhighlight lang="cpp" inline="1">std::basic_string</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">std::basic_string_view</syntaxhighlight> construction from <syntaxhighlight lang="cpp" class="" style="" inline="1">nullptr</syntaxhighlight>.
  • <syntaxhighlight lang="cpp" inline="1">std::invoke_r</syntaxhighlight>.
  • Improvements on <syntaxhighlight lang="cpp" inline="1">std::format</syntaxhighlight>.
  • Adding default arguments for <syntaxhighlight lang="cpp" inline="1">std::pair</syntaxhighlight>'s forwarding constructor.

After the autumn 2021 ISO C++ standards plenary virtual meeting of October 2021, new features and defect reports were approved by straw polls:[147]

  • Non-literal variables, labels, and gotos in <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight> functions, but still ill-formed to evaluate them at compile-time.
  • Explicit <syntaxhighlight lang="cpp" class="" style="" inline="1">this</syntaxhighlight> object parameter.
  • Changes on character sets and encodings.
  • New preprocessors: <syntaxhighlight lang="cpp" inline="1">#elifdef</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">#elifndef</syntaxhighlight>. Both directives were added to C23 (C language update) and GCC 12.[148]
  • Allowing alias declarations in init-statement.
  • Overloading multidimensional subscript operator (e.g. <syntaxhighlight lang="cpp" inline="1">arr[1, 2]</syntaxhighlight>).
  • Decay copy in language: <syntaxhighlight lang="cpp" inline="1">auto(x)</syntaxhighlight> or <syntaxhighlight lang="cpp" inline="1">auto{x}</syntaxhighlight>.
  • Changes in text formatting library:
    • Fixing locale handling in chrono formatters.
    • Use of forwarding references in format arguments to allow <syntaxhighlight lang="cpp" inline="1">std::generator</syntaxhighlight>-like types.
  • Addition of type alias <syntaxhighlight lang="cpp" inline="1">std::pmr::stacktrace</syntaxhighlight> which is equivalent to <syntaxhighlight lang="cpp" inline="1">std::basic_stacktrace<std::pmr::polymorphic_allocator></syntaxhighlight>.[149]
  • Changes in ranges library:
    • Refined definition of a view.
    • Replacing function template <syntaxhighlight lang="cpp" inline="1">std::ranges::istream_view</syntaxhighlight> with alias templates <syntaxhighlight lang="cpp" inline="1">std::ranges::istream_view</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">std::ranges::wistream_view</syntaxhighlight>, and customization point object <syntaxhighlight lang="cpp" inline="1">std::views::istream</syntaxhighlight>.
    • <syntaxhighlight lang="cpp" inline="1">zip</syntaxhighlight> range adaptor family:
      • <syntaxhighlight lang="cpp" inline="1">zip_view</syntaxhighlight>
      • <syntaxhighlight lang="cpp" inline="1">zip_transform_view</syntaxhighlight>
      • <syntaxhighlight lang="cpp" inline="1">adjacent_view</syntaxhighlight> (and <syntaxhighlight lang="cpp" inline="1">std::views::pairwise</syntaxhighlight> being equivalent to <syntaxhighlight lang="cpp" inline="1">std::views::adjacent<2></syntaxhighlight>)
      • <syntaxhighlight lang="cpp" inline="1">adjacent_transform_view</syntaxhighlight> (and <syntaxhighlight lang="cpp" inline="1">std::views::pairwise_transform</syntaxhighlight> being equivalent to <syntaxhighlight lang="cpp" inline="1">std::views::adjacent_transform<2></syntaxhighlight>)
  • <syntaxhighlight lang="cpp" inline="1">std::move_only_function</syntaxhighlight>.
  • Monadic operations for <syntaxhighlight lang="cpp" inline="1">std::optional</syntaxhighlight>.
  • Member function template <syntaxhighlight lang="cpp" inline="1">std::basic_string::resize_and_overwrite</syntaxhighlight>.
  • Printing <syntaxhighlight lang="cpp" class="" style="" inline="1">volatile</syntaxhighlight> pointers (<syntaxhighlight lang="cpp" inline="1">volatile T*</syntaxhighlight>).
  • <syntaxhighlight lang="cpp" inline="1">std::byteswap</syntaxhighlight>.
  • Heterogeneous erasure overloads for associative containers.
  • Every specialization of <syntaxhighlight lang="cpp" inline="1">std::span</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">std::basic_string_view</syntaxhighlight> is trivially copyable.
  • Adding conditional <syntaxhighlight lang="cpp" inline="1">noexcept</syntaxhighlight> specifications to <syntaxhighlight lang="cpp" inline="1">std::exchange</syntaxhighlight>.[150]
  • Revamped specification and use of integer-class types.[151]
  • Clarify C headers. "The headers are not useful in code that is only required to be valid C++. Therefore, the C headers should be provided by the C++ standard library as a fully-supported, not deprecated part, but they should also be discouraged for use in code that is not polyglot interoperability code. [..] This proposal makes the C headers no longer deprecated, so there is no formal threat of future removal. The effective discouragement to use the C headers in pure C++ code is now spelled out explicitly as normative discouragement."[152]

After the virtual WG21 meeting of 7 February 2022, the following features are added where they were approved by straw polls:[153]

  • Allowed attributes on the function call operator of a lambda
  • <syntaxhighlight lang="cpp" inline="1">std::expected</syntaxhighlight>
  • <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight> for cmath and cstdlib
  • Function to mark unreachable code
  • <syntaxhighlight lang="cpp" inline="1">ranges::to</syntaxhighlight>
  • A type trait to detect reference binding to temporary
  • Making <syntaxhighlight lang="cpp" inline="1">std::unique_ptr</syntaxhighlight> <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight>
  • Pipe support for user-defined range adaptors
  • <syntaxhighlight lang="cpp" inline="1">ranges::iota</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">ranges::shift_left</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">ranges::shift_right</syntaxhighlight>
  • <syntaxhighlight lang="cpp" inline="1">views::join_with</syntaxhighlight>
  • Windowing range adaptors: <syntaxhighlight lang="cpp" inline="1">views::chunk</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">views::slide</syntaxhighlight>
  • <syntaxhighlight lang="cpp" inline="1">views::chunk_by</syntaxhighlight>

After the virtual WG21 meeting of 25 July 2022, the following features and defect reports are added where they were approved by straw polls:[154]

  • Made rewriting equality in expressions less of a breaking change.
  • Reverted the deprecation of bitwise assignment to <syntaxhighlight lang="cpp" inline="1">volatile</syntaxhighlight> variables.
  • Added the <syntaxhighlight lang="cpp" inline="1">#warning</syntaxhighlight> preprocessor directive.
  • Removed non-encodable wide character literals and multicharacter wide character literals.
  • Allowed labels to appear at the end of compound statements.
  • Added escape sequences delimited with curly braces for octal and hexadecimal numbers and universal character names.
  • Allowed <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight> functions to never be constant expressions.
  • Simplified some implicit move rules from C++20 and allowed implicit move when returning an rvalue reference.
  • Add a way to specify unicode characters by name. For example, <syntaxhighlight lang="cpp" inline="1">U'\N{LATIN CAPITAL LETTER A WITH MACRON}' // Equivalent to U'\u0100'</syntaxhighlight>
  • Allowed <syntaxhighlight lang="cpp" class="" style="" inline="1">operator()</syntaxhighlight> and lambdas to be <syntaxhighlight lang="cpp" class="" style="" inline="1">static</syntaxhighlight>.
  • Allowed the this pointer and references of unknown origin to appear in constant expressions.
  • Allowed implementations to define extended floating-point types in addition to the three standard floating-point types. Added the type aliases std::float16_t, std::float32_t, std::float64_t, std::float128_t, std::bfloat16_t for these extended types accessible through the header <stdfloat>, their corresponding literal suffixes f16 f32 f64 f128 bf16or F16 F32 F64 F128 BF16 and added overloads to various standard library functions that take floats as arguments.
  • Added the <syntaxhighlight lang="cpp" inline="1">assume(expression)</syntaxhighlight> attribute which allows the compiler to assume the provided expression is true to allow optimizations.
  • Made support for UTF-8 source files mandatory, providing a portable encoding for source files.
  • Allowed arrays of <syntaxhighlight lang="cpp" inline="1">char</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">unsigned char</syntaxhighlight> to be initialized with UTF-8 string literals.
  • Removed the requirement that <syntaxhighlight lang="cpp" class="" style="" inline="1">wchar_t</syntaxhighlight> can encode all characters of the extended character set, in effect allowing UTF-16 to be used for wide string literals.
  • Added std::mdspan, a multidimensional array view analogous to std::span.
  • <syntaxhighlight lang="cpp" inline="1">flat_map</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">flat_set</syntaxhighlight> were added to the standard library.
  • Added the <syntaxhighlight lang="cpp" inline="1">std::print</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">std::println</syntaxhighlight> functions for printing formatted text to stdout.
  • Provide the named modules <syntaxhighlight lang="cpp" inline="1">std</syntaxhighlight> and <syntaxhighlight lang="cpp" inline="1">std.compat</syntaxhighlight> for importing the standard library.
  • Added support for exclusive mode fstreams, analogous to the "x" flag in fopen.
  • Allowed std::format to handle ranges, tuples, and other containers.
  • Added std::forward_like.
  • Made std::string::substr use move semantics.
  • Added <syntaxhighlight lang="cpp" inline="1">std::generator</syntaxhighlight> which implements a coroutine generator that models <syntaxhighlight lang="cpp" inline="1">std::ranges::input_range</syntaxhighlight>
  • <syntaxhighlight lang="cpp" inline="1">views::cartesian_product</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">views::repeat</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">views::stride</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">views::as_const</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">views::as_rvalue</syntaxhighlight>.
  • Added new algorithms: <syntaxhighlight lang="cpp" inline="1">ranges::find_last</syntaxhighlight>, <syntaxhighlight lang="cpp" inline="1">ranges::contains</syntaxhighlight>, and ranges fold algorithms.
  • Made std::tuple compatible with other tuple-like objects.
  • Explicit lifetime management for implicit-lifetime types.
  • Made std::bitset and integral overloads of std::to_chars and std::from_chars <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight>-compatible.
  • Adding move-only types support for comparison concepts.
  • Ranges iterators as inputs to non-ranges algorithms.
  • Relaxing range adaptors to allow for move-only types.

After the hybrid WG21 meeting of 7 November 2022, the following features and defect reports are added where they were approved by straw polls:[155]

  • Allowed <syntaxhighlight lang="cpp" inline="1">operator[]</syntaxhighlight> to be <syntaxhighlight lang="cpp" inline="1">static</syntaxhighlight>.
  • Allowed <syntaxhighlight lang="cpp" inline="1">static</syntaxhighlight> and <syntaxhighlight lang="cpp" class="" style="" inline="1">thread_local</syntaxhighlight> variables to appear in <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight> functions if they are usable in constant expressions.
  • <syntaxhighlight lang="cpp" class="" style="" inline="1">consteval</syntaxhighlight> propagates upwards, that is, certain existing <syntaxhighlight lang="cpp" inline="1">constexpr</syntaxhighlight> functions become <syntaxhighlight lang="cpp" inline="1">consteval</syntaxhighlight> functions when those functions can already only be invoked during compile time.
  • Extended the lifetime of temporaries that appear in the for-range-initializer of a range-based <syntaxhighlight lang="cpp" inline="1">for</syntaxhighlight> loop to cover the entire loop.
  • Reverted the deprecation of (all, not just bitwise) compound assignment to <syntaxhighlight lang="cpp" inline="1">volatile</syntaxhighlight> variables.
  • Monadic functions for <syntaxhighlight lang="cpp" inline="1">std::expected</syntaxhighlight>.
  • Synchronize the output of <syntaxhighlight lang="cpp" inline="1">std::print</syntaxhighlight> with the underlying stream if the native Unicode API is used.[156]

After the final hybrid WG21 meeting of 6-11 February 2023, the following features and defect reports are added where they were approved by straw polls:[157]

  • Referencing the Unicode Standard.[158]
  • Stashing stashing iterators for proper flattening.[159]
  • views::enumerate
  • making multi-param constructors of views explicit
  • relaxing ranges just a smidge
  • escaping improvements in std::format
  • improving std::format's width estimation
  • std::format fill character allowances
  • formatting thread::id and stacktrace
  • A type trait std::is_implicit_lifetime
  • std::common_reference_t of std::reference_wrapper should be a reference type
  • disallowing user specialization of std::allocator_traits
  • std::pmr::generator
  • deprecating std::numeric_limits::has_denorm
  • std::barrier's phase completion guarantees

References

  1. ^ "Working Draft, Standard for Programming Language C++" (PDF). Open Standards. ISO/IEC. 2023-05-10. Archived (PDF) from the original on Feb 16, 2024.
  2. ^ "N4951 Editors' Report: Programming Languages - C++". Open Standards. 2023-05-10. Archived from the original on 2023-06-05.
  3. ^ Dusíková, Hana (2019-11-06). "N4817: 2020 Prague Meeting Invitation and Information" (PDF). Open Standards. Archived (PDF) from the original on 2019-12-29. Retrieved 2020-02-13.
  4. ^ Voutilainen, Ville (2019-11-25). "To boldly suggest an overall plan for C++23". Open Standards. Archived from the original on 2019-12-24. Retrieved 2020-02-13.
  5. ^ Lelbach, Bryce Adelstein; Winters, Titus; Fracassi, Fabio; Baker, Billy; Liber, Nevin; Bastien, JF; Stone, David; Ballo, Botond; Keane, Erich; Honermann, Tom (2020-04-20). "P2145R0: Evolving C++ Remotely". Open Standards. Archived from the original on Feb 12, 2024.
  6. ^ 6.0 6.1 Sutter, Herb (29 July 2020). "Business Plan and Convener's Report: ISO/IEC JTC1/SC22/WG21 (C++)" (PDF).
  7. ^ 7.0 7.1 7.2 "Upcoming Meetings, Past Meetings : Standard C++". isocpp.org.
  8. ^ "C++23 "Pandemic Edition" is complete (Trip report: Winter ISO C++ standards meeting, Issaquah, WA, USA)". herbsutter.com. 13 February 2023.
  9. ^ Gašper Ažman; Sy Brand; Ben Deane; Barry Revzin (2021-07-12). "Deducing this".
  10. ^ Barry Revzin; Richard Smith; Andrew Sutton; Daveed Vandevoorde (2021-03-22). "if consteval".
  11. ^ Mark Hoemmen; Daisy Hollman; Corentin Jabot; Isabella Muerte; Christian Trott (2021-09-14). "Multidimensional subscript operator" (PDF).
  12. ^ "static operator()". 2022-04-08.
  13. ^ "static operator[]" (PDF). 2022-11-11.
  14. ^ "Simpler implicit move". 2022-03-23.
  15. ^ Zhihao Yuan (2021-07-12). "auto(x): decay-copy in the language".
  16. ^ Melanie Blower (2021-04-30). "Add support for preprocessing directives elifdef and elifndef" (PDF).
  17. ^ Aaron Ballman (2022-01-13). "Support for #warning" (PDF).
  18. ^ "Wording for P2644R1 Fix for Range-based for Loop". 2022-11-11.
  19. ^ "Portable assumptions" (PDF). 2022-04-22.
  20. ^ Timur Doumler (2022-05-20). "Wording for class template argument deduction from inherited constructors" (PDF).
  21. ^ "Labels at the end of compound statements (C compatibility)" (PDF). 2022-01-13.
  22. ^ Jens Maurer (2021-04-13). "Extend init-statement to allow alias-declaration".
  23. ^ JeanHeyd Meneide; Rein Halbersma (2019-11-24). "Literal Suffix for (signed) size_t".
  24. ^ "Extended floating-point types and standard names". 2022-04-22.
  25. ^ Alex Christensen; JF Bastien (2020-12-11). "P1102R2: Down with ()!".
  26. ^ "Attributes on Lambda-Expressions" (PDF).
  27. ^ Ville Voutilainen (2021-07-12). "Non-literal variables (and labels and gotos) in constexpr functions".
  28. ^ "Permitting static constexpr variables in constexpr functions". 2022-11-07.
  29. ^ "Relaxing some constexpr restrictions". 2022-01-27.
  30. ^ Andrzej Krzemieński (2021-04-12). "Narrowing contextual conversions to bool".
  31. ^ Corentin Jabot (2021-04-13). "Trimming whitespaces before line splicing" (PDF).
  32. ^ Pal Balog (2021-04-02). "Make declaration order layout mandated" (PDF).
  33. ^ "Delimited escape sequences" (PDF). 2022-02-25.
  34. ^ "Named universal character escapes". 2022-03-25.
  35. ^ "Support for UTF-8 as a portable source file encoding" (PDF). 2022-07-01.
  36. ^ Corentin Jabot (2021-09-14). "Consistent character literal encoding" (PDF).
  37. ^ Jens Maurer (2021-09-21). "Character sets and encodings".
  38. ^ "Standard Library Modules std and std.compat" (PDF).
  39. ^ "(std::generator: Synchronous Coroutine Generator for Ranges)" (PDF).
  40. ^ Vicente Botet; JF Bastien; Jonathan Wakely (2022-01-07). "std::expected".
  41. ^ Sy Brand (2021-04-27). "Monadic operations for std::optional".
  42. ^ Jeff Garland (2022-09-28). "P2505R5 Monadic Functions for std::expected".
  43. ^ JeanHeyd Meneide (2021-01-22). "std::to_underlying for enumerations".
  44. ^ Matt Calabrese; Ryan McDougall (2021-07-09). "move_only_function".
  45. ^ Gašper Ažman (2022-05-13). "std::forward_like" (PDF).
  46. ^ Zhihao Yuan (2020-04-29). "invoke_r".
  47. ^ 47.0 47.1 Barry Revzin (2021-12-17). "Pipe support for user-defined range adaptors".
  48. ^ Isabella Muerte; Corentin Jabot (2021-09-17). "Byteswapping for fun&&nuf".
  49. ^ Melissa Mears; Jens Maurer (2021-10-15). "Function to mark unreachable code" (PDF).
  50. ^ Corentin Jabot (2022-07-15). "Compatibility between tuple, pair and tuple-like objects" (PDF).
  51. ^ Hui Xie; S. Levent Yilmaz; Tim Song (2023-02-07). "common_reference_t of reference_wrapper Should Be a Reference Type".
  52. ^ "Wording for P2644R1 Fix for Range-based for Loop". 2022-11-11.
  53. ^ Peter Dimov (2021-05-01). "Making std::type_info::operator== constexpr".
  54. ^ Daniil Goncharov (2022-06-25). "A more constexpr bitset" (PDF).
  55. ^ Andreas Fertig (2021-11-06). "Making std::unique_ptr constexpr" (PDF).
  56. ^ Edward J. Rosten; Oliver J. Rosten (2021-11-12). "constexpr for <cmath> and <cstdlib>" (PDF).
  57. ^ Daniil Goncharov; Alexander Karaev (2021-09-18). "Add Constexpr Modifiers to Functions to_chars and from_chars for Integral Types in <charconv> Header" (PDF).
  58. ^ Juan Alday (2020-10-12). "A proposal for a type trait to detect scoped enumerations" (PDF).
  59. ^ Timur Doumler; Vittorio Romeo (2022-11-11). "A trait for implicit lifetime types" (PDF).
  60. ^ Tim Song (2021-10-13). "A type trait to detect reference binding to temporary".
  61. ^ Justin Bassett (2022-07-02). "Move-only types for equality_comparable_with, totally_ordered_with, and three_way_comparable_with" (PDF).
  62. ^ 62.0 62.1 Corentin Jabot; Eric Niebler; Casey Carter (2022-01-21). "Conversions from ranges to containers" (PDF).
  63. ^ Christopher Di Bella (2021-02-19). "starts_with and ends_with".
  64. ^ Christopher Di Bella (2021-04-16). "std::ranges::contains".
  65. ^ Zach Laine (2022-06-17). "find_last" (PDF).
  66. ^ Tim Song (2021-12-05). "ranges::iota, ranges::shift_left, and ranges::shift_right".
  67. ^ Barry Revzin (2022-04-22). "ranges::fold".
  68. ^ Tim Song (2021-06-11). "zip".
  69. ^ Barry Revzin (2022-01-28). "views::join_with".
  70. ^ Tim Song (2021-12-05). "Windowing range adaptors: views::chunk and views::slide".
  71. ^ Tim Song (2021-11-19). "views::chunk_by".
  72. ^ Barry Revzin (2022-02-14). "views::as_rvalue".
  73. ^ 73.0 73.1 Barry Revzin (2022-06-17). "cbegin should always return a constant iterator".
  74. ^ Michał Dominiak (2022-07-13). "views::repeat".
  75. ^ Christopher Di Bella; Tim Song (2022-07-08). "stride_view".
  76. ^ Sy Brand; Michał Dominiak (2022-07-13). "views::cartesian_product".
  77. ^ Corentin Jabot (2022-12-07). "views::enumerate" (PDF).
  78. ^ David Olsen (2022-04-22). "Ranges iterators as inputs to non-Ranges algorithms".
  79. ^ Michał Dominiak (2022-07-13). "Relaxing range adaptors to allow for move only types".
  80. ^ Ville Voutilainen (2022-11-12). "Making multi-param constructors of views explicit".
  81. ^ JeanHeyd Meneide; Todor Buyukliev; Isabella Muerte (2021-04-15). "out_ptr - a scalable output pointer abstraction".
  82. ^ Jonathan Wakely; Chris Kennelly (2021-01-22). "Providing size feedback in the Allocator interface".
  83. ^ Timur Doumler; Richard Smith (2022-07-15). "Explicit lifetime management" (PDF).
  84. ^ Pablo Halpern (2023-02-08). "Disallow User Specialization of allocator_traits".
  85. ^ Wim Leflere; Paul Fee (2020-06-13). "string contains function".
  86. ^ Yuriy Chernyshov (2020-09-06). "A Proposal to Prohibit std::basic_string and std::basic_string_view construction from nullptr".
  87. ^ Corentin Jabot (2021-03-17). "Range constructor forstd::string_view 2: Constrain Harder" (PDF).
  88. ^ Chris Kennelly; Mark Zeren (2021-09-14). "basic_string::resize_and_overwrite".
  89. ^ "std::string::substr() &&".
  90. ^ "Formatting Ranges". 16 May 2022.
  91. ^ Barry Revzin (2022-07-15). "Improve default container formatting".
  92. ^ Corentin Jabot; Victor Zverovich (2023-02-09). "Formatting thread::id and stacktrace" (PDF).
  93. ^ Alexey Gorgurov; Antony Polukhin (2020-09-16). "A Proposal to add stacktrace library".
  94. ^ "Formatted output".
  95. ^ Peter Sommerlad (2021-02-26). "A strstream replacement using span<charT> as buffer" (PDF).
  96. ^ "Support exclusive mode for fstreams".
  97. ^ Bryce Adelstein Lelbach (2021-09-25). "Printing volatile Pointers".
  98. ^ "MDSPAN". 13 July 2022.
  99. ^ "index_type & size_type in mdspan" (PDF).
  100. ^ "mdspan: rename pointer and contiguous". 15 June 2022.
  101. ^ "Add the missing empty to mdspan".
  102. ^ "A Standard flat_map" (PDF).
  103. ^ "A Standard flat_set" (PDF).
  104. ^ Arthur O'Dwyer; Mike Spertus (2021-03-14). "Stop overconstraining allocators in container deduction guides".
  105. ^ Konstantin Boyarinov; Sergey Vinogradov; Ruslan Arutyunyan (2020-12-15). "Heterogeneous erasure overloads for associative containers".
  106. ^ Corentin Jabot (2021-03-05). "Iterators pair constructors for stack and queue" (PDF).
  107. ^ Nevin Liber (2021-03-19). "Require span & basic_string_view to be TriviallyCopyable" (PDF).
  108. ^ Hans-J. Boehm (2020-10-23). "P0943R6: Support C atomics in C++".
  109. ^ Steve Downey; Zach Laine; Tom Honermann; Peter Bindels; Jens Maurer (2021-04-12). "C++ Identifier Syntax using Unicode Standard Annex 31".
  110. ^ Erich Keane (2020-07-02). "Allow Duplicate Attributes" (PDF).
  111. ^ Barry Revzin (2021-09-14). "Change scope of lambda trailing-return-type".
  112. ^ "The Equality Operator You Are Looking For". 2022-01-13.
  113. ^ "De-deprecating volatile compound operations" (PDF).
  114. ^ "Core Language Working Group NB comment resolutions for the November, 2022 meeting : 2654. Un-deprecation of compound volatile assignments".
  115. ^ "char8_t Compatibility and Portability Fix". 2022-06-17.
  116. ^ "Relax requirements on wchar_t to match existing practices" (PDF). 2022-07-15.
  117. ^ "Using unknown pointers and references in constant expressions". 8 April 2022.
  118. ^ "consteval needs to propagate up". 2022-11-11.
  119. ^ Barry Revzin (2020-02-19). "Conditionally borrowed ranges".
  120. ^ Tim Song (2021-01-12). "Repairing input range adaptors and counted_iterator".
  121. ^ Tim Song (2021-05-06). "join_view should join all views of ranges".
  122. ^ Barry Revzin (2021-03-05). "Superior String Splitting".
  123. ^ Barry Revzin (2021-05-14). "Views should not be required to be default constructible".
  124. ^ Barry Revzin; Tim Song (2021-08-15). "What is a view?".
  125. ^ Nicolai Josuttis (2021-09-24). "Fix istream_view" (PDF).
  126. ^ Barry Revzin (2022-01-18). "Expose std::basic-format-string<charT, Args...>".
  127. ^ Victor Zverovich (2021-02-05). "std::format improvements".
  128. ^ Victor Zverovich; Corentin Jabot (2021-09-11). "Fixing locale handling in chrono formatters".
  129. ^ Corentin Jabot (2022-12-02). "format's width estimation is too approximate and not forward compatible" (PDF).
  130. ^ Tom Honermann (2023-02-08). "std::format() fill character allowances".
  131. ^ Victor Zverovich (2021-09-24). "Add support for std::generator-like types to std::format".
  132. ^ Barry Revzin (2021-02-11). "Missing constexpr in std::optional and std::variant".
  133. ^ Barry Revzin (2020-10-30). "Inheriting from std::variant".
  134. ^ JF Bastien; Alisdair Meredith (2021-04-16). "Removing Garbage Collection Support".
  135. ^ Jens Maurer (2021-04-12). "Mixed string literal concatenation".
  136. ^ "Remove non-encodable wide character literals and multicharacter wide character literals" (PDF).
  137. ^ CJ Johnson (2021-11-22). "Deprecate std::aligned_storage and std::aligned_union" (PDF).
  138. ^ Matthias Kretz (2022-11-08). "Deprecate numeric_limits::has_denorm" (PDF).
  139. ^ "Programming Languages — Technical specification for C++ extensions for concurrency 2" (PDF).
  140. ^ "C++ Support in Clang".
  141. ^ "C++ Standards Support in GCC - GNU Project".
  142. ^ Ranns, Nina (2020-11-19). "WG21 2020-11 Virtual Meeting: Minutes of Meeting" (PDF).
  143. ^ Ranns, Nina (2021-02-22). "WG21 2021-02 Virtual Meeting: Minutes of Meeting" (PDF).
  144. ^ Alexey Dmitriev; Howard Hinnant (2020-10-22). "Relax Requirements for time_point::clock".
  145. ^ Tim Song (2020-11-13). "Locks lock lockables".
  146. ^ Ranns, Nina (2021-06-07). "WG21 2021-06 Virtual Meeting Minutes of Meeting" (PDF).
  147. ^ Ranns, Nina (2021-10-04). "WG21 2021-10 Virtual Meeting Minutes of Meeting" (PDF).
  148. ^ "GCC 12 Adds Support For New #elifdef #elifndef Directives". phoronix. May 12, 2021. Archived from the original on December 27, 2022.
  149. ^ Steve Downey (2021-06-14). "Add a pmr alias for std::stacktrace".
  150. ^ Giuseppe D'Angelo (2021-06-28). "Add a conditional noexcept specification to std::exchange".
  151. ^ Tim Song (2021-08-06). "Cleaning up integer-class types".
  152. ^ Thomas Köppe (2021-06-11). "Clarifying the status of the "C headers"".
  153. ^ Ranns, Nina (2022-02-07). "WG21 2022-02 Virtual Meeting: Minutes of Meeting" (PDF).
  154. ^ Ranns, Nina (2022-08-09). "WG21 2022-07 Virtual Meeting: Minutes of Meeting" (PDF).
  155. ^ Ranns, Nina (2022-12-05). "WG21 2022-11 Hybrid Meeting: Minutes of Meeting" (PDF).
  156. ^ Victor Zverovich (2022-11-08). "Should the output of std::print to a terminal be synchronized with the underlying stream?".
  157. ^ Ranns, Nina (2023-03-06). "WG21 2023-02 Hybrid Meeting: Minutes of Meeting" (PDF).
  158. ^ Corentin Jabot (2023-02-09). "Referencing The Unicode Standard" (PDF).
  159. ^ Tim Song (2023-01-31). "Stashing stashing iterators for proper flattening".
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