C++ 202a

-C++ 202a +C++ 2020 ISO C++ 2020 @@ -26,17 +26,20 @@ not in any particular release. The following table lists new library features that have been accepted into -the C++2a working draft. The "Proposal" column provides a link to the +the C++20 working draft. The "Proposal" column provides a link to the ISO C++ committee proposal that describes the feature, while the "Status" column indicates the first version of GCC that contains an implementation of this feature (if it has been implemented). -The "SD-6 Feature Test" column shows the corresponding macro or header from +A dash (—) in the status column indicates that the changes in the proposal +either do not affect the code in libstdc++, or the changes are not required for conformance. +The "SD-6 Feature Test / Notes" column shows the corresponding macro or header from SD-6: -Feature-testing recommendations for C++. +Feature-testing recommendations for C++ (where applicable) +or any notes about the implementation. - -C++ 2020 Implementation Status +

+C++ 2020 Library Features @@ -48,44 +51,309 @@ Feature-testing recommendations for C++. Library Feature Proposal Status - SD-6 Feature Test + SD-6 Feature Test / Notes - Endian just Endian - - - P0463R1 - + + Compile-time programming - 8.1 - + + + + Add constexpr modifiers to functions in <algorithm> and <utility> Headers + + + P0202R3 + + 10.1 + __cpp_lib_constexpr_algorithms >= 201703L + + + + Constexpr for swap and swap related functions + + + P0879R0 + + 10.1 + __cpp_lib_constexpr_algorithms >= 201806L + + + + Constexpr for std::complex + + + P0415R1 + + 9.1 + __cpp_lib_constexpr_complex >= 201711L (since 9.4, see Note 1) + + + + P0595R2 std::is_constant_evaluated() + + + P0595R2 + + 9.1 + __cpp_lib_is_constant_evaluated >= 201811L + + + + More constexpr containers + + + P0784R7 + + 10.1 + __cpp_lib_constexpr_dynamic_alloc >= 201907L - Extending make_shared to Support Arrays + Making std::string constexpr - - P0674R1 - + + P0980R1 + + + __cpp_lib_constexpr_string >= 201907L + + + + + Making std::vector constexpr + + + P1004R2 + + + __cpp_lib_constexpr_vector >= 201907L + + + + Constexpr in std::pointer_traits + + + P1006R1 + + 9.1 + __cpp_lib_constexpr_memory >= 201811L (since 9.4, see Note 1) + + + + constexpr for <numeric> algorithms + + + P1645R1 + + 10.1 + __cpp_lib_constexpr_numeric >= 201911L + + + + Constexpr iterator requirements + + + P0858R0 + + 9.1 + + + __cpp_lib_array_constexpr >= 201803L + __cpp_lib_string_view >= 201803L + (both since 9.4, see Note 1) + + + + + + constexpr comparison operators for std::array + + + P1023R0 + + 10.1 + __cpp_lib_array_constexpr >= 201806 + + + + Misc constexpr bits + + + P1032R1 + + 10.1 + + + __cpp_lib_array_constexpr >= 201811L + __cpp_lib_constexpr_functional >= 201811L + __cpp_lib_constexpr_iterator >= 201811L + __cpp_lib_constexpr_string_view >= 201811L + __cpp_lib_constexpr_tuple >= 201811L + __cpp_lib_constexpr_utility >= 201811L + + + + + + constexpr INVOKE + + + P1065R2 + + 10.1 + __cpp_lib_constexpr_functional >= 201907L + + + + + Transformation Trait remove_cvref + + + P0550R2 + + 9.1 + __cpp_lib_remove_cvref >= 201711L (since 9.4, see Note 1) + + + + Implicit conversion traits and utility functions + + + P0758R1 + + 9.1 + __cpp_lib_is_nothrow_convertible >= 201806L (since 9.4, see Note 1) + + + + The identity metafunction + + + P0887R1 + + 9.1 + __cpp_lib_type_identity >= 201806L (since 9.4, see Note 1) + + + + + unwrap_ref_decay and unwrap_reference + + + P0318R1 + + 9.1 + __cpp_lib_unwrap_ref >= 201811L (since 9.4, see Note 1) + + + + + Improving Completeness Requirements for Type Traits + + + P1285R0 + + Partial + + + + + Missing feature test macros + + + P1353R0 + + 9.1 + + + + + Making std::underlying_type SFINAE-friendly + + + P0340R3 + + 9.1 + + + + + Traits for [Un]bounded Arrays + + + P1357R1 + + 9.1 + __cpp_lib_bounded_array_traits >= 201902L + + + + + Layout-compatibility and pointer-interconvertibility traits + + + P0466R5 + + + __cpp_lib_is_layout_compatible >= 201907L + __cpp_lib_is_pointer_interconvertible >= 201907L + + + + + + Integrating feature-test macros into the C++ WD + + + P0941R2 + + 5.1 + + <version> + + + P0754R2 + + 9.1 + __has_include(<version>) + + + + + + Synchronization + + + + + Atomic Ref + + + P0019R8 + + 10.1 + __cpp_lib_atomic_ref >= 201806L + + Floating Point Atomic - P0020R6 - + P0020R6 10.1 - + __cpp_lib_atomic_float >= 201711L @@ -93,98 +361,41 @@ Feature-testing recommendations for C++. C++ Synchronized Buffered Ostream - P0053R7 - + P0053R7 - + __cpp_lib_syncbuf >= 201711L - Add constexpr modifiers to functions in <algorithm> and <utility> Headers + + Manipulators for C++ Synchronized Buffered Ostream - - P0202R3 - + + P0753R2 - 10.1 - __cpp_lib_constexpr_algorithms >= 201703L - - - - Constexpr for std::complex - - - P0415R1 - - - 9.1 - + + __cpp_lib_syncbuf >= 201803L Make std::memory_order a scoped enumeration - P0439R0 - + P0439R0 9.1 - String Prefix and Suffix Checking + + The Curious Case of Padding Bits, Featuring Atomic Compare-and-Exchange - - P0457R2 - + + P0528R3 - 9.1 - - - - - Transformation Trait remove_cvref - - - P0550R2 - - - 9.1 - - - - - nodiscard in the Library - - - P0600R1 - - - 9.1 - - - - - de-pessimize legacy algorithms with std::move - - - P0616R0 - - - 9.1 - - - - - Utility to convert a pointer to a raw pointer - - - P0653R2 - - - 8.1 + @@ -193,57 +404,156 @@ Feature-testing recommendations for C++. Atomic shared_ptr - P0718R2 - + P0718R2 - + __cpp_lib_atomic_shared_ptr >= 201711L - - Deprecate POD + std::stop_token and std::jthread - - P0767R1 - - - - - - - - - Library Support for the Spaceship (Comparison) Operator - - - P0768R1 - - - - - - - - Treating Unnecessary decay - - - P0777R1 - - - 9.1 - - - - - <span> - - - P0122R7 - + + P0660R10 10.1 - __cpp_lib_span >= 201803L + __cpp_lib_jthread >= 201907L + + + + Rename condition_variable_any interruptible wait methods + + + P1869R1 + + 10.1 + __cpp_lib_jthread >= 201911L + + + + + Atomic waiting and notifying, std::semaphore, std::latch and std::barrier + + + P1135R6 + + + + + __cpp_lib_atomic_lock_free_type_aliases >= 201907L + __cpp_lib_atomic_flag_test >= 201907L + __cpp_lib_atomic_wait >= 201907L + __cpp_lib_semaphore >= 201907L + __cpp_lib_latch >= 201907L + __cpp_lib_barrier >= 201907L + + + + + + Fixing Atomic Initialization + + + P0883R2 + + 10.1 + __cpp_lib_atomic_value_initialization >= 201911L + + + + + + + Ranges and Concepts + + + + + Standard Library Concepts + + + P0898R3 + + 10.1 + __cpp_lib_concepts >= 201806L + + + + Rename concepts to standard_case for C++20, while we still can + + + P1754R1 + + 10.1 + __cpp_lib_concepts >= 201907L + + + + Wording for boolean-testable + + + P1964R2 + + 10.1 + __cpp_lib_concepts >= 202002L + + + + The One Ranges Proposal + + + P0896R4 + + 10.1 + __cpp_lib_ranges >= 201811L + + + + Input Range Adaptors + + + P1035R7 + + 10.1 + __cpp_lib_ranges >= 201907L + + + + ranges compare algorithm are over-constrained + + + P1716R3 + + 10.1 + __cpp_lib_ranges >= 201911L + + + + Remove CommonReference requirement from StrictWeakOrdering (a.k.a Fixing Relations) + + + P1248R1 + + 10.1 + + + + + Ranges Design Cleanup + + + P1252R2 + + 10.1 + + + + + + + + Time, dates, calendars, time zones + @@ -251,43 +561,234 @@ Feature-testing recommendations for C++. Extending chrono to Calendars and Time Zones - P0355R7 - + P0355R7 - - + + __cpp_lib_chrono >= 201803L - Thou Shalt Not Specialize std Function Templates! + Miscellaneous minor fixes for chrono - - P0551R3 - + + P1466R3 - + + __cpp_lib_chrono >= 201907L + + + + <chrono> zero(), min(), and max() should be noexcept + + + P0972R0 + + 9.1 + + + + Three-way comparison + + + + + Library Support for the Spaceship (Comparison) Operator + + + P0768R1 + + 10.1 + __cpp_lib_three_way_comparison >= 201711L + + + + Symmetry for spaceship + + + P0905R1 + + 10.1 + + + + + Adding <=> to the standard library + + + P1614R2 + + 10.1 + + __cpp_lib_three_way_comparison >= 201907L + + + + + + + Strings and text + + + - Manipulators for C++ Synchronized Buffered Ostream + string::reserve Should Not Shrink - - P0753R2 - + + P0966R1 - <version> + char8_t: A type for UTF-8 characters and strings - - P0754R2 - + + P0482R6 + + 9.1 + __cpp_lib_char8_t >= 201811L + + + + char8_t backward compatibility remediation + + + P1423R3 + + 10.1 + __cpp_lib_char8_t >= 201907L + + + + + Text formatting + + + P0645R10 + + + + __cpp_lib_format >= 201907L + + + + + + Integration of chrono with text formatting + + + P1361R2 + + + + __cpp_lib_format >= 201907L + + + + + + Printf corner cases in std::format + + + P1652R1 + + + + __cpp_lib_format >= 201907L + + + + + String Prefix and Suffix Checking + + + P0457R2 + + 9.1 + __cpp_lib_starts_ends_with >= 201711L (since 9.4, see Note 1) + + + + + Update The Reference To The Unicode Standard + + + P1025R1 + + + + + + + + + Containers + + + + + span: bounds-safe views for sequences of objects + + + P0122R7 + + 10.1 + __cpp_lib_span >= 201803L + + + + + Usability Enhancements for std::span + + + + P1024R3 + + 10.1 + __cpp_lib_span >= 201902L + + + + Should Span be Regular? + + + P1085R2 + + 10.1 + + + + + Fixed-size <span> construction from dynamic range + + + P1976R2 + + 10.1 + __cpp_lib_span >= 202002L + + + + std::to_array + + + P0325R4 + + 10.1 + __cpp_lib_to_array >= 201907L + + + + Checking for Existence of an Element in Associative Containers + + + P0458R2 9.1 @@ -298,372 +799,111 @@ Feature-testing recommendations for C++. Comparing Unordered Containers - P0809R0 - + P0809R0 - Constexpr iterator requirements + + Heterogeneous lookup for unordered containers - - P0858R0 - + + P0919R3 + + + __cpp_lib_generic_unordered_lookup >= 201811 + + + + Adopt Consistent Container Erasure from Library Fundamentals 2 for C++20 + + + P1209R0 9.1 - __cpp_lib_string_view >= 201803L - and __cpp_lib_array_constexpr >= 201803L - - - - - Symmetry for spaceship - - - P0905R1 - - - - - - - - - string::reserve Should Not Shrink - - - P0966R1 - - - - - - - - Atomic Ref - - - P0019R8 - - - 10.1 - __cpp_lib_atomic_ref >= 201806L - - - - Checking for Existence of an Element in Associative Containers - - - P0458R2 - - - 9.1 - - - - - LWG 2511: guaranteed copy elision for piecewise construction - - - P0475R1 - - - 7.1 - - - - - - Bit-casting object representations - - - P0476R2 - - - - - - - - - The Curious Case of Padding Bits, Featuring Atomic Compare-and-Exchange - - - P0528R3 - - - - - - - - - Support for contract based programming in C++ - - - P0542R5 - - - - - - - - Integral power-of-2 operations - - - P0556R3 - - - 9.1 - - - - - - Reviewing Deprecated Facilities of C++17 for C++20 - - - P0619R4 - - - - + __cpp_lib_erase_if >= 201811L Improving the Return Value of Erase-Like Algorithms - P0646R1 - + P0646R1 9.1 __cpp_lib_list_remove_return_type >= 201806L + + Improving the Return Value of Erase-Like Algorithms II: Free erase/erase_if + + + P1115R3 + + 9.1 + + + __cpp_lib_erase_if >= 202002L + (defined to 201900L for GCC 9.1 and 9.2 so use > 201811L) + + + + + + Signed ssize() functions, unsigned size() functions + + + P1227R2 + + 10.1 + __cpp_lib_ssize >= 201902L + + + + + + Memory management + + + + + Utility to convert a pointer to a raw pointer + + + P0653R2 + + 8.1 + __cpp_lib_to_address >= 201711L (since 9.4, see Note 1) + + + + + Extending make_shared to Support Arrays + + + P0674R1 + + + __cpp_lib_shared_ptr_arrays >= 201707L + + Efficient sized delete for variable sized classes - P0722R3 - + P0722R3 9.1 __cpp_lib_destroying_delete >= 201806L - - Implicit conversion traits and utility functions - - - P0758R1 - - - 9.1 - - - - - fpos Requirements - - - P0759R1 - - - Note 1 - - - - - - Add shift to <algorithm> - - - P0769R2 - - - - - - - - - Standard Library Specification in a Concepts and Contracts World - - - P0788R3 - - - - - - - - Constexpr for swap and swap related functions - - - P0879R0 - - - 10.1 - __cpp_lib_constexpr_algorithms >= 201806L - - - - The identity metafunction - - - P0887R1 - - - 9.1 - - - - - explicit(bool) - - - P0892R2 - - - Note 1 - - - - - Standard Library Concepts - - - P0898R3 - - - 10.1 - __cpp_lib_concepts >= 201806L - - - - Eradicating unnecessarily explicit default constructors from the standard library - - - P0935R0 - - - 9.1 - - - - - Integrating feature-test macros into the C++ WD - - - P0941R2 - - - 5.1 - - - - - constexpr comparison operators for std::array - - - P1023R0 - - - 10.1 - - - - - - Update The Reference To The Unicode Standard - - - P1025R1 - - - - - - - - - Consistency improvements for <=> and other comparison operators - - - P1120R0 - - - - - - - - unwrap_ref_decay and unwrap_reference - - - P0318R1 - - - 9.1 - - - - - Simplified partial function application - - - P0356R5 - - - 9.1 - __cpp_lib_bind_front >= 201811L - - - - reference_wrapper for incomplete types - - - P0357R3 - - - 9.1 - - - - - char8_t: A type for UTF-8 characters and strings - - - P0482R6 - - - 9.1 - __cpp_lib_char8_t >= 201811L - - - - - Fixing operator>>(basic_istream&, CharT*) (LWG 2499) - - - P0487R1 - - - - - - Utility functions to implement uses-allocator construction - P0591R4 - + P0591R4 9.1 @@ -672,44 +912,217 @@ Feature-testing recommendations for C++. - P0595R2 std::is_constant_evaluated() + std::assume_aligned - - P0595R2 - + + P1007R3 9.1 - + __cpp_lib_assume_aligned >= 201811L (since 9.4, see Note 1) - variant and optional should propagate copy/move triviality + + Smart pointer creation with default initialization - - P0602R4 - + + P1020R1 - 8.3 - + + __cpp_lib_smart_ptr_for_overwrite >= 201811L - A sane variant converting constructor + Make stateful allocator propagation more consistent for operator+(basic_string) - - P0608R3 - + + P1165R1 10.1 - visit<R>: Explicit Return Type for visit - - P0655R1 - + polymorphic_allocator<> as a vocabulary type + + + + P0339R6 + + 9.1 + + __cpp_lib_polymorphic_allocator >= 201902L (since 9.4, see Note 1) + + + + + LWG 2511: guaranteed copy elision for piecewise construction + + + P0475R1 + + 7.1 + + + + + + + Miscellaneous + + + + + nodiscard in the Library + + + P0600R1 + + 9.1 + + + + + de-pessimize legacy algorithms with std::move + + + P0616R0 + + 9.1 + + + + + Deprecate POD + + + P0767R1 + + 10.1 + + + + + Treating Unnecessary decay + + + P0777R1 + + 9.1 + + + + + + Thou Shalt Not Specialize std Function Templates! + + + P0551R3 + + + + + + + + Bit-casting object representations + + + P0476R2 + + + __cpp_lib_bit_cast >= 201806L + + + + Integral power-of-2 operations + + + P0556R3 + + 9.1 + __cpp_lib_int_pow2 >= 201806L (since 9.4, see Note 1) + + + + On the names of low-level bit manipulation functions + + + P1956R1 + + 10.1 + __cpp_lib_int_pow2 >= 202002L + + + + Safe integral comparisons + + + P0586R2 + + 10.1 + __cpp_lib_integer_comparison_functions >= 202002L + + + + + Reviewing Deprecated Facilities of C++17 for C++20 + + + P0619R4 + + + + + + + fpos Requirements + + + P0759R1 + + — + + + + + + Add shift to <algorithm> + + + P0769R2 + + 10.1 + __cpp_lib_shift >= 201806L + + + + + Standard Library Specification in a Concepts and Contracts World + + + P0788R3 + + + + + + + explicit(bool) + + + P0892R2 + + — + + + + + Eradicating unnecessarily explicit default constructors from the standard library + + + P0935R0 9.1 @@ -719,124 +1132,100 @@ Feature-testing recommendations for C++. std::function move constructor should be noexcept - P0771R1 - + P0771R1 7.2 - - The One Ranges Proposal + Simplified partial function application - - P0896R4 - + + P0356R5 + + 9.1 + __cpp_lib_bind_front >= 201811L + + + + bind_front should not unwrap reference_wrapper + + + P1651R0 + + 9.3 + __cpp_lib_bind_front >= 201907L + + + + reference_wrapper for incomplete types + + + P0357R3 + + 9.1 + + + + + + Fixing operator>>(basic_istream&, CharT*) (LWG 2499) + + + P0487R1 + + variant and optional should propagate copy/move triviality + + + P0602R4 + + 8.3 + + + + + A sane variant converting constructor + + + P0608R3 + + 10.1 + + + + + visit<R>: Explicit Return Type for visit + + + P0655R1 + + 9.1 + + + P0899R1 - LWG 3016 is not a defect - P0899R1 - + P0899R1 7.1 - - - Heterogeneous lookup for unordered containers - - - P0919R3 - - - - - - - - <chrono> zero(), min(), and max() should be noexcept - - - P0972R0 - - - 9.1 - - - - - Constexpr in std::pointer_traits - - - P1006R1 - - - 9.1 - - - - - std::assume_aligned - - - P1007R3 - - - 9.1 - - - - - - Smart pointer creation with default initialization - - - P1020R1 - - - - - - - - - Misc constexpr bits - - - P1032R1 - - - - - - - - Should Span be Regular? - - - P1085R2 - - - 10.1 - __cpp_lib_span >= 201902L - - Editorial Guidance for merging P0019r8 and P0528r3 - P1123R0 - + P1123R0 - Note 1 + — @@ -845,142 +1234,43 @@ Feature-testing recommendations for C++. Cleaning up Clause 20 - P1148R0 - + P1148R0 - - Make stateful allocator propagation more consistent for operator+(basic_string) - - - P1165R1 - - - 10.1 - - - - - Adopt Consistent Container Erasure from Library Fundamentals 2 for C++20 - - - P1209R0 - - - 9.1 - __cpp_lib_erase_if >= 201811L - - Completing the Rebase of Library Fundamentals, Version 3, Working Draft - P1210R0 - + P1210R0 - Alternative Wording for P0907R4 Signed Integers are Two's Complement - P1236R1 - + P1236R1 - - + — + - - Remove CommonReference requirement from StrictWeakOrdering (a.k.a Fixing Relations) - - - P1248R1 - - - - - - - - - Improving Completeness Requirements for Type Traits - - - P1285R0 - - - Partial - - - - - Well-behaved interpolation for numbers and pointers - - - P0811R3 - - - 9.1 - __cpp_lib_interpolate >= 201902L - - - - Missing feature test macros - - - P1353R0 - - - 9.1 - - - - - - polymorphic_allocator<> - as a vocabulary type - - - - P0339R6 - - - 9.1 - - - - - Making std::underlying_type SFINAE-friendly - - - P0340R3 - - - 9.1 - - - - - I Stream, You Stream, We All Stream for istream_iterator - P0738R2 - + P0738R2 - + 10.1 @@ -991,11 +1281,10 @@ Feature-testing recommendations for C++. - P1458R1 - + P1458R1 - - Note 1 + — + @@ -1005,11 +1294,10 @@ Feature-testing recommendations for C++. - P1459R1 - + P1459R1 - - Note 1 + — + @@ -1019,11 +1307,10 @@ Feature-testing recommendations for C++. - P1462R1 - + P1462R1 - - Note 1 + — + @@ -1033,10 +1320,9 @@ Feature-testing recommendations for C++. - P1463R1 - + P1463R1 - 10 + 10.1 @@ -1048,8 +1334,7 @@ Feature-testing recommendations for C++. - P1464R1 - + P1464R1 @@ -1060,212 +1345,84 @@ Feature-testing recommendations for C++. P1164R1 - + 8.3 Treated as a DR for C++17 - Target Vectorization Policies from Parallelism V2 TS to C++20 - P1001R2 - - - - - - - - Signed ssize() functions, unsigned size() functions - - - P1227R2 - - - 10.1 - - - - - - Ranges Design Cleanup - - - P1252R2 - - - - - - - - - Usability Enhancements for std::span - - - - P1024R3 - - - 10.1 - __cpp_lib_span >= 201902L - - - - Traits for [Un]bounded Arrays - - - P1357R1 - + P1001R2 9.1 - __cpp_lib_bounded_array_traits >= 201902L + __cpp_lib_execution >= 201902L (since 9.4, see Note 1) - std::to_array + Merge Coroutines TS into C++20 working draft - - P0325R4 - + + P0912R5 10.1 - __cpp_lib_to_array >= 201907L + __cpp_lib_coroutines >= 201902L + + + + Endian just Endian + + + P0463R1 + + 8.1 + __cpp_lib_endian >= 201907L Bit operations - P0553R4 - + P0553R4 10.1 - __cpp_lib_bitops >= 201907L + __cpp_lib_bitops >= 201907L (since 9.4, see Note 1) + + + + Well-behaved interpolation for numbers and pointers + + + P0811R3 + + 9.1 + __cpp_lib_interpolate >= 201902L Mathematical constants - P0631R8 - + P0631R8 10.1 __cpp_lib_math_constants >= 201907L - - - Layout-compatibility and pointer-interconvertibility traits - - - P0466R5 - - - - - __cpp_lib_is_layout_compatible >= 201907L, - __cpp_lib_is_layout_interconvertible >= 201907L, - - - - - std::stop_token and std::jthread - - - P0660R10 - - - 10.1 - __cpp_lib_jthread >= 201907L - - - - - Text formatting - - - P0645R10 - - - - - __cpp_lib_format >= 201907L, - - - - - constexpr std::invoke and related utilities - - - P1065R2 - - - 10.1 - __cpp_lib_constexpr_invoke >= 201907L - - - - constexpr std::allocator and related utilities - - - P0784R7 - - - 10.1 - __cpp_constexpr_dynamic_alloc >= 201907L - - - - - Atomic waiting and notifying, std::semaphore, std::latch and std::barrier - - - P1135R6 - - - - - __cpp_lib_atomic_lock_free_type_aliases >= 201907L in <atomic>, - __cpp_lib_atomic_flag_test >= 201907L in <atomic>, - __cpp_lib_atomic_wait >= 201907L in <atomic>, - __cpp_lib_semaphore >= 201907L in <semaphore>, - __cpp_lib_latch >= 201907L in <latch>, - __cpp_lib_barrier >= 201907L in <barrier> - - - std::source_location - P1208R6 - + P1208R6 - __cpp_lib_source_location >= 201907L, - - - - - - Adding <=> to the standard library - - - P1614R2 - - - - - __cpp_lib_spaceship >= 201907L, + __cpp_lib_source_location >= 201907L @@ -1274,8 +1431,7 @@ Feature-testing recommendations for C++. Efficient access to std::basic_stringbuf's Buffer - P0408R7 - + P0408R7 @@ -1286,23 +1442,9 @@ Feature-testing recommendations for C++.

-Note 1: The changes in the proposal either do not affect the code in libstdc++, -or the changes are not required for conformance. +Note 1: This feature is supported in older releases but the +__cpp_lib macro is not defined to the right value +(or not defined at all) until the version shown in parentheses. - -

Implementation Specific Behavior - - For behaviour which is also specified by previous standards, - see C++ 1998/2003 Implementation - Specific Behavior, C++ - 2011 Implementation Specific Behavior and C++ 2017 Implementation Specific - Behavior. - This section only documents behaviour which is new in the 202a draft. - - - -