libc++ C++2a Status

In July 2017, the C++ standard committee created a draft for the next version of the C++ standard, known here as "C++2a" (probably to be C++20).

This page shows the status of libc++; the status of clang's support of the language features is here.

Reminder: Features in unreleased drafts of the standard are subject to change.

The groups that have contributed papers:

Paper Status

Paper #GroupPaper NameMeetingStatusFirst released version
P0463R1LWGEndian just EndianTorontoComplete7.0
P0674R1LWGExtending make_shared to Support ArraysToronto
P0020R6LWGFloating Point AtomicAlbuquerque
P0053R7LWGC++ Synchronized Buffered OstreamAlbuquerque
P0202R3LWGAdd constexpr modifiers to functions in <algorithm> and <utility> HeadersAlbuquerqueIn Progress7.0
P0415R1LWGConstexpr for std::complexAlbuquerqueIn Progress7.0
P0439R0LWGMake std::memory_order a scoped enumerationAlbuquerque
P0457R2LWGString Prefix and Suffix CheckingAlbuquerqueComplete6.0
P0550R2LWGTransformation Trait remove_cvrefAlbuquerqueComplete6.0
P0600R1LWGnodiscard in the LibraryAlbuquerqueIn Progress7.0
P0616R0LWGde-pessimize legacy algorithms with std::moveAlbuquerque
P0653R2LWGUtility to convert a pointer to a raw pointerAlbuquerqueComplete6.0
P0718R2LWGAtomic shared_ptrAlbuquerque
P0767R1CWGDeprecate PODAlbuquerqueComplete7.0
P0768R1CWGLibrary Support for the Spaceship (Comparison) OperatorAlbuquerque
P0777R1LWGTreating Unnecessary decayAlbuquerqueComplete7.0
P0122R7LWG<span>JacksonvilleIn Progress
P0355R7LWGExtending chrono to Calendars and Time ZonesJacksonville
P0551R3LWGThou Shalt Not Specialize std Function Templates!Jacksonville
P0753R2LWGManipulators for C++ Synchronized Buffered OstreamJacksonville
P0754R2LWG<version>JacksonvilleComplete7.0
P0809R0LWGComparing Unordered ContainersJacksonville
P0858R0LWGConstexpr iterator requirementsJacksonville
P0905R1CWGSymmetry for spaceshipJacksonville
P0966R1LWGstring::reserve Should Not ShrinkJacksonville
P0019R8LWGAtomic RefRapperswil
P0458R2LWGChecking for Existence of an Element in Associative ContainersRapperswil
P0475R1LWGLWG 2511: guaranteed copy elision for piecewise constructionRapperswil
P0476R2LWGBit-casting object representationsRapperswil
P0528R3CWGThe Curious Case of Padding Bits, Featuring Atomic Compare-and-ExchangeRapperswil
P0542R5CWGSupport for contract based programming in C++Rapperswil
P0556R3LWGIntegral power-of-2 operationsRapperswil
P0619R4LWGReviewing Deprecated Facilities of C++17 for C++20Rapperswil
P0646R1LWGImproving the Return Value of Erase-Like AlgorithmsRapperswil
P0722R3CWGEfficient sized delete for variable sized classesRapperswil
P0758R1LWGImplicit conversion traits and utility functionsRapperswil
P0759R1LWGfpos RequirementsRapperswil
P0769R2LWGAdd shift to <algorithm>Rapperswil
P0788R3LWGStandard Library Specification in a Concepts and Contracts WorldRapperswil
P0879R0LWGConstexpr for swap and swap related functions Also resolves LWG issue 2800.Rapperswil
P0887R1LWGThe identity metafunctionRapperswil
P0892R2CWGexplicit(bool)Rapperswil
P0898R3LWGStandard Library ConceptsRapperswil
P0935R0LWGEradicating unnecessarily explicit default constructors from the standard libraryRapperswil
P0941R2CWGIntegrating feature-test macros into the C++ WDRapperswil
P1023R0LWGconstexpr comparison operators for std::arrayRapperswil
P1025R1CWGUpdate The Reference To The Unicode StandardRapperswil
P1120R0CWGConsistency improvements for <=> and other comparison operatorsRapperswil

[ Note: "Nothing to do" means that no library changes were needed to implement this change -- end note]

The missing bits in P0600 are in [mem.res.class], [mem.poly.allocator.class], and [container.node.overview]

The missing bits in P0202 are in copy, copy_backwards, move, and move_backwards (and the ones that call them: copy_n, rotate_copy, merge, set_union, set_difference, and set_symmetric_difference). This is because the first four algorithms have specializations that call memmove which is not constexpr. See Bug 25165

Library Working group Issues Status

Issue #Issue NameMeetingStatus
2070allocate_shared should use allocator_traits<A>::constructTorontoResolved by P0674R1
2444Inconsistent complexity for std::sort_heapToronto
2593Moved-from state of AllocatorsToronto
2597std::log misspecified for complex numbersToronto
2783stack::emplace() and queue::emplace() should return decltype(auto)TorontoComplete
2932Constraints on parallel algorithm implementations are underspecifiedToronto
2937Is equivalent("existing_thing", "not_existing_thing") an errorTorontoComplete
2940result_of specification also needs a little cleanupToronto
2942LWG 2873's resolution missed weak_ptr::owner_beforeTorontoComplete
2954Specialization of the convenience variable templates should be prohibitedTorontoComplete
2961Bad postcondition for set_default_resourceToronto
2966Incomplete resolution of US 74TorontoNothing to do
2974Diagnose out of bounds tuple_element/variant_alternativeTorontoComplete
2779[networking.ts] Relax requirements on buffer sequence iteratorsAlbuquerque
2870Default value of parameter theta of polar should be dependentAlbuquerqueComplete
2935What should create_directories do when p already exists but is not a directory?Albuquerque
2941[thread.req.timing] wording should apply to both member and namespace-level functionsAlbuquerqueNothing to do
2944LWG 2905 accidentally removed requirement that construction of the deleter doesn't throw an exceptionAlbuquerqueNothing to do
2945Order of template parameters in optional comparisonsAlbuquerqueComplete
2948unique_ptr does not define operator<< for stream outputAlbuquerqueComplete
2950std::byte operations are misspecifiedAlbuquerqueComplete
2952iterator_traits should work for pointers to cv TAlbuquerqueComplete
2953LWG 2853 should apply to deque::erase tooAlbuquerque
2958Moves improperly defined as deletedAlbuquerque
2964Apparently redundant requirement for dynamic_pointer_castAlbuquerque
2965Non-existing path::native_string() in filesystem_error::what() specificationAlbuquerque
2972What is is_trivially_destructible_v<int>?AlbuquerqueComplete
2976Dangling uses_allocator specialization for packaged_taskAlbuquerqueComplete
2977unordered_meow::merge() has incorrect Throws: clauseAlbuquerque
2978Hash support for pmr::string and friendsAlbuquerque
2979aligned_union should require complete object typesAlbuquerqueComplete
2980Cannot compare_exchange empty pointersAlbuquerque
2981Remove redundant deduction guides from standard libraryAlbuquerque
2982Making size_type consistent in associative container deduction guidesAlbuquerque
2988Clause 32 cleanup missed one typenameAlbuquerque
2993reference_wrapper conversion from T&&Albuquerque
2998Requirements on function objects passed to {forward_,}list-specific algorithmsAlbuquerqueNothing to do
3001weak_ptr::element_type needs remove_extent_tAlbuquerque
3024variant's copies must be deleted instead of disabled via SFINAEAlbuquerque
2164What are the semantics of vector.emplace(vector.begin(), vector.back())?Jacksonville
2243istream::putback problemJacksonvilleComplete
2816resize_file has impossible postconditionJacksonvilleNothing to do
2843Unclear behavior of std::pmr::memory_resource::do_allocate()Jacksonville
2849Why does !is_regular_file(from) cause copy_file to report a "file already exists" error?JacksonvilleNothing to do
2851std::filesystem enum classes are now underspecifiedJacksonvilleNothing to do
2946LWG 2758's resolution missed further correctionsJacksonvilleComplete
2969polymorphic_allocator::construct() shouldn't pass resource()Jacksonville
2975Missing case for pair construction in scoped and polymorphic allocatorsJacksonville
2989path's stream insertion operator lets you insert everything under the sunJacksonvilleCompleted
3000monotonic_memory_resource::do_is_equal uses dynamic_cast unnecessarilyJacksonville
3002[networking.ts] basic_socket_acceptor::is_open() isn't noexceptJacksonville
3004§[string.capacity] and §[vector.capacity] should specify time complexity for capacity()JacksonvilleNothing to do
3005Destruction order of arrays by make_shared/allocate_shared only recommended?Jacksonville
3007allocate_shared should rebind allocator to cv-unqualified value_type for constructionJacksonville
3009Including <string_view> doesn't provide std::size/empty/dataJacksonvilleComplete
3010[networking.ts] uses_executor says "if a type T::executor_type exists"Jacksonville
3013(recursive_)directory_iterator construction and traversal should not be noexceptJacksonvilleComplete
3014More noexcept issues with filesystem operationsJacksonvilleComplete
3015copy_options::unspecified underspecifiedJacksonvilleNothing to do
3017list splice functions should use addressofJacksonville
3020[networking.ts] Remove spurious nested value_type buffer sequence requirementJacksonville
3026filesystem::weakly_canonical still defined in terms of canonical(p, base)JacksonvilleComplete
3030Who shall meet the requirements of try_lock?JacksonvilleNothing to do
3034P0767R1 breaks previously-standard-layout typesJacksonvilleComplete
3035std::allocator's constructors should be constexprJacksonvilleComplete
3039Unnecessary decay in thread and packaged_taskJacksonvilleComplete
3041Unnecessary decay in reference_wrapperJacksonvilleComplete
3042is_literal_type_v should be inlineJacksonvilleComplete
3043Bogus postcondition for filesystem_error constructorJacksonville
3045atomic<floating-point> doesn't have value_type or difference_typeJacksonville
3048transform_reduce(exec, first1, last1, first2, init) discards execution policyJacksonville
3051Floating point classifications were inadvertently changed in P0175JacksonvilleNothing to do
3075basic_string needs deduction guides from basic_string_viewJacksonvilleComplete
2139What is a user-defined type?Rapperswil
2970Return type of std::visit misspecifiedRapperswil
3058Parallel adjacent_difference shouldn't require creating temporariesRapperswil
3062Unnecessary decay_t in is_execution_policy_v should be remove_cvref_tRapperswil
3067recursive_directory_iterator::pop must invalidateRapperswilNothing to do
3071[networking.ts] read_until still refers to "input sequence"RapperswilNothing to do
3074Non-member functions for valarray should only deduce from the valarrayRapperswil
3076basic_string CTAD ambiguityRapperswilComplete
3079LWG 2935 forgot to fix the existing_p overloads of create_directoryRapperswil
3080Floating point from_chars pattern specification breaks round-trippingRapperswil
3083What should ios::iword(-1) do?RapperswilNothing to do
3094[time.duration.io]p4 makes surprising claims about encodingRapperswil
3100Unnecessary and confusing "empty span" wordingRapperswilNothing to do
3102Clarify span iterator and const_iterator behaviorRapperswil
3104Fixing duration divisionRapperswilComplete

Last Updated: 11-Jun-2018