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:

• LWG - Library working group
• CWG - Core Language Working group
• SG1 - Study group #1 (Concurrency working group)

Paper Status

Paper #	Group	Paper Name	Meeting	Status	First released version
P0463R1	LWG	Endian just Endian	Toronto	Complete	7.0
P0674R1	LWG	Extending make_shared to Support Arrays	Toronto
P0020R6	LWG	Floating Point Atomic	Albuquerque
P0053R7	LWG	C++ Synchronized Buffered Ostream	Albuquerque
P0202R3	LWG	Add constexpr modifiers to functions in <algorithm> and <utility> Headers	Albuquerque	In Progress	7.0
P0415R1	LWG	Constexpr for std::complex	Albuquerque	In Progress	7.0
P0439R0	LWG	Make std::memory_order a scoped enumeration	Albuquerque
P0457R2	LWG	String Prefix and Suffix Checking	Albuquerque	Complete	6.0
P0550R2	LWG	Transformation Trait remove_cvref	Albuquerque	Complete	6.0
P0600R1	LWG	nodiscard in the Library	Albuquerque	In Progress	7.0
P0616R0	LWG	de-pessimize legacy algorithms with std::move	Albuquerque
P0653R2	LWG	Utility to convert a pointer to a raw pointer	Albuquerque	Complete	6.0
P0718R2	LWG	Atomic shared_ptr	Albuquerque
P0767R1	CWG	Deprecate POD	Albuquerque	Complete	7.0
P0768R1	CWG	Library Support for the Spaceship (Comparison) Operator	Albuquerque
P0777R1	LWG	Treating Unnecessary decay	Albuquerque	Complete	7.0
P0122R7	LWG	<span>	Jacksonville	Complete	7.0
P0355R7	LWG	Extending chrono to Calendars and Time Zones	Jacksonville
P0551R3	LWG	Thou Shalt Not Specialize std Function Templates!	Jacksonville
P0753R2	LWG	Manipulators for C++ Synchronized Buffered Ostream	Jacksonville
P0754R2	LWG	<version>	Jacksonville	Complete	7.0
P0809R0	LWG	Comparing Unordered Containers	Jacksonville
P0858R0	LWG	Constexpr iterator requirements	Jacksonville
P0905R1	CWG	Symmetry for spaceship	Jacksonville
P0966R1	LWG	string::reserve Should Not Shrink	Jacksonville
P0019R8	LWG	Atomic Ref	Rapperswil
P0458R2	LWG	Checking for Existence of an Element in Associative Containers	Rapperswil
P0475R1	LWG	LWG 2511: guaranteed copy elision for piecewise construction	Rapperswil
P0476R2	LWG	Bit-casting object representations	Rapperswil
P0528R3	CWG	The Curious Case of Padding Bits, Featuring Atomic Compare-and-Exchange	Rapperswil
P0542R5	CWG	Support for contract based programming in C++	Rapperswil
P0556R3	LWG	Integral power-of-2 operations	Rapperswil
P0619R4	LWG	Reviewing Deprecated Facilities of C++17 for C++20	Rapperswil
P0646R1	LWG	Improving the Return Value of Erase-Like Algorithms	Rapperswil
P0722R3	CWG	Efficient sized delete for variable sized classes	Rapperswil
P0758R1	LWG	Implicit conversion traits and utility functions	Rapperswil
P0759R1	LWG	fpos Requirements	Rapperswil
P0769R2	LWG	Add shift to <algorithm>	Rapperswil
P0788R3	LWG	Standard Library Specification in a Concepts and Contracts World	Rapperswil
P0879R0	LWG	Constexpr for swap and swap related functions Also resolves LWG issue 2800.	Rapperswil
P0887R1	LWG	The identity metafunction	Rapperswil
P0892R2	CWG	explicit(bool)	Rapperswil
P0898R3	LWG	Standard Library Concepts	Rapperswil
P0935R0	LWG	Eradicating unnecessarily explicit default constructors from the standard library	Rapperswil
P0941R2	CWG	Integrating feature-test macros into the C++ WD	Rapperswil
P1023R0	LWG	constexpr comparison operators for std::array	Rapperswil
P1025R1	CWG	Update The Reference To The Unicode Standard	Rapperswil
P1120R0	CWG	Consistency improvements for <=> and other comparison operators	Rapperswil

[ 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 Name	Meeting	Status
2070	allocate_shared should use allocator_traits<A>::construct	Toronto	Resolved by P0674R1
2444	Inconsistent complexity for std::sort_heap	Toronto
2593	Moved-from state of Allocators	Toronto
2597	std::log misspecified for complex numbers	Toronto
2783	stack::emplace() and queue::emplace() should return decltype(auto)	Toronto	Complete
2932	Constraints on parallel algorithm implementations are underspecified	Toronto
2937	Is equivalent("existing_thing", "not_existing_thing") an error	Toronto	Complete
2940	result_of specification also needs a little cleanup	Toronto
2942	LWG 2873's resolution missed weak_ptr::owner_before	Toronto	Complete
2954	Specialization of the convenience variable templates should be prohibited	Toronto	Complete
2961	Bad postcondition for set_default_resource	Toronto
2966	Incomplete resolution of US 74	Toronto	Nothing to do
2974	Diagnose out of bounds tuple_element/variant_alternative	Toronto	Complete
2779	[networking.ts] Relax requirements on buffer sequence iterators	Albuquerque
2870	Default value of parameter theta of polar should be dependent	Albuquerque	Complete
2935	What 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 functions	Albuquerque	Nothing to do
2944	LWG 2905 accidentally removed requirement that construction of the deleter doesn't throw an exception	Albuquerque	Nothing to do
2945	Order of template parameters in optional comparisons	Albuquerque	Complete
2948	unique_ptr does not define operator<< for stream output	Albuquerque	Complete
2950	std::byte operations are misspecified	Albuquerque	Complete
2952	iterator_traits should work for pointers to cv T	Albuquerque	Complete
2953	LWG 2853 should apply to deque::erase too	Albuquerque
2958	Moves improperly defined as deleted	Albuquerque
2964	Apparently redundant requirement for dynamic_pointer_cast	Albuquerque
2965	Non-existing path::native_string() in filesystem_error::what() specification	Albuquerque	Nothing to do
2972	What is is_trivially_destructible_v<int>?	Albuquerque	Complete
2976	Dangling uses_allocator specialization for packaged_task	Albuquerque	Complete
2977	unordered_meow::merge() has incorrect Throws: clause	Albuquerque
2978	Hash support for pmr::string and friends	Albuquerque
2979	aligned_union should require complete object types	Albuquerque	Complete
2980	Cannot compare_exchange empty pointers	Albuquerque
2981	Remove redundant deduction guides from standard library	Albuquerque
2982	Making size_type consistent in associative container deduction guides	Albuquerque
2988	Clause 32 cleanup missed one typename	Albuquerque
2993	reference_wrapper conversion from T&&	Albuquerque
2998	Requirements on function objects passed to {forward_,}list-specific algorithms	Albuquerque	Nothing to do
3001	weak_ptr::element_type needs remove_extent_t	Albuquerque
3024	variant's copies must be deleted instead of disabled via SFINAE	Albuquerque
2164	What are the semantics of vector.emplace(vector.begin(), vector.back())?	Jacksonville
2243	istream::putback problem	Jacksonville	Complete
2816	resize_file has impossible postcondition	Jacksonville	Nothing to do
2843	Unclear behavior of std::pmr::memory_resource::do_allocate()	Jacksonville
2849	Why does !is_regular_file(from) cause copy_file to report a "file already exists" error?	Jacksonville	Nothing to do
2851	std::filesystem enum classes are now underspecified	Jacksonville	Nothing to do
2946	LWG 2758's resolution missed further corrections	Jacksonville	Complete
2969	polymorphic_allocator::construct() shouldn't pass resource()	Jacksonville
2975	Missing case for pair construction in scoped and polymorphic allocators	Jacksonville
2989	path's stream insertion operator lets you insert everything under the sun	Jacksonville	Completed
3000	monotonic_memory_resource::do_is_equal uses dynamic_cast unnecessarily	Jacksonville
3002	[networking.ts] basic_socket_acceptor::is_open() isn't noexcept	Jacksonville
3004	§[string.capacity] and §[vector.capacity] should specify time complexity for capacity()	Jacksonville	Nothing to do
3005	Destruction order of arrays by make_shared/allocate_shared only recommended?	Jacksonville
3007	allocate_shared should rebind allocator to cv-unqualified value_type for construction	Jacksonville
3009	Including <string_view> doesn't provide std::size/empty/data	Jacksonville	Complete
3010	[networking.ts] uses_executor says "if a type T::executor_type exists"	Jacksonville
3013	(recursive_)directory_iterator construction and traversal should not be noexcept	Jacksonville	Complete
3014	More noexcept issues with filesystem operations	Jacksonville	Complete
3015	copy_options::unspecified underspecified	Jacksonville	Nothing to do
3017	list splice functions should use addressof	Jacksonville
3020	[networking.ts] Remove spurious nested value_type buffer sequence requirement	Jacksonville
3026	filesystem::weakly_canonical still defined in terms of canonical(p, base)	Jacksonville	Complete
3030	Who shall meet the requirements of try_lock?	Jacksonville	Nothing to do
3034	P0767R1 breaks previously-standard-layout types	Jacksonville	Complete
3035	std::allocator's constructors should be constexpr	Jacksonville	Complete
3039	Unnecessary decay in thread and packaged_task	Jacksonville	Complete
3041	Unnecessary decay in reference_wrapper	Jacksonville	Complete
3042	is_literal_type_v should be inline	Jacksonville	Complete
3043	Bogus postcondition for filesystem_error constructor	Jacksonville	Complete
3045	atomic<floating-point> doesn't have value_type or difference_type	Jacksonville
3048	transform_reduce(exec, first1, last1, first2, init) discards execution policy	Jacksonville
3051	Floating point classifications were inadvertently changed in P0175	Jacksonville	Nothing to do
3075	basic_string needs deduction guides from basic_string_view	Jacksonville	Complete
2139	What is a user-defined type?	Rapperswil
2970	Return type of std::visit misspecified	Rapperswil
3058	Parallel adjacent_difference shouldn't require creating temporaries	Rapperswil
3062	Unnecessary decay_t in is_execution_policy_v should be remove_cvref_t	Rapperswil
3067	recursive_directory_iterator::pop must invalidate	Rapperswil	Nothing to do
3071	[networking.ts] read_until still refers to "input sequence"	Rapperswil	Nothing to do
3074	Non-member functions for valarray should only deduce from the valarray	Rapperswil
3076	basic_string CTAD ambiguity	Rapperswil	Complete
3079	LWG 2935 forgot to fix the existing_p overloads of create_directory	Rapperswil
3080	Floating point from_chars pattern specification breaks round-tripping	Rapperswil
3083	What should ios::iword(-1) do?	Rapperswil	Nothing to do
3094	[time.duration.io]p4 makes surprising claims about encoding	Rapperswil
3100	Unnecessary and confusing "empty span" wording	Rapperswil	Nothing to do
3102	Clarify span iterator and const_iterator behavior	Rapperswil
3104	Fixing duration division	Rapperswil	Complete

Last Updated: 23-Jul-2018