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	In progress
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	Complete	8.0
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	In Progress
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	Complete	8.0
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	In progress
P1023R0	LWG	constexpr comparison operators for std::array	Rapperswil	Complete	8.0
P1025R1	CWG	Update The Reference To The Unicode Standard	Rapperswil
P1120R0	CWG	Consistency improvements for <=> and other comparison operators	Rapperswil
P0318R1	LWG	unwrap_ref_decay and unwrap_reference	San Diego	Complete	8.0
P0356R5	LWG	Simplified partial function application	San Diego
P0357R3	LWG	reference_wrapper for incomplete types	San Diego
P0482R6	CWG	char8_t: A type for UTF-8 characters and strings	San Diego
P0487R1	LWG	Fixing operator>>(basic_istream&, CharT*) (LWG 2499)	San Diego	Complete	8.0
P0591R4	LWG	Utility functions to implement uses-allocator construction	San Diego
P0595R2	CWG	P0595R2 std::is_constant_evaluated()	San Diego
P0602R4	LWG	variant and optional should propagate copy/move triviality	San Diego	Complete	8.0
P0608R3	LWG	A sane variant converting constructor	San Diego
P0655R1	LWG	visit<R>: Explicit Return Type for visit	San Diego
P0771R1	LWG	std::function move constructor should be noexcept	San Diego	Complete	6.0
P0896R4	LWG	The One Ranges Proposal	San Diego
P0899R1	LWG	P0899R1 - LWG 3016 is not a defect	San Diego	Nothing to do
P0919R3	LWG	Heterogeneous lookup for unordered containers	San Diego
P0972R0	LWG	<chrono> zero(), min(), and max() should be noexcept	San Diego	Complete	8.0
P1006R1	LWG	Constexpr in std::pointer_traits	San Diego	Complete	8.0
P1007R3	LWG	std::assume_aligned	San Diego
P1020R1	LWG	Smart pointer creation with default initialization	San Diego
P1032R1	LWG	Misc constexpr bits	San Diego
P1085R2	LWG	Should Span be Regular?	San Diego	Complete	8.0
P1123R0	LWG	Editorial Guidance for merging P0019r8 and P0528r3	San Diego
P1148R0	LWG	Cleaning up Clause 20	San Diego
P1165R1	LWG	Make stateful allocator propagation more consistent for operator+(basic_string)	San Diego
P1209R0	LWG	Adopt Consistent Container Erasure from Library Fundamentals 2 for C++20	San Diego	Complete	8.0
P1210R0	LWG	Completing the Rebase of Library Fundamentals, Version 3, Working Draft	San Diego
P1236R1	CWG	Alternative Wording for P0907R4 Signed Integers are Two's Complement	San Diego
P1248R1	LWG	Remove CommonReference requirement from StrictWeakOrdering (a.k.a Fixing Relations)	San Diego
P1285R0	LWG	Improving Completeness Requirements for Type Traits	San Diego
P1353R0	CWG	Missing feature test macros	San Diego

[ 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	Complete
2958	Moves improperly defined as deleted	Albuquerque	We already do this
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	Complete
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	Complete
3104	Fixing duration division	Rapperswil	Complete
2183	Muddled allocator requirements for match_results constructors	San Diego	Complete
2184	Muddled allocator requirements for match_results assignments	San Diego	Complete
2412	promise::set_value() and promise::get_future() should not race	San Diego
2499	operator>>(basic_istream&, CharT*) makes it hard to avoid buffer overflows	San Diego	Resolved by P0487R1
2682	filesystem::copy() won't create a symlink to a directory	San Diego	Nothing to do
2697	[concurr.ts] Behavior of future/shared_future unwrapping constructor when given an invalid future	San Diego
2797	Trait precondition violations	San Diego	Resolved by 1285R0
2936	Path comparison is defined in terms of the generic format	San Diego	Complete
2943	Problematic specification of the wide version of basic_filebuf::open	San Diego	Nothing to do
2960	[fund.ts.v3] nonesuch is insufficiently useless	San Diego
2995	basic_stringbuf default constructor forbids it from using SSO capacity	San Diego
2996	Missing rvalue overloads for shared_ptr operations	San Diego
3008	make_shared (sub)object destruction semantics are not specified	San Diego
3022	is_convertible<derived*, base*> may lead to ODR	San Diego	Resolved by 1285R0
3025	Map-like container deduction guides should use pair<Key, T>, not pair<const Key, T>	San Diego
3031	Algorithms and predicates with non-const reference arguments	San Diego
3037	polymorphic_allocator and incomplete types	San Diego
3038	polymorphic_allocator::allocate should not allow integer overflow to create vulnerabilities	San Diego
3054	uninitialized_copy appears to not be able to meet its exception-safety guarantee	San Diego
3065	LWG 2989 missed that all path's other operators should be hidden friends as well	San Diego	Complete
3096	path::lexically_relative is confused by trailing slashes	San Diego	Complete
3116	OUTERMOST_ALLOC_TRAITS needs remove_reference_t	San Diego
3122	__cpp_lib_chrono_udls was accidentally dropped	San Diego	We've already made the update; but we don't support all the test macros. When we do, this will be closed
3127	basic_osyncstream::rdbuf needs a const_cast	San Diego
3128	strstream::rdbuf needs a const_cast	San Diego	Nothing to do
3129	regex_token_iterator constructor uses wrong pointer arithmetic	San Diego
3130	§[input.output] needs many addressof	San Diego
3131	addressof all the things	San Diego
3132	Library needs to ban macros named expects or ensures	San Diego	Nothing to do
3134	[fund.ts.v3] LFTSv3 contains extraneous [meta] variable templates that should have been deleted by P09961	San Diego	Resolved by P1210R0
3137	Header for __cpp_lib_to_chars	San Diego	We've already made the update; but we don't support all the test macros. When we do, this will be closed
3145	file_clock breaks ABI for C++17 implementations	San Diego	Complete
3147	Definitions of "likely" and "unlikely" are likely to cause problems	San Diego
3148	<concepts> should be freestanding	San Diego
3153	Common and common_type have too little in common	San Diego
3154	Common and CommonReference have a common defect	San Diego

Last Updated: 28-Nov-2018