VS 2022 17.12

• Merged C++26 features:
  • P0952R2 #4740 #4850 A New Specification For generate_canonical()
  • P2407R5 #4743 Freestanding Library: Partial Classes
  • P2833R2 #4743 Freestanding Library: inout expected span
  • P2968R2 #4777 Make std::ignore A First-Class Object
  • P2997R1 #4816 Removing The Common Reference Requirement From The Indirectly Invocable Concepts
• Merged C++23 features:
  • P2286R8 Formatting Ranges, completed by:
    • Implemented range-default-formatter. #4716
    • Implemented formatter for the container adaptors stack, queue, and priority_queue. #4825
• Merged LWG issue resolutions:
  • LWG-3944 #4784 Formatters converting sequences of char to sequences of wchar_t
  • LWG-4061 #4758 Should std::basic_format_context be default-constructible/copyable/movable?
  • LWG-4074 #4814 compatible-joinable-ranges is underconstrained
  • LWG-4083 #4786 views::as_rvalue should reject non-input ranges
  • LWG-4096 #4785 views::iota(views::iota(0)) should be rejected
  • LWG-4098 #4815 views::adjacent<0> should reject non-forward ranges
  • LWG-4106 #4757 basic_format_args should not be default-constructible
• Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • LWG-4139 #4902 [time.zone.leap] recursive constraint in <=>
• Fixed bugs:
  • Fixed static analysis warning C26818 "Switch statement does not cover all cases. Consider adding a 'default' label (es.79)." #4715
    • Note: The STL has always attempted to be /W4 /analyze clean, but does not yet attempt to be clean with respect to all additional static analysis rulesets.
  • Fixed atomic_ref::is_lock_free() on x64 to return true for 1, 2, 4, 8, and 16 bytes only. #4729
  • Fixed uniform_real_distribution<RealType>{min, max} to stay within the inclusive-exclusive range [min, max) and never generate the max value exactly. #4740
  • Fixed filesystem::weakly_canonical() to avoid failing on Windows 11 24H2 in certain scenarios. #4844
  • Fixed condition_variable_any::wait_for() to consistently use steady_clock. #4755
  • Removed a broken and useless visualizer for ranges::view_interface. #4835
  • Fixed the visualizer for move_iterator to use the updated name of its internal data member. #4836
    • This fixed a regression that was introduced by #1080 in VS 2019 16.8.
  • Fixed expected to conditionally delete its copy constructor and copy assignment operator as depicted in the Standard, which affects overload resolution in unusual scenarios. #4837
  • Fixed time_put/put_time() to avoid crashing for:
    • Unknown conversion specifiers. (Now they're copied unchanged.) #4840
    • Out-of-range tm fields. (Now they're replaced with a ? character.) #4883
  • Fixed compiler errors in ranges::inplace_merge and ranges::minmax in unusual scenarios. #4841
  • Fixed truncation warnings when:
    • Using conjunction and disjunction with non-bool_constant arguments. #4846
    • Calling algorithms with contiguous iterators whose difference types are narrower than ptrdiff_t. #4898
  • Improved array::size() and <mdspan> static analysis annotations, fixing warnings in some scenarios. #4856
  • Fixed lexicographical_compare_three_way() to enforce the Standard's mandate that the comparison returns a comparison category type. #4878
  • Fixed compiler errors in the parallel scan algorithms inclusive_scan(), exclusive_scan(), transform_inclusive_scan(), and transform_exclusive_scan() when the intermediate and output types are different. #4701
  • Fixed the vectorized implementation of floating-point ranges::min, ranges::max, and ranges::minmax to return correct results for negative zeros. #4734
  • Fixed Clang compiler errors for certain constexpr variant scenarios by adding a compiler bug workaround. #4903
  • Fixed compiler errors when using <random> machinery (e.g. generate_canonical(), uniform_real_distribution) via Standard Library Modules or Standard Library Header Units by adding compiler bug workarounds. #4906
  • Fixed compiler errors when using <format> machinery in user-defined modules by adding compiler bug workarounds. #4919
  • Fixed <format> to avoid crashing when formatting floating-point values with large precisions combined with the # (alternate form) or L (locale-specific form) options. #4907
• Improved performance:
  • Overhauled condition_variable and condition_variable_any, improving their performance and simplifying their implementation. #4720
    • As a result, condition_variable, timed_mutex, and recursive_timed_mutex are now trivially destructible.
  • Improved the performance of search(), find_end(), and their ranges forms by removing calls to memcmp() that were surprisingly harmful. #4654 #4753
  • Improved the ARM64 performance of popcount() by using new compiler intrinsics. #4695 #4733
  • Further improved the vectorized implementations of:
    • The minmax_element() and minmax() algorithm families. #4659 #4739
  • Slightly improved the performance of ranges::min, ranges::max, and ranges::minmax for certain iterator types. #4775
  • On x86, the STL is now built with /arch:SSE2 (which is the default) instead of /arch:IA32. #4741
    • See /arch (x86) on Microsoft Learn.
  • Used Clang builtins to improve the performance of <cmath>'s floating-point comparison functions for mixed types. #4648
  • On x64, atomic_ref<16 bytes> now always uses the cmpxchg16b instruction. #4751
  • Streaming a small bitset to a basic_ostream now avoids dynamically allocating memory. #4818
  • Slightly improved performance for Clang ARM64 <atomic>. #4870
  • Updated char_traits<wchar_t/char16_t>::compare/find/length, find, and ranges::find to call wmemcmp/wmemchr/wcslen when possible, which will improve performance after a future UCRT header update. #4873 #4894
  • Optimized equality comparisons for empty strings and string_views. #4904
• Improved throughput:
  • Improved <queue> and <stack> throughput by dragging in fewer headers. #4707
• Enhanced behavior:
  • P0608R3 Improving variant's Converting Constructor/Assignment is now unconditionally active (i.e. in C++17 mode and above), instead of being restricted to C++20 mode and above. #4713
    • This C++20 behavioral change was originally implemented by #1629 in VS 2019 16.10. While it can have source-breaking impact, it generally has highly desirable effects.
  • Changed the machinery for copy...

VS 2022 17.11

• Merged C++26 features:
  • P2875R4 #4532 Undeprecate polymorphic_allocator::destroy
  • P3142R0 #4611 Printing Blank Lines With println()
• Merged partial C++23 features:
  • P2286R8 Formatting Ranges:
    • Implemented formatter for pair and tuple. #4438 #4631 #4681
    • Implemented range_formatter. #4642
• Merged LWG issue resolutions:
  • LWG-3767 #4542 codecvt<charN_t, char8_t, mbstate_t> incorrectly added to locale
  • LWG-3919 #4526 enumerate_view may invoke UB for sized common non-forward underlying ranges
  • LWG-3950 #4510 std::basic_string_view comparison operators are overspecified
  • LWG-3984 #4543 ranges::to's recursion branch may be ill-formed
  • LWG-4012 #4529 common_view::begin/end are missing the simple-view check
  • LWG-4013 #4530 lazy_split_view::outer-iterator::value_type should not provide default constructor
  • LWG-4016 #4539 container-insertable checks do not match what container-inserter does
  • LWG-4035 #4525 single_view should provide empty
  • LWG-4053 #4685 Unary call to std::views::repeat does not decay the argument
  • LWG-4054 #4540 Repeating a repeat_view should repeat the view
• Fixed bugs:
  • Fixed condition_variable::wait_until() and condition_variable_any::wait_until() to consistently use the given time_point's clock type, instead of also depending on the system clock. This also fixed condition_variable::wait_for() to consistently use steady_clock. #4457
  • Fixed <format> to always perform compile-time format string checking for wchar_t, even when the narrow execution character set doesn't support it. #4459
  • Fixed compiler errors when constexpr basic_string interacted with the undocumented compiler option /d1initall. #4474
  • Fixed atomic_ref for 16-byte objects to correctly report is_lock_free() and is_always_lock_free on x64 (when the optional mode _STD_ATOMIC_ALWAYS_USE_CMPXCHG16B is defined to be 1) and ARM64 (always). #4478
  • Removed the vectorized implementation of ranges::find with unreachable_sentinel as it was fundamentally incompatible with ASan (Address Sanitizer). #4486
    • This was introduced by #2434 in VS 2022 17.3.
  • Fixed incorrect results from the vectorized implementation of ranges::find_last for certain combinations of value and element types. #4561
    • This fixed a regression that was introduced by #3925 in VS 2022 17.9.
  • Fixed the STL to avoid emitting the off-by-default warning C4365 (signed/unsigned mismatch) when the /ZI compiler option (debug info for Edit and Continue) is used. #4487
    • These warnings were most noticeable when building the Standard Library Modules, but they were also emitted by classic includes.
  • Fixed the STL to avoid emitting the off-by-default warning C5246 (brace elision). #4527
  • Fixed compiler errors involving incomplete types in:
    • pair and tuple machinery. #4488
  • Fixed make_from_tuple() to properly implement LWG-3528 with a constraint instead of a static_assert. #4528
  • Added integral overloads for <cmath>'s classification functions fpclassify(), isfinite(), isinf(), isnan(), isnormal(), and signbit(). #4537
  • Fixed is_trivial to correctly handle unusual types. #4576
  • Avoided mentioning __vectorcall for ARM64EC, where it is not yet supported. #4600
  • Fixed std.ixx to include <intrin.h> in the Global Module Fragment, fixing compiler errors with import std; in certain scenarios. #4626
  • Fixed compiler errors when a user-defined formatter calls basic_format_parse_context::next_arg_id() with an empty format-spec. #4640
  • Fixed compiler errors when using <expected> in /permissive mode. #4658
    • Note: While /permissive mode is discouraged, it's currently supported for most STL components.
  • Fixed compiler errors when inheriting expected's constructors in certain scenarios. #4664
  • Fixed pair's self-swap() behavior to follow the Standard by self-swapping its elements. #4674
  • Fixed atomic<void*> and atomic_ref<void*> to provide difference_type. #4689
• Improved performance:
  • Helped the compiler auto-vectorize:
    • replace_copy(), replace_copy_if(), ranges::replace_copy, and ranges::replace_copy_if. #4431
    • iota(). #4627
    • ranges::iota. #4647
  • Added vectorized implementations of:
    • find_first_of() and ranges::find_first_of. #4466 #4557 #4563 #4587 #4623
    • mismatch() and ranges::mismatch. #4495 #4538 #4584
    • replace() and ranges::replace for 32-bit and 64-bit elements. #4554 #4584
    • lexicographical_compare(), ranges::lexicographical_compare, and lexicographical_compare_three_way(). #4552
  • Further improved the vectorized implementations of:
    • count(), find(), ranges::count, ranges::find, and ranges::find_last. #4570 #4614
  • Used Clang builtins to improve the performance of <cmath>'s floating-point classification and comparison
    functions: #4612
    • Classification: isfinite(), isinf(), isnan(), isnormal()
    • Comparison: isgreater(), isgreaterequal(), isless(), islessequal(), islessgreater(), isunordered()
  • Improved normal_distribution::operator()(engine, param) by avoiding unnecessarily recomputing coefficients. #4618
• Improved throughput:
  • Slightly improved <mdspan> throughput by using short-circuiting conjunction_v instead of fold expressions. #4559
  • Refactored floating-point machinery, improving throughput by reducing inclusion of various headers. #4615
  • Improved <string_view> throughput by no longer dragging in most of <string>'s contents. #4633
• Improved diagnostics:
  • Improved compiler error messages when formatter<UDT>::format() isn't const. #4461
  • Massively improved the compiler error messages for get<T>(tuple<Types...>) when T doesn't occur exactly once in Types. #4578
  • Significantly improved compiler error messages when ranges::to is unable to construct the requested result. #4608
• Enhanced behavior:
  • To reduce risk, the STL no longer attempts to activate vectorized implementations of algorithms for ancient processors that support SSE2 but not SSE4.2. #4550
    • This consolidated the STL's levels of vectorization to none, SSE4.2, and AVX2.
    • This also slightly improved performance (for non-ancient processors) by taking advantage of newe...

VS 2022 17.10

• Merged C++26 features:
  • P2510R3 #4198 Formatting Pointers
  • P2937R0 #4203 Freestanding Library: Remove strtok
• Merged C++23 features:
  • P2836R1 #4188 basic_const_iterator Should Follow Its Underlying Type's Convertibility
• Merged partial C++23 features:
  • P2286R8 Formatting Ranges:
    • Implemented formatter<vector<bool>::reference>. #4133
• Merged C++20 Defect Reports:
  • P2905R2 #4196 Runtime Format Strings
  • P2909R4 #4189 Fix Formatting Of Code Units As Integers
• Merged LWG issue resolutions:
  • LWG-3749 #4190 common_iterator should handle integer-class difference types
  • LWG-3809 #4194 Is subtract_with_carry_engine<uint16_t> supposed to work?
  • LWG-3897 #4186 inout_ptr will not update raw pointer to null
  • LWG-3946 #4187 The definition of const_iterator_t should be reworked
  • LWG-3947 #4195 Unexpected constraints on adjacent_transform_view::base()
  • LWG-3949 #4204 atomic<bool>'s trivial destructor dropped in C++17 spec wording
  • LWG-3953 #4167 iter_move for common_iterator and counted_iterator should return decltype(auto)
  • LWG-3974 #4214 mdspan::operator[] should not copy OtherIndexTypes
  • LWG-4001 #4193 iota_view should provide empty
• Fixed bugs:
  • Fixed mutex's constructor to be constexpr. #3824 #4000 #4339
    • Note: Programs that aren't following the documented restrictions on binary compatibility may encounter null dereferences in mutex machinery. You must follow this rule:

      When you mix binaries built by different supported versions of the toolset, the Redistributable version must be at least as new as the latest toolset used by any app component.

    • You can define _DISABLE_CONSTEXPR_MUTEX_CONSTRUCTOR as an escape hatch.
  • Fixed <format>'s compile-time format string checking:
    • To detect when user-defined formatter specializations reject omitted format specifications like "{}". #4078
    • To require that dynamic width and precision arguments have integral types. #4155
  • Fixed how format() handles empty strings like format("{:a<10}", ""). #4243
  • Fixed <format> to properly handle floating-point values in a specific situation. When a format-specifier appears without any precision or type, shortest round-trip formatting should be used instead of chars_format::general. #4327
    • Example format strings: "{:}" and "{0:}" were affected, as they have an optional arg-id (0) followed by a format-specifier (:) with an empty format-spec (nothing after the :).
    • More common format strings like "{}" and "{0}" were unaffected, as they entirely lack a format-specifier.
    • Example value: For 12345678.0, the shortest round-trip rules produce "12345678", while the chars_format::general rules produce "1.2345678e+07".
  • Fixed <format> to properly handle locale-specific floating-point formatting with a minimum field width, taking digit separators into account. #4421
  • Fixed format() to accept %X and %EX for chrono::duration and chrono::hh_mm_ss. #4250
  • Fixed chrono::duration formatting to respect dynamically provided widths. #4283
  • Fixed crashes and incorrect results in the vectorized implementation of ranges::find with unreachable_sentinel. #4450
    • This fixed regressions that were introduced by #2434 in VS 2022 17.3.
  • Fixed ranges::to to properly reject certain invalid uses with compiler errors, instead of trapping compilers in infinite loops of doom. #4142
  • Fixed ranges::to to accept certain container constructors taking a range followed by more than one argument. #4218
  • Fixed compiler errors involving range adaptor closure objects in unusual scenarios. #4211
  • Fixed ranges::ssize to be conditionally noexcept as required by the Standard. #4231
  • Fixed join_view and join_with_view's iterators to be default constructible. #4264
  • Fixed truncation warnings when using views::repeat. #4255
  • Fixed compiler errors when using views::zip_transform with ranges that must be non-const to be iterated through, such as views::filter. #4416
  • Fixed compiler errors when using views::pairwise_transform and views::adjacent_transform via Standard Library Modules. #4420
  • Fixed incorrect output from iostreams (like "i.nf") when printing infinity and NaN values with setprecision(0) << showpoint << fixed. #4212
  • Fixed problems involving unusual allocators with size types other than size_t:
    • Compiler errors in basic_stringbuf::overflow(). #4219
    • Truncation warnings in basic_stringbuf's constructor, string/vector iterator subtraction, ranges::is_permutation, and allocate_shared(). #4228 #4237 #4252
  • Fixed <atomic> correctness issues for ARM64 CHPE (_M_HYBRID_X86_ARM64). #4222
  • Fixed atomic by adding atomic& operator=(const atomic&) volatile = delete; as required by the Standard. #4287
  • Fixed atomic<shared_ptr>::wait() and atomic<weak_ptr>::wait() to properly detect equivalent smart pointers. #3655
  • Fixed sign-compare warnings in <mdspan> when using extents with different index types. #4227
  • Fixed compiler errors in <mdspan> when constructing unusual mappings. #4236
  • Fixed bugs specific to extremely unusual fancy pointers:
    • Fixed how such vectors interact with ranges algorithms. #4244
    • Fixed how such vectors and basic_strings interact with classic algorithms and iterator spaceship comparisons. #4275
  • Fixed compiler errors when constructing locale{nullptr}. #4245
    • Rejoice, for now you can get a guaranteed runtime_error!
  • Fixed compiler errors when overloading next(), prev(), shift_left(), and shift_right() with concept-constrained functions that should be preferred during overload resolution. #4249
  • Fixed compiler errors when comparing a sub_match with the spaceship operator <=> to a basic_string with a custom traits and/or allocator type. #4253
  • Fixed sequence container constructors to avoid interfering with CTAD (class template argument deduction) for (Iter, Iter, BadAlloc); now this will SFINAE away instead of emitting a hard compiler error. #4254
  • Fixed compiler errors in parallel transform_reduce() when performing narrowing conversions. #4260
    • As usual, asking the STL to perform conversions on your behalf may emit sign/truncation compiler warnings; this is by design.
  • Fixed compiler errors during constexpr evaluation of vector<bool> caused by improper casting in iterator debugging machinery. #4276
  • Fixed compiler errors (by adding a compiler bug workaround) when using constexpr invoke() to call pointers to data members with reference_wrapper arguments. #4277
  • Added macroization defenses for the STL's non-Standard extensions (e.g. type_info's raw_name member function). #4285
  • Fixed ...

VS 2022 17.9

• Merged C++23 features:
  • P0009R18 #3972 #4037 <mdspan>
    • P2599R2 mdspan: index_type, size_type
    • P2604R0 mdspan: data_handle_type, data_handle(), exhaustive
    • P2613R1 mdspan: empty()
    • P2763R1 Fixing layout_stride's Default Constructor For Fully Static Extents
  • P1169R4 #4053 static operator()
    • This updates CTAD (class template argument deduction) for std::function and packaged_task to work with a C++23 Core Language feature, currently supported for Clang only. When MSVC and IntelliSense implement this Core feature, this will automatically "light up" the STL's CTAD for them too.
• Merged partial C++23 features:
  • P2286R8 Formatting Ranges:
    • Implemented formatter::set_debug_format(). #3913
    • Implemented formattable, range_format, and format_kind. #4116
• Merged LWG issue resolutions:
  • LWG-3561 #4066 Issue with internal counter in discard_block_engine
• Fixed bugs:
  • Fixed incorrect results from iostreams floating-point parsing (e.g. "1e-07" was incorrectly parsed as 1e-06). #3982
    • This fixed a regression that was introduced by #3364 in VS 2022 17.7.
    • We backported this fix to VS 2022 17.8.
  • Fixed compiler errors when using expected together with any. #4013
  • Fixed incorrect behavior when self-move-assigning any, and fixed compiler errors in any involving incomplete types. #3965
  • Fixed bugs in basic_string's copy assignment operator, specific to non-equal propagate_on_container_copy_assignment allocators, involving ASan annotations or fancy pointers. #4031
  • Fixed get() and comparison operators to handle program-defined specializations of array. #4041
  • Fixed compiler errors in to_array() involving incomplete types. #4042
  • Fixed linker errors involving stl_asan.lib by disabling ASan annotations in the STL for unsupported platforms (e.g. ARM, ARM64, ARM64EC). #4058
  • Fixed not_fn() to return a perfect forwarding call wrapper in C++20 mode as required by P0356R5. #4057
  • Fixed deque to preserve its internal invariants when taking advantage of allocators that provide allocate_at_least(). #4017
  • Fixed deque emplace() and insert() to not require elements to be swappable; this change also improved performance. #4022
  • Fixed deque to handle highly unusual fancy pointers. #4049
  • Fixed deque::shrink_to_fit() to avoid requiring the allocator to be default constructible. #4071
  • Fixed allocate_shared() for unbounded arrays to handle fancy pointers. #4074
  • Fixed the implementation of P0408R7 Efficient Access To basic_stringbuf's Buffer to properly destroy fancy pointers. #4047
  • Fixed this_thread::sleep_until() to consistently use the given time_point's clock type, instead of also depending on the system clock. This also fixed this_thread::sleep_for() to consistently use steady_clock. #3914
  • Fixed minor conformance issues in <random>: #4120
    • Removed non-Standard base_type typedefs from discard_block_engine, independent_bits_engine, and shuffle_order_engine.
    • Fixed discard_block_engine(Engine&&) to move-construct the base engine instead of copying it.
• Improved performance:
  • Optimized the copy(), copy_n(), and move() algorithms for vector<bool> iterators, with speedups varying from 1.8x (times, not percent) to an incredible 3200x, depending on the size and alignment of the bits being copied. #3353 #4045
  • Optimized priority_queue::push_range() for small ranges. #4025
  • Improved debug codegen for deque by using unchecked iterators internally. #4071
  • Optimized basic_string's range constructors to use memmove() for contiguous ranges when possible. #4073
  • Added a vectorized implementation of ranges::find_last. #3925
• Enhanced behavior:
  • Added debug checks to <valarray> binary operations, verifying that the operands have the same size. #3911
  • Deprecated basic_istream's ipfx()/isfx() and basic_ostream's opfx()/osfx() member functions as they're non-Standard extensions. #4006
  • Added compiler bug workarounds for the upcoming Clang 17 release. #4014
  • Improved the STL's error messages so that error logs will record specific static_asserts like "error STL1000: Unexpected compiler version, expected Clang 16.0.0 or newer." instead of just "Error in C++ Standard Library usage." #4020
  • Silenced /Wall warnings:
    • When building the Standard Library Modules. #4026
    • Warning C4868 "compiler may not enforce left-to-right evaluation order in braced initializer list" throughout the STL. #4067
    • Note: /Wall is not intended for regular production use, as it contains a large number of extremely noisy and low-value warnings. In general, the STL does not attempt to be /Wall clean.
  • Changed num_get::do_get() to tolerate 80-bit long double by removing a static_assert that was added in 2018. #4032
    • Note: 80-bit long double remains unsupported by MSVC.
  • Improved source_location::function_name(): #4055
    • It will return detailed information for Clang 17.
    • Added an "escape hatch" for all compilers: define _USE_DETAILED_FUNCTION_NAME_IN_SOURCE_LOCATION to 0.
    • For example, given template <typename T> void cats() called with cats<vector<int>>(), MSVC's detailed info (implemented in VS 2022 17.6) is "void __cdecl cats<class std::vector<int,class std::allocator<int> >>(void)". Clang 17's detailed info is "void __cdecl cats(void) [T = std::vector<int>]". The escape hatch will return the basic info "cats".
  • Changed the ranges algorithms to be ordinary function objects. #4098
    • For example, this allows code like views::transform(ranges::distance) to compile.
  • Marked internal extern "C" functions as noexcept. #4106 #4150
    • This improves codegen for /EHs (versus /EHsc, where extern "C" already implies noexcept).
• Improved test coverage:
  • Added an STL-ASan-CI pipeline. #3987 #3989 #4029 #4052 #4068 #4069 #4075
  • The test harness now cleans up emitted files as it runs. #4086
  • Simplified the feature-test macro test. #4103
  • Enabled test coverage for basic_string's ASan annotations when exception handling interacts with the Small String Optimization. #4118
• Code cleanups:
  • Removed unused code. #3964 #4005
  • Removed compiler bug workarounds. #4012 #4028 #4039 #4083
  • Various cleanups (described in detail in the PRs, not repeated here). #3940 #3973 #3974 #3984 #4015 #4016 #4036 #4087 #4111 [#4113](https://g...

VS 2022 17.8

• Merged C++26 features:
  • P2013R5 #3837 Freestanding Language: Optional ::operator new
  • P2198R7 #3837 Freestanding Feature-Test Macros And Implementation-Defined Extensions
  • P2338R4 #3837 Freestanding Library: Character Primitives And The C Library
  • P2538R1 #3822 ADL-Proof projected
• Merged C++23 features:
  • P2675R1 #3903 Improving std::format's Width Estimation
  • P2693R1 #3861 Formatting thread::id And stacktrace
• Merged C++20 extension:
  • The C++23 named modules std and std.compat are now available when compiling in C++20 mode. #3977
    • This extension should eventually be portable to the major Standard Library implementations via an informal agreement between implementers.
    • Build systems - including the Visual Studio IDE - will need changes to support import std in C++20. This change makes it possible for them to do so.
• Merged LWG issue resolutions:
  • LWG-3631 #3745 basic_format_arg(T&&) should use remove_cvref_t<T> throughout
  • LWG-3843 #3737 std::expected<T, E>::value() & assumes E is copy constructible
  • LWG-3893 #3782 LWG-3661 broke atomic<shared_ptr<T>> a; a = nullptr;
  • LWG-3904 #3781 lazy_split_view::outer-iterator's const-converting constructor isn't setting trailing_empty_
• Fixed bugs:
  • Fixed the deque(size_type) constructor to properly destroy elements when constructing one of them throws an exception. #3720
  • Removed a non-Standard operator basic_istream >> setfill(c). #3725
  • Fixed linker errors when linking x64 object files into ARM64EC programs. #3732
    • We backported this fix to VS 2022 17.6.6 and VS 2022 17.7.
  • Fixed the debug mode check in cartesian_product_view::size() to always accept empty views. #3733
  • Fixed formatter<char, wchar_t> to format the char as a character instead of an integer. #3723
  • The STL now avoids dragging in the non-reserved name ISA_AVAILABILITY. #3721
  • Fixed chrono::hh_mm_ss formatting to accept values of 24 hours or more. #3727
  • Changed the STL's usage of compiler-specific custom attributes to further defend against macros. #3760
  • Fixed condition_variable_any::wait_until() to handle time_points with unsigned representations instead of waiting forever. #3761
  • Fixed counting_semaphore to add compile-time enforcement of the Standard's mandates. #3747
  • Fixed a bug, affecting UWP apps only, where locking a mutex could throw a bogus exception. #3763
  • Fixed the signatures of char_traits member functions to exactly match the Standard. #3739
    • This Standardese was updated by N2349 in C++11.
  • Fixed compiler errors when visit_format_arg() is called with highly unusual visitors. #3787
  • Fixed incorrect output when format() is asked to format a floating-point value in the alternate form without a type specifier. #3815
  • Added a compiler bug workaround for MSVC modules, allowing <format> machinery to work with /utf-8 via import std;. #3816
  • Fixed a subtle bug affecting constexpr basic_string's copy assignment operator, where it wasn't starting element lifetimes for the unused capacity. #3712 #3819
  • Fixed Clang compiler errors when calling function::target<FunctionType>() on const function objects. #3844
    • This is an obscure corner case, because such calls are guaranteed to return null.
  • Fixed compiler errors when using array<T, 0> in constexpr contexts. #3863
  • Improved function call operator overload resolution for the bind(), bind_front(), and bind_back() function objects. #3775
  • Fixed iostreams with imbued locales to print infinities and NaNs correctly. #3868 #3877
  • Fixed incorrect noexcepts within the implementations of filesystem::current_path(), filesystem::current_path(error_code&), read_symlink(const path&), and read_symlink(const path&, error_code&). #3869 #3881
  • Fixed shared_ptr<void> to not be constructible from void*. #3873
  • Fixed a complicated modules scenario by removing #pragma once from all STL headers. #3895
    • #pragma once is no longer needed to improve throughput because modern compilers automatically detect the idempotency guard idiom.
  • Fixed <stacktrace>'s internal use of snprintf() in extreme situations. #3916
  • Fixed an extremely obscure runtime correctness bug in basic_string's copy assignment operator, specific to non-equal propagate_on_container_copy_assignment allocators. #3862
  • Fixed ASan annotations in basic_string::replace(). #3884
  • Fixed ASan annotations in basic_string::assign() and basic_string::resize_and_overwrite(). #3956
• Improved performance:
  • Changed some helper member functions to be static, slightly improving debug codegen. #3755
  • mutex and condition_variable now avoid virtual function calls within their implementations. #3770
  • Optimized steady_clock::now() when QueryPerformanceFrequency() is exactly 24 MHz, which is very common for ARM64. #3832
  • Optimized filesystem::path::lexically_normal(). #3850
  • basic_string, basic_stringbuf, basic_syncbuf, deque, and vector now take advantage of allocators that provide allocate_at_least(). #3864 #3891
  • Optimized <format> slightly. #3826
  • Optimized bitset::to_string(). #3838 #3904
  • Added an attribute to as_const(), to_integer(), and to_underlying() that allows the MSVC compiler to intrinsically implement them without emitting function calls. #3664
  • Made a tiny tweak to valarray (access the stored size directly instead of via calling size()) to improve debug codegen. #3968
• Improved throughput:
  • Moved machinery: #3719
    • Moved integer_sequence, make_integer_sequence, index_sequence, make_index_sequence, and index_sequence_for from <type_traits> to <utility>, which is where the Standard provides them.
    • Moved allocator_arg, allocator_arg_t, uses_allocator, and uses_allocator_v so that they're dragged in by slightly fewer headers. (The Standard provides them in <memory>.)
  • Some headers now avoid including <limits>. #3777
  • In C++17 mode and later, improved Clang throughput for an internal helper wrapping is_same_v. #3933
• Enhanced behavior:
  • Added precondition checking in debug mode to the iota_view(value) constructor. #3731
  • Improved precondition checking in debug mode for barrier. #3757
  • Fixed static analysis warnings. #3734 #3743
    • Note: The STL has always attempted to be /W4 /analyze clean, but does not yet attempt to be clean with respect to all additional static analysis rulesets.
  • Strengthened the exception specifications for:
    • Internal <ranges> machinery used in join_view iterators and lazy_split_view. #3762
    • basic_string_view::compare(const charT*). [#3738](https://github.com/microso...

VS 2022 17.7

• Merged C++23 features:
  • P1467R9 #3583 Extended Floating-Point Types
    • Note: This means that we provide the <stdfloat> header containing an empty namespace std {}, as we don't support any optional extended floating-point types.
  • P2093R14 #3337 <print>: Formatted Output
    • P2539R4 Synchronizing print() With The Underlying Stream
  • P2164R9 #3472 views::enumerate
  • P2165R4 #3372 Compatibility Between tuple, pair, And tuple-like Objects
  • P2321R2 zip, completed by implementing:
    • views::adjacent and views::pairwise. #3508
    • views::adjacent_transform and views::pairwise_transform. #3546
  • P2374R4 #3561 views::cartesian_product
    • P2540R1 Empty Product For Certain Views
  • P2572R1 #3629 std::format Fill Character Allowances
  • P2609R3 #3486 Relaxing Ranges Just A Smidge
  • P2614R2 #3482 Deprecating float_denorm_style, numeric_limits::has_denorm, numeric_limits::has_denorm_loss
  • P2652R2 #3542 Disallowing User Specialization Of allocator_traits
  • P2655R3 #3513 common_reference_t Of reference_wrapper Should Be A Reference Type
  • P2736R2 #3556 Referencing The Unicode Standard
    • <format> now understands Unicode 15.
  • P2770R0 #3466 Stashing Stashing Iterators For Proper Flattening
• Merged partial C++23 features:
  • P2286R8 Formatting Ranges:
    • Implemented the ? format specifier for strings and characters. #3656
• Merged LWG issue resolutions:
  • LWG-2195 #3506 Missing constructors for match_results
  • LWG-2309 #3469 mutex::lock() should not throw device_or_resource_busy
  • LWG-2381 #3364 Inconsistency in parsing floating point numbers
  • LWG-3204 #3494 sub_match::swap only swaps the base class
  • LWG-3655 #3495 The INVOKE operation and union types
  • LWG-3677 #3396 Is a cv-qualified pair specially handled in uses-allocator construction?
  • LWG-3720 #3511 Restrict the valid types of arg-id for width and precision in std-format-spec
  • LWG-3733 #3496 ranges::to misuses cpp17-input-iterator
  • LWG-3734 #3503 Inconsistency in inout_ptr and out_ptr for empty case
  • LWG-3821 #3509 uses_allocator_construction_args should have overload for pair-like
  • LWG-3833 #3477 Remove specialization template<size_t N> struct formatter<const charT[N], charT>
  • LWG-3836 #3587 std::expected<bool, E1> conversion constructor expected(const expected<U, G>&) should take precedence over expected(U&&) with operator bool
  • LWG-3847 #3479 ranges::to can still return views
  • LWG-3851 #3517 chunk_view::inner-iterator missing custom iter_move and iter_swap
  • LWG-3860 #3480 range_common_reference_t is missing
  • LWG-3862 #3471 basic_const_iterator's common_type specialization is underconstrained
  • LWG-3865 #3476 Sorting a range of pairs
    • This can be a source-breaking change in unusual scenarios.
  • LWG-3869 #3487 Deprecate std::errc constants related to UNIX STREAMS
  • LWG-3870 #3475 Remove voidify
  • LWG-3872 #3470 basic_const_iterator should have custom iter_move
  • LWG-3875 #3485 std::ranges::repeat_view<T, IntegerClass>::iterator may be ill-formed
  • LWG-3877 #3504 Incorrect constraints on const-qualified monadic overloads for std::expected
  • LWG-3887 #3589 Version macro for allocate_at_least
• Fixed bugs:
  • Fixed the ios_base constants (e.g. ios_base::binary, ios_base::failbit, ios_base::hex) to have the correct bitmask types. #3405
  • Fixed compiler errors found with Clang 16. #3483
  • Fixed <ranges> to avoid using list-initialization when the difference between braces and parentheses is observable. #3493
  • Fixed pmr::unsynchronized_pool_resource to respect pmr::pool_options::max_blocks_per_chunk when it's smaller than the default initial number of blocks per chunk. #3510
  • Fixed technically undefined behavior in <regex> and <sstream> found by Clang/LLVM's Undefined Behavior Sanitizer (UBSan). #3452
  • Fixed compiler errors when calling ranges::equal with ranges involving views::iota. #3551
  • Fixed the STL's iterator unwrapping machinery to avoid requiring a _Prevent_inheriting_unwrap typedef. #3566
  • Fixed spurious warnings from Clang's -Wzero-as-null-pointer-constant when comparing the spaceship operator's return types (partial_ordering, weak_ordering, strong_ordering) with literal 0. #3581
  • Fixed bind() function objects to have constrained function call operators, so they interact properly with is_invocable and related scenarios. #3577
  • Reverted #2654 (which affected <future>'s use of <ppltasks.h> in Desktop XAML apps) because it introduced an ole32.dll dependency that broke multiple scenarios. #3607
    • We backported this revert to VS 2022 17.6.
  • Fixed views::cartesian_product to avoid compiler errors in pathological scenarios. #3609
  • Fixed incorrect results for ranges larger than 4 GB passed to the vectorized implementations of min_element(), max_element(), and minmax_element(). #3619
    • This also affected ranges::min_element, ranges::max_element, ranges::minmax_element, ranges::min, ranges::max, ranges::minmax, and the min(), max(), and minmax() overloads for initializer_list.
    • This fixed a regression that was introduced by #2447 #2821 #2825 in VS 2022 17.4.
  • Added a compiler bug workaround for MSVC in shared_ptr's operator<=>. #3647
    • This avoids compiler errors when comparing shared_ptr<const int> to shared_ptr<void>.
  • Added a space to chrono::ambiguous_local_time's message to exactly match the Standard. #3650
  • Fixed compiler errors when formatting unusual chrono::duration types. #3649
  • Fixed optional::transform() to avoid terminating when the callable object throws an exception. #3668
  • Fixed <charconv> floating-point from_chars() to correctly handle two scenarios involving exponents with large absolute values. #3670
  • Fixed iostreams floating-point parsing to produce correct results for many different scenarios. [#3364](...

VS 2022 17.6

• Merged C++23 features:
  • P1223R5 #3268 ranges::find_last, ranges::find_last_if, ranges::find_last_if_not
  • P2167R3 #3258 Improving boolean-testable Usage
  • P2278R4 #3187 #3234 cbegin Should Always Return A Constant Iterator
  • P2404R3 #3345 Move-Only Types For Comparison Concepts
  • P2467R1 #3065 ios_base::noreplace: Exclusive Mode For fstreams
  • P2474R2 #3142 views::repeat
  • P2505R5 #3361 Monadic Functions For expected
  • P2588R3 #3455 barrier's Phase Completion Guarantees
  • P2602R2 #3215 Poison Pills Are Too Toxic
  • P2711R1 #3451 Making Multi-Param Constructors Of Views explicit
• Merged partial C++23 features:
  • P2165R4 Compatibility Between tuple, pair, And tuple-like Objects:
    • Changes to pair. #3323
  • P2321R2 zip:
    • views::zip_transform. #3322
    • Note: views::adjacent and views::adjacent_transform remain to be implemented.
• Merged LWG issue resolutions:
  • LWG-3515 #3236 [stacktrace.basic.nonmem]: operator<< should be less templatized
  • LWG-3545 #3242 std::pointer_traits should be SFINAE-friendly
  • LWG-3594 #3276 inout_ptr - inconsistent release() in destructor
  • LWG-3629 #3272 make_error_code and make_error_condition are customization points
  • LWG-3646 #3261 std::ranges::view_interface::size returns a signed type
  • LWG-3717 #3266 common_view::end should improve random_access_range case
  • LWG-3736 #3318 move_iterator missing disable_sized_sentinel_for specialization
  • LWG-3737 #3320 take_view::sentinel should provide operator-
  • LWG-3743 #3269 ranges::to's reserve may be ill-formed
  • LWG-3746 #3265 optional's spaceship with U with a type derived from optional causes infinite constraint meta-recursion
  • LWG-3769 #3459 basic_const_iterator::operator== causes infinite constraint recursion
  • LWG-3772 #3462 repeat_view's piecewise constructor is missing preconditions
  • LWG-3778 #3332 vector<bool> missing exception specifications
  • LWG-3785 #3319 ranges::to is over-constrained on the destination type being a range
  • LWG-3798 #3359 Rvalue reference and iterator_category
  • LWG-3810 #3421 CTAD for std::basic_format_args
  • LWG-3823 #3231 Unnecessary precondition for is_aggregate
  • LWG-3848 #3410 slide_view missing base accessor
  • LWG-3850 #3423 views::as_const on empty_view<T> should return empty_view<const T>
  • LWG-3853 #3468 basic_const_iterator<volatile int*>::operator-> is ill-formed
• Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • LWG-3857 #3348 basic_string_view should allow explicit conversion when only traits vary
  • LWG-3867 #3367 Should std::basic_osyncstream's move assignment operator be noexcept?
• Fixed bugs:
  • Fixed linker errors when using time_put<wchar_t> from the Standard Library Modules. #3232
  • Fixed another unintentionally dllexported symbol in the import library. #3233
    • This would emit a spurious message "Creating library meow.lib and object meow.exp" (while building meow.exe) when using <stacktrace> or importing the Standard Library Modules.
  • Fixed a binary compatibility break in basic_string, which could lead to missing null terminators causing crashes and other runtime misbehavior, when linking code that was built with different versions of the STL. #3235
    • This ABI break was introduced by #1735 activating the Small String Optimization for constexpr basic_string in VS 2022 17.4.
    • The affected scenarios involved mixing VS 2022 17.3 (or earlier) with VS 2022 17.4 (or later, until this fix).
    • We backported this fix to VS 2022 17.4.5 and VS 2022 17.5.
  • Fixed a binary compatibility break in ppltasks.cpp powering std::async(), which could lead to crashes caused by an invalid_operation exception slamming into noexcept. #3255
    • This ABI break was introduced by #2654, and appeared in VS 2022 17.4 when the VCRedist was "unlocked".
    • The affected scenarios involved building with VS 2015 (or possibly early versions of VS 2017), using "Single-Threaded Apartments", and running on an end user's machine with the VS 2022 17.4 VCRedist installed.
    • We backported this fix to VS 2022 17.4.5 and VS 2022 17.5.
  • Fixed incorrect results from find(), count(), ranges::find(), and ranges::count(). #3247
    • This fixed a regression that was introduced by #2434 in VS 2022 17.3.
    • The affected scenarios involved mixing certain signed and unsigned types; for example, finding/counting occurrences of the int -1 in a range of unsigned int elements should consider the element 0xFFFF'FFFFu to be equal (due to C++'s usual arithmetic conversions), but it was incorrectly considered to be non-equal.
    • We backported this fix to VS 2022 17.4.5 and VS 2022 17.5.
  • Fixed the visualizer for optional<T> to work when T has a custom visualizer. #3243
  • Fixed compiler warnings when passing long double to copysign(). #3253
  • Re-enabled ASan (Address Sanitizer) annotations in <string> after fixing significant bugs. #3164
    • Also fixed ASan annotations in <vector> that were failing when pmr::vector was used with pmr::monotonic_buffer_resource on x86.
  • Fixed compiler errors when passing ranges types to std::copy(). #3270
  • Fixed shared_future<void>'s move assignment operator to be noexcept as required by the Standard. #3284
  • Fixed Clang compiler errors involving intrinsics by including <intrin.h>, which is a header that Clang recognizes and supports. #3285
  • Fixed numeric_limits to correctly report that is_signed is true for the STL's internal 128-bit signed-integer-class type. #3291
  • Fixed <stacktrace> to correctly pass SYMOPT_FAIL_CRITICAL_ERRORS to the Windows API. #3292
  • Fixed <charconv> (and headers that include it, like <chrono> and <format>) to avoid emitting warning C4365 "signed/unsigned mismatch" when being compiled with /J. #3295
    • Note: We strongly discourage any use of the /J compiler option, as it's a recipe for One Definition Rule violations and it doesn't improve Standard conformance.
  • Fixed ranges::cbegin, ranges::cend, ranges::crbegin, ranges::crend, and ranges::cdata to behave like their non-const counterparts when given array rvalues. [#3316](https://github.com/microsoft...

VS 2022 17.5

• Merged C++23 features:
  • P2322R6 #3099 ranges::fold_left, ranges::fold_right, etc.
  • P2465R3 #3108 Standard Library Modules std And std.compat
    • Initially supported for MSVC only; see tracking issue #1694 for lists of known compiler bugs and upcoming fixes.
    • Build system support is a work in progress; currently, build systems must be manually taught to compile std.ixx so you can reference std.ifc and link std.obj. (Similarly for building std.compat.ixx into std.compat.ifc and std.compat.obj.)
    • IntelliSense support is a work in progress; STL test coverage is not yet enabled.
    • Will be supported for Clang after compiler support for modules is available; see Clang's C++20 implementation status.
  • P2508R1 #3074 basic_format_string, format_string, wformat_string
• Merged partial C++23 features:
  • P2278R4 cbegin Should Always Return A Constant Iterator:
    • The "Iterators" section, including basic_const_iterator, make_const_iterator(), and make_const_sentinel(). #3043
  • P2321R2 zip:
    • views::zip. #3035
    • Note: views::zip_transform, views::adjacent, and views::adjacent_transform are the parts that remain to be implemented.
• Merged LWG issue resolutions:
  • LWG-3711 #2949 Missing preconditions for slide_view constructor
  • LWG-3788 #3130 jthread::operator=(jthread&&) postconditions are unimplementable under self-assignment
• Fixed bugs:
  • Fixed compiler warnings when using Standard Library Header Units. #3069
  • Removed a non-Standard member function locale::c_str(). #3088
  • Fixed narrowing warnings when calling piecewise_constant_distribution<float>::densities() and piecewise_linear_distribution<float>::densities(). #3107
  • Fixed compiler errors when calling ranges::is_permutation with predicates that return highly unusual boolean-testable types. #3113
  • Fixed compiler errors when building the Standard Library Modules with static RTTI disabled. #3115
    • Now, building std.ixx with /GR- /D_HAS_STATIC_RTTI=0 will succeed, and std::any will simply be unavailable (as it inherently requires static RTTI).
    • Additionally, including <any> with static RTTI disabled will emit a warning message but not an error, and the feature-test macro __cpp_lib_any will indicate (by its absence) that the feature is unavailable.
  • Fixed compiler errors in reference_wrapper, thread, and variant involving incomplete types. #3101 #3148
  • When chrono::time_zone::get_info() throws an exception, fixed it to report GetLastError() as intended, instead of "The operation completed successfully." #3122
  • Fixed incorrect results returned by ellint_2(). #3077
  • Fixed error_category's default constructor to be constexpr. #3139 #3176
  • Fixed all headers to avoid emitting the off-by-default "warning C5262: implicit fall-through occurs here; are you missing a break statement? Use [[fallthrough]] when a break statement is intentionally omitted between cases". #3162
  • Fixed compiler errors in certain <ranges> scenarios by properly constraining movable-box's copy constructors. #3171
• Improved performance:
  • Added support for unwrapping to move_sentinel. #3098
  • Improved the performance of uniform_int_distribution by implementing Daniel Lemire's algorithm Fast Random Integer Generation in an Interval. #3012
  • Optimized gcd() to avoid a redundant shift. #3127
  • Optimized locale::classic() for a 10x speedup (times, not percent). #3048
  • Added an attribute to move(), forward(), move_if_noexcept(), and forward_like() that will allow the MSVC compiler to intrinsically implement them without emitting function calls. #3182
• Improved throughput:
  • Significantly improved compile times for <variant> visit(). #3070
  • <format> now includes fewer headers. #3128
  • Moved random number generator machinery out of <xutility>, one of the STL's central internal headers. #3157
• Enhanced behavior:
  • Clarified get_future()'s [[nodiscard("message")]]. #3068
  • The internal headers <xatomic.h>, <xbit_ops.h>, and <xerrc.h> are now core headers. #3116
  • Improved <format>'s compiler error messages for unformattable types. #3080
• Improved test coverage:
  • Added test coverage for <variant> visit() invoking pointers to members. #3070
  • Expanded test coverage for forward_like(). #3072
  • Updated test coverage for views::as_rvalue. #3089
  • Expanded test coverage for bind_front() and bind_back(). #3117
  • Updated our LLVM submodule reference, including new tests, and updates to the any/optional/variant shared test code. #2976
  • Fixed bogus test code discovered by Clang 15. #3135
  • Fixed the off-by-default "exhaustive" mode of the parallel is_partitioned() test. #3174
• Code cleanups:
  • Various cleanups (described in detail in the PRs, not repeated here). #3082 #3083 #3084 #3085 #3086 #3090 #3091 #3092 #3093 #3177 #3178
  • Improved Python scripts. #3123
  • Removed compiler bug workarounds. #3155
  • Moved <atomic> implementation details, preparing for later changes. #3124
  • Removed unnecessary partial specializations of common_type for the STL's internal 128-bit integer-class types. #3153
• Infrastructure improvements:
  • The PR/CI system now uses spot VMs again. #3071
  • Configured Azure Pipelines to avoid running checks for draft PRs. #3078
  • Added GitHub Actions to allow contributors to move their PR cards in the Code Reviews project. #2584
  • Updated dependencies. #3104 #3155
    • Updated build compiler to VS 2022 17.4 Preview 3.
    • Updated Boost.Math to 1.80.0 (now also used by the MSVC-internal build). #3077
    • Updated Clang to 15.0.1 (now required).
    • Updated CMake to 3.24 (now required).
    • Updated Google Benchmark to 1.7.0. #3151
    • Updated Python to 3.10.8.
• Updated _MSVC_STL_UPDATE. #3073 #3147

VS 2022 17.4

• Merged C++23 features:
  • P0849R8 #2808 auto(x): decay-copy In The Language
    • The compiler part is not yet implemented; the library part was implemented in C++20 mode when Ranges were initially implemented.
  • P0881R7 #2502 <stacktrace>
    • P2301R1 Add A pmr Alias For std::stacktrace
  • P1206R7 #2806 #3026 #3028 Conversions From Ranges To Containers
  • P1328R1 #2793 constexpr type_info::operator==()
  • P1899R3 #2981 views::stride
  • P2291R3 #3049 constexpr Integral <charconv>
  • P2302R4 #2911 ranges::contains, ranges::contains_subrange
  • P2387R3 #2661 Pipe Support For User-Defined Range Adaptors
  • P2408R5 #2960 #3056 Ranges Iterators As Inputs To Non-Ranges Algorithms
  • P2417R2 #2972 More constexpr bitset
  • P2419R2 #2977 Clarify Handling Of Encodings In Localized Formatting Of chrono Types
  • P2438R2 #3057 string::substr() &&
  • P2440R1 #2580 ranges::iota, ranges::shift_left, ranges::shift_right
  • P2441R2 #2619 views::join_with
  • P2445R1 #2974 forward_like()
  • P2446R2 #3008 views::as_rvalue
  • P2494R2 #2965 Relaxing Range Adaptors To Allow Move-Only Types
  • P2499R0 #2947 string_view Range Constructor Should Be explicit
  • P2517R1 #2959 Conditional noexcept For apply()
  • P2520R0 #2958 #2994 move_iterator<T*> Should Be A Random-Access Iterator
• Merged LWG issue resolutions:
  • LWG-3564 #2961 transform_view::iterator<true>::value_type and iterator_category should use const F&
  • LWG-3617 #2966 function/packaged_task deduction guides and deducing this
  • LWG-3656 #2880 Inconsistent bit operations returning a count
  • LWG-3671 #2905 atomic_fetch_xor missing from stdatomic.h
  • LWG-3672 #2907 common_iterator::operator->() should return by value
  • LWG-3683 #2879 operator== for polymorphic_allocator cannot deduce template argument in common cases
  • LWG-3701 #2957 Make formatter<remove_cvref_t<const charT[N]>, charT> requirement explicit
  • LWG-3707 #2883 chunk_view::outer-iterator::value_type::size should return unsigned type
  • LWG-3710 #2878 The end of chunk_view for input ranges can be const
  • LWG-3712 #2943 chunk_view and slide_view should not be default_initializable
  • LWG-3715 #2946 view_interface::empty is overconstrained
  • LWG-3719 #2902 Directory iterators should be usable with default sentinel
  • LWG-3721 #2906 Allow an arg-id with a value of zero for width in std-format-spec
  • LWG-3724 #2903 decay-copy should be constrained
• Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • LWG-3705 #2741 Hashability shouldn't depend on basic_string's allocator
• Fixed bugs:
  • Fixed linker errors when using <any> with our unofficially supported mode to disable exceptions. #2193
  • Fixed compiler errors when using <format> with the new compiler option /presetPadding by adding a compiler bug workaround. #2746
  • Fixed division by complex zero to behave consistently with other implementations. #2758
  • Fixed a memory leak in <syncstream>. #2763
  • Fixed compiler errors when formatting long or unsigned long values with formatter. #2768
  • Fixed a binary compatibility break in the unordered associative containers, which could cause memory corruption when linking code that was built with different versions of the STL. #2774
    • Original Versions: VS 2015 through VS 2019 16.2 inclusive.
    • Modified Versions: VS 2019 16.3 through VS 2022 17.3 inclusive.
    • Fixed Versions: VS 2022 17.4 and later.
    • The bincompat break happened when mixing Original with Modified code. All other mixing is safe: Original with Original, Modified with Modified, Fixed with Fixed, Original with Fixed, and Modified with Fixed.
  • Fixed a bug in the unordered associative containers, specific to user-defined allocators, where the containers sometimes called deallocate() with null pointers. User-defined allocators aren't required to tolerate that, so the containers now avoid such calls. #2790
  • Fixed a bug in deque, specific to rarely-used fancy pointers, where some fancy pointers weren't being destroyed. #2775
  • <chrono> formatting now accepts %x ("The locale's date representation") for year_month_day, year_month_day_last, year_month_weekday, and year_month_weekday_last. #2762
  • std::filesystem::directory_entry's constructors, assign(), and replace_filename() now call refresh() as required by the Standard and will propagate any errors (via exceptions or error_codes), except that "file not found" is not considered an error. #1343
  • Added a compiler bug workaround to construct_at(), allowing immovable objects to be emplaced via copy elision. #2624
  • Fixed leap second validation when parsing time_points. #2705
  • lerp() now avoids overflowing to infinity when it can calculate the correct result with a fallback approach. #1918
  • Fixed a debugger visualization issue, specific to Clang in C++20 mode (or later), where the debugger wouldn't display the contents of a list, forward_list, or ordered/unordered associative container. #2782
  • Fixed the visualizers for the non-Standard stdext::hash_map container family. #2784
  • Fixed the visualizers for make_shared() and allocate_shared(). #2811
  • put_time() (and the time_put::do_put() machinery powering it) now avoids modifying errno when it succeeds. #2049
  • Added a compiler bug workaround to fix compiler errors with source_location::current() in certain scenarios. #2824
  • Fixed compiler errors when using <format> to print durations with extremely small periods (e.g. femtoseconds, attoseconds). #2814
  • Fixed "istreambuf_iterator is not dereferenceable" assertions when attempting to use time_get::get() or get_time() to parse certain formats when there's insufficient input. #2851
    • For example, with the format "%X", the input "3:04:05" succeeds. The input "3:04" previously asserted/crashed; now it sets ios_base::failbit | ios_base::eofbit as required by the Standard.
  • ...

VS 2022 17.3

• Merged C++23 features:
  • P0323R12 #2643 <expected>
    • P2549R1 #2643 #3075 unexpected<E>::error()
  • P1413R3 #2583 Deprecate aligned_storage And aligned_union
  • P2273R3 #2582 constexpr unique_ptr
  • P2442R1 #2670 #2685 Windowing Range Adaptors: views::chunk, views::slide
  • P2443R1 #2565 views::chunk_by
• Merged partial C++23 features:
  • P2321R2 zip:
    • Changes to tuple, pair, and vector<bool>::reference. #2687
• Merged LWG issue resolutions:
  • LWG-3121 #2640 tuple constructor constraints for UTypes&&... overloads
  • LWG-3525 #2639 uses_allocator_construction_args fails to handle types convertible to pair
  • LWG-3570 #2418 basic_osyncstream::emit should be an unformatted output function
  • LWG-3571 #2418 flush_emit should set badbit if the emit call fails
• Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • LWG-3234 #2703 Sufficient Additional Special Math Overloads
  • LWG-3627 #2607 Inconsistent specifications for std::make_optional overloads
• Fixed bugs:
  • Fixed vector<bool> to properly invalidate iterators during reallocation, which fixes compiler errors with constexpr usage of vector<bool>. #2441
  • empty_view rvalues are now considered borrowed_ranges as required by the Standard. #2576
  • Added compiler bug workarounds to is_convertible and common_reference, so contiguous_iterator<const volatile int*> is now true. #2592
  • Added missing constraints to functions that were implied by "Effects: Equivalent to" Standardese: make_any(), make_optional(), shared_ptr::operator=(), shared_ptr::reset(), and weak_ptr::operator=().
  • Fixed filesystem::path's comparison operators and some other member functions being IF-NDR (ill-formed, no diagnostic required) in C++23 mode. #2457
    • This fixed a regression that was introduced by #2000 implementing P1989R2 Range Constructor For string_view in VS 2022 17.0.
  • Fixed C++20 <chrono> parsing to fail when the input is insufficient to supply the entire format string. #2523
    • For example, the input "23:59" is insufficient for the format string "%H:%M:%S".
  • Fixed an out-of-bounds read in ranges::find() with unreachable_sentinel. #2434
  • Added compiler bug workarounds for CUDA (involving [[nodiscard]] friend) to fix spurious cases of "warning C5240: 'nodiscard': attribute is ignored in this syntactic position". #2622
  • Removed ExecutionPolicy overloads of copy_backward() and move_backward() that were mistakenly implemented. They don't appear in the Standard because they would be useless. #2627
  • Added compiler bug workarounds for Clang (involving the ordering of constrained and unconstrained destructors) to fix compiler errors in <ranges> machinery. #2630
  • Fixed a bug affecting <future>'s use of <ppltasks.h> in Desktop XAML apps. #2654
  • Fixed a bug that prevented C++20 <chrono> from parsing fractional seconds as floating-point durations. #2638
  • Fixed <bit>'s countl_zero() returning incorrect results on ARM64 for 8-bit and 16-bit types. #2647
  • Added macroization guards to the STL's usage of compiler-specific custom attributes. #2649
  • Fixed get_time() and time_get's 2-digit year logic. #2666
  • Fixed system_category().message() to behave correctly instead of returning "???" when the user language and system language are different. #2669
  • Fixed the ARM64EC implementations of atomic_thread_fence() and atomic<8-byte type>::store(). #2702
  • Fixed compiler errors in atomic<shared_ptr<T[]>>, atomic<shared_ptr<T[N]>>, atomic<weak_ptr<T[]>>, and atomic<weak_ptr<T[N]>>. #1339
  • Added overloads of <cmath>'s lerp() for arithmetic types. #2113
  • Fixed filesystem::directory_entry to work with FAT32 and exFAT. #2373
  • <filesystem> now handles special system files like hiberfil.sys. #2715
  • filesystem::copy_file() now tolerates other processes having opened the source file or the target file for reading or writing (as much as possible, depending on the choice of copy_options). #2718
  • Fixed the visualizers for shared_ptr<void>, weak_ptr<void>, and unique_ptr<void, Deleter>. #2706
  • Fixed compiler errors in move_only_function when compiling <functional> in /std:c++latest mode with /Zc:alignedNew-. #2712
  • Implemented C++20's removal of the explicit specialization for allocator<void>. #2726
    • Note that allocator<void> is still supported, it just uses the primary template now.
  • Fixed "unresolved external symbol" linker errors in certain scenarios involving separately compiled third-party libraries. #2734 #2738
    • On x64, these errors mentioned __imp___std_init_once_begin_initialize and __imp___std_init_once_complete.
    • On x86, these errors mentioned __imp____std_init_once_begin_initialize@16 and __imp____std_init_once_complete@12.
    • This fixed a regression that was introduced by #2381 in VS 2022 17.2.
    • This fix was backported to VS 2022 17.2.5.
• Improved performance:
  • Optimized rotl() and rotr() in <bit> for 8-bit and 16-bit integers by using compiler intrinsics. #2611
  • Optimized the vectorized implementation of reverse() for 32-bit trivial types. #2383
  • Improved <format> performance when the execution character set isn't self-synchronizing, by caching expensive calls to get codepage info. #2600
  • Added vectorized implementations of find(), count(), ranges::find(), and ranges::count(), with speedups ranging from 2.0x to 27.6x (times, not percent). #2434
  • Slightly improved the performance of <charconv> floating-point from_chars(). #2623
• Improved throughput:
  • Used if constexpr instead of tag dispatch, overloads, or specializations in:
    • is_permutation(), sample(), rethrow_if_nested(), and default_searcher. #2219
    • <map> and <set>'s common machinery. #2287
    • polymorphic_allocator. #2471
    • basic_string_view and basic_string's find_first_of(), find_last_of(), find_first_not_of(), and find_last_not_of(). #2479 #2660
    • <regex>. #2484
    • Parallel inclusive_scan() and transform_inclusive_scan(). #2662
    • scoped_allocator_adaptor's operator==(). #2677
    • function, move_only_function, and bind(). #2668
    • vector<bool>::insert(). #2694
  • Replaced tag dispatch with SFINAE in subtract_with_carry_engine's internal machinery. #2693
  • Split <chrono> into a smaller internal header, improving throughput when other headers need only pre-C++20 <chrono> machinery. #2604
• Enhanced behavior:
  • Changed <deque> to use scope guards instead of `thro...