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Stephan T. Lavavej edited this page Nov 11, 2025 · 8 revisions

Table of Contents

For newer releases, see the current Changelog.

C++20 and C++23 features generally require the /std:c++20 and /std:c++latest compiler options, respectively.

VS 2022 17.14

  • Merged C++26 features:
    • P3323R1 #5213 Forbid atomic<cv T>, Specify atomic_ref<cv T>
  • Merged partial C++26 features:
    • P3471R4 #5274 Standard Library Hardening
      • Currently disabled by default.
      • This can be enabled (for any Standard mode) by defining _MSVC_STL_HARDENING to 1 project-wide.
      • As C++26 Contracts are not yet implemented, this defaults to calling __fastfail() for hardened precondition violations.
  • Related behavior enhancement:
    • Implemented "destructor tombstones" to mitigate use-after-free mistakes. #5318
      • Currently disabled by default.
      • This can be enabled by defining _MSVC_STL_DESTRUCTOR_TOMBSTONES to 1 project-wide.
  • Merged LWG issue resolutions:
    • LWG-3133 #5157 Modernizing numeric type requirements
    • LWG-3886 #5232 Monad mo' problems (in optional and expected)
    • LWG-3899 #5303 co_yielding elements of an lvalue generator is unnecessarily inefficient
    • LWG-3900 #5150 The allocator_arg_t overloads of generator::promise_type::operator new should not be constrained
    • LWG-3918 #5135 #5170 std::uninitialized_move/_n and guaranteed copy elision
    • LWG-3956 #5334 chrono::parse uses from_stream as a customization point
    • LWG-4014 #5132 LWG-3809 changes behavior of some existing std::subtract_with_carry_engine code
    • LWG-4027 #5221 possibly-const-range should prefer returning const R&
    • LWG-4084 #5151 std::fixed ignores std::uppercase
    • LWG-4112 #5152 has-arrow should require operator->() to be const-qualified
    • LWG-4119 #5220 generator::promise_type::yield_value(ranges::elements_of<R, Alloc>)'s nested generator may be ill-formed
    • LWG-4124 #5155 Cannot format zoned_time with resolution coarser than seconds
    • LWG-4135 #5131 The helper lambda of std::erase for list should specify return type as bool
    • LWG-4140 #5129 Useless default constructors for bit reference types
    • LWG-4144 #5201 Disallow unique_ptr<T&, D>
    • LWG-4169 #5128 std::atomic<T>'s default constructor should be constrained
    • LWG-4172 #5337 unique_lock self-move-assignment is broken
  • Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
    • LWG-3424 #5232 optional::value_or should never return a cv-qualified type
  • Fixed bugs:
    • Fixed system_category().message() to prefer US English, followed by the system locale, with an ultimate fallback of FormatMessageA's behavior for dwLanguageId == 0. #5104
      • This is consistent with generic_category().message() (which always returns US English in our implementation) and has the best chance of returning something intelligible instead of "unknown error" or "???".
      • This fixed a regression that was introduced by #2669 in VS 2022 17.3.
    • Fixed regex's behavior:
      • To reject bogus character class ranges like R"([\d-e])". #5158
      • For negated character class escapes (\D for non-digits, \S for non-whitespace, \W for non-words) when matching against Unicode characters:
        • Outside square-bracket character classes. #5160
        • Inside square-bracket character classes (partially fixed). #5214
      • For character ranges in case-insensitive mode. #5164
      • For the basic grammar to parse a single digit for backreferences. #5167
      • For its internal buffers to grow geometrically. #5175
      • For the special character . (dot). #5192
      • For its constructor to accept (null, zero) arguments. #5211
    • Fixed filesystem::equivalent() to return correct results when shared folders are involved. #5130
    • Fixed chrono::weekday's constructor to avoid integer overflow for extreme inputs. #5156
    • Fixed push_range() for stack, queue, and priority_queue to forward the range to c.append_range() when possible, exactly as depicted in the Standard. #5168
    • Fixed code to call ranges::begin and ranges::end exactly as depicted in the Standard:
    • Fixed compiler errors in range_formatter involving highly unusual contiguous ranges. #5187
    • Fixed heterogeneous lookup for unordered containers to follow the Standard, allowing braced initializer lists to be used as arguments. #5208
    • Fixed compiler errors in views::counted involving highly unusual types. #5223
    • Fixed integer overflow in this_thread::sleep_for() with extremely small units (e.g. picoseconds). #5237
    • Fixed basic_string::reserve()'s ASan annotations to detect writes to its unused capacity. #5252
    • Fixed how <format> handles field width for alternate form general floating-point. #5261
    • Fixed compiler errors when constructing a basic_ispanstream from a modifiable basic_string. #5309
      • This fixed a regression that was introduced by #4938 in VS 2022 17.13.
    • Fixed compiler errors when using <format> in a CUDA project, by adding a compiler bug workaround. #5335
    • Fixed compiler errors when converting between different specializations of basic_const_iterator. #5325
  • Improved performance:
    • Added vectorized implementations of:
      • basic_string::find() for a character. #5101
    • Improved the vectorized implementations of:
      • basic_string::find_first_of() and basic_string::find_last_of(). #5029
    • regex_traits::translate() is now an identity function, as required by the Standard, instead of an expensive locale operation. #5209
    • The STL now takes advantage of compiler support for C++23 P1169R4 static operator() in earlier Standard modes, slightly improving codegen. #5284 #5312
    • Optimized the minstd_rand and minstd_rand0 random number engines by avoiding constant divisions. #5256
    • Slightly improved move_only_function's constructors to do less work when setting the object to be empty. #5328
  • Enhanced behavior:
    • std::expected, std::unexpected, and all STL exception types are now marked [[nodiscard]]. #5174
      • This affects all user-defined functions returning these types by value. It also affects any directly constructed temporaries that are immediately discarded.
    • Deprecated the non-Standard locale::empty() static member function. #5197
    • Changed the STL to avoid using is_trivial, which is being deprecated in C++26. #5202
    • Improved the STL's debug checks with better messages and fewer branches. #5270
  • Improved debugger visualization:
    • Improved the visualizers for basic_string_view and its iterators by suppressing irrelevant pointer values. #5176
    • Dramatically simplified how the visualizers for basic_string and its iterators are implemented. #5177
  • Improved test coverage:
    • Simplified the test harness by dropping ctest. Now we always directly invoke stl-lit.py. #5169
    • Improved the test harness to warn only once when a compiler is missing. #5199
    • Categorized libcxx test failures. #5231
    • Updated our LLVM submodule, including new tests. #5235
    • Added test coverage for the ASan annotations in basic_string::reserve() and vector::reserve(). #5241
    • Skipped libcxx tests in response to a new compiler warning C5321, which warns when the resolution to CWG-1656 affects a u8 string literal. #5283
  • Code cleanups:
    • Removed compiler bug workarounds. #5186 #5247 #5257 #5284 #5335
    • Removed usage of [[likely]] and [[unlikely]], which are discouraged by the compiler team. #5255
    • Various cleanups (described in detail in the PRs, not repeated here). #5336
  • Infrastructure improvements:
    • Updated dependencies. #5186 #5247 #5257 #5284 #5335
      • Updated build compiler to VS 2022 17.14 Preview 2 (now required).
      • Updated Clang to 19.1.5 (now required).
      • Updated Google Benchmark to 1.9.1.
      • Updated Python to 3.13.2.
      • Updated VMs to compute-optimized F32as_v6.
  • Updated _MSVC_STL_UPDATE. #5162 #5217 #5264 #5323

VS 2022 17.13

  • Merged C++23 features:
  • Merged C++23 Defect Reports:
    • P3107R5 #4821 Permit An Efficient Implementation Of <print>
      • P3235R3 std::print More Types Faster With Less Memory
  • Fixed bugs:
    • Fixed an infinite loop in deque::shrink_to_fit(). #4955
      • This fixed a regression that was introduced by #4091 in VS 2022 17.10.
    • Fixed compiler errors when constructing highly unusual unique_ptrs (storing fancy pointers) from unspeakably evil relics of the forgotten past. #4922
    • Fixed compiler errors when calling ranges::inplace_merge with certain combinations of elements, projections, and comparisons. #4927
    • Fixed compiler errors in basic_ispanstream's constructor and basic_ispanstream::span() taking ReadOnlyRange&& with highly unusual types. #4938
    • Fixed compiler errors in the highly unusual scenario of calling basic_string and basic_string_view's find_first_of() family of member functions for program-defined "unicorn" character types. #4951
    • Fixed compiler errors when constructing optional from highly unusual types. #4961
    • Fixed sequence container emplacement functions (e.g. vector::emplace_back()) to avoid emitting "warning C5046: Symbol involving type with internal linkage not defined" for highly unusual types. #4963 #4980
      • This also fixed ODR violations when mixing C++14 with C++17-and-later translation units calling sequence container emplacement functions for any types.
    • Fixed ODR violations when mixing C++17 with C++20-and-later translation units calling list/forward_list::remove/remove_if/unique(). #4975
    • Fixed compiler errors in variant's converting constructor and converting assignment operator for certain types. #4966
    • Fixed bitset's streaming operator operator>>(basic_istream<CharT, Traits>&, bitset<N>&) to use the stream's Traits to compare characters. #4970
    • Fixed basic_string and list's internal constructors to avoid disrupting highly unusual scenarios. #4976
    • Fixed compiler errors when constructing a packaged_task from a move-only function object. #4946
    • For Clang /fp:fast, fixed <cmath> and <limits> to avoid emitting -Wnan-infinity-disabled warnings, except when numeric_limits::infinity()/quiet_NaN()/signaling_NaN() are specifically called. #4990
    • Fixed ranges::copy_n to properly handle negative values of n (as a no-op) when activating our memmove() optimization. #5046
      • Also fixed our memmove() optimization (used by copy_n(), ranges::copy_n, and more) to avoid emitting compiler warnings with certain iterators.
    • Fixed filesystem::directory_entry::refresh() to avoid sporadically failing for nonexistent network paths on Windows 11 24H2. #5077
    • Fixed basic_istream::get() and basic_istream::getline() to never write a null terminator into zero-sized buffers, and to always write a null terminator otherwise. #5073
    • Fixed assign_range() for sequence containers to static_assert that the container elements are assignable from the range's reference type. #5086
    • Fixed compiler errors in various ranges algorithms when used with views::iota in certain scenarios. #5091
  • Improved performance:
    • Added vectorized implementations of:
      • basic_string::find_first_of(). #4744
      • basic_string::find_last_of(). #4934
      • basic_string::find() for a substring. #5048
      • basic_string::rfind() for a substring. #5057
      • basic_string::rfind() for a single character. #5087
      • search(), ranges::search, and default_searcher, for 1-byte and 2-byte elements. #4745
      • find_end() and ranges::find_end, for 1-byte and 2-byte elements. #4943 #5041 #5042
      • bitset's constructors from strings. #4839
      • remove() and ranges::remove. #4987
    • Improved the vectorized implementations of:
      • ranges::minmax, now activated for 1-byte and 2-byte elements. #4913
      • The minmax_element() and minmax() algorithm families. #4917 #5016
    • Helped the compiler auto-vectorize:
    • ranges algorithms now unwrap output iterators, avoiding unnecessary checking. #5015 #5027
    • Optimized bitset's streaming operators. #5008
    • Optimized the newline-printing overloads println(FILE*), println(ostream&), and nullary println(). #4672
    • Updated array and vector's spaceship comparison operators to take advantage of the vectorized implementation of lexicographical_compare_three_way(). #5078
    • Extended the "key extraction" optimization in the unique associative containers (both ordered and unordered) to handle more types. #5050
    • Optimized filesystem::symlink_status() by avoiding unnecessary Windows API calls. #5071
  • Improved throughput:
    • Improved C++23 throughput by not including all of <ostream> (which drags in <format>) unless the Standard requires it. #4936
    • Improved C++23 throughput of <queue>, <stack>, <stacktrace>, and <thread> by not including all of <format>. #5003
    • Moved system_clock, high_resolution_clock, and chrono_literals from a commonly-included internal header to <chrono>. #5105
      • This has source-breaking impact. If you see compiler errors complaining that it doesn't recognize chrono types like system_clock or UDLs like 1729ms, you need to include <chrono> specifically, instead of assuming that headers like <thread> will drag it in.
  • Enhanced behavior:
    • Changed an internal pair constructor to be private. #4979
    • Fixed a CodeQL warning by replacing a squirrelly memcpy() call in the filesystem implementation (that was intentionally performing a read overrun) with two cromulent memcpy() calls. #4933
    • Silenced CodeQL warnings. #4942 #4985 #5072
    • Added a visualizer for system_clock::time_point. #5005
    • Changed some vector machinery to use scope guards instead of throw;, making debugging easier when exceptions are thrown. #4977
    • Improved regex_error::what()'s message for regex_constants::error_badbrace. #5025
    • Improved optional<T>::swap()'s static_assert messages when T isn't both move constructible and swappable. #5065
    • Removed locale::id's non-Standard constructor from size_t and implicit conversion operator to size_t. #5067
      • For user-visible headers, at least. They remain dllexported for binary compatibility.
    • Improved mutex assertions to distinguish "unlock of unowned mutex" from "unlock of mutex not owned by the current thread". #5099
  • Improved test coverage:
    • Updated tests to work with Clang 18. #4932 #4937
    • Fixed sporadic failures in a timed_mutex test. #4973
    • Extended CUDA test coverage beyond C++14, adding C++17 and C++20. #4974
    • When Python psutil is installed, the test harness now supports a priority parameter, defaulting to idle. #5032
    • Increased the consistency of the swap_ranges() benchmark by adding allocators to control alignment. #5043
    • Updated our LLVM submodule, including new tests. #5038
    • Divided the increasingly large test for vectorized algorithms into smaller parts, extracting mismatch(), lexicographical_compare(), and lexicographical_compare_three_way() into a separate test. #5063
  • Code cleanups:
    • Removed compiler bug workarounds. #4939 #4944 #4947 #5017 #5103
    • Explicitly marked packaged_task's defaulted move constructor and move assignment operator as noexcept. #4940
    • Various cleanups (described in detail in the PRs, not repeated here). #4945 #5014 #5058
    • Refactored internal usage of the tuple-like and pair-like concepts. #4983
    • Used if constexpr to simplify eldritch horrors from beyond spacetime locale facets. #5001
    • Simplified control flow in basic_string::find_first_not_of()/find_last_not_of(). #5006
    • Refactored the vectorized implementation of bitset::to_string(). #5013
    • Replaced SFINAE with concepts in C++20-and-later code. #5044
  • Improved documentation:
    • Removed an inaccurate comment in list's move assignment operator. #5024
  • Infrastructure improvements:
    • Updated dependencies. #4947 #5017 #5082
      • Updated build compiler to VS 2022 17.13 Preview 1 (and 17.12 is now required).
      • Updated Clang to 18.1.8 (now required).
      • Updated CMake to 3.30 (now required).
      • Updated Python to 3.13.0 (now required).
      • Updated the PR/CI system to Windows Server 2025.
  • Build system improvements:
    • Removed a workaround in the benchmark build. #4928
  • Updated _MSVC_STL_UPDATE. #4926 #4994 #5064

VS 2022 17.12

  • Merged C++26 features:
  • 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):
  • 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
    • 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 copying map/set nodes to use scope guards instead of throw;, making debugging easier when exceptions are thrown. #4749
    • Added debug checks to gcd() and lcm() for precondition violations. #4776
    • Added "lifetimebound" attributes to min, max, clamp, ranges::min, ranges::max, and ranges::clamp, allowing MSVC code analysis and Clang -Wdangling to detect dangling references in improper usage. #4838
    • Updated the precondition check in vector::pop_back() to be guarded by _CONTAINER_DEBUG_LEVEL. #4849
    • Renamed the parameters of views::iota and views::repeat to provide better IDE guidance. #4908
    • Simplified internal locale facet machinery to use class-specific operator new and operator delete overloads in both release and debug mode. #4916
  • Improved debugger visualization:
    • Inserted the debug visualizer changes from #3848, #4274, #4835, and #4836 in the VS repo so they'll finally ship.
  • Improved test coverage:
    • Updated LLVM-derived test coverage for <any>, <optional>, and <variant>. #4713
    • Properly tested the resolution of LWG-4053 "Unary call to std::views::repeat does not decay the argument". #4748
    • Improved the benchmarks for bitset::to_string(). #4817
    • Updated our LLVM submodule, including new tests. #4862 #4910
    • Re-enabled tests that were previously skipped in the libcxx test suite. #4721 #4732 #4911
    • Skipped tests that were sporadically failing due to incorrect timing assumptions. #4885
    • Added compiler bug workarounds. #4895
    • Tested the resolution of LWG-4105 "ranges::ends_with's Returns misses difference casting". #4897
    • Updated tests to work with Clang 19. #4912
    • Avoided unnecessary usage of rand(), which is considered harmful. #4921
  • Code cleanups:
    • Removed compiler bug workarounds. #4725 #4782 #4889
    • Various cleanups (described in detail in the PRs, not repeated here). #4724 #4900 #4920
    • Replaced SFINAE with concepts in C++20-and-later code. #4718 #4819
    • Removed a significant amount of unused code calling GetCurrentPackageId. #4742
    • Simplified how ranges::equal compares sizes. #4864
  • Reverted change:
    • Removed then temporarily restored support for targeting Windows 7 and Server 2008 R2. This will be permanently removed in the future. #4742 #4857
  • Infrastructure improvements:
    • The STL now clearly rejects attempts to:
      • Build a preset whose architecture doesn't match the compiler command prompt. #4709
      • Test a build whose architecture doesn't match the compiler command prompt. #4717
    • Updated dependencies. #4725 #4824 #4889
      • Updated build compiler to VS 2022 17.12 Preview 1 (and 17.11 is now required).
      • Updated CMake to 3.29 (now required).
      • Updated Ninja to 1.12.1.
      • Updated Python to 3.12.5.
      • Updated Google Benchmark to 1.8.5. #4851
  • Build system improvements:
    • Added /Zc:preprocessor to build the STL with the conformant preprocessor. #4886
    • Improved how CMake searches for the clang-format executable. #4888
  • Updated _MSVC_STL_UPDATE. #4706 #4708 #4754 #4872

VS 2022 17.11

  • Merged C++26 features:
  • Merged partial C++23 features:
  • 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 newer instructions in codepaths that previously restricted themselves to SSE2.
    • Added precondition checking in debug mode to:
      • views::take. #4551
      • The iota_view(first, last) constructor. #4616
    • Improved the wording of [[nodiscard("reason")]] messages for empty(). #4572
    • Extended C++20's static_assert(is_clock_v<Clock>) enforcement for various codepaths to C++14/17 (with internal machinery; is_clock_v itself remains guarded by C++20 mode). #4585
    • Changed the internal constructors of basic_format_arg::handle and basic_format_context to be private. #4489
    • Deprecation warnings for several non-Standard extensions are now emitted in all Standard modes, not just C++17 and later. These extensions will be removed in the future; you have been warned: #4605
      • stdext::checked_array_iterator, stdext::make_checked_array_iterator(), stdext::unchecked_array_iterator, and stdext::make_unchecked_array_iterator().
      • basic_istream's ipfx()/isfx() and basic_ostream's opfx()/osfx() member functions.
      • discard_block, linear_congruential, mersenne_twister, subtract_with_carry, uniform_int, and uniform_real.
  • Removed non-Standard code:
    • Deleted the <cvt/meow> subdirectory of headers, shrinking VS installations by 4.8 MB across 78 files. #4458
    • Deleted the <experimental/meow> headers that provided std::experimental::erase()/erase_if(). #4470
    • Removed the non-Standard _FPOSOFF macro and the non-Standard std::fpos::seekpos() member function. #4606
    • Removed the non-Standard lower_bound()/upper_bound() member functions from the unordered associative containers. #4607
  • Improved test coverage:
    • Added benchmarks for vectorized swap_ranges(). #4589
    • Added a workaround for an ASan failure in an ancient STL test. #4652
    • Reduced the execution time of the vectorized algorithms test by using the result of mismatch() when testing lexicographical_compare() and lexicographical_compare_three_way(). #4656
    • Improved the <filesystem> test, including its coverage of rename() and how it generates names for temporary files and directories. #4665
    • Re-enabled tests that were previously skipped in the libcxx test suite. #4698
    • Updated our LLVM submodule, including new tests. #4702
  • Code cleanups:
    • Removed compiler bug workarounds. #4475 #4576
    • Various cleanups (described in detail in the PRs, not repeated here). #4465 #4490 #4493
    • Improved the script for downloading Unicode data files when updating <format>. #4469
    • Consistently centralized how algorithms invoke their vectorized implementations. #4544
    • Simplified how condition_variable is implemented as a wrapper around the Windows API CONDITION_VARIABLE. #4545
    • Removed inline from constexpr variable templates. #4546
      • This became possible after all of our supported compilers implemented CWG-2387. Note that for constexpr variables, only primary templates and partial specializations no longer need to be marked as inline; explicit specializations and ordinary non-templates still need to be marked as inline.
    • Changed machinery for updating chrono::tzdb::version to activate the Named Return Value Optimization. #4577
    • Updated tests to use C++17 terse static_assert. #4588
    • Simplified function templates to use static_assert(false) as permitted by CWG-2518. #4591
    • Simplified debug checks for comparison function objects by using if constexpr. #4610
    • Simplified char_traits::assign() by removing unnecessary codepaths for constant evaluation. #4613
    • Changed checks for damaged logic in the STL itself to use internal static_assert macros, which expand to nothing outside of the STL's test suites. #4624
    • Simplified ranges::stable_sort to use iter_value_t instead of an internal helper. #4628
    • Changed the STL to use in_range<T>() more and numeric_limits<T>::min()/max() less. #4634
    • Replaced SFINAE with concepts in C++20-and-later code. #4637
    • Simplified the vectorized implementation of the minmax() family for 64-bit elements. #4661
    • Modernized our usage of Google Benchmark. #4662
  • Infrastructure improvements:
    • Overhauled our Azure Pipelines machinery: #4594 #4687
      • Introduced "Early Build" stages to quickly find compiler errors when building the STL.
      • Improved the reliability of the submodule checkout task.
      • Improved how clang-format diffs are uploaded and logged.
    • Updated dependencies. #4475 #4492 #4576 #4568 #4594 #4687
      • Updated build compiler to VS 2022 17.11 Preview 1.
      • Updated to Windows 11 SDK 22621. This is now required for building and testing the STL, but not for using it.
      • Updated CUDA to 12.4.0 (now required).
      • Updated Python to 3.12.3.
      • Updated Boost.Math to 1.85.0. #4599
      • Updated Google Benchmark to 1.8.4. #4694
  • Updated _MSVC_STL_UPDATE. #4467 #4556 #4655

VS 2022 17.10

  • Merged C++26 features:
  • Merged C++23 Defect Reports:
    • 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:
  • 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 floating-point to_chars() on ARM64 to return correct results. #4304
    • Fixed compiler errors when defining variadic alias templates for is_nothrow_convertible. #4318
    • Fixed filesystem::is_empty() and filesystem::directory_iterator to handle empty volumes (before they've been assigned a drive letter). #4311
    • Fixed compiler errors in algorithms involving highly unusual types. #4233 #4419
    • Fixed basic_stringbuf to avoid implementing moving with swapping, which is a correctness issue for unusual custom allocators. #4239
    • Fixed deque::shrink_to_fit() to follow the Standard instead of unconditionally moving elements. #4091
    • Fixed allocate_shared_for_overwrite() to directly destroy objects, instead of using Alloc::destroy(). #4274
    • Removed ios_base::hexfloat, a non-Standard bitmask element. #4345
      • The Standard ways to request hexadecimal floating-point output are to use the ios_base::fixed | ios_base::scientific bitmask elements together or to use the std::hexfloat manipulator.
    • Fixed std.ixx to export VCRuntime machinery with Standard-conforming techniques. #4375
      • This affects things like std::exception, std::type_info, and ::operator new. The MSVC compiler currently doesn't enforce the rule in question here, but stricter tools might notice this.
    • Fixed basic_ostream::operator<<(basic_streambuf*) to rethrow caught exceptions only when failbit is set in exceptions(). #4372
    • Fixed unordered_map and unordered_set's equality operators to test elements for equality (via their operator==), not just equivalence (via the container's predicate for keys). #4406
      • unordered_multimap and unordered_multiset already behaved correctly.
    • Silenced "warning C4324: structure was padded due to alignment specifier" in all STL headers. #4426
      • This was spuriously emitted by certain combinations of code, e.g. views::cartesian_product with views::filter.
    • Fixed time_get::date_order() to correctly return time_base::mdy for the "C" locale, instead of picking up the date order for the current user locale. #4437
    • Fixed seed_seq::generate(RanIt, RanIt) to static_assert that the iterator's value type is at least a 32-bit unsigned integer type. #4447
    • Fixed compiler errors involving incomplete types in:
      • Non-modifying algorithms. #4138
      • erase(), erase_if(), remove(), remove_if(). #4217
      • [alg.min.max], [alg.clamp], [alg.lex.comparison], [alg.three.way] algorithms. #4216
      • atomic and atomic_ref. #4221
      • Modifying algorithms. #4256
      • Container operations taking iterator pairs. #4258
      • is_nothrow_convertible. #4318
      • Comparison operators. #4334
      • Merge algorithms, set operations, heap operations, and permutation generators. #4347
      • Sorting and related algorithms. #4367
      • vector's destructor and other member functions. #4373
      • Uninitialized memory algorithms. #4374
      • default_searcher. #4379
      • <ranges> views. #4389
      • Numeric algorithms. #4391
      • ranges::advance, ranges::distance, span constructors, and condition_variable::wait_for. #4402
      • shared_ptr creation functions and atomic smart pointers. #4403
      • function, move_only_function, packaged_task, promise, and optional. #4430
  • Improved performance:
    • Improved <atomic> performance: #4222
      • For ARM64, significantly improved the performance of atomic<T>::load() (taking no arguments, requesting sequential consistency), matching how #3399 in VS 2022 17.6 improved atomic<T>::load(memory_order_seq_cst).
      • For ARM64 CHPE (_M_HYBRID_X86_ARM64), atomic<T>'s exchange/compare_exchange_MEOW/fetch_MEOW now respect memory_order arguments instead of always providing sequential consistency. Also, ARM64 CHPE now benefits from all of #3399's major improvements.
    • Improved atomic::wait family performance by internally using memory_order_acq_rel instead of memory_order_seq_cst when initializing OS support functions. #4288
    • Slightly improved the codegen for uniform_int_distribution. #4234
    • Optimized filesystem::path's operator/ to perform a single memory allocation for common cases. #4136
    • Slightly improved performance by taking advantage of P1169R4 static operator() in the STL's stateless function objects and lambdas. #4358
      • This is conditional on compiler feature availability (currently implemented by Clang), but not on Standard mode. Like C++17 if constexpr and C++20 explicit(bool), compilers will support C++23 static operator() in earlier Standard modes (emitting warnings that Future Technology is being used, which the STL internally suppresses).
    • Added a vectorized implementation of bitset::to_string(). #3960 #4382 #4422
    • Improved the vectorized implementations of min_element(), max_element(), minmax_element(), and related algorithms:
      • Extended them to handle floating-point types. #3928
      • Further improved performance by restructuring control flow. #4401
    • Improved the vectorized implementations of ranges::min, ranges::max, ranges::minmax, and the min(), max(), and minmax() overloads for initializer_list. #4384
      • These algorithms only need to track values, not locations.
    • Changed the destructors of mutex and recursive_mutex to be trivial. #4390
      • This especially benefits variables with static storage duration, as they no longer need "dynamic atexit destructors".
    • Slightly improved performance by replacing CRITICAL_SECTION with SRWLOCK in:
      • get_new_handler() and set_new_handler(). #4407
      • At-thread-exit machinery. #4408
  • Enhanced behavior:
    • Wrapped the STL in extern "C++" as a temporary workaround to allow #include <meow> to coexist with import std; in the same translation unit, in that order. #4154
      • The other order, import std; before #include <meow>, will still cause compiler errors. We're working on a long-term solution.
    • The C++17 Standard added invoke() and the C++20 Standard made it constexpr. Previously, MSVC made non-constexpr invoke() unconditionally available, and constexpr invoke() available in C++17 mode, as minor extensions. Now, constexpr invoke() is unconditionally available. #4080
    • Improved shared_ptr constructor constraints to avoid forming invalid types. #4290
    • Updated <charconv> to use the __umulh intrinsic for ARM64 CHPE (_M_HYBRID_X86_ARM64). #4330
    • Improved expected's copy/move assignment operators to be trivial when possible, like how optional and variant already behave. #4271
    • Improved <random>'s TR1 legacy code: #4284
      • Deprecated the non-Standard engines (discard_block, linear_congruential, mersenne_twister, subtract_with_carry) and distributions (uniform_int, uniform_real) that are still provided in the std namespace.
      • Removed non-Standard machinery from Standard engines and distributions. (For example, certain static constexpr data members in mersenne_twister_engine and an extra function call operator overload in uniform_int_distribution.)
    • Changed basic_regex's constructor to throw an exception instead of stack overflowing when the pattern contains an excessive number of capture groups. #4451
      • Currently, this arbitrarily limits the number of capture groups to 1000.
  • Improved test coverage:
    • Updated the STL-ASan-CI pipeline. #4240 #4295
    • Added support for building the STL's separately compiled code with ASan instrumentation and enabled this in the STL-ASan-CI pipeline. #4313
    • Updated our LLVM submodule, including new tests. #4263 #4267 #4270 #4272 #4328 #4336 #4348 #4355
    • Minor test improvements, including printing exit codes in both decimal and hex. #4309
    • Improved output for "unresolved" test failures. #4323
    • Fixed sporadic "unresolved" test failures. #4366
    • Updated CTest to avoid running 2N tests in parallel, where N is the number of cores available. #4335
    • Enabled __cpp_lib_concepts for our command-line test coverage of the EDG compiler front-end. #4296 #4297 #4440
      • __cpp_lib_concepts was already enabled for EDG-powered IntelliSense in the VS IDE, so this change isn't directly observable by users, it'll just help the STL work better with IntelliSense in the future.
    • Enabled compiler warnings when building the STL's benchmarks. #4356
    • Added benchmarks for vectorized ranges::find and ranges::count. #4387
      • This also covers classic find() and count(), which share the same vectorized implementation.
    • Fixed the test harness to handle paths case-insensitively. #4395
    • Updated tests to work with Clang 18. #4452
    • Enabled more test coverage for the off-by-default warning C4668 "'MEOW' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'". #4441
  • Code cleanups:
    • Various cleanups (described in detail in the PRs, not repeated here). #4143 #4145 #4146 #4147 #4149 #4151 #4192 #4229 #4230 #4362 #4439 #4442 #4443 #4444 #4445
    • Removed unnecessary typename keywords in C++20 mode and later. #4191
    • Removed compiler bug workarounds. #4197 #4259 #4340 #4392
    • Removed an enormous amount of code that was dealing with __cpp_lib_concepts missing in C++20 mode. #4298 #4364
      • Now, the STL's product and test code assumes that concepts are always available in C++20 mode, with targeted workarounds for reported compiler bugs.
    • Unified our internal stringizing macros. #4405
    • Added top-level const to function parameters in the vectorized implementations of algorithms. #4410
    • Added a script to download Unicode data files when updating <format>. #4435
    • Simplified how we handle Unicode field widths when updating <format>. Now we use a single script to process all Unicode data files, emitting tables into a single generated header. #4446
    • Used if constexpr to simplify helper functions for allocating and deallocating memory. #4432
  • Infrastructure improvements:
    • Updated dependencies. #4197 #4206 #4259 #4303 #4392
      • Updated build compiler to VS 2022 17.10 Preview 1 (now required).
      • Updated CMake to 3.28 (now required).
      • Updated Clang to 17.0.3 (now required).
      • Updated Python to 3.12.2.
      • Updated Boost.Math to 1.84.0. #4280
  • Updated _MSVC_STL_UPDATE. #4213 #4226 #4293 #4361

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:
  • Improved documentation:
    • Improved the consistency of preprocessor comments. #3950
  • Infrastructure improvements:
    • Updated dependencies. #4028 #4039 #4083
      • Updated build compiler to VS 2022 17.8 Preview 3 (now required).
      • Updated CMake to 3.27 (now required).
      • Updated Python to 3.12.0 (now required).
      • Updated Google Benchmark to 1.8.3. #4021
  • Updated _MSVC_STL_UPDATE. #4003 #4062

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:
  • 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
      • Constructors of locale::facet and related base classes. #3855
      • Many functions in <complex>. #3880
      • Many functions in <random>, some functions in <valarray>, and 3-arg hypot() in <cmath>. #3887
    • The STL now avoids conflicting with non-Standard macros of reserved names that were defined by old versions of the ICU library. #3776
    • Updated stdext::checked_array_iterator and stdext::unchecked_array_iterator: #3818
      • Added constness conversions.
      • Deprecated these iterators, which have been superseded by std::span and gsl::span.
    • Added "lifetimebound" attributes to minmax and ranges::minmax, allowing MSVC code analysis and Clang -Wdangling to detect dangling references in improper usage. #3831
    • Improved how views::cartesian_product detects ranges with maximum sizes that are known at compile time. #3839
    • Improved how parallel algorithms perform compile-time iterator type checking. #3899
    • The STL now calls abort() instead of terminate() for unrecoverable conditions, when the Standard doesn't require terminate() to be called. #3906 #3909
    • Improved the visualizer for vector<char> and the other character types. #3772
    • Improved the visualizer for mutex and recursive_mutex. #3848
    • Updated chrono::duration_cast() to use if constexpr, improving debug codegen. #3958
  • Improved test coverage:
    • Added properly functioning test coverage for ranges::owning_view. #3753
    • Added test coverage for calling tellg() while reading an LF file in text mode. #3773 #3841
    • Added test coverage for LWG-2295 Locale name when the provided Facet is a nullptr. #3823
    • Added test coverage for LWG-2682 filesystem::copy() won't create a symlink to a directory. #3827
    • Updated tests to use lvalue references for the LHS of is_assignable_v and is_nothrow_assignable_v. #3898
    • Added more tests for views::as_const, views::stride, and views::zip. #3920
    • Test code now consistently uses override to avoid mistakes, following the same convention as product code. #3934
    • Fixed precondition violations in is_permutation() tests. #3967
    • Fixed precondition violations in regex_iterator and regex_token_iterator tests. #3990
  • Code cleanups:
    • Removed compiler bug workarounds. #3722 #3769 #3866 #3939
    • Improved SFINAE to follow modern conventions. #3736
    • Various cleanups (described in detail in the PRs, not repeated here). #3758 #3759 #3765 #3768 #3912 #3927 #3935
    • Removed comments that were citing proposed resolutions for LWG issues, now that those issues have been officially resolved by the June 2023 meeting. #3784 #3785
    • Marked internal machinery as [[noreturn]]. #3865 #3882
    • Removed unnecessary typename keywords in C++20 mode and later. #3892 #3893 #3894
    • Improved type safety by using an enum class for internal machinery within <condition_variable>, <mutex>, and <thread>. #3897
    • Improved the consistency of code that should never be called. #3905
    • Removed unused code. #3936
    • Improved the clarity and maintainability of basic_string's implementation. #3862
    • Deprecated the non-standard <cvt/meow> headers and their provided character encoding conversion machinery. #3924
  • Improved documentation:
    • Added comments where the Standard requires terminate() to be called. #3907
    • Improved the consistency of preprocessor comments. #3900 #3951
  • Infrastructure improvements:
    • Modernized code format validation to use <print>. #3919
    • Updated dependencies. #3769 #3866 #3939
      • Updated build compiler to VS 2022 17.8 Preview 1.
      • Updated Boost.Math to 1.83.0. #3952
      • Updated Clang to 16.0.5.
      • Updated Python to 3.11.4.
  • Build system improvements:
    • Added CMakePresets.json to simplify the process of building the repo. #3730 #3930
  • Updated _MSVC_STL_UPDATE. #3742 #3851 #3918

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
    • Fixed compiler errors when importing the Standard Library Modules and calling typeid(T).name(). #3677
    • Fixed some nasty corner cases in cartesian_product_view. #3678
    • Fixed some issues with parsing numbers with grouping separators. #3684
    • Fixed a bug that could result in unordered_meow containers allocating too few buckets. #3687
  • Improved performance:
    • Slightly optimized mutex and recursive_mutex construction by avoiding a Windows API call. #3522
    • Slightly optimized unique_ptr move assignment by avoiding an unnecessary branch. #3540
    • Optimized chrono::time_zone::to_sys and chrono::time_zone::to_local, with a speedup of approximately 3x (times, not percent). #3579
    • Optimized type_index::operator<=> to avoid calling the comparison function twice. #3600
    • Inserted the VZEROUPPER instruction at the end of every AVX2 codepath in the STL's vectorized algorithms, improving performance in non-optimized debug mode when the compiler doesn't automatically insert this instruction. #3630
    • Optimized the constructors system_error(error_code) and system_error(int, const error_category&). #3635
  • Improved throughput:
    • <optional> and <variant> now include fewer headers. #3624
    • Moved internal machinery into <regex> where it's needed. #3625
    • C++20 <chrono> now avoids including <algorithm>. #3626
    • <compare> now avoids including <bit>. #3627
    • Refactored a central internal header so that the rest of the STL includes fewer headers and provides less machinery beyond what's required. #3623 #3654
      • Common source-breaking impact:
        • Need to include <cstdlib> for exit, quick_exit, etc.
        • Need to include <initializer_list> for initializer_list.
          • Sometimes initializer_list is used implicitly when only braces appear in the source code.
        • Need to include <functional> for unary_function and binary_function.
          • Note that unary_function and binary_function were deprecated in C++11 and removed in C++17, so it's best to stop using them completely.
      • Uncommon source-breaking impact:
        • Need to include <memory> for addressof.
        • Need to include <functional> for less, less_equal, greater, greater_equal, equal_to, not_equal_to, plus, minus, and multiplies.
    • When the STL needs to call swap via Argument-Dependent Lookup, it now does so directly; the internal helper function _Swap_adl has been removed. #3700
  • Enhanced behavior:
    • Silenced CodeQL warnings. #3489 #3585
    • Silenced occurrences (in bitset::reference and test code) of MSVC's new off-by-default warning C5267 for deprecated implicit copy constructors/assignment operators. #3497
    • Enabled <source_location> for Clang. #3584
    • Removed the non-Standard xtime type from <chrono>. #3594
    • Added static_asserts to containers, container adaptors, and allocator to improve the error messages when they're given non-object types. #2436 #3660
      • allocator<void> is still permitted as a special case.
  • Improved test coverage:
    • Added test coverage with Clang/LLVM's Undefined Behavior Sanitizer (UBSan). #3452
    • Added more tests for views::empty, views::iota, views::istream, views::repeat, and views::single. #3553
    • Fixed nonconformant code in the test for Standard Library Header Units and Modules. #3588
    • Added test coverage for C++23's customization point objects. #3610
    • Added more tests for ranges::ref_view, ranges::subrange, views::common, views::filter, views::join, views::reverse, and views::transform. #3612
  • Code cleanups:
  • Improved documentation:
    • Added documentation about the STL's import library. #2141
  • Infrastructure improvements:
    • The internal test runner now understands compile-only tests and libcxx/expected_results.txt. Consequently, (1) compile-only tests (test.compile.pass.cpp) no longer need a redundant int main() {} // COMPILE-ONLY, and (2) we no longer need to redundantly update libcxx/skipped_tests.txt (which has been removed) identically to libcxx/expected_results.txt. #3484
    • Enforced the usage of only core headers when building the STL's import library. #3621
    • Updated dependencies. #3490 #3651 #3711
      • Updated build compiler to VS 2022 17.7 Preview 1 (17.6 now required).
      • Updated Clang to 16.0.1 (now required).
      • Updated CMake to 3.26.0 (now required).
      • Updated Python to 3.11.3.
      • Updated Boost.Math to 1.82.0. #3657
  • Updated _MSVC_STL_UPDATE. #3518 #3643 #3680

VS 2022 17.6

  • Merged C++23 features:
  • Merged partial C++23 features:
    • P2165R4 Compatibility Between tuple, pair, And tuple-like Objects:
    • 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
    • Added compiler bug workarounds:
      • For Clang in <expected>. #3326
      • For Clang in <ranges>. #3328
      • For MSVC modules in <filesystem>. #3331
    • Fixed constexpr basic_string to correctly start the lifetimes of its elements, avoiding compiler errors. #3334
    • Fixed views::istream constraints to precisely follow the Standard. #3335
    • Implemented C++17's parallel specialized <memory> algorithms. #3145
      • These were mistakenly omitted when P0040R3 Extending Memory Management Tools and P0024R2 Parallel Algorithms were implemented (in VS 2017 15.3 and 15.7, respectively).
    • Fixed vector<bool, Alloc> on 32-bit platforms with 64-bit difference_types to support storing more than 232 bits. #3342
    • Fixed a compiler error when calling ranges::prev on an iota_view iterator in debug mode. #3356
    • Fixed ranges::minmax to avoid moving from an element twice when called with a single-element range of move_iterators. #3366
    • Fixed a minor conformance issue in the std.ixx Standard Library Module. #3373
      • When module; introduces a global module fragment, it is required to be the first thing in the file other than comments, although MSVC doesn't enforce this rule yet.
    • Changed the STL's usage of a compiler-specific custom attribute to defend against macros. #3380
    • Fixed Clang -Wdeprecated warnings that said "out-of-line definition of constexpr static data member is redundant in C++17 and is deprecated". #3381
    • Changed vformat_to() to instantiate its machinery in a lazier way. #3403
      • When merely including <format> or <chrono>, this avoids instantiating dynamic initializers for facet IDs, and improves throughput slightly.
  • Improved performance:
    • Avoided constructing unnecessary strings in locale::operator==(). #3250
    • Activated count()'s vectorized implementation for more eligible iterators in C++14/17 modes. #3262
    • Activated the vectorized implementations of find(), count(), ranges::find(), and ranges::count() for more scenarios involving pointer elements. #3267
    • Optimized <atomic> for ARM64, massively improving load-acquire and store-release (measured 14.1x to 23.8x speedups - times, not percent) and significantly improving sequentially consistent stores (measured 1.58x speedup). #3399
    • ranges::find now calls memchr() in more situations (when the vectorized implementation isn't available). #3386
  • Improved throughput:
    • Moved user-defined literals for the STL's internal 128-bit integer-class types from product code to test code. #3252
    • Removed unnecessary operator== and operator!= overloads for internal types in C++20 mode. #3256
    • Used if constexpr instead of overloads in internal machinery. #3389
  • Enhanced behavior:
    • The STL now supports /clr for C++11 multithreading (mutex, condition_variable, future, etc.) and C++17 parallel algorithms. Additionally, the STL now allows /clr to be used in C++20 mode. #3194 #3201
      • See tracking issue #3193 for a list of compiler bugs that affect these newly enabled /clr scenarios.
    • Added visualizers for error_category and error_code. #3204
    • Improved the output of source_location::function_name(). #3206
      • For example, it now returns "int __cdecl square(int)" instead of "square".
    • When iterator debugging detects bogus usage of an invalidated vector iterator, it now displays an assertion message instead of abruptly crashing. #3282
    • Changed <mutex> to use scope guards instead of throw;, making debugging easier when exceptions are thrown. #3321
    • Strengthened the exception specifications for:
      • mutex::unlock(), recursive_mutex::unlock(), and unique_lock's move assignment operator. #3321
      • Various member functions and swap() overloads for stream types. #3314
      • Various non-member and member functions in <condition_variable>, <mutex>, <shared_mutex>, and <thread>. #3388
    • Added modules/modules.json to support build systems. #3358 #3488
    • Refactored ranges::minmax and ranges::minmax_element to detect the single-element case naturally. #3384
    • Changed the STL's user-defined literals to be consistently defined as operator""meow without a space, because CWG-2521 is deprecating the form operator"" woof with a space. #3453
  • Improved documentation:
    • Clarified the error message when including the internal header <__msvc_cxx_stdatomic.hpp> in C mode. #3192
  • Improved test coverage:
    • Enabled <stdatomic.h> test coverage for Clang. #3186
    • Updated the modules tests after a compiler bugfix for source_location. #3339
    • Added more tests for views::elements. #3350
    • Updated our LLVM submodule reference, including new tests. #3344 #3357
    • Added more tests for views::drop, views::drop_while, views::take, and views::take_while. #3390
  • Code cleanups:
    • Removed compiler bug workarounds. #3202 #3288 #3351 #3350
    • Removed comments that were citing proposed resolutions for LWG issues, now that those issues have been officially resolved by the November 2022 and February 2023 meetings. #3238 #3461
    • Improved consistency in preprocessor comments. #3208
    • Simplified a line in experimental::filesystem::recursive_directory_iterator::operator++(). #3279
    • Various cleanups (described in detail in the PRs, not repeated here). #3293 #3300
    • Removed unused internal machinery. #3299
    • Simplified types by defaulting some of their special member functions:
      • promise and packaged_task. #3315
      • shared_mutex, shared_timed_mutex, and shared_lock. #3352
    • Changed more temporary objects to be constructed with braces instead of parentheses. #3277
    • Updated comments after a compiler bug was fixed. #3394
    • Updated tests and separately compiled sources to directly use the [[nodiscard]] attribute. #3397
    • Updated notes for skipped tests in the libcxx test suite. #3464
  • Infrastructure improvements:
    • Added GitHub Actions to automatically add PR cards to the Code Reviews project. #3393
    • Fixed the build system to properly pass options when assembling the "alias objects". #3402
    • Updated dependencies. #3202 #3288 #3340 #3351 #3467
      • Updated build compiler to VS 2022 17.5 Preview 6 (now required).
      • Updated CMake to 3.25 (now required).
      • Updated Python to 3.11.2.
      • Updated Boost.Math to 1.81.0. #3312
  • Updated _MSVC_STL_UPDATE. #3191 #3264 #3362 #3395

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:
  • 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.
    • Removed std::filesystem::directory_entry::clear_cache(), which was a non-Standard extension. #2854
    • Fixed incorrect results from <complex> log()/log10()/pow() on ARM64. #2870
    • Fixed path::lexically_relative() to handle UNC drive paths like \\?\C:\meow.txt. #2867
    • Fixed filesystem::read_symlink() and filesystem::copy() to handle junctions. #2877
    • Fixed compiler errors in ranges::uninitialized_copy_n and ranges::uninitialized_move_n with certain input iterators. #2964
    • Fixed ranges::enable_view to properly reject references and to avoid compiler errors in certain unusual situations. #2978
    • Temporarily disabled ASan (Address Sanitizer) annotations in <string> while significant bugs are under investigation. #2990
    • Fixed compiler errors in views::chunk_by with unusual predicates returning non-bool types. #2890
    • Fixed compiler errors in visit<R>() involving conversions to immovable types. #2971 #2999
    • Fixed compiler errors in chrono::abs() in certain unusual situations. #2988
    • Fixed <format> to always print NaNs as "nan", "-nan", or uppercase versions as required by the Standard, never "-nan(ind)". #3001
    • Fixed ranges::shuffle and ranges::sample to accept uniform_random_bit_generators that don't provide result_type. #3002
    • Fixed vector<bool>::insert(where, first, last) and vector<bool>::insert_range(where, range) to meet the Standard's complexity requirements. #3021
    • Fixed how chunk_view and stride_view iterators validate their preconditions. #3023
    • Fixed a compiler warning emitted by the unusual scenario of basic_string_view<char_like_struct>. #3032
    • Fixed move_only_function to behave correctly when passed between DLLs. #3038
    • Fixed compiler errors when dllexporting classes derived from pair or tuple. #3045
      • This fixed a regression that was introduced by #2687 implementing P2321R2's changes to pair and tuple in VS 2022 17.3.
    • Fixed <regex> integer overflows when parsing huge numbers in backreferences, braced repetitions, and decimal escapes. #2169
      • These will now properly throw regex_errors with codes of error_backref, error_badbrace, and error_escape, respectively.
    • Fixed ranges::distance to follow the Standard, which depicts two overloads (for sized and unsized sentinels). #2987
    • Overhauled how the STL unwraps iterators and sentinels, fixing various issues. #3024
    • basic_string::substr() now uses a default-constructed allocator as required by the Standard. #3057
    • Fixed CUDA compiler errors with std::_Bit_cast by using __builtin_bit_cast instead of a memcpy workaround. #3066
  • Improved performance:
    • Improved clamp() codegen with conditional move instructions. #2336
    • Massively improved iostreams performance for signed char, unsigned char, char8_t, and byte elements, matching the performance of char by avoiding a slow codepath. #2739
    • vector's range constructor, insert(), and assign() now efficiently handle iterators that satisfy the forward_iterator concept, even when their classic iterator_category isn't convertible to forward_iterator_tag. #1794
    • Reduced the size of the lookup tables used for <format> grapheme clusterization, saving 2670 bytes. #2757
    • std::filesystem::path::lexically_relative() now avoids unnecessary memory allocations. #1915
    • Added vectorized implementations of min_element(), max_element(), minmax_element(), ranges::min_element(), ranges::max_element(), and ranges::minmax_element(), with speedups ranging from 1.5x to 26.6x (times, not percent). #2447 #2821 #2825
    • Reduced binary size for programs using atomic::wait. #2781
    • Avoided an unnecessary OS call in thread::join(). #2820
    • VS 2022 doesn't support targeting Windows Vista and Server 2008, but the STL still had runtime branches for those unsupported OSes. We've removed that code to improve performance, notably in mutex::try_lock(). #2317
      • The STL still supports targeting Windows 7 and Server 2008 R2.
    • Removed more unused code for Windows XP/Vista, reducing the size of the STL's DLL by 2 KB, and reducing the number of OS calls during STL startup. #2841
    • Reduced the number of OS calls in filesystem::resize_file() and experimental::filesystem::resize_file(). #2771
    • Improved the optimized codegen for T + complex<T>, T * complex<T>, complex<T> * T, and complex<T> / T. Improved the debug codegen for complex<T> + T and complex<T> - T. #2855
    • Improved the optimized codegen for unreachable(). #3055
  • Improved throughput:
    • Used if constexpr instead of tag dispatch in:
      • get<I>() and get<T>() for pair. #2756
    • optional, pair, and tuple now use conditional explicit instead of SFINAE in all Standard modes, for all supported compilers. #2796
    • The STL now uses "hidden friends" for all operators that are required to exist but aren't required to be namespace-scope functions (e.g. n + vector::iterator). This improves throughput by not polluting unqualified name lookup. #2797
    • <charconv>'s large lookup tables are now separately compiled, so translation units including <charconv> will emit significantly smaller object files. #2125
    • The STL now uses helper function templates for testing bitmask types, replacing a significant number of function overloads. #2865
    • <unordered_map> and <unordered_set> now avoid including most of <string>. #2996
      • This also improves throughput for <functional>, which internally uses <unordered_map> to implement boyer_moore_searcher.
      • Escape hatch: define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS. #3027
    • <functional> now avoids including <memory>. #2998
      • Escape hatch: define _LEGACY_CODE_ASSUMES_FUNCTIONAL_INCLUDES_MEMORY. #3027
  • Enhanced behavior:
    • <tuple> is now a core header. #2730
    • The STL now supports enabling C++20 char8_t in C++14 and C++17 modes via /Zc:char8_t. #2748
    • complex<NonFloating> now emits a deprecation warning explaining that it has unspecified behavior according to the Standard. #2759
    • When wchar_t is a real type, the STL now avoids emitting many specializations for unsigned short that are intended for fake wchar_t only (i.e. the non-Standard /Zc:wchar_t- option). #2164
    • The STL now marks all of its namespace-scope constexpr variables as inline in C++17-and-later mode. #2792
      • This consistency improvement will also avoid emitting a new compiler warning that MSVC is implementing for C++20 header units: "warning C5260: the constant variable 'std::_Meow' has internal linkage in an included header file context, but external linkage in imported header unit context; consider declaring it 'inline' as well if it will be shared across translation units, or 'static' to express intent to use it local to this translation unit".
    • constexpr basic_string now uses the Small String Optimization. #1735
    • error_codes with 0 values and future_category or iostream_category now return "success" from message(), matching the behavior of generic_category. #2742
    • <system_error> now maps: #2744 #2899
      • WAIT_TIMEOUT, ERROR_TIMEOUT, and ERROR_SEM_TIMEOUT to errc::timed_out
      • ERROR_BAD_NET_NAME to errc::no_such_file_or_directory
      • ERROR_FILENAME_EXCED_RANGE to errc::filename_too_long
    • Added visualizers for unique_ptrs and vectors storing character sequences. #2843
    • Added more visualizers for <any>, <format>, <functional>, <mutex>, and <ranges>. #2191
    • <cstdlib> now makes its using-declarations for std::getenv() and std::system() available to UWP apps. #2850
    • <filesystem> and <experimental/filesystem> now use GetTempPath2W() when it's available on Windows 11. #2302
      • This is a security improvement for processes running as SYSTEM; there's no behavioral change for ordinary processes.
      • Follow-up: Fixed linker errors involving _Init_locks::operator= in unusual situations. #3011
    • Added a couple of warning numbers for easier lookup: #2061
      • STL4038 warns "The contents of <meow> are available only with C++NN or later."
      • STL4039 warns "The contents of <coroutine> are not available with /await."
    • <unordered_map> and <unordered_set> no longer provide a non-Standard hash_compare class template in namespace std. #2996
    • Improved how STL error messages (like "Unexpected compiler version") are displayed. #2897
    • Further improved how STL warnings and errors are displayed. #2973
    • Added explanations to the STL's [[nodiscard]] warnings, when the compiler supports [[nodiscard("message")]] and the reason is more complex than the common/simple scenario of pure observers. #2211
      • For example, discarding the return value of std::remove_if() now emits a detailed warning message, explaining the classic erase-remove idiom, and suggesting C++20 std::erase_if() instead.
    • vector::assign(num, val) and std::swap_ranges() now have debug checks for forbidden aliasing. #1263
    • Strengthened exception specifications on:
      • Iterator machinery. #1347 #2991
      • <optional> and the classic comparison function objects (less<T>, equal_to<T>, etc.). #1937 #3041
    • Added support for defining _ENFORCE_ONLY_CORE_HEADERS, limiting STL usage to the subset of core headers. #2068
    • Updated the STL's internal 128-bit integer-class types for C++14/17 compatibility, which will be useful for future performance work. #3036
  • Improved test coverage:
    • Enabled tests now that Clang 14 supports <coroutine>. #2861
    • Slightly accelerated test runs by running memory leak tests with only debug configurations (where memory leak tracking is available). #2853
    • Fixed a test that failed at runtime on ARM64. #2864
    • Added /permissive configurations to tests that can successfully compile in this discouraged-but-supported mode. #3015
    • Taught VSCode's Python extension where to find our test support machinery. #3040
    • Updated the <source_location> test for an upcoming compiler fix. #3046
    • Added test coverage for a <string> bug (specific to ASan annotations being enabled) that was fixed. #3039
  • Code cleanups:
    • Removed compiler bug workarounds. #2791 #2861
    • Various cleanups (described in detail in the PRs, not repeated here). #2798 #2801 #2802 #2815 #2766 #2828 #2863 #2950 #3019
    • Removed visualizers for VS 2013's binary-incompatible representations of various data structures. #2804
    • Simplified tuple_cat()'s implementation. #2833
    • Improved how <system_error> maps Windows error codes to errc values. #2837
    • Refactored <atomic> to share code with C11 atomics (work in progress). #2846
    • Updated most files (with limited exceptions) to consistently include the <cmeow> wrapper headers instead of the <meow.h> CRT headers. #2852
    • Simplified <random>'s static constexpr data members. #3006
    • Finished changing all aliases from typedef to using. #3018
    • Cleaned up several tests to avoid unnecessary dependencies on macros and non-Standard code. #3034
    • Updated <functional> and <memory> to consistently use modern int = 0 SFINAE. #2124
    • Cleaned up feature-test macro usage to be simpler and more consistent. #3053
  • Improved documentation:
    • Added a comment explaining why basic_string doesn't use templated static constexpr data members as internal helpers. #2980
  • Infrastructure improvements:
    • Eliminated duplicate builds of the "alias objects". #2743
    • Fixed distributed test runs to split up the test suite deterministically, avoiding missed or repeated tests. #2795
    • Properly applied /analyze to PR/CI builds, and fixed warnings in the STL's separately compiled sources. #2812
    • Fixed cross-PR/CI contamination by cleaning both before and after checkout. #2832
    • Fixed cross-PR/CI contamination by ignoring submodules during code format validation. #3033
    • Added support for writing benchmarks with google/benchmark. #2780
    • The PR/CI system now uses "1ES Hosted Pools". #3054
    • Updated dependencies. #2754 #2791 #2831 #2861 #3017
      • Updated build compiler to VS 2022 17.4 Preview 1 (now required).
      • Updated Clang to 14.0.5 (now required).
      • Updated CMake to 3.23 (now required).
      • Updated Ninja to 1.11.0.
      • Updated Python to 3.10.6.
      • Updated CUDA to 11.6.0 (now required).
  • Updated _MSVC_STL_UPDATE. #2764 #2840 #3020

VS 2022 17.3

  • Merged C++23 features:
  • 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 throw;, making debugging easier when exceptions are thrown. #2308
    • Merged an MSVC-specific attribute, allowing the compiler to improve its handling of constexpr dynamic allocation and constexpr unique_ptr. #2658
    • Implemented <format> grapheme clusterization when determining the width of a string for padding and alignment purposes. This is a "quality of implementation" feature recommended by N4910 [format.string.std]/11. #2119
    • Changed <strstream> to deprecate its classes instead of the entire header. #2680
    • C++98's unexpected() in <exception> was removed by C++17. As with almost all removals, we support an escape hatch to restore unexpected(), by defining _HAS_UNEXPECTED to 1. However, this escape hatch conflicts with C++23, which is reusing the identifier for unexpected<E> in <expected>. Therefore, the escape hatch is now blocked with an #error in C++23 mode. #2709
    • Added ASan (Address Sanitizer) annotations to <string>, allowing additional errors to be detected. #2196
    • <ciso646> now emits a warning in C++20 mode, as it was removed in that Standard. #2710
    • Temporarily disabled join_view for non-forward_ranges until LWG-3698 is resolved. #2727
    • <random> distributions now have non-const function call operators, making it easier to write portable code. #2732
  • Improved documentation:
    • Added comments to the test suite citing GitHub issues and LWG issues. #2433
    • Expanded a comment about the build system's use of /Os. #2708
  • Improved test coverage:
    • Dramatically improved the compiler memory consumption and compile time of two ranges algorithm tests. #2657
    • Removed /Za test coverage. #2714
  • Code cleanups:
    • Removed compiler bug workarounds. #2611
    • Various cleanups (described in detail in the PRs, not repeated here). #2595 #2621 #2656 #2673 #2674 #2675 #2676 #2678 #2679 #2686
    • Simplified the preprocessor logic in <stdatomic.h> for non-compiler tools. #2615
    • Removed test workarounds now that VCRuntime properly recognizes Clang's /std:c++20 and /std:c++latest modes. #2637
  • Infrastructure improvements:
    • Fixed the build system to avoid relinking any DLLs when rerunning CMake and Ninja with no other changes. #2606
    • Added format and validate targets to CMake, so it can run clang-format in parallel, and improved how Azure Pipelines runs the Code Format Validation check. #2671 #2697
    • Updated dependencies. #2611 #2651 #2714
      • Updated build compiler to VS 2022 17.3 Preview 1 (17.2 is now required).
      • Updated to Windows 11 SDK 22000. This is now required for building and testing the STL, but not for using it. #2729
      • Updated Python to 3.10.4.
  • Updated _MSVC_STL_UPDATE. #2634 #2696

VS 2022 17.2

  • Merged C++20 Defect Reports:
    • P2216R3 #2221 std::format Improvements
    • P2418R2 #2323 Add Support For std::generator-like Types To std::format
    • With a final bit of work to implement an integer-class type (per P1522R1) for iota_view, declare <ranges> and <format> stable and make them fully available under /std:c++20. #2518
  • Merged C++23 features:
  • Merged LWG issue resolutions:
    • LWG-2762 #2376 unique_ptr operator*() should be noexcept
    • LWG-2774 #2098 std::function construction vs assignment
    • LWG-3146 #2409 Excessive unwrapping in std::ref/cref
    • LWG-3392 #2421 ranges::distance() cannot be used on a move-only iterator with a sized sentinel
    • LWG-3470 #2414 convertible-to-non-slicing seems to reject valid case
    • LWG-3471 #2567 polymorphic_allocator::allocate does not satisfy Cpp17Allocator requirements
    • LWG-3480 #2340 directory_iterator and recursive_directory_iterator are not C++20 ranges
    • LWG-3519 #2208 Incomplete synopses for <random> classes
    • LWG-3543 #2424 Definition of when counted_iterators refer to the same sequence isn't quite right
    • LWG-3557 #2406 The static_cast expression in convertible_to has the wrong operand
    • LWG-3563 #2426 keys_view example is broken
    • LWG-3574 #2410 common_iterator should be completely constexpr-able
    • LWG-3580 #2417 iota_view's iterator's binary operator+ should be improved
    • LWG-3589 #2425 The const lvalue reference overload of get for subrange does not constrain I to be copyable when N == 0
    • LWG-3590 #2404 split_view::base() const & is overconstrained
    • LWG-3591 #2411 lazy_split_view<input_view>::inner-iterator::base() && invalidates outer iterators
    • LWG-3592 #2411 lazy_split_view needs to check the simpleness of Pattern
    • LWG-3593 #2448 Several iterators' base() const & and lazy_split_view::outer-iterator::value_type::end() missing noexcept
    • LWG-3595 #2410 Exposition-only classes proxy and postfix-proxy for common_iterator should be fully constexpr
    • LWG-3598 #2560 system_category().default_error_condition(0) is underspecified
    • LWG-3610 #2542 iota_view::size sometimes rejects integer-class types
    • LWG-3612 #2586 Inconsistent pointer alignment in std::format
    • LWG-3618 #2566 Unnecessary iter_move for transform_view::iterator
    • LWG-3621 #2543 Remove feature-test macro __cpp_lib_monadic_optional
    • LWG-3648 #2587 format should not print bool with 'c'
    • LWG-3654 #2528 basic_format_context::arg(size_t) should be noexcept
    • LWG-3657 #2564 std::hash<std::filesystem::path> is not enabled
    • LWG-3660 #2549 iterator_traits<common_iterator>::pointer should conform to [iterator.traits]
    • LWG-3661 #2544 constinit atomic<shared_ptr<T>> a(nullptr); should work
  • Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • Fixed bugs:
    • Fixed Clang compiler errors when using ranges::join_view. #2352
    • Fixed several runtime correctness bugs in std::string. #2305
    • Fixed a memory leak affecting a specific scenario in P0408R7 Efficient Access To basic_stringbuf's Buffer. #2361
    • Each call to ranges::clamp now correctly performs at most three projections. #1898
    • The STL no longer rejects Clang in CUDA mode, nor the cl /showIncludes /D__CUDACC__ ... command used by CUDA's msbuild integration to gather dependencies. #2075
    • Fixed allocator::is_always_equal to be deprecated, not removed, in C++20 mode. (It was deprecated by LWG-3170.) #2423
    • Fixed begin()/end() crashing for empty valarrays, which also affected range-based for-loops. #2435
    • Fixed regression in ranges::distance (from LWG-3392 which broke ranges::distance(some_array, s)) by speculatively implementing LWG-3664. #2522
    • Fixed basic_string::resize_and_overwrite() to no longer emit "warning C4018: signed/unsigned mismatch" when given certain user-defined function objects. #2525
    • Increased __cpp_lib_concepts to its final value for C++20, 202002L. #2559
      • It should have been updated in VS 2019 16.6 when P1964R2 "Replacing boolean With boolean-testable" was implemented by #565. The presence of that release (or any later release) can be detected by inspecting our implementation-specific macro _MSVC_STL_UPDATE. Coincidentally, the value of _MSVC_STL_UPDATE for VS 2019 16.6 was also 202002L.
    • Fixed numerous tiny bugs discovered by the libcxx test suite. #2499
    • Fixed a bug in <format> that sporadically caused incorrect output when formatting floating-point values in hex or scientific notation with extremely large precisions. #2569
    • Fixed a bug in <charconv> from_chars() float tiebreaking that produced incorrect results. This affected decimal strings that were at the exact midpoint of consecutive float values, within a narrow range (the smallest and largest affected values were "32768.009765625" and "131071.98828125"), where the tiebreaker rule wanted to round to "even" and "even" happened to be "down", but the implementation incorrectly rounded "up". (double was unaffected.) #2366
    • promise<T> now compiles when !is_default_constructible_v<T>. #2568
    • Moving from an optional<const T> now behaves like moving from a const T: it selects T's copy constructor. #2460
    • Fixed a bug in <format> that incorrectly accepted volatile arguments; the Standard currently says that they should be rejected. #2579
  • Improved performance:
    • Optimized rotl() and rotr() in <bit> for 32-bit and 64-bit integers by using compiler intrinsics. #2369
    • reverse_copy()'s vectorized implementation is now activated (for eligible types) in all Standard modes. Previously, only the C++14/17 modes activated this optimization; C++20/23 modes unintentionally used the plain implementation (correct but slower). #2416
    • Improved codegen for gcd() and lcm(). #2343
    • Improved <format> performance when the execution character set is self-synchronizing. For example, code page 1252 "ANSI Latin 1; Western European (Windows)" activates this optimization. The /utf-8 compiler option also activates this optimization. #2493
    • Improved codegen for generate_canonical. #2498
  • Improved throughput:
    • Used if constexpr instead of tag dispatch in:
      • Optimizations in find(). #2380
      • experimental::filesystem::directory_iterator. #2478
      • basic_string(first, last). #2480
  • Enhanced behavior:
    • Fixed new warnings emitted by Clang 13: -Wdeprecated-copy (in product and test code) and -Wunused-but-set-variable (in test code only). #2266
    • Added ASan (Address Sanitizer) annotations to <vector>, allowing additional errors to be detected. #2071 #2420 #2464 #2508
    • Added a debug assertion to allocator::deallocate(); passing a null pointer with a non-zero size is an error. #2412
    • For supply chain security, replaced checked-in OBJ files (generated by an internal tool aliasobj) with the linker's /ALTERNATENAME option (which is strictly more reproducible, although not officially documented). #2381
      • In certain scenarios involving separately compiled third-party libraries, this can cause "unresolved external symbol" linker errors. See issue #2655 for an explanation and workarounds.
  • Improved documentation:
    • Clarified the messages emitted by <format> and <ranges>. #2382
    • Added a comment explaining how LWG-3632 "unique_ptr 'Mandates: This constructor is not selected by class template argument deduction'" was already implemented. #2548
  • Improved test coverage:
    • Added test cases for the _BitScanForward optimization used by countr_zero() on older CPUs. #2337
    • Added tests for gcd() and lcm(). #2507
    • Added test coverage for deduplicated (topologically sorted) header units. #2516 #2563
    • Updated the libcxx test suite. #2499
  • Code cleanups:
    • Removed compiler bug workarounds. #2338 #2351 #2357 #2474 #2496
    • Updated test code to directly pass a format string to printf(), allowing the compiler to check it. #2346
    • Cleaned up clang-formatting. #2356
    • Changed the <charconv> test headers to use include guards, for closer alignment with libc++. #2372
    • Improved the clarity of vectorized algorithm implementations by replacing the magic numbers 27 and 78. #2377
    • Improved consistency by always saying friend constexpr instead of the reverse order. #2419
    • Simplified <ratio>'s implementation by using constexpr functions instead of template metaprogramming. #2450
    • Simplified an internal function for opening files. #2095
  • Infrastructure improvements:
    • Updated dependencies. #2474 #2496 #2514
      • Updated build compiler to VS 2022 17.1 Preview 5 (now required).
      • Updated Clang to 13.0.0 (now required).
      • Updated CMake to 3.22 (now required).
      • Updated Python to 3.10.2.
    • Added scripts to set INCLUDE, LIB, and PATH after building the repo. #2578
    • Azure Pipelines now uploads test logs as artifacts, making it easier to investigate test failures when lengthy command lines, compiler output, or runtime output are truncated in the web UI. #2575
  • Updated _MSVC_STL_UPDATE. #2374 #2455 #2519 #2602

VS 2022 17.1

  • Merged C++20 Defect Reports:
  • Merged C++23 features:
  • Merged LWG issue resolutions:
    • P2259R1 #2059 Repairing Input Range Adaptors And counted_iterator
      • Completed by implementing the input range adaptors part.
    • LWG-3422 #2260 Issues of seed_seq's constructors
    • LWG-3506 #1994 Missing allocator-extended constructors for priority_queue
    • LWG-3520 #2200 iter_move and iter_swap are inconsistent for transform_view::iterator
    • LWG-3522 #1994 Missing requirement on InputIterator template parameter for priority_queue constructors
    • LWG-3527 #2194 uses_allocator_construction_args handles rvalue pairs of rvalue references incorrectly
    • LWG-3528 #2160 make_from_tuple can perform (the equivalent of) a C-style cast
    • LWG-3536 #2037 Should chrono::from_stream() assign zero to duration for failure?
    • LWG-3546 #1991 common_iterator's postfix-proxy is not quite right
    • LWG-3549 #2198 view_interface is overspecified to derive from view_base
    • LWG-3554 #2261 chrono::parse needs const charT* overloads
  • Fixed bugs:
    • Fixed <complex> exp() and polar() for infinity and NaN inputs. #1584
    • Fixed compiler errors when comparing common_iterators of different types for equality. #2066
    • Attempting to actually call declval() now emits a static_assert citing the paragraph of the Standard that forbids this. (Previously, declval() was declared but not defined, which was too permissive.) #2101
    • Fixed basic_streambuf::seekoff() and basic_streambuf::seekpos() to work with custom pos_types. #2121
    • Restored our guarantee beyond the Standard that string_view is trivially move constructible. #2128
      • This fixed a regression that was introduced by #2000 implementing P1989R2 Range Constructor For string_view in VS 2022 17.0.
    • Fixed a bug where vector and string would terminate via noexcept instead of throwing length_error as desired when a size_t would be truncated to an allocator's narrower size_type. #2139
    • <istream> and <ostream> now properly catch and rethrow internal IO exceptions. #2033
    • Fixed <format> to correctly print hexfloats with large precisions. #2157
    • Fixed compiler errors when using constexpr vectors with certain user-defined allocators. #2161
    • Fixed silent bad codegen in ranges::stable_sort(), where for certain inputs it would neither sort nor permute the range. ranges::inplace_merge() was also affected. #2188
    • subtract_with_carry_engine's textual representation is now correct. #2088
    • Fixed a deadlock in the overload of condition_variable_any::wait_until taking stop_token. #2220
    • u8streampos, u16streampos, and u32streampos are now declared by <iosfwd> as required by the Standard after P0482R6 and P1148R0 were accepted. #2223
    • Fixed ARM64EC compiler errors in <limits>. #2306
    • Fixed heap corruption in fstream when calling putback() followed by close(). #2189
    • Fixed views::reverse to work properly with ranges::reverse_view lvalues. #2313
    • Fixed a bug where the STL's DLL was using Windows Vista's APIs for critical sections and condition variables, instead of the more efficient APIs that were introduced in Windows 7. This was specific to /MD (dynamic release) and the STL's GitHub CMake build system; it did not affect the legacy build system that's currently used for official builds of the MSVC toolset. #2314
    • Fixed a bug affecting older CPUs where the STL generated the newer tzcnt instruction instead of the fallback bsf instruction. This affected <bit>'s countr_zero() and countr_one(), <numeric>'s gcd() and lcm(), and vector<bool>'s optimized implementations of find() and relational/spaceship operators. #2333
    • Fixed minor conformance issues in basic_string. These changes were specified by P1148R0 "Cleaning Up [strings]", which was almost a pure rewording paper without normative impact. Oops! #2222
    • Fixed ranges::find_end() to return correct values for bidirectional common ranges. #2270
    • Fixed compiler errors affecting ranges::sort(), ranges::search(), and other ranges machinery. #2290
    • Fixed array<T, 0>, allowing it to compile when T is not default constructible. #2296
    • Fixed allocator::allocate_at_least() which was improperly annotated with __declspec(allocator). #2328
  • Improved performance:
    • Optimized steady_clock::now() when QueryPerformanceFrequency() is exactly 10 MHz, which is very common for modern PCs. #2086
    • Improved codegen for x86 atomic loads. #2110
    • Optimized the fallback implementation of popcount(), which is used when compiler intrinsics are unavailable (and is also used at compile time). #2079
    • Slightly improved codegen when <format> prints a pointer in hexadecimal. #2097
    • Optimized <ranges> non-propagating-cache for trivially destructible types. #2118
    • Improved ARM64 codegen for popcount(), using compiler intrinsics. #2127
    • Extended the memcpy(), memmove(), and memcmp() optimizations in various algorithms to handle more types. #2158
    • Significantly improved the performance of bitset::count() by using the same machinery as popcount(). #2201
    • Also improved the performance of std::count() for vector<bool> by using popcount() machinery in a more optimizer-friendly way. #2203
    • weak_ptr's converting constructors now avoid locking except when necessary to ensure correctness in virtual inheritance scenarios. #2282
      • For example, converting weak_ptr<T> to weak_ptr<const T> now avoids locking.
    • Removed a duplicated assignment in filesystem::create_directories(). #2304
    • Optimized is_permutation() for reversed sequences. #2043
  • Improved throughput:
    • Replaced tag dispatch with if constexpr in container copy/move assignment. #2217
    • <format> now avoids instantiating vformat() unless and until it's called. #2331
  • Enhanced behavior:
    • Changed numeric_limits<long double>::max_digits10 to handle both 64-bit and 80-bit long double, by restoring the original logic that was used before VS 2017 15.8.
      • Note: 80-bit long double remains unsupported by MSVC.
    • C++ headers now emit clear #error messages when they're compiled as C. #2148
      • This applies to both the "C++ library headers" like <vector> and the "C++ headers for C library facilities" like <cstdio>.
    • Improved the wording of binary_semaphore's debug check messages. #2293
  • Improved documentation:
    • Cited LWG-3581 "The range constructor makes basic_string_view not trivially move constructible" in our implementation of its proposed resolution. #2175
    • Removed comments that were citing GH-489, now that LWG-3530 "BUILTIN-PTR-MEOW should not opt the type out of syntactic checks" has been officially resolved by the June 2021 virtual plenary meeting. #2186
  • Improved test coverage:
    • Removed a constructible_from test case that was invalidated by recent changes to the Core Language. #2107
    • Fixed a test for next_permutation() and prev_permutation(); the algorithms were fine, but the test never worked and was never called. #2137
    • Fixed the test harness to handle non-English Visual Studio installations running on Windows with non-UTF-8 encodings. #2145
    • Added /arch:AVX2 to the matrix of compiler options that's used when testing <bit>. #2150
    • Skipped more flaky tests in the legacy tr1 test suite. #2202
    • Fixed flaky tests in the legacy tr1 test suite that were generating collisions between temporary filenames. #2210
    • Fixed test failures on Windows 11. #2265
    • Fixed <chrono> formatting test failures related to locale-dependent time zone abbreviations. #2231
  • Code cleanups:
    • Moved a helper struct from a central internal header to <optional>. #2117
    • Cleaned up comments and clang-formatting. #2136
    • Removed a spurious overload of operator>>(basic_istream&&, basic_string&). This didn't affect correctness, but it was neither necessary nor depicted by the Standard. #2138
    • Cleaned up various things, notably simplifying exception_ptr's operators for C++20 and emitting a clear error message when compiling <stdatomic.h> as C. #2140
    • Removed unnecessary code in <cctype> that was attempting to defend against macroized isalnum etc. #2147
    • Removed an unnecessary reinterpret_cast, and changed some reinterpret_casts from void* to T* to use static_cast instead. #2096
    • Removed an unnecessary definition of our internal macro _HAS_CXX23 from our central internal header yvals_core.h. #2226
    • Removed comments that were citing proposed resolutions for LWG issues, now that those issues have been officially resolved by the October 2021 virtual plenary meeting. #2269
    • Removed unnecessary (void) casts now that MSVC emits fewer spurious warnings about unreferenced parameters. #2280
    • Removed compiler bug workarounds. #2327
  • Infrastructure improvements:
    • Updated dependencies. #2115 #2204 #2277 #2327
      • Updated build compiler to VS 2022 17.1 Preview 1.
      • Updated CMake to 3.21 (now required).
      • Updated Python to 3.10.0.
    • Replaced vcpkg with boostorg/math 1.77 in standalone mode. #2151
  • Updated _MSVC_STL_UPDATE. #2183 #2233 #2321

VS 2022 17.0

  • Merged C++20 Defect Reports:
    • P2325R3 #2012 Views Should Not Be Required To Be Default Constructible
    • P2328R1 #2038 join_view Should Join All views Of ranges
    • P2367R0 #2026 Remove Misuses Of List-Initialization From Clause 24 Ranges
  • Enabled C++20 features for Clang: #2064
  • Merged C++23 features:
    • P0401R6 #2036 Providing Size Feedback In The Allocator Interface
    • P1048R1 #1950 is_scoped_enum
    • P1132R7 #1998 out_ptr(), inout_ptr()
    • P1679R3 #1478 contains() For basic_string/basic_string_view
    • P1682R3 #1828 to_underlying() For Enumerations
    • P1951R1 #2009 Default Template Arguments For pair's Forwarding Constructor
    • P1989R2 #2000 Range Constructor For string_view
    • P2162R2 #2006 Inheriting From variant
    • P2166R1 #1995 Prohibiting basic_string And basic_string_view Construction From nullptr
      • This is a common source-breaking change - code that previously had undefined behavior at runtime will now be rejected with compiler errors.
    • P2186R2 #2010 Removing Garbage Collection Support
  • Merged LWG issue resolutions:
    • LWG-3430 #1968 std::fstream & co. should be constructible from string_view
    • LWG-3494 #1877 Allow ranges to be conditionally borrowed
    • LWG-3502 #1878 elements_view should not be allowed to return dangling references
    • LWG-3518 #2080 Exception requirements on char trait operations unclear
    • LWG-3533 #1993 Make base() const & consistent across iterator wrappers that support input_iterators
    • LWG-3541 #1992 indirectly_readable_traits should be SFINAE-friendly for all types
    • LWG-3548 #2007 shared_ptr construction from unique_ptr should move (not copy) the deleter
    • LWG-3553 #1990 Useless constraint in split_view::outer-iterator::value_type::begin()
    • LWG-3555 #1989 {transform,elements}_view::iterator::iterator_concept should consider const-qualification of the underlying range
  • Merged partial LWG issue resolutions:
    • P2259R1 #1939 Repairing Input Range Adaptors And counted_iterator
      • The counted_iterator part is implemented; the input range adaptors part is not yet implemented.
  • Fixed bugs:
    • Fixed time_put::do_put to avoid crashing when the invalid parameter handler has been changed to not end execution. #1563
    • Fixed a compiler error in ranges::take_view. #1844
    • Fixed improper partitioning of forward ranges in the parallel algorithms. #1753
    • Fixed an unintentionally dllexported symbol in the import library. #1927
    • Fixed a bug in which ranges::unique_copy would fail to compile with a non-input output iterator. #1933
    • Fixed a compiler error when calling format_to() in a specialization of formatter (see #1961 for an example). #1874
    • Fixed compiler errors when calling views::drop and views::take with types that aren't integers, but are convertible to integers (e.g. integral_constant). #1958
    • Fixed a compiler error when calling constexpr vector::emplace(position, args...). #1962
    • Fixed jthread to provide native_handle(). #1966
    • Fixed filesystem::remove() to delete read-only files, as required by the Standard. #1559
    • Fixed mersenne_twister_engine: #1631
      • Fixed the seeding algorithm to follow N4892 [rand.eng.mers]/8, avoiding an all-zero state. (This is a runtime special case.)
      • Fixed the engine's behavior when m == n or n == 1. (This is a compile-time special case, which doesn't affect mt19937 and mt19937_64 at all.)
      • Fixed operator<<() to avoid printing a trailing space after the engine's textual representation.
    • Fixed <chrono> to adjust for leap seconds when formatting file_time. #1879
    • Fixed chrono::from_stream() to allow a year and a day-of-year to be parsed to a time_point. #1940
    • Fixed filesystem::u8path() to accept char8_t sources. #1943
    • Fixed <chrono> to parse subseconds for time_points. #1987
      • Also fixed the parsing of local_time with a UTC offset.
    • Fixed <chrono> formatting to correctly estimate string widths (see N4892 [format.string.std]/9). #2017
    • Fixed a major regression in the _ITERATOR_DEBUG_LEVEL == 2 machinery, where a multithreaded program in debug mode could crash when one thread is modifying a container and another thread is destroying iterators. #2060
      • This regression affected all Standard modes (C++14/17/20/23) and was introduced by #1546 in VS 2019 16.10.
      • Fixed in both VS 2019 16.11.4 and VS 2022 17.0.
    • Fixed a compiler error in pmr::map<K, pair<A, B>>::operator[]. #2023
    • Fixed compiler errors in basic_string's getline() and operator>>() caused by the source-breaking change C++23 P2266R1 "Simpler Implicit Move", first implemented in Clang 13. #2025
    • bit_ceil() now enforces its precondition during constexpr evaluation, as required by the Standard. #2041
    • clog is no longer tied to cout, and similarly for wclog and wcout, following the Standard. #2056
    • In <ranges>, when filter_view, drop_view, drop_while_view, and reverse_view store a cached position into an underlying view, they now properly invalidate that cached position when the underlying view is moved from. #1931
  • Improved performance:
    • Slightly improved debug codegen for vector<bool>, basic_string, and map/multimap/set/multiset's empty() member functions. #1836
    • Fixed bloated codegen for <format>. #1874
    • Dramatically improved the performance of std::find() and std::count() for vector<bool>, with measured speedups between 19x and 26x (times, not percent). #1131
    • Extended our memcmp/memcpy/memchr optimizations to ranges with contiguous iterators and unreachable sentinels. #1810
    • <format> now detects when it's writing to a back_insert_iterator for a basic_string or a vector, and performs a faster call to insert() at the end() of the container. #1894
    • std::byte now activates the "trivially swappable" optimization in reverse() and variant::swap(), so it'll have the same performance as unsigned char. #2044
    • Extended the vectorization optimization in std::swap_ranges() to ranges::swap_ranges(), and enhanced it to work for arbitrary contiguous iterators. #2048
    • Reduced debug codegen size; an internal assertion macro was emitting completely unused, potentially long strings for function names. #2054
  • Improved throughput:
    • <format> and <chrono> now avoid including <array>. #2031
  • Enhanced behavior:
    • Added a visualizer for source_location. #1837
    • Added [[nodiscard]] to the stoi() family of functions in <string> and to various functions in <locale> (collate member functions, has_facet(), and the isalnum() and tolower() families). #1809
    • Added a debug mode precondition check to forward_list::splice_after(). #2057
    • Added visualizers for bind_front(), u8string (and its iterators), default_sentinel_t, unreachable_sentinel_t, ranges::empty_view, ranges::single_view, ranges::iota_view (and its iterator/sentinel), ranges::ref_view, thread, thread::id, jthread, and filesystem::path. #1856
  • Improved test coverage:
    • Added test coverage for our implementation-specific guarantees that span and basic_string_view are trivially copyable; P2251 may eventually Standardize these guarantees. #2015
    • Fixed the ranges test machinery to properly specialize std::basic_common_reference; it was unintentionally relying on identical bugs in MSVC and Clang, but EDG correctly diagnosed that the code was non-Standard. #2013
    • Fixed a test (for the abs() overloads in <cmath> and <cstdlib>) that unintentionally hadn't been running in our new GitHub test harness. #2070
  • Code cleanups:
    • Removed compiler bug workarounds. #1759 #1778 #1920
    • Removed unnecessary C casts. #1843
    • The STL now uses Standard _Pragma instead of non-Standard __pragma (when possible) to internally suppress warnings. #1342
    • <format> now uses _First/_Last parameter names (instead of _Begin/_End) to be consistent with the rest of the STL. (The connotations are that first/last refers to an arbitrary range that might be a subrange, while begin/end refers to an entire container/view.) #1951
    • Removed comments that were citing proposed resolutions for LWG issues, now that those issues have been officially resolved by the June 2021 virtual plenary meeting. #1967
    • Improved vector's implementation, also using if constexpr to simplify code. #1771
    • Simplified <format>'s implementation of type-erased argument storage. #1907
    • Filed LWG-3566 "Constraint recursion for operator<=>(optional<T>, U)" and updated our implementation's comment accordingly. #2011
    • Simplified the backwards loop in char_traits::move(). #2055
    • Marked all overriding functions with override, and removed redundant virtual keywords. #2069
    • REMOVED THE "SHOUTY COMMENT BANNERS" LIKE // CLASS TEMPLATE vector; SEE #306 FOR THE RATIONALE. #2074
    • Removed an unnecessary check for self-assignment in the compile-time implementation of char_traits::move(). #2083
  • Infrastructure improvements:
    • Updated dependencies. #1884 #1920 #1953 #2014 #2064 #2081
      • Updated build compiler to VS 2022 17.0 Preview 2 (now required).
      • Updated Clang to 12.0.0 (now required).
      • Updated CMake to 3.20 (now required).
      • Updated Python to 3.9.6.
      • Updated vcpkg for Boost 1.76.0 (now required).
  • Build system improvements:
  • Updated _MSVC_STL_UPDATE. Also updated _MSVC_STL_VERSION to 143 for the VS 2022 release series. #1897 #1955 #2035 #2091

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