Changelog (original) (raw)

Table of Contents

• MSVC Build Tools 14.51 Preview - see the VS 2026 Insiders Release Notes
• MSVC Build Tools 14.50 - latest production version, see the VS 2026 Release Notes
• VS 2022 Changelog - see the VS 2022 Release History
• VS 2019 Changelog - see the VS 2019 Release History

C++23 features generally require the /std:c++23preview or /std:c++latest compiler options.

MSVC Build Tools 14.51

MSVC Build Tools 14.51 Preview

• Removed non-Standard features:
  • TR1, including the std::tr1 namespace, the old array::assign() member function, the old <random> engines, and the old <random> distributions uniform_int and uniform_real.#5763
    * Deprecated since VS 2017 15.5 in December 2017.
  • <hash_map> and <hash_set>. #5764
    * Deprecated since VS 2015 in July 2015.
  • <experimental/filesystem>. #5765
    * Deprecated since VS 2019 16.3 in September 2019.
  • stdext::checked_array_iterator and stdext::unchecked_array_iterator. #5817
    * Deprecated since VS 2022 17.8 in November 2023 (for C++17 and later) and VS 2022 17.11 in August 2024 (unconditionally).
  • basic_istream::ipfx()/isfx() and basic_ostream::opfx()/osfx(). #5834
    * Deprecated since VS 2022 17.9 in February 2024 (for C++17 and later) and VS 2022 17.11 in August 2024 (unconditionally).
  • locale::empty(). #5834
    * Deprecated since VS 2022 17.14 in May 2025.
• Merged C++26 features:
  • P3349R1 #5683 Converting Contiguous Iterators To Pointers
  • P3503R3 #5630 Make Type-Erased Allocator Use In promise And packaged_task Consistent
• Merged C++23 features:
  • P2255R2 #5537 Type Traits To Detect References Binding To Temporaries
    * Initially supported for Clang only.
  • P2674R1 #5445 is_implicit_lifetime
    * Initially supported for Clang only.
• Merged partial C++20 features:
  • P0466R5 Layout-Compatibility And Pointer-Interconvertibility Traits
    * This feature was fully implemented for MSVC by #1575 in VS 2019 16.10.
    * is_layout_compatible and is_pointer_interconvertible_base_of are now implemented for Clang, as the necessary compiler builtins recently became available. #5621
    * is_pointer_interconvertible_with_class() and is_corresponding_member() remain to be implemented for Clang, as the necessary compiler builtins are not yet available.
• Merged LWG issue resolutions:
  • LWG-3343 #5912 Ordering of calls to unlock() and notify_all() in Effects element of notify_all_at_thread_exit() should be reversed
  • LWG-3617 #5921 function/packaged_task deduction guides and deducing this
    * This was originally implemented for MSVC by #2966 in VS 2022 17.4. It's now implemented for Clang, after Clang 19 added complete support for P0847R7 "Deducing this".
  • LWG-4243 #5867 as_bytes/as_writable_bytes is broken with span<volatile T>
  • LWG-4253 #5868 basic_const_iterator should provide iterator_type
  • LWG-4257 #5895 Stream insertion for chrono::local_time should be constrained
  • LWG-4266 #5880 layout_stride::mapping should treat empty mappings as exhaustive
  • LWG-4272 #5900 For rank == 0, layout_stride is atypically convertible
  • LWG-4274 #5893 The chrono::hh_mm_ss constructor is ill-formed for unsigned durations
  • LWG-4294 #5869 bitset(const CharT*) constructor needs to be constrained
  • LWG-4301 #5885 #5940 condition_variable{_any}::wait_{for, until} should take timeout by value
  • LWG-4312 #5904 Const and value category mismatch for allocator_arg_t/allocator_arg in the description of uses-allocator construction
  • LWG-4366 #5896 Heterogeneous comparison of expected may be ill-formed
  • LWG-4398 #5883 enable_nonlocking_formatter_optimization should be disabled for container adaptors
  • LWG-4399 #5897 enable_nonlocking_formatter_optimization for pair and tuple needs remove_cvref_t
• Fixed bugs:
  • Fixed <regex> to perform matching non-recursively, avoiding stack overflows and improving performance. #5703 #5714 #5734 #5745 #5762 #5774 #5790 #5798 #5818 #5828 #5835 #5865 #5889 #5918 #5939 #5954
  • Fixed <regex> bugs when parsing repetitions in extremely unusual cases. #5716
  • Fixed <regex> to avoid throwing a regex_error when a repeated pattern contains a lookahead assertion. #5793
    * This fixed a regression that was introduced by #5456 in the MSVC Build Tools 14.50.
  • Fixed <regex> to perform matching correctly when a loop has a bounded number of repetitions and a context-dependent empty alternative. #5820
  • Fixed basic_string::resize_and_overwrite() to require the given operation to return an integer-like type. #5695
  • Added a compiler bug workaround for Clang x86, fixing 64-bit atomic behavior. #5708
  • Fixed the vector<bool> optimization for copy() to avoid a forbidden negative shift in a specific scenario. #5726
  • Fixed independent_bits_engine to avoid forbidden full shifts in specific scenarios. #5740
  • Fixed compiler errors in vector when programs are taking advantage of our non-Standard legacy support for mismatched allocator types (i.e. vector<T, MyAlloc<U>>, which is forbidden by the Standard). #5729
    * This fixed a regression that was introduced by #4977 in VS 2022 17.13.
  • Fixed compiler warnings and errors in basic_string for allocators with unusual size_types. #5562 #5775
  • Fixed a crash in the x64/x86 vectorized implementations of wstring::find_first_of() and wstring::find_last_of() that was specific to searching for certain combinations of characters inside and outside the [0, 255] range. #5758
    * This fixed a regression that was introduced by #5029 in VS 2022 17.14.
    * This fix was backported to VS 2022 17.14.20 and the MSVC Build Tools 14.50.
  • Fixed std::pow(dbl, 2) to return dbl * dbl as a special case, working around an accuracy issue in UCRT ::pow() that affects ~0.04% of double values. #5771
    * This fixed a regression that was introduced by #903 in VS 2019 16.8.
    * For example, the square of 0.96211481342217475276612503876094706356525421142578125 (hexfloat 0x1.ec9a50154a6f9p-1) is mathematically 0.9256649142063861358000347706773514725967013405547974870554600612150564220570458928705193102359771728515625, which cannot be exactly represented as a 64-bit double. UCRT ::pow(x, 2.0) returns 0.92566491420638608023097049226635135710239410400390625 (hexfloat 0x1.d9f0c06b2463dp-1), but x * x returns 0.9256649142063861912532729547820053994655609130859375 (hexfloat 0x1.d9f0c06b2463ep-1). The double value of x * x is slightly closer to the mathematically exact square, therefore it is correctly rounded and should be returned.
  • Fixed ranges::to, allowing it to create unions. #5794
  • Fixed stable_sort(), stable_partition(), and inplace_merge() to handle over-aligned elements by default. #5807
  • Fixed ranges::partition to meet the Standard's complexity requirements for bidirectional non-common ranges. #5887
  • Fixed the noexcept specification of an internal helper function for debug checks of strict weak orderings, affecting extremely unusual comparison function objects with non-bool return types. #5931
  • Fixed various classes and functions to accept only cv-unqualified types as standard signed and unsigned integer types. #5946
  • Fixed compiler errors in <chrono> formatting for durations with unsigned representation types. #5947
• Improved performance:
  • Improved <ranges> performance by adding an optimized implementation of divide-ceiling for 128-bit integers. #5637
  • Updated <complex> to use Fused Multiply-Add (FMA) intrinsics for Clang. #5721
  • Optimized sample(), shuffle(), ranges::sample, and ranges::shuffle by using Daniel Lemire's algorithm Fast Random Integer Generation in an Interval.
    * This was originally implemented for uniform_int_distribution by #3012 in VS 2022 17.5.
  • Added x64/x86 vectorized implementations of:
    * includes() and ranges::includes. #5590
  • Added ARM64 vectorized implementations of:
    * swap_ranges() and ranges::swap_ranges. #5819
    * rotate() and ranges::rotate. #5845
    * reverse(), reverse_copy(), ranges::reverse, and ranges::reverse_copy. #5870
  • Improved the x64/x86 vectorized implementations of:
    * search_n() and ranges::search_n. #5544
    * mismatch() and ranges::mismatch. #5591
    * count(), find(), find_last(), remove(), remove_copy(), replace(), and their ranges counterparts. #5767
  • Optimized any::swap() by avoiding unnecessary copies. #5710
  • Optimized transform() for vector<bool> with the unary function object logical_not and the binary function objects logical_and, logical_or, equal_to, and not_equal_to. #5769
  • Constructing a move_only_function from a std::function now avoids double-wrapping. #5808 #5919
  • Optimized steady_clock::now() to more efficiently convert from a performance counter frequency of 24 MHz (commonly seen on ARM64 systems) to nanoseconds. #5832
• Enhanced behavior:
  • For C++20, enabled P2404R3 Move-Only Types For Comparison Concepts. #5928
    * This was originally implemented for C++23 by #3345 in VS 2022 17.6.
  • Unconditionally enabled LWG-3187 for uses-allocator construction.
    * This was originally implemented for C++20 by #1668 in VS 2019 16.10.
  • Deprecated the non-Standard <experimental/coroutine>, <experimental/generator>, and <experimental/resumable> headers. #5804
  • Removed the confusing escape hatch macro _ALLOW_RTCc_IN_STL. The STL doesn't support the /RTCc compiler option because it rejects conformant code with runtime termination. Previously, the STL blocked /RTCc with a compiler error, but provided an escape hatch macro to suppress that compiler error (so that compile-time STL components, like <type_traits>, could theoretically be used). This escape hatch intentionally did nothing to the STL's conformant code that would attempt to avoid runtime termination, occasionally confusing users. Now that the escape hatch has been removed, users must remove the /RTCc compiler option. #5906
    * Note: The /RTCs and /RTCu compiler options (combined into /RTC1) are good and unaffected. They only complain about undefined behavior, and the STL is perfectly compatible with them.
  • Implemented compiler warnings when the Standard forbids user-defined specializations of Standard Library templates. #5536 #5937
    * This uses the recently-implemented attributes [[msvc::no_specializations("reason")]] and [[clang::no_specializations("reason")]].
  • Silenced spurious static analysis warnings in vector<bool>::max_size(). #5707
  • Silenced CodeQL warnings. #5711
  • Improved <random>'s engines and distributions to no longer derive from their non-Standard TR1 predecessors. #5712
  • Updated tuple to apply the resolution of LWG-3677 "Is a _cv_-qualified pair specially handled in uses-allocator construction?". #5669
    * This was originally implemented for pair by #3396 in VS 2022 17.7.
  • Updated <format> to handle Unicode 17. #5571 #5803
  • Updated the Standard Library Modules, when used with the UCRT from the Windows 11 SDK 10.0.26100.6901 or newer, to remove a workaround that affected various <ctime> functions. #5805
  • Updated C++23 move_only_function to prepare for future interactions with C++26 features. #5849
  • Improved is_clock_v to perform stricter checks beyond the Standard's minimum requirements. #5892
  • Improved the accuracy of poisson_distribution and binomial_distribution by calling the UCRT's lgamma() function instead of highly inaccurate handwritten code. #5891
  • Improved num_put::do_put() to avoid any possibility of casting a negative sprintf_s() return value to size_t. #5925
• Improved test coverage:
  • Enabled ARM64EC test coverage for Clang. #5717
  • Removed /analyze from the libcxx test suite to reduce compiler memory consumption, as we have sufficient test coverage elsewhere. #5724
  • Fixed bogus tests for the most triumphant type trait functions is_corresponding_member() and is_pointer_interconvertible_with_class(). #5730 #5737
  • Added test coverage for constexpr vector<bool>. #5728
  • Reactivated test coverage using Clang's Undefined Behavior Sanitizer (UBSan). #5746
  • Improved test coverage for <filesystem>. #5749
  • Added test coverage for <filesystem>'s long path support. #5783 #5799
  • Added benchmarks for <charconv>'s floating-point to_chars(). #5700
  • Centralized test machinery for exercising code with varying levels of Instruction Set Architecture (ISA) extensions, and added assertions to verify that tests are being run on machines that actually support the highest level of ISA extensions being used. #5874
  • Updated our LLVM submodule, including new tests. #5888 #5955
  • Improved messages for syntax errors in expected test results. #5948
• Code cleanups:
  • Reduced code duplication for:
    * <bit> machinery. #5696
    * vector<bool> benchmarks. #5732 #5742
    * move_only_function. #5810
  • Removed compiler bug workarounds. #5717 #5783 #5809
  • Fixed a typo. #5713
  • Reworked internal macros to make it easier to add vectorized algorithms for ARM64. #5801
  • Cleaned up the separately compiled implementations of x64/x86 vectorized algorithms:
    * Added template and typename keywords as required by the Standard. #5743
    * Removed unused functions. #5744
    * Avoided unnecessary unaligned memory accesses in bitset's constructors from strings. #5759
    * Avoided unnecessary unaligned memory accesses in swap_ranges(), ranges::swap_ranges, rotate(), and ranges::rotate. #5760
    * Removed a bogus assumption (which was fortunately harmless). #5761
  • Various cleanups (described in detail in the PRs, not repeated here). #5753 #5922 #5924
  • Simplified <any>'s implementation. #5784
  • Updated the STL's internal implementation to be compatible with .NET 8.0. #5814
  • Avoided internal usage of a deprecated type trait. #5811
  • Deleted dozens of files containing thousands of lines of unnecessary code for floating-point functions. #5836
  • Avoided compiler warnings in the STL's separately compiled source files. #5875 #5876
  • Removed comments that were citing proposed resolutions for LWG issues, now that those issues have been officially resolved by the November 2025 meeting. #5909
  • Simplified how <chrono> formatting validates modifier characters. #5905
  • Improved zoned_time's constructors to be constrained with concepts instead of SFINAE. #5907
  • Used if constexpr to simplify:
    * Locale helper functions. #5923
    * lock() and try_lock(). #5941
• Infrastructure improvements:
  • Added ARM64 runtime test coverage. #5815
  • Added ARM64EC runtime test coverage. #5831
  • Added a Configure Tests stage to Azure Pipelines, validating that test paths are properly listed in various files. #5888
  • Improved CI reliability by not building the benchmarks with Clang for x86. #5704
    * This avoids a sporadic crash in lld-link.exe.
  • Updated the CI to print a histogram of test run times and a list of the slowest running tests. #5878
  • Updated dependencies. #5717 #5783 #5879 #5888 #5955
    * Updated MSVC Compiler to 19.50.35720 (now required).
    * Updated Clang to 20.1.8 (now required).
    * Updated CMake to 4.1.1 (now required).
    * Updated Python to 3.14.0 (now required).
    * Updated Boost.Math to 1.89.0.
• Build system improvements:
  • Added compiler and linker options to the GitHub CMake build system, fixing divergence with the MSVC-internal MSBuild build system. #5652
  • The STL now clearly rejects attempts to build a preset or test a build whose architecture doesn't match the Developer Command Prompt (which is x86-native, but very slightly different from the x86 Native Tools Command Prompt where enforcement was previously validated). #5731
• Updated _MSVC_STL_UPDATE. #5709 #5752 #5822 #5930

MSVC Build Tools 14.50

This shipped in VS 2026 18.0.

• The STL no longer supports targeting Windows 7 / Server 2008 R2, Windows 8 / Server 2012, and Windows 8.1 / Server 2012 R2:
  • Improved the performance of system_clock::now() and atomic::wait() by directly calling APIs that were added in Windows 8. #5432 #5496
  • Improved the performance of STL Hardening by using the MSVC __fastfail intrinsic that was added in Windows 8, and the Clang __builtin_verbose_trap intrinsic. #5433 #5458
  • Simplified the <filesystem> implementation by unconditionally calling APIs that were added in Windows 8. #5434
  • Windows 10 / Server 2016 are our minimum supported operating systems. #5510
• The STL no longer supports targeting 32-bit ARM. #5594
• Merged C++26 features:
  • P0472R3 #5382 Put monostate In <utility>
  • P3223R2 #5604 Making istream::ignore() Less Surprising
• Merged partial C++26 features:
  • P3697R1 #5650 Minor Additions To Standard Library Hardening
• Merged LWG issue resolutions:
  • LWG-2503 #5535 multiline option should be added to syntax_option_type
    * For us, this is a regex behavioral change, so we added an escape hatch. By default, we define _REGEX_LEGACY_MULTILINE_MODE to 0, which requests Standard behavior:
    * For ECMAScript, matching is non-multiline by default, but regex_constants::multiline can be requested.
    * For POSIX grammars, matching is non-multiline, and regex_constants::multiline is ignored; see N5008 [tab:re.synopt].
    * Defining _REGEX_LEGACY_MULTILINE_MODE to 1 requests legacy behavior:
    * For all grammars, matching is multiline, and regex_constants::multiline is redundant.
  • LWG-4186 #5444 regex_traits::transform_primary mistakenly detects typeid of a function
  • LWG-4222 #5602 expected constructor from a single value missing a constraint
  • LWG-4242 #5603 ranges::distance does not work with volatile iterators
• Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • LWG-4270 #5572 Diagnose misuse of std::projected::operator*
  • LWG-4273 #5578 Standard execution policy types should be conventional tag class types
  • LWG-4303 #5603 std::decay_t in the specification of ranges::distance is problematic
• Fixed bugs:
  • Fixed regex's behavior:
    * For the basic and grep grammars to properly handle ^ caret characters. #5165
    * For the basic and grep grammars to properly handle $ dollar characters. #5362
    * For the basic and grep grammars to make backreferences to unmatched capture groups fail to match anything, instead of matching the empty string "". #5376
    * For the basic and grep grammars to properly handle backslashes inside square-bracket character classes. #5523
    * For POSIX grammars to allow a ] right square bracket at the beginning of a character range. #5364
    * For POSIX grammars to avoid resetting matched capture groups. #5377
    * For the ECMAScript grammar's (?!pattern) negative lookahead assertions to make capture groups within them always match nothing after the assertions succeed. #5366
    * For the ECMAScript grammar's \b word boundary assertion to not match the empty string "" (and inversely for the \B negative word boundary assertion). #5375
    * For the ECMAScript grammar's \c escapes to require the following ControlLetter to be an ASCII alphabetic character. #5524
    * That is, only \ca through \cz and \cA through \cZ are allowed.
    * For the ECMAScript grammar to reset all capture groups to "unmatched" at the start of each repetition of a loop. #5456
    * For the ECMAScript grammar to reject bogus groups by throwing a regex_error with the code regex_constants::error_badrepeat, removing the non-Standard code regex_constants::error_syntax that was previously used. #5542
    * That is, only non-capture groups (?:meow) and positive/negative lookahead assertions (?=meow)/(?!meow) are allowed; other characters following (? are bogus. Notably, the C++ Standard doesn't support the lookbehind assertions (?<=meow)/(?<!meow) that were added in later versions of ECMAScript.
    * For the ECMAScript, basic, grep, and awk grammars to properly handle escape sequences. #5380
    * POSIX grammars now accept \] as an identity escape for a right square bracket. #5399
    * For capture groups to follow ECMAScript's depth-first and POSIX's leftmost-longest matching rules. #5218
    * Removed unnecessary code for POSIX's leftmost-longest rule, reducing stack space consumption. #5405
    * For empty matches to follow ECMAScript's and POSIX's slightly different rules. #5494
    * For negated character class escapes (\D for non-digits, \S for non-whitespace, \W for non-words) inside square-bracket character classes when matching against Unicode characters. #5403 #5487
    * This completes a series of fixes started by #5160 and #5214 in VS 2022 17.14.
    * For combinations of character class escapes inside square-bracket character classes (like [\w\s] for words and whitespace) when matching against Unicode characters. #5438
    * For character ranges with regex_constants::collate to follow the locale's collation order. #5238
    * For collating symbols and equivalence classes. #5392 #5444
    * For small character ranges containing U+00FF and U+0100. #5437
    * For regex_constants::icase and regex_constants::collate to translate each character exactly once before any comparisons. #5553
    * For extremely unusual user-defined character types. #5592 #5675
    * To avoid requiring non-Standard typedefs in custom regex traits classes. #5671
  • Fixed collate<wchar_t> to follow the locale's collation order when compiling with /Zc:wchar_t- (making wchar_t a non-Standard typedef for unsigned short) and linking to the STL dynamically (with /MD or /MDd). #5361
  • Fixed how collate::do_transform() handles wrongly encoded input. #5431
  • Fixed collate::do_hash() to return equal hashes for strings that collate as equivalent. #5469
  • Fixed ranges::enable_view to correctly report false for ranges::view_interface itself. #5369 #5407
  • Fixed <filesystem> status functions to avoid failing for invalid paths when the current directory is a network path. #5381
  • Fixed compiler errors in repeat_view's piecewise constructor for certain scenarios. #5388
  • Fixed compiler errors in constexpr copy() for vector<bool>. #5347
    * This fixed a regression that was introduced by #3353 in VS 2022 17.9.
  • Fixed the barrier constructor's exception specification to be conditionally "strengthened", instead of unconditionally. #5398
  • Fixed heap-use-after-free bugs in our undocumented/quasi-supported _HAS_EXCEPTIONS=0 mode when constructing system_error, chrono::ambiguous_local_time, and chrono::nonexistent_local_time. #5406
  • Fixed compiler errors when passing volatile ranges to basic_string's from_range constructor and append_range(), assign_range(), insert_range(), and replace_with_range() member functions. #5409
  • Fixed nth_element() and ranges::nth_element to have worst-case linear complexity, instead of quadratic. #5100
  • Fixed compiler errors when passing iterators with unusual integer-class difference types to vectorized algorithms. #5471
  • Fixed destroy(), destroy_at(), destroy_n(), ranges::destroy, ranges::destroy_at, and ranges::destroy_n to destroy objects during constant evaluation even when they're trivially destructible. #5449
  • Fixed num_get::do_get() for bool to properly handle bad digit groupings. #5476
  • Fixed thread::hardware_concurrency() to correctly report the total number of logical processors when more than 64 are available, for both single-socket and multi-socket machines. #5459
  • Fixed <mdspan>'s layout_stride::mapping<E>::is_exhaustive() to correctly handle unusual extents. #5477
  • Fixed reverse_copy() and ranges::reverse_copy being improperly vectorized for pair<T&, U&> on x86 (where such pairs are 8 bytes). #5528
    * This fixed a regression that was introduced by #804 in VS 2019 16.8.
  • Fixed chrono::zoned_time to provide a fallback time zone abbreviation (of the form "-05" or "+0530") when the system's code page can't represent the localized abbreviation that would normally be returned. #5558
  • Fixed counting_semaphore::try_acquire_for() to consistently use steady_clock. #5575
  • Silenced a static analysis warning C6510 emitted by the extremely unusual scenario of basic_string<char_like_struct>. #5563
  • Fixed compiler errors involving incomplete types in <chrono>. #5629
  • Fixed occurrences of Clang 21's new -Wcharacter-conversion warning in <locale> by avoiding implicit conversions between charN_t types. #5653
  • Fixed integer overflow in stable_sort() and ranges::stable_sort when sorting huge inputs on x86. #5677
    * This affected 32-bit architectures with over a billion 1-byte elements. 64-bit architectures were immune.
    * This fix was backported to VS 2022 17.14.20.
  • Fixed filesystem::temp_directory_path(error_code&) to return an empty filesystem::path when an error is encountered. #5570
• Improved performance:
  • Improved performance for regex matching:
    * When a regex starts with a ? question mark quantifier or several alternatives, by avoiding quadratic complexity. #5457
    * When a regex starts with a + plus quantifier (or {min,} or {min,max} quantifiers requiring at least 1 repetition). #5509
    * When a regex contains no capture groups, by avoiding unnecessary allocations. #5518
    * For all regex patterns, by not generating unnecessary "if" nodes with a single branch. #5539
    * When a regex starts with positive/negative word boundary assertions \b/\B and lookahead assertions (?=meow)/(?!meow). #5576
    * By calling std::search() internally. #5586
    * By avoiding unnecessary work in regex_constants::collate mode. #5672
  • Started using [[msvc::no_unique_address]] as a space optimization in several C++23 components. #4960
  • Added x64/x86 vectorized implementations of:
    * basic_string::find_first_not_of() and basic_string::find_last_not_of() for one character. #5102
    * basic_string::find_first_not_of() and basic_string::find_last_not_of() for multiple characters. #5206
    * adjacent_find() and ranges::adjacent_find. #5331
    * unique() and ranges::unique. #5092 #5363
    * search_n() and ranges::search_n for small values of n. #5352
    * remove_copy(), ranges::remove_copy, unique_copy(), and ranges::unique_copy. #5355
    * is_sorted_until() and ranges::is_sorted_until. #5420 #5540
    * search(), ranges::search, default_searcher, find_end(), and ranges::find_end, for 4-byte and 8-byte elements. #5484 #5519
    * They were vectorized for 1-byte and 2-byte elements in VS 2022 17.13.
    * rotate() and ranges::rotate. #5502 #5525
  • Improved the x64/x86 vectorized implementations of:
    * reverse_copy() and ranges::reverse_copy. #5493
  • Improved the ARM64EC vectorized implementations of:
    * find() and ranges::find. #5597
  • Improved the performance of ranges::find for 2-byte elements on ARM64, matching find()'s behavior. #5628
  • Used Clang's builtin __is_trivially_equality_comparable to improve the performance of equal(), ranges::equal, and many vectorized algorithms for more types. #5527
  • Optimized search_n() and ranges::search_n for n=1 to internally call find() and ranges::find. #5346
  • Improved codegen for has_single_bit(), especially when popcount() intrinsics are unconditionally available. #5367 #5534
    * For example, x86/x64 with /arch:AVX and ARM64 can unconditionally use popcount() intrinsics.
  • Optimized poisson_distribution's constructor by avoiding unnecessary work. #5411
  • Implemented an exponential speedup (yes, literally) for minstd_rand and minstd_rand0's discard() member function. #5412
  • Improved linear_congruential_engine performance by using our modern internal implementation of 128-bit integers. #5436 #5473
  • Significantly improved performance for chrono::tzdb::locate_zone() by using binary searches for time zone names. #5548
  • Improved std::includes() to have the same performance as ranges::includes. #5543 #5595
  • Improved the performance of count() for vector<bool>. #5640
• Enhanced behavior:
  • Used a new Clang compiler intrinsic to implement is_scoped_enum. #5358
  • Added debug checks for overlapping ranges in replace_copy(), replace_copy_if(), reverse_copy(), rotate_copy(), and their ranges counterparts. #5495
  • Improved <mdspan>'s debug checks in layout_stride::mapping<E>'s constructor. #5505
  • Avoided compiler warnings in vector<bool>::max_size() with the compiler's upcoming implementation of Defect Report P2280R4. #5550 #5566
  • Updated several checks for precondition violations and impossible situations to use the STL's usual error reporting mechanism. #5560
  • Improved regex parsing to detect excessive recursion (caused by extreme numbers of non-capturing groups or lookahead assertions) and throw a regex_error with the code regex_constants::error_stack. #5588
  • Changed <regex> matching to use heap allocations for saved match state, slightly reducing stack pressure. #5682
  • Silenced CodeQL warnings. #5625
  • Silenced a new compiler warning C5291 throughout the STL. #5645
• Improved debugger visualization:
  • Fixed an off-by-one mistake in the displayed year for system_clock::time_point. #5389
  • Updated the visualizer for system_clock::time_point to recognize the synonymous but slightly different type name emitted by Clang. #5390
• Improved test coverage:
  • Updated our LLVM submodule, including new tests. #5349 #5467 #5688
  • Changed the benchmark build from /O2 /Ob1 to /O2 /Ob2, producing more realistic and useful results. #5370
  • Added benchmarks for:
    * fill() and fill_n(). #5400
    * reverse() and reverse_copy(). #5493
    * The count() optimization for vector<bool>. #5684
  • Improved the consistency of how normal_distribution is used in benchmarks and tests. #5404
  • Increased the consistency of several benchmarks by adding allocators to control alignment. #5443
  • Updated the benchmarks to support being built with Clang. #5533
  • Updated an iter_rvalue_reference_t test in response to a compiler change. #5378
  • Fixed sporadic test failures by avoiding excessive compiler memory consumption. #5383
  • Improved the runtime performance of the major test for vectorized algorithms. #5425
  • Added more test coverage for search_n() and ranges::search_n. #5439 #5440
  • Updated the test harness to properly detect the locale name "Czech_Czechia.1250". #5480
  • Updated source_location test coverage to handle upcoming changes in the EDG front-end used for IntelliSense. #5551
  • Categorized the remaining <regex> test failures in the libcxx suite. #5587
  • Avoided/suppressed compiler warnings in tests. #5654 #5655 #5656 #5657 #5676
  • Worked around assertions in the lerp() test on ARM64. #5687
• Improved documentation:
  • Clarified our machine-searchable SPDX-License-Identifier comments to properly describe how we used Ryu to implement <charconv>. #5401
  • Fixed confusing comments around the control macro for vectorizing algorithms with floating-point types. #5417
• Code cleanups:
  • Simplified the control flow in ranges::search_n. #5343
  • Simplified the implementation of regex quantifiers. #5253
  • Removed comments that were citing proposed resolutions for LWG issues, now that those issues have been officially resolved by the November 2024 and June 2025 meetings. #5360 #5584
  • Removed compiler bug workarounds. #5410 #5580 #5634 #5661 #5674
  • Significantly cleaned up the implementation of x64/x86 vectorized algorithms. #5429 #5450 #5485 #5532
  • Removed an unnecessarily verbose internal macro. #5475
  • Removed unnecessary code for constant evaluation in char_traits::assign(). #5488
  • Various cleanups (described in detail in the PRs, not repeated here). #5498 #5500 #5541 #5565 #5636
  • Restructured code to if constexpr (condition) { ... } else { ... }, improving clarity and avoiding unreachable code. #5643
  • Simplified how <chrono> initializes a tm struct. #5662
• Infrastructure improvements:
  • Added ARM64EC stages to Azure Pipelines. #5492 #5517 #5521
    * Including an Early Build, benchmarks, and tests.
  • Improved code format validation to report line numbers in error messages. #5559
  • Updated dependencies. #5370 #5410 #5478 #5512 #5530 #5580 #5641 #5659 #5674
    * Updated build compiler to VS 2022 17.14.12 Preview 1.
    * Updated CMake to 3.31 (now required).
    * Updated Google Benchmark to 1.9.4.
    * Updated Python to 3.13.6.
    * Updated to Windows 11 SDK 26100. This is now required for building and testing the STL, but not for using it.
• Updated _MSVC_STL_UPDATE and _MSVC_STL_VERSION. #5385 #5464 #5568 #5633 #5664

Older Versions

• VS 2022 Changelog
• VS 2019 Changelog