title	What's new for the C++ docs
ms.date	7/9/2021
description	The new docs and doc updates for the Microsoft C/C++ compiler, ATL/MFC, C runtime, and standard library docs.

Microsoft C++ docs: What's new for June 2021

This article lists major changes to the Microsoft C++ docs through June 2021.

• See what's new history for info about what was new in previous months.
• See What's new for C++ in Visual Studio for info about what's new in Visual Studio.
• See C++ conformance improvements in Visual Studio for the latest C and C++ conformance status.

Build insights

New articles

• HeaderUnit class
• Module class
• PrecompiledHeader class
• TRANSLATION_UNIT_TYPE enum
• TRANSLATION_UNIT_TYPE_DATA enum
• TranslationUnitType class

Updated articles

• C++ Build Insights SDK: event table - add new C++ Build Insights events
• Get started with C++ Build Insights - add new C++ Build Insights events

C language

Updated articles

• _Static_assert keyword and static_assert macro (C11) - update the SDK to use
• Alignment (C11) - update the SDK to use
• Generic selection (C11) - update the SDK to use

C runtime library

Updated articles

In addition to the changes below, many articles were updated to prevent the machine translation of code elements.

• _cprintf_p, _cprintf_p_l, _cwprintf_p, _cwprintf_p_l - printf() rounding behavior change
• _cprintf_s, _cprintf_s_l, _cwprintf_s, _cwprintf_s_l - printf() rounding behavior change
• _cprintf, _cprintf_l, _cwprintf, _cwprintf_l - printf() rounding behavior change
• _fprintf_p, _fprintf_p_l, _fwprintf_p, _fwprintf_p_l - printf() rounding behavior change
• _get_printf_count_output - printf() rounding behavior change
• _printf_p, _printf_p_l, _wprintf_p, _wprintf_p_l - printf() rounding behavior change
• _scprintf_p, _scprintf_p_l, _scwprintf_p, _scwprintf_p_l - printf() rounding behavior change
• _scprintf, _scprintf_l, _scwprintf, _scwprintf_l - printf() rounding behavior change
• _vcprintf_p, _vcprintf_p_l, _vcwprintf_p, _vcwprintf_p_l - printf() rounding behavior change
• _vcprintf_s, _vcprintf_s_l, _vcwprintf_s, _vcwprintf_s_l - printf() rounding behavior change
• _vscprintf, _vscprintf_l, _vscwprintf, _vscwprintf_l - printf() rounding behavior change
• _vsprintf_p, _vsprintf_p_l, _vswprintf_p, _vswprintf_p_l - printf() rounding behavior change
• _snprintf_s, _snprintf_s_l, _snwprintf_s, _snwprintf_s_l - printf() rounding behavior change
• errno constants - improve readability
• fprintf, _fprintf_l, fwprintf, _fwprintf_l - printf() rounding behavior change
• freopen_s, _wfreopen_s - new C11 flags
• freopen, _wfreopen - added C11 flags
• pow, powf, powl - note change to pow(T,int) starting in VS 2015 update 1
• printf_s, _printf_s_l, wprintf_s, _wprintf_s_l - printf() rounding behavior change
• setlocale, _wsetlocale - clarified UTF-8 string mode
• sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l - printf() rounding behavior change
• cprintf - printf() rounding behavior change
• fprintf_s, _fprintf_s_l, fwprintf_s, _fwprintf_s_l - printf() rounding behavior change
• sprintf_s, _sprintf_s_l, swprintf_s, _swprintf_s_l - printf() rounding behavior change
• strcpy_s, wcscpy_s, _mbscpy_s, _mbscpy_s_l - fixed code examples
• strncat_s, _strncat_s_l, wcsncat_s, _wcsncat_s_l, _mbsncat_s, _mbsncat_s_l - printf() rounding behavior change
• Type-generic math - updated the SDK version to use
• vprintf, _vprintf_l, vwprintf, _vwprintf_l - printf() rounding behavior change
• vsprintf_s, _vsprintf_s_l, vswprintf_s, _vswprintf_s_l - printf() rounding behavior change

C++ in Visual Studio

Updated articles

• _variant_t::operator= - add remarks for operator= and make the article easier to read.
• Abstract classes (C++) - add Microsoft-specific extension information for inline pure virtual destructor
• Attributes in C++ - add missing errors and warnings: C7000-C7999, C4834
• char, wchar_t, char8_t, char16_t, char32_t - clarified whether char is signed or unsigned

C++ porting and upgrade guide

Updated articles

• Introduction to Microsoft C++ for UNIX Users - Visual Studio 16.10 updates to C17 conformance
• Visual C++ What's New 2003 through 2015 - note change to pow(T,int) starting in VS 2015 update 1

C/C++ compiler and tools errors and warnings

New articles

• Command-line error D8048
• Compiler Error C7510
• Compiler Error C7536
• Compiler errors C7000 through C7499
• Compiler errors C7500 through C7999
• Compiler Warning (error) C4597
• Compiler warning (level 1) C4834
• Compiler Warning (level 1) C5050
• Compiler warning (level 3) C4698
• Compiler Warning (level 3) C4768
• Compiler Warning (level 4) C4841
• Compiler Warning (level 4) C4843
• Compiler warning C5037
• Fatal Error C1090

Updated articles

• Compiler Error C2139 - added some version 2017 diagnostics
• Compiler Error C2201 - added some version 2017 diagnostics
• Compiler Error C2276 - update C2276
• Compiler Error C2668 - added some version 2017 diagnostics
• Compiler Error C2855 - add remarks about how to resolve this error
• Compiler errors C2000 - C3999, C7000 - C7999 - add missing errors and warnings: C7000-C7999, C4834
• Compiler errors C7500 through C7999 - added some version 2017 diagnostics; add error C7510; add missing errors and warnings: C7000-C7999, C4834
• Compiler Warning (level 1) C4179 - added some version 2017 diagnostics
• Compiler Warning (level 1) C5208 and Error C7626 - add missing errors and warnings: C7000-C7999, C4834
• Compiler Warning (level 4) C4189 - added some version 2017 diagnostics
• Compiler Warning C5038 - added some version 2017 diagnostics
• Compiler warnings by compiler version - update Visual Studio 16.10 conformance improvements and new warnings; Add new 16.10 warnings, version info; update version strings for Visual Studio 16.8, 16.9, and 16.10
• Compiler warnings C4400 Through C4599 - added some Visual Studio version 2017 diagnostics
• Compiler warnings C4800 through C5999 - update Visual Studio 16.10 conformance improvements and new warnings; add new 16.10 warnings, version info; added some version 2017 diagnostics; add missing errors and warnings: C7000 - C7999, C4834
• Vectorizer and parallelizer messages - add vectorizer failure reason 505; add 1204 reason code

C/C++ compiler intrinsics and assembly language

Updated articles

• Microsoft Macro Assembler BNF Grammar - cleanup formatting and machine translation issues

C/C++ in Visual Studio overview

New articles

• C++ Conformance improvements, behavior changes, and bug fixes in Visual Studio 2017
• Microsoft C++ docs: What's new for Visual Studio 16.8
• What's new for C++ in Visual Studio 2017

Updated articles

• C++ Conformance improvements, behavior changes, and bug fixes in Visual Studio 2017 - added version 2017 diagnostics
• C++ Conformance improvements, behavior changes, and bug fixes in Visual Studio 2019 - Visual Studio 16.10 updates to C17 conformance; update 16.10 conformance improvements and new warnings; add error C7510; add missing errors and warnings: C7000 - C7999, C4834; update conformance docs for 16.9
• C++ in Visual Studio - Visual Studio 16.10 updates to C17 conformance
• Install C11 and C17 support in Visual Studio - Visual Studio 16.10 updates to C17 conformance
• Microsoft C/C++ language conformance by Visual Studio version - Visual Studio 16.10 updates to C17 conformance; update conformance table for Visual Studio 16.10 and Visual Studio 16.9
• Microsoft C++ docs: What's new for Visual Studio 16.8 - Visual Studio 16.10 updates to C17 conformance
• What's new for C++ in Visual Studio 2017 - Visual Studio 16.10 updates to C17 conformance; update Visual Studio 16.9 release conformance docs

C/C++ preprocessor reference

Updated articles

• Compiler warnings that are off by default - update Visual Studio 16.10 conformance improvements and new warnings; added some version 2017 diagnostics
• Predefined macros - add new Visual Studio 16.10 warnings, version info; update version strings for Visual Studio 16.8, 16.9, and 16.10

C/C++ projects and build systems

New articles

• /external (External headers diagnostics)
• /headerName (Build a header unit from the specified header)
• /sourceDependencies:directives (List module and header unit dependencies)
• CMakePresets.json and CMakeUserPresets.json Microsoft vendor maps
• Configure and build with CMake Presets in Visual Studio
• HeaderUnit class
• Module class
• PrecompiledHeader class
• TRANSLATION_UNIT_TYPE enum
• TRANSLATION_UNIT_TYPE_DATA enum
• TranslationUnitType class
• Walkthrough: Build and import header units in Microsoft Visual C++
• Walkthrough: Import STL libraries as header units

Updated articles

• /experimental:module (Enable module support) - new content for header-units
• /Qspectre - update for VS 2019
• /Y (precompiled headers) - new content for header-units
• /analyze (Code analysis) - update with up-to-date options list, add more information, and restructure for better organization of related options
• /await (Enable coroutine support) - add /await:strict for Visual Studio 16.10
• /clr (Common Language Runtime Compilation) - include version for support of /clr:netcore option
• /exportHeader (Create header units) - add new content related to header-units
• /external (External headers diagnostics) - /external not experimental in Visual Studio 16.10
• /F (Set Stack Size) - update for VS 2019
• /FC (Full path of source code file in diagnostics) - Classify behavior by version.
• /GL (Whole program optimization) - fix loc issue in /GL docs
• /headerUnit (Use header unit IFC) - new content for header-units
• /INTEGRITYCHECK (Require signature check) - updated signing guidance for integritycheck binaries
• /openmp (Enable OpenMP Support) - add /openmp:llvm compiler switch docs
• /reference (Use named module IFC) - new content for header-units
• /sourceDependencies (List all source-level dependencies) - new content for header-units
• /std (Specify Language Standard Version) - Visual Studio 16.10 updates to C17 conformance
• /translateInclude (Translate include directives into import directives) - new content for header-units
• Advanced Property Page - add Windows Desktop Compatible property for Visual Studio 16.10; Add LLVM toolset version option for Visual Studio 16.9
• ARM Exception Handling - fix ComputeXdataSize samples for ARM/ARM64
• ARM64 exception handling - fix ComputeXdataSize samples for ARM/ARM64
• C++ Build Insights SDK: event table - add New C++ Build Insights Events to documentation
• Clang/LLVM support in Visual Studio projects - add LLVM toolset version option for Visual Studio 16.9; update clang-support-msbuild.md
• CMake projects in Visual Studio - add advanced details about using CMake file-api
• Compiler options listed alphabetically - new content for header-units
• Compiler options listed by category - new content for header-units
• Configure and build with CMake Presets in Visual Studio - improve readability
• General Property Page (Project) - add Windows Desktop Compatible property for Visual Studio 16.10
• Get started with C++ Build Insights - add New C++ Build Insights Events to documentation
• How to: Modify the Target Framework and Platform Toolset - improve readability
• Open Folder support for C++ build systems in Visual Studio - fix CppProperties.json MinGW-w64 contents
• Unicode support in the compiler and linker - add info about how to save using a different encoding
• Use the Microsoft C++ toolset from the command line - updated for VS 2019
• Walkthrough: Compile a C program on the command line - Visual Studio 16.10 updates to C17 conformance
• Walkthrough: Compiling a Native C++ Program on the Command Line - clarified notepad behavior when opening source file

C++ Standard Library (STL) reference

New articles

• <ranges>
• day class
• month_day_last class
• month_day class
• month_weekday_last class
• month_weekday class
• year_month class

Updated articles

• bitset class - improve readability
• vector class - fix typo in code sample

Code quality

New articles

• C6389: MARK_INTERNAL_OR_MISSING_COMMON_DECL

Updated articles

• C6031 - add note about ignoring a function's return value
• C26432 DEFINE_OR_DELETE_SPECIAL_OPS - update code examples
• C26497 USE_CONSTEXPR_FOR_FUNCTION - add note about when warning won't be issued

Linux with C++ in Visual Studio

Updated articles

• Connect to your target Linux system in Visual Studio - add section about host key verification
• ConnectionManager reference - add note about host key fingerprint flags added in Visual Studio 16.10.

Overview of Windows programming in C++

Updated articles

• Determining Which DLLs to Redistribute - updated for Visual Studio 2019

Parallel programming in C++ in Visual Studio

Updated articles

• C++ AMP Overview - add note about C++ AMP library deprecation
• Walkthrough: Debugging a C++ AMP application - fixed code sample

Community contributors

The following people contributed to the C++, C, and Assembler docs during this period. Thank you! See Microsoft Docs contributor guide overview if you'd like to learn how to contribute.

• 0xbadfca11 (1)
• bclehmann - Benjamin Lehmann (1)
• Brian-Taylor8 (1)
• cartwrightluke (2)
• ccawley2011 - Cameron Cawley (1)
• EddieBreeveld - Edward Breeveld (1)
• FrankAtHexagon - Frank Edwards (1)
• fsb4000 - Igor Zhukov (1)
• Jaiganeshkumaran - Jaiganesh Kumaran (2)
• jayvient - Jayvien (1)
• KishkinJ10 (1)
• kokosxD - kokos (1)
• langemol - Jacco Mol (1)
• MUzairS15 (1)
• nadavsu - Nadav (1)
• NegiAkash890 - Akash Negi (1)
• pjessesco - Jino Park (1)
• pramodkirchki (1)
• Radfordhound - Graham Scott (1)
• sapant-msft (1)
• sebgod - Sebastian Godelet (1)
• seedkar1 (1)
• ShamanCoder (1)
• sheila-stewart (1)
• softmac (1)
• Thieum - Matthieu Penant (2)
• tjs137 (1)
• urmyfaith - zx (1)
• ValZapod - Valerii Zapodovnikov (1)
• westinn - Nicolas Westin (1)

What's new history

The following section provides the previous months of what's new in the Visual Studio docs.

February 2021

C language

New articles

• _Noreturn keyword and noreturn macro (C11)
• _Static_assert keyword and static_assert macro (C11)

Updated articles

• C Assignment Operators - lexical grammar update for C17
• C enumeration declarations - fixed lexical grammar
• C Keywords - lexical grammar update for C17
• C Lexical grammar - lexical grammar update for C17
• Parsing C Command-Line Arguments - Document exceptions to the rules for parsing C arguments
• Summary of C statements - updated for __leave, __try keywords
• Summary of Declarations - lexical grammar update for C17
• Summary of Expressions - lexical grammar update for C17
• Type Qualifiers - added restrict

C runtime library

New articles

• Type-generic math

Updated articles

• _cwait - fixed code example
• assert Macro, _assert, _wassert - Clarified assert behavior
• qsort - added note about stability
• realloc - added C99 conformance notes
• round, roundf, roundl - Clarified rounding code example
• setlocale, _wsetlocale - added C Runtime UTF-8 support info
• vsnprintf_s, _vsnprintf_s, _vsnprintf_s_l, _vsnwprintf_s, _vsnwprintf_s_l - Clarified return values
• Compatibility - added C99 conformance notes
• CRT Library Features - added C99 conformance notes
• Function family overview - added operator new and delete

C/C++ preprocessor reference

Updated articles

• MSVC new preprocessor overview - updated preprocessor content
• Predefined macros - updated to Visual Studio 16.8 release notes, C11/C17 /std support and SDK install docs

Code quality

New articles

• C33001 - VC Code Analysis - add for new rules in Visual Studio 16.8
• C33004 - VC Code Analysis - add for new rules in Visual Studio 16.8
• C33005 - VC Code Analysis - add for new rules in Visual Studio 16.8
• C33010 - VC Code Analysis - add for new rules in Visual Studio 16.8
• C33011 - VC Code Analysis - add for new rules in Visual Studio 16.8
• C33020 - VC Code Analysis - add for new rules in Visual Studio 16.8
• C33022 - VC Code Analysis - add for new rules in Visual Studio 16.8

Updated articles

• C6262 - address cpp-docs.zh-tw issue 20
• C26401 DONT_DELETE_NON_OWNER - added example and Core Guidelines link to C26401
• C26402 DONT_HEAP_ALLOCATE_MOVABLE_RESULT - added example for C26402
• C26408 NO_MALLOC_FREE - added example and Core Guidelines link to C26408
• C26409 NO_NEW_DELETE - added example for C26409
• C26432 DEFINE_OR_DELETE_SPECIAL_OPS - added example for C26432
• C26434 DONT_HIDE_METHODS - added example for C26434
• C26436 NEED_VIRTUAL_DTOR - added example and Core Guidelines link to C26436
• C26439 SPECIAL_NOEXCEPT - added example and link to Core Guidelines for C26439
• C26440 DECLARE_NOEXCEPT - added example and link to Core Guidelines for C26440
• C26446 USE_GSL_AT - added an example for C26446
• C26447 DONT_THROW_IN_NOEXCEPT - adding example to C26447
• C26460 USE_CONST_REFERENCE_ARGUMENTS - added description and example to C26460
• C26461 USE_CONST_POINTER_ARGUMENTS: - added description and example to C26461
• C26462 USE_CONST_POINTER_FOR_VARIABLE - added description and example to C26462
• C26465 NO_CONST_CAST_UNNECESSARY - added example to C26465
• C26466 NO_STATIC_DOWNCAST_POLYMORPHIC - added Example to C26466
• C26471 NO_REINTERPRET_CAST_FROM_VOID_PTR - added Example to C26471
• C26474 NO_IMPLICIT_CAST - updated to clarify base/derived cases
• C26482 NO_DYNAMIC_ARRAY_INDEXING - added example to C26482
• C26483 STATIC_INDEX_OUT_OF_RANGE - added example to C26483
• C26490 NO_REINTERPRET_CAST - added example to C26490
• C26492 NO_CONST_CAST - added example to C26492
• C26493 NO_CSTYLE_CAST - added example to C26493
• C26494 VAR_USE_BEFORE_INIT - added example to C26494
• C26495 MEMBER_UNINIT - updated examples and links in C26495
• C26496 USE_CONST_FOR_VARIABLE - added example to C26496
• C26497 USE_CONSTEXPR_FOR_FUNCTION - added example to C26497

Linux with Microsoft C++ in Visual Studio

New articles

• Configure a Linux CMake project in Visual Studio

Updated articles

• Configure a Linux CMake project in Visual Studio - updated to reflect latest UI
• ConnectionManager reference - added commands for modify, clean
• Create a Linux MSBuild C++ project in Visual Studio - updated instructions to create a Linux project
• Deploy, run, and debug your Linux MSBuild project - added GDB Path

C/C++ compiler and tools errors and warnings

New articles

• Compiler Warning (level 4) C4388 - added warning C4388, updated Visual Studio 16.7 warnings

Updated articles

• Compiler Error C3381 - address cpp-docs 2493; update remarks and example
• Compiler Warning (level 3) C4018 - updated Visual Studio 16.7 warnings
• Compiler Warning (level 4) C4389 - updated Visual Studio 16.7 warnings
• Compiler Warnings by compiler version - updated Visual Studio 16.7 warnings
• Compiler warnings C4800 through C5999 - updated Visual Studio 16.7 warnings

C/C++ compiler intrinsics and assembly language

Updated articles

• C++ conformance improvements in Visual Studio - updated to Visual Studio 16.8 release notes
• C++ in Visual Studio - updated DevCom and Microsoft Docs Q&A links
• Microsoft C/C++ help and community - updated DevCom and Microsoft Docs Q&A links
• Microsoft C/C++ language conformance - updated C++20 library conformance table, update language feature table for Visual Studio 16.7

C++ in Visual Studio

Updated articles

• __restrict
• union - fixed code snippet
• if-else statement (C++) - added description for if/else grammar

C/C++ projects and build systems

New articles

• .vcxproj files and wildcards
• /headerUnit (Use header unit IFC)
• /module:exportHeader (Create header units)
• /module:reference (Use named module IFC)
• /translateInclude (Translate include directives into import directives)
• /Zc:preprocessor (Enable preprocessor conformance mode)

Updated articles

• /clr (Common Language Runtime Compilation) - added description for /clr
• /permissive- (Standards conformance) - updated to Visual Studio 16.8 release notes
• Importing data using __declspec(dllimport) - updated example
• pgosweep - added more pgosweep options

C++ porting and upgrade guide

Updated articles

• How to: Use existing C++ code in a Universal Windows Platform app - reworked for clarity and updated examples

C++ Standard Library (STL) reference

New articles

• <bit>
• <bit> functions
• endian enum

Updated articles

• <bit> functions - updated nodiscard syntax
• <ios> typedefs - updated example
• basic_string_view Class - added starts_with(), ends_with()
• basic_string Class - added _starts_with(), ends_with()
• ios_base Class
• map class
• multimap Class - added contains()
• multiset Class - added contains()
• set Class - added contains()
• unordered_map Class - added contains()
• unordered_multimap Class - added contains()
• unordered_multiset Class - added contains()
• unordered_set Class - added contains()

Community contributors

The following people contributed to the C++, C, and Assembler docs during this period. Thank you! See Microsoft Docs contributor guide overview if you'd like to learn how to contribute.

• BeardedFish - Darian B. (1)
• codevenkat (1)
• definedrisk - Ben (3)
• eltociear - Ikko Ashimine (1)
• fsb4000 - Igor Zhukov (1)
• Jaiganeshkumaran - Jaiganesh Kumaran (1)
• jogo- (1)
• justanotheranonymoususer (1)
• matrohin - Dmitry Matrokhin (1)
• mhemmit (1)
• MSDN-WhiteKnight - MSDN.WhiteKnight (1)
• OdinTemple - Odin Temple (1)
• r00tdr4g0n - r00tdr4g0n (1)
• sebkraemer - Sebastian Krämer (1)
• vtjnash - Jameson Nash (1)
• yecril71pl - Christopher Yeleighton (4)
• Youssef1313 - Youssef Victor (1)
• zecozephyr - Jonathan Bailey (1)