{"id":28674,"date":"2021-09-02T21:18:28","date_gmt":"2021-09-02T21:18:28","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/cppblog\/?p=28674"},"modified":"2021-09-02T21:20:36","modified_gmt":"2021-09-02T21:20:36","slug":"msvc-cpp20-and-the-std-cpp20-switch","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/msvc-cpp20-and-the-std-cpp20-switch\/","title":{"rendered":"MSVC C++20 and the \/std:c++20 Switch"},"content":{"rendered":"

We are excited to announce that in Visual Studio 2019 version 16.11, we have added the \/std:c++20<\/code> switch to the set of language mode switches available. The addition of this switch indicates that we\u2019ve reached a point of sufficient stabilization of the MSVC C++20 feature set for it be used in production, with full support in VS servicing updates.<\/p>\n

This blog post focuses on describing our level of C++20 feature support, compiler-supported extensions, and the remaining feature set differences between MSVC and the ISO C++ standard as of Visual Studio 2019 version 16.11 and Visual Studio 2022 version 17.0<\/p>\n

C++ Language Modes and Compatibility Guarantees<\/span><\/h2>\n

First introduced in Visual Studio 2015<\/a>, the MSVC compiler has included C++ language mode switches to indicate the targeted level of standard conformance and we now support three stable language modes: \/std:c++14<\/code>, \/std:c++17<\/code>, \/std:c++20<\/code> (as of VS 2019 v16.11) and one preview mode (\/std:c++latest<\/code>).<\/p>\n

The stable modes indicate that features under those modes are ready for production use and have ABI compatibility guarantees. The \/std:c++latest<\/code> mode contains ISO C++ features without strong guarantees for compatibility, allowing iteration based upon issues identified in testing, ISO C++ standard changes, and community feedback which may impact ABI stability of those features. Once stabilized, features under \/std:c++latest will be moved under an applicable stable mode.<\/p>\n\n\n\n\n\n\n\n
Language Mode<\/strong><\/td>\nLanguage Mode enables strict-conformance (\/permissive-)<\/strong><\/td>\nABI Stable<\/strong><\/td>\nNotes<\/strong><\/td>\n<\/tr>\n
\/std:c++14<\/td>\nNo<\/td>\nYes<\/td>\nSee **Note A<\/em><\/strong><\/td>\n<\/tr>\n
\/std:c++17<\/td>\nNo<\/td>\nYes<\/td>\nSee **Note A<\/em><\/strong><\/td>\n<\/tr>\n
\/std:c++20<\/td>\nYes<\/td>\nYes<\/td>\nSee **Note B<\/em><\/strong><\/td>\n<\/tr>\n
\/std:c++latest<\/td>\nYes<\/td>\nNo<\/td>\nSee **Note B<\/em><\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

**<\/em><\/strong>Note A<\/em><\/strong>: Strict conformance mode is opt-in via the \/permissive- compiler switch<\/em><\/p>\n

**Note B<\/em><\/strong>: Some functionality such as C++20 Modules require strict-conformance mode to be enabled due to strong dependency on ISO C++ semantic behaviors. Compatibility mode (\/permissive) is supported as an opt-in switch \u00a0with some C++20 functionality disabled.<\/em><\/p>\n

C++20 Features added in VS 2019 v16.9 and later<\/span><\/h2>\n

Below is a summary of language and library C++20 features implemented since the last feature update.<\/p>\n

A more detailed changelog<\/a> is available for the STL on its GitHub repo<\/a> including information on the awesome community contributors who have provided feature implementations and bug fixes to the STL<\/p>\n

VS 2019 v16.9<\/span><\/h3>\n

C++20 Language Features<\/p>\n