{"id":18805,"date":"2018-04-09T10:00:02","date_gmt":"2018-04-09T17:00:02","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vcblog\/?p=18805"},"modified":"2022-06-23T20:58:46","modified_gmt":"2022-06-23T20:58:46","slug":"msvc-now-correctly-reports-__cplusplus","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/msvc-now-correctly-reports-__cplusplus\/","title":{"rendered":"MSVC now correctly reports __cplusplus"},"content":{"rendered":"

The MSVC compiler\u2019s definition of the __cplusplus<\/code> predefined macro leaps ahead 20 years in Visual Studio 2017 version 15.7 Preview 3. This macro has stubbornly remained at the value “199711L”, indicating (erroneously!) that the compiler conformed to the C++98 Standard. Now that our conformance catch-up work is drawing to a close<\/a> we\u2019re updating the __cplusplus<\/code> macro to reflect the true state of our implementation. The value of the __cplusplus<\/code> macro doesn\u2019t imply that we no longer have any conformance bugs. It\u2019s just that the new value is much more accurate than always reporting “199711L”.<\/p>\n

\/Zc:__cplusplus<\/h3>\n

You need to compile with the \/Zc:__cplusplus<\/code> switch to see the updated value of the __cplusplus<\/code> macro. We tried updating the macro by default and discovered that a lot of code doesn\u2019t compile correctly when we change the value of __cplusplus<\/code>. We\u2019ll continue to require use of the \/Zc:__cplusplus<\/code> switch for all minor versions of MSVC in the 19.xx family.<\/p>\n

The version reported by the __cplusplus<\/code> macro also depends upon the standard version switch used. If you\u2019re compiling in C++14 mode the macro will be set to “201402L”. If you compile in C++17 mode the macro will be set to “201703L”. And the \/std:c++latest<\/code> switch<\/a>, used to enable features from the Standard currently in development, sets a value that is more than the current Standard. This chart shows the values of the __cplusplus<\/code> macro with different switch combinations:<\/p>\n\n\n\n\n\n\n\n\n\n
\/Zc:__cplusplus switch<\/th>\n\/std:c++ switch<\/th>\n__cplusplus value<\/th>\n<\/tr>\n
Zc:__cplusplus<\/code><\/td>\nCurrently defaults to C++14<\/td>\n201402L<\/td>\n<\/tr>\n
Zc:__cplusplus<\/code><\/td>\n\/std:c++14<\/code><\/td>\n201402L<\/td>\n<\/tr>\n
Zc:__cplusplus<\/code><\/td>\n\/std:c++17<\/code><\/td>\n201703L<\/td>\n<\/tr>\n
Zc:__cplusplus<\/code><\/td>\n\/std:c++latest<\/code><\/td>\n201704L<\/td>\n<\/tr>\n
Zc:__cplusplus-<\/code> (disabled)<\/td>\nAny value<\/td>\n199711L<\/td>\n<\/tr>\n
Zc:__cplusplus<\/code> not specified<\/td>\nAny value<\/td>\n199711L<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Note that the MSVC compiler does not, and never will, support a C++11, C++03, or C++98 standards version switch. Also, the value of the __cplusplus<\/code> macro is not affected by the \/permissive- switch<\/a>.<\/p>\n

We\u2019re updating IntelliSense to correctly reflect the value of __cplusplus<\/code> when compiling with MSVC. We expect IntelliSense to be correct in the next preview of 15.7.<\/p>\n

_MSC_VER and _MSVC_LANG<\/h3>\n

For finer-grained detection of changes in the MSVC toolset you can continue to use the _MSC_VER<\/code> predefined macro<\/a>. We have updated the value of this built-in macro with every toolset update in Visual Studio 2017 and will continue to do so.<\/p>\n

The _MSVC_LANG<\/code> predefined macro<\/a> continues to report the Standard version switch regardless of the value of \/Zc:__cplusplus<\/code>. _MSVC_LANG<\/code> is set whether or not the \/Zc:__cplusplus<\/code> option is enabled. When \/Zc:__cplusplus<\/code> is enabled, __cplusplus == _MSVC_LANG<\/code>.<\/p>\n

Please look for usage in your code<\/h3>\n

We\u2019ve heard repeatedly from developers<\/a> as we\u2019ve gotten closer to complete conformance that we need to update the value of this macro. Now we need help from you. We tried to define __cplusplus<\/code> correctly by default but discovered that a lot of code expects MSVC to always set the macro to “199711L”.<\/p>\n

Please take a moment to search your code for references to __cplusplus<\/code> and compile with the \/Zc:__cplusplus<\/code> switch enabled. Your code might be using this macro to determine if it\u2019s being compiled with MSVC or Clang in MSVC-emulation mode. If your codebase is really old, it might be using this macro to determine if you\u2019re using VC++ 6.0! Take a moment to compile with this switch enabled. We need the ecosystem to move forward so we can set __cplusplus<\/code> accurately by default.<\/p>\n

In closing<\/h3>\n

As always, we welcome your feedback. We can be reached via the comments below or via email (visualcpp@microsoft.com<\/a>).<\/p>\n

If you encounter other problems with MSVC in Visual Studio 2017 please let us know through Help > Report A Problem in the product<\/a>, or via Developer Community<\/a>. Let us know your suggestions through UserVoice<\/a>. You can also find us on Twitter (@VisualC<\/a>) and Facebook (msftvisualcpp<\/a>).<\/p>\n","protected":false},"excerpt":{"rendered":"

The MSVC compiler\u2019s definition of the __cplusplus predefined macro leaps ahead 20 years in Visual Studio 2017 version 15.7 Preview 3. This macro has stubbornly remained at the value “199711L”, indicating (erroneously!) that the compiler conformed to the C++98 Standard. Now that our conformance catch-up work is drawing to a close we\u2019re updating the __cplusplus […]<\/p>\n","protected":false},"author":312,"featured_media":35994,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-18805","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-cplusplus"],"acf":[],"blog_post_summary":"

The MSVC compiler\u2019s definition of the __cplusplus predefined macro leaps ahead 20 years in Visual Studio 2017 version 15.7 Preview 3. This macro has stubbornly remained at the value “199711L”, indicating (erroneously!) that the compiler conformed to the C++98 Standard. Now that our conformance catch-up work is drawing to a close we\u2019re updating the __cplusplus […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/posts\/18805","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/users\/312"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/comments?post=18805"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/posts\/18805\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/media\/35994"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/media?parent=18805"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/categories?post=18805"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/tags?post=18805"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}