问题描述

我正在尝试使用 CMake 将 /std:c++17 编译器标志添加到 VS2017.到目前为止，我正在使用现代"跨平台方式:

I'm trying to add the /std:c++17 compiler flag to VS2017 with CMake. I'm using the "modern" cross-platform way so far:

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF) # -std=c++11 instead of -std=gnu++11
set(MY_CXX_COMPILE_FEATURES cxx_generic_lambdas cxx_range_for cxx_strong_enums)

add_library(mylib INTERFACE)
target_compile_features(mylib INTERFACE ${MY_CXX_COMPILE_FEATURES})

这在 VS2017 中添加了 /std:c++14(这可能是默认值?).但是，我无法将其切换到 C++17(即添加 /std:c++17).如果我只是手动添加它，我会收到不太好的警告，因为两个标志都存在:

This adds /std:c++14 in VS2017 (which might be the default anyway?). However I'm having trouble switching this to C++17 (i.e. having it add /std:c++17). If I just add it manually, I get the not-so-nice warning because both flags are present:

1>cl : 命令行警告 D9025: 用 '/std:c++17' 覆盖 '/std:c++14'

我试过 set(CMAKE_CXX_STANDARD 17) 但它没有效果，事实上 CMake 文档提到 CMAKE_CXX_STANDARD 无论如何对 VS 没有影响.

I've tried set(CMAKE_CXX_STANDARD 17) but it has no effect, in fact the CMake documentation mentions that CMAKE_CXX_STANDARD has no effect on VS anyway.

至于向 target_compile_features 添加 C++17 特性，似乎还没有(即使在 CMake-3.9.0-rc5 中)，即使有，我专门只使用 C++17 中的 std::optional，并且没有像 std::optional 这样的库功能的 target_compile_features 标志.

As for adding a C++17 feature to target_compile_features, it doesn't seem like there are any yet (even in CMake-3.9.0-rc5), and even if there were, I'm specifically only using std::optional from C++17, and there's no target_compile_features flags for library features like std::optional.

所以我的问题是，使用 CMake 执行此操作的最佳(或最不丑陋)方法是什么?在某种程度上，它也适用于 gcc 和 clang?我很高兴使用最新的 CMake 版本(3.8 或 3.9).我更喜欢它不错"，而不是手动循环遍历 CXX_COMPILE_FLAGS 并删除字符串/std:c++14"或类似的一些hack.

So my question is, what's the best (or least ugly) way to do this with CMake? And in a way so it'll also work for gcc and clang? I'm happy to use a very recent CMake version (3.8 or 3.9). I prefer it to be "nice" and not manually looping through CXX_COMPILE_FLAGS and removing the string "/std:c++14" or some hack like that.

(编辑:它也可以是 VS/std:c++latest 开关 - 以可能的为准.两者都适用.)

(Edit: It can also be the VS/std:c++latest switch - whichever is possible. Both work for the purpose.)

推荐答案

将我的评论转化为答案

1. CMake 团队正在为 VS2017 开发它(对于 2017 年 7 月，即将推出的 CMake 版本 3.10):

1. The CMake team is working on it for VS2017 (as for July 2017, for upcoming CMake version 3.10):

CMake:MSVC 标准版本切换

那些标志似乎是相当新的开关(与此问题的日期有关):

Those flags seem to be rather new switches (as related to the date of this question):

VS 2017 15.3 预览版现在支持/std:c++17

VS 2017 15.3 preview now supports /std:c++17

因此，对于 Visual Studio，您必须手动"替换或附加编译器开关，直到 CMake 正式支持它为止.

So for Visual Studio you have to "manually" replace or append the compiler switches until CMake officially does support it.

这是我为 std:c++latest 测试的代码片段(已经支持，例如在我的 CMake 3.8.0 版本中):

Here is a code snippet that I've tested for std:c++latest (which is already supported e.g. in my CMake 3.8.0 version):

if (MSVC_VERSION GREATER_EQUAL "1900")
    include(CheckCXXCompilerFlag)
    CHECK_CXX_COMPILER_FLAG("/std:c++latest" _cpp_latest_flag_supported)
    if (_cpp_latest_flag_supported)
        add_compile_options("/std:c++latest")
    endif()
endif()