我正在使用 CMake 开发一个项目.我的代码包含 constexpr 方法，在 Visual Studio 2015 中允许，但在 Visual Studio 2013 中不允许.
I'm developing a project with CMake. My code contains constexpr methods, that are allowed in Visual Studio 2015, but not in Visual Studio 2013.
如果指定的编译器支持该功能，我如何检查 CMakeLists.txt ?我在 CMake 文档中看到 CMAKE_CXX_KNOWN_FEATURES，但我不明白如何使用它.
How can I check in the CMakeLists.txt if the feature is supported by the specified compiler? I've seen in CMake documentation CMAKE_CXX_KNOWN_FEATURES, but I didn't understand how to use it.
您可以使用 target_compile_features 需要 C++11(/14/17) 特性:
You can use target_compile_features to require a C++11(/14/17) feature:
target_compile_features(target PRIVATE|PUBLIC|INTERFACE feature1 [feature2 ...])
feature1 是 <代码>CMAKE_CXX_KNOWN_FEATURES.例如，如果你想在你的公共 API 中使用 constexpr，你可以使用:
add_library(foo ...)
target_compile_features(foo PUBLIC cxx_constexpr)
<小时>
您还应该查看 WriteCompilerDetectionHeader 模块，它允许将特性检测为选项，并在编译器不支持某些特性时提供向后兼容性实现:
You should also take a look at the WriteCompilerDetectionHeader module which allows to detect features as options, and provides a backward compatibility implementation for some features if the compiler does not support them:
write_compiler_detection_header(
FILE foo_compiler_detection.h
PREFIX FOO
COMPILERS GNU MSVC
FEATURES cxx_constexpr cxx_nullptr
)
如果关键字constexpr可用，这里将生成一个文件foo_compiler_detection.h，其中定义了FOO_COMPILER_CXX_CONSTEXPR:
Here a file foo_compiler_detection.h will be generated with FOO_COMPILER_CXX_CONSTEXPR defined if the keyword constexpr is available:
#include "foo_compiler_detection.h"
#if FOO_COMPILER_CXX_CONSTEXPR
// implementation with constexpr available
constexpr int bar = 0;
#else
// implementation with constexpr not available
const int bar = 0;
#endif
此外，如果当前编译器存在该功能，FOO_CONSTEXPR 将被定义并扩展为 constexpr.否则为空.
Moreover, FOO_CONSTEXPR will be defined and will expand to constexpr if the feature exists for the current compiler. It will be empty otherwise.
FOO_NULLPTR 将被定义并扩展为 nullptr 如果当前编译器存在该功能.否则它将扩展为兼容性实现(例如 NULL).
FOO_NULLPTR will be defined and will expand to nullptr if the feature exists for the current compiler. It will expand to a compatibility implementation otherwise (e.g. NULL).
#include "foo_compiler_detection.h"
FOO_CONSTEXPR int bar = 0;
void baz(int* p = FOO_NULLPTR);
请参阅 CMake 文档.
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