如何用 CMake 检测编译器对 C + + 11的支持

有没有办法让 CMake 自动检测编译器是否支持 C + + 11？

因为在 CMake 运行期间，最好通知用户代码将不会编译，因为编译器不支持 C + + 11。现在我设置了 C + + 11标志。但是，如果编译器不支持它，用户在 CMake 运行期间将得到编译错误，而不是错误。

完美的应该是像 find_package()那样工作的东西。然而，我还没有找到任何提供所需功能的模块或函数。

另外，如果能够检测编译器是否需要标志 std=c++0x或 std=c++11的特性就更好了。

是否有可用的东西，或者我需要自己开发这个？

下面是我到目前为止使用的一些代码，但是它只能用于 GNU’c GCC 编译器。如果有一个更普遍的解决方案就好了。

if(CMAKE_COMPILER_IS_GNUCXX)
execute_process(COMMAND ${CMAKE_C_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION)
if (GCC_VERSION VERSION_GREATER 4.7 OR GCC_VERSION VERSION_EQUAL 4.7)
message(STATUS "C++11 activated.")
add_definitions("-std=gnu++11")
elseif(GCC_VERSION VERSION_GREATER 4.3 OR GCC_VERSION VERSION_EQUAL 4.3)
message(WARNING "C++0x activated. If you get any errors update to a compiler which fully supports C++11")
add_definitions("-std=gnu++0x")
else ()
message(FATAL_ERROR "C++11 needed. Therefore a gcc compiler with a version higher than 4.3 is needed.")
endif()
else(CMAKE_COMPILER_IS_GNUCXX)
add_definitions("-std=c++0x")
endif(CMAKE_COMPILER_IS_GNUCXX)
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At this point, CMake does not have a convenient form to support C++11. Ideally, you would specify a C++11 project like this:

project(foo CXX11)

at the beginning of your CMakeLists.txt. But the CXX11 project type does not exist (yet). Until then, you may use a two-staged technique:

  1. Determine the compiler type and version
  2. Adjust build flags accordingly.

For example, this is what I use to support C++11 with Clang and GCC:

# Initialize CXXFLAGS.
set(CMAKE_CXX_FLAGS                "-Wall -std=c++11")
set(CMAKE_CXX_FLAGS_DEBUG          "-O0 -g")
set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG")
set(CMAKE_CXX_FLAGS_RELEASE        "-O4 -DNDEBUG")
set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g")


# Compiler-specific C++11 activation.
if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
execute_process(
COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION)
if (NOT (GCC_VERSION VERSION_GREATER 4.7 OR GCC_VERSION VERSION_EQUAL 4.7))
message(FATAL_ERROR "${PROJECT_NAME} requires g++ 4.7 or greater.")
endif ()
elseif ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
else ()
message(FATAL_ERROR "Your C++ compiler does not support C++11.")
endif ()
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At the time of this writing (pre-GCC 4.8), it may not be a good idea to detect C++11 flags and add them. This is because changing the standard (at least for GCC) breaks ABI compatibility, which can result in link errors.

Therefore, the use of the C++11 standard should explicitly specified with the compiler setting during the initial CMake configuration of the project, e.g.

CXX='g++ -std=c++11' cmake /path/to/source

That is, the use of -std=c++11 should be treated like a separate compiler, which should not be mixed or changed in a project.

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We've written a CMake module for detecting and enabling C++11 support which you can find here:
https://github.com/NitroShare/CXX11-CMake-Macros

It's still a work-in-progress, but we are using it for a number of Qt projects that target Windows/Linux/Mac. Currently only MSVC++, GCC, and Clang are supported.

Example:

include(CXX11)


check_for_cxx11_compiler(CXX11_COMPILER)


# If a C++11 compiler is available, then set the appropriate flags
if(CXX11_COMPILER)
enable_cxx11()
endif()
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最佳答案

If you have CMake version 3.1.0 or later you can detect what C++ features your C++ compiler supports

cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)
project(foobar CXX)
message("Your C++ compiler supports these C++ features:")
foreach(i ${CMAKE_CXX_COMPILE_FEATURES})
message("${i}")
endforeach()

But normally you don't need to use the CMake variable CMAKE_CXX_COMPILE_FEATURES in your CMake scripts. Instead there are two ways of how to tell CMake under which C++ standard your C++ files should be compiled, either by specifying the C++ standard explicitly or by specifying the required C++ features and let CMake induce the C++ standard. CMake will make sure the C++ compiler is invoked with the correct command line flags (e.g. -std=c++11).

  1. Specifying the C++ standard explicitly

You could specify the C++ standard explicitly, by setting the CMake properties CXX_STANDARD and CXX_STANDARD_REQUIRED for your CMake target.

$ cat /tmp/src/CMakeLists.txt
project(foobar CXX)
cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)
add_executable(prog main.cc)
set_property(TARGET prog PROPERTY CXX_STANDARD 11)
set_property(TARGET prog PROPERTY CXX_STANDARD_REQUIRED ON)
$ cat /tmp/src/main.cc
int main() {
return 0;
}
$ mkdir /tmp/build
$ cd /tmp/build
$ cmake /tmp/src
-- The CXX compiler identification is GNU 4.8.2
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /tmp/build
$ make VERBOSE=1 | grep main.cc | grep -- "-c"
/usr/bin/c++    -std=gnu++11 -o CMakeFiles/prog.dir/main.cc.o -c /tmp/src/main.cc
$
  1. Specifying the required C++ features and let CMake induce the C++ standard

You could use the CMake command target_compile_features to specify the C++ features that are made use of in your CMake target. From this list CMake will induce the C++ standard to be used. The CMake global property CMAKE_CXX_KNOWN_FEATURES lists the C++ features you can choose from.

cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)
message("Your CMake version supports these C++ features:")
get_property(known_features GLOBAL PROPERTY CMAKE_CXX_KNOWN_FEATURES)
foreach(i ${known_features})
message("${i}")
endforeach()

For example, this C++ program with the filename main.cc makes use of the C++11 features: cxx_strong_enums, cxx_constexpr, cxx_auto_type

#include <cstdlib>


int main(int argc, char *argv[]) {
enum class Color { Red, Orange, Yellow, Green, Blue, Violet };
constexpr float a = 3.1415f;
auto b = a;
return EXIT_SUCCESS;
}

This CMakeLists.txt file would build it

cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)
project(foobar CXX)
add_executable(foobar main.cc)
set(needed_features
cxx_strong_enums
cxx_constexpr
cxx_auto_type)
target_compile_features(foobar PRIVATE ${needed_features})
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Use:

include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX11)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
elseif(COMPILER_SUPPORTS_CXX0X)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
else()
message(FATAL_ERROR "Compiler ${CMAKE_CXX_COMPILER} has no C++11 support.")
endif()

This is from Enabling C++11 (C++0x) in CMake with minor changes.

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If you are using CMake 3.8 or newer, you can use the feature cxx_std_11, which requests C++11 or above:

target_compile_features(Hello PUBLIC cxx_std_11)

In CMake 3.1* and newer, the proper, simple way to do this is to use the CXX_STANDARD property for a given target. For example, given this simple example using auto (named main.cpp):

#include <iostream>


int main() {
auto num = 10;
std::cout << num << std::endl;
return 0;
}

The following CMakeLists.txt will enable C++11 support:

cmake_minimum_required(VERSION 3.3)
project(Hello CXX)


set(SOURCE_FILES main.cpp)
add_executable(Hello ${SOURCE_FILES})


set_property(TARGET Hello PROPERTY
CXX_STANDARD 11
CXX_STANDARD_REQUIRED ON
)

This will add any flags necessary such as -std=c++11. Note that the CXX_STANDARD_REQUIRED property will prevent the standard from decaying to an earlier version.

Another proper but not as simple way to specify the CMAKE_CXX_KNOWN_FEATURES that you use, such as cxx_auto_type:

cmake_minimum_required(VERSION 3.3)
project(Hello CXX)


set(SOURCE_FILES main.cpp)
add_executable(Hello ${SOURCE_FILES})
target_compile_features(Hello PRIVATE cxx_auto_type)

* I have not tried this on CMake 3.1, but have verified it works in CMake 3.3. The documentation for 3.1 does document this so it should work.


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