How to detect C++11 support of a compiler with CMake

Question

Is there a way to let CMake detect automatically if a compiler supports C++11 or not?

As it would be nice to inform the users during the CMake run that the code will not compile as the compiler does not support C++11. At the moment I set the C++11 flags. However, if a compiler does not support it the user gets compile errors instead of an error during the CMake run.

Perfect would be something that works like find_package(). However, I have not found any module or function which provides the functionality needed.

Additional it would be nice to have the feature to detect if the compiler needs the flags std=c++0x or std=c++11.

Is there something available or do I need to develop this on my own?

Below is some code I use so far, however it works only with GNU'c GCC compilers. It would be nice if there would be a more general solution.

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) 

Answer 1

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 $ 

2. 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})