Cmake doesn't honour -D CMAKE_CXX_COMPILER=g++

Question

I'm trying to force cmake to build my cpp code with g++, as by default it uses clang instead. So I use: cmake -D CMAKE_CXX_COMPILER=g++ ../src/CMakeLists.txt after which cmake checks for gcc and g++ (with success), but nonetheless make VERBOSE=1 yields

/usr/bin/c++     -o CMakeFiles/trial_cpp.dir/trial.cpp.o -c "/Users/Kuba/Code/Sketchpad/Trial     project/src/trial.cpp"
Linking CXX executable trial_cpp
/opt/etlocal/bin/cmake -E cmake_link_script CMakeFiles/trial_cpp.dir/link.txt --verbose=1
/usr/bin/c++    -Wl,-search_paths_first -Wl,-headerpad_max_install_names   CMakeFiles/trial_cpp.dir/trial.cpp.o  -o trial_cpp 

As it calls /usr/bin/c++ not /usr/bin/g++ I concur it still uses clang. Any idea what's the problem? I know I have g++ and it's in /usr/bin/. I'm running Mac OS X 10.8.2

Answer 1

CMAKE_CXX_COMPILER can only be set the first time cmake is run in a given build directory. On subsequent runs it is ignored. In order to change CMAKE_CXX_COMPILER you first need to delete the contents of the build directory and then run cmake again with that option.

Source: http://www.cmake.org/Wiki/CMake_Useful_Variables

I believe the reasoning for only using that variable on the first run is because changing it later would potentially invalidate everything already built including the configuration checks so cmake would have to start from scratch anyway.