CMake command line for C++ #define

Question

I need to compile different versions of a certain project by adding compiler switches. Usually I would do this by using add_definitions or something like

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Answer 1

To pass a C++ or C pre-processor define without modifying any CMake source files, use the environment variables CFLAGS for C or CXXFLAGS for C++ respectively, e.g.:

$ export CXXFLAGS="-D_MY_DEFINE=1 -D_MY_OTHER_DEFINE=1"
$ mkdir build
$ cd build
$ cmake ..