cmake: Selecting a generator within CMakeLists.txt

Question

I would like to force CMake to use the \"Unix Makefiles\" generator from within CMakeLists.txt.

This is the command I use n

Answer 1

It seems to me that the variable CMAKE_GENERATOR is set too late if set in the CMakeLists.txt. If you use (even at the beginning of CMakeLists.txt)

set(CMAKE_GENERATOR "Ninja")
message("generator is set to ${CMAKE_GENERATOR}")

you can see in the output something like

% cmake ../source
-- The C compiler identification is GNU 4.9.2
...
-- Detecting CXX compile features - done
generator is set to Ninja
-- Configuring done
-- Generating done
-- Build files have been written to: /tmp/build

So the variable is only set at the very end of the generation procedure. If you use something like

set(CMAKE_GENERATOR "Ninja" CACHE INTERNAL "" FORCE)

in CMakeLists.txt, then in the very first run of cmake ../source (without -G) the default generator is used. The variable CMAKE_GENERATOR is stored in the cache, though. So if you rerun cmake ../source afterwards, it will use the generator as specified in the CMAKE_GENERATOR variable in the cache.

This is surely not the most elegant solution, though ;-) Maybe use a batch file that will actually execute the cmake -G generator for the user...