How to detect if 64 bit MSVC with cmake?

Question

I have a project which uses cmake, one target is set to only build with MSVC:

 if (MSVC)
     add_library(test SHARED source.cpp) 
 endif()

Answer 1

On recent versions of CMake/Visual Studio the bitness is selected with CMAKE_GENERATOR_PLATFORM, which can be specified on the command line with -A option:

cmake -G "Visual Studio 16 2019" -A Win32 -DCMAKE_BUILD_TYPE=Release ..

So, based on this feature you can then query the value from within the CMakeLists.txt:

if(NOT ("${CMAKE_GENERATOR_PLATFORM}" STREQUAL "Win64"))
    ...
ENDIF()