Option to force either 32-bit or 64-bit build with cmake

Question

I would like to offer a way that always builds my target as a 32-bit or always as 64-bit executable executable with cmake independent of the host system (Adding the "-m32" or "-m64" flag for gcc, not sure yet what to do for other compilers).

I can think of three ways to do this, which one should I use?

1. an option (-DUSE32bit=true)
2. a tool chain (-DCMAKE_TOOLCHAIN_FILE=64bit.toolchain)
3. build types (-DCMAKE_BUILD_TYPE=release32)

In my case the forced 32-bit build will be the default and should be easy to use. A forced 64-bit build is the also useful for some cases and should not be too difficult. Using the bit width of the host system rarely makes sense for my case and I don't want to support it.

I found a related question here (The proper way of forcing a 32-bit compile using CMake) but the answers mostly discuss how it can be done at all, not how best to make it configurable.

Solution 1

For Visual Studio and per https://cmake.org/cmake/help/latest/variable/CMAKE_GENERATOR_PLATFORM.html

For Visual Studio Generators with VS 2005 and above this specifies the target architecture.

cmake . -DCMAKE_GENERATOR_PLATFORM=x64

Solution 2

thanks for all your inputs, but on my side i've finally chosen the -m32 hack with cmake

# cmake windows 32 bits mode bug: 32 bits link mode must be explicit (otherwise cmake will always guess a 64 bits target)
#  1- run "vcbarsall.bat x86" to setup Visual Studio build profile
#  2- "set cflags=-m32" and "set cxxflags=-m32"
#  3- let the cmake plugin "automatically" guess the target platform