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

Just encountered a similar issue myself and discovered CMAKE_VS_PLATFORM_NAME, which is calculated based on the generator and I think it's worth a mention.

I've tried it with cmake 3.16.1 (According to the docs it's been available since 3.1.3) using: -GVisual Studio 15 2017, -GVisual Studio 15 2017 Win64 and -GVisual Studio 15 2017 -Ax64 and it was set to: Win32, x64 and x64 respectively. So for this scenario I think checking against Win32 should work e.g.

if ("${CMAKE_VS_PLATFORM_NAME}" STREQUAL "Win32")
    ...
endif ()