Does CMake have a higher-level abstraction for detecting 32-bit/64-bit builds?

Question

CMake's global property, FIND_LIBRARY_USE_LIB64_PATHS, has the following documentation:

FIND_LIBRARY_USE_LIB64_PATHS is a boolean specifying whether the FIND_LIBRARY command should automatically search the lib64 variant of directories called lib in the search path when building 64-bit binaries.

Reading "when building 64-bit binaries" implies CMake somehow knows my target architecture, and automatically toggles the behavior on/off depending. Am I just reading too far into this, or does CMake have a higher-level abstraction for dealing with 32-bit/64-bit compilation?

If there is, how do I configure whatever mechanism is used by FIND_LIBRARY_USE_LIB64_PATHS, to force a 32-bit/64-bit compiliation?

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I realize there are existing questions dealing with forcing 32-bit/64-bit, but they deal with CMAKE_C_FLAGS and the like. If CMake has a higher level abstraction, I'd prefer it to messing with CFLAGS.

Answer 1

tl;dr; CMake does not have a general mechanism for forcing 32- or 64-bit compilation. You do that with selection of compilers or compilation switches.

But CMake can actually find out if the compilation is for 64- or 32-bit (or probably many other word lengths too) target. As described in this answer and the CMake docs you should use:

if (CMAKE_SIZEOF_VOID_P EQUAL 8)
    message (STATUS "Compiling for 64-bit")
endif()

That is probably the underlying mechanism for "when building 64-bit binaries". But there are no variables explicitly for this.

NOTE that the variable CMAKE_SIZEOF_VOID_P is cached so that if you alter compiler options, say CMAKE_C_FLAGS to use '-m32' for a 32-bit compile it won't affect CMAKE_SIZEOF_VOID_P unless you clean your build directory.

So, in a way there seems to be a somewhat general mechanism for 32/64-bit handling. It is used in some situations, but to use it more extensively you have to handle that in your CMakeLists, which is not great.