[CMake] How can I know the target is 32-bit, or 64bit

[Michael Wild]

On Tue 30 Aug 2011 07:54:45 AM CEST, Dongsheng Song wrote:
> Hi,
> 
> In CMakeLists.txt, I want to know whether cmake has built-in mechanism that
> I can know the target is 32-bit, or 64bit ?
> 
> Thanks,
> Dongsheng

Look at the CMAKE_SIZEOF_VOID_P variable. However, normally this is 
better handled in the code through #ifdef's, because on some platforms 
(e.g. Mac) it is possible to compile for multiple architecture at once 
with a single compiler invocation. I.e., something like

gcc -arch i386 -arch ppc -arch x86_64 -arch ppc64 hello.c

will compile hello.c *four* times, first with __i386__ defined, then 
with __ppc__, followed by __x86_64__ and finally with __ppc64__. If you 
ever plan to support Mac OS X and allow your users to set the 
CMAKE_OSX_ARCHITECTURES variable to a list of architectures with 
varying bit-sex and pointer sizes, you should *not* rely on 
CMAKE_SIZEOF_VOID_P, since that will only contain the pointer size of 
the *first* architecture.

HTH

Michael