[CMake] [Insight-developers] 64 bit build detection

[Hendrik Sattler]

Am Sonntag 14 Juni 2009 22:05:14 schrieb Michael Wild:
> On Mac OS X one shouldn't do this kind of detection during configure
> step, because as has been mentioned a single file can be compiled
> multiple times for different architectures during one single compiler
> invocation. The size of void* and even endianness can change. It is
> preferable to have a central config.h.in (or similar) containing
> something like this:
>
> #if defined(__APPLE__)
> #  if defined(__i386__)
> #    undef HAVE_64_BIT
> #    undef HAVE_BIG_ENDIAN
> #  elif defined(__ppc__)
> #    undef HAVE_64_BIT
> #    define HAVE_BIG_ENDIAN
> #  elif defined(__x86_64__)
> #    define HAVE_64_BIT
> #    undef HAVE_BIG_ENDIAN
> #  elif defined(__ppc64__)
> #    define HAVE_64_BIT
> #    define HAVE_BIG_ENDIAN
> #  else
>       // oops
> #    error "Unknown architecture!"
> #  endif
> #else
> #  cmakedefine HAVE_64_BIT
> #  cmakedefine HAVE_BIG_ENDIAN
> #endif

Where do you need to know that you have 32bit vs. 64bit?
When including inttypes.h, you can use e.g. uint64_t portably (you can find 
inttypes.h for MSVC on googlecode), else use you can even use:
	if (sizeof(void*) == 8) {
		...
	} else {
		...
	}
and let the compiler optimize one of them away.  Or do something else with C 
preprocessor.
Not _everything_ has to be done with CMake.

HS