[Cmake] Comments, questions from my first CMake'd app

[Amitha Perera]

On Tue 18 Mar 2003, Ian Main wrote:
> I had a few little problems with some things.  The return from
> 
> INCLUDE(${CMAKE_ROOT}/Modules/CheckIncludeFile.cmake)
> CHECK_INCLUDE_FILE(sys/types.h HAVE_SYS_TYPES_H)
> 
> will set HAVE_SYS_TYPES_H to 1 if it exists, or nothing if it
> does not.  This makes it hard to use in a config.h.in style
> arrangement, as you have to do funky #if stuff.  I am
> currently using:
> 
> #if 0 at HAVE_SYS_TYPES_H@
> #define HAVE_SYS_TYPES_H 1
> #endif
> 
> which will make the first line '#if 0' or '#if 01' depending
> on the result.  This works but it's a bit hackish.  Note that
> you can't just do:
> 
> #define HAVE_SYS_TYPES_H @HAVE_SYS_TYPES_H@ because then when
> you test for it you have to use #if still, and you end up 
> with the same problem.

I think you can use #ifdef and #ifndef instead of the #if. Also, I'm
reasonably sure that

  #if ABC
    do abc
  #else
    do def
  #endif

should do def if ABC is not a preprocessor macro (i.e., if it is not
#define'd). However, my experience is from the C++ preprocessor, and
this may somehow be subtly different from the C preprocessor.

The advantage of set to 1 or nothing is that you can both #if or
#ifdef will work.

Cheers,
Amitha.