[CMake] How to query compiler definitions?

[Michael Wild]

On 01/19/2011 09:30 AM, SF Markus Elfring wrote:
> Hello,
> 
> I know that some source code will only be needed in my example project
> if the preprocessor symbol "NDEBUG" is not defined.
> This is usual for conditional compilation. The corresponding bit of
> debug code calls functions which are implemented in a few other source
> files.
> Now I am looking for ways whether these files can be added on demand to
> the build process.
> 
> I try to query the settings by a programming interface from CMake 2.8.3
> on my openSUSE 11.3 system.
> 
> get_directory_property(info COMPILE_DEFINITIONS)
> message(STATUS "info: ${info}")
> 
> The corresponding display indicates that this variable is empty. I guess
> that this fact should be interpreted also in the way that the specified
> property is not defined in my situation.
> Now I wonder why this approach does not work as expected. (A few
> definitions are passed to my compiler of course.)
> 
> I would appreciate your advices.
> 
> Regards,
> Markus


The NDEBUG flag is "special" and gets set by CMake for non-debug builds
automagically. Also, such an approach as you propose would work for
Makefile generators, but would completely fail for multi-config IDE
generators, such as Xcode or VisualStudio. Why don't you include the
check for NDEBUG in in your "debug-sources"? Like this:

debug-functions.c:
----------<8----------
#ifndef NDEBUG
void some_debug_function(void)
{
  /* whathever */
}
#endif
----------<8----------

The time you'll waste compiling these files will be negligible, and it
would work with mult-config IDE's.

Michael