[CMake] issue with CHECK FUNCTION EXISTS() and friends

[Alexander Neundorf]

Hi,  
  
there is the family of CHECK_XXX_EXISTS() macros in the cmake Modules.  
They work quite well but I have a problem with them.  
If the item which was searched for has been found HAVE_FOO is set to "1".  
This is ok and works in all cases:  
  
in config.h.cmake:  
  
#define HAVE_FOO ${HAVE_FOO}  
  
in the sources:  
  
//works, since it's defined 
#ifdef HAVE_FOO  
...  
#endif  
  
  
//works, becomes "#if 1" 
#if HAVE_FOO  
...  
#endif  
  
It leads to some problems in the case that it wasn't found, then HAVE_FOO  
is empty.  
  
So I get:  
  
#define HAVE_FOO // the empty string, but still it is defined, an undef  
would be better  
  
//this will succeed, although it shouldn't, since HAVE_FOO is defined  
#ifdef HAVE_FOO  
...  
#endif  
  
//this will lead to a syntax error, since HAVE_FOO is empty: "#if" 
#if HAVE_FOO   
...  
#endif  
  
What's the right way to solve this situation ? Changing the sources is no  
option.  
  
Attached is a patch to CheckFunctionExists.cmake which introduces the  
variable CMAKE_ZERO_ON_FAILURE. If set, HAVE_FOO will be set to 0 instead  
to empty if the test failed. Then I could write code like this:  
  
config.h.cmake:  
  
#if ${HAVE_FOO}  
#  define HAVE_FOO  
#else  
#  undef HAVE_FOO  
#endif  
  
and   
  
#define HAVE_FOO ${HAVE_FOO}  
  
will have the desired effect in the sources:  
  
//this will become "#if 0" , so everything is ok  
#if HAVE_FOO   
...  
#endif  
  
What do you think ? Is there a better way to do this ? If you think this  
is a good idea, I can also post patches for the other CHECK_XXX() macros.  
  
Bye  
Alex  
  

-- 
5 GB Mailbox, 50 FreeSMS http://www.gmx.net/de/go/promail
+++ GMX - die erste Adresse für Mail, Message, More +++
-------------- next part --------------
A non-text attachment was scrubbed...
Name: CheckFunctionExists.cmake.diff
Type: text/x-diff
Size: 755 bytes
Desc: not available
Url : http://public.kitware.com/pipermail/cmake/attachments/20050629/6681f33e/CheckFunctionExists.cmake.bin