[CMake] Problem with CHECK_INCLUDE_FILE macro

[Philippe Poilbarbe]

Brad King a écrit :

> Philippe Poilbarbe wrote:
>
>> Hello,
>>
>> I have a problem with the macro CHECK_INCLUDE_FILE which never find 
>> anything.
>>
>> Here are some lines:
>> INCLUDE(${CMAKE_ROOT}/Modules/CheckIncludeFile.cmake)
>> CHECK_INCLUDE_FILE("udunits.h" HAVE_UDUNITS_H)
>>
>> on exit HAVE_UDUNITS_H is always false.
>>
>> I have put some message trace in the macro and it seams that it never 
>> reaches
>> the second line; the line after:
>>   IF("${VARIABLE}" MATCHES "^${VARIABLE}$")
>> because the test is always false in this macro (if I do the same test 
>> outside
>> the macro like "HAVE_UDUNITS_H" MATCHES "^HAVE_UDUNITS_H$"
>> it is true as expected).
>>
>> Is there something special to do ?
>>
>> As a subsidiary question, why is this test here since it should 
>> always be true ?
>> I don't understand it or I should miss something.
>
>
> Read the documentation of the IF command carefully.  This kind of IF 
> test is a hack to test if a variable is defined left from before we 
> had the IF(DEFINED ...) option.  If HAVE_UDUNITS_H is defined then the 
> IF command will replace it with its value before evaluating the 
> MATCHES. If it is not defined then the strings will match.
>
> You probably have HAVE_UDUNITS_H in your CMakeCache.txt file so it is 
> always defined already when this macro executes.  The idea is once the 
> test is done the first time the result does not change so it is put in 
> the cache.  Once it is in the cache the test is not run again.  This 
> policy is not perfect but works well most of the time.
>
> -Brad

I have reread the IF description but nothing of this kind appears to me 
(I use the book Mastering CMake), there is only a description of DEFINED 
(but perhaps my english is not good enough :)).
Anyway, I have found the source of my problem: there was garbages in the 
cache file (due to previous tries). After deleting this file it worked well.

Thanks for the answer.
Ph. Poilbarbe