[CMake] CMAKE_COMPILER_IS_GNUC vs. CMAKE_COMPILER_IS_GNUCC

[Michael Wild]

On 5. Jul, 2010, at 12:00 , Todd Gamblin wrote:

> 
> On Jul 5, 2010, at 1:23 AM, Michael Wild wrote:
> 
>> 
>> On 5. Jul, 2010, at 7:46 , Todd Gamblin wrote:
>> 
>>> The documentation here:
>>> 
>>> 	http://*www.*cmake.org/cmake/help/cmake2.6docs.html#variable:CMAKE_COMPILER_IS_GNULANG
>>> 
>>> is in conflict with the documentation here:
>>> 
>>> 	http://*www.*cmake.org/Wiki/CMake_Useful_Variables
>>> 
>>> And this thread (though it's from 2008) seems to imply that the second link above is right, even though the first is more current:
>>> 
>>> 	http://*www.*mail-archive.com/cmake@cmake.org/msg16863.html
>>> 
>>> 
>>> I'm using CMake 2.8.2, and I'm noticing that CMAKE_COMPILER_IS_GNUC is empty, which conflicts with the latest documentation on the wiki.  This makes it hard to do things like this:
>>> 
>>>> 	for (lang C CXX Fortran)
>>>> 		if (CMAKE_COMPILER_IS_GNU${lang})
>>>> 			...
>>>> 		endif()
>>>> 	endfor()
>>> 
>>> Looking through the CMake source, it doesn't look like CMAKE_COMPILER_IS_GNUFortran is used anywhere.  I tested it, and it looks like it's empty too.  Would it be possible to add CMAKE_COMPILER_IS_GNUC and CMAKE_COMPILER_IS_GNUFortran so that they actually work?  I think this would be more consistent than the current setup.
>>> 
>>> These issues are coming up in the platform files I'm making for BlueGeneP.  I think writing things like this would be easier if this were more consistent.
>>> 
>>> -Todd
>> 
>> The variables are called CMAKE_COMPILER_IS_GNUC, CMAKE_COMPILER_IS_GNUCXX and CMAKE_COMPILER_IS_GNUG77 (the latter is admittedly weird)
> 
> I don't think this is correct, at least not in the platform files in CMake 2.8.2.  If I look at the value of CMAKE_COMPILER_IS_GNUC, it's empty.  If I look at CMAKE_COMPILER_IS_GNUCC, it's getting set to what I'd expect.  Is CMAKE_COMPILER_IS_GNUC set somewhere else, after the platform file gets included?
> 
> G77 is weird, since as far as I can tell it's "Fortran" for all the other variables.  Like I said, that really precludes you from doing something like this, especially if you try to set something inside the loop:
> 
> 	for (lang C CXX Fortran)
> 		if (CMAKE_COMPILER_IS_GNU${lang})
> 			set(CMAKE_SHARED_LIBRARY_CREATE_${lang}_FLAGS "-shared")
> 		endif()
> 	endfor()
> 
> Since now ${lang} needs to be something different in all those places.

Well, I got this information by simply grepping through the sources:

$ egrep -roh 'CMAKE_COMPILER_IS_GNU[A-Z0-9]*' Modules | sort -u
CMAKE_COMPILER_IS_GNUCC
CMAKE_COMPILER_IS_GNUCXX
CMAKE_COMPILER_IS_GNUG77

And you're right, it is CMAKE_COMPILER_IS_GNUCC and not CMAKE_COMPILER_IS_GNUC. But that is kind of consistent with the variable names used in GNU Makefiles to refer to the C, C++ and G77 compilers. If you are not happy with the names (for the reason you posted above), you can use CMAKE_<LANG>_COMPILER_ID which should be set to GNU if it is a GNU compiler:

for(lang C CXX Fortran)
  if(CMAKE_${lang}_COMPILER_ID STREQUAL GNU)
    set(CMAKE_SHARED_LIBRARY_CREATE_${lang}_FLAGS "-shared")
   endif()
endforeach()


HTH

Michael