[CMake] [CMake ] Specify linker for a mixed language Fortran/C++ application (linux)

[Michael Hertling]

On 06/29/2011 10:04 AM, Yngve Inntjore Levinsen wrote:
>  Tirsdag 28 juni 2011 18.52.48 skrev Raphael Muenster :
>> Yep, great) setting the LINKER_LANGUAGE to Fortran did it.
>>
>> Thanks,
>> Raphael
>>
>> Am 28.06.2011 15:48, schrieb Brad King:
>>> On 06/27/2011 02:39 PM, Raphael Münster wrote:
>>>> # name of the project
>>>> PROJECT(Q2P1)
>>>>
>>>> enable_language (Fortran)
>>> Languages can also be specified in the project command:
>>>
>>>    project(Q2P1 C CXX Fortran)
>>>
>>>> I invoke cmake like this "CC=mpicc CXX=mpic++ cmake -DCMAKE_Fortran_COMPILER=mpif90"
>>> FYI, you can use
>>>
>>>    CC=mpicc CXX=mpic++ FC=mpif90 cmake ...
>>>
>>> and you do not need to set CMAKE_Fortran_COMPILER at all in the cmake code.
>>>
>>>> So the question is how can I tell cmake to use mpif90 to link the program?
>>> Set the LINKER_LANGUAGE target property:
>>>
>>>    http://www.cmake.org/cmake/help/cmake-2-8-docs.html#prop_tgt:LINKER_LANGUAGE
>>>
>>> with code like
>>>
>>>    set_property(TARGET Q2P1 PROPERTY LINKER_LANGUAGE Fortran)
>>>
>>> -Brad
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> 
> 
> Just as a side-note, mpif90 is a wrapper compiler for mpi right? Have a look at this thread, which discusses the recommended way to
> compile MPI code with cmake:
> http://www.cmake.org/pipermail/cmake/2011-June/045032.html
> 
> My preferred way is also to specify in the project() command which languages are used. That way if you have a pure fortran project cmake doesn't test your c/c++ compiler etc.
> 
> Cheers,
> Yngve

Presumedly, the OP's concern isn't related to MPI but to the selection
of the linker in a mixed-language target; as Raphael says, the linker
command succeeds when mpic++ is replaced by mpif90. My assumption is
rather that the C++ library the Fortran program is linked against
is a static one, so the default settings

CMAKE_CXX_LINKER_PREFERENCE = 30
CMAKE_Fortran_LINKER_PREFERENCE = 20
CMAKE_CXX_LINKER_PREFERENCE_PROPAGATES = 1

bring the C++ linker into play, and it will preempt the Fortran one.
The solution is - as already suggested - to set the target's linker
language manually, switch off the linker preference's propagation
for static C++ libraries or provide Fortran with a higher linker
preference than C++.

Regards,

Michael