[CMake] MPI: Undefined symbol

[Rafael Sadowski]

On Mon Aug 20, 2018 at 04:24:07PM +0200, Florian Lindner wrote:
> Hello,
> 
> copied from a working MPI CMakeLists.txt:
> 
> find_package(MPI REQUIRED)

https://cmake.org/cmake/help/v3.0/module/FindMPI.html

MPI_<lang>_FOUND           TRUE if FindMPI found MPI flags for <lang>
MPI_<lang>_COMPILER        MPI Compiler wrapper for <lang>
MPI_<lang>_COMPILE_FLAGS   Compilation flags for MPI programs
MPI_<lang>_INCLUDE_PATH    Include path(s) for MPI header
MPI_<lang>_LINK_FLAGS      Linking flags for MPI programs
MPI_<lang>_LIBRARIES       All libraries to link MPI programs against

Looks like you forgot <lang>.

> include_directories(${MPI_INCLUDE_PATH})
> set(COMPILE_FLAGS  ${COMPILE_FLAGS} ${MPI_COMPILE_FLAGS})
> set(LINK_FLAGS ${LINK_FLAGS} ${MPI_LINK_FLAGS})
> 
> 
> add_executable(StructureSolverParallel
>   "StructureSolver_Parallel/structureDataDisplay.cpp"
>   "StructureSolver_Parallel/StructureSolver.cpp"
>   "StructureSolver_Parallel/structureComputeSolution.cpp")
> 
> target_link_libraries(StructureSolverParallel PUBLIC ${PRECICE_LIBRARY})
> target_link_libraries(StructureSolverParallel PUBLIC ${MPI_LBRARIES})
> 
> configuration runs smooth:
> 
> % cmake -DMPI_CXX_COMPILER=/opt/mpich/bin/mpicxx -DMPI_C_COMPILER=/opt/mpich/bin/mpicc . && make               
> -- The CXX compiler identification is GNU 8.2.0
> [...]
> -- Found MPI_CXX: /opt/mpich/lib/libmpicxx.so (found version "3.1") 
> -- Found MPI: TRUE (found version "3.1")  
> 
> make however:
> 
> [ 69%] Linking CXX executable StructureSolverParallel
> /usr/bin/cmake -E cmake_link_script CMakeFiles/StructureSolverParallel.dir/link.txt --verbose=1
> /usr/bin/c++   -Wall -Wextra -Wno-unused-parameter -g   CMakeFiles/StructureSolverParallel.dir/StructureSolver_Parallel/structureDataDisplay.cpp.o CMakeFiles/StructureSolverParallel.dir/StructureSolver_Parallel/StructureSolver.cpp.o CMakeFiles/StructureSolverParallel.dir/StructureSolver_Parallel/structureComputeSolution.cpp.o  -o StructureSolverParallel /home/lindnefn/precice/build/last/libprecice.so 
> /usr/bin/ld: CMakeFiles/StructureSolverParallel.dir/StructureSolver_Parallel/StructureSolver.cpp.o: undefined reference to symbol 'MPI_Init'
> /usr/bin/ld: /opt/mpich/lib/libmpi.so.12: error adding symbols: DSO missing from command line
> 
> when I just take the last command line and -lmpi to it, it works.
> 
> What could be missing there in CMakeLists?
> 
> Thanks,
> Florian
> 
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