[petsc-dev] petsc/master: unable to link in C++ with last night PETSC_WITH_EXTERNAL_LIB variable changes

[Jed Brown]

Éric Chamberland <Eric.Chamberland at giref.ulaval.ca> writes:

> ok, let put our in-house code away, simply try this simple example:
>
> ----------
>
> #include <mpi.h>
>
> int main() {
> /*empty!! let's see the .o */
>
> return 1;
>
> }
> ---------
>
> then:
>
> g++ -c test.cc -I/opt/openmpi-1.10.2/include -o test.o
>
> nm -C test.o | grep "MPI::" | grep " U "
>
>                   U MPI::Win::Free()
>                   U MPI::Comm::Comm()
>                   U MPI::Datatype::Free()
>
> so: as soon you are compiling a c++ file with this openmpi 1.10.2 (even 
> if you use gcc -c test.cc -I/opt/openmpi-1.10.2/include -o test.o in my 
> example) it *requires* you to link with mpi_cxx lib...

That's sad, but is this not avoided by defining OMPI_SKIP_MPICXX before
including mpi.h?  (There is also MPICH_SKIP_MPICXX if you want.)  This
is done by default in petscsys.h, but you might not include it in that
file or don't include it before mpi.h is included.