On Aug 19, 2016, at 2:30 PM, Matt Thompson <fort...@gmail.com> wrote: > > I'm slowly trying to learn and transition to 'use mpi_f08'. So, I'm writing > various things and I noticed that this triggers an error: > > program hello_world > use mpi_f08 > implicit none > type(MPI_Comm) :: comm = MPI_COMM_NULL > end program hello_world > > when compiled (Open MPI 2.0.0 with GCC 6.1): > > (380) $ mpifort test1.F90 > test1.F90:7:27: > > type(MPI_Comm) :: comm = MPI_COMM_NULL > 1 > Error: Parameter ‘mpi_comm_null’ at (1) has not been declared or is a > variable, which does not reduce to a constant expression > > Why is that? Obviously, I can just do: > > type(MPI_Comm) :: comm > comm = MPI_COMM_NULL > > and that works just fine (note MPI_COMM_NULL doesn't seem to be special as > MPI_COMM_WORLD triggers the same error).
I am *not* a Fortran expert, but I believe the difference between the two is: 1. The first one is a compile-time assignment. And you can only do those with constants. MPI_COMM_NULL is not a compile-time constant, hence, you get an error. 2. The second one is a run-time assignment. You can do that between any compatible entities, and so that works. > I'm just wondering why the first doesn't work, for my own edification. I > tried reading through the Standard, but my eyes started watering after a bit > (though that might have been the neon green cover). Is it related to the fact > that when one declares: > > type(MPI_Comm) :: comm > > that the comm == MPI_COMM_WORLD evaluates to .TRUE.? I discovered that once > when I was printing some stuff. That might well be a coincidence. type(MPI_Comm) is not a boolean type, so I'm not sure how you compared it to .true. -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/ _______________________________________________ users mailing list users@lists.open-mpi.org https://rfd.newmexicoconsortium.org/mailman/listinfo/users
