The type matching rules for communication in MPI are not changed: the datatype specification for each item sent should match, in type signature, the datatype specification used to receive this item (unless one of the types is MPI_PACKED). Also, the type of a message item should match the type declaration for the corresponding communication buffer location, unless the type is MPI_BYTE or MPI_PACKED. Interlanguage communication is allowed if it complies with these rules.
Example
In the example below, a Fortran array is sent from Fortran and received in
C.
! FORTRAN CODE SUBROUTINE MYEXAMPLE() USE mpi_f08 REAL :: R(5) INTEGER :: IERR, MYRANK, AOBLEN(1) TYPE(MPI_Datatype) :: TYPE, AOTYPE(1) INTEGER (KIND=MPI_ADDRESS_KIND) :: AODISP(1) ! create an absolute datatype for array R AOBLEN(1) = 5 CALL MPI_GET_ADDRESS( R, AODISP(1), IERR) AOTYPE(1) = MPI_REAL CALL MPI_TYPE_CREATE_STRUCT(1, AOBLEN,AODISP,AOTYPE, TYPE, IERR) CALL MPI_TYPE_COMMIT(TYPE, IERR) CALL MPI_COMM_RANK( MPI_COMM_WORLD, MYRANK, IERR) IF (MYRANK.EQ.0) THEN CALL MPI_SEND( MPI_BOTTOM, 1, TYPE, 1, 0, MPI_COMM_WORLD, IERR) ELSE CALL C_ROUTINE(TYPE%MPI_VAL) END IF END SUBROUTINE
/* C code */ void C_ROUTINE(MPI_Fint *fhandle) { MPI_Datatype type; MPI_Status status; type = MPI_Type_f2c(*fhandle); MPI_Recv( MPI_BOTTOM, 1, type, 0, 0, MPI_COMM_WORLD, &status); }
MPI implementors may weaken these type matching rules, and allow messages to be sent with Fortran types and received with C types, and vice versa, when those types match. I.e., if the Fortran type INTEGER is identical to the C type int, then an MPI implementation may allow data to be sent with datatype MPI_INTEGER and be received with datatype MPI_INT. However, such code is not portable.