4.12.10 Interlanguage Communication

The type matching rules for communications 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 4..14   In the example below, a Fortran array is sent from Fortran and received in C.

! FORTRAN CODE
REAL R(5)
INTEGER TYPE, IERR, MYRANK
INTEGER(KIND=MPI_ADDRESS_KIND) ADDR

! create an absolute datatype for array R
CALL MPI_GET_ADDRESS( R, ADDR, IERR)
CALL MPI_TYPE_CREATE_STRUCT(1, 5, ADDR, MPI_REAL, 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)
END IF

/* 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.

MPI-Standard for MARMOT