MPI_Status status; MPI_Recv( ..., &status ); ... status.MPI_TAG; ... status.MPI_SOURCE; MPI_Get_count( &status, datatype, &count );MPI_TAG and MPI_SOURCE primarily of use when MPI_ANY_TAG and/or MPI_ANY_SOURCE in the receive.
MPI_Get_count may be used to determine how much data of a particular type was received.