must-example.c

#include <mpi.h>
#include <stdio.h>

int main (int argc, char** argv)
{
    int rank, size, buf[8];

    MPI_Init(&argc,&argv);
    MPI_Comm_rank (MPI_COMM_WORLD, &rank);
    MPI_Comm_size (MPI_COMM_WORLD, &size);
    MPI_Datatype type;

    MPI_Type_contiguous(2, MPI_INTEGER, &type);

    MPI_Recv(buf, 2, MPI_INT, size-rank-1, 123, MPI_COMM_WORLD, MPI_STATUS_IGNORE);

    MPI_Send(buf, 2, type, size-rank-1, 123, MPI_COMM_WORLD);

    printf ("Hello, I am rank %d of %d.\n", rank, size);

    MPI_Finalize ();

    return 0;
}