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

/*----< main() >------------------------------------------------------------*/
int main(int argc, char **argv) {
    int          i, err, rank, np, buf_size, *buf;
    int          sizes[2], starts[2], counts[2];
    MPI_File     fh;
    MPI_Datatype ftype;
    MPI_Status   status;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &np);

    if (np != 4) {
        printf("number of processes must be 4, exiting ... \n");
        MPI_Finalize();
        return 1;
    }

    /* a 8x10 2D array is block-* partitioned among 4 processes */
    sizes[0]  = sizes[1] = 10;
    counts[0] = 2;
    counts[1] = sizes[1];
    starts[0] = 2 * rank;
    starts[1] = 0;

    /* create file type */
    MPI_Type_create_subarray(2, sizes, counts, starts, MPI_ORDER_C,
                             MPI_INT, &ftype) ;
    MPI_Type_commit(&ftype);

    /* open the file */
    err = MPI_File_open(MPI_COMM_WORLD, "testfile",
                        MPI_MODE_CREATE | MPI_MODE_WRONLY,
                        MPI_INFO_NULL, &fh);
    if (err != MPI_SUCCESS) {
        printf("Error: MPI_File_open() filename %s\n",argv[1]);
	MPI_Abort(MPI_COMM_WORLD, -1);
	exit(1);
    }

    /* set the file view */
    MPI_File_set_view(fh, 0, MPI_INT, ftype, "native", MPI_INFO_NULL);
    MPI_Type_free(&ftype);

    buf_size = counts[0] * counts[1];
    buf = (int*) malloc(buf_size*sizeof(int));

    /* MPI collective write */
    MPI_File_write_all(fh, buf, buf_size, MPI_INT, &status);

    MPI_File_close(&fh);
    free(buf);

    MPI_Finalize();
    return 0;
}