mpiio.c

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

#define DATASIZE   64
#define WRITER_ID   0

void mpiio_writer(int, int *, int);


int main(int argc, char *argv[])
{
    int my_id, ntasks, i, localsize;
    int *localvector;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
    MPI_Comm_rank(MPI_COMM_WORLD, &my_id);

    if (ntasks > 64) {
        fprintf(stderr, "Datasize (64) should be divisible by number "
                "of tasks.\n");
        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
    }

    if (DATASIZE % ntasks != 0) {
        fprintf(stderr, "Datasize (64) should be divisible by number "
                "of tasks.\n");
        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
    }

    localsize = DATASIZE / ntasks;
    localvector = (int *) malloc(localsize * sizeof(int));

    for (i = 0; i < localsize; i++) {
        localvector[i] = i + 1 + localsize * my_id;
    }

    mpiio_writer(my_id, localvector, localsize);

    free(localvector);

    MPI_Finalize();
    return 0;
}

void mpiio_writer(int my_id, int *localvector, int localsize)
{
    MPI_File fh;
    MPI_Offset offset;

    MPI_File_open(MPI_COMM_WORLD, "mpiio.dat",
                  MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL, &fh);

    offset = my_id * localsize * sizeof(int);

    MPI_File_write_at_all(fh, offset, localvector,
                          localsize, MPI_INT, MPI_STATUS_IGNORE);

    MPI_File_close(&fh);
}