io35.c

The example for Boor USING MPI2

/* parallel MPI read with arbitrary number of processes*/
#include "mpi.h"
#include <stdio.h>
int main(int argc, char *argv[])
{
    int myrank, numprocs, bufsize, *buf, count;
    MPI_File thefile;
    MPI_Status status;
    MPI_Offset filesize;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_File_open(MPI_COMM_WORLD, "testfile", MPI_MODE_RDONLY,
		  MPI_INFO_NULL, &thefile);
    MPI_File_get_size(thefile, &filesize); /* in bytes */
    filesize = filesize / sizeof(int);     /* in number of ints */
    bufsize = filesize / numprocs + 1;     /* local number to read */
    buf = (int *) malloc (bufsize * sizeof(int));
    MPI_File_set_view(thefile, myrank * bufsize * sizeof(int),
		      MPI_INT, MPI_INT, "native", MPI_INFO_NULL);
    MPI_File_read(thefile, buf, bufsize, MPI_INT, &status);
    MPI_Get_count(&status, MPI_INT, &count);
    printf("process %d read %d ints\n", myrank, count);
    MPI_File_close(&thefile);
    MPI_Finalize();
    return 0;
}