io.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <mpi.h>
 
#define SIZE (65536)
#define FILENAME "iodata"
 
/*Each process writes to separate files and reads them back. The file name is “iodata” and the process rank is appended to it.*/
 
main(argc, argv)
 
     int argc;
     char **argv;
 
{
        int *buf, i, rank, nints, len, flag;
        char *filename;
        MPI_File fh;
        MPI_Status status;
 
        MPI_Init(&argc, &argv);
        MPI_Comm_rank(MPI_COMM_WORLD, &rank);
 
        buf = (int *) malloc(SIZE);
        nints = SIZE/sizeof(int);
        for (i=0; i<nints; i++) buf[i] = rank*100000 + i;
 
        /* each process opens a separate file called FILENAME.'myrank' */
 
        filename = (char *) malloc(strlen(FILENAME) + 10);
        sprintf(filename, "%s.%d", FILENAME, rank);
 
        MPI_File_open(MPI_COMM_SELF, filename,
                      MPI_MODE_CREATE | MPI_MODE_RDWR,
                      MPI_INFO_NULL, &fh);
 
        MPI_File_set_view(fh, (MPI_Offset)0, MPI_INT, MPI_INT, "native",
                          MPI_INFO_NULL);
        MPI_File_write(fh, buf, nints, MPI_INT, &status);
        MPI_File_close(&fh);
 
        /* reopen the file and read the data back */
 
        for (i=0; i<nints; i++) buf[i] = 0;
        MPI_File_open(MPI_COMM_SELF, filename,
                      MPI_MODE_CREATE | MPI_MODE_RDWR,
                      MPI_INFO_NULL, &fh);
        MPI_File_set_view(fh, (MPI_Offset)0, MPI_INT, MPI_INT, "native",
                          MPI_INFO_NULL);
        MPI_File_read(fh, buf, nints, MPI_INT, &status);
        MPI_File_close(&fh);
 
        /* check if the data read is correct */
        flag = 0;
        for (i=0; i<nints; i++)
                if (buf[i] != (rank*100000 + i)) {
                        printf("Process %d: error, read %d, should be %d\n",
                               rank, buf[i], rank*100000+i);
                        flag = 1;
                }
 
        if (!flag) {
                printf("Process %d: data read back is correct\n", rank);
                MPI_File_delete(filename, MPI_INFO_NULL);
        }
 
        free(buf);
        free(filename);
 
        MPI_Finalize();
        exit(0);
}