CODEWITHSUNDEEP
cmultiprocessingmpiopenmpi
Anirudh
Anirudh

Reputation: 15807

MPI: writing and read integers to a file

Just started off with Openmpi. Trying to write and read ints to a file .. code for writing:

the characters getting written to the file are unrecognizable, mostly garbage. 

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

#define BUFSIZE 10
#define FIRSTCHAR 1
#define FILENAME "file1.dat"

int main(int argc, char* argv[]) {
  int i, np, me;
  int buf[BUFSIZE];     /* The buffer to write */
  MPI_File myfile;       /* Shared file */

  /* Initialize MPI */
  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &me);
  MPI_Comm_size(MPI_COMM_WORLD, &np);

  /* Initialize buf with characters. Process 0 uses 'a', process 1 'b', etc. */
  for (i=0; i<BUFSIZE; i++) {
    buf[i] = FIRSTCHAR+(me);
  }

  /* Open the file */
  MPI_File_open (MPI_COMM_WORLD, FILENAME, MPI_MODE_CREATE | MPI_MODE_WRONLY,
         MPI_INFO_NULL, &myfile);
  /* Set the file view */
  MPI_File_set_view(myfile, me*BUFSIZE*sizeof(int), MPI_INT, MPI_INT, 
            "native", MPI_INFO_NULL);
  /* Write buf to the file */
  MPI_File_write(myfile, buf, BUFSIZE*sizeof(int), MPI_INT, MPI_STATUS_IGNORE);
  /* Close the file */
  MPI_File_close(&myfile);
  MPI_Finalize();
  exit(0);
}

dosen't work .. Please help!

Upvotes: 2

Views: 4864

Answers (3)

Aeternus
Aeternus

Reputation: 365

Here is a more concise command to view your binary file in ascii On Linux: Backup your file, as pyCthon suggested:

cp file temp

Then, run the following command to print out file as ascii characters:

od -c temp

If your data happens to be integers:

od -i temp

Upvotes: 1

unkulunkulu
unkulunkulu

Reputation: 11912

The ints are being written to the file in binary mode, i.e. they're not converted to strings and printed like you do screen output using printf, instead their memory representation is copied to the file somehow. If you write code to read them from the file (using MPI_File_read), it will work properly.

Note that that binary format can be quite tricky to read by yourself, because MPI tries to be cross-platform and probably writes some additional type information, so you should use MPI to read from those files.

Upvotes: 1

pyCthon
pyCthon

Reputation: 12341

The files written are not garbage they are just in binary

if your on linux

first backup your file

cp file file2

then

try this command to convert from binary to ascii

hexdump -v -e '7/4 "%10d "' -e '"\n"' file2

also a side note: unless your writing millions of lines to file, you might not even need the mpi_file write /load functions

Upvotes: 6

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