Hi all Open MPI users,

I write a simple MPI program to send a text message to another process. The code is below.

(test.c)

#include "mpi.h"

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

 

int main(int argc, char* argv[]) {

    int dest, noProcesses, processId;

    MPI_Status status;

   

    char* buffer;

   

    char* text = "ABCDEF";

   

    MPI_Init(&argc, &argv);

    MPI_Comm_size(MPI_COMM_WORLD, &noProcesses);

    MPI_Comm_rank(MPI_COMM_WORLD, &processId);

   

    buffer = (char*) malloc(256 * sizeof(char));

   

    if (processId == 0) {

      fprintf(stdout, "Master: sending %s to %d\n", text, 1);

      MPI_Send((void *)&text, strlen(text) + 1, MPI_CHAR, 1, 0, MPI_COMM_WORLD);

    } else {

      MPI_Recv(&buffer, 128, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);

      fprintf(stdout, "Slave: received %s from %d\n", buffer, status.MPI_SOURCE);

    }

    MPI_Finalize();

    return 0;

}

After compiling and executing it I get the following output:

[root@cluster Desktop]# mpicc -o test test.c

[root@cluster Desktop]# mpirun -np 2 test

Master: sending ABCDEF to 1

Slave: received ABCDEF from 0

 

In the source code above, I replace

char* text = "ABCDEF";

by

char* text = argv[1];

then compile and execute it again with the following commands:

[root@cluster Desktop]# mpicc -o test test.c

[root@cluster Desktop]# mpirun -np 2 test ABCDEF

Then I get the following output:

Master: sending ABCDEF to 1

[cluster:03917] *** Process received signal ***

[cluster:03917] Signal: Segmentation fault (11)

[cluster:03917] Signal code: Address not mapped (1)

[cluster:03917] Failing at address: 0xbfa445a2

[cluster:03917] [ 0] [0x959440]

[cluster:03917] [ 1] /lib/libc.so.6(_IO_fprintf+0x22) [0x76be02]

[cluster:03917] [ 2] test(main+0x143) [0x80488b7]

[cluster:03917] [ 3] /lib/libc.so.6(__libc_start_main+0xdc) [0x73be8c]

[cluster:03917] [ 4] test [0x80486c1]

[cluster:03917] *** End of error message ***

--------------------------------------------------------------------------

mpirun noticed that process rank 1 with PID 3917 on node cluster.hpc.org exited on signal 11 (Segmentation fault).

--------------------------------------------------------------------------

I’m very confused because the only difference between the two source codes is the difference between

char* text = "ABCDEF";

and

char* text = argv[1];

Can any one help me why the results are so different? How can I send argv[i] to another process?

Thank you very much!