Error on sending argv

This is a discussion on Error on sending argv within the C Programming forums, part of the General Programming Boards category; Hi all, I write a simple MPI program to send a text message to another process. The code is below. ...

  1. #1
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    Error on sending argv

    Hi all,
    I write a simple MPI program to send a text message to another process. The code is below.
    (test.c)
    Code:
    #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:
    Code:
    [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
    Code:
    char* text = "ABCDEF";
    by
    Code:
    char* text = argv[1];
    then compile and execute it again with the following commands:
    Code:
    [root@cluster Desktop]# mpicc -o test test.c
    [root@cluster Desktop]# mpirun -np 2 test ABCDEF
    Then I get the following output:
    Code:
    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
    Code:
    char* text = "ABCDEF";
    and
    Code:
    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!
    Last edited by awiles; 04-20-2010 at 02:30 AM. Reason: Added [code][/code] tags

  2. #2
    and the hat of wrongness Salem's Avatar
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    Drop the & from these two lines?

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

    MPI_Recv(&buffer, 128, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
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    Thanks for your reply but I encounter segmentation fault error again.

  4. #4
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    Quote Originally Posted by awiles View Post
    Thanks for your reply but I encounter segmentation fault error again.
    Probably because argv[1] for test is NULL. Ensure that "ABCDEF" is indeed being passed to your program test.
    Last edited by itCbitC; 04-19-2010 at 06:40 PM.

  5. #5
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    Quote Originally Posted by itCbitC View Post
    Probably because argv[1] for test is NULL. Ensure that "ABCDEF" is indeed being passed to your program test.
    The line
    Code:
    fprintf(stdout, "Master: sending %s to %d\n", text, 1);
    produces the following output:
    Code:
    Master: sending ABCDEF to 1
    which means argv[1] cannot be NULL.

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