Using popen() to invoke a shell command?

Question

When running the following code through xcode I get inconsistent behavior. Sometimes it prints the git version correctly, other times it doesn't print anything. The return code from the shell command is always 0 though. Any ideas on why this might be? What am I doing wrong?

#define BUFFER_SIZE 256 
int main (int argc, const char * argv[])  
{   
    FILE *fpipe;
    char *command="/opt/local/bin/git --version";
    char line[BUFFER_SIZE];

    if ( !(fpipe = (FILE*)popen(command, "r")) )
    {   // If fpipe is NULL
        perror("Problems with pipe");
        exit(1);
    }

    while ( fgets( line, sizeof(char) * BUFFER_SIZE, fpipe))
    {
         // Inconsistent (happens sometimes) 
         printf("READING LINE");
         printf("%s", line);
    }

    int status = pclose(fpipe);

    if (status != 0)
    {
        // Never happens
        printf("Strange error code: %d", status);
    }

    return 0;
}

Answer 1

It sounds suspiciously like as if the output is buffered, have you considered flushing the output buffer..use fflush() to do so. See here for further information.

Hope this helps, Best regards, Tom.

Answer 2

I think I have found the source of the strange behavior. It seems as Xcode is doing something funky in the built in terminal window which results in me not seeing the output. If I try to run the code directly in a standard terminal window this behavior does not appear, and the text is consistently printed out.