How do I get the return value of a execv?

Question

I am really new to C++ and I am trying to get the output from:

execv("./rdesktop",NULL);

I am programming in C++ and on RHEL 6.

Like a FTP client, I would like to get all the status updates from my external running program. Can someone please tell me how I could do this?

Answer 1

You can examine the exit status of a child process by calling wait, waitpid, wait3 or wait4.

#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main () {
  pid_t pid = fork();
  switch(pid) {
  case 0:
    // We are the child process
    execl("/bin/ls", "ls", NULL);

    // If we get here, something is wrong.
    perror("/bin/ls");
    exit(255);
  default:
    // We are the parent process
    {
      int status;
      if( waitpid(pid, &status, 0) < 0 ) {
        perror("wait");
        exit(254);
      }
      if(WIFEXITED(status)) {
        printf("Process %d returned %d\n", pid, WEXITSTATUS(status));
        exit(WEXITSTATUS(status));
      }
      if(WIFSIGNALED(status)) {
        printf("Process %d killed: signal %d%s\n",
          pid, WTERMSIG(status),
          WCOREDUMP(status) ? " - core dumped" : "");
        exit(1);
      }
    }
  case -1:
    // fork failed
    perror("fork");
    exit(1);
  }
}

Answer 2

execv replaces the current process, so immediately after executing it what's executing will be whatever executable you specified.

Normally you do a fork, and then execv only in the child process. The parent process receives the PID of the new child, which it can use to monitor the child's execution.