/* file: fork_exec.c

   Illustrates the use of exec() with fork(), and environ.

   Also illustrates separate compilation and linking separately
   compiled code with main program.

   To compile this program:

     gcc -c print_child_status.c
     gcc -o fork_exec print_child_status.o fork_exec.c

*/

#define _XOPEN_SOURCE 500

#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <wait.h>
#include <signal.h>

#define SLEEP_TIME 1

extern char ** environ;  /* see "man environ" for explanation */
extern void print_child_status (int status);


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

  pid_t child;
  int status;
  char *argument_list[] = {"child", NULL};
  int i;

  if (argc !=1) {
    fprintf (stderr, "This program does not accept command-line arguments\n");
    exit (-1);
  }
  for (i = 0; environ[i]; i++) {
    fprintf (stdout, "environ[%d] = \"%s\"\n", i, environ[i]);
  }

  /* create a child process */

  child = fork();

  if (child == -1) { /* call to fork failed */
    perror ("fork failed"); exit (-1);
  }

  if (child != 0) {
     fprintf (stdout, "This is the parent process, with own pid %d\n",
       getpid());

     if (waitpid (child, &status, 0) == -1) {
       perror ("waitpid failed"); exit (-1);
     }
     print_child_status (status);

  } else {
    fprintf (stdout, "This is the child process, with own pid %d "
       "and parent pid %d\n",
       (int) getpid(), (int) getppid());

    if (execve ("child", argument_list, environ) == -1) {
       perror ("execve failed");
    }

    fprintf (stderr, "execution should never reach here");
  }
  return 0;
}