如何获取由exec执行的程序的返回值？

pid_t pid = fork();
if (pid == -1) {
  // error,no child created
}
else if (pid == 0) {
  // child
}
else {
  // parent
  int status;
  if (waitpid(pid,&status,0) == -1) {
    // handle error
  }
  else {
    // child exit code in status
    // use WIFEXITED,WEXITSTATUS,etc. on status
  }
}