I am working with a Debian (Linux like) OS writing code in c.
I am a running process (let’s call it “A”) which needs to launch an executable program AND to get its PID when the new process “B” starts running.
Both processes “A” and “B” have to remain running (i.e. neither one must terminate).

MY QUESTION:
How can I make the process “A” to get the PID of process “B” once this last has been launched?

I tried to do it by using fork and execlp c functions. But the most I obtained is the PID of the child process, which is not the PID of process “B”. The test code I used fro this is shown here:

int main() {
  pid_t child_pid = fork();

  if (child_pid == 0) {
    // Child process
    char *program_name = "my/Path";            // Path
    char *arguments[] = {"Process_B", NULL};   // Program to be launched

    if (execlp(program_name, arguments[0], NULL) == -1) {
      perror("execlp_error");
      return 1;
    }
  } else if (child_pid > 0) {
    // Parent process
    printf("Parent process (PID: %d) launched child with PID: %dn", getpid(), child_pid);

  } else {
    perror("fork_error");
    return 1;
  }

  return 0;
}

An example code will be highly appreciated.