/*
  testPipes.c

  Demonstrates a parent talking to a child,
  and the child listening.

 */

#include <unistd.h>	// close, for, pipe, read, write
#include <stdio.h>	// printf, fprintf, stderr
#include <stdlib.h>  	// exit
 
const int MAXLINE = 80;

int main() {

  int fd[2];
  pid_t pid;
  char line[MAXLINE];

  // After a successful pipe, fd[0] is the end to read from
  // and fd[1] is the end to write to.
  if (pipe (fd) < 0) {
    fprintf(stderr, "Failed to create pipe\n");
    exit(1);
  }

  // Create a child process.
  if ((pid = fork()) < 0) {
    fprintf(stderr, "Failed to fork\n");
    exit(1);
  }
  else if (pid > 0) {
    // parent
    close(fd[0]);
    printf("Parent: %d about to send message\n", getpid());
    write(fd[1], "Listen to me!\n", 15);
    //    wait(NULL);  // Waiting for child to finish.
  }
  else {
    // child
    close(fd[1]);
    read(fd[0], line, MAXLINE);  // listen to your parent.
    printf("Child: %d receiving message from parent: %d\n",
	   getpid(), getppid());
    printf("%s", line);  // This is just to show that we heard them.
  }
}