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

#define MAXLINE 256

/**
 * This program sets up a pipe, forks a child, and closes the appropriate
 *  descriptors for a one-way pipe from the parent to the child.
 * The parent then sends a string down the pipe, which the child reads
 *  from the pipe and then prints to stdout.
 */

int main()
{
   pid_t pid;
   int n;
   char line[MAXLINE];

   int pipefd[2];

   if (pipe(pipefd) < 0)/* Create a pipe. */
     {
       fprintf(stderr, "Pipe error!\n");
       exit(-1);
     }

   pid = fork();        /* fork another process */

   if (pid < 0)         /* Forking error! */
      {   exit(-1);   }
   else if (0 == pid)   /* Child process */
      {
	close(pipefd[1]);  /* Child closes write end of pipe. */

	// It doesn't matter if the child gets to the read() function
	//  before the parent has called write(); the child will
	//  wait here until there is something to read from the pipe.
	n = read(pipefd[0], line, MAXLINE);

	if (n > 0)
	  printf("Child got %s\n", line);

	close(pipefd[0]);  /* Done with pipe. */
	exit(0);
      }
   else                 /* pid > 0: Parent process */
      {  
	close(pipefd[0]);  /* Parent closes read end of pipe. */

	// Parent sends a string down the pipe to the child.
	write(pipefd[1], "Hello World!", 12);

	wait(NULL);
	close(pipefd[1]);  /* Done with pipe. */
	exit(0);
      }
}