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

#define MAX 256

/**
 * This program shows what can happen when multiple processes
 *  try to indiscrimately share a file descriptor, in this
 *  stdin.
 * For best results, pipe the output of some "difficult" UNIX
 *  command into this sample, like 'du', which calculates hard
 *  disk usage between printing out lines.
 *
 *       du -s /usr/lib/* | ./sharedIn
 *
 * What determines which process gets an input line?
 * Run the command again; what are some of the factors that cause
 *  different results across runs?
 * What is the important lesson to learn here about sharing open
 *  file descriptors (like stdin and stdout)?
 */

int main()
{
   pid_t pid;
   char s[MAX + 1];
   int i = 0;
   
   for (i = 0; i < MAX + 1; i++) s[i] = '\0';

   i = 0;

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

   if (pid < 0)         /* Forking error! */
      {   exit(-1);   }
   else if (0 == pid)   /* Child process */
      {
	// Read in characters until string is full or EOF.
	while ((i < MAX) && ( (s[i++] = getchar()) != EOF) && !feof(stdin))
	  ;
	// Print out what we got.
	printf("Child got \"%s\"\n", s);
	exit(0);
      }
   else                 /* pid > 0: Parent process */
      {   
	// Read in characters until string is full or EOF.
	while ((i < MAX) && ( (s[i++] = getchar()) != EOF) && !feof(stdin))
	  ;
	// Print out what we got.
	printf("Parent got \"%s\"\n", s);
	// Wait for the child; this is good etiquette, and ensures that
	//  the O/S cleans up certain resources.
	wait(NULL);
        // What happens if the parent process exits without waiting for
	//  the child process to finish?
	exit(0);
	
      }
}