/* This program creates a new process and provides a simple pipe to
   allow the parent to communicate with the child 
   Version 1 -- explicitly using pipe and byte-oriented read/write */

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

#define MAX 25            /* maximum number of letters communicated */

int main (void)
{  int fd[2];             /* provide file descriptor pointer array for pipe */
                          /* within pipe:
                                 fd[0] will be input end
                                 fd[1] will be output end */
   pid_t pid;

   char line[MAX];        /* character array (string) for reading */
   
   if (pipe (fd) < 0)     /* create pipe and check for an error */
     { perror("pipe error");
       exit (1);
     }

   if ((pid = fork()) < 0)  /* apply fork and check for error */
     { perror ("error in fork");  
       exit (1);
     }

   if (0 == pid)             
     { /* processing for child */
       printf ("The child process is active.\n");
       close (fd[1]);       /* close output end, leaving input open */
       read(fd[0], line, MAX);
       printf ("The string received is '%s'\n", line);
     } 
   else 
     { /* processing for parent */
       printf ("The parent process is active.\n");
       close (fd[0]);       /* close input end, leaving output open */
       write (fd[1], "Your parent is calling", 22);
                            /* print string and indicate byte length */
     }

   exit (0);                 /* quit by reporting no error */
}