Question

Write a “C” program(Linux) that creates a pipe and forks a child process. The parent then sends the following message on his side of the pipe “I am your daddy! and my name is <pid-of the-parent-process>\n”, the child receives this message and prints it to its stdout verbatim. The parent then blocks reading on the pipe from the child. The child writes back to its parent through its side ofthe pipe stating “Daddy, my name is <pid-of-the-child>”. The parent then writes the message received from the child to its stdout. Make sure the parent waits on the child exit as to not creating orphans or zombies. Include Makefile.

Answer 1

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

int main()
{
   // We use two pipes
   // First pipe to send input string from parent
   // Second pipe to send concatenated string from child

   int fd1[2]; // Used to store two ends of first pipe
   int fd2[2]; // Used to store two ends of second pipe

  
   pid_t p;

   if (pipe(fd1)==-1)
   {
       fprintf(stderr, "Pipe Failed" );
       return 1;
   }
   if (pipe(fd2)==-1)
   {
       fprintf(stderr, "Pipe Failed" );
       return 1;
   }

  
   p = fork();

   if (p < 0)
   {
       fprintf(stderr, "fork Failed" );
       return 1;
   }

   // Parent process
   else if (p > 0)
   {
       char concat_str[100];
       char input_str[]="I am your daddy! and my name is ";
char s[100];
       close(fd1[0]); // Close reading end of first pipe
       int i=getpid();
sprintf(s, "%d", i);
strcat(input_str,s);
       // Write input string and close writing end of first
       // pipe.
  
       write(fd1[1], input_str, strlen(input_str)+1);
      
close(fd1[0]); // Close reading end of first pipe
       close(fd1[1]); // Close writing end of first pipe

       // Wait for child to send a string
       wait(NULL);

       close(fd2[1]); // Close writing end of second pipe

       // Read string from child, print it and close
       // reading end.
       read(fd2[0], concat_str, 100);
       printf("string received from child in parent Process: %s\n", concat_str);
       close(fd2[0]);
   }

   // child process
   else
   {
       close(fd1[1]); // Close writing end of first pipe

       // Read a string using first pipe
       char parent_str[100];
       read(fd1[0], parent_str, 100);
  
       printf("string received from parent in child process : %s\n", parent_str);

       // Close both reading ends
       close(fd1[0]);
       close(fd2[0]);
       char child_str[]="Daddy, my name is ";
char s[100];
       int i=getpid();
sprintf(s, "%d", i);
strcat(child_str,s);
       // Write concatenated string and close writing end
       write(fd2[1], child_str, strlen(child_str)+1);
       close(fd2[1]);

       exit(0);
   }
}