Notes

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

#define BUFFER_SIZE 50

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

char child_msg1[100];
char child_msg2[100];

pid_t p;

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

char parent_msg[] = "Hello! Child";
p = fork();

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

// Parent process
else if (p > 0)
{

close(fd1[0]); // Close reading end of first pipe

// Write input string and close writing end of first
// pipe.
write(fd1[1], parent_msg, strlen(parent_msg)+1);
close(fd1[1]);

// 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], child_msg1, 100);
printf("Child message: %sn", child_msg1);
close(fd2[0]);
}

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

// Read a string using first pipe
char child_msg[]="hello parent";
read(fd1[0], child_msg2, 100);
printf("Parent message: %sn", child_msg2);


// Close both reading ends
close(fd1[0]);
close(fd2[0]);

// Write concatenated string and close writing end
write(fd2[1], child_msg, strlen(child_msg)+1);
close(fd2[1]);

exit(0);
}
}