Question

Operating system C language question:

How to use pipes and file descriptors in Linux C? I don't understand why people can use 1 newly created array int fd[2] and then they can communicate with each others..

Answer 1

I have written a program to demonstrate how pipe and fd are used.

you can go through the code and the comments.

Program:

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

int main(void)
{
        int     fd[2];       //for storing file descriptors given by pipe()
       pid_t pid;           //for storing pid returned by pid
      
        pipe(fd);           //creating pipe
      
        pid = fork();        //creating child
      
        if( pid == -1)
        {
                perror("fork failed");
                exit(1);
        }
      
       /*the semantics of fork is that,
       whole data is copied from parent to child
       this means that fd[2], pid can be used by both
       parent and child */
      
       //if child
        if(pid == 0)
        {
                /* Child process close it's input side fd[0]
                   which it has */
                close(fd[0]);

                /* write the string to it's output side fd[1] */
                write(fd[1], "Hello I'm Child", 16);
                exit(0);
        }
        //if parent
        else
        {
           char buffer[20];
                /* Parent process closes it's output side fd[1] */
                close(fd[1]);

                /* Read string from it's input side */
                read(fd[0], buffer, sizeof(buffer));
                printf("\nReceived from Child: %s\n\n", buffer);
        }
        return(0);
}

Execution and Output: