Question

C programing language

pretend parent process is reading data and child process is writing data.

explain with pipe and fork function.

Answer 1

// C program to demonstrate use of fork() and pipe()
#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

   char fixed_str[] = "xyz.org";
   char input_str[100];
   pid_t p;

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

   scanf("%s", input_str);
   p = fork();

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

   // Parent process
   else if (p > 0)
   {
       char concat_str[100];

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

       // Write input string and close writing end of first
       // pipe.
       write(fd1[1], input_str, strlen(input_str)+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], concat_str, 100);
       printf("Concatenated string %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 concat_str[100];
       read(fd1[0], concat_str, 100);

       // Concatenate a fixed string with it
       int k = strlen(concat_str);
       int i;
       for (i=0; i<strlen(fixed_str); i++)
           concat_str[k++] = fixed_str[i];

       concat_str[k] = '\0'; // string ends with '\0'

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

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

       exit(0);
   }
}