// Simple pipe example

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

int main(void) {
   int fd[2];
   pid_t pid;  
  
   if( pipe(fd) < 0){
        perror(NULL);
        exit(1);
   }
   pid = fork();
   assert(pid >= 0);
   if (pid != 0) {  // parent
     
      close(fd[1]); // reader: don't need fd[1]
      FILE *f0 = fdopen(fd[0],"r");
      
      int c;
      while((c = fgetc(f0)) != EOF){
         putchar(c);
      }
      fclose(f0);
      waitpid(pid, NULL, 0);
   }
   else {       
      close(fd[0]); // writer, don't need fd[0]
      FILE *f1 = fdopen(fd[1], "w");
      
      fprintf(f1, "123456789\n");
      fclose(f1);
   }
   return 0;
}