#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> int main(){   int stdout_bak = dup(STDOUT_FILENO); // make a backup of stdout   system("rm -f mystery.txt");         // remove file using a shell command   int out_fd = open("mystery.txt",     // open file mystery.txt                     O_WRONLY|O_CREAT,  // for writing, create if needed                     S_IRUSR|S_IWUSR);  // give user read/write permission   if(out_fd == -1){                    // check for errors opening file     perror("Couldn't open file 'mystery.txt'");     exit(1);                           // bail out if open fails   }   printf("1. Now you see me.\n");      // print to the screen   dup2(out_fd, STDOUT_FILENO);         // change stdout to go to mystery.txt   printf("2. Now you don't!\n");       // print goes to mystery.txt   close(out_fd);                       // close mystery.txt   dup2(stdout_bak, STDOUT_FILENO);     // restore stdout to screen   printf("3. How mysterious...\n");    // print goes to screen   return 0; } Awsner all parts: A) The `open()' system call is used to open a file for writing.  What is returned by this system call?B) What's the output for `switch_stdout' when this is run?C) How is the `dup()' system call is used? How is 'dub2()' used?

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

int main(){
  int stdout_bak = dup(STDOUT_FILENO); // make a backup of stdout

  system("rm -f mystery.txt");         // remove file using a shell command

  int out_fd = open("mystery.txt",     // open file mystery.txt
                    O_WRONLY|O_CREAT,  // for writing, create if needed
                    S_IRUSR|S_IWUSR);  // give user read/write permission

  if(out_fd == -1){                    // check for errors opening file
    perror("Couldn't open file 'mystery.txt'");
    exit(1);                           // bail out if open fails
  }

  printf("1. Now you see me.\n");      // print to the screen

  dup2(out_fd, STDOUT_FILENO);         // change stdout to go to mystery.txt

  printf("2. Now you don't!\n");       // print goes to mystery.txt

  close(out_fd);                       // close mystery.txt

  dup2(stdout_bak, STDOUT_FILENO);     // restore stdout to screen

  printf("3. How mysterious...\n");    // print goes to screen

  return 0;
}

Awsner all parts:

A) The `open()' system call is used to open a file for writing.  What is returned by this system call?
B) What's the output for `switch_stdout' when this is run?
C) How is the `dup()' system call is used? How is 'dub2()' used?

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