8.2. Empty a File#

Sometimes we want empty the file contents instead of deleting the file and then recreating it. Opening a filehandle with flag O_TRUNC will clear all data from the file.

Note

This lab builds on Lab 5. Writing to a file.

You need three flags to empty or create the file using open.

  1. O_WRONLY opens the file in write only mode.

  2. O_TRUNC empties the file of any data.

  3. O_CREAT creates the file if it does not exit.
    This flags requires that file permissions are send with the the open command.

Template Code#

Required Include Files

#include <fcntl.h>

Basic Usage

char *file_name = "test-empty.txt";
int flags = O_WRONLY | O_TRUNC | O_CREAT;
int file_permissions = 0644;

// open a file handle that creates or empties the file.
int empty_fd = open(file_name, flags, file_permissions);
close(empty_fd);

Task: Empty a File#

Create a file called lab8.2.c for this task.

  1. Create a function that empties an existing file or creates the file if it does not exist.

    • The function should accept the name or path of the file to empty.

      • Hint: Use a pointer to a char array.

    • The function should return a bool value.

      • Return true if the file emptied successfully.

      • Return false if an error occurred while emptying or creating the file.

  2. Test the function by:

    • Writing some data to the file

    • Emptying the file

    • Verifying that the file is empty.

Source & license

Reproduced verbatim, without modification from © 2022, BilimEdtech Labs, licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).

Source page: https://labs.bilimedtech.com/operating-systems/8/2.html

See LICENSE for the full license text.