Deleting file in codeigniter 3.1.4

I am using codeigniter 3.1.4.I am trying to delete a file in a folder in root directory.When i use unlink function as

$path=base_url()."files/image.jpg";
   unlink($path);

I got following Error:

A PHP Error was encountered

Severity: Warning

Message: unlink(): http does not allow unlinking

Filename: controllers/Deletion.php

Line Number: 12

Backtrace:

File: C:\xampp\htdocs\deletiontesting\application\controllers\Deletion.php
Line: 12
Function: unlink

File: C:\xampp\htdocs\deletiontesting\index.php
Line: 315
Function: require_once

When I use file helper for this purpose as

$this->load->helper('file');
        $path=base_url()."files/image.jpg";
        delete_files($path);

The file is not deleted.file name is image.jpg folder name is files .Please help me to delete that file