Unlink file in CodeIgniter

If you try to use unlink in CI as

$filestring = base_url().'uploads/'.$filename;
unlink ( $filestring );

you will face such error message:

A PHP Error was encountered
Severity: Warning
Message: unlink() [function.unlink]: http does not allow unlinking
Filename: controllers/face.php
Line Number: 109

because CI does not understand the  path we specified, therefore to remove a file we have to either use:

$filestring = APPPATH.'../uploads/'.$filename;unlink ($filestring);

or

 define('PUBPATH',str_replace(SELF,'',FCPATH)); // in index.php

and

$filestring = PUBPATH.'uploads/'.$filename;   // in controller