how do you know the extension of the browsed file

[eluser]NEHIL[/eluser]
When you are uploading an image, you pass a config array. this is how mine looks like

Code:

$config = array(
            'allowed_types' => 'jpg|jpeg|gif|png',
            'upload_path' => $this->gallery_path,
            'file_name' => '$filename'
        );
$this->load->library('upload',$config);
$this->upload->do_upload();

So know, knowing the fact that i have allowed so many types while giving the file_name i don't know what extension to put?
please help! :roll: