How to get file name?

[eluser]Unknown[/eluser]
I follow user guide at http://ellislab.com/codeigniter/user-gui...ading.html to create my upload file application.

But I have a problem when I try to get the original file name.

Code:

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$config['upload_path'] = './uploads/';
$config['allowed_types'] = 'gif|jpg|png';
$config['max_size']    = '100';
$config['file_name']    = time().'_original_name'; // I tried = time().'_'.$_POST['userfile']; but it doesn't work
$config['max_width']  = '1024';
$config['max_height']  = '768';
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Thanks for help