$this->uri->segment(3);


$product_id = $this->uri->segment(3, 0);
if ($this->uri->segment(3) === FALSE)
{
    $product_id = 0;
}
else
{
    $product_id = $this->uri->segment(3);
}

$this->uri->uri_string()
	http://example.com/index.php/news/local/345
	
	return 
		news/local/345