Need help with PayPal URLs

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Code:

$str_get = parse_str($_SERVER['QUERY_STRING'], $_GET);

//Remove everything before (and including)
//the question mark and then parse into $_GET array.
$str_get = parse_str(substr(strrchr($_SERVER['REQUEST_URI'], "?"), 1), $_GET);
echo ' Using rebuilt $_GET array with xss protection: ' . $this->input->xss_clean($_GET['foo']);