<?php

$vals = Array(  'REMOTE_ADDR' => $_SERVER["REMOTE_ADDR"],
        'HTTP_CLIENT_IP' => $_SERVER["HTTP_CLIENT_IP"],
        'HTTP_FORWARDED' => $_SERVER["HTTP_FORWARDED"],
        'HTTP_X_FORWARDED_FOR' => $_SERVER["HTTP_X_FORWARDED_FOR"]
    );

foreach($vals as $key => $v) {
    echo sprintf("%s: sprintf %%s: %s (%s), sprintf %%u: %u (%u)<br />\n", $key, $v, ip2long($v), $v, ip2long($v));
}

?>