PHP 获取在线IP

<?php

function getonlineip() {
if(empty($onlineip)) {
if (! empty ( $_SERVER ["HTTP_CLIENT_IP"] )) { 
$cip = $_SERVER ["HTTP_CLIENT_IP"]; 
} else if (! empty ( $_SERVER ["HTTP_X_FORWARDED_FOR"] )) { 
$cip = $_SERVER ["HTTP_X_FORWARDED_FOR"]; 
} else if (! empty ( $_SERVER ["REMOTE_ADDR"] )) { 
$cip = $_SERVER ["REMOTE_ADDR"]; 
} else { 
$cip = ''; 
} 
preg_match ( "/[\d\.]{7,15}/", $cip, $cips ); 
$onlineip = isset ( $cips [0] ) ? $cips [0] : 'unknown'; 
unset ( $cips ); 
} 
return $onlineip; 
}

?>