取客户端IP 如果使用多级代理的用户，真实IP是取不到的。

getOnlineIp.php

<?php
function getOnlineIp() {  
    $strOnlineIp = "";  
    if(getenv('HTTP_CLIENT_IP') && strcasecmp(getenv('HTTP_CLIENT_IP'), 'unknown')) {  
        $onlineip = getenv('HTTP_CLIENT_IP');  
    } elseif(getenv('HTTP_X_FORWARDED_FOR') && strcasecmp(getenv('HTTP_X_FORWARDED_FOR'), 'unknown')) {  
        $onlineip = getenv('HTTP_X_FORWARDED_FOR');  
    } elseif(getenv('REMOTE_ADDR') && strcasecmp(getenv('REMOTE_ADDR'), 'unknown')) {  
        $onlineip = getenv('REMOTE_ADDR');  
    } elseif(isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], 'unknown')) {  
        $onlineip = $_SERVER['REMOTE_ADDR'];  
    }  
    preg_match("/[\d\.]{7,15}/", $onlineip, $onlineipmatches);  
    $strOnlineIp = $onlineipmatches[0] ? $onlineipmatches[0] : 'unknown';  
    return $strOnlineIp;  
}