PHP如何获取用户的真实IP，和IP138一样的

function getIp(){ 
    $onlineip=''; 
    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']; 
    } 
    return $onlineip; 
}

Discuz里面提取的函数

function getip() {
$unknown = 'unknown';
if (isset($_SERVER['HTTP_X_FORWARDED_FOR']) && $_SERVER['HTTP_X_FORWARDED_FOR'] && strcasecmp($_SERVER['HTTP_X_FORWARDED_FOR'], $unknown)) {
$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
}
elseif(isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], $unknown)) {
$ip = $_SERVER['REMOTE_ADDR'];
}
/*
处理多层代理的情况
或者使用正则方式：$ip = preg_match("/[\d\.]{7,15}/", $ip, $matches) ? $matches[0] : $unknown;
*/
if (false !== strpos($ip, ',')) $ip = reset(explode(',', $ip));
return $ip;
}
echo "来访者的真实IP是：".getip();
这是经本人实测过的。