PHP获取当前用户真实IP的方法

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; 
}