PHP获取用户真实IP

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;
}