PHP获取用户的真实IP地址，非代理IP

function getClientIP(){
global $ip;
if(getenv("HTTP_CLIENT_IP")){
$ip = getenv("HTTP_CLIENT_IP");
}else if(getenv("HTTP_X_FORWARDED_FOR")){
$ip = getenv("HTTP_X_FORWARDED_FOR");
}else if(getenv("REMOTE_ADDR")){
$ip = getenv("REMOTE_ADDR");
}else{
$ip = "NULL";
}
return $ip;
}