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;  
}