function getIp(){ 
    if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown")) 
    {
        $ip = getenv("HTTP_CLIENT_IP"); 
    }
    else 
    {
        if (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown")) 
        {
            $ip = getenv("HTTP_X_FORWARDED_FOR"); 
        }
        else 
        {
            if (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknown"))
	    {
                $ip = getenv("REMOTE_ADDR"); 
	    }
	    else 
	    {
                if (isset ($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], "unknown")) 
		{
                    $ip = $_SERVER['REMOTE_ADDR']; 
		}
		else 
		{
                    $ip = "unknown"; 
		}
	    }
        }
    }
    return ($ip); 
}

使用方法：

echo getIp();