使用php获取登录IP

/**
     * IP地址获取
     * @return string 如：192.168.1.1 失败的情况下，返回空
     */
    public static function getClientIp()
    {
        $unknown = 'unknown';
        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 = '';
        }
        return $ip;

}