较好的两个函数，获取文件扩展名&返回随机文件名

//获取文件扩展名
    public static function fileext($filename){
        return pathinfo($filename,PATHINFO_EXTENSION);

    }

    //返回随机文件名
    public static function randfilename($length = 10)
    {
        $hash = '';
        $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz';
        $max = strlen($chars) - 1;
        //mt_srand((double) microtime() * 1000000);
        for($i = 0;$i < $length;$i ++)
        {
            $hash .= $chars[mt_rand(0, $max)];
        }
        return $hash;
    }