如何纠正致命错误：未捕获的错误：未找到类'mysqli'？

Question

我今天将文件上传到实时托管服务器上，并在加载网址后显示此错误。

致命错误：未捕获错误：在/home3/maalu/public_html/php_action/db_connect.php:9中找不到类'mysqli'：堆栈跟踪：＃0 /home3/maalu/public_html/index.php(2）：include_once （）在第9行的/home3/maalu/public_html/php_action/db_connect.php中抛出＃1 {main}

下面是我的数据库连接。

<?php   

$localhost = "localhost";
$username = "maalu";
$password = "********";
$dbname = "stock";

// db connection
$connect = new mysqli($localhost, $username, $password, $dbname);

// check connection
if (mysqli_connect_errno($connect)) 
{ // creation of the connection object has some other error
    die("Connect failed: ".mysqli_connect_errno()." : ". mysqli_connect_error());
}

?>

请帮助。