"Call to a member function prepare() on a non-object" when using prepared statement

Question

So i've made a forum for my site and i run intro a problem and here it is

Fatal error: Call to a member function prepare() on a non-object in /home/a8479867/public_html/pages/forum/index.php on line 3

Here is my code

<?php
//...
$query=$db->prepare('SELECT cat_id, cat_nom, 
forum_forum.forum_id, forum_name, forum_desc, forum_post, forum_topic, auth_view, forum_topic.topic_id,  forum_topic.topic_post, post_id, post_time, post_createur, membre_pseudo, 
membre_id 
FROM forum_categorie
LEFT JOIN forum_forum ON forum_categorie.cat_id = forum_forum.forum_cat_id
LEFT JOIN forum_post ON forum_post.post_id = forum_forum.forum_last_post_id
LEFT JOIN forum_topic ON forum_topic.topic_id = forum_post.topic_id
LEFT JOIN forum_membres ON forum_membres.membre_id = forum_post.post_createur
WHERE auth_view <= :lvl 
ORDER BY cat_ordre, forum_ordre DESC');
$query->bindValue(':lvl',$lvl,PDO::PARAM_INT);
$query->execute();
?>

Answer 1

you haven't created the "db" object that you're calling on line 3

for mysqli it is $db = new mysqli('localhost', 'my_user', 'my_password', 'db');

as it seems your using pdo its $db = new PDO('mysql:host=localhost;dbname=testdb;charset=utf8', 'username', 'password');