##fichier forum.class.php##
<?php
class Forum{

    private $db;
    private $results;

    function __construct() {
        $db = new DBConnect();

    }

    function show_topics() {
        $results = $this->results;
        $results = $this->db->query('SELECT * FROM forum_topics');
        $results = $results->fetch();

        return $results;
    }

    function show_replies($id) {

    }

}
?>

##fichier dbconnect.class.php##
<?php

class DBconnect extends PDO {

private $db_user = 'root';
private $db_pass = '';
private $db_name = 'mysql:host=127.0.0.1;dbname=blog';

      function  __construct() {

        parent::__construct($this->db_name, $this->db_user, $this->db_pass);
        parent::setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);


       }

}
?>

##fichier index.php##
<?php
require("core.php");
loadclass('dbconnect');
loadclass('forum');

$res = new Forum();
$results = $res->show_topics();


print_r($results);

foreach($results as $a => $b) {
    echo "<pre>";
    echo "$a => $b";
    echo "</pre>";
}
?>