如何在php文件中使用类的概念

I use Easyphp5, but when I do an instance of a class in php file

triggered an error

i have instance this class in another file or php class but any error

Fatal error: Class 'db_connect' not found in C:\Program Files (x86)\EasyPHP-12.1\www\testPDA\create_client.php on line 11

here is this class

<?php

class DB_Connect {

    // constructor
    function __construct() {

    }

    // destructor
    function __destruct() {
        // $this->close();
    }

    // Connecting to database
    public function connect() {
        require_once 'config.php';
        // connecting to mysql
        $con = mysql_connect(DB_HOST, DB_USER, DB_PASSWORD);
        // selecting database
        mysql_select_db(DB_DATABASE);

        // return database handler
        return $con;
    }

    // Closing database connection
    public function close() {
        mysql_close();
    }

} 
?>

I have tried to use

$conn = new DB_Connect();

but I still don't understand why it can't work.

Maybe you can try to access with function.

$conn = DB_Connect::connect();