db_connect.php

<?php

/**
 * A class file to connect to database
 */
class DB_CONNECT {

    public $con;
    
    // constructor
    function __construct() {
        // connecting to database
        $this->connect();
    }

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

    /**
     * Function to connect with database
     */
    function connect() {
        // import database connection variables
        require_once __DIR__ . '/db_config.php';

        global $con;

        // Connecting to mysql database
        $con = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE) or die(mysql_error());
        
        // Selecing database
        // $db = mysqli_select_db(DB_DATABASE) or die(mysql_error()) or die(mysql_error());
        
        // returing connection cursor
        return $con;
    }

    /**
     * Function to close db connection
     */
    function close() {
        global $con;
        // closing db connection
        mysqli_close($con);
    }

}

?>