/includes/db.inc.php

<?php

    if (!$config){
        $error = 'No config! Please, specify config before using `db.inc.php`';
        include $_SERVER['DOCUMENT_ROOT'] . '/error.html.php';
        exit();
    }

    $mysqli = new mysqli('localhost', $config['username'], $config['password']);
    if ($mysqli->connect_errno) {
        echo "Failed to connect to MySQL: " . $mysqli->connect_error;
        exit();
    }

    if (!$mysqli->set_charset('utf8'))
    {
        $output = 'Unable to set Database connection encoding';
        include $_SERVER['DOCUMENT_ROOT'] .'/output.html.php';
        exit();
    }
    if (!$mysqli->select_db($config['dbname']))
    {
        $error = 'Unable to locate database.';
        include $_SERVER['DOCUMENT_ROOT'] . '/error.html.php';
        exit();
    }
 ?>