Database not selected php 5.3
$host = 'localhost'
$user = 'root'
$password = ''
$db = 'mydb'

class Conf{

    private $_userdb;
    private $_passdb;
    private $_hostdb;
    private $_db;
    static $_instance;

    private function __construct(){
               require 'config.php';
           $this->_userdb=$user;
           $this->_passdb=$password;
           $this->_hostdb=$host;
           $this->_db=$db;
    }

    private function __clone(){ }

    public static function getInstance(){
            if (!(self::$_instance instanceof self)){
                self::$_instance=new self();
            }
            return self::$_instance;
    }

    public function getUserDB(){
            $var=$this->_userdb;
            return $var;
    }

    public function getHostDB(){
            $var=$this->_hostdb;
            return $var;
    }
    public function getPassDB(){
            $var=$this->_passdb;
            return $var;
    }

    public function getDB(){
            $var=$this->_db;
            return $var;
    }
}

class Db {
     private $server;
     private $user;
     private $password;
     private $data_base;
     private $link;
     private $result;
     static $_instance;


     private function __construct() {
            $this->setConnection();
        $this->connect();
        $this->result = null;
     }

     private function setConnection() {
            $conf = Conf::getInstance();
        $this->server = $conf->getHostDB();
        $this->data_base = $conf->getDB();
        $this->user = $conf->getUserDB();
        $this->password = $conf->getPassDB();
     }

     private function __clone(){ }

     public static function getInstance() {

            if (!(self::$_instance instanceof self)){
                      self::$_instance=new self();
            }          return self::$_instance;

     }


         private function connect() {

            $link=mysql_connect($this->server, $this->user, $this->password);
            if ($link){
                mysql_select_db($this->data_base,$link);
            }
            if (!$link){
                die('Can not connect');
            }else{
                $this->link = $link;
            }

     }
}