Singleton Pattern for PDO MySQL

gistfile1.txt

<?php
class DB{
    //variable to hold connection object.
    protected static $db;
    //private construct - class cannot be instatiated externally.
    private function __construct() {
        try {
            // assign PDO object to db variable
            self::$db = new PDO( 'mysql:host='.DB_HOST.';dbname='.DB_NAME, DB_USER, DB_PASS );
            self::$db->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
        }
        catch (PDOException $e) {
            //Output error - would normally log this to error file rather than output to user.
            echo "Connection Error: " . $e->getMessage();
        }
    }
    // get connection function. Static method - accessible without instantiation
    public static function getConnection() {
        //Guarantees single instance, if no connection object exists then create one.
        if (!self::$db) {
            //new connection object.
            new db();
        }
        //return connection.
        return self::$db;
    }
}