未定义的常量和通过引用分配new的返回值Error

我有一个数据库类，在其中我使用required_once调用配置文件。在这里，我使用define（）声明了一些常量。我得到了未定义常量的错误，还通过引用分配了new的返回值。这是配置文件代码：

<?php
// Database Constants
defined("DB_SERVER") ? null : define("DB_SERVER", "localhost");
defined("DB_USER")   ? null : define("DB_USER", "root");
defined("DB_PASS")   ? null : define("DB_PASS", "");
defined("DB_NAME")   ? null : define("DB_NAME", "shareysmile");
?>

这是我的数据库类代码（两者都在同一目录中，所以这不是问题所在）：

<?php
require_once("config.php");
class MySQLDatabase {
    private $connection;
    public $last_query;
    private $magic_quotes_active;
    private $real_escape_string_exists;
  function __construct() {
    $this->open_connection();
        $this->magic_quotes_active = get_magic_quotes_gpc();
        $this->real_escape_string_exists = function_exists( "mysql_real_escape_string" );
  }
    public function open_connection() {
        $this->connection = mysql_connect(DB_SERVER, DB_USER, DB_PASS);
        if (!$this->connection) {
            die("Database connection failed: " . mysql_error());
        } else {
            $db_select = mysql_select_db(DB_NAME, $this->connection);
            if (!$db_select) {
                die("Database selection failed: " . mysql_error());
            }
        }
    }
    public function close_connection() {
        if(isset($this->connection)) {
            mysql_close($this->connection);
            unset($this->connection);
        }
    }
    public function query($sql) {
        $this->last_query = $sql;
        $result = mysql_query($sql, $this->connection);
        $this->confirm_query($result);
        return $result;
    }
    public function escape_value( $value ) {
        if( $this->real_escape_string_exists ) { // PHP v4.3.0 or higher
            // undo any magic quote effects so mysql_real_escape_string can do the work
            if( $this->magic_quotes_active ) { $value = stripslashes( $value ); }
            $value = mysql_real_escape_string( $value );
        } else { // before PHP v4.3.0
            // if magic quotes aren't already on then add slashes manually
            if( !$this->magic_quotes_active ) { $value = addslashes( $value ); }
            // if magic quotes are active, then the slashes already exist
        }
        return $value;
    }
    // "database-neutral" methods
  public function fetch_array($result_set) {
    return mysql_fetch_array($result_set);
  }
  public function num_rows($result_set) {
   return mysql_num_rows($result_set);
  }
  public function insert_id() {
    // get the last id inserted over the current db connection
    return mysql_insert_id($this->connection);
  }
  public function affected_rows() {
    return mysql_affected_rows($this->connection);
  }
    private function confirm_query($result) {
        if (!$result) {
        $output = "Database query failed: " . mysql_error() . "<br /><br />";
        //$output .= "Last SQL query: " . $this->last_query;
        die( $output );
        }
    }
}
$database = new MySQLDatabase();

?>

我不明白这个问题，有人能帮忙吗？以下是我得到的确切错误：

Deprecated: Assigning the return value of new by reference is deprecated in D:'xampp'php'PEAR'Config.php on line 80
Deprecated: Assigning the return value of new by reference is deprecated in D:'xampp'php'PEAR'Config.php on line 166
Notice: Use of undefined constant DB_SERVER - assumed 'DB_SERVER' in D:'xampp'htdocs'sharesmile'src'database.php on line 18
Notice: Use of undefined constant DB_USER - assumed 'DB_USER' in D:'xampp'htdocs'sharesmile'src'database.php on line 18
Notice: Use of undefined constant DB_PASS - assumed 'DB_PASS' in D:'xampp'htdocs'sharesmile'src'database.php on line 18