奇怪的PHP要求/包含錯誤

Question

我是一個相對較新的開發人員，但確實了解一些知識。

除了Lynda的基礎知識之外，我還在做有關PHP的教程，並試圖制作數據庫類。

在課堂上寫完所有內容后，我嘗試查看是否建立了連接。

require_once("../includes/database.php");
if(isset($database)) {
    echo "true<br />";
}else {
    echo "false<br />";
}

上面的代碼是我的測試，看是否還好

問題是當我嘗試使用“ require_once（” config.php“）;”時 在數據庫類中。

require_once("config.php");//line 13

class MySQLDatabase{
   //code that is not important for this issue
}

這使我在頁面上出現以下錯誤：

 Notice: Use of undefined constant DB_SERVER - assumed 'DB_SERVER' in       E:\ProgramFiles\xampp\htdocs\photo_gallery\includes\database.php on line 13

 Notice: Use of undefined constant DB_USER - assumed 'DB_USER' in E:\ProgramFiles\xampp\htdocs\photo_gallery\includes\database.php on line 13

 Notice: Use of undefined constant DB_PASS - assumed 'DB_PASS' in      E:\ProgramFiles\xampp\htdocs\photo_gallery\includes\database.php on line 13
 Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in E:\ProgramFiles\xampp\htdocs\photo_gallery\includes\database.php on line 13

 Warning: mysql_connect(): php_network_getaddresses: getaddrinfo failed: No such host is known. in E:\ProgramFiles\xampp\htdocs\photo_gallery\includes\database.php on line 13

 Warning: mysql_connect(): php_network_getaddresses: getaddrinfo failed: No such host is known. in E:\ProgramFiles\xampp\htdocs\photo_gallery\includes\database.php on line 13

數據庫連接失敗：php_network_getaddresses：getaddrinfo失敗：此類主機未知

如果我使用（下面的代碼）代替了require / require_once / include / include_once部分，它就可以工作！

define("DB_SERVER", "localhost");
define("DB_USER", "gallery");
define("DB_PASS", "123465");
define("DB_NAME", "photo_gallery");

這不是我第一次使用require / include ...，但是我真的很困惑為什么這種方法不起作用：-/（一旦我完成了DB類，我將把所有內容更改為mysqli，因為它是教程。不，我無權訪問練習文件）

（對不起，很長的帖子）

Answer 1

聽起來在config.php中，定義常量時缺少引號。

wrong:
define(DB_SERVER, "localhost");
right:
define("DB_SERVER", "localhost");

仔細檢查一下，或從config.php中發布相關部分：）

Answer 2

嘗試通過以下方式定義常量。

defined('DB_SERVER') ? null : define("DB_SERVER", "localhost");
defined('DB_USER')   ? null : define("DB_USER", "gallery");
defined('DB_PASS')   ? null : define("DB_PASS", "123456");
defined('DB_NAME')   ? null : define("DB_NAME", "photo_gallery");

除去Notice: Use of undefined constant DB_SERVER通知。

看起來我們丟失了什么或者您的mysql數據庫已關閉？