您应该学习如何利用

Instead of that dreadful abomination, you should learn how to utilize spl_autoload_register():

spl_autoload_register( function( $classname ){

    $filename = 'inc/classes/' . $classname . '.class.php';

    if ( !file_exists( $filename) ){
        throw new Exception("Could not load class '$classname'.". 
                            "File '$filename' was not found !");
    }

    require $filename;

});

并且您应该在index.php或bootstrap.php文件中注册自动加载器，并且每个加载器仅执行一次(此功能可让您定义多个加载器，但是当您拥有第三方库时使用该库autoloader ..就像SwiftMailer一样).

And you should register the autoloader in your index.php or bootstrap.php file, and do it only once per loader (this ability lets you define multiple loaders, but that's used, when you have third party library, which has own autoloader .. like in case of SwiftMailer).

P.S.请学习将准备好的语句与MySQLi或PDO一起使用.

P.S. please learn to use prepared statements with MySQLi or PDO.

更新

由于您现在正在学习OOP，因此以下几件事可能会有用:

Since you are just now learning OOP, here are few things, which you might find useful:

讲座:

• 高级OO模式
• 继承，多态和测试
• 识别臭味的代码
• 全局状态和单例
• 不要找东西！

• Advanced OO Patterns
• Inheritance, Polymorphism, & Testing
• Recognizing smelly code
• Global State and Singletons
• Don't Look For Things!

书籍:

• PHP面向对象的解决方案
• 企业应用程序体系结构的模式

• PHP Object-Oriented Solutions
• Patterns of Enterprise Application Architecture