如何自定义 PHP 异常类？

class MyException extends Exception
{
    public function __construct($message, $code = 0, Exception $previous = null)
    {
        // 调用父类的构造函数传递消息、错误码和前一个异常（可选）
        parent::__construct($message, $code, $previous);
    }
}

class FileOpenException extends Exception
{
    public function __construct($message, $code = 0, Exception $previous = null)
    {
        parent::__construct($message, $code, $previous);
    }
}

try {
    // 尝试打开一个不存在的文件
    $handle = fopen('non-existent-file.txt', 'r');
} catch (FileOpenException $e) {
    // 捕获并处理自定义异常
    echo '无法打开文件：' . $e->getMessage();
}

class FileOpenException extends Exception
{
    public function __construct($filename, $code = 0, Exception $previous = null)
    {
        $message = "无法打开文件 $filename。";
        parent::__construct($message, $code, $previous);
    }
}