因为您要扩展 CodeIgniter 库而不是核心组件，所以您希望将其放置在 application/libraries(而不是 应用程序/核心).

Because you're extending a CodeIgniter library and not a core component, you want to place that in application/libraries (not application/core).

当然，不要忘记在您的控制器代码中加载 Form_validation 库.

And of course, don't forget to load the Form_validation library within your controller code.

$this->load->library('form_validation');

其他需要检查的事项:

• 文件名区分大小写(MY_Form_validation.php 加载而My_Form_validation.php 不会)
• 类名区分大小写(class MY_Form_validation extends CI_Form_validation)

• Filename case sensitivity (MY_Form_validation.php loads while My_Form_validation.php won't)
• Class name case sensitivity (class MY_Form_validation extends CI_Form_validation)

参考资料:

• 扩展核心类
• 扩展本地库