Question

I have started playing with CodeIgniter now.
And I use their user guide and other third-party tutorials available for learning. I’m a bit stuck at the naming of private functions. Based on the user guide, I have to prefix a _ in the name of private functions. But in this tutorial, check the Add Logout section. In it, there is a private function: private function check_isvalidated(). Here, it is not prefixed with the character _.

So that’s also an accepted naming convention ?
At the same time, there is another one called _output(): Processing Output.
It’s a public function with the naming convention of a private function !

It’s a bit of confusing when I try to learn in a systematic manner.

Answer 1

The _ prefix is a convention for functions defined in the CONTROLLER.

The user guide says:

In some cases you may want certain functions hidden from public access. To make a function private, simply add an underscore as the name prefix and it will not be served via a URL request.

http://www.codeigniter.com/user_guide/general/controllers.html#private-methods

Adding an _ is CodeIgniter’s own way of declaring functions in the controller (only in the controller) that cannot be called directly by the user:

• Controller functions are mapped to parts of the URL (controller/function)

• there are functions in the controller which should NOT be mapped to the URL

  - they are declared as `private` (available since PHP5)
  OR
  - their names start with `_` (works also for PHP4)
  

Regarding _output function, it is public, but it cannot be called directly since it contains _.

Why is public?

The function is called by the system, so it needs to be accessible from outside the class, it is not a private function. But, it contains _ to make sure it is not called via the URL.

To sum up, if you have functions in your controller which you don’t want to be called directly via the url, add _ prefix OR use the private access operator. Either one of them is good enough.

FYI, other frameworks like Yii or Zend framework, use the action prefix for all controller functions which CAN be called via the URL (are mapped).