Extended Controllers can be extremely helpful when building CodeIgniter applications. You might find, when developing different applications with CodeIgniter, that some of your Controllers have overlapping functionality. Instead of recreating the functions each time, you can make use of an extended Controller class.
Essentially what you do is create a new file in the libraries folder called MY_Controller.php—simply create this Controller like you would any other Controller. This file will be called by the system automatically.
If you want to have a number of extending Controllers, however, you may want to use a different name for your files.
Note
I have given these controllers a suffix of _controller so that I can easily identify them as a Controller file and not a general purpose library. You may use any type of naming convention that you please as long as it works for you. I simply do it this way because I find it easy and it helps me work better.