A controller is the intermediary between models and views to process the HTTP request and generates a web page. It is the center of every request on your web application.

Consider following URI,

abc.com/index.php/front/
In this URI, CodeIgniter try to find Front.php file and Front class.

In CodeIgniter, a controller is a crucial component of the MVC (Model-View-Controller) architecture. It serves as an intermediary between the model (data) and the view (user interface). Controllers handle user requests, process data, and determine which view to display.

Here’s a breakdown of the key aspects and functionalities of a controller in CodeIgniter:

Routing and Request Handling: Controllers are responsible for receiving and handling incoming HTTP requests. They define methods (functions) that correspond to specific URI routes. When a request matches a route configured in the application’s routing system, the corresponding controller method is invoked.
Data Processing: Controllers handle data processing tasks such as fetching data from models, processing input data from users, and preparing data to be sent to views. They interact with model components to perform CRUD (Create, Read, Update, Delete) operations on data stored in a database or any other data source.
Business Logic: Controllers encapsulate the application’s business logic. They contain the logic that determines how data should be manipulated and which actions should be taken based on user input and application requirements.
Loading Views: Once the necessary data processing is done, controllers load appropriate views to generate HTML output. Views are typically HTML files with embedded PHP code that displays data to users. Controllers pass data to views for presentation using variables.
Middleware and Filters: Controllers can also act as middleware by intercepting requests before or after they reach the intended controller method. This allows for implementing authentication, authorization, logging, and other cross-cutting concerns.
Request Lifecycle Management: Controllers manage the entire request lifecycle, from receiving the request to sending the response. They orchestrate the flow of control within the application, ensuring that data is processed correctly and views are rendered appropriately.

Overall, controllers play a central role in structuring CodeIgniter applications, promoting separation of concerns, and facilitating modular development. They help maintain clean, organized code by keeping business logic separate from presentation logic.