CodeIgniter is an open source and powerful MVC(Model-View-Controller) based framework used for developing web applications on PHP.

It is loosely based on MVC pattern and similar to Cake PHP. CodeIgniter contains libraries, simple interface and logical structure to access these libraries, plug-ins, helpers and some other resources which solve the complex functions of PHP more easily maintaining high performance.

It simplifies the PHP code and brings out a fully interactive, dynamic website at a much shorter time.

The framework is available as open-source software under the MIT License and follows the model-view-controller (MVC) structure for web development.

• It is an open source framework and free to use.
• It is extensible. You can easily extend the system by using your libraries, helpers.
• It is extremely light weighted.
• Nearly zero configuration.
• Excellent documentation.
• Strong Security.
• Simple solutions over complexity.
• It has full featured database classes and support for several platforms.
• It is based on the Model View Controller (MVC) pattern.

CodeIgniter’s hooks will provide a way to change the internal workings or framework functionalities without any need for hacking the core files. It permits script execution with a particular path within the CodeIgniter.

We can globally enable/disable the hooks feature.

• pre_system
• pre_controller
• post_controller_constructo
• post_controller
• display_override
• cache_override
• post_system

In system/core/CodeIgniter.php, check CI_VERSION constant value define(‘CI_VERSION’, ‘3.0.6’);

Helper	Library
It is not written in object-oriented format.	It is written in an object-oriented format.
All built-in helper file names are suffixed with a word _helper	All built-in library files do not have a specific suffix.
It can be called in the same manner you call PHP functions.	You must create an object of the class to call library functions by using the $this->library_name->method()

Routing is a technique used in CodeIgniter, by which you can define your URLs based on the requirement instead of using the predefined URLs.

So, whenever there is a request made and matches the URL pattern defined by us, it will automatically direct to the specified controller and function.

The file is located at application/config/routes.php

A driver is a type of library that has a parent class and multiple child classes. These child classes can access their parent class, but they can’t access their siblings.

Drivers can be found in the system/libraries folder.

Because it does not follow a strict MVC pattern during application creation. It is not important to create a model, we can use only view and controllers for creating an application. In addition, one can modify CodeIgniter to utilize HMVC(Hierarchical Model View Controller) as well.

• MySQL.
• PostgreSQL.
• SQLite.
• Interbase/Firebird.
• Oracle.
• ODBC.
• MS SQL.

application/config/autoload.php file and add your model to the autoload array.

Application

1. cache
2. Config
3. Controllers
4. core
5. errors
6. helpers
7. hooks
8. language
9. libraries
10. logs
11. models
12. third-party
13. views

1. core
2. database
3. fonts
4. helpers
5. language
6. libraries

An inhibitor is an error handling class in Codeigniter.

It uses PHP ‘s native functions like register_shutdown_function , set_exception_handler, set_error_handler to handle parse errors, exceptions, and fatal errors.

1. Built-in libraries
2. Data abstraction
3. Security
4. Active Developer Community
5. Easy to Use
6. Collaboration with Expression Engine
7. Immigration Features

Model - The Controller manages models. It represents your data structure. Model classes contain functions through which you can CRUD (Create, Read, Update and Delete) operations in your database.

View - View is the information that is presented in front of users. It can be a web page or parts the page like header and footer. In this part you can write your HTML, CSS and Javascript code.

Controllers - Controller is the intermediary between models and view to process HTTP request and generates a web page. All the requests received by the controller are passed on to models and view to process the information. It works like a Bridge to pass data from model to view and view to model.

$this->load->view('page_name'); 

There are 3 key details about the architecture of CodeIgniter -

• It is dynamically instantiated making it extremely lightweight
• The components are mostly independent, making it loosely coupled
• Every class and function focuses on its own purpose, giving it component singularity

1. index.php is the default file of CodeIgniter. This file initializes the base resources.
2. The router determines what should be done with the information.
3. If the requested cache file exists, then the information is moved directly to the browser and ignores the further processes.
4. The application controller will load the models, libraries, helpers, plugins, and scripts required according to the request.
5. A view is used for fetching the data from the application controller that will be represented to the user, and they pass the data to the caching file to the fastest access for future requests.

You can set this default controller in application/config/routes.php

The essential part of a CodeIgniter framework is its libraries. It provides a rich set of libraries, which indirectly increase the speed of developing an application. The system library is located at system/libraries.

Class name is the name of the library that we want to load.

To load a library in CodeIgniter, you have to include the below code inside a controller: $this->load->library(‘class_name’);

CSRF(Cross-Site Request Forgery) token is a randomly generated value that gets modified with every HTTP request sent by webform.

To protect from CSRF we need to connect both the HTTP requests, form request and form submission. There are several ways to do this, but in CodeIgniter hidden field is used which is called CSRF token. The CSRF token is a random value that changes with every HTTP request sent.

When CSRF token is inserted in the website form, it also gets saved in the user's session. When the form is submitted, the website matches both the token, the submitted one and one saved in the session. If they match, request is made legitimate. The token value changes each time the page is loaded, which makes it tough for the hackers to guess the current token.

Laravel	CodeIgniter
It is object-oriented.	It is relational object-oriented.
Follows MVC structure of filing with a command-line tool known as Artisan.	Follows the MVC structure but it provides easier boarding based on object-oriented programming.
It comes along with a built-in module.	It does not come with a built-in module.
Supports Explicit routing.	Supports both Explicit and Implicit routing.
Provide their own official documentation which is very helpful.	Provides a lot of built-in functionality

The Second segment of URI determines which method is being called. If you want to override it, you can use _remap() method. The _remap method always get called even if URI is different. It overrides the URI.

Anchor tag creates a standard HTML anchor link based on the URL of your local site.

Sending an email is a simple process here. You can configure an email on the fly or set your preferences in the app/Config/Email.php file.

$this->uri->segment(n); // n=1 for controller, n=2 for method, etc

1. Place your parent class in the core folder.
2. Place an include statement at the beginning of all classes that include the parent class.

1. To improve the number of page visits.
2. To hide the code complexities from the user.

Codeigniter has got a Cross-Site Scripting(XSS) hack prevention filter. This filter either automatically runs or you can run it based on item, to filter all data related to POST and COOKIE.

This filter will prevent any malicious JavaScript code or any other code that attempts to hijack cookie and do malicious activities. To filter data through the XSS filter, use the xss_clean() method

The XSS filter will target the frequently used methods to trigger JavaScript code or other types of code that attempt to hijack cookies or do any other malicious activity. If it identifies anything suspicious or anything disallowed is encountered, then it will convert the data to character entities.

In application/config/config.php file and switch the following setting to ‘TRUE’ as shown below.

1. CSRF (Cross-site Request Forgery)
2. XSS filtering
3. Class reference

In CodeIgniter Session class allows you maintain a user’s “state” and track their activity while they are browsing your website.
In order to use session, you need to load Session class in your controller.

$this->load->library(‘session’); method is used to sessions in CodeIgniter

$this->session->userdata(); method of session class to read session data in CodeIgniter.

CLI is a text-based command-line interface for interacting with computers via a set of commands.

In Codeigniter, we can use CLI for

1. Run your cronjobs without needing to use wget or curl
2. Make interactive "tasks" that can do things like set permissions, prune cache folders, run backups, etc.
3. Helps to integrate Codeigniter with other applications in other languages. Like a random C++ script.

Object-relational mapping (ORM) is programming technique for converting data between incompatible type systems using object-oriented programming languages.

• DataMapper
• Doctrine
• Gas ORM

By default, all logs in Codeigniter are stored in logs/ directory.

To enable error logging you must set the threshold for logging in application/config/config.php.

• Error Messages
• Debug Messages
• Informational Messages

• Making file structure
• Making driver list
• Making driver(s)

1. libraries
2. config
3. helpers
4. language
5. models

The default URL patter in codeigniter is split up into four functions which start with the server name, controller class name,  controller function name and finally function parameters to accesses the URL pattern.

Model in the CodeIgniter is generally responsible to handle all the data logic and the representation and loading of the data that are present in the views.

The model in the CodeIgniter is stored in the application/models folder.

All the markup files like header, footer, sidebar, etc are present in the view folder. In order to reuse them the programmer has to embed them in the controller file anywhere.

The intermediary present between the models and the views to process the HTTP request and is used to generate a web page is known as a controller.

It is basically known as the center of each request that exists on the web application of the user.