Code Igniter Tutorial – Part 1 – Hello world

What this tutorial series will cover

In this series, I aim to give you an overview of how Code Igniter works, how it can give you nice clean URLs, how to use the MVC in your applications and how to interact with databases from within Code Igniter.

We will be building a simple application for managing todo lists, where the items are arranged in lists, and can be assigned to categories. I may even further extend this tutorial to add more functionality, and show how to create your own libraries which you can reuse in your own applications.

Installing Code Igniter

This is the first in my tutorial series, and we will discuss the very basics of setting up the Code Igniter environment, checking that all works, and creating a basic Hello World page.

First of all, you need to have a local web development environment. I’m using the XAMPP for linux package, as it provides an all in one solution, including apache, mySQL, phpmyadmin and a range of other stuff you don’t need to worry about. If you don’t have XAMPP, download it now (available for Windows, Linux, Mac and Solaris). Once you’ve installed that, you’ll need to download the latest version of the Code Igniter framework, which is is version 1.6.2 at the time of writting.

Once you’ve got XAMPP up and running (if you have any problems, consult the XAMPP documentation, trouble shooting XAMPP is beyond this tutorial), unzip the Code Igniter file you just downloaded into the web root (htdocs in the directory you created XAMPP).

Now if you go to http://localhost/CodeIgniter_1.6.2/, or whatever version you installed, you should see the default Code Igniter welcome page. If you don’t, you most probably didn’t start the XAMPP server correctly.

Understanding the file structure, and moving things around

Now if you look inside the Code Igniter folder, you should see index.php, license.txt, system and user_guidhttp://localhost/index.php/helloe. Now this default file structure works fine, but i prefer some seperation. This is entirely optional, but for the rest of the tutorial, I will assume you have your structure as follows.

In the system folder, you’ll find an application folder, this is the blood and guts of our applications, and is where almost all the code you write will go. Everything else in the system folder is the framework itself, so you don’t need to worry about it. Move the contents of the application folder up a level, so its in the same directory as index.php. It is also recommended that you move the framework itself out of the web root as you won’t need to access it directly. I recommend moving it to be above htdocs, and rename it to Code_Igniter_1.6.2, this way, you can have several versions of the framework installed, and switch between them easily. Finally, move everything index.php and todo into the web root. At this point you may delete the CodeIgniter_1.6.2 folder in the web root (which has got the user_guide and license.txt, both of which are online). You should now have just index.php and the contents of the application directory in the web root, with the framework one level above.

Now if you go to http://localhost/, you should get an error. This is because we’ve rearranged the file structure, and not told it where to find everything. To fix this, we need to edit index.php, so open it up in your favourite text editor. On line 26 (or there abouts) you should see it declare the location of the system folder, $system_folder = “system”;

Change this to point to your code igniter installation, which is now ‘../Code_Igniter_i.6.2′, and change the application path to be a period (current directory). If you now refresh your browser, you should once again see the welcome page.

So whats in each directory?

Config – This is where you do all the boring site configuration, such as setting up a database connection, site wide configuration and URL handling amongst other things.

Controllers – This is where you write your program logic, with a file for each class, made up of functions, more on this later.

Errors – Just defines what the various error pages are like, such as 404 errors etc.

Helpers – These are site wide collections of functions which you can write yourself, you won’t need to do much here.

Hooks – Not important at this stage, might talk about them at a later stage.

Language – Not important unless you plan on dealing in more then one language.

Libraries – Groups of related functions, which you can use i your controllers.

Models – Used to represent objects, do all the interaction with the database.

Views – This is where all the lovely HTML goes that the end user sees.

Hello world

So lets finally get down to it then.

Create a new controller called hello.php in the controller directory, snd enter the following code into it.

<?php
  class Hello extends Controller{
    function index(){
      echo "Hello World!";
    }
  }
?>

 
Seeing is believing
So now, go have a look at what you just done... go on, I'll wait.
Now matter how many time you refresh, you still get the welcome message, this is because we need to explicitly tell Code Igniter where to find the page we're looking for, or explicitly tell it in a configuration file. So lets tell it where to find our new Hello controller. Point your browser to http://localhost/index.php/hello, and you should see a message saying Hello World!
In the next installment, I'll show you how to set the default page to be your Hello world message instead of the welcome screen, and how to get rid of the need for index.php/... in the URL, and how to use views for output.
I hope you enjoyed this little tutorial, and found it useful, if you have any comments or came across any problems, let me know in the comments.
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Part 2 is now online


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