Exploring the file structure

Once you have installed the CI files, have a look at the new directories that have been created. Understanding what different type of files and folders do is critical.

The initial files and folders we can see are:

These are our main site's files and folders, the index.php file being the most important one, it will act as the main controller and will route application requests to the required controllers. Without this file, CodeIgniter can't work.

Next in importance is the system folder. The framework's base files and libraries are present in this folder. We, as programmers, won't need to modify those files for our normal usage. However, it's important to know what those files are and what they do.

The application folder is placed inside the system folder. Our site's files and code will be put here. This separation of the system and application folders has two purposes:

Of course, there are more files and folders. If you have opened the system folder you would have glanced through them. We are going to see them one by one. If you've ever looked at any other PHP framework, the structure will look fairly familiar. The folder structure is similar to the following:

system

user_guide: This folder contains help documents for CI, they are the same as those on CodeIgniter's site.

index.php: This file must be in the document root of your server so that CodeIgniter can work.

license.txt: This file is the license document, you should read it.

Does it work?—checking our CI installation

Now that we have taken a look at our CI files and structure, we are going to check if it's working. An easy way to see if your site is working is to navigate to it using your browser. For example, if you have installed CI in a folder called codeigniter inside your wamp installation, you can see it by using the path http://127.0.0.1/codeigniter/ in your browser. You should see something similar to the following screenshot:

This means CI is up and running. Did you see how easy it is? We will need to make some configuration changes to adapt it to our needs, but that will be very easy.

The configuration file

Remember we were going to take two minutes to set up our site. The second minute is spent doing some basic configuration.

The config folder contains a group of files that set basic configurations for your site. Open the system/application/config/config.php file and tell the site where to find itself. The first few lines of the file should say something like:

/*
|------------------------------------------------
| Base Site URL
|------------------------------------------------
|
| URL to your Code Igniter root. Typically this
| will be your base URL, WITH a trailing slash:
|
| http://www.your-site.com/
|
*/
$config['base_url'] = "http://127.0.0.1/";
/*

Notice, how well CI files are commented! Alter the values in quotes to match your own website's root. If you have a problem, more detailed set up instructions are given in the online manual. Some functions such as anchor and base_url use this configuration, so modify it carefully.

As a basic principle, use the config.php file to store information about your site rather than scattering it around your files. In the first place, it is easier to update if it's all in one place. Second, when you transfer your site from the development server to the production server, you'll have to make only one set of changes. Lastly, many CI functions assume that certain information is to be found there.

There are other config files in the config folder. The database connection file, the routes file, and the autoload file are some of the most important files we will be changing for our application to work correctly. Should your CI installation produce a 404 error, after this basic configuration, look at line 44 of the config file:

$config['uri_protocol'] = "AUTO";

This line determines which global variable will be used to retrieve the query string. This is needed to create nice URLs and know which part of the URL is our path to the file and which part contains the variables we are passing between pages. Sometimes one of those variables is not available, though usually AUTO will work, on other occasions we will have to specify which one should be used, manually.

For example, take this URL:

http://localhost/demo/sayhello.php?to=Fred.

In my server configuration, PATH_INFO and ORIG_PATH_INFO return nothing, but the others return:

As we can see, they work in a different way, if PATH_INFO had been active it would have returned the values before the question mark, that is:

If the AUTO option doesn't work for you, try to change this setting with the other options, and if none of them works for you then change your index_page variable to:

$config['index_page'] = "index.php?";

The only difference is the question mark (?), which should solve your problem. As we have seen before, these methods are used to determine which part of the URL is our path to the file and which part contains the variables. For some reason the question mark (?) is not automatically appended to the URL, the reason couldn't be determined. At these times we will put the question mark manually.

Autoloading libraries, helpers, and so on

Inside the config folder you will also find the autoload.php file. This file will help you determine which libraries, helpers, and so on, should be autoloaded within your application. But at this point you may not know what libraries or helpers are. Don't worry about that, we will summarize this concept. Libraries are like classes, which contain methods that help us while working with some tasks such as, session control, database access, and a lot of other things. Helpers work in the same way but in a smaller scope.

You need to load the library first and then you can use it. Usually, to load a library you need to do something like:

$this->load->library('pagination');

Similarly for helper loading you need:

$this->load->helper('form');

After doing that you can use the library or helper. If you need to use a particular library or helper once or twice in your application there is no problem with that. But now imagine, you have to write those lines in every controller function of your site.

If you want to save some time, and forget about the repetitive task of adding the loading lines, you can put those libraries and helpers in the autoload.php file. For example, if you are using the pagination library you could add it to the autoload file this way:

$autoload['libraries'] = array('pagination');

Now you will have access to the functions of the pagination library in every function of your application, without the need to load it first. Another good candidate library to be autoloaded is the database library, you can add it in the same array (don't do it now, just take a look at how it works):

$autoload['libraries'] = array('pagination', 'database');

If your application is using a database, you will end up putting the database library in the autoload array, eliminating the necessity to load the library every time you need access to the database.

Helpers, plugins, and extra configuration files could be added to the autoload.php file the same way, in their corresponding arrays. You maybe tempted to put all libraries and helpers you will be using in this file. But remember that all the libraries and helpers you put here add to the loading time and your application will load slowly.

If your site has only a few visitors you don't need to look after these things. But as time passes by and, luckily, your site becomes popular, all these things count and you need to take everything into account.

Don't worry about this, after you have built some sites with CI, you will know which libraries, helpers, plugins, and so on should be put here and you will be doing that soon. That means CI is up and running. Did it take more than two minutes?

Mod rewrite and apache .htaccess to achieve nice URL rewrites

Earlier we saw the welcome page of CI, it is there by default, thanks to the welcome controller and welcome view. The welcome controller is the default controller (this is configured in the routes.php file of the config directory), so it is loaded on the home page of our application.

If we want to see it and if the default controller isn't there, we would have to put this URL:

http://127.0.0.1/codeigniter/index.php/welcome

Note the index.php in the path between the base URL and the controller we want to load. If you try to put the URL like:

http://127.0.0.1/codeigniter/welcome

You will get an error page, but this can be solved, so we can get rid of the index.php. This, we have to admit, doesn't make our URLs easy to write. The first thing that we need to do is put an .htaccess file in our application's root. Of course our server needs to support the use of these files (you can ask your hosting provider about this).

We can find a sample .htaccess file for CI on Wiki:

http://codeigniter.com/wiki/mod_rewrite/

Create a file called .htaccess in your application root (where the index.php file was located), and copy the code you found on Wiki:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
#Removes access to the system folder by users.
#Additionally this will allow you to create a System.php
#controller, previously this would not have been possible.
#'system' can be replaced if you have renamed your system folder.
RewriteCond %{REQUEST_URI} ^system.*
RewriteRule ^(.*)$ /codeigniter/index.php?/$1 [L]
#Checks to see if the user is attempting to access a valid file,
#such as an image or css document, if this isn't true it sends
#the request to index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /codeigniter/index.php?/$1 [L]
</IfModule>
<IfModule !mod_rewrite.c>
# If we don't have mod_rewrite installed, all 404's
# can be sent to index.php, and everything works as normal.
# Submitted by: ElliotHaughin
ErrorDocument 404 /index.php
</IfModule>

If you cannot create the .htaccess file (Windows needs a file name to be put before the extension), then create it on a Linux server and download it, after that you will be able to edit it. For example, you can connect it to an FTP tool (like FileZilla), to another hosting you have, and create the file and download it to your PC.

After creating the file and copying the code from Wiki into it, you may need to change it to adapt to your hosting configuration. If we have to add our base URL /codeigniter at some places (it is in bold so you can recognize it), we need to change the config.php file, located at system/application/config. The only thing you need to do is change this line:

$config['index_page'] = "index.php";

To this:

$config['index_page'] = "";

After that you will be able to go to http://127.0.0.1/codeigniter/welcome and you won't need to put index.php in between your base URL and your controller. Now it is much easier to write, and for your visitors to remember, it's also better for your website's SEO.

Moving the application directory and the system directory—benefits

Here we are making the final changes to our CI installation.

To make these changes, open the index.php file, go to the system folder, and move the application folder and all it's content to the same level as the index.php file (cut and paste the entire folder with all it's subfolders). Now put the system folder outside the document root and change the following line in index.php file from:

$system_folder = "system";

To:

$system_folder = "../CI_system";

We can change the name of the folder from system to CI_system, or whatever you want.

So now our structure will look similar to the following:

CI_system
www (or htdocs in xampp)
codeigniter
application
user_guide
.htaccess
index.php
license.txt

This way we get some benefits. First, by moving the system folder outside the document root we prevent possible attacks on CI core files. In this case if some vulnerability is discovered, in one of those files, the attacker will have a difficult time trying to reach for them. Second, separating the application folder from the system folder we can have as many CI applications as we need and only one CI core folder. This way if we need to upgrade CI, we only need to do it in one directory.