CodeIgniter Home
- What is CodeIgniter?
- Features of CodeIgniter
- Advantages over other PHP frameworks
- CodeIgniter version history
CodeIgniter Overview
- Key Components of CodeIgniter
- MVC design pattern explained
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- System and Application folders overview
CodeIgniter Installing CodeIgniter
- System Requirements (PHP, MySQL, Extensions)
- Downloading & Extracting CodeIgniter
- Folder structure explained
- Setting base URL
- Configuring index.php file
- Running first application
CodeIgniter Application Architecture
- Folder structure in detail
- Application vs System folders
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CodeIgniter MVC Framework
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CodeIgniter Configuration
- Configuration files overview
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CodeIgniter Working with Database
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- Active Record class
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CodeIgniter Error Handling
- Error reporting levels
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- Using log_message()
- Displaying errors in development vs production
CodeIgniter File Uploading
- Upload library setup
- File upload configuration (path, allowed types, max size)
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CodeIgniter Sending Email
- Email library configuration
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CodeIgniter Form Validation
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CodeIgniter Session Management
- Session library configuration
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CodeIgniter Flashdata
- What is Flashdata?
- Creating flashdata messages
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CodeIgniter Tempdata
- Difference between flashdata & tempdata
- Creating tempdata
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CodeIgniter Cookie Management
- Setting cookies
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- Cookie security
CodeIgniter Common Functions
- base_url()
- site_url()
- redirect()
- form_open() & form helper functions
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CodeIgniter Page Caching
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CodeIgniter Page Redirection
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CodeIgniter Application Profiling
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CodeIgniter Adding JS and CSS
- Loading assets in views
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- Best practices for assets organization
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CodeIgniter Internationalization
- Language files in CodeIgniter
- Loading language files
- Switching languages dynamically
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CodeIgniter Security
- Input filtering and XSS cleaning
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- Using HTTPS with CodeIgniter

Folder structure explained

Last modified on: September 7, 2025

<h1 data-start="499" data-end="544">📝 CodeIgniter Folder Structure Explained</h1>
<h2 data-start="546" data-end="566">🔎 Introduction</h2>
<p data-start="567" data-end="786">After downloading and installing CodeIgniter, you&rsquo;ll notice that the project is divided into multiple folders. Each folder has a specific purpose, which makes the framework <strong data-start="740" data-end="783">organized, lightweight, and easy to use</strong>.</p>
<p data-start="788" data-end="868">Here&rsquo;s a breakdown of the <strong data-start="814" data-end="848">CodeIgniter 4 folder structure</strong> (latest version).</p>
<hr data-start="870" data-end="873" />
<h2 data-start="875" data-end="904">📂 Main Folder Structure</h2>
<div class="contain-inline-size rounded-2xl relative bg-token-sidebar-surface-primary">
<div class="sticky top-9">
<div class="absolute end-0 bottom-0 flex h-9 items-center pe-2">
<div class="bg-token-bg-elevated-secondary text-token-text-secondary flex items-center gap-4 rounded-sm px-2 font-sans text-xs">
<pre class="language-php"><code>codeigniter-app/
├── app/
├── public/
├── system/
├── writable/
├── tests/
├── vendor/
├── .env
├── composer.json
└── spark
</code></pre>
</div>
</div>
</div>
</div>
<p data-start="1039" data-end="1084">Now let&rsquo;s understand each folder in detail:</p>
<hr data-start="1086" data-end="1089" />
<h2 data-start="1091" data-end="1129">📁 1. <code data-start="1100" data-end="1106">app/</code> (Application Folder)</h2>
<p data-start="1130" data-end="1220">This is the <strong data-start="1142" data-end="1171">heart of your application</strong>. It contains all the files you will work with.</p>
<h3 data-start="1222" data-end="1253">Subfolders inside <code data-start="1244" data-end="1250">app/</code>:</h3>
<ul data-start="1254" data-end="1727">
<li data-start="1254" data-end="1336">
<p data-start="1256" data-end="1336"><strong data-start="1256" data-end="1272">Controllers/</strong> &rarr; Handles user requests and communicates with Models &amp; Views.</p>
</li>
<li data-start="1337" data-end="1410">
<p data-start="1339" data-end="1410"><strong data-start="1339" data-end="1350">Models/</strong> &rarr; Interacts with the database and handles business logic.</p>
</li>
<li data-start="1411" data-end="1469">
<p data-start="1413" data-end="1469"><strong data-start="1413" data-end="1423">Views/</strong> &rarr; Stores the HTML/PHP files shown to users.</p>
</li>
<li data-start="1470" data-end="1549">
<p data-start="1472" data-end="1549"><strong data-start="1472" data-end="1483">Config/</strong> &rarr; Contains configuration files (database, routes, email, etc.).</p>
</li>
<li data-start="1550" data-end="1593">
<p data-start="1552" data-end="1593"><strong data-start="1552" data-end="1564">Helpers/</strong> &rarr; Custom helper functions.</p>
</li>
<li data-start="1594" data-end="1648">
<p data-start="1596" data-end="1648"><strong data-start="1596" data-end="1609">Language/</strong> &rarr; For localization and translations.</p>
</li>
<li data-start="1649" data-end="1727">
<p data-start="1651" data-end="1727"><strong data-start="1651" data-end="1663">Filters/</strong> &rarr; Middleware-like functionality (request/response filtering).</p>
</li>
</ul>
<p data-start="1729" data-end="1798">👉 Example:<br data-start="1740" data-end="1743" /><code data-start="1743" data-end="1769">app/Controllers/Home.php</code> &rarr; Your default controller.</p>
<hr data-start="1800" data-end="1803" />
<h2 data-start="1805" data-end="1841">📁 2. <code data-start="1814" data-end="1823">public/</code> (Public Folder)</h2>
<p data-start="1842" data-end="1892">This is the <strong data-start="1854" data-end="1869">entry point</strong> of your application.</p>
<ul data-start="1893" data-end="2046">
<li data-start="1893" data-end="1962">
<p data-start="1895" data-end="1962">Contains the <code data-start="1908" data-end="1919">index.php</code> file, which is the <strong data-start="1939" data-end="1959">front controller</strong>.</p>
</li>
<li data-start="1963" data-end="2046">
<p data-start="1965" data-end="2006">Stores publicly accessible assets like:</p>
<ul data-start="2009" data-end="2046">
<li data-start="2009" data-end="2016">
<p data-start="2011" data-end="2016">CSS</p>
</li>
<li data-start="2019" data-end="2033">
<p data-start="2021" data-end="2033">JavaScript</p>
</li>
<li data-start="2036" data-end="2046">
<p data-start="2038" data-end="2046">Images</p>
</li>
</ul>
</li>
</ul>
<p data-start="2048" data-end="2122">👉 Example:<br data-start="2059" data-end="2062" /><code data-start="2062" data-end="2105">http://localhost/project/public/index.php</code> loads the app.</p>
<hr data-start="2124" data-end="2127" />
<h2 data-start="2129" data-end="2166">📁 3. <code data-start="2138" data-end="2147">system/</code> (Framework Core)</h2>
<p data-start="2167" data-end="2231">This folder contains the <strong data-start="2192" data-end="2228">core CodeIgniter framework files</strong>.</p>
<ul data-start="2232" data-end="2364">
<li data-start="2232" data-end="2265">
<p data-start="2234" data-end="2265">Handles the MVC architecture.</p>
</li>
<li data-start="2266" data-end="2364">
<p data-start="2268" data-end="2364">You should <strong data-start="2279" data-end="2316">never modify these files directly</strong>, as they will be overwritten during upgrades.</p>
</li>
</ul>
<p data-start="2366" data-end="2414">👉 Think of it as the &ldquo;engine&rdquo; of your car 🚗.</p>
<hr data-start="2416" data-end="2419" />
<h2 data-start="2421" data-end="2460">📁 4. <code data-start="2430" data-end="2441">writable/</code> (Writable Files)</h2>
<p data-start="2461" data-end="2520">This folder is for files that need <strong data-start="2496" data-end="2517">write permissions</strong>.</p>
<ul data-start="2521" data-end="2697">
<li data-start="2521" data-end="2557">
<p data-start="2523" data-end="2557"><strong data-start="2523" data-end="2533">cache/</strong> &rarr; Stores cached data.</p>
</li>
<li data-start="2558" data-end="2607">
<p data-start="2560" data-end="2607"><strong data-start="2560" data-end="2569">logs/</strong> &rarr; Application error and debug logs.</p>
</li>
<li data-start="2608" data-end="2641">
<p data-start="2610" data-end="2641"><strong data-start="2610" data-end="2623">sessions/</strong> &rarr; Session data.</p>
</li>
<li data-start="2642" data-end="2697">
<p data-start="2644" data-end="2697"><strong data-start="2644" data-end="2656">uploads/</strong> &rarr; User-uploaded files (if configured).</p>
</li>
</ul>
<p data-start="2699" data-end="2768">👉 Example: If you upload a profile picture, it can be stored here.</p>
<hr data-start="2770" data-end="2773" />
<h2 data-start="2775" data-end="2804">📁 5. <code data-start="2784" data-end="2792">tests/</code> (Testing)</h2>
<ul data-start="2805" data-end="2892">
<li data-start="2805" data-end="2841">
<p data-start="2807" data-end="2841">Contains <strong data-start="2816" data-end="2838">PHPUnit test files</strong>.</p>
</li>
<li data-start="2842" data-end="2892">
<p data-start="2844" data-end="2892">Used for writing unit tests and feature tests.</p>
</li>
</ul>
<p data-start="2894" data-end="2944">👉 Example: <code data-start="2906" data-end="2942">tests/app/Controllers/HomeTest.php</code></p>
<hr data-start="2946" data-end="2949" />
<h2 data-start="2951" data-end="2986">📁 6. <code data-start="2960" data-end="2969">vendor/</code> (Dependencies)</h2>
<ul data-start="2987" data-end="3145">
<li data-start="2987" data-end="3045">
<p data-start="2989" data-end="3045">Created when you install CodeIgniter via <strong data-start="3030" data-end="3042">Composer</strong>.</p>
</li>
<li data-start="3046" data-end="3096">
<p data-start="3048" data-end="3096">Stores third-party libraries and dependencies.</p>
</li>
<li data-start="3097" data-end="3145">
<p data-start="3099" data-end="3145">Includes <code data-start="3108" data-end="3122">autoload.php</code> for package loading.</p>
</li>
</ul>
<p data-start="3147" data-end="3218">👉 Example: If you install <strong data-start="3174" data-end="3187">PHPMailer</strong> with Composer, it goes here.</p>
<hr data-start="3220" data-end="3223" />
<h2 data-start="3225" data-end="3261">📄 7. <code data-start="3234" data-end="3240">.env</code> (Environment File)</h2>
<ul data-start="3262" data-end="3450">
<li data-start="3262" data-end="3309">
<p data-start="3264" data-end="3309">Stores environment-specific configurations.</p>
</li>
<li data-start="3310" data-end="3450">
<p data-start="3312" data-end="3323">Examples:</p>
<ul data-start="3326" data-end="3450">
<li data-start="3326" data-end="3350">
<p data-start="3328" data-end="3350">Database credentials</p>
</li>
<li data-start="3353" data-end="3379">
<p data-start="3355" data-end="3379">Error reporting levels</p>
</li>
<li data-start="3382" data-end="3450">
<p data-start="3384" data-end="3450">Application environment (<code data-start="3409" data-end="3422">development</code>, <code data-start="3424" data-end="3436">production</code>, <code data-start="3438" data-end="3447">testing</code>)</p>
</li>
</ul>
</li>
</ul>
<p data-start="3452" data-end="3465">👉 Example:</p>
<div class="contain-inline-size rounded-2xl relative bg-token-sidebar-surface-primary">
<div class="sticky top-9">
<div class="absolute end-0 bottom-0 flex h-9 items-center pe-2">
<div class="bg-token-bg-elevated-secondary text-token-text-secondary flex items-center gap-4 rounded-sm px-2 font-sans text-xs">
<pre class="language-php"><code>app.env = development
database.default.hostname = localhost
</code></pre>
</div>
</div>
</div>
</div>
<hr data-start="3535" data-end="3538" />
<h2 data-start="3540" data-end="3566">📄 8. <code data-start="3549" data-end="3564">composer.json</code></h2>
<ul data-start="3567" data-end="3672">
<li data-start="3567" data-end="3613">
<p data-start="3569" data-end="3613">Defines project dependencies for Composer.</p>
</li>
<li data-start="3614" data-end="3672">
<p data-start="3616" data-end="3672">Example: Requires CodeIgniter framework, PHPUnit, etc.</p>
</li>
</ul>
<hr data-start="3674" data-end="3677" />
<h2 data-start="3679" data-end="3708">📄 9. <code data-start="3688" data-end="3695">spark</code> (CLI Tool)</h2>
<ul data-start="3709" data-end="3852">
<li data-start="3709" data-end="3760">
<p data-start="3711" data-end="3760">CodeIgniter&rsquo;s <strong data-start="3725" data-end="3757">command-line interface (CLI)</strong>.</p>
</li>
<li data-start="3761" data-end="3852">
<p data-start="3763" data-end="3852">Helps run commands like serving the app, creating controllers, running migrations, etc.</p>
</li>
</ul>
<p data-start="3854" data-end="3867">👉 Example:</p>
<div class="contain-inline-size rounded-2xl relative bg-token-sidebar-surface-primary">
<div class="sticky top-9">
<div class="absolute end-0 bottom-0 flex h-9 items-center pe-2">
<div class="bg-token-bg-elevated-secondary text-token-text-secondary flex items-center gap-4 rounded-sm px-2 font-sans text-xs">
<pre class="language-php"><code>php spark serve
php spark make:controller User
</code></pre>
</div>
</div>
</div>
</div>
<hr data-start="3928" data-end="3931" />
<h2 data-start="3933" data-end="3951">🎯 Conclusion</h2>
<p data-start="3952" data-end="4024">The <strong data-start="3956" data-end="3988">CodeIgniter folder structure</strong> is simple and easy to understand:</p>
<ul data-start="4025" data-end="4208">
<li data-start="4025" data-end="4062">
<p data-start="4027" data-end="4062"><strong data-start="4027" data-end="4035">app/</strong> &rarr; Your application logic</p>
</li>
<li data-start="4063" data-end="4101">
<p data-start="4065" data-end="4101"><strong data-start="4065" data-end="4076">public/</strong> &rarr; Entry point &amp; assets</p>
</li>
<li data-start="4102" data-end="4136">
<p data-start="4104" data-end="4136"><strong data-start="4104" data-end="4115">system/</strong> &rarr; Framework engine</p>
</li>
<li data-start="4137" data-end="4177">
<p data-start="4139" data-end="4177"><strong data-start="4139" data-end="4152">writable/</strong> &rarr; Logs, cache, uploads</p>
</li>
<li data-start="4178" data-end="4208">
<p data-start="4180" data-end="4208"><strong data-start="4180" data-end="4191">vendor/</strong> &rarr; Dependencies</p>
</li>
</ul>
<p data-start="4210" data-end="4331">By understanding this structure, you can organize your project better and build scalable applications with CodeIgniter.</p>

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