Organizing your code: include, structure, constants

Split your site into reusable files with include and require, a clear project structure, and centralized constants.

7 min · 3 questions

As soon as your site grows beyond two pages, duplicating the header, footer, and functions in every file becomes unmanageable. PHP provides four inclusion statements: include, require, and their include_once / require_once variants. They all insert the contents of a file at the point of the call; the difference lies in error handling and repeated inclusions. The _once variants keep track of already-loaded files and include them only once - essential for function files, which cannot be redeclared.

PHP

<?php

declare(strict_types=1);

function e(string $value): string
{
    return htmlspecialchars($value, ENT_QUOTES);
}

function formatPrice(float $amount): string
{
    return number_format($amount, 2, '.', ',') . ' €';
}

src/functions.php: helpers reusable across the whole site.

A clear project structure is worth a thousand comments. A common convention: public/ holds the pages served to the browser (it's the only exposed folder), src/ gathers configuration and functions, templates/ contains page fragments (header.php, footer.php). PHP's built-in development server is launched by pointing it at public/.

BASH

mkdir -p my-site/public my-site/src
mkdir -p my-site/templates
cd my-site
php -S localhost:8000 -t public

Creating the structure, then launching the development server.

The project's fixed values (site name, paths, settings) deserve constants rather than variables: they can't be overwritten by accident. const is resolved at compile time, define() at runtime; in practice, prefer const in your configuration files. For paths, always prefix with __DIR__, the folder of the current file: your inclusions will work no matter where the script is launched from.

PHP

<?php

declare(strict_types=1);

const SITE_NAME = 'La Bonne Pizza';
const ITEMS_PER_PAGE = 12;
const UPLOAD_DIR = __DIR__ . '/../public/uploads';

define('BASE_URL', 'http://localhost:8000');

src/config.php: all the configuration in one place.

Each page then becomes a short assembly: load the configuration and functions with require, then include the templates around the specific content.

HTML

<?php
require __DIR__ . '/../src/config.php';
require_once __DIR__ . '/../src/functions.php';

$pageTitle = SITE_NAME . ' - Home';
include __DIR__ . '/../templates/header.php';
?>
<main>
  <h1><?= e($pageTitle) ?></h1>
  <p>Pizza of the day: <?= formatPrice(9.5) ?></p>
</main>
<?php include __DIR__ . '/../templates/footer.php'; ?>

public/index.php: the page is now just an assembly.

include emits a mere warning if the file can't be found and the script continues; require stops with a fatal error. For configuration and functions, on which everything else depends, always use require: better a page in error than a half-broken page.

Knowledge check

Make sure you remember the key points of this lesson.

What is the difference between include and require?
- include is faster than require
- require only works with absolute paths
- require stops the script with a fatal error if the file is missing, include emits a warning and continues
- None, they are two aliases
What is require_once for?
- To guarantee a file is included only once, even if several files request it
- To include a file only in production
- To include a file without executing its PHP code
Why prefix inclusion paths with __DIR__?
- It's mandatory since PHP 8
- The path becomes relative to the current file and no longer depends on the folder the script is launched from
- It enables a cache of included files