Include vs Require in PHP (and When to Use Each)

As your PHP project grows, you do not want one giant file. You split code into smaller files and reuse them across pages.

PHP gives you:

• include
• require
• include_once
• require_once

The difference (simple and important)

include

If the file is missing, PHP shows a warning and continues.

require

If the file is missing, PHP throws a fatal error and stops.

Example

<?php
include "header.php"; // if missing, page may still load
require "config.php"; // if missing, stop (safer for config)
?>

When to use what

• Use require for critical files:

  • database config
  • authentication helpers
  • autoloaders

• Use include for optional parts:

  • UI parts like header/footer
  • optional widgets

Use *_once to prevent double loading

require_once "config.php";
require_once "config.php"; // will not load twice

This avoids duplicate function/class errors.

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