Explain PHP Include Files with example

PHP include files are a way to reuse code across multiple PHP files. This practice helps in maintaining code consistency and makes it easier to manage large applications by breaking down code into smaller, reusable components.

How include and require Work

PHP provides two main functions for including files:

• include
• require

Both functions do the same thing: they include and evaluate the specified file. The difference is in how they handle errors:

• include will produce a warning but the script will continue execution if the file is not found.
• require will produce a fatal error and stop the script if the file is not found.

Example 1: Using include

main.php

<?php
include 'header.php';
echo "<p>This is the main content of the page.</p>";
include 'footer.php';
?>

header.php

<?php
echo "<h1>Welcome to My Website</h1>";
?>

footer.php

<?php
echo "<footer>© 2024 My Website</footer>";
?>

Output of main.php

<h1>Welcome to My Website</h1>
<p>This is the main content of the page.</p>
<footer>© 2024 My Website</footer>

Example 2: Using require

main.php

<?php
require 'header.php';
echo "<p>This is the main content of the page.</p>";
require 'footer.php';
?>

If header.php or footer.php is missing, main.php will produce a fatal error and stop execution.

Handling Missing Files

main.php with include

<?php
include 'nonexistent.php'; // This will produce a warning but continue execution
echo "<p>This is the main content of the page.</p>";
?>

Output

Warning: include(nonexistent.php): failed to open stream: No such file or directory in /path/to/main.php on line 2

Warning: include(): Failed opening 'nonexistent.php' for inclusion (include_path='.:/usr/share/php') in /path/to/main.php on line 2
<p>This is the main content of the page.</p>

main.php with require

<?php
require 'nonexistent.php'; // This will produce a fatal error and stop execution
echo "<p>This is the main content of the page.</p>";
?>

Output

Fatal error: require(): Failed opening required 'nonexistent.php' (include_path='.:/usr/share/php') in /path/to/main.php on line 2

Using include_once and require_once

These functions ensure that a file is included only once during the script execution, avoiding issues with multiple inclusions.

main.php

<?php
include_once 'header.php';
include_once 'header.php'; // This will not include header.php again
echo "<p>This is the main content of the page.</p>";
?>

Conclusion

Using include, require, include_once, and require_once helps in managing large codebases by breaking down the code into smaller, reusable components. It also makes the code easier to maintain and debug.