The require_once Function
The require_once function includes the specified file in the current script. If the file has already been included previously, the function will not include it again. This is especially useful for including files with classes or functions, where re-inclusion can cause errors.
Syntax
require_once 'path/to/file.php';
Example
Let's include the config.php file:
<?php
require_once 'config.php';
echo $config['site_name'];
?>
Code execution result (if the $config array is defined in config.php):
'My Site'
Example
Attempting to re-include the same file:
<?php
require_once 'functions.php';
require_once 'functions.php'; // This call will be ignored
echo sum(2, 3);
?>
Code execution result:
5
Difference from require
Unlike require, the require_once function checks if the file has already been included and does not perform re-inclusion. This prevents errors when including the same file multiple times.
See Also
-
the
includefunction,
which also includes files but does not check for their re-inclusion -
the
include_oncefunction,
which works similarly to require_once but does not cause a fatal error if the file is missing
