(PHP 4, PHP 5, PHP 7, PHP 8)
The require_once expression is identical to require except PHP will check if the file has already been included, and if so, not include (require) it again.
See the include_once documentation for information about the _once behaviour, and how it differs from its non _once siblings.
14 years ago
If your code is running on multiple servers with different environments (locations from where your scripts run) the following idea may be useful to you:
a. Do not give absolute path to include files on your server.
b. Dynamically calculate the full path (absolute path)
Hints:
Use a combination of dirname(__FILE__) and subsequent calls to itself until you reach to the home of your '/index.php'. Then, attach this variable (that contains the path) to your included files.
One of my typical example is:
<?php
define('__ROOT__', dirname(dirname(__FILE__)));
require_once(__ROOT__.'/config.php');
?>
instead of:
<?php require_once('/var/www/public_html/config.php'); ?>
After this, if you copy paste your codes to another servers, it will still run, without requiring any further re-configurations.
[EDIT BY danbrown AT php DOT net: Contains a typofix (missing ')') provided by 'JoeB' on 09-JUN-2011.]
bobray99 at softville dot com ¶
3 years ago
Be careful when using include_once and require_once for files that return a value:
fiddle2.php
<?php
return "Some String";fiddle.php
<?php
$s = require_once('fiddle2.php');
echo "\n" . $s;
$s = require_once('fiddle2.php');
echo "\n" . $s;The second time require_once occurs, it returns 1 because the file has already been included. boda0128318 at gmail dot com ¶
4 years ago
1 - "require" and "require_once" throw a fatal error if the file is not
existing and stop the script execution
2 - "include" and "include_once" throw a warning and the execution
continues
3 - "require_once" and "include_once" as their names suggests ,
they will not include the file if the file was already included with
"require", "require_once", "include" or "include_once"
try the following code:
create a file called "index.php"
<?phprequire "first.php"; include_once "first.php"; require_once "first.php"; ?>
and another file that is called "first.php" and write the following header
-------------------------------
<h1>Hello every one</h1>
--------------------------------
i hope this will help you
powtac at gmx dot de ¶
9 years ago
"require_once" and "require" are language constructs and not functions. Therefore they should be written without "()" brackets!
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