LAMPlights Personal anecdotes from my experiences using the LAMP stack

Using the PHP 5.3 __DIR__ magic constant

There is a new magic constant in PHP 5.3: __DIR__. This new constant does not actually do anything new. It replaces the use of dirname(__FILE__) that is commonly found code using prior PHP versions.

One of the troubles with including files is that the current directory is constantly a moving target. Consider the following structure:

index.php
admin/index.php
includes/
    foo.php
    bar.php

Imagine for a moment that both index.php and admin/index.php include includes/foo.php. If foo.php includes bar.php, the relative directory is either "../" or "../admin/" depending on whether index.php or admin/index.php was executed. The use of the dirname() function along with the __FILE__ magic constant solved this problem for a long time.

The __FILE__ magic constant gives the full path and filename of the current file. The dirname() function gives the directory name of a file path. This was used prior to PHP 5.3 to solve the include problem described above.

<?php
// foo.php
require_once dirname(__FILE__) . '/bar.php';
?>

In PHP 5.3, this has been super-ceded by the use of the __DIR__ magic constant.

<?php
// foo.php
require_once __DIR__ . '/bar.php';
?>

Why the change? Well, it is more succinct and more clear on what is going on. Also, the magic constant is part of the Zend engine, so it is a little more performant as well.