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phpautoloader

Why include __DIR__ in the require_once?

For example, I always see autoloaders called like this:

require_once __DIR__ . '/../vendor/autoload.php';

What is the difference between that and the more concise

require_once '../vendor/autoload.php';

?

Solution

  • PHP scripts run relative to the current path (result of getcwd()), not to the path of their own file. Using __DIR__ forces the include to happen relative to their own path.

    To demonstrate, create the following files (and directories):

    - file1.php
- dir/
   - file2.php
   - file3.php

    If file2.php includes file3.php like this:

    include `file3.php`.

    It will work fine if you call file2.php directly. However, if file1.php includes file2.php, the current directory (getcwd()), will be wrong for file2.php, so file3.php cannot be included.