relative path in require_once doesn't work - php

Question

I have the following structure
otsg
> class
> authentication.php
> database.php
> user.php
> include
> config.inc.php
> encryption.php
> include.php
> session.php
> index.php
> registration.php
include.php file has the following
ini_set('display_errors', 1);
error_reporting(E_ALL);
ini_set('include_path',ini_get('include_path').':/Applications/MAMP/htdocs/otsg/:');
require_once 'config.inc.php';
require_once '../class/database.php';
require_once '../class/user.php';
require_once 'encryption.php';
require_once 'session.php';
require_once '../class/authentication.php';
and in the index.php page I had included
require_once 'include/include.php';
When I open the page index.php I get the following warning and fatal error. I don't understand what causes this error. When I gave the absolute path it works. But absolute path is not a good idea i believe.
Warning: require_once(../class/database.php) [function.require-once]: failed to open stream: No such file or directory in /Applications/MAMP/htdocs/otsg/include/include.php on line 9
Fatal error: require_once() [function.require]: Failed opening required '../class/database.php' (include_path='.:/Applications/MAMP/bin/php5.3/lib/php:/Applications/MAMP/htdocs/otsg/include/:') in /Applications/MAMP/htdocs/otsg/include/include.php on line 9

Answer 1

Use
__DIR__
to get the current path of the script and this should fix your problem.
So:
require_once(__DIR__.'/../class/user.php');
This will prevent cases where you can run a PHP script from a different folder and therefore the relatives paths will not work.
Edit: slash problem fixed

Answer 2

for php version 5.2.17 __DIR__ will not work it will only works with php 5.3
But for older version of php dirname(__FILE__) perfectly
For example write like this
require_once dirname(__FILE__) . '/db_config.php';

Answer 3

In my case it doesn't work, even with __DIR__ or getcwd() it keeps picking the wrong path, I solved by defining a costant in every file I need with the absolute base path of the project:
if(!defined('THISBASEPATH')){ define('THISBASEPATH', '/mypath/'); }
require_once THISBASEPATH.'cache/crud.php';
/*every other require_once you need*/
I have MAMP with php 5.4.10 and my folder hierarchy is basilar:
q.php
w.php
e.php
r.php
cache/a.php
cache/b.php
setting/a.php
setting/b.php
....

Answer 4

I just came across this same problem, where it was all working fine, up until the point I had an includes within another includes.
require_once '../script/pdocrud.php'; //This worked fine up until I had an includes within another includes, then I got this error:
Fatal error: require_once() [function.require]: Failed opening required '../script/pdocrud.php' (include_path='.:/opt/php52/lib/php')
Solution 1. (undesired hardcoding of my public html folder name, but it works):
require_once $_SERVER["DOCUMENT_ROOT"] . '/orders.simplystyles.com/script/pdocrud.php';
Solution 2. (undesired comment above about DIR only working since php 5.3, but it works):
require_once __DIR__. '/../script/pdocrud.php';
Solution 3. (I can't see any downsides, and it works perfectly in my php 5.3):
require_once dirname(__FILE__). '/../script/pdocrud.php';