require_once path / to / file.php vs file.php

Question

I'm having the following issue when including a file that includes another file:

// path: /ajax/request.php
require_once("../classes/obj/Car.php");


// path: /classes/obj/Car.php;
require_once("Vehicle.php"); // superclass,  this works
require_once("../exception/NoWheelException");  // this doesn't work when Car.php is require_once()'d from /ajax/request.php

the problem seems to be that if a file A requires a file B that requires files C and D, it only works if C and D are used without "../", or "./" previous to the file name, when using require_once().

Is there any workaround or any ideas to fix this?

Answer 1

Use __FILE__ so you know where it's being included from:

require_once(dirname(__FILE__) . '/../exception/NoWheelException');

Where:

__FILE__ == "/classes/obj/Car.php";
dirname(__FILE__) == "/classes/obj";

Also, a note I didn't know - if your version of PHP is new enough, __DIR__ appears to be equivalent to dirname(__FILE__)

More info on __FILE__ and other magic constants here