class not found when extending class that implements interface in PHP

Question

<?php

class A extends B {}

class B implements C {}

interface C {}

the code above throws "Fatal error: Class 'B' not found"... Is it a php bug? Or?

Environment: "PHP 5.3.6-13ubuntu3.2 with Suhosin-Patch (cli) (built: Oct 13 2011 23:19:13) Copyright (c) 1997-2011 The PHP Group Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies with Xdebug v2.1.0, Copyright (c) 2002-2010, by Derick Rethans "

Answer 1

You have trouble specifically with the order of your class definitions. As long as the interface is defined in the same file, it can be declared anywhere - but classes must be defined before they can be extended.

The following is perfectly valid order in PHP:

class B implements C { ... }
class A extends B { ... }
interface C { ... }

There is a closed bug requesting clarification in the PHP5 docs.

An answer to a similar question (Does the order of class definition matter in PHP?) mentions Autoloading. You may want to look into this if you're using multiple files.