class not found when extending class that implements interface in PHP

Question

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

Answer 1

You are declaring the classes and interfaces in the wrong order. This is correct:

interface C {}

class B implements C {}

class A extends B {}

Answer 2

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.