ency checking.</p>

<p>In Java there is a built-in concept called an interface that provides this
functionality. What I have done therefore is to mimic the Java interface in
C++.</p>


<h2 id="classes">Interface Classes</h2>

<p>I define a C++ interface to be a class with one or more methods, some or
all of which are abstract. The user indicates that they are providing the
interface by making their class a derivative of the interface class.</p>

<p>An abstract method is one which has "<code>= 0</code>" plac