Two classes with member functions taking a pointer to an object from the other class
<pre><code>class a {
public:
void f2(b * elem);
};

class b {
public:
void f1(a * elem);
};
</code></pre>

<p>There will be a problem here.</p>

<pre><code>void f2(b * elem);
</code></pre>

<p>How do I declare class <code>b</code> in such a way that I can use function <code>f2</code>?</p>