title: What does "class example;" mean in a Header File?
body: <p>I've a question about something what really confuses me!</p>
  
  <p>Let's watch this code righ here:</p>
  
  <pre><code>#ifndef HEADER_H
  #define HEADER_H
  #include &lt;iostream&gt;
  
  class example;
  class anything_else;
  
  class A {
        public:
             A();
  };
  
  ...
  </code></pre>
  
  <p>What does <code>class example;</code> and <code>class anything_else;</code> mean,
  while <code>class A {};</code> gets declared? Inside the CPP File i saw definitions like <code>void example::release() { ... }</code> and so on...</p>
  
  <p>I'm really confused, does anyone have a example with <code>class example;</code> ... ?</p>