title: Whats the meaning of "Class1::Class2" in C++?
body: <p>I'm analysing a code and encountered the following structure. Whats the relation of Class1 and Class2? (the project has been developed on Qt framework).</p>
  
  <p>Simpilified Code:</p>
  
  <pre><code>class Class1
  {
      ...
  
  private:
      class Class2
  }
  
  class Class1::Class2: public BaseClass
  {
      ...
  }
  </code></pre>
  
  <p>Thanks for any help.</p>