title: Cross referencing included headers in c++ program
body: <p>I am curious about a scenario set up like the following example:</p>
  
  <p>Here is code that would be placed in a file called Header1.h:</p>
  
  <pre><code>#ifndef HEADER1_H
  #define HEADER1_H
  
  #include "Header2.h"
  
  class Class1
  {
   Class2 class2Instance;
  };
  
  #endif
  </code></pre>
  
  <p>Here is code that would be placed in a file called Header2.h:</p>
  
  <pre><code>#ifndef HEADER2_H
  #define HEADER2_H
  
  #include "Header1.h"
  
  class Class2
  {
   Class1 class1Instance;
  };
  
  #endif
  </code></pre>
  
  <p>I get error messages when I do this (because of the includes I assume), but it feels like I would need to do this in order to include each of the objects in the separate classes.  Can anyone help me accomplish this, what am I doing wrong?</p>