title: error c2036 : unknown size if structure
body: <p>I have 2 class(A &amp; C) defined in a file <code>allocate.h</code> and class B defined in <code>work.h</code>.<br>
  I included allocate.h inside work.h file<br>
  My code looks like :  </p>
  
  <pre><code>Class A{  
  }  
  
  Class C
  {  
  public:  
      struct xyz{  
          A ob;  
      };  
  }  
  
  include"allocate.h"   
  Class C;   
  Class B{  
    void test(){  
        xyz obj; // `Error : error c2036 : xyz unknown size`  
    }  
  }  
  </code></pre>
  
  <p>Can someone tell me how can i communicate the size of xyz structure in function test?</p>