title: How to use extern to declare an enum type
body: <p>Now I have two VC projects: A and B. I'm working with Project B, I need to use an <code>enum</code> type defined in a header file in Project A, I cannot include this header file.</p>
  
  <p>Can I use <code>extern</code> to extend the visibility of the enum type to Project B?</p>
  
  <p>If so, how can I do it? And if not, is there any other way to use this <code>enum</code> type in Project B?</p>