title: What is the `uIdSubclass` in the third `SetWindowSubclass` Parameter?
body: <p>According to: <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/bb762102(v=vs.85).aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/library/windows/desktop/bb762102(v=vs.85).aspx</a></p>
  
  <p>the SetWindowSubclass prototype is:</p>
  
  <pre><code>BOOL SetWindowSubclass(
     __in  HWND hWnd,
     __in  SUBCLASSPROC pfnSubclass,
     __in  UINT_PTR uIdSubclass,
     __in  DWORD_PTR dwRefData
  );
  </code></pre>
  
  <p>Ok, I understand <code>hWnd</code>, <code>pfnSubclass</code>, and <code>dwRefData</code>.</p>
  
  <p>What I can not find good information on is, what do I set <code>uIdSubclass</code> to?</p>
  
  <p>MSDN says:</p>
  
  <blockquote>
    <p>The subclass ID. This ID together with the subclass procedure uniquely identify
    a subclass. To remove a subclass, pass the subclass procedure and this value to the
    RemoveWindowSubclass function. This value is passed to the subclass procedure in the
    uIdSubclass parameter.</p>
  </blockquote>
  
  <p>Ok, understood, but still, where do I get this ID?  Is it something I create or do I get it someplace?  If it something I create, what should it look like?</p>
  
  <p>I am doing this in C++ and Win32 API, nothing else.</p>
  
  <p>Thanks.</p>