title: What does uMsg parameter mean in the definition of CALLBACK DialogProc()
body: <p>The MSDN link <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/ms645469%28v=vs.85%29.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/windows/desktop/ms645469(v=vs.85).aspx</a> </p>
  
  <p>explains about the <strong>DialogProc callback function</strong>. </p>
  
  <p>Here I don't see any explanation given about the 2nd parameter (UINT uMsg) in the following signature::</p>
  
  <pre><code>INT_PTR CALLBACK DialogProc(   
    __in  HWND hwndDlg,   
    __in  UINT uMsg,   
    __in  WPARAM wParam,   
    __in  LPARAM lParam   
  );   
  </code></pre>
  
  <p>Can anyone kindly explain what does this 2nd parameter (UINT uMsg) mean. Some detailed explanation (Why we need this uMsg parameter, what is its usage how is it used etc...)  on this will be really appreciated. Thanks a lot. </p>
  
  <p>PS: I am new to Callbacj functions, Win32 API programming. </p>