Re: Why does this cause "data abort" ?

"Giovanni Dicanio" <>
Wed, 24 Oct 2007 10:04:49 +0200
"Lisa Pearlson" <no@spam.plz> ha scritto nel messaggio

class CSomeWnd
   int m_hWnd;
   virtual LRESULT SomeWndProc(HWND hWnd, MSG msg, WPARAM wParam, LPARAM

CSomeWnd* g_pSomeWnd = new CSomeWnd();
g_pSomeWnd->CreateWindow( ... );
LRESULT GlobalWndProc(HWND hWnd, MSG msg, WPARAM wParam, LPARAM lParam)
   return g_pSomeWnd->SomeWndProc(hWnd,msg,lParam,wParam);


However, the above construction causes data abort exceptions.

I don't know what *exactly* "data abort exceptions" are...

However, I can't see anything wrong in the above code. Maybe the exception
is thrown somewhere else...

Frankly speaking, I don't like using the global instance as shown above. I
prefer the following code you posted:

understand why, but it's resolved by something like this:

CSomeWnd* g_pSomeWnd = new CSomeWnd();
g_pSomeWnd->CreateWindow( ... );
SetWindowLong(g_pSomeWnd->GetSafeHwnd(), GWL_USERDATA, (LONG) this);

LRESULT GlobalWndProc(HWND hWnd, MSG msg, WPARAM wParam, LPARAM lParam)
   CSomeWnd* pWnd = (CSomeWnd*) GetWindowLong(hWnd, GWL_USERDATA);
   return pWnd->SomeWndProc(hWnd,msg,lParam,wParam);

If you don't want to use GWL_USERDATA, you may consider also Window
Properties technique (i.e. use the SetProp and GetProp Win32 APIs to store
the class instance pointer "this", associating it to a string property); or
you can use extra window bytes (the "cbWndExtra" field in the WNDCLASSEX
structure) to store the "this" pointer (e.g. set windowClass.cbWndExtra =
sizeof( YourClass * ), and use SetWindowLong and GetWindowLong using 0-byte
offset to set and get the "this" instance pointer).

There are also more advanced techniques, like using assembly language
"thunks". This is done by ATL/WTL, IIRC.

However, if you use ATL (or MFC) you can just derive your class from the
base window class (or some other window class), using just C++ inheritance.


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