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POWhy does this window subclassing code crash?
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copied!<p>I am trying to subclass the window that currently has focus. I do this by monitoring for <code>HCBT_ACTIVATE</code> events using a CBT hook, and set and unset the <code>WndProc</code> of the focused and previously focused windows.</p> <p><strong>The problem is that it only works whenever I have a breakpoint set somewhere in the code</strong>. </p> <p>If there is no breakpoint, once my application exits, all the windows that I have subclassed crashes in order, even though I have removed the subclassing and restored the original WndProc.</p> <p>I have verified that <code>Unsubclass()</code> is called whenever my application shuts down.</p> <pre><code>// code extracts HINSTANCE hInst; HHOOK hHook; #pragma data_seg(".shared") HWND hWndSubclass = 0; FARPROC lpfnOldWndProc = NULL; #pragma data_seg() #pragma comment(linker, "/section:.shared,rws") void Unsubclass() { // if the window still exists if (hWndSubclass != 0 && IsWindow(hWndSubclass)) { SetWindowLongPtr(hWndSubclass, GWLP_WNDPROC, (LPARAM)lpfnOldWndProc); hWndSubclass = 0; } } static LRESULT CALLBACK SubClassFunc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) { if (message == WM_MOVING) { // this is just test code so I can see it works (it does) RECT* r = (RECT*)lParam; r->right = r->left + 500; r->bottom = r->top + 500; return TRUE; } else if (message == WM_DESTROY) { Unsubclass(); } return CallWindowProc((WNDPROC)lpfnOldWndProc, hWndSubclass, message, wParam, lParam); } void SubclassWindow(HWND hWnd) { // remove the subclassing for the old window Unsubclass(); // subclass the new window lpfnOldWndProc = (FARPROC)SetWindowLongPtr(hWnd, GWLP_WNDPROC, (LPARAM)SubClassFunc); hWndSubclass = hWnd; } static LRESULT CALLBACK CBTProc(int nCode, WPARAM wParam, LPARAM lParam) { if (nCode == HCBT_ACTIVATE) { SubclassWindow((HWND)wParam); } return 0; } // ... code that initializes the CBT proc __declspec(dllexport) BOOL Setup() { hHook = SetWindowsHookEx(WH_CBT, CBTProc, hInst, 0); } __declspec(dllexport) BOOL Teardown() { UnhookWindowsHookEx(hHook); Unsubclass(); } BOOL APIENTRY DllMain( HINSTANCE hInstance, DWORD Reason, LPVOID Reserved ) { switch(Reason) { case DLL_PROCESS_ATTACH: hInst = hInstance; return TRUE; case DLL_PROCESS_DETACH: Unsubclass(); return TRUE; } return TRUE; } </code></pre>

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