WM_CLOSE message and application freeze - c++

Question

Having such supers simple Win app:
int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPWSTR lpCmdLine,
_In_ int nCmdShow) {
...
MyRegisterClass(hInstance);
// Perform application initialization:
if (!InitInstance(hInstance, nCmdShow)) {
return FALSE;
}
HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_GL1WIN));
MSG msg;
// Main message loop:
while (GetMessage(&msg, nullptr, 0, 0)) {
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return (int)msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) {
switch (message) {
case WM_COMMAND: {
int wmId = LOWORD(wParam);
// Parse the menu selections:
switch (wmId) {
case IDM_ABOUT:
DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
}
break;
case WM_CLOSE:
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
When the WM_CLOSE case is disabled (commented out) everything works OK - when i click the X button the window closes but when the WM_CLOSE case is enabled like in the above code the app seems to freeze - doesn't react when clicking the X button and i have to kill it from the task manager.

Answer 1

On WM_CLOSE the window should normally be destroyed with DestroyWindow, like:
case WM_CLOSE:
DestroyWindow(hWnd);
break;
In your case you just return without doing anything with that window, so it simple 'freezes'.

Answer 2

Without WM_CLOSE case, the message is passed to DefWindowProc that reacts to it by destroying the window. With WM_CLOSE case, you handle the message and don't pass it to DefWindowProc - then it's your responsibility to do something in response to that message.