Why doesn't the window set cursor correctly? - c

Question

As MSDN describes:
When the mouse moves over a window, the window receives a WM_SETCURSOR message (unless another window has captured the mouse).
If the application passes WM_SETCURSOR to DefWindowProc, the DefWindowProc function uses the following algorithm to set the cursor image:
If the window has a parent, forward the WM_SETCURSOR message to the parent to handle.
Otherwise, if the window has a class cursor, set the cursor to the class cursor.
If there is no class cursor, set the cursor to the arrow cursor.
And here's my source code:
#include <tchar.h>
#include <Windows.h>
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
int APIENTRY _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInsTance, LPTSTR lpCmdLine, int nCmdShow)
{
WNDCLASSEX wcex = { 0 };
HWND hWnd;
BOOL ret;
MSG msg;
wcex.cbSize = sizeof(wcex);
wcex.lpfnWndProc = WndProc;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
// wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.lpszClassName = TEXT("MainWindow");
wcex.hIconSm = wcex.hIcon;
RegisterClassEx(&wcex);
hWnd = CreateWindow(wcex.lpszClassName, TEXT("Test"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, HWND_DESKTOP, NULL, hInstance, NULL);
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
while (ret = GetMessage(&msg, NULL, 0, 0))
{
if (ret == -1)
{
return EXIT_FAILURE;
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_DESTROY:
PostQuitMessage(EXIT_SUCCESS);
break;
default:
return DefWindowProc(hWnd, uMsg, wParam, lParam);
}
return 0;
}
When I move my cursor quickly over the window, the cursor doesn't change to an arrow, it become a resize arrow; if I set wcex.hCursor to LoadCursor(NULL, IDC_ARROW), everything will be all right. My question is: why doesn't my code work as MSDN says?
I mean, if I don't set wcex.hCursor, and I don't handle the WM_SETCURSOR message, the DefWindowProc should "set the cursor to the arrow cursor", but it seems it doesn't. Why is that?

Answer 1

See description of the hCursor member of the WNDCLASSEX:
A handle to the class cursor. This member must be a handle to a cursor
resource. If this member is NULL, an application must explicitly set
the cursor shape whenever the mouse moves into the application's
window.
WNDCLASSEX structure