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The WM_KEYDOWN message is posted to the window with the keyboard focus when a nonsystem key is pressed. A nonsystem key is a key that is pressed when the ALT key is not pressed.
A window receives this message through its WindowProc function.
LRESULT CALLBACK WindowProc( HWND hwnd, // handle to window UINT uMsg, // WM_KEYDOWN WPARAM wParam, // virtual-key code LPARAM lParam // key data );
An application should return zero if it processes this message.
If the F10 key is pressed, the DefWindowProc function sets an internal flag. When DefWindowProc receives the WM_KEYUP message, the function checks whether the internal flag is set and, if so, sends a WM_SYSCOMMAND message to the top-level window. The wParam parameter of the message is set to SC_KEYMENU.
Because of the autorepeat feature, more than one WM_KEYDOWN message may be posted before a WM_KEYUP message is posted. The previous key state (bit 30) can be used to determine whether the WM_KEYDOWN message indicates the first down transition or a repeated down transition.
For enhanced 101- and 102-key keyboards, extended keys are the right ALT and CTRL keys on the main section of the keyboard; the INS, DEL, HOME, END, PAGE UP, PAGE DOWN, and arrow keys in the clusters to the left of the numeric keypad; and the divide (/) and ENTER keys in the numeric keypad. Other keyboards may support the extended-key bit in the lParam parameter.
Windows 2000 or later: Applications must pass wParam to TranslateMessage without altering it at all.
Windows NT/2000 or later: Requires Windows NT 3.1 or later. Windows 95/98/Me: Requires Windows 95 or later. Header: Declared in Winuser.h; include Windows.h.
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Notebook exported on Monday, 7 July 2008, 18:56:50 PM Eastern Daylight Time