The WM_SYSKEYUP message is posted to the window with the keyboard focus when the user releases a key that was pressed while the ALT key was held down. It also occurs when no window currently has the keyboard focus; in this case, the WM_SYSKEYUP message is sent to the active window. The window that receives the message can distinguish between these two contexts by checking the context code in the lKeyData parameter.
WM_SYSKEYUP nVirtKey = (int) wParam; // virtual-key code lKeyData = lParam; // key data
|
Value |
Description |
|
0-15 |
Specifies the repeat count for the current message. The value is the number of times the keystroke is auto-repeated as a result of the user holding down the key. The repeat count is always one for a WM_SYSKEYUP message. |
|
16-23 |
Specifies the scan code. The value depends on the original equipment manufacturer (OEM). |
|
24 |
Specifies whether the key is an extended key, such as the right-hand ALT and CTRL keys that appear on an enhanced 101- or 102-key keyboard. The value is 1 if it is an extended key; otherwise, it is 0. |
|
25-28 |
Reserved; do not use. |
|
29 |
Specifies the context code. The value is 1 if the ALT key is down while the key is released; it is 0 if the WM_SYSKEYDOWN message is posted to the active window because no window has the keyboard focus. |
|
30 |
Specifies the previous key state. The value is always 1 for a WM_SYSKEYUP message. |
|
31 |
Specifies the transition state. The value is always 1 for a WM_SYSKEYUP message. |
An application should return zero if it processes this message.
The DefWindowProc function sends a WM_SYSCOMMAND message to the top-level window if the F10 key or the ALT key was released. The wParam parameter of the message is set to SC_KEYMENU.
When the context code is zero, the message can be passed to the TranslateAccelerator function, which will handle it as though it were a normal key message instead of a system character-key message. This allows accelerator keys to be used with the active window even if the active window does not have the keyboard focus.
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 lKeyData parameter.
For non-U.S. enhanced 102-key keyboards, the right ALT key is handled as a CTRL+ALT key. The following table shows the sequence of messages that result when the user presses and releases this key:
|
Message |
Virtual-key code |
|
WM_KEYDOWN |
VK_CONTROL |
|
WM_KEYDOWN |
VK_MENU |
|
WM_KEYUP |
VK_CONTROL |
|
WM_SYSKEYUP |
VK_MENU |
DefWindowProc, TranslateAccelerator, WM_SYSCOMMAND, WM_SYSKEYDOWN