This 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.
At a Glance
| Header file: | Winuser.h |
| Windows CE versions: | 1.0 and later |
Syntax
WM_SYSKEYUP nVirtKey = (int) wParam; lKeyData = lParam;
Parameters
nVirtKey
Specifies the virtual-key code of the key being released.
lKeyData
Specifies the repeat count, context code, previous key-state flag, and transition-state flag, as shown in the following table.
| Value | Description |
| 0–15 | Specifies the repeat count. The value is the number of times the keystroke is repeated as a result of the user holding down the key. |
| 29 | Specifies the context code. The value is 1 if the ALT key is held down while the key is pressed; otherwise, the value is 0. |
| 30 | Specifies the previous key state. The value is 1 if the key is down before the message is sent, or it is 0 if the key is up. |
| 31 | Specifies the transition state. The value is 1 if the key is being released, or it is 0 if the key is being pressed. |
Return Values
An application should return zero if it processes this message.
Default Action
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.
Remarks
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 character-key message. This enables 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 |
See Also