Windows Mobile 6.5
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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.

WM_SYSKEYUP nVirtKey = (int) wParam; 
    lKeyData = lParam;


Specifies the virtual-key code of the key being released.


Specifies the repeat count, context code, previous key-state flag, and transition-state flag, as shown in the following table.

Value Description


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.


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.


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.


Specifies the transition state. The value is 1 if the key is being released, or it is 0 if the key is being pressed.

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.

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









Windows Embedded CEWindows CE 1.0 and later
Windows MobileWindows Mobile Version 5.0 and later