WM_KEYUP

The WM_KEYUP message is posted to the window with the keyboard focus when a nonsystem key is released. A nonsystem key is a key that is pressed when the alt key is not pressed, or a keyboard key that is pressed when a window has the keyboard focus.

WM_KEYUP 
nVirtKey = (int) wParam;    // virtual-key code 
lKeyData = lParam;          // key data

Parameters

nVirtKey

Value of wParam. Specifies the virtual-key code of the nonsystem key.

lKeyData

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

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_KEYUP 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 always 0 for a WM_KEYUP message.
30	Specifies the previous key state. The value is always 1 for a WM_KEYUP message.
31	Specifies the transition state. The value is always 1 for a WM_KEYUP message.

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

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.

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