WM_KEYDOWN
wVkey = wParam; /* virtual-key code */
dwKeyData = lParam; /* key data */The WM_KEYDOWN message is sent when a nonsystem key is pressed. A nonsystem key is a key that is pressed when the ALT key is not pressed, or it is a key that is pressed when a window has the input focus.
wVkey
Value of wParam. Specifies the virtual-key code of the given key.
dwKeydata
Value of lParam. Specifies the repeat count, scan code, extended key, context code, previous key state, and key-transition state, as shown in the following table:
| Bit | 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. |
| 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 a function key or a key on the numeric keypad. The value is 1 if it is an extended key; otherwise, it is 0. |
| 25–26 | Not used. |
| 27–28 | Used internally by Windows. |
| 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 key-transition state. The value is 1 if the key is being released, or it is 0 if the key is being pressed. |
For a WM_KEYDOWN message, the value of bit 29 (context code) is 0 and the value of bit 31 (key-transition state) is 0.
An application should return zero if it processes this message.
Because of the autorepeat feature, more than one WM_KEYDOWN message may occur before a WM_KEYUP message is sent. 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 IBM Enhanced 101- and 102-key keyboards, enhanced keys are the right ALT key and the right CTRL key 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 division (/) and ENTER key on the numeric keypad. Some other keyboards may support the extended-key bit in the dwKeyData parameter.