WM_KEYDOWN
nVirtKey = (int) wParam; /* virtual-key code */
lKeyData = lParam; /* key data */
The WM_KEYDOWN message is posted to the window with the keyboard focus when a nonsystem key is pressed. A nonsystem key is a keyboard 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.
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. 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 key pad. The value is 1 if it is an extended key; otherwise, it is 0. |
| 25–28 | Reserved. |
| 29 | Specifies the context code. The value is always 0 for a WM_KEYDOWN message. |
| 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 always 0 for a WM_KEYDOWN message. |
An application should return zero if it processes this message.
Because of auto-repeat, more than one WM_KEYDOWN message may be posted before a WM_KEYUP message is posted. 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, extended keys are the right ALT and the right CONTROL keys on the main section of the keyboard; the INSERT, DELETE, HOME, END, PAGE UP, PAGE DOWN and DIRECTION keys in the clusters to the left of the numeric key pad; and the divide (/) and ENTER keys in the numeric key pad. Some other keyboards may support the extended-key bit in the lKeyData parameter.
WM_CHAR, WM_KEYUP