WM_KEYDOWN message

Posted to the window with the keyboard focus when a nonsystem key is pressed. A nonsystem key is a key that is pressed when the ALT key is not pressed.

#define WM_KEYDOWN                      0x0100

Parameters

wParam

The virtual-key code of the nonsystem key. See Virtual-Key Codes.

lParam

The repeat count, scan code, extended-key flag, context code, previous key-state flag, and transition-state flag, as shown following.

Bits	Meaning
0-15	The repeat count for the current message. The value is the number of times the keystroke is autorepeated as a result of the user holding down the key. If the keystroke is held long enough, multiple messages are sent. However, the repeat count is not cumulative.
16-23	The scan code. The value depends on the OEM.
24	Indicates 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	The context code. The value is always 0 for a WM_KEYDOWN message.
30	The previous key state. The value is 1 if the key is down before the message is sent, or it is zero if the key is up.
31	The transition state. The value is always 0 for a WM_KEYDOWN message.

For more detail, see Keystroke Message Flags.

Return value

An application should return zero if it processes this message.

Example

LRESULT CALLBACK HostWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message) 
    {
    case WM_KEYDOWN:
        if (wParam == VK_ESCAPE)
        {
            if (isFullScreen) 
            {
                GoPartialScreen();
            }
        }
        break;

    // ...
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;  
}

Example from Windows Classic Samples on GitHub.

Remarks

If the F10 key is pressed, the DefWindowProc function sets an internal flag. When DefWindowProc receives the WM_KEYUP message, the function checks whether the internal flag is set and, if so, sends a WM_SYSCOMMAND message to the top-level window. The WM_SYSCOMMAND parameter of the message is set to SC_KEYMENU.

Because of the autorepeat feature, 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 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 lParam parameter.

Applications must pass wParam to TranslateMessage without altering it at all.

Requirements

See also

• DefWindowProc
• TranslateMessage
• WM_CHAR
• WM_KEYUP
• WM_SYSCOMMAND
• Keyboard Input
• About Keyboard Input