Respond to only the first WM_KEYDOWN notification?

Question

How can a Win32 application respond to only the first WM_KEYDOWN notification? The MSDN docs claim bit 30 "Specifies 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." but bit 30 is always 0 in my WndProc.

case WM_KEYDOWN:
    // ToDo - stop multiple notifications for repeating keys
    printf("WM_KEYDOWN %i %i", wParam, lParam & 30);
 return 0;

Is lParam & 30 the wrong way to ask for this? Am I doing something else wrong?

Answer 1

To get bit 30, you need this:

(lParam & 0x40000000)

An alternative would be to use bits 0-15 to get the repeat count:

int repeatCount = (lParam & 0xffff)

and only do anything if the repeat count is 0 (or possibly 1; I'm not sure whether the first message gets a repeat count of 0 or 1, and it's not clear from the documentation).

Answer 2

To test bit 30 don't AND with 30, instead AND with 1 << 30.

const bool isBitSet = lParam & (1 << 30);

Answer 3

The problem with doing lParam & 30 is that, '30' over here is considered to be in decimal, which when converted to binary would '11110'. Hence you are not testing bit 30 but just getting the result for lparam & 11110.

Hope this helps in clarifying the problem a bit.