收到 WM_KEYDOWN 消息时 lParam 的行为是什么？

Question

I started learning winapi using c++ language. I am trying to understand the lParam on WM_KEYDOWN message.

From the Microsoft documentation:

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.

I am handling this message by this way:

case WM_KEYDOWN:
    cout << ((lParam & 0b11111111111111110000000000000000) >> 16) << ", ";
    cout << ((lParam & 0b00000000000000001111111100000000) >> 8) << ", ";
    cout << ((lParam & 0b00000000000000000000000010000000) >> 7) << ", ";
    cout << ((lParam & 0b00000000000000000000000000000100) >> 2) << ", ";
    cout << ((lParam & 0b00000000000000000000000000000010) >> 1) << ", ";
    cout << ((lParam & 0b00000000000000000000000000000001) >> 0) << endl;

And if I press "A" button on my keyboard I get ouput: 30, 0, 0, 0, 0, 1

If I hold "A" button I get muliple outputs:

16414, 0, 0, 0, 0, 1
16414, 0, 0, 0, 0, 1
16414, 0, 0, 0, 0, 1

If I press other letter button, I get same result but with other first number. (For example, for "B" button I get 48 as simple press, 49200 as holding)

How can I understand it?

Answer 1

I didn't test this, but your bit ordering appears to be reversed. According to MS Documentation , bits 0-15 are the LOW bits.

case WM_KEYDOWN:
    cout << ((lParam & 0b00000000000000001111111111111111) >> 0) << ", ";
    cout << ((lParam & 0b00000000111111110000000000000000) >> 16) << ", ";
    cout << ((lParam & 0b00000001000000000000000000000000) >> 24) << ", ";
    cout << ((lParam & 0b00100000000000000000000000000000) >> 29) << ", ";
    cout << ((lParam & 0b01000000000000000000000000000000) >> 30) << ", ";
    cout << ((lParam & 0b10000000000000000000000000000000) >> 31) << ", ";