Keyboard buffer

Posted on 1998-12-06
Last Modified: 2008-02-20
I would like to clear the keyboard buffer in VB. Is there an API that will examine the buffer contents and allow removal or manipulation of the buffer contents.
Question by:ashmore
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LVL 44

Expert Comment

ID: 1448425
Hi ashmore,

You can use SetKeyboardState and GetKeyboardState. Came across a good example at the microsoft site with a form and a button and this was the code

Private Declare Sub GetKeyboardState Lib "user32" (lpKeyState As Any)
Private Declare Sub SetKeyboardState Lib "user32" (lpKeyState As Any)
Const VK_CAPITAL = &H14
Const VK_NUMLOCK = &H90

Private Sub Command1_Click()
    ReDim KeyboardBuffer(256) As Byte

    GetKeyboardState KeyboardBuffer(0)

    If KeyboardBuffer(VK_CAPITAL) And 1 Then
        KeyboardBuffer(VK_CAPITAL) = 0
        KeyboardBuffer(VK_CAPITAL) = 1
    End If

    If KeyboardBuffer(VK_NUMLOCK) And 1 Then
        KeyboardBuffer(VK_NUMLOCK) = 0
        KeyboardBuffer(VK_NUMLOCK) = 1
    End If

    SetKeyboardState KeyboardBuffer(0)
End Sub


Aah... found the link so you can check it for yourself

LVL 15

Expert Comment

ID: 1448426
If by 'buffer' you mean 'system queue' you can use:

- the return value is nonzero if the function detects a mouse click or keyboard event in the system queue. Otherwise, it is zero.

GetQueueStatus (fuFlags)
- returns a value that indicates the type of messages in the queue.
QS_KEY      WM_CHAR message is in the queue.

Both functions are very fast and typically used inside speed-critical loops.
There is API SetMessageQueue, but I wouldn't try it in VB
(The function must be called before any windows are created and before any messages are sent)


Author Comment

ID: 1448427
Dear Bruintje
Thanks for your reply but I need to explain more.
The GetKeyboardstate lets you know the state of any of the 256 virtual keys. The problem I am trying to solve is that if for  example the <esc> or <enter> key has been pressed 6 times it only registers in  GetKeyboardstate as being pressed once, not how many times. What I need to do is to look at the the most recent unprocessed keystrokes, analyse what the user is doing and then set the buffer to null. It must be a feature that is used in writing games. It was easy in DOS but maybe thats showing my age.
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LVL 15

Expert Comment

ID: 1448428
ameba wrote:
>by 'buffer' you mean 'system queue'
You do!
LVL 44

Expert Comment

ID: 1448429
Hi Ashmore,

Well reject my answer and give ameba a chance. Thinks his comments are more of an solution to your problem.
LVL 15

Expert Comment

ID: 1448430
I don't have solution. I suggest ashmore use
  If GetQueueStatus(QS_KEY)<>0 Then ' something new is in the queue
    If GetKeyState(VK_ENTER) < 0 Then
        ' set some public flags that indicate enter pressed
    ElseIf GetKeyState(VK_ESCAPE) < 0 Then
        ' set some other public flags
    End If
  End If

and use some logic that examines flags in key processing routine.


Author Comment

ID: 1448431
Rejected on  bruintje advice. Thank you for your help.

Accepted Solution

kishor33 earned 200 total points
ID: 1448432
You are not required to use a API call for clearing the content of the keyboard instead use the combination of doevent procedure and keydown event to clear the content of the keyboard buffer.

Hope it will help

Thank you,

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