Using GetKeyboardState

Posted on 1998-11-14
Last Modified: 2013-11-20

How can I use the GetKeyboardState function?  I mean, I know how to get the array filled with information, but I don't know how to interpret it.  Can someone give me an example of how I can, for example, get whether or not any of the arrow keys are pushed down?

Thank you very much for you help.
Question by:a121496
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 5
  • 3
LVL 86

Accepted Solution

jkr earned 100 total points
ID: 1324697
Well, you could use it in this way:

BYTE aKeyState[ 256];

if ( GetKeyboardState( aKeyStaze))
 if ( 0x80000000 & aKeyState [ V_UP])
   // 'cursor up' is pressed...

Or you alternatively could use

if ( 0x80000000 & GetKeyState( VK_UP))
   // 'cursor up' is pressed...

(0x80000000 represents the bit mask for the highest bit in the highest byte. If this is set to '1', the key is pressed)
LVL 86

Expert Comment

ID: 1324698
Ooops sorry, a typo ;-)

if ( GetKeyboardState( aKeyStaze))

should of course read

if ( GetKeyboardState( aKeyState))


Author Comment

ID: 1324699
Thank you, but I have one more question now, how can I find out which elements in the array correspond to things like the letters on the keyboard ("asdf...") etc?  What numbers are associated with them?  If you answer this as well (I'm sure you can), I will give you an 'A'.
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

LVL 86

Expert Comment

ID: 1324700
That's easy ;-)
the 'VK_ *' constants can be used as indices to the array, and the ASCII codes for the characters correspond directly to the virtual keycodes:
(from 'winuser.h')
/* VK_0 thru VK_9 are the same as ASCII '0' thru '9' (0x30 - 0x39) */
/* VK_A thru VK_Z are the same as ASCII 'A' thru 'Z' (0x41 - 0x5A) */


Author Comment

ID: 1324701
Huh.  That does not seem to work.  I have included "stdafx.h" so winuser should be included too, but the compiler says that those constants are undefined

"O:\stuff\newgame\AsteroidDlg.cpp(256) : error C2065: 'VK_A' : undeclared identifier"


Author Comment

ID: 1324702
I also tried using the character constants like so:

but the if statment I'm using isn't called when the a key is pressed.

Things I checked:
1) The obvious: Caps lock is off.

2) I know the code is right.  Here it is though:
  if (0x80 & keys['a'])  // 'a'
  { m_Players[1].AdjustDegrees (-10);
    if (m_Players[1].GetDegrees () < 0)
    { m_Players[1].AdjustDegrees (360); }
  if (0x80 & keys['d'])  // 'd'
  { m_Players[1].AdjustDegrees (10);
    if (m_Players[1].GetDegrees () > 359)
    { m_Players[1].AdjustDegrees (-360); }

  if (0x80 & keys['w'])  // 'w'
  { m_Players[1].Accelerate (.025); }
  if (0x80 & keys[VK_SHIFT])
  { m_Players[1].Fire (1); }

The only 'if' that is called is the shift key one (the last one).  The others are ignored.

Forgot to mention also that 0x80000000 didn't work, I had to cut off a bunch of zeros.  I know that is not the problem because I am using this same code in another area with the VK_LEFT, UP, etc constants and it works there.

Author Comment

ID: 1324703
I am using VC++ 5.0 compiler.  Perhaps you are using a different version in which those constants were defined?

Author Comment

ID: 1324704
Ignore all that.  After experimenting, I found that I had to use CAPITAL letters in the [ ] like

Anyway, thanks for the help.

Featured Post

Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

In this article, I'll describe -- and show pictures of -- some of the significant additions that have been made available to programmers in the MFC Feature Pack for Visual C++ 2008.  These same feature are in the MFC libraries that come with Visual …
This is to be the first in a series of articles demonstrating the development of a complete windows based application using the MFC classes.  I’ll try to keep each article focused on one (or a couple) of the tasks that one may meet.   Introductio…
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
Exchange organizations may use the Journaling Agent of the Transport Service to archive messages going through Exchange. However, if the Transport Service is integrated with some email content management application (such as an antispam), the admini…

732 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question