Detecting if 'Control' or 'Shift' key was down when key pressed

I have been looking into detecting key stuff, it works great, I am trying to figure out if control or shift was pressed, I read in some MSDN documentation (I use Visual C++), that lParam is 0 if ctrl or shift isn't down, or 1 if they are, but how do I tell which one?

I may be wrong, it had a table structure saying stuff like:

0-15 repeat count
16-18 reserved, do not use

19-23 = something

24 = if the right hand shift or control key is down on an extended 101-102 key keyboard.. returns 1 if it is, otherwise returns 0

My code for keys:

Code:

---

CASE WM_KEYDOWN:
    {
    if (LOWORD(lParam) == 1)
    {
        MessageBox(hWnd, _T("Ctrl Or Shift down"), _T("CAP"), 0);
    }
    int iKey = LOWORD(wParam);
    if (iKey == 37) //LEFT ARROW
    {
        MessageBox(hWnd, _T("LA"), _T("CAP"), 0);
    }
    else if (iKey == 39) //RIGHT ARROW
    {
        MessageBox(hWnd, _T("RA"), _T("CAP"), 0);
    }
    }

---

I get the message Ctrl Or Shift down, when I hold either of them down, but I don't if I don't hold them down...

How do I tell which one was pressed? Thanks

Your code does not make much sense to me but if you want to check the state of other keys, such as Ctrl, Alt, or Shift while processing WM_KEYUP/DOWN, you can use GetKeyState API function.

Hi Icyculyr,

I have been reading information about keyboard messages recently, at one point, I was exposed to the topic you are investigating.

Like Boris K K suggested, you can use GetKeyState( virtual key) to discover if a shift key, such as SHIFT, CTRL, and ALT, is pressed.
For example,

Code:

---

nRet = GetKeyState ( VK_SHIFT ) ;

---

You can obtain a more detailed usage on MSDN GetKeyState () ;

However, according to the book I was reading, it mentioned a flaw of using GetKeyState. GetKeyState does not check keyboard status in real-time.

Quote:

---

It refects the keyboard status up to and including the current message being processed.

---

If this is not what you want, you can also check VK_SHIFT at WM_KEYDOWN

Hope this helps.

kab

Actually it is not a flow. You are interested if Ctrl was down at the time the other key was pressd, not whether it is down or up at the moment you are processing the message.

Hi Boris K K,

I was confused with GetKeyState after I was reading the book. After reading your post, I guess I am still confused

Here is my understanding of GetKeyState:
Let's say we are using GetKeyState to determine if a letter should be displayed as capitalized or not
Let's say the message queue contains ['a']['p']['p']['shift']['l']['e'], so we know the user types 'appLe'
If we hold 'shift' key while the message queue is being processed, we will get 'APPLE' instead of 'appLe'

I believe your statement

Quote:

---

Originally Posted by Boris K K

not whether it is down or up at the moment you are processing the message.

---

is targeting this case I just described.

The lesson that I got out of this is that "it is not a good practice to use GetKeyState to determine if a letter is capitalized or not."


Question:
Could you give me an example of when you will want to use GetKeyState?

kab

You can use ::GetAsyncKeyState().

Cheers

Hi all, thanks for your input,

I have read the MSDN documentation on this a little while ago,

GetKeyState() checks if the key was pressed at the same time as the WM_KEYDOWN message came,


GetAsyncKeyState() checks if it is still down...

(As far as I know)

Thanks alot guys

Quote:

---

Originally Posted by kabilius

...Let's say the message queue contains ['a']['p']['p']['shift']['l']['e'], so we know the user types 'appLe'
If we hold 'shift' key while the message queue is being processed, we will get 'APPLE' instead of 'appLe'

I believe your statement
is targeting this case I just described.

The lesson that I got out of this is that "it is not a good practice to use GetKeyState to determine if a letter is capitalized or not."

---

No, using GetAsyncKeyState (is Shift down right now) may result in incorrect capitalization. GetKeyState (was Shift down when 'l' was pressed; was Shift down when 'e' was pressed, etc.) should be OK.

void CMousepresentView::OnDraw(CDC* pDC)
{
int shiftValue=::GetKeyState(VK_SHIFT);
if(!shiftValue)
pDC->TextOut(0,50,"Shift not pressed");
else
pDC->TextOut(0,50,"Shift pressed");

int ctrlValue=::GetKeyState(VK_CONTROL);
if(!ctrlValue)
pDC->TextOut(0,100,"Ctrl not pressed");
else
pDC->TextOut(0,100,"Ctrl pressed");
}
In this program when I run the program output is
shift pressed

ctrl not pressed

Why "shift pressed" comes even I don't press shift.

Like for Ctrl+A, Try

Code:

---

if (GetKeyState(VK_CONTROL) != 1)
                {
                                switch(wParam)
                                {
                                case 65:
                                        //statements
                                }
                }

---

If this is in your OnDraw routine, you'll need to invalidate your drawing area to get a repaint. Try handling WM_KEYDOWN, and call Invalidate() from it's handler.