Using GetKeyState()

Question

I would like to have a boolean event toggle when a key is pressed. Specifically, the \'s\' key. I have been pointed to the function GetKeyState(), which supposedly works und

Answer 1

From what I understand you need to do:

if( GetKeyState(115) & 0x8000 )
{
    <EVENT>
}

The highest bit tells if key is pressed. The lowest tells if key is toggled (like, if caps lock is turned on).

Answer 2

Bit late for this but the high order bit is 0x80000000 not 0x8000, change this and it will work fine.

The other bit - useful for nothing - it acts as if you pressed CAPS LOCK when you pressed LSHIFT.

Answer 3

Since SHORT is signed, high-order bit equals sign bit.

Therefore to test if a given key is pressed, simply test if the value returned by GetKeyState() is negative:

if (GetKeyState('S') < 0) {
    // The S key is down.
} else {
    // The S key is up.
}

Besides, 115 is ASCII code for 's'. I believe, you should use capital case 83 to test the 'S' key.

Answer 4

I use a global variable bool altgr

Example:

void Editor::HandleKey(char car) {

    bool shift = false;
    //bool altgr = false;
    bool printable = false;

    if (car == 27) SendMessage(hwnd, WM_DESTROY, 0, 0);

    if ((GetKeyState(VK_CAPITAL) & 0x0001) == 1) shift = true;
    if ((GetKeyState(VK_SHIFT) & 0x8000) == 0x8000) shift = true;
    // if(GetKeyState(VK_RMENU) & 0x80000000 == 0x80000000) altgr = true;
    if (car == 18) altgr = true; 

Answer 5

Sometimes you want to use a combination of keys.

To avoid the situations when a combination of keys (eg: VK_SHIFT && VK_LEFT) satisfies two conditions:

std::cout << "Shift RIGHT pressed" << std::endl;
std::cout << "LEFT key pressed" << std::endl;

just use Sleep(...); and GetAsyncKeyState(VK_...)

GetKeyState() vs. GetAsyncKeyState() vs. getch()?

#include <windows.h>  

    ...

    while (1)
    {
        if ((GetKeyState(VK_SHIFT) & 0x8000) && (GetAsyncKeyState(VK_LEFT) & 0x8000))
        {
            Sleep(200);
            std::cout << "Shift LEFT pressed" << std::endl;
        }

        if ((GetKeyState(VK_SHIFT) & 0x8000) && (GetAsyncKeyState(VK_RIGHT) & 0x8000))
        {
            Sleep(200);
            std::cout << "Shift RIGHT pressed" << std::endl;
        }

        if (GetAsyncKeyState(VK_RIGHT))
        {
            std::cout << "RIGHT key pressed" << std::endl;
        }

        if (GetAsyncKeyState(VK_LEFT))
        {
            std::cout << "LEFT key pressed" << std::endl;
        }
   }