C++ boolean infinite loop - c++

Question

so I've got this code:
bool toggl = false;
while (!GetAsyncKeyState(VK_END)) {
if (GetAsyncKeyState(VK_INSERT)) {
if (toggl) {
toggl = false;
std::cout << "Off" << std::endl;
}
else {
toggl = true;
std::cout << "On" << std::endl;
}
}
}
The problem is whenever I click insert it just creates a infinite loop changing from false to true. When I use break my whole window just closes.
Any help appreciated.
Thanks,
Ossie

Answer 1

From the documentation for GetAsyncKeyState: "If the function succeeds, the return value specifies whether the key was pressed since the last call to GetAsyncKeyState, and whether the key is currently up or down. If the most significant bit is set, the key is down, and if the least significant bit is set, the key was pressed after the previous call to GetAsyncKeyState."
hi lo
1000 0000 0000 0001
^ ^
| |
| pressed since last call
key down (0 for up)
For the infinite loop you only need to have the key state be non-zero. Better tests...
0 != (GetAsyncKeyState(VK_INSERT) & 1) // pressed since last call
0 != (GetAsyncKeyState(VK_INSERT) & 0x8000) // key down
The same documentation warns about use of this last bit for mouse clicks and when other processes are using GetAsyncKeyState at the same time. Worth reading.
Current URL to documentation: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getasynckeystate

Answer 2

The problem is that when insert is tapped, your program will have looped on GetAsyncKeyState 20 or 30 times. And then your toggl flag is getting flipped each time. Hence, a new print statement.
I suspect this is what you really want:
bool toggl = false;
while (!GetAsyncKeyState(VK_END)) {
bool isInsertDown = (GetAsyncKeyState(VK_INSERT) != 0);
if (toggl && !isInsertDown)
{
toggl = false;
std::cout << "Off" << std::endl;
}
else if (!toggl && isInsertDown)
{
toggl = true;
std::cout << "On" << std::endl;
}
}
The above will flip the togl state to true when the insert key is down, and set it back to false when you lift your finger off the key.
But if you want to have toggl state changed on individual key presses. That is, first insert tap sets toggl to true and the next key press sets it back to false, then you'll need another variable. Hence:
bool toggl = false;
bool lastWasDown = false;
while (!GetAsyncKeyState(VK_END)) {
bool isInsertDown = GetAsyncKeyState(VK_INSERT) != 0;
if (isInsertDown == lastWasDown) {
continue;
}
if (isInsertDown && !toggl) {
toggl = true;
std::cout << "On" << std::endl;
}
else if (isInsertDown && toggl) {
toggl = false;
std::cout << "Off" << std::endl;
}
lastWasDown = isInsertDown;
}