Why are my hotkeys bugging out when using `GetAsyncKeyState()` in Win32?

Question

main.c:

#include <stdio.h>
#include <windows.h>
#include <stdbool.h>

int main(void) {
    while (true) {
        if (GetAsyncKeyState(VK_CONTROL)) {
            if (GetAsyncKeyState('1')) {
                printf("Set grenades to 100!\n");
                Sleep(500);
            }
        }

        Sleep(100);
    }

    return 0;
}

I've tried changing between debug and release mode, between the mingw and VS compilers, and I tired both C and C++. The same bug happens in all cases.

The idea is so that the hotkey is Control + 1. Whenever the user presses both the Control key and the 1 key at the same time, I want the code printf("Set grenades to 100!\n"); to be ran.

However, there is a bug. If the user presses and release the 1 key. Waits any amount of time (seconds, minutes) and then presses the Control key, printf("Set grenades to 100!\n"); is executed.

This bug happens even if the user presses keys in between. For example: printf("Set grenades to 100!\n"); is executed if the user does the following:

Presses the 1 key.
Releases the 1 key.
Presses and releases the following keys: 'H', 'i', 'S', 't', 'a', 'c', 'k', 'o', 'v', 'e', 'r', 'f', 'l', 'o', 'w', and '2'.
Presses and releases the control key.

On step 4, the code is executed. How do I fix this bug?

I want to use GetAsyncKeyState not GetKeyState because I want the input to be captured even if the user switches to another program.

I'm not familiar with GetAsyncKeyState, but would a compound if statement work? if(GetAsyncKeyState(VK_CONTROL) && GetAsyncKeyState('1'))? — nhgrif
– nhgrif, Commented Oct 26, 2013 at 2:39
I'd prefer not to use a compound if statement because I have multiple hotkeys I want to use. Control + 1, Control + 2, Control + 3, etc... I will try to see if that fixes the bug though. — user2922027
– user2922027, Commented Oct 26, 2013 at 2:40
The result of GetAsyncKeyState should be masked with 0x8000 to check if the key is down (as per the documentation). Anyway, hotkeys can be set using RegisterHotKey. — Qaz
– Qaz, Commented Oct 26, 2013 at 2:40
The bug seems to still happen even if I use a compound if statement. — user2922027
– user2922027, Commented Oct 26, 2013 at 2:40
GetAsyncKeyState answers the question of "Is this key down right now?", not the question of if they were pressed at the same time, any keys were pressed in the middle, or a cat is on your keyboard. If you need to track those things you need to provide that additional logic yourself or choose a different method of handling input. — Retired Ninja
– Retired Ninja, Commented Oct 26, 2013 at 2:44

ryyker · Accepted Answer · 2013-10-28 16:52:14Z

Regarding the return value of GetAsyncKeyState(), according to Microsoft, If the most significant bit is set, the key is down.
An important take-away here is: for signed types, such as short, when the most significant bit is set, it is read as a negative number. GetAsyncKeyState() returns short.

This suggests the logic used in your code to interpret the result of GetAsyncKeyState() is opposite of what it needs to be in its current application. That is, your condition statement should be checking for negative numbers instead of positive.

One more note: as others have suggested, the purpose of GetAsyncKeyState() is to check the condition of the key now. But it's return value also contains information to determine whether the key has been pressed recently. In fact, that is what you would be doing by looking at the LSB. In the same link, it is explained that the LSB is an indicator of recent status However this is not a recommended practice. The recent bit status can be set by any process running in another thread, at any time, therefore, should only be used with caution.

So, try this instead. I tested this on 64 bit windows, it seems to work fine, no matter how many times I press the 1 first, or press the ctrl key, the popup does not occur. But, when I press both simultaneously, then it pops up.

#include <stdio.h>
#include <windows.h>
//#include <stdbool.h>//I did not need this, you might.

int main(void) {
    while (1) 
    {
        if (GetAsyncKeyState(VK_CONTROL)<0) 
        {

            if (GetAsyncKeyState('1')<0) 
            {
                printf("Set grenades to 100!\n");
                Sleep(200);//changed here for my test, you might need to change again
            }
        }
        Sleep(200);//changed here for my test, you might need to change again
    }                                      

    return 0;//unreachable code warning
}

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