MapVirtualKey goes wrong - c

Question

I made a program that captures every keystroke and prints it in the terminal. The problem is it is all in upper case and I can't figure how to do it properly. I can post the code if it is gonna help.
Main:
#include <stdio.h>
#include <stdlib.h>
#include <Windows.h>
#include <TestLibrary.h>
#pragma comment( lib, "user32" )
int main()
{
fun();
printf("Loading library\n");
HMODULE libHandle = LoadLibraryA("TestLibrary");
if (libHandle == NULL) printf("***ERROR*** loading library\n");
printf("Getting address of hook procedure\n");
HOOKPROC procAddress = (HOOKPROC)GetProcAddress(libHandle, "KeyboardProc");
if (procAddress == NULL) printf("***ERROR*** getting address\n");
printf("Installing hook\n");
HHOOK hook = SetWindowsHookEx(WH_KEYBOARD_LL, procAddress, libHandle, 0);
if (hook == NULL) printf("***ERROR*** installing hook\n");
printf("Entering message loop\n");
while (GetMessage(NULL, NULL, 0, 0));
}
DLL:
#include "pch.h"
#include <stdio.h>
#include <stdlib.h>
#include "TestLibrary.h"
void fun()
{
printf("Program started\n");
}
LRESULT CALLBACK KeyboardProc(_In_ int code, _In_ WPARAM wParam, _In_ LPARAM lParam)
{
if (wParam == WM_KEYDOWN)
{
PKBDLLHOOKSTRUCT tmp = (PKBDLLHOOKSTRUCT)lParam;
char c = MapVirtualKeyA(tmp->vkCode, 2);
if (tmp->vkCode == VK_RETURN)
printf("\n");
else if (tmp->vkCode == VK_BACK)
printf("\b \b");
else
printf("%c", c);
}
return CallNextHookEx(NULL, code, wParam, lParam);

Answer 1

MapVirtualKey[A]/[W]/[ExA]/[ExW] has a known broken behaviour.
The docs are lying you about MAPVK_VK_TO_CHAR or 2 mode. It is said:
The uCode parameter is a virtual-key code and is translated into an
unshifted character value in the low order word of the return value.
Dead keys (diacritics) are indicated by setting the top bit of the
return value. If there is no translation, the function returns 0.
But according to experiments and leaked Windows XP source code (in \windows\core\ntuser\kernel\xlate.c file) it contains different behaviour for 'A'..'Z' VKs (that are specifically not defined in Win32 API WinUser.h header and are equivalent to 'A'..'Z' ASCII chars):
case 2:
/*
* Bogus Win3.1 functionality: despite SDK documenation, return uppercase for
* VK_A through VK_Z
*/
if ((wCode >= (WORD)'A') && (wCode <= (WORD)'Z')) {
return wCode;
}
For other buttons it works as described. And this behavior is even more annoying considering that, for example for US English keyboard layout it returns:
VK_Q (0x51) -> `Q` (U+0051 Latin Capital Letter Q)
VK_OEM_PERIOD (0xbe) -> `.` (U+002E Full Stop)
But for Russian keyboard layout it returns:
VK_Q (0x51) -> `Q` (U+0051 Latin Capital Letter Q) <- here it should return `й` (U+0439 Cyrillic Small Letter Short I) according to docs
VK_OEM_PERIOD (0xbe) -> `ю` (U+044E Cyrillic Small Letter Yu)
Not sure why MS decided to pull this bug from Win 3.1 but current situation on my Windows 10 is like this.
As a workaround I can recommend you to use ToUnicode[Ex] API that can do this mapping for you:
wchar_t VkToChar(uint16_t vk, bool isShift = false)
{
uint16_t sc = MapVirtualKeyW(vk, MAPVK_VK_TO_VSC);
const uint32_t flags = 1 << 2; // Do not change keyboard state of this thread
static uint8_t state[256] = { 0 };
state[VK_SHIFT] = isShift << 7; // Modifiers set the high-order bit when pressed
wchar_t unicodeChar;
if (ToUnicode(vk, sc, state, &unicodeChar, 1, flags) != 1)
return L'\0';
if (!std::iswprint(unicodeChar))
return L'\0';
return unicodeChar;
}
Or even better: if you have Win32 message loop - just use TranslateMessage() (that calls ToUnicode() inside its code) and then process WM_CHAR message.