How can I convert a vk constant to text? - c

Question

I'm trying to translate vk constants (possibly joined together) to their names (e.g., 81 (VK_CONTROL|VK_SHIFT|VK_A) = “Control+Shift+A.”
I tried using the GetKeyNameText function (both with vk and scancode constants), but it does not seem to work (the string is blank, it returns 0, and GetLastError returns 0 as well).

Answer 1

As far as I know, there is no API function that directly converts the combined virtual keys into text. For non-character keys (VK_CONTROL, VK_SHIFT, etc.), you need to manually concatenate strings.
For character keys, MapVirtualKey works fine for me.
I tested the code you provided:
UINT t = MapVirtualKey(VK_A, MAPVK_VK_TO_CHAR);
I can get its return value:

Answer 2

Filter out the control and shift with
char keybuff[64] = {0};
if (keys & VK_CONTROL) {
strcat(keybuff, "Control+");
keys &= ~VK_CONTROL; // turn bits OFF
}
if (keys & VK_SHIFT) {
strcat(keybuff, "Shift+");
keys &= ~VK_SHIFT;
}
And use MapVirtualKey to map the VK code to a character
https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-mapvirtualkeya
So in the following case key becomes 65 which is the ascii value for capital 'A'. Cast it to a char and you have the letter. This works for all codes below ascii 127.
UINT key = MapVirtualKey(VK_A, MAPVK_VK_TO_CHAR);
char c = (char)key; // 'A'

Answer 3

I advise you not to use GetKeyNameText API at all since this an outdated shit that is broken for non-US layouts. Create and use some lookup table youself instead. :)
If you still decide to use it then proper call of GetKeyNameText is tricky:
// Get keyboard layout specific localized key name
std::string GetKeyNameTextWrapper(uint16_t scanCode)
{
wchar_t name[128];
int charCount = 0;
// GetKeyNameText is not working for these keys
// due to use of broken MAPVK_VK_TO_CHAR under the hood
// See https://stackoverflow.com/a/72464584/1795050
const uint16_t vkCode = LOWORD(::MapVirtualKeyW(scanCode, MAPVK_VSC_TO_VK_EX));
if ((vkCode >= (uint16_t)'A') && (vkCode <= (uint16_t)'Z'))
{
const uint32_t flags = 1 << 2; // Do not change keyboard state of this thread
static uint8_t state[256] = { 0 };
// This call can produce multiple UTF-16 code points
// in case of ligatures or non-BMP Unicode chars that have hi and low surrogate
// See examples: https://kbdlayout.info/features/ligatures
charCount = ::ToUnicode(vkCode, scanCode, state, name, 128, flags);
// negative value is returned on dead key press
if (charCount < 0)
charCount = -charCount;
}
else
{
const LONG lParam = MAKELONG(0, ((scanCode & 0xff00) != 0 ? KF_EXTENDED : 0) | (scanCode & 0xff));
charCount = ::GetKeyNameTextW(lParam, name, 128);
}
return utf8::narrow(name, charCount);
}
Also note that GetKeyNameText will return different string according to string data that is sewn into keyboard layout dll. And that layout dlls may have bugs.