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I am learning the Win32 api and C++ and I wanted to do a simple keylogger. Here's what I've came up with : 

#include <Windows.h>
#include <string>
#include <iostream>
#include <sstream>

using namespace std;

LRESULT CALLBACK kbLog1(int code, WPARAM wParam, LPARAM lParam);

void initKbLogger();
void kbLog2(int code, WPARAM wParam, LPARAM lParam);

HHOOK keyHook;

void Hworld() {
    initKbLogger();
}

void initKbLogger() {
    keyHook = SetWindowsHookEx(WH_KEYBOARD_LL, kbLog1, NULL, NULL);
    bool caps;

    if ((GetKeyState(VK_CAPITAL) & 0x0001) != 0) {
        caps = true;
    }

    MSG msg;

    while (GetMessage(&msg, NULL, NULL, NULL) != 0);

    UnhookWindowsHookEx(keyHook);

}


// from https://stackoverflow.com/a/3999597
// will convert LPCWSTR to std::string
std::string utf8_encode(const std::wstring& wstr)
{
    if (wstr.empty()) return std::string();
    int size_needed = WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), NULL, 0, NULL, NULL);
    std::string strTo(size_needed, 0);
    WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), &strTo[0], size_needed, NULL, NULL);
    return strTo;
}


// main hook fn, supposed to run CallNextHookEx no matter what happens in kbLog2
LRESULT CALLBACK kbLog1(int code, WPARAM wParam, LPARAM lParam) {
    OutputDebugStringA("heya");
    kbLog2(code, wParam, lParam);
    OutputDebugStringA("heya2");
    return CallNextHookEx(keyHook, code, wParam, lParam);
}

void kbLog2(int code, WPARAM wParam, LPARAM lParam) {
    if ((code != 0) || (wParam != WM_KEYDOWN)) {
        return;
    }

    LPKBDLLHOOKSTRUCT kbHookData = (LPKBDLLHOOKSTRUCT)lParam;
    BYTE keyboard_state[256];

    GetKeyboardState(keyboard_state);

    WCHAR wChar[4];

    int ret = ToUnicode((UINT)kbHookData->vkCode, kbHookData->scanCode, keyboard_state, wChar, 4, 0);

    if (ret == -1) {
        return;
    }

    string lol = utf8_encode(wChar);

    std::ostringstream out;
    out << wChar;

    string ss = "hello, you typed the following key: " + lol + " " + out.str();

    MessageBoxA(0, ss.c_str(), "Heya", 0);
}

However the problem is that this code can't display the accentued characters that I type in my keyboard. For example, pressing "A" works just fine but pressing "é" doesn't display the actual character. What is wrong? I suppose there is something wrong with converting the vkCode to a string, but I don't see what I've done wrong... Any help? Thanks

vvv99292
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  • What "non nefarious" reasons do you have for writing a "key logger"? Just currious. – Jesper Juhl Apr 11 '20 at 18:16
  • UTF-8 encoding is rarely used in MS Windows. – Ripi2 Apr 11 '20 at 18:19
  • @JesperJuhl Simply for the sake of learning. I've always wanted to learn C++, and coming from a Javascript background I can't think of anything simple that I can't do in JS. Therefore I came up with this idea. – vvv99292 Apr 11 '20 at 18:24
  • @Ripi2 how should I handle the vkCode prop then? – vvv99292 Apr 11 '20 at 18:25
  • It notifies you about *virtual* keycodes, they are the same anywhere in the world. What letter they produce, if any, depends on the user's selected keyboard layout, the state of the modifier keys (Shift, Alt, Ctrl, Win) and the keyboard state affected by keys like AltGr. That translation can only be done reliably in the thread that receives the notification. That's why there is also a WH_KEYBOARD hook, the non-low-level flavor. Much, much harder to get going. – Hans Passant Apr 11 '20 at 20:12
  • ááá forward quote a, single ' is quote space.. this reminds me of the old DOS and Windows95 days.. I tried it in CBuilder 3, ended up with emulating MY keyboard strokes, their control and shift states.. Then I had to re-implement it for MY laptop keyboard.. and then.. it did not work on my friend's keyboard. If you happen to have a Norwegian or German key mapping, all turned out different when using the hook. DOS did not have culture.. so in DOS (or W3) you could write a "macro sequence " working elsewhere. Good old days stuff.. dunno in W10 culture things got complicated ! – Goodies Apr 11 '20 at 21:05

0 Answers0