Win32 C++ Low Level Keyboard Hook causing strange behavior

Question

I am having a problem trying to use a keyboard hook. What I am trying to do (and does) is from any window/ focus, I can hit a key that runs a function (that moves the mouse and clicks.)

It works just fine from the front, but as soon as I start doing something else, everything acts strange (even when after closing the problem.)

On firefox it will have a "select and highlight all to where the mouse is when I click"; if I try to type, all numeric characters come out as if the shift button was down and no way around it. If I click on my compiler on the taskbar (wxDev C++), it automatically starts a new instance of the program.

That is just the start of the problems, I have a restart my computer to get normal behavior again.

I figure that I might be using it wrong:

In int WinMain:

keyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL, LowLevelKeyboardProc, hThisInstance, 0);

In the main procedure:

case WM_KEY_WPARAM_VK: 
keyid = wParam; // 65 == 'a'
letterid = keyid - 65;
if ('a'+letterid == 'q') {  DoFunction(); }
return 0;

So that when I hit q on the keyboard, the function is called.

This is the procedure, I am trying to not lock the keyboard from typing (so I added the extra line.) I cannot figure this out...

LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam ) {
  KBDLLHOOKSTRUCT *pKeyBoard = (KBDLLHOOKSTRUCT *)lParam;
  // When a key is pressed
  if (WM_KEYDOWN == wParam) {
    PostMessage(hWnd, WM_KEY_WPARAM_VK, pKeyBoard->vkCode, 0);
    CallNextHookEx(keyboardHook, pKeyBoard->vkCode, 0, 0);
  }
}

Thanks for reading.

Answer 1

You need to put the CallNextHookEx function outside the if statement! (and also update it to properly pass wParam and lParam to the next hook)

return CallNextHookEx(keyboardHook, pKeyBoard->vkCode, wParam, lParam);

The way you currently have it, your code will block all "key-up" strokes from the rest of the OS, hence the strange behavior.

It's absolutely imperative that CallNextHookEx gets called regardless of what you do within the hook. I would also avoid performing any lengthy (blocking) operations while inside your hook.