WH_GETMESSAGE global hook not working

Question

I am trying to set a global GetMessage hook on all threads. This is my DLL:

#include <windows.h>

__declspec(dllexport) LRESULT CALLBACK GetMsgProc(int nCode, WPARAM wParam, LPARAM lParam)
{
  MessageBeep(0);

  return CallNextHookEx(NULL, nCode, wParam, lParam);
}

As you can see, it's not much. I just want it to call MessageBeep whenever it's called.

#include <windows.h>

typedef LRESULT (CALLBACK *LPGetMsgProc)(int nCode, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR pCmdLine, int nCmdShow)
{
  if(!(HMODULE hDll = LoadLibrary("library.dll")))
    return 1;
  if(!(LPGetMsgProc pfnProc = (LPGetMsgProc)GetProcAddress(hDll, "GetMsgProc@12")))
    return 2;

  HHOOK hMsgHook = SetWindowsHookEx(WH_GETMESSAGE, pfnProc, hInstance, 0);

  MSG msg;
  while(GetMessage(&msg, NULL, 0, 0) > 0) {}

  UnhookWindowsHookEx(hMsgHook);

  return 0;
}

My WinMain loads the library, gets the procedure and sets the hook. However, MessageBeep is never being called. Is there something I'm doing wrong here?

Also, one other thing has been bothering me. In this call:

if(!(LPGetMsgProc pfnProc = (LPGetMsgProc)GetProcAddress(hDll, "GetMsgProc@12")))

I was forced to use "GetMsgProc@12" because I couldn't get it right any other way. Can somebody please tell me how I'm supposed to use a .def file or something else so I can just have it as "GetMsgProc"? Though MSDN stated that since I have __declspec(dllexport) in my declaration I wouldn't need it...

My IDE is Code::Blocks with MinGW. Thanks in advance.

Answer 1

The third parameter...

HHOOK hMsgHook = SetWindowsHookEx(WH_GETMESSAGE, pfnProc, hInstance, 0);

...is the handle passed into your WinMain function. But it needs to refer to the DLL where the callback function resides - in your case, that'd be hDLL.