Question

I have a DLL that I use to hook the Notepad and catch keystrokes. All works well, but I’d like to have access to the KeyboardHook Callback from within my exe. So that everytime the Callback in the .dll is triggered, it passes it’s values to the .exe Is this possible?

** HOOK.dll (hookDll.cpp) **

#include "windows.h"

#pragma data_seg (".SHARED")  
     HHOOK keyboardHook = 0;  
     HINSTANCE g_hInstance = 0;  
#pragma data_seg()  

#pragma comment(linker, "/SECTION:.SHARED,RWS")

extern "C" __declspec(dllexport) LRESULT CALLBACK KeyboardHook(int nCode, WPARAM wParam, LPARAM lParam)
{
    if(0 > nCode)
    return CallNextHookEx(keyboardHook, nCode, wParam, lParam);

    {
        MessageBox(NULL, L"Got Keyboard Event !", L"Event", 0);
    }

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

extern "C" __declspec(dllexport) bool InstallKeyboardHook(unsigned long threadID)
{
    keyboardHook = SetWindowsHookEx(WH_KEYBOARD, &KeyboardHook, g_hInstance, threadID);
    return true;
}

extern "C" __declspec(dllexport) bool UnInstallKeyboardHook()
{
    UnhookWindowsHookEx(keyboardHook);  
    return true;
}

BOOL APIENTRY DllMain( HMODULE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved ) 
{     
switch (ul_reason_for_call){
    case DLL_PROCESS_ATTACH:
        g_hInstance  = (HINSTANCE) hModule;
        break;
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
}     
return TRUE; 
}

** Hook.exe (hook.h) **

#pragma once

#include "afxwin.h"

typedef bool(*InstallHook)(unsigned long);
typedef bool(*UnInstallHook)();
typedef LRESULT (*KeyboardHook)(int nCode, WPARAM wParam, LPARAM lParam);

LRESULT CALLBACK MyCallback(int nCode, WPARAM wParam, LPARAM lParam)
{
    //Id like this to get called whenever the CALLBACK in the dll is called
    MessageBox(NULL, L"test", L"test", 0);
    return NULL;
}


class CTrayMeApp : public CWinApp
{
public:
CTrayMeApp(){};
~CTrayMeApp(){};

virtual BOOL InitInstance();
};

extern CTrayMeApp theApp;

** Hook.exe (hook.cpp) **

#include "hook.h"

CTrayMeApp theApp;

BOOL CTrayMeApp::InitInstance()
{
BOOL bReturn = FALSE;

CWinApp::InitInstance();

HMODULE hModule = LoadLibrary(_T("Hook.dll"));

//Get the function address which installs the keyboard events filter.
InstallHook fpKeyboardHook = (InstallHook) GetProcAddress(hModule,"InstallKeyboardHook");

//Install the Keyboard Event Hook (Filter).
fpKeyboardHook(GetTargetThreadIdFromWindow("Notepad", "Untitled - Notepad"));

//Install the Callback
KeyboardHook cpKeyboardHook = (KeyboardHook) GetProcAddress(hModule,"_KeyboardHook@12");

//OK, are callback is here, now how do we make use of it?
KeyboardHook(MyCallback); //of course this won't work, but it gives an idea of what I'm trying to do.

FreeLibrary(hModule);

Sleep(10000); //give us 10 seconds to test it out
return bReturn;
}

Answer 1

Inside your DLL:

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

extern "C" __declspec(dllexport) void InstallMyHook(LRESULT CALLBACK (*MyCallback)(int nCode, WPARAM wParam, LPARAM lParam))
{
   myCallbackRef = MyCallback;
}

Use myCallbackRef with parameters inside KeyboardHook.

In your program
Call

InstallMyHook(MyCallBack);