typedef struct _MY_SEND_DATA{	//Data is collected in a call to CollectData(...) from a hook proc
	TCHAR cmdLine[MAX_PATH];
	TCHAR modPath[MAX_PATH];
	TCHAR imgPath[MAX_PATH];
}MY_SEND_DATA, *LPMY_SEND_DATA;

typedef struct _MY_DATA{
	BOOL bRes;		//Set to TRUE if hook processed data
	HOOK hHook;		//Hook handle
	HWND hTgdWnd;		//Handle of target window
	HWND hCtlWnd;		//Main (control) window
	UINT uPrivMessage;	//Private message we trigger hook proc with
}MY_DATA, *LPMY_DATA;

//Global variables (loaded for each instance of DLL)
static MY_SEND_DATA MySendData = {0};
static HINSTANCE hDLLInst = NULL;
static HANDLE hFileMapping = NULL;
static MY_DATA* pMySharedMem = NULL;	//Pointer to shared memory segment


BOOL APIENTRY DllMain(HANDLE hModule, 
                      DWORD  ul_reason_for_call, 
                      LPVOID lpReserved)
{
	switch (ul_reason_for_call)
	{
	case DLL_PROCESS_ATTACH:
		//Called once when this DLL is loaded and each time from SetWindowsHookEx(...)
		//in fnRunHook9x(...)
		hDLLInst = (HINSTANCE)hModule;

		//Open file mapping object
		pMySharedMem = NULL;
		hFileMapping = CreateFileMapping((HANDLE)INVALID_HANDLE_VALUE,
				NULL, PAGE_READWRITE, 0, sizeof(MY_DATA), _T("Name_My_File_Mapping_123"));
		if(hFileMapping)
		{
			//Map file into virtual memory
			pMySharedMem = (MY_MESSAGE_DATA1*)
				MapViewOfFile(hFileMapping, FILE_MAP_ALL_ACCESS, 0, 0, sizeof(MY_DATA));
		}
		break;


	case DLL_PROCESS_DETACH:
		//Uninitialization of DLL
		if(pMySharedMem)
			UnmapViewOfFile(pMySharedMem);
		if(hFileMapping)
			CloseHandle(hFileMapping);
		break;
	}

    return TRUE;
}

WINIDHOOK_API BOOL fnRunHook9x(HWND hWndCaller, HWND hWndTarget)
{
	//EXPORTED -- called from the main (control) app
	//Installs and runs hook on Win9x system
	//(Sends data back in WM_COPYDATA message to hWndCaller window)
	//RETURN: - TRUE if success

	//Check if we have shared mem and it's accessible
	if(!pMySharedMem)
		return FALSE;
	if(IsBadReadPtr(pMySharedMem, sizeof(MY_DATA)) ||
		IsBadWritePtr(pMySharedMem, sizeof(MY_DATA)))
		return FALSE;

	//Get private message
	UINT uPrivateMsg = RegisterWindowMessage("My_Private_message_123");

	//Set up shared memory data
	pMySharedMem->bRes = FALSE;
	pMySharedMem->hTgdWnd = hWndTarget;
	pMySharedMem->hCtlWnd = hWndCaller;
	pMySharedMem->uPrivMessage = uPrivateMsg;

	//Set hook
	//(I'm using WH_CALLWNDPROCRET because of the way WH_CALLWNDPROC is called on Win9x:
	//See more details here: http://msdn.microsoft.com/library/de...allwndproc.asp)
	pMySharedMem->hHook = SetWindowsHookEx(WH_CALLWNDPROCRET, CallMyWndProc9x, hDLLInst, 
		GetWindowThreadProcessId(hWndTarget, NULL));

	if(!pMySharedMem->hHook)
		return FALSE;

	//Trigger hook with a message
	DWORD nMesRes;
	SendMessageTimeout(hWndTarget, uPrivateMsg, 0, 0,
		SMTO_ABORTIFHUNG | SMTO_NORMAL, 100, &nMesRes);

	//Check results
	BOOL bResult = pMySharedMem->bRes ? TRUE : FALSE;

	//Remove hook
	bResult &= UnhookWindowsHookEx(pMySharedMem->hHook);

	return bResult;
}


LRESULT CALLBACK CallMyWndProc9x(int nCode, WPARAM wParam, LPARAM lParam)
{
	//Hook callback procedure
	if(pMySharedMem)
	{
		//Only if we have pointer to shared memory
		CWPSTRUCT* pCwp = (CWPSTRUCT*)lParam;
		if(nCode == HC_ACTION)
		{
			if(pCwp)
				if(pCwp->message == pMySharedMem->uPrivMessage)
				{
					//Our hook -> Run data collecting routine
					CollectData(pMySharedMem);
					return 0;
				}
		}

		//Otherwise call next hook
		return CallNextHookEx(pMySharedMem->hHook, nCode, wParam, lParam);
	}
	else
	{
		//Lost shared memory
		ASSERT(NULL);
		return 0;
	}
}

void CollectData(MY_DATA* pSharedMem)
{
	//Collect data and send it back to the main app
	if(pSharedMem)
	{
		//Check if data is accessible in Shared mem
		if(IsBadReadPtr(pSharedMem, sizeof(MY_DATA)) ||
			IsBadWritePtr(&pSharedMem->bRes, sizeof(pSharedMem->bRes)))
			return;

		HWND hTrgWnd = pSharedMem->hTgdWnd;
		HWND hClrWnd = pSharedMem->hCtlWnd;

		//Get command line params
		LPTSTR pCmdLine = GetCommandLine();
		lstrcpyn(MySendData.cmdLine, pCmdLine ? pCmdLine : _T(""), MAX_PATH);

		//Get module path
		GetModuleFileName((HMODULE)GetClassLongPtr(hTrgWnd, GCLP_HMODULE), MySendData.modPath, MAX_PATH);

		//Get image path
		if(GetModuleFileName(NULL, MySendData.imgPath, MAX_PATH) == 0)
			MySendData.imgPath[0] = _T('\0');

		//Send data back
		COPYDATASTRUCT cds;
		cds.lpData = &MySendData;
		cds.dwData = 0x123;	//ID of the message
		cds.cbData = sizeof(MySendData);
		::SendMessage(hClrWnd, WM_COPYDATA, (WPARAM)hTrgWnd, (LPARAM)&cds);

		//Report success
		pSharedMem->bRes = TRUE;
	}
}