C / C++ / MFC

//==================================================================
// stdafx.h
// User-defined messages.
#define WM_MITSOS	(WM_APP + 14)
#define WM_TAKIS	(WM_APP + 15)
//==================================================================
// CDialogMsg.h
class CDialogMsg : public CDialog
{	DECLARE_DYNAMIC(CDialogMsg)
public:
	CDialogMsg(CWnd* pParent = NULL);   // standard constructor
	virtual ~CDialogMsg();
// Dialog Data
	enum { IDD = IDD_DIALOG_MSG };
	CInvisibleWnd* pWnd;                // the invisible window
// Message Handlers declaration.
DECLARE_MESSAGE_MAP()
public:
	afx_msg void OnBnClickedOk();
	afx_msg void OnBnClickedCancel();
	afx_msg void OnBnClickedButtonCreate();
//=================================================================== 
// CDialogMsg.cpp
// ...after implementing constructor we have handler implementation...
BEGIN_MESSAGE_MAP(CDialogMsg, CDialog)
	ON_BN_CLICKED(IDOK, &CDialogMsg::OnBnClickedOk)
	ON_BN_CLICKED(IDCANCEL, &CDialogMsg::OnBnClickedCancel)
	ON_BN_CLICKED(IDC_BUTTON_CREATE, &CDialogMsg::OnBnClickedButtonCreate)
END_MESSAGE_MAP()

void CDialogMsg::OnBnClickedOk()
{  // Post first message with some ints for parameters
   SendMessage(WM_MITSOS, (WPARAM)1, (LPARAM)3);
}

void CDialogMsg::OnBnClickedCancel()
{  // Post second message with some ints for parameters
   SendMessage(WM_TAKIS, (WPARAM)2, (LPARAM)4);
}

void CDialogMsg::OnBnClickedButtonCreate()
{  // Create the message-only CWnd
   pWnd = new CInvisibleWnd;
}
//==================================================================
// CInvisibleWnd.h
class CInvisibleWnd : public CWnd
{	DECLARE_DYNAMIC(CInvisibleWnd)
public:
	CInvisibleWnd();
	virtual ~CInvisibleWnd();
protected:
	DECLARE_MESSAGE_MAP()
	afx_msg LRESULT OnMitsos(WPARAM w, LPARAM l);
	afx_msg LRESULT OnTakis(WPARAM w, LPARAM l);
};
//==================================================================
// CInvisibleWnd.cpp
// Construction/Creation:
IMPLEMENT_DYNAMIC(CInvisibleWnd, CWnd)

CInvisibleWnd::CInvisibleWnd()
{
CString wnd_class_name = ::AfxRegisterWndClass(NULL);
this->CreateEx(0,wnd_class_name,_T("CMyMessageOnlyWindowClass"),0 ,0 ,0 ,0 ,0 ,HWND_MESSAGE,0);
AfxMessageBox(_T("Invisible Window created!"));
}
// Message Map & Handler implementation
BEGIN_MESSAGE_MAP(CInvisibleWnd, CWnd)
   ON_MESSAGE(WM_MITSOS, &CInvisibleWnd::OnMitsos)
   ON_MESSAGE(WM_TAKIS, &CInvisibleWnd::OnTakis)
END_MESSAGE_MAP()
// CInvisibleWnd message handlers
LRESULT CInvisibleWnd::OnMitsos(WPARAM w, LPARAM l)
{
   AfxMessageBox(_T("Hi Mitsos"));
   return LRESULT(true);
}
LRESULT CInvisibleWnd::OnTakis(WPARAM w, LPARAM l)
{
   AfxMessageBox(_T("Hi Takis"));
   return LRESULT(true);
}