C / C++ / MFC

void SomeDLLFunction( void )
{
    CRect rect(1, 2, 3, 4);
    ::PostMessage(HwndOfEXE, MY_MESSAGE, 0, (LPARAM) &rect);
}

void SomeDLLFunction( void )
{
    CRect *rect;

    rect = new CRect(1, 2, 3, 4);
    ::PostMessage(HwndOfEXE, MY_MESSAGE, 0, (LPARAM) rect);
}

BEGIN_MESSAGE_MAP(...)
    //{{AFX_MSG_MAP
    ON_MESSAGE(MY_MESSAGE, OnMyMessage)
    //}}AFX_MSG_MAP
END_MESSAGE_MAP

LRESULT OnMyMessage(WPARAM, LPARAM lParam)
{
    CRect *rect = (CRect *) lParam;
    ...
    delete rect;
}

void mySplitterWnd::OnLButtonDown(...)
{
    CWnd::OnLButtonDown(...);
}

void mySplitterWnd::OnMouseMove(...)
{
    CWnd::OnMouseMove(...);
}

BOOL mySplitterWnd::OnSetCursor(...)
{
    return CWnd::OnSetCursor(...);
}