Advanced MFC Programming

Chapter 9. Font
We find out if the left button is held down when the mouse is moving by checking MK_LBUTTON bit of
parameter nFlags. If so, function CGDIDoc::SetCaret(…) is called to set the selection and update the client
window. Function CGDIView::OnLButtonUp(…) is implemented exactly the same except that we don’t need
to check the status of left button here:
void CGDIView::OnLButtonUp(UINT nFlags, CPoint point)
{
CGDIDoc *ptrDoc;
}
ptrDoc=(CGDIDoc *)GetDocument();
if(::GetCursor() == m_hCur)ptrDoc->SetCaret(point);
CScrollView::OnLButtonUp(nFlags, point);
With the above knowledge, it is very easy for us to implement selection by using left/right ARROW
key when SHIFT key is held down. To implement this, we need to check SHIFT key’s status when either
left or right ARROW key is pressed. If it is held, we can update the selection indices and redraw the client
window.
9.9 One Line Text Editor, Step 6: Cut, Copy and Paste
Global Memory
Cut, copy and paste are supported almost by every application. They provide a way to exchange data
among different applications. We must use globally shared data to implement clipboard data transfer. Once
we send some data to the clipboard, it becomes public and can be accessed by all the programs. Any
process in the system can clear the clipboard.
Because of this, we must allocate global memory to store our data in the clipboard. In Windows
programming, the following API functions can be used to manage global memory:
HGLOBAL ::GlobalAlloc(UINT uFlags, DWORD dwBytes);
LPVOID ::GlobalLock(HGLOBAL hMem);
HGLOBAL ::GlobalReAlloc(HGLOBAL hMem, DWORD dwBytes, UINT uFlags);
BOOL ::GlobalUnlock(HGLOBAL hMem);
HGLOBAL ::GlobalFree(HGLOBAL hMem);
Global memory is also managed through using handle. Unlike memory allocated using new key word,
function ::GlobalAlloc(…) returns an HGLOBAL type handle to the allocated memory block if we allocate
non-fixed global memory.
Generally, before accessing a non-fixed block of global memory, we must lock it by calling function
::GlobalLock(…), which will return the address of the memory block. After reading from or writing to this
memory block, we need to call function ::GlobalUnlock(…) to unlock the memory again. We can free a
block of global memory by calling function ::GlobalFree(…) (We can not free a block of memory when it
is being locked).
We can also allocate fixed global memory, in which case the address of the memory will be returned
by function ::GlobalAlloc(…) directly, and we do not need lock or unlock operation in order to access the
memory.
Parameter nFlags of function ::GlobalAlloc(…) specifies how the memory will be allocated. There
are many possible choices. For example, we can make the memory movable or fixed, and fill all the buffers
with zero. The following is a list of some commonly used flags:
Flag
Meaning
GMEM_FIXED Allocate fixed global memory
GMEM_MOVEABLE Allocate movable global memory
GMEM_ZEROINIT Initialize all the buffers to zero
GMEM_SHARE Used for clipboard implementation or DDE
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