All you ever wanted to know about the Clipboard...

Adding clipboard support to a VC++ / MFC application is extremely simple. This article covers the basic steps involved in getting your applictions talking to the clipboard. In it are examples of the following:

• Reading and writing text
• Reading and writing WMF data
• Reading and writing a bitmap
• Setting up and using your own custom format
• Getting notified of clipboard changes
• Pasting data to another app's window

The following source code demonstrates how to place text (contained in the CString "source") onto the clipboard.

CString source; 
//put your text in source

if(OpenClipboard())
{
	HGLOBAL clipbuffer;
	char * buffer;
	EmptyClipboard();
	clipbuffer = GlobalAlloc(GMEM_DDESHARE, source.GetLength()+1);
	buffer = (char*)GlobalLock(clipbuffer);
	strcpy(buffer, LPCSTR(source));
	GlobalUnlock(clipbuffer);
	SetClipboardData(CF_TEXT,clipbuffer);
	CloseClipboard();
}

The source code below demonstrates the converse, how to retrieve text from the clipboard.

char * buffer = NULL;
//open the clipboard

CString fromClipboard;
if ( OpenClipboard() ) 
{
	HANDLE hData = GetClipboardData( CF_TEXT );
	char * buffer = (char*)GlobalLock( hData );
	fromClipboard = buffer;
	GlobalUnlock( hData );
	CloseClipboard();
}

Writing and reading images to and from the clipboard can be very useful, and it is really very easy! The following example writes an enhanced metafile to the clipboard.

if ( OpenClipboard() )
{
	EmptyClipboard();

	//create the metafile DC

	CMetaFileDC * cDC = new CMetaFileDC();
	cDC->CreateEnhanced(GetDC(),NULL,NULL,"the_name");

	//call draw routine here that makes GDI calls int cDC


	//close meta CMetafileDC and get its handle

	HENHMETAFILE handle = cDC->CloseEnhanced();

	//place it on the clipboard

	SetClipboardData(CF_ENHMETAFILE,handle);
	CloseClipboard();

	//delete the dc

	delete cDC;
}

Here is the converse. We get the metafile from the clipboard and draw it into our own client DC (just as a test, really you would want to make a copy).

if ( OpenClipboard() )
{
	//Get the clipboard data

	HENHMETAFILE handle = (HENHMETAFILE)GetClipboardData(CF_ENHMETAFILE);

	//play it into a DC (our own DC in this example)

	CClientDC dc(this);
	CRect client(0,0,200,200);
	dc.PlayMetaFile(handle,client);		

	//close the clipboard

	CloseClipboard();
}

Reading and writing a bitmap is only marginally trickier. The basic idea remains the same. Here is an example of saving a bitmap to the clipboard.

if ( OpenClipboard() )
{
	EmptyClipboard();
	//create some data

	CBitmap * junk = new CBitmap();
	CClientDC cdc(this);
	CDC dc;
	dc.CreateCompatibleDC(&cdc);
	CRect client(0,0,200,200);
	junk->CreateCompatibleBitmap(&cdc,client.Width(),client.Height());
	dc.SelectObject(junk);

	//call draw routine here that makes GDI calls

	DrawImage(&dc,CString("Bitmap"));

	//put the data on the clipboard

	SetClipboardData(CF_BITMAP,junk->m_hObject);
	CloseClipboard();

	//copy has been made on clipboard so we can delete

	delete junk;
}

As with the other examples, here is an example of getting a bitmap from the clipboard. In this simple example we will just Blt it to the cleint DC.

if ( OpenClipboard() )
{

	//Get the clipboard data

	HBITMAP handle = (HBITMAP)GetClipboardData(CF_BITMAP);
	CBitmap * bm = CBitmap::FromHandle(handle);

	CClientDC cdc(this);
	CDC dc;
	dc.CreateCompatibleDC(&cdc);
	dc.SelectObject(bm);
	cdc.BitBlt(0,0,200,200,&dc,0,0,SRCCOPY);

	CloseClipboard();

}

By using the RegisterClipboardFormat() API you can copy and paste any type of data you want. This can be very useful in moving data between your own applications. Let's say we have a structure:

struct MyFormatData
{
	long val1;
	int val2;
};

that we want to move on the clipboard. We can copy as follows:

UINT format = RegisterClipboardFormat("MY_CUSTOM_FORMAT");
if(OpenClipboard())
{
	//make some dummy data

	MyFormatData data;
	data.val1 = 100;
	data.val2 = 200;

	//allocate some global memory

	HGLOBAL clipbuffer;
	EmptyClipboard();
	clipbuffer = GlobalAlloc(GMEM_DDESHARE, sizeof(MyFormatData));
	MyFormatData * buffer = (MyFormatData*)GlobalLock(clipbuffer);

	//put the data into that memory

	*buffer = data;

	//Put it on the clipboard

	GlobalUnlock(clipbuffer);
	SetClipboardData(format,clipbuffer);
	CloseClipboard();
}

To read it back off we do the inverse:

//second call with just get format already registered

UINT format = RegisterClipboardFormat("MY_CUSTOM_FORMAT");
MyFormatData data;
if ( OpenClipboard() ) 
{
	//get the buffer

	HANDLE hData = GetClipboardData(format);
	MyFormatData * buffer = (MyFormatData *)GlobalLock( hData );

	//make a local copy

	data = *buffer;

	GlobalUnlock( hData );
	CloseClipboard();
}

It is very useful to be notified (via a windows message) whenever the clipboard has changed. To do this you use SetClipboardViewer() and then catch WM_DRAWCLIPBOARD

In your initialization code call:
	SetClipboardViewer();  //add us to clipboard change notification chain


In your message map add:
	ON_MESSAGE(WM_DRAWCLIPBOARD, OnClipChange)  //clipboard change notification


Which is declared as:
	afx_msg void OnClipChange();  //clipboard change notification


Finally implement:
void CDetectClipboardChangeDlg::OnClipChange() 
{
	//do something here, for example

	CTime time = CTime::GetCurrentTime();
	SetDlgItemText(IDC_CHANGED_DATE,time.Format("%a, %b %d, %Y -- %H:%M:%S"));

	DisplayClipboardText();
}

One thing that I have found useful is to copy text to the clipboard (see above) and then to "paste" it to ANOTHER application!. I wrote a nice localization app that used a third party language translation package using this technique.

Simply get the handle to the target window and send a "PASTE" to it.

	SendMessage(m_hTextWnd, WM_PASTE, 0, 0);