Inserting an RTF string using StreamIn

Step 1: Define the EditStreamCallBack() callback function

One of the arguments passed to the callback function is an application defined value. We will use this value to pass in a CString object's address. The second argument is the address of the buffer where the data is to be written by the function, the third argument specifies the number of bytes requested by the rich edit control. The final argument is pointer to a long value. The callback function should set this value to the number of bytes actually copied to the buffer. If this value is less than the number of bytes requested by the control, then the control assumes that there is no more text available and it will stop calling this function.

We have defined the EditStreamCallBack() function as a file static function. This makes the function local to the file. We can define a function with the same name in another file. We could have defined this function as a class function but it would have had to be a class static function. Note the type CALLBACK. Forgetting to specify this can be cause for major headaches.

If you are a performance freak, you'll notice that this function is not very efficient for long strings. Also, this function modifies the string. You might want to enhance this if it is important to your application. For strings less than about 4KB this function is OK since it gets called only once.

static DWORD CALLBACK EditStreamCallBack(DWORD dwCookie, LPBYTE pbBuff, LONG cb, 
					LONG *pcb)
{
	CString *pstr = (CString *)dwCookie;

	if( pstr->GetLength() < cb )
	{
		*pcb = pstr->GetLength();
		memcpy(pbBuff, (LPCSTR)*pstr, *pcb );
		pstr->Empty();
	}
	else
	{
		*pcb = cb;
		memcpy(pbBuff, (LPCSTR)*pstr, *pcb );
		*pstr = pstr->Right( pstr->GetLength() - cb );
	}
	return 0;
}

Step 2: Call StreamIn() with the right arguments

To build the RTF string, we use a prefix string with the preliminary information such as the font table, font size etc. We append our text to this string and at the end we add the postfix string, that completes the RTF string.

Here's the code snippet that calls the StreamIn() function. Note that in the call to StreamIn(), the first argument is a combination of SF_RTF and SFF_SELECTION. The first flag indicates that the text inserted into the rich edit control contains rich text formatting. The second flag indicates that the control should replace the selection with the inserted text. If you don't specify the SFF_SELECTION flag any previous text in the rich edit control will be cleared out.

The second argument to the function is the EDITSTREAM structure. This structure has three members. The first member is simply a value that is passed on to the callback function we defined. This member will contain the address of our string variable. The second argument is the error code returned by EditStreamCallBack() via the StreamIn() function. The last member is a pointer to EditStreamCallBack() - the callback function.

	CString rtfPrefix, rtfPostfix;
	rtfPrefix = "{\\rtf1\\ansi\\deff0\\deftab720{\\fonttbl{\\f0\\froman "
		"Times New Roman;}}\n{\\colortbl\\red0\\green0\\blue0;}\n"
		"\\deflang1033\\pard\\tx360\\tx720\\tx1080\\tx1440\\tx1800"
		"\\tx2160\\tx2520\\tx2880\\tx3240\\tx3600\\tx3960\\tx4320"
		"\\tx4680\\tx5040\\tx5400\\tx5760\\tx6120"
		"\\tx6480\\plain\\f3\\fs20 ";
	rtfPostfix = "\n\\par }";


	// The rtfString contains the word Bold in bold font.
	CString rtfString = rtfPrefix + "\\b Bold\\b0" + rtfPostfix;

	EDITSTREAM es = {(DWORD)&rtfString, 0, EditStreamCallBack};

	// richEd is the rich edit control
	richEd.StreamIn(SF_RTF | SFF_SELECTION, es);