// My callback procedure that reads the rich edit control contents
// from a file.
static DWORD CALLBACK 
MyStreamOutCallback(DWORD dwCookie, LPBYTE pbBuff, LONG cb, LONG *pcb)
{
   CFile* pFile = (CFile*) dwCookie;

   pFile->Write(pbBuff, cb);
   *pcb = cb;

   return  0 ;
}

// The example code.
   // The pointer to my rich edit control.
   extern CRichEditCtrl* pmyRichEditCtrl;
   // The file to store the contents of the rich edit control.
   CFile cFile(TEXT("myfile.rtf"), CFile::modeCreate|CFile::modeWrite);
   EDITSTREAM es;

   es.dwCookie = (DWORD) &cFile;
   es.pfnCallback = MyStreamOutCallback; 
   pmyRichEditCtrl->StreamOut(SF_RTF, es);