FORMATETC for IDataObject::DAdvise Must be Validated

• Microsoft OLE Libraries for Windows and Win32s, version 2.01
• Microsoft OLE Libraries, included with:

      - Microsoft Windows NT, versions 3.5 and 3.51
      - Microsoft Windows 95
  

SUMMARY

Applications implementing IDataObject must validate the FORMATETC structure that is passed to IDataObject::DAdvise(). Some commercial applications, such as Microsoft Excel 5.0, will try to set up an Advise on their own native format before setting up an Advise on the format selected by the user in the Paste Special dialog box while creating a link.

MORE INFORMATION

When validating the FORMATETC structure, the server application needs to allow wildcard Advises to succeed. A Wildcard Advise is an Advise set up by the default link object so that it can properly maintain the time-of-last- change. A Wildcard Advise is requested by passing a FORMATETC with cfFormat = 0, ptd = NULL, dwAspect = -1L, and tymed = -1L. Code to validate the FORMATETC structure might look as follows:

   // if not a Wildcard Advise and the data format is not supported,
   // return failure.

   if( !(pfmtetc->cfFormat == NULL  &&
         pfmtetc->ptd      == NULL  &&
         pfmtetc->dwAspect == -1L   &&
         pfmtetc->lindex   == -1L   &&
         pfmtetc->tymed    == -1L)
      && FAILED(hres = QueryGetData(pfmtetc)) )
      return hres;

   // Now pass on to the Data Advise holder