FIX: Clipboard Assistant - Paste Fails or Causes Hard Break (148687)


The information in this article applies to:

  • Microsoft Visual C++ 4.0
  • Microsoft Visual C++ 4.1
  • Microsoft Visual C++, 32-bit Enterprise Edition 4.2
  • Microsoft Visual C++, 32-bit Professional Edition 4.2
This article was previously published under Q148687

SYMPTOMS

Code generated by the Clipboard Assistant for a Custom Clipboard Format may cause the following problems:

  • Copying to the clipboard fails to replace what was previously placed on the clipboard.
  • An access violation occurs with a message similar to the following:
    Exception: access violation (0xc0000005),
    Address: 0x5f82cf37
  • An unexpected memory overwrite occurs after several clipboard operations.
  • On the Checked build of Windows NT, a Cut, Copy, or Paste operation causes a hard-coded breakpoint to be encountered and a trace message similar to the following to be generated:
    BASE: GlobalFree called with a locked object.

CAUSE

The first three problems can occur because of the OnEditPaste function generated by the Clipboard Assistant. The code is not correct because it frees the HGLOBAL that it retrieves from the clipboard when doing a paste operation. This memory should not be freed because the Clipboard will free it when necessary. The code also fails to call CloseClipboard for all possible calls to OpenClipboard.

The fourth problem is caused by a separate bug in the CSharedFile::Detach() function. For more details on this problem, please see the following article in the Microsoft Knowledge Base:

148455 CSharedFile::Detach() Does Not Call GlobalUnlock()

RESOLUTION

The sample code in this article shows new versions of the OnEditCopy, OnEditCut, and OnEditPaste functions. You should use this code to replace the versions previously generated by the Clipboard Assistant.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem has been fixed in Visual C++ version 5.0.

MORE INFORMATION

Sample Code to Resolve Problem

   /* Compile options needed: Default AppWizard options  */ 
   void CMyView::OnEditCopy()
   {
   // CG: This block was added by the Clipboard Assistant component
     {
       CSharedFile memFile;
       CArchive ar(&memFile, CArchive::store|CArchive::bNoFlushOnDelete);
       // serialize data to archive object
       DoCutCopyPaste(ar, FALSE);
       ar.Flush();
       HGLOBAL hData = memFile.Detach();
       //Resolution for CSharedFile::Detach() problem
       //Check <WWLINK TYPE="ARTICLE" VALUE="Q148455">Q148455</WWLINK> for current status.
       // _MFC_VER might need to be updated.
       #if _MFC_VER <= 0x0420
         ::GlobalUnlock(hData);
       #endif
       if (OpenClipboard())
       {
         ::SetClipboardData(m_nClipboardFormat, hData);
         CloseClipboard();
       }
       else
         AfxMessageBox(CG_IDS_CANNOT_OPEN_CLIPBOARD);
     }
   }
   void CMyView::OnEditCut()
   {
     // CG: This block was added by the Clipboard Assistant component
     {
       CSharedFile memFile;
       CArchive ar(&memFile, CArchive::store|CArchive::bNoFlushOnDelete);
       // Serialize data to archive object
       DoCutCopyPaste(ar, TRUE);
       ar.Flush();
       HGLOBAL hData = memFile.Detach();
       //Resolution for CSharedFile::Detach() problem
       //Check <WWLINK TYPE="ARTICLE" VALUE="Q148455">Q148455</WWLINK> for current status.
       // _MFC_VER might need to be updated.
       #if _MFC_VER <= 0x0420
         ::GlobalUnlock(hData);
       #endif
       if (OpenClipboard())
       {
         ::SetClipboardData(m_nClipboardFormat, hData);
         CloseClipboard();
       }
       else
         AfxMessageBox(CG_IDS_CANNOT_OPEN_CLIPBOARD);
     }
   }
   void CMyView::OnEditPaste()
   {
     // CG: This block was added by the Clipboard Assistant component
     {
       if (OpenClipboard())
       {
         HANDLE hData = ::GetClipboardData(m_nClipboardFormat);
         if (hData != NULL)
         {
           CSharedFile memFile;
           memFile.SetHandle(hData,FALSE);
           CArchive ar(&memFile, CArchive::load);
           // Serialize data to document
           DoCutCopyPaste(ar, FALSE);
           ar.Close();
           //Resolution for CSharedFile::Detach() problem
           //Check <WWLINK TYPE="ARTICLE" VALUE="Q148455">Q148455</WWLINK> for current status.
           // _MFC_VER might need to be updated.
           #if _MFC_VER <= 0x0420
             ::GlobalUnlock(memFile.Detach());
           #else
             memFile.Detach();
           #endif
         }
         else
           AfxMessageBox(CG_IDS_CANNOT_GET_CLIPBOARD_DATA);
         CloseClipboard();
       }
       else
         AfxMessageBox(CG_IDS_CANNOT_OPEN_CLIPBOARD);
     }
   }
Modification Type:MajorLast Reviewed:12/2/2003
Keywords:kbbug kbcode kbfix kbide kbProgramming KB148687
©2003 Microsoft Corporation. All rights reserved.