BUG: Error in Requery When Set Null Date Parameter to Not Null

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

SYMPTOMS

When you set a previously Null date parameter to no longer be Null, using either CRecordset::SetParamNull() or CRecordset::SetFieldNull(), it may cause a subsequent call to CRecordset::Requery() to generate the following exception:

Invalid string or buffer length

CAUSE

During a call to CRecordset::Open, no memory is allocated for a Null date field. However, CRecordset::Requery expects the memory to exist.

RESOLUTION

Create a replacement for the RFX_Date function which always allocates memory for the date field. See the MORE INFORMATION section.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

This problem only occurs with the version of RFX_Date that takes a CTime argument.

Steps to Reproduce Behavior

    CMySet rs;
    try
    {
        rs.SetParamNull( 0, TRUE );
        rs.Open( CRecordset::snapshot, "{Call Query1(?)}" );
        rs.m_paramDate = CTime( 1996, 10, 13, 0, 0, 0 );
        rs.SetParamNull( 0, FALSE );
        rs.Requery();
    }
    catch( CDBException* e )
    {
        AfxMessageBox( e->m_strError );
        e->Delete();
    }
    rs.Close(); 

Steps to Replace the RFX_Date Function

1. Copy the implementation of RFX_Date() (DEVSTUDIO\VC\MFC\SRC\DBRFX.CPP) into a new .cpp file, and rename the function to something such as RFX_Date2(). Create a header file for the .cpp file and include that in your recordset .cpp file. Be sure to type:

   
         #include "stdafx.h" 

   at the top of your new .cpp file, and include the .cpp file in your project.



2. Change all RFX_Date() calls for date parameters in your recordset's DoFieldExchange() to calls to RFX_Date2().



3. In your new RFX_Date2() implementation, comment out the following lines, which appear under the CFieldExchange::BindParam case:

   
          if (pFX->m_prs->IsParamStatusNull(nField - 1))
          {
              pts = NULL;
              *plLength = SQL_NULL_DATA;
          }
          else 




4. To reduce the amount of code, you may want to remove all of the cases from the select statement except the case for CFieldExchange::BindParam, and add the following lines to the top of your replacement function:

   
          if( CFieldExchange::BindParam != pFX->m_nOperation ) {
              RFX_Date(pFX, szName, value);
              return;
          } 

Additional query words: kbVC500bug kbVC600bug kbmfc kbdatabase kbodbc

Keywords          : kbVC500bug kbVC600bug 
Version           : 5.0,6.0
Platform          : NT WINDOWS 
Issue type        : 

Last Reviewed: July 30, 1999