Q157876: FIX: SetFieldNull() Asserts in DBCORE.CPP Line 4055 or 4062

Article: Q157876
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbDatabase kbMFC kbVC420bug kbVC500fix kbDSupport kbNoUpdate
Last Modified: 04-AUG-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.2 
-------------------------------------------------------------------------------

SYMPTOMS
========

Calling SetFieldNull() for a date or, in UNICODE builds, a text field causes an
assert in DBCORE.CPP at line 4055 or line 4062:

     void CRecordset::SetNullParamStatus(DWORD nParam)
     {
       ASSERT(nParam < m_nParams);                         // <= Line 4055

       m_pbParamFlags[nParam] |= AFX_SQL_FIELD_FLAG_NULL;
     }

     void CRecordset::ClearNullParamStatus(DWORD nParam)
     {
       ASSERT(nParam < m_nParams);                         // <= Line 4062

       m_pbParamFlags[nParam] &= ~AFX_SQL_FIELD_FLAG_NULL;
     }

CAUSE
=====

During Update(), both the RFX_Date() and RFX_Text() functions incorrectly add
the date or unicode text field to the parameter map:

     case CFieldExchange::NameValue:
       ...
       // Fall through

     case CFieldExchange::Value:
       ...
       // Add the member address to the param map
       pFX->m_prs->m_mapParamIndex.SetAt(&value, (void*)nField);

A subsequent call to SetFieldNull() will try to determine whether the field is a
parameter by checking the index returned by GetBoundParamIndex(). An index >=
0 implies that the field is a parameter:

     void CRecordset::SetFieldNull(void* pv, BOOL bNull)
     {
       ...
      int nIndex = GetBoundParamIndex(pv);
       if (nIndex >= 0)
       {
        if (bNull)
           SetNullParamStatus(nIndex);
         else
           ClearNullParamStatus(nIndex);
         return;
       }
       ... // Handle the case where the field is not a parameter
     }

Because the RFX function incorrectly added the field to the parameter map, an
index >= 0 is returned by GetBoundParamIndex(). Because of this,
SetFieldNull() incorrectly calls the function to set or clear the Null parameter
status rather than the Null field status. If the index returned by
GetBoundParamIndex() is less the member variable CRecordset::m_nParams, then the
assert will occur:

     ASSERT(nParam < m_nParams);

RESOLUTION
==========

Create your own RFX_Date() or RFX_Text() function and comment out the line that
adds the field to the parameter map. See the MORE INFORMATION section below for
more for the steps to accomplish this.

STATUS
======

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

MORE INFORMATION
================

The following steps detail one method of making the needed changes in RFX_Date
or RFX_Text:

1. Copy the implementation of RFX_Date() or RFX_Text() (MSDEV\MFC\SRX\DBRFX.CPP)
  into a new .cpp file, and rename the function to something such as
  RFX_Date2() or RFX_Text2(). 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 in your recordset's DoFieldExchange() to calls to
  RFX_Date2(), or change all RFX_Text() to RFX_Text2().

3. In your new RFX_Date2() or RFX_Text2() implementation, comment out the
  following line, which appears under the CFieldExchange::Value case:

     //      pFX->m_prs->m_mapParamIndex.SetAt(&value, (void*)nField);

Additional query words: crash gpf

======================================================================
Keywords          : kbDatabase kbMFC kbVC420bug kbVC500fix kbDSupport kbNoUpdate 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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