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

ID: Q157876

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++ 32-bit Edition, 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:

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.

Change all RFX_Date() calls in your recordset's DoFieldExchange() to calls to RFX_Date2(), or change all RFX_Text() to RFX_Text2().

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: kbVC420bug kbDSupport crash gpf

Keywords : kbtshoot kbDatabase kbMFC kbODBC kbVC kbVC500fix
Version : winnt:
Platform : winnt
Issue type : kbbug