Article: Q166756
Product(s): Microsoft C Compiler
Version(s): 5.0,6.0
Operating System(s):
Keyword(s): kbVC500bug kbVC600bug kbDSupportkbbuglist
Last Modified: 11-FEB-2002
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The information in this article applies to:
- The Microsoft Foundation Classes (MFC), used with:
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
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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.
This problem was corrected in Microsoft Visual C++ .NET.
MORE INFORMATION
================
This problem only occurs with the version of RFX_Date that takes a CTime
argument.
Steps to Reproduce Behavior
---------------------------
The following code displays the problem for a predefined query named Query1,
which takes one date parameter:
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
--------------------------------------
The following steps detail one method of making the needed changes in RFX_Date:
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
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Keywords : kbVC500bug kbVC600bug kbDSupport kbbuglist
Technology : kbAudDeveloper kbMFC
Version : :5.0,6.0
Issue type : kbbug
Solution Type : kbfix
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