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Q135666: FIX: Assertion Failure in CFieldExchange::GetColumnType()

Article: Q135666
Product(s): Microsoft C Compiler
Version(s): 2.0 2.1 2.2 4.0 4.1 4.2
Operating System(s): 
Keyword(s): kbDatabase kbMFC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420bug kbVC
Last Modified: 02-AUG-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
-------------------------------------------------------------------------------

SYMPTOMS
========

Using the MFC database classes with the Microsoft SQL Server ODBC driver
versions 2.50.0121 or 2.50.0126 may cause an assertion failure after a call to
SQLNumResultCols() in the CFieldExchange::GetColumnType() function.

CAUSE
=====

This error is caused by a bug in the ODBC driver that is exposed when the cursor
library is used, and happens after calling CRecordset::Requery() and then trying
to edit more than one record.

The following code in Dbrfx.cpp produces the assertion:

  #ifdef _DEBUG
    SWORD nResultColumns;
    AFX_SQL_ASYNC(m_prs,
                  ::SQLNumResultCols(m_prs->m_hstmt, &nResultColumns));
    ASSERT(nColumn >= 1 && (long)nColumn <= (long)nResultColumns);
  #endif //_DEBUG

::SQLNumResultCols returns 0 in nResultColumns, which causes an assertion on the
next line. This is due to a bug in the driver which sets the number of columns
in the result set to 0. The subsequent call to ::SQLDescribeCol will also fail
with SQL State S1002 "Invalid Column number" regardless of the column number
specified.

RESOLUTION
==========

To work around this problem, use a dynaset instead of a snapshot or get the
2.65.0240 version of the SQL Server driver that is included with Visual C++
5.0.


STATUS
======

Microsoft has confirmed this to be a bug with the ODBC 2.5 components. This bug
has been fixed in the 2.65.0240 version of the SQL Server driver that is
included with Visual C++ 5.0.

Additional query words: kbVC400bug DBRFX.CPP line 2185 line 2231

======================================================================
Keywords          : kbDatabase kbMFC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420bug kbVC500fix 
Technology        : kbAudDeveloper kbMFC
Version           : 2.0 2.1 2.2 4.0 4.1 4.2
Issue type        : kbbug
Solution Type     : kbfix

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