Article: Q156135
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s):
Keyword(s): kbDatabase kbMFC kbODBC kbVC kbVC500fix
Last Modified: 30-JUL-2001
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The information in this article applies to:
- The Microsoft Foundation Classes (MFC), included with:
- *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 4.2, 4.2b
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SYMPTOMS
========
CRecordset::m_lCurrentRecord does not correctly decrement when
CRecordset::MovePrev() is invoked.
CAUSE
=====
CRecordset::m_lCurrentRecord tracks the absolute position of a record within a
recordset. It is modified using a value passed to the CRecordset::Move() method.
The CRecordset::MovePrev() method incorrectly increments the value of
m_lCurrentRecord instead of decrementing it.
The source for CRecordset::MovePrev(), from Afxdb.inl, line 83-84 is shown
below:
_AFXDBCORE_INLINE void CRecordset::MovePrev()
{ ASSERT(IsOpen()); Move(1, SQL_FETCH_PRIOR); }
The value should be as follows:
_AFXDBCORE_INLINE void CRecordset::MovePrev()
{ ASSERT(IsOpen()); Move(-1, SQL_FETCH_PRIOR); }
However, since CRecordset::MovePrev() is not virtual, it is not possible to
correctly override this method.
WORKAROUND
==========
The solution is to override the CRecordset::SetRowsetCurrencyStatus() so that it
properly decrements the m_lCurrentRecord member for a MovePrev() call. This is
done in the switch statement for wFetchType == SQL_FETCH_PRIOR as shown in the
sample code below.
STATUS
======
Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been fixed in Visual C++ version 5.0.
MORE INFORMATION
================
The use of CRecordsetStatus should be restricted to information display, and
should not be relied on in a robust environment. m_lCurrentRecord is not
relational, and is not be accurate in a multi-user environment. A better
approach is to use bookmarks, which are more persistent. See the following
methods:
CRecordset::SetBookmark()
CRecordset::GetBookmark()
Use of some methods may cause the bookmark to be invalidated. To determine when a
bookmark is persistent and when it is not, see the following method:
CRecordset::GetBookmarkPersistence()
The workaround presented below, however, ensures that
CRecordset::m_lCurrentRecord is as accurate as possible.
Sample Code
-----------
extern void AFXAPI AfxSetCurrentRecord(long* plCurrentRecord,
long nRows, RETCODE nRetCode);
extern void AFXAPI AfxSetRecordCount(long* plRecordCount,
long lCurrentRecord, long nRows, BOOL bEOFSeen, RETCODE nRetCode);
void CMyRecSet::SetRowsetCurrencyStatus(RETCODE nRetCode,
UWORD wFetchType, long nRows, DWORD dwRowsFetched)
{
// dwRowsFetched is not used, avoid warning with dummy call
dwRowsFetched = 0;
int nDirection;
// Set the fetch direction
switch (wFetchType)
{
case SQL_FETCH_FIRST:
nDirection = 1;
if (nRetCode == SQL_NO_DATA_FOUND)
{
m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED;
m_lRecordCount = 0;
}
else
m_lCurrentRecord = 0;
break;
case SQL_FETCH_NEXT:
nDirection = 1;
AfxSetCurrentRecord(&m_lCurrentRecord, nRows, nRetCode);
AfxSetRecordCount(&m_lRecordCount, m_lCurrentRecord, 1,
m_bEOFSeen, nRetCode);
// This is the only way to know you've hit the end (m_bEOFSeen)
if (!m_bEOFSeen && nRetCode == SQL_NO_DATA_FOUND
&& m_lRecordCount == m_lCurrentRecord + 1)
m_bEOFSeen = TRUE;
break;
case SQL_FETCH_LAST:
nDirection = -1;
if (nRetCode == SQL_NO_DATA_FOUND)
{
m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED;
m_lRecordCount = 0;
}
else if (m_bEOFSeen)
m_lCurrentRecord = m_lRecordCount - 1;
else
m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED;
break;
case SQL_FETCH_PRIOR:
nDirection = -1;
AfxSetCurrentRecord(&m_lCurrentRecord, -1, nRetCode);
break;
case SQL_FETCH_RELATIVE:
nDirection = nRows;
AfxSetCurrentRecord(&m_lCurrentRecord, nRows, nRetCode);
AfxSetRecordCount(&m_lRecordCount, m_lCurrentRecord, 1,
m_bEOFSeen, nRetCode);
break;
case SQL_FETCH_ABSOLUTE:
nDirection = nRows;
if (nRetCode != SQL_NO_DATA_FOUND)
{
if (nRows > 0)
m_lCurrentRecord = nRows - 1;
else if (m_bEOFSeen)
m_lCurrentRecord = m_lRecordCount + nRows;
else
m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED;
}
else
m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED;
AfxSetRecordCount(&m_lRecordCount, m_lCurrentRecord, 1,
m_bEOFSeen, nRetCode);
break;
case SQL_FETCH_BOOKMARK:
nDirection = 0;
m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED;
break;
}
// Set the BOF/EOF flags
if (nRetCode == SQL_NO_DATA_FOUND)
{
if (wFetchType == SQL_FETCH_FIRST
|| wFetchType == SQL_FETCH_LAST
|| wFetchType == SQL_FETCH_BOOKMARK)
{
// If MoveFirst/MoveLast fails, result set is empty
// If SetBookmark fails, currency undefined
m_bEOF = m_bBOF = TRUE;
}
else
{
m_bEOF = nDirection >= 0 ? TRUE : FALSE;
m_bBOF = !m_bEOF;
}
}
else
{
m_bEOF = m_bBOF = FALSE;
}
}
Additional query words: kbVC420bug
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Keywords : kbDatabase kbMFC kbODBC kbVC kbVC500fix
Technology : kbAudDeveloper kbMFC
Version : winnt:
Issue type : kbbug
Solution Type : kbfix
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