FIX: CFile Exception: badSeek, OS error information = -1 (128831)

SYMPTOMS

When calling IsFieldDirty() twice, directly or indirectly, the following exception occurs:

CFile exception: badSeek, OS error information = -1.

This simplified example demonstrates how to see the error:

   CSomeRecordset rs;
   rs.Open();
   rs.Edit();
   rs.IsFieldDirty(NULL);
   rs.m_field1="somevalue";
   rs.Update();
   rs.Close();

IsFieldDirty() is called twice -- once explicitly and then indirectly in the Update() call.

CAUSE

The problem lies in the MarkForUpdate() function. Here is the code shown in \MSVC20\MFC\SRC\DBCORE.CPP:

void CRecordset::MarkForUpdate()
{
   ASSERT_VALID(this);
   ASSERT(m_hstmt != SQL_NULL_HSTMT);

   // Must have already stored field values in memfile
   ASSERT(m_pmemfile != NULL);

   CFieldExchange fx(CFieldExchange::MarkForUpdate, this);
   m_pmemfile->SeekToBegin();

   ASSERT(m_par != NULL);
   delete m_par;
   m_par = NULL;
   m_par = new CArchive(m_pmemfile, CArchive::load);
   fx.m_par = m_par;

   DoFieldExchange(&fx);
}

The SeekToBegin() call is made while the CArchive object pointed to by m_par is still attached to the file. The CArchive doesn't know that the memfile's file pointer has been moved by the SeekToBegin() call. When the archive is deleted, its Flush() member function is called. In that function, the archive attempts to move the file pointer back from where it thinks the current file position is to the beginning of the file. Because the current file position is already at the beginning of the file, a bad seek CFileException is thrown.

RESOLUTION

The solution is to move the SeekToBegin() function to a position following the delete of the CArchive that is attached to the file.

To do this, copy four functions (Update(),UpdateInsertDelete(), IsFieldDirty(), and MarkForUpdate()) from DBCORE.CPP to your CRecordset .CPP file. The Update() function is virtual so by copying these functions to your recordset class, you will guarantee that your new (instead of old) MarkForUpdate() function is called.

The only change you need to make to the code is to the MarkForUpdate() function. Place the code that deletes the archive before the call to SeekToBegin() as shown here:

void CSomeRecordset::MarkForUpdate()
{
   ASSERT_VALID(this);
   ASSERT(m_hstmt != SQL_NULL_HSTMT);

   // Must have already stored field values in memfile
   ASSERT(m_pmemfile != NULL);

   ASSERT(m_par != NULL);
   delete m_par;
   m_par = NULL;

   CFieldExchange fx(CFieldExchange::MarkForUpdate, this);
   m_pmemfile->SeekToBegin();

   m_par = new CArchive(m_pmemfile, CArchive::load);
   fx.m_par = m_par;

   DoFieldExchange(&fx);
}

Again, copy the Update(), UpdateInsertDelete(), and IsFieldDirty() functions from the code in DBCORE.CPP to functions of the same name in your new CRecordset-derived class.

FIX: CFile Exception: badSeek, OS error information = -1 (128831)

SYMPTOMS

CAUSE

RESOLUTION

STATUS