FIX: Memory Leak when Requerying with a CTime Parameter

ID: Q115035

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++ for Windows, 16-bit edition, version 1.5

SYMPTOMS

When running an MFC application that uses the database classes, the following message may appear in the Output Window of the debugger:


   Detected memory leaks!
   Dumping objects -&gt;
   {45}dbrfx.cpp(1331) : non-object block at $3FF74442, 16 bytes long
   Object dump complete.

The message only occurs when you select a date/time field of a table, use RFX_Date() to map a CTime variable to the field, and call Requery().

CAUSE

Line 1331 in DBRFX.CPP includes the following code:


    // Allocate TIMESTAMP_STRUCT for SQLBindCol
    pFX->m_prs->m_pvFieldProxy[nField-1] = new TIMESTAMP_STRUCT;

This line runs each time date/time fields are bound to CTime recordset variables using the RFX_Date() record field exchange function. When doing a Requery(), the fields of the result set must be rebound to the CRecordset's variables, and thus a Requery() causes the memory leak to occur. The line of code shown above assigns a new value to an element of a pointer array, leaving the previous allocation stranded in memory.

RESOLUTION

To resolve the memory leak, override the virtual Requery() function of CRecordset and delete the elements of the m_pvFieldProxy array. The following code demonstrates what to do:


BOOL CMyAppRecordSet::Requery()
{
    // delete proxies for recordset fields
    if (m_pvFieldProxy != NULL)
    {
        for (UINT nField = 0; nField != m_nFields; nField++)
            delete m_pvFieldProxy[nField];
    }

    return CRecordset::Requery();
}

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 1.51.

Additional query words: ODBC 1.50 2.50


Keywords          : kb16bitonly kbDatabase kbMFC kbODBC kbVC 
Version           : 1.50
Platform          : WINDOWS 
Issue type        :

Last Reviewed: July 27, 1999