FIX: Visual C++ Breaks ODBC CLongBinary w/ GlobalReAll Misuse

ID: Q149139

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, version 4.0

SYMPTOMS

Running an application built using the MFC ODBC classes from Visual C++ 4.0 to retrieve CLongBinary data from a database may result in one or both of the following behaviors when performing a recordset move or requery:

Access violations.

Out of memory exceptions.

CAUSE

There is a programming error in the MFC code that can lead to this behavior where GlobalReAlloc is used incorrectly. The return value of GlobalReAlloc is not used, so the global handle embedded in the CLongBinary recordset member variable becomes invalid if GlobalReAlloc moves the virtual memory block. Refer to the MFC source code, Dbrfx.cpp in Mfc\Src, and look at the use of GlobalReAlloc in the CFieldExchange::ReallocLongBinary() function.

RESOLUTION

A new implementation of RFX_LongBinary that avoids this defect in the MFC code is available to assist you in correcting this problem. Simply download the file as described below, run the .exe file to expand the source files, and then incorporate them into your project. Replace all occurrences of RFX_LongBinary with the new RFX_LongBinary_Alloc and rebuild.

The following file is available for download from the Microsoft Software Library:

Alloc.exe

For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base:

Q119591 How to Obtain Microsoft Support Files from Online Services

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 4.1.

Additional query words: kbVC400bug

Keywords : kbfile kbDatabase kbMFC kbODBC kbVC kbVC410fix
Version : 4.0
Platform : NT WINDOWS
Issue type : kbbug