FIX: Assertion Fails When Use RFX_Text() w/ SQL_VARCHAR Column

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++ for Windows, versions 1.5, 1.51, 2.0
  • Microsoft Visual C++ 32-bit Edition, version 2.0

SYMPTOMS

An assertion failure occurs when using RFX_Text() with a column of type SQL_VARCHAR that has a column width greater than 255 bytes.

CAUSE

The column width for a column with SQL type of SQL_VARCHAR is usually less than 256 bytes. The ASSERT on line 1747 is verifying that the column width is less than 256 bytes unless the column type is SQL_LONGVARCHAR or SQL_LONGBINARY. However some drivers implement SQL_VARCHAR type columns that allow more than 255 bytes; in which case, the assertion is not valid.

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++ versions 1.52 and 2.1.

RESOLUTION

The problem occurs in the function CFieldExchange::GetColumnType(). Because this function is not virtual, there is no easy workaround.

You could replace the GetColumnType function as well as the RFX_Text() function but that would entail adding all of the RFX_Text() function to your application to take care of a problem occurs only in a _DEBUG build because ASSERTs are removed in release builds.

Instead of re-implementing RFX_Text here are two other approaches:

• Ignore the invalid assertion failure by choosing the Ignore button on the Assertion failed message box. This might not be an option if the assertion failure is raised frequently.



• Modify the assertion in the MFC code. This requires that you rebuild the MFC libraries. For details on rebuilding the MFC Libraries, please see the section titled "How To Build Other Library Versions" in the "Class Library User's Guide." Or read the README.TXT file located in the MFC source directory (the default is: \MSVC\MFC\SRC). To modify the assertion, change the code in the CFieldExchange::GetColumnType function in DBRFX.CPP: From:

  
        ASSERT(dwT <= 255 || nSqlType == SQL_LONGVARBINARY ||
               nSqlType == SQL_LONGVARCHAR); 

  To:

  
        ASSERT(dwT <= 255 || nSqlType == SQL_VARCHAR ||
               nSqlType == SQL_LONGVARBINARY ||
               nSqlType == SQL_LONGVARCHAR); 

Additional query words: 1.50 2.00 2.50 2.51 3.00 ORACLE

Keywords : kbDatabase kbMFC kbODBC kbVC
Version : winnt:
Platform : winnt
Issue type :