Q234146: BUG: ATL Consumer Wizard truncates SQL Server Field to TCHAR

Article: Q234146
Product(s): Microsoft C Compiler
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbwizard kbATL210bug kbDatabase kbSQL kbATL300bug kbGrpDSVCDB kbSQLProg
Last Modified: 28-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

The ATL consumer wizard maps DBTYPE_STR fields, such as SQL Server's text
fields, to TCHAR arrays of 1024 bytes instead of an ISequentialStream pointer.
The data for the columns is truncated to 1024 bytes.

CAUSE
=====

This behavior is by design.

RESOLUTION
==========

If data larger than 1024 is expected, you can increase the size of the array in
your accessor class. For example, by default your code may look like the
following:

  TCHAR m_TextColumn[1024];
  ...
  COLUMN_ENTRY(3, m_TextColumn);

Change the 1024 to the desired maximum length of the data.

Another alternative is to use ISequentialStream to retrieve and set the data.
ISequentialStream allows an application to read and write pieces at a time and a
predefined maximum buffer size is not required. You would change the code above
to:

  ISequentialStream * m_TextColumn;
  ...
  BLOB_ENTRY(3, IID_ISequentialStream, STGM_READ,m_TextColumn);

REFERENCES
==========

See Q190958 AOTBLOB for example of how to read and update using an
ISequentialStream pointer.

Additional query words:

======================================================================
Keywords          : kbwizard kbATL210bug kbDatabase kbSQL kbATL300bug kbGrpDSVCDB kbSQLProg 
Technology        : kbVCsearch kbAudDeveloper kbVC600 kbVC32bitSearch
Version           : WINDOWS:6.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.