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Q259035: PRB: GetChunk/AppendChunk Methods Are Not Clearly Explained

Article: Q259035
Product(s): Microsoft C Compiler
Version(s): winnt:3.51,3.6
Operating System(s): 
Keyword(s): kbdocfix kbGrpDSVBDB kbDSupport kbDAO360bug
Last Modified: 04-MAY-2001

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The information in this article applies to:

- The DAO SDK, versions 3.51, 3.6 
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SYMPTOMS
========

In the Microsoft Data Access Object (DAO) 3.51 document, the
GetChunk/AppendChunk methods that belong to the Field object are not clearly
explained. For both methods, the variant that holds the data that is being
transferred is said to be of subtype string. This is not true when the database
field is of type dbLongBinary (BLOB). In this case the correct variant subtype
is an array of bytes.

RESOLUTION
==========

Put binary data in arrays of bytes. Never assign arrays of bytes onto strings
unless they have text semantic; that is, each byte represents an ASCII value
that can be converted to a Unicode character.

MORE INFORMATION
================

If you choose a variant of subtype string or a string to store binary data, that
choice can lead to the following two problems if a byte-to-Unicode conversion
occurs:

1. The physical size of the field is twice as big as the original binary data.

2. The conversion is dependent on the current code page for the process (that is
  usually inherited from the system settings). An application may be unable to
  read its data if a different code page is currently selected because the data
  was written. Also, changes to a given code page to add new symbols can lead
  to the same problem.

Additional query words: vbwin SP4 Win98 98

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Keywords          : kbdocfix kbGrpDSVBDB kbDSupport kbDAO360bug 
Technology        : kbAudDeveloper kbDAOsearch kbSDKDAOSearch kbSDKSearch kbSDKDAO360 kbSDKDAO351
Version           : winnt:3.51,3.6
Issue type        : kbprb
Solution Type     : kbfix

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