Q251023: BUG: CComVariant::operator=(BSTR) Does Not Copy Embedded NULL

Article: Q251023
Product(s): Microsoft C Compiler
Version(s): WINDOWS:2.0,2.1,3.0
Operating System(s): 
Keyword(s): kbATL kbATL200bug kbATL210 kbCOMt kbVC500bug kbVC600bug kbATL300bug kbGrpDSMFCATL
Last Modified: 26-JUN-2001

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The information in this article applies to:

- The Microsoft Active Template Library (ATL), versions 2.0, 2.1, 3.0 
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SYMPTOMS
========

When you assign BSTR to a CComVariant instance using
CComVariant::operator=(BSTR), any characters after an embedded NULL character in
BSTR are not copied.

CAUSE
=====

This is due to the implementation of CComVariant::operator=(BSTR) not accounting
for NULL characters inside BSTR being copied.

RESOLUTION
==========

Instead of using CComVariant::operator=(BSTR) to copy BSTR inside of
CComVariant, use the CComVariant::Copy() function and place BSTR inside of
VARIANT. The following code snippet could be used to replace
CComVariant::operator=(BSTR) if you need to make sure embedded NULL characters
and characters after embedded NULL characters are copied.

  void Function(BSTR bstrValue)
  {
    VARIANT v;
    v.vt = VT_BSTR;
    v.bstrVal = bstrValue;

    CComVariant a;
    a.Copy(&v); //Use this instead of the next line.
    //a = bstrValue; //This would not copy embedded NULLs or chars after NULL.

    //Use variant now to do whatever you need.
  }

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

Additional query words: CComVariant =

======================================================================
Keywords          : kbATL kbATL200bug kbATL210 kbCOMt kbVC500bug kbVC600bug kbATL300bug kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbATLsearch kbATL200 kbATL300 kbATL210
Version           : WINDOWS:2.0,2.1,3.0
Issue type        : kbbug
Solution Type     : kbfix

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