Q191626: FIX: CComVariant > and < Operators Cause LNK2001 Errors

Article: Q191626
Product(s): Microsoft C Compiler
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): kbservicepack kbnokeyword kbCOMt kbVC600bug kbATL300bug kbVS600sp2 kbVS600SP1 kbVS600sp
Last Modified: 28-JUN-2001

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The information in this article applies to:

- The Microsoft Active Template Library (ATL) 3.0, used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

If you use the "greater than" (>) or "less than" (<) comparison operators
for CComVariant, you receive the following linker error:

  error LNK2001: unresolved external symbol _VarCmp@12

CAUSE
=====

You use VarCmp() to compare two VARIANTS. This function is supposed to take four
arguments. The declaration for VarCmp() in Oleauto.h is incorrect, and it takes
only three arguments. ATL also calls VarCmp() incorrectly with three arguments
in CComVariant::operator < and CComVariant::operator >.

RESOLUTION
==========

In OLEAUTO.H, change the declaration for VarCmp() from:

  STDAPI VarCmp(LPVARIANT pvarLeft, LPVARIANT pvarRight, LCID lcid);

to the following:

  STDAPI VarCmp(LPVARIANT pvarLeft, LPVARIANT pvarRight, LCID lcid,
                   ULONG dwFlags);

In Atlbase.h, change the calls to VarCmp() by passing in a fourth argument of
zero. Change the code from:

  bool operator<(const VARIANT& varSrc) const
  {

     return VarCmp((VARIANT*)this, (VARIANT*)&varSrc,
                   LOCALE_USER_DEFAULT)==VARCMP_LT;

  }
  bool operator>(const VARIANT& varSrc) const
  {

     return VarCmp((VARIANT*)this, (VARIANT*)&varSrc,
                   LOCALE_USER_DEFAULT)==VARCMP_GT;

  }

to the following:

  bool operator<(const VARIANT& varSrc) const
  {

     return VarCmp((VARIANT*)this, (VARIANT*)&varSrc,
                   LOCALE_USER_DEFAULT, 0)==VARCMP_LT;

  }
  bool operator>(const VARIANT& varSrc) const
  {

     return VarCmp((VARIANT*)this, (VARIANT*)&varSrc,
                   LOCALE_USER_DEFAULT, 0)==VARCMP_GT;

  }

You must do a "Rebuild All" to bring in the new changes.

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 Studio 6.0 Service
Pack 3. For more information about Visual Studio service packs, please see the
following articles in the Microsoft Knowledge Base:

Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

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

VarCmp() is implemented only in a newer version of Oleaut32.dll (2.30.4261 or
later). If you use the CComVariant > or < operators, you must distribute
Oleaut32.dll via Vbrun60.exe. For more information, refer to Redist.wri in the
VC98\Redist directory on the Visual C++ CD.

Additional query words:

======================================================================
Keywords          : kbservicepack kbnokeyword kbCOMt kbVC600bug kbATL300bug kbVS600sp2 kbVS600SP1 kbVS600sp3fix kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbATLsearch
Version           : WINDOWS:3.0
Issue type        : kbbug
Solution Type     : kbfix

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

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