FIX: CComVariant > and < Operators Cause LNK2001 Errors

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This article was previously published under Q191626

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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

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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 >.

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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.

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are 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:

194022 (http://support.microsoft.com/kb/194022/EN-US/ ) INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 (http://support.microsoft.com/kb/194295/EN-US/ ) HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

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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.

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