Comparing COleVariant objects

Patrice Buriez -- patriceb@businessline.tm.fr
Wednesday, September 04, 1996

Environment: VC++ 4.1, NT 3.51
Version: #define _MFC_VER 0x0410, #define _MFC_BUILD 6038

I have just browsed the MFC source code of the COleVariant class, and I
humbly think there is a potential bug when comparing COleVariant objects of
type VT_ARRAY.

In "msdev\mfc\src\olevar.cpp", line 228, the COleVariant::operator== relies
on the static function CompareSafeArrays() to achieve comparison of VT_ARRAYs.

In the implementation of this static function, lines 891-893 read:
    // Increment the element count
    nTotalElements *=
        (pUBound1[dwIndex] - pLBound1[dwIndex] + 1)/dwSize1;

I cannot figure out the reason for this division by dwSize1 (previously
obtained from SafeArrayGetElemsize()).
May be I'm a fool... but I guess that this division results in an
under-estimated number of elements in the arrays, which then results in
comparing fewer elements than actually present in these arrays.
Consequently, arrays that only differ on the last elements would compare OK...

Any ideas ?

Patrice

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Patrice BURIEZ
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Email:	patriceb@businessline.tm.fr
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Mike Blaszczak -- mikeblas@nwlink.com
Thursday, September 05, 1996

At 07:18 PM 9/4/96 +0200, you wrote:
>Environment: VC++ 4.1, NT 3.51
>Version: #define _MFC_VER 0x0410, #define _MFC_BUILD 6038

>I have just browsed the MFC source code of the COleVariant class, and I
>humbly think there is a potential bug when comparing COleVariant objects of
>type VT_ARRAY.

>In "msdev\mfc\src\olevar.cpp", line 228, the COleVariant::operator== relies
>on the static function CompareSafeArrays() to achieve comparison of VT_ARRAYs.
>
>In the implementation of this static function, lines 891-893 read:
>    // Increment the element count
>    nTotalElements *=
>        (pUBound1[dwIndex] - pLBound1[dwIndex] + 1)/dwSize1;
>
>I cannot figure out the reason for this division by dwSize1 (previously
>obtained from SafeArrayGetElemsize()).

It doesn't seem like MFC 4.2 has that same code.  Maybe the whole algorithm
chagned, maybe only this line changed... I don't have a free moment to compare
the code and reverse engineer what is happening.

.B ekiM
http://www.nwlink.com/~mikeblas/
These words are my own. I do not speak on behalf of Microsoft.

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