Re: how to use CComVariant data type as key in hash_map?

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.atl
Date:
Tue, 14 Nov 2006 23:26:35 -0500
Message-ID:
<uA$w84GCHHA.3476@TK2MSFTNGP04.phx.gbl>
"thinktwice" <memorialday@gmail.com> wrote in message
news:1163563361.304253.192110@e3g2000cwe.googlegroups.com

stdext::hash_map<CComVariant, long> _map;
std::pair<CComVariant, long> _pair;

_map.insert(_pair);//can't compile , can't convert CComVariant to
_size_t.


You need to write a suitable hash_compare class - one that would provide
comparison and hash function for variants. None is predefined, you need
to roll your own. Something like this:

struct variant_hash_compare :
    public stdext::hash_compare<CComVariant> {

    size_t operator( )( const CComVariant& ?ey ) const {
        // Calculate and return hash value here
    }

    bool operator( )(
            const CComVariant& key1, const CComVariant& key2) const {
        // Return true if key1 should be ordered before key2, false
otherwise
    }
};

Remember that whenever your comparison considers two elements equivalent
(neither is less than the other, that is, !(a < b) and !(b < a) ), your
hash function must return the same value for both.
--
With best wishes,
    Igor Tandetnik

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