Re: hash_map not reporting true size when used with hash_comp

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Fri, 28 Dec 2007 08:11:59 -0500

Message-ID:

<#IqJ8MVSIHA.4584@TK2MSFTNGP03.phx.gbl>

"Nilesh" <gajjar.nilesh@gmail.com> wrote in message
news:9ccb13cf-fdfc-46e6-a6fe-80ef6bec3e2a@s19g2000prg.googlegroups.com

I have observed that when we use the hash_comp and define our own
comparison function, hash_map::size() always reports the size of 1,
doesn't matter how many elements we add in the map. We have to use the
hash_comp with user defined comparison function to use the key as
char*.

This just means your comparison function makes all keys compare equal to
each other, so only one is ever stored.

struct eqint
{
bool operator()(int i1, int i2) const
{
if(i1==i2)
return true ;
else
return false ;
}
};

typedef hash_map<int, int, hash_compare<int, eqint>> MYHMAP2;

The second parameter of hash_compare should be a "less than" comparator,
not an "equals to" one.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925