Re: Problem in deleting entries from Hash_set

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 7 Mar 2009 03:33:13 -0800 (PST)

Message-ID:

<b19a80bb-525c-4dea-810a-b8ad205ec241@l16g2000yqo.googlegroups.com>

On Mar 6, 10:02 pm, Prafulla T <prafulla.tekaw...@gmail.com> wrote:

Is following correct way of deleting entries from stl hashset.
Will it create any memory corruption ?
One of my program uses this way and it is crashing in strange way but
purify or valgrind does not
show up anything. I am suspecting this piece of code as a problem.
Can anyone comment on it ?

    for (hash_set<UserType*>::iterator hashIt = hashSet.begin();
         hashIt != hashSet.end(); hashIt++)
    {
        UserType *pUserType = *hashIt;
        hashIt++;
        delete pUserType;
        pUserType = NULL;
    }

I don't know; it's hard to say without more context. But there
are at least two problems: you're incrementing the iterator
twice, so if the table contains an odd number of entries, you'll
run off the end (into undefined behavior); and you're deleting
what the pointer in the table points to while leaving the
pointer in the table (you only null a local variable which
immediately goes out of scope)---if you do just about anything
with the pointer later, it's undefined behavior.

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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