Re: Problem in deleting entries from Hash_set

From:

srdgame <srdgame@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 6 Mar 2009 23:51:37 +0000 (UTC)

Message-ID:

<goscu9$3d5$4@news.cn99.com>

??? Fri, 06 Mar 2009 13:02:17 -0800???Prafulla T?????????

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;
    }

Anyway, according to my understanding that you are deleting the UserType
objects but not any item of your hashSet.

And the crash could came from the DOUBLE "hashIt++". As I can image your
code should either in this:
for (hash_set<UserType*>::iterator ptr = hashSet.being(); ptr !=
hashSet.end(); )
{
    UserType* pUserType = *ptr;
    ptr++;
    delete pUserType;
    // pUserType = NULL // you no longer need to set it to NULL,
since this is local pointer.
}
// You have to clear the hashSet
hashSet.clear();

Or in this:
for (hash_set<UserType*>::iterator ptr = hashSet.being(); ptr !=
hashSet.end(); ++ptr)
{
    UserType* pUserType = *ptr;
    // ptr++; // Since you are deleteing the UserType object which
is referenced by ptr, but ptr is still valid after you deleted the
UserType objects.
    delete pUserType;
    // pUserType = NULL // you no longer need to set it to NULL,
since this is local pointer.
}
// You have to clear the hashSet
hashSet.clear();

Yours,
srdgame