Re: need help creating a two dimensional vector that holds pointers of a user defined type

From:

Victor Bazarov <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Wed, 08 Apr 2009 08:35:53 -0400

Message-ID:

<gri5na$g81$1@news.datemas.de>

James Kanze wrote:

On Apr 8, 5:13 am, Victor Bazarov <v.Abaza...@comAcast.net> wrote:

dwightarmyofchampi...@hotmail.com wrote:

[...]

...and in my destructor I have:

for (std::vector<ABC*>::iterator it = vec.begin();
     it != vec.end();
     it++)
{
  delete *it; *it = 0;

I can understand deleting (since you allocated it using
'new'), but why do you care to set it to 0? The vector is
going to be destroyed right after the destructor's body
finishes...

Because technically, leaving a pointer to deleted memory in the
vector is undefined behavior.

Could you substantiate this with anything, please?

> In fact, I think that even the

way he does it is undefined behavior (according to the
standard); you have to null the pointer in the vector *before*
the delete, with something like:

    ABC* p = *it ;
    *it = NULL ;
    delete p ;

In practice, this is one case of undefined behavior I wouldn't
worry about. The standard may say undefined behavior, but his
original code, with or without the "*it = 0", is going to work,
everywhere.

}

V
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