Re: stl::map iterator

From:

=?ISO-8859-1?Q?=D6=F6_Tiib?= <ootiib@hot.ee>

Newsgroups:

comp.lang.c++

Date:

Sun, 30 Jun 2013 20:54:56 -0700 (PDT)

Message-ID:

<fdd7c614-2d87-4873-a884-1d78ef8cfb80@googlegroups.com>

On Monday, 1 July 2013 05:30:05 UTC+3, HungryGoat wrote:

Hi, I found this code in "The C++ Standard Library" book by Nikolai.

template <class Cont>
inline bool replace_key (Cont& c,
                         const typename Cont::key_type& old_key,
                         const typename Cont::key_type& new_key)
{
    typename Cont::iterator pos;
    pos = c.find(old_key);
    if (pos != c.end()) {
        //insert new element with value of old element
        c.insert(typename Cont::value_type(new_key,
        pos->second));

        //remove old element
        c.erase(pos);
        return true;
    }
    else {
        //key not found
        return false;
    }
}

My question is, in the call to c.erase(pos), aren't there chances that
pos is invalidated by the previous call to insert?

No. std::map<4>::insert may not invalidate any iterators.

I am under the impression that insert or delete invalidates the iterators.

'delete' is keyword that yes invalidates everything that was pointed at.
I assume you meant 'erase' however. std::map<4>::erase invalidates only
iterators, pointers and references referring to elements removed. All others
must keep validity.

When you want to replace 'std::map' with 'boost::flat_map' then you must be
careful since that thing is based on 'std::vector' and so 'insert'
potentially invalidates all iterators.