Re: Last element in a container

From:

cbarron3@ix.netcom.com (Carl Barron)

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 23 Dec 2007 14:16:19 CST

Message-ID:

<1i9joj1.1dgp52b1m0y5pyN%cbarron3@ix.netcom.com>

<pr2345@gmail.com> wrote:

Hi,

I want to get an iterator pointing to the last element of a container,
where the container is any of the standard containers (vector, list,
set, map, etc). For example:

  typedef std::set<int> Container;
  typedef Container::iterator Iter;

  Iter last_element(Container & c)
  {
    if (c.empty())
      return c.end();

    Iter it = c.end();
    return --it;
  }

Is this guaranteed to work? Is it legal to decrement the end iterator
of a container (provided the container is non-empty), and will that
always give the last element?

This requires member functions empty() and end() which I believe all
STL containers have, All the provided containers in the lib as per c++98
are bidirectional but the iterators of additional containers from tr1
are only required to have forward iterators.

  you require
  1) empty() - ok
  2) end() - ok
  3 iterator::operator --(). not guaranteed for unsorted_* containers.

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