Re: Problem with iterators

 James Kanze <>
Fri, 08 Jun 2007 08:25:27 -0000
On Jun 7, 3:39 pm, desktop <> wrote:

I have this code:

        std::list<int> mylist;

        std::list<int>::iterator it_p = mylist.begin();
        std::list<int>::iterator it_q = mylist.end();

        std::set<int> myset(it_p,it_q);

        int first = *myset.begin();
        int second = *myset.end();
        std::cout << "first = " << first << std::endl;
        std::cout << "second = " << second << std::endl;

I copy the elements from the "list" to the "set" with the two
iterators: "it_p" and "it_q". When I print "first" and
"second" I get 1 and 4. But should:

int second = *myset.end();

not return the value of the element *after* the last which is
undefined? I thought that I had to decrement myset.end() by
one to get the value 4.

It's undefined behavior, of course. Just for the record, this
code core dumps with both g++ and VC++, at least in "debug"

Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators while set supports
bidirectional iterators.

But where (have tried) google do I find a list of each iterator that a
container supports?

The Dinkumware site has some very good documentation, try:

James Kanze (GABI Software)
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