Re: Problem with iterators

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 7 Jun 2007 10:01:56 -0400

Message-ID:

<f4934l$abg$1@news.datemas.de>

desktop wrote:

1)

I have this code:

std::list<int> mylist;
mylist.push_back(1);
mylist.push_back(2);
mylist.push_back(3);
mylist.push_back(4);

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();

This causes undefined behaviour. The iterator returned by 'end()' is
non-dereferenceable. You probably want '*myset.rbegin()'.

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.

Whatever you think your program should do, it's all wrong. The code
has undefined behaviour.

2)

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

Wrong. std::list supports bidirectional iterators.

while set supports
bidirectional iterators.

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

Get a copy of the Standard.

V
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