Question

Is there a reason that the STL does not provide functions to return an iterator into a container via an index?

For example, let’s say I wanted to insert an element into a std::list but at the nth position. It appears that I have to retrieve an iterator via something like begin() and add n to that iterator. I’m thinking it would be easier if I could just get an iterator at the nth position with something like, std::list::get_nth_iterator(n).

I suspect I have misunderstood the principles of the STL. Can anyone help explain?

Thanks
BeeBand

Answer 1

You can use advance() from the <iterator> header:

list<foo>::iterator iter = advance(someFooList.begin(), n);

list<foo>::iterator iter = someFooList.begin();

std::advance( iter, n);

If the iterator supports random access (like vector) it’ll work quite efficiently, if it only supports increasing (or decreasing) the iterator, like list, it’ll work but only as well as can be.