std::string::iterator to offset and back

Question

• Can I set an iterator to position 5 in a string via some member or do I have to do a for(i = 0; i < 5; ++i) iterator++;?
• Given an Iterator, how can I convert that to a numeric offset in the string?
• If this is not possible with std::iterators can boost do it?

Iterators <-> Offsets

Answer 1

Can I set an iterator to position 5 in a string via some member

You can use std::advance

std::advance(iterator, 5);

or

iterator += 5;

Given an Iterator, how can I convert that to a numeric offset in the string?

You can use std::distance

std::distance(string.begin(), iterator);

or

iterator - string.begin()

Answer 2

std::string iterators are random access iterators, which define the +operator. You can get a iterator to position 5 with begin(str) + 5. Offset can be computed via std::distance which uses -operator for random access iterators.