Is there an equivalent of the at function for iterators?

For example

std::vector example(10, 0);
const auto it = example.cbegin();
const auto it2 = it + 10;
std::cout << *it2 << std::endl; // does not throw

whereas with at

example.at(10); // throws

Is there an equivalent of the at function for iterators?

For example

std::vector example(10, 0);
const auto it = example.cbegin();
const auto it2 = it + 10;
std::cout << *it2 << std::endl; // does not throw

whereas with at

example.at(10); // throws

• c++
• iterator

• 3 There is nothing built in. You are responsible to check the iterator after you modify it. – NathanOliver Commented Feb 2 at 21:41
• 2 Some tool-chains have checking iterators in debug mode, but that's an additional feature and not required. – Richard Critten Commented Feb 2 at 22:08
• @NathanOliver actually, you'd have to check the iterator before modification. After it + 11, for example, any access to the iterator is undefined behavior. Including comparing it with another iterator. You really have to do something like if ( example.end() - it < example.size() ) .... – James Kanze Commented Feb 2 at 22:08

1 Answer 1

Iterators do not have at() member function because it would violate "you only pay for what you use" C++ design principle. In a fully optimized build, a vector iterator is equivalent to a pointer. To support at(), the iterator must carry valid range information - even when at() is not used. There are implementation-specific debug builds with "checked iterators" that carry this extra info and fail an assert in case of invalid iterator use.