On an empty vector, data() can either return a null pointer, or a pointer to some allocated memory with suitable alignment for that type, but there doesn't have

On an empty vector, data() can either return a null pointer, or a pointer to some allocated memory with suitable alignment for that type, but there doesn't have to be a existing object. What is the range [ data(), data() + size() ) anyway? It consists of n + 1 iterators. All but the last one can be dereferenced. You can take one iterator in the range and add or subtract to get another one, as long as you stay in the range. You can subtract iterators to get a signed integer. You can compare iterators with all six operators ==, !=, <, >, <= and >=. For any valid pointer p, null or not, [p, p) is a valid range of length 0. It has one iterator, p, but you can't dereference it. You can add or subtract 0. You can subtract p from itself, getting 0. And you can compare it with itself.