What is the difference between &vector[0] and vector.begin()?

Question

This question is related with item 16 of effective stl book which states that while using vector(lets assume vectorvec) instead of array in a legacy

Answer 1

vec.begin() has type std::vector::iterator. &vec[0] has type pointer to std::vector::value_type. These are not necessarily the same type.

It is possible that a given implementation uses pointers as the iterator implementation for a vector, but this is not guaranteed, and thus you should not rely on that assumption. In fact most implementations do provide a wrapping iterator type.

Regarding your question about pointers being iterators, this is partly true. Pointers do meet the criteria of a random access iterator, but not all iterators are pointers. And there are iterators that do not support the random access behavior of pointers.