C++ STL Vectors: Get iterator from index?

Question

So, I wrote a bunch of code that accesses elements in an stl vector by index[], but now I need to copy just a chunk of the vector. It looks like vector.insert(pos, fir

Answer 1

way mentioned by @dirkgently ( v.begin() + index ) nice and fast for vectors

but std::advance( v.begin(), index ) most generic way and for random access iterators works constant time too.

EDIT
differences in usage:

std::vector<>::iterator it = ( v.begin() + index );

or

std::vector<>::iterator it = v.begin();
std::advance( it, index );

added after @litb notes.