Turn an iterator into a scalar index?

Question

Is there a way to determine the position of an iterator inside it's container? The "position" I'm looking would take the form of an integer value, that describes how far from the beginning of the container the iterator is.

For example,vector.front() would be 0, and vector.back() would be vector.size() - 1

Answer 1

std::distance:

size_t index = std::distance( vector.begin(), it );

What it does behind the scenes is just it - v.begin() (for random access iterators, such as vector's). Otherwise, it just increments first argument until it reaches the second (which isn't particularly efficient).