I'm iterating over a vector and need the index the iterator is currently pointing at. AFAIK this can be done in two ways:
it - vec.begin()
std::distance(vec.begin(), it)
What are the pros and cons of these methods?
Random-Access Iterators: They are the most powerful iterators. They are not limited to moving sequentially, as their name suggests, they can randomly access any element inside the container.
I would prefer it - vec.begin()
precisely for the opposite reason given by Naveen: so it wouldn't compile if you change the vector into a list. If you do this during every iteration, you could easily end up turning an O(n) algorithm into an O(n^2) algorithm.
Another option, if you don't jump around in the container during iteration, would be to keep the index as a second loop counter.
Note: it
is a common name for a container iterator,std::container_type::iterator it;
.
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