Generic function to flatten a container of containers

Question

I am trying to get a better hold on iterators and generic functions. I thought it would be a useful exercise to write a function that converts container1 < contain

Answer 1

std::accumulate can do it for you. You need to gather up the contents of each of the inside vectors into the outside vector.

vector> v_of_v;
vector v = std::accumulate(
    v_of_v.begin(), v_of_v.end(),
    vector(),
    [](vector a, vector b) {
        a.insert(a.end(), b.begin(), b.end());
        return a;
    });