title: Difference between std::vector::empty and std::empty
body: <p>To check if a vector <code>v</code> is empty, I can use <a href="https://en.cppreference.com/w/cpp/iterator/empty" rel="noreferrer"><code>std::empty(v)</code></a> or <a href="https://en.cppreference.com/w/cpp/container/vector/empty" rel="noreferrer"><code>v.empty()</code></a>. I looked at the signatures on cppreference, but am lacking the knowledge to make sense of them. How do they relate to each other? Does one implementation call the other?</p>
  <p>I know that one comes from the containers library and the other from the iterators library, but that is about it.</p>