std::vector capacity after copying

Question

• Does vector::operator= change vector capacity? If so, how?
• Does vector's copy constructor copy capacity?

I looked through documentation but could not find a specific answer. Is it implementation dependent?

Answer 1

All you're guaranteed is that:

1. The vector has enough capacity to store its elements. (Obviously.)
2. The vector won't get a new capacity until it's current capacity is full.*

So how much extra or little an implementation wants to put is up to the implementation. I think most will make capacity match size, when copying, but it cannot lower capacity. (Because of number 2 above; reallocating while there's enough room is not allowed.)

_{* Mostly. See Charles' comments below.}