How to retrieve the element of the container with unique_ptr in c++?

Question

I used vector like this:

int main(void) {
  std::vector<int> queue;
  queue.push_back(5);
  queue.push_back(4);
  if (!queue.empty()) {
    int data = queue.back();
    if (something_happens) {
      queue.pop_back();
    }
  }
}

However, If I use vectors with unique_ptr:

std::vector<unique_ptr<int>> queue;

how to use back()?

Should I pass the ownership to the element of unique_ptr to the caller of back() even if the pop() does not occur?

If I have to pass the ownership, how the container again takes the ownership?

Answer 1

how to use back()?

It depends. If you don't want to transfer the ownership of queue.back(), then you can use reference to accept it

auto&& data = queue.back();

Or you can use std::move to transfer its ownership to the temporary variable

auto data = std::move(queue.back());

If I have to pass the ownership, how the container again takes the ownership?

Similarly, just use std::move to transfer the ownership of data back to queue.back()

queue.back() = std::move(data);