title: Fastest way to add a deque onto the end of a vector?
body: <p>This question is about speed.</p>
  
  <p>I am using a function in the openCV libraries (in FaceRecognizer class) which requires the input of a vector. I need to build this vector by combining several deque. Are there any faster ways other than iterating through the deque and pushing back each element to the vector? </p>
  
  <p><strong>Some info about the deque</strong>: it is a deque of 15 elements where I continuously push_back and if it has 16+ elements I pop_front. Order matters.</p>
  
  <p>Alternatively I could change the deque's to vectors if that might speed up everything, but from what I understand that will be slow when I delete the first element of the vector when it reaches size 16.</p>