Question

Queue and Stack are a structures widely mentioned. However, in C++, for queue you can do it in two ways:

#include <queue>
#include <deque>

but for stack you can only do it like this

#include <stack>

My question is, what’s the difference between queue and deque, why two structures proposed? For stack, any other structure could be included?

Answer 1

Moron/Aryabhatta is correct, but a little more detail may be helpful.

Queue and stack are higher level containers than deque, vector, or list. By this, I mean that you can build a queue or stack out of the lower level containers.

For example:

  std::stack<int, std::deque<int> > s;
  std::queue<double, std::list<double> > q;

Will build a stack of ints using a deque as the underlying container and a queue of doubles using a list as the underlying container.

You can think of s as a restricted deque and q as a restricted list.

All that is necessary is that the lower level container implements the methods needed by the higher level container. These are back(), push_back(), and pop_back() for stack and front(), back(), push_back(), and pop_front() for queue.

See stack and queue for more detail.

With respect to the deque, it is much more than a queue where you can insert at both ends. In particular, it has the random access operator[]. This makes it more like a vector, but a vector where you can insert and delete at the beginning with push_front() and pop_front().

See deque for detail.