The std::queue class is a container adapter that gives the programmer the functionality of a queue.
It is a FIFO (first-in, first-out) data structure.
In queue elements are inserted at the back and can only be accessed from the front and the back.

A sample demo program using queue

#include <iostream>
#include <queue>

using namespace std;

int main()
{
            queue <int> q; // declaring a queue which will hold integers
            for ( int i = 0; i < 10; i++) {
                    q.push(i); // adding elements to the queue
            }

            while (!q.empty()) {
                    cout << "Element at front in queue " << q.front();
                    cout << " " << "Size of queue : " << q.size() << endl;
                    q.pop(); //this will remove element from the front
            }

            return 0;
}

The output of the following program :

Element at front in queue 0 Size of queue : 10
Element at front in queue 1 Size of queue : 9
Element at front in queue 2 Size of queue : 8
Element at front in queue 3 Size of queue : 7
Element at front in queue 4 Size of queue : 6
Element at front in queue 5 Size of queue : 5
Element at front in queue 6 Size of queue : 4
Element at front in queue 7 Size of queue : 3
Element at front in queue 8 Size of queue : 2
Element at front in queue 9 Size of queue : 1

Member functions

Element access
front
back

Capacity
empty
size

Modifiers
push
emplace
pop
swap

Queue has many real life implementation. For e.g. Circular queue is used in Round Robin Scheduling algorithm which allocates resources to the cpu/processes.