<queue> provides std::queue<T> (FIFO) and std::priority_queue<T> (min/max heap). They are container adapters—wrappers around a deque or vector that expose only the queue semantics.

Use queue for FIFO (front end, back end), and priority_queue for keeping elements sorted by a comparator.

This example demonstrates FIFO queuing and priority queue behavior where the largest element is always at the top.

// compile: g++ -std=c++11 -o queueexample queueexample.cpp
// run: ./queueexample
// description: FIFO queue and priority queue
 
#include <queue>
#include <iostream>
 
int main() {
    std::queue<int> fifo;
    fifo.push(1);
    fifo.push(2);
    fifo.push(3);
 
    std::cout << "fifo front: " << fifo.front() << "\n";
    fifo.pop();
    std::cout << "after pop, front: " << fifo.front() << "\n";
 
    std::priority_queue<int> pq;
    pq.push(3);
    pq.push(1);
    pq.push(2);
 
    std::cout << "priority_queue top: " << pq.top() << "\n";
 
    return 0;
}