Difference between revisions of "cpp/container/queue"

Revision as of 21:19, 2 August 2024

The std::queue class is a container adaptor that gives the functionality of a queue - specifically, a FIFO (first-in, first-out) data structure.

The class template acts as a wrapper to the underlying container - only a specific set of functions is provided. The queue pushes the elements on the back of the underlying container and pops them from the front.

Template parameters

Member types

Member objects

Member functions

Non-member functions

Helper classes

Notes

Example

#include <cassert>
#include <iostream>
#include <queue>
 
int main()
{
    std::queue<int> q;
 
    q.push(0); // back pushes 0
    q.push(1); // q = 0 1
    q.push(2); // q = 0 1 2
    q.push(3); // q = 0 1 2 3
 
    assert(q.front() == 0);
    assert(q.back() == 3);
    assert(q.size() == 4);
 
    q.pop(); // removes the front element, 0
    assert(q.size() == 3);
 
    // Print and remove all elements. Note that std::queue does not
    // support begin()/end(), so a range-for-loop cannot be used.
    std::cout << "q: ";
    for (; !q.empty(); q.pop())
        std::cout << q.front() << ' ';
    std::cout << '\n';
    assert(q.size() == 0);
}

q: 1 2 3

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

1. ↑ Such as containers similar to std::vector<bool> with additional support of pop_front(). The resolution of this DR
   added support of std::vector<bool> for std::stack and std::priority_queue. The changes involving std::queue
   are for maintaining consistency.

See also