std::priority_queue

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

 

std::priority_queue

Member functions

priority_queue::priority_queue

priority_queue::~priority_queue

priority_queue::operator=

Element access

priority_queue::top

Capacity

priority_queue::empty

priority_queue::size

Modifiers

priority_queue::push

priority_queue::emplace

priority_queue::pop

priority_queue::swap

 

Defined in header <queue>
template<     class T,     class Container = std::vector<T>,     class Compare = std::less<typename Container::value_type> > class priority_queue;

A priority queue is a container adaptor that provides constant time lookup of the largest (by default) element, at the expense of logarithmic insertion and extraction.

A user-provided Compare can be supplied to change the ordering, e.g. using std::greater<T> would cause the smallest element to appear as the top().

Working with a priority_queue is similar to managing a heap in some random access container, with the benefit of not being able to accidentally invalidate the heap.

Template parameters

T	-	The type of the stored elements.
Container	-	The type of the underlying container to use to store the elements. The container must satisfy the requirements of SequenceContainer, and its iterators must satisfy the requirements of RandomAccessIterator. Additionally, it must provide the following functions with the usual semantics: front() push_back() pop_back() The standard containers std::vector and std::deque satisfy these requirements.
Compare	-	A Compare type providing a strict weak ordering.

Member types

Member type	Definition
container_type	Container
value_type	Container::value_type
size_type	Container::size_type
reference	Container::reference
const_reference	Container::const_reference

Member functions

(constructor)	constructs the priority_queue (public member function)
(destructor)	destructs the priority_queue (public member function)
operator=	assigns values to the container adaptor (public member function)
Element access
top	accesses the top element (public member function)
Capacity
empty	checks whether the underlying container is empty (public member function)
size	returns the number of elements (public member function)
Modifiers
push	inserts element and sorts the underlying container (public member function)
emplace (C++11)	constructs element in-place and sorts the underlying container (public member function)
pop	removes the top element (public member function)
swap	swaps the contents (public member function)
Member objects
Container c	the underlying container (protected member object)
Compare comp	the comparison function object (protected member object)

Non-member functions

std::swap(std::priority_queue)

specializes the std::swap algorithm (function template)

Helper classes

std::uses_allocator<std::priority_queue> (C++11)

specializes the std::uses_allocator type trait (function template)

Example

Run this code

#include <functional>
#include <queue>
#include <vector>
#include <iostream>
 
template<typename T> void print_queue(T& q) {
    while(!q.empty()) {
        std::cout << q.top() << " ";
        q.pop();
    }
    std::cout << '\n';
}
 
int main() {
    std::priority_queue<int> q;
 
    for(int n : {1,8,5,6,3,4,0,9,7,2})
        q.push(n);
 
    print_queue(q);
 
    std::priority_queue<int, std::vector<int>, std::greater<int> > q2;
 
    for(int n : {1,8,5,6,3,4,0,9,7,2})
        q2.push(n);
 
    print_queue(q2);
 
    // Using lambda to compare elements.
    auto cmp = [](int left, int right) { return (left ^ 1) < (right ^ 1);};
    std::priority_queue<int, std::vector<int>, decltype(cmp)> q3(cmp);
 
    for(int n : {1,8,5,6,3,4,0,9,7,2})
        q3.push(n);
 
    print_queue(q3);
 
}

Output:

9 8 7 6 5 4 3 2 1 0 
0 1 2 3 4 5 6 7 8 9 
8 9 6 7 4 5 2 3 0 1