std::priority_queue

 

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Adaptors

stack

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priority_queue

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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::push_range (C++23)

priority_queue::emplace (C++11)

priority_queue::pop

priority_queue::swap (C++11)

Non-member functions

swap(std::priority_queue) (C++11)

Helper classes

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

formatter<std::priority_queue> (C++23)

Deduction guides(C++17)

 

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. The behavior is undefined if T is not the same type as Container::value_type.
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 LegacyRandomAccessIterator. Additionally, it must provide the following functions with the usual semantics: front() push_back() pop_back(). The standard containers std::vector (including std::vector<bool>) and std::deque satisfy these requirements.
Compare	-	A Compare type providing a strict weak ordering. Note that the Compare parameter is defined such that it returns true if its first argument comes before its second argument in a weak ordering. But because the priority queue outputs largest elements first, the elements that "come before" are actually output last. That is, the front of the queue contains the "last" element according to the weak ordering imposed by Compare.

Member types

Member type	Definition
container_type	Container
value_compare	Compare
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 container adaptor 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)
push_range (C++23)	inserts a range of elements and sorts the underlying container (public member function)
pop	removes the top element (public member function)
swap (C++11)	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) (C++11)

specializes the std::swap algorithm (function template)

Helper classes

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

specializes the std::uses_allocator type trait (class template specialization)

Deduction guides

(since C++17)

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_containers_ranges	202202L	(C++23)	Ranges construction and insertion for containers

Example

Run this code

#include <concepts>
#include <functional>
#include <iostream>
#include <queue>
#include <ranges>
#include <string_view>
#include <vector>
 
template<typename T>
void print(std::string_view name, T const& q)
{
    std::cout << name << ": \t";
    for (auto const& n : q)
        std::cout << n << ' ';
    std::cout << '\n';
}
 
template<typename Adaptor>
requires (std::ranges::input_range<typename Adaptor::container_type>)
void print(std::string_view name, const Adaptor& adaptor)
{
    struct Printer : Adaptor // to access protected Adaptor::Container c;
    {
        void print(std::string_view name) const { ::print(name, this->c); }
    };
 
    static_cast<Printer const&>(adaptor).print(name);
}
 
int main()
{
    const auto data = {1, 8, 5, 6, 3, 4, 0, 9, 7, 2};
    print("data", data);
 
    std::priority_queue<int> q1; // Max priority queue
    for (int n : data)
        q1.push(n);
 
    print("q1", q1);
 
    // Min priority queue
    // std::greater<int> makes the max priority queue act as a min priority queue
    std::priority_queue<int, std::vector<int>, std::greater<int>>
        minq1(data.begin(), data.end());
 
    print("minq1", minq1);
 
    // Second way to define a min priority queue
    std::priority_queue minq2(data.begin(), data.end(), std::greater<int>());
 
    print("minq2", minq2);
 
    // Using a custom function object to compare elements.
    struct
    {
        bool operator()(const int l, const int r) const { return l > r; }
    } customLess;
    std::priority_queue minq3(data.begin(), data.end(), customLess);
 
    print("minq3", minq3);
 
    // 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)> q5(cmp);
 
    for (int n : data)
        q5.push(n);
 
    print("q5", q5);
}

Output:

data:   1 8 5 6 3 4 0 9 7 2
q1:     9 8 7 6 5 4 3 2 1 0
minq1:  0 1 2 3 4 5 6 7 8 9
minq2:  0 1 2 3 4 5 6 7 8 9
minq3:  0 1 2 3 4 5 6 7 8 9
q5:     8 9 6 7 4 5 2 3 0 1

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 307	C++98	Container could not be std::vector<bool>	allowed
LWG 2684	C++98	priority_queue takes a comparator but lacked member typedef for it	added

See also

vector	dynamic contiguous array (class template)
vector<bool>	space-efficient dynamic bitset (class template specialization)
deque	double-ended queue (class template)