From cppreference.com
template<classT,classContainer=std::vector<T>,classCompare=std::less<typenameContainer::value_type>>classpriority_queue;The
is a
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
.
Working with a priority_queue is similar to managing a
in some random access container, with the benefit of not being able to accidentally invalidate the heap.
All member functions of std::priority_queue are constexpr: it is possible to create and use std::priority_queue objects in the evaluation of a constant expression.
However, defining a constexprstd::priority_queue variable is generally an error, because constant evaluation requires any dynamically allocated storage to be released in the same evaluation, which is usually not the case with std::priority_queue's initializer.
(since C++26)Template parameters
T - The type of the stored elements. The program is ill-formed 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
, and its iterators must satisfy the requirements of
. Additionally, it must provide the following functions with the
: front(), e.g.,
,
push_back(), e.g.,
,
pop_back(), e.g.,
.
The standard containers
(not including
) and
satisfy these requirements.
Compare - A
type providing a strict weak ordering. Note that the
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
.
Member types
Member Definition container_typeContainer
value_compareComparevalue_typeContainer::value_type
size_typeContainer::size_type
referenceContainer::reference
const_referenceContainer::const_reference
Member objects
Member Description Container c
the underlying container
(protected member object)
Compare comp
the comparison function object
(protected member object)Member functions
constructs the priority_queue
(public member function)
destructs the priority_queue
(public member function)
assigns values to the container adaptor
(public member function)
Element access
accesses the top element
(public member function)
Capacity
checks whether the container adaptor is empty
(public member function)
returns the number of elements
(public member function)
Modifiers
inserts element and sorts the underlying container
(public member function)
(C++23)
inserts a range of elements and sorts the underlying container
(public member function)
(C++11)
constructs element in-place and sorts the underlying container
(public member function)
removes the top element
(public member function)
(C++11)
swaps the contents
(public member function)
Non-member functions
Helper classes
Notes
macro ValueStdFeature
(C++23)
construction and insertion for containers
(C++26)Constexpr std::priority_queueExample
Run this code
#include<functional>#include<iostream>#include<queue>#include<string_view>#include<vector>template<typenameT>voidpop_println(std::string_viewrem,T&pq){std::cout<<rem<<": ";for(;!pq.empty();pq.pop())std::cout<<pq.top()<<' ';std::cout<<'\n';}template<typenameT>voidprintln(std::string_viewrem,constT&v){std::cout<<rem<<": ";for(constauto&e:v)std::cout<<e<<' ';std::cout<<'\n';}intmain(){constautodata={1,8,5,6,3,4,0,9,7,2};println("data",data);std::priority_queue<int>max_priority_queue;// Fill the priority queue.for(intn:data)max_priority_queue.push(n);pop_println("max_priority_queue",max_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>>min_priority_queue1(data.begin(),data.end());pop_println("min_priority_queue1",min_priority_queue1);// Second way to define a min priority queue.std::priority_queuemin_priority_queue2(data.begin(),data.end(),std::greater<int>());pop_println("min_priority_queue2",min_priority_queue2);// Using a custom function object to compare elements.struct{booloperator()(constintl,constintr)const{returnl>r;}}customLess;std::priority_queuecustom_priority_queue(data.begin(),data.end(),customLess);pop_println("custom_priority_queue",custom_priority_queue);// Using lambda to compare elements.autocmp=[](intleft,intright){return(left^1)<(right^1);};std::priority_queue<int,std::vector<int>,decltype(cmp)>lambda_priority_queue(cmp);for(intn:data)lambda_priority_queue.push(n);pop_println("lambda_priority_queue",lambda_priority_queue);}Output:
data: 1 8 5 6 3 4 0 9 7 2 max_priority_queue: 9 8 7 6 5 4 3 2 1 0 min_priority_queue1: 0 1 2 3 4 5 6 7 8 9 min_priority_queue2: 0 1 2 3 4 5 6 7 8 9 custom_priority_queue: 0 1 2 3 4 5 6 7 8 9 lambda_priority_queue: 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
C++98 Container could not be std::vector<bool>allowed
C++98 Missing the requirement for Container::value_typeill-formed if T is not the same type as Container::value_type
C++98 priority_queue takes a comparator
but lacked member typedef for it added See also