Standard library header <queue>

 

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Language support <cfloat> <climits> <compare>(C++20) <contracts>(C++26) <coroutine>(C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint>(C++11) <cstdlib> <exception> <initializer_list>(C++11)    <limits> <new> <source_location>(C++20) <stdfloat>(C++23) <typeinfo> <version>(C++20) Concepts <concepts>(C++20) Diagnostics <cassert> <cerrno> <debugging>(C++26) <stacktrace>(C++23) <stdexcept> <system_error>(C++11) Memory management <memory> <memory_resource>(C++17) <scoped_allocator>(C++11) Metaprogramming <type_traits>(C++11) <ratio>(C++11)

General utilities <any>(C++17) <bitset> <bit>(C++20) <charconv>(C++17) <expected>(C++23) <format>(C++20) <functional> <optional>(C++17) <stdbit.h>(C++26) <tuple>(C++11) <typeindex>(C++11) <utility> <variant>(C++17) Containers <array>(C++11) <deque> <flat_map>(C++23) <flat_set>(C++23) <forward_list>(C++11) <hive>(C++26) <inplace_vector>(C++26)    <list> <map> <mdspan>(C++23) <queue> <set> <span>(C++20) <stack> <unordered_map>(C++11) <unordered_set>(C++11) <vector> Iterators <iterator> Ranges <generator>(C++23) <ranges>(C++20)

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This header is part of the containers library.

Includes
<compare> (C++20)	Three-way comparison operator support
<initializer_list> (C++11)	std::initializer_list class template
Classes
queue	adapts a container to provide queue (FIFO data structure) (class template)
priority_queue	adapts a container to provide priority queue (class template)
std::uses_allocator<std::queue> (C++11)	specializes the std::uses_allocator type trait (class template specialization)
std::uses_allocator<std::priority_queue> (C++11)	specializes the std::uses_allocator type trait (class template specialization)
Functions
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)	lexicographically compares the values of two queues (function template)
std::swap(std::queue) (C++11)	specializes the std::swap algorithm (function template)
std::swap(std::priority_queue) (C++11)	specializes the std::swap algorithm (function template)

Synopsis

#include <compare>#include <initializer_list>   namespace std {// class template queuetemplate<class T, class Container = deque<T>>class queue;   template<class T, class Container>bool operator==(const queue<T, Container>& x, const queue<T, Container>& y);template<class T, class Container>bool operator!=(const queue<T, Container>& x, const queue<T, Container>& y);template<class T, class Container>bool operator<(const queue<T, Container>& x, const queue<T, Container>& y);template<class T, class Container>bool operator>(const queue<T, Container>& x, const queue<T, Container>& y);template<class T, class Container>bool operator<=(const queue<T, Container>& x, const queue<T, Container>& y);template<class T, class Container>bool operator>=(const queue<T, Container>& x, const queue<T, Container>& y);template<class T, three_way_comparable Container> compare_three_way_result_t<Container> operator<=>(const queue<T, Container>& x, const queue<T, Container>& y);   template<class T, class Container>void swap(queue<T, Container>& x, queue<T, Container>& y)noexcept(noexcept(x.swap(y)));template<class T, class Container, class Alloc>struct uses_allocator<queue<T, Container>, Alloc>;   // formatter specialization for queuetemplate<class CharT, class T, formattable<CharT> Container>struct formatter<queue<T, Container>, CharT>;   // class template priority_queuetemplate<class T, class Container = vector<T>, class Compare = less<typename Container::value_type>>class priority_queue;   template<class T, class Container, class Compare>void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y)noexcept(noexcept(x.swap(y)));template<class T, class Container, class Compare, class Alloc>struct uses_allocator<priority_queue<T, Container, Compare>, Alloc>;   // formatter specialization for priority_queuetemplate<class CharT, class T, formattable<CharT> Container, class Compare>struct formatter<priority_queue<T, Container, Compare>, CharT>;}

Class template std::queue

namespace std {template<class T, class Container = deque<T>>class queue {public:using value_type =typename Container::value_type;using reference =typename Container::reference;using const_reference =typename Container::const_reference;using size_type =typename Container::size_type;using container_type = Container;   protected: Container c;   public: queue(): queue(Container()){}explicit queue(const Container&);explicit queue(Container&&);template<class InputIter> queue(InputIter first, InputIter last);template<container-compatible-range<T> R> queue(from_range_t, R&& rg);template<class Alloc>explicit queue(const Alloc&);template<class Alloc> queue(const Container&, const Alloc&);template<class Alloc> queue(Container&&, const Alloc&);template<class Alloc> queue(const queue&, const Alloc&);template<class Alloc> queue(queue&&, const Alloc&);template<class InputIter, class Alloc> queue(InputIter first, InputIter last, const Alloc&);template<container-compatible-range<T> R, class Alloc> queue(from_range_t, R&& rg, const Alloc&);   bool empty()const{return c.empty();} size_type size()const{return c.size();} reference front(){return c.front();} const_reference front()const{return c.front();} reference back(){return c.back();} const_reference back()const{return c.back();}void push(const value_type& x){ c.push_back(x);}void push(value_type&& x){ c.push_back(std::move(x));}template<container-compatible-range<T> R>void push_range(R&& rg);template<class... Args> decltype(auto) emplace(Args&&... args){return c.emplace_back(std::forward<Args>(args)...);}void pop(){ c.pop_front();}void swap(queue& q)noexcept(is_nothrow_swappable_v<Container>){usingstd::swap; swap(c, q.c);}};   template<class Container> queue(Container)-> queue<typename Container::value_type, Container>;   template<class InputIter> queue(InputIter, InputIter)-> queue</*iter-value-type*/<InputIter>>;   template<ranges::input_range R> queue(from_range_t, R&&)-> queue<ranges::range_value_t<R>>;   template<class Container, class Allocator> queue(Container, Allocator)-> queue<typename Container::value_type, Container>;   template<class InputIter, class Allocator> queue(InputIter, InputIter, Allocator)-> queue</*iter-value-type*/<InputIter>, deque</*iter-value-type*/<InputIter>, Allocator>>;   template<ranges::input_range R, class Allocator> queue(from_range_t, R&&, Allocator)-> queue<ranges::range_value_t<R>, deque<ranges::range_value_t<R>, Allocator>>;   template<class T, class Container, class Alloc>struct uses_allocator<queue<T, Container>, Alloc>: uses_allocator<Container, Alloc>::type{};}

Class template std::priority_queue

namespace std {template<class T, class Container = vector<T>, class Compare = less<typename Container::value_type>>class priority_queue {public:using value_type =typename Container::value_type;using reference =typename Container::reference;using const_reference =typename Container::const_reference;using size_type =typename Container::size_type;using container_type = Container;using value_compare = Compare;   protected: Container c; Compare comp;   public: priority_queue(): priority_queue(Compare()){}explicit priority_queue(const Compare& x): priority_queue(x, Container()){} priority_queue(const Compare& x, const Container&); priority_queue(const Compare& x, Container&&);template<class InputIter> priority_queue(InputIter first, InputIter last, const Compare& x = Compare());template<class InputIter> priority_queue(InputIter first, InputIter last, const Compare& x, const Container&);template<class InputIter> priority_queue(InputIter first, InputIter last, const Compare& x, Container&&);template<container-compatible-range<T> R> priority_queue(from_range_t, R&& rg, const Compare& x = Compare());template<class Alloc>explicit priority_queue(const Alloc&);template<class Alloc> priority_queue(const Compare&, const Alloc&);template<class Alloc> priority_queue(const Compare&, const Container&, const Alloc&);template<class Alloc> priority_queue(const Compare&, Container&&, const Alloc&);template<class Alloc> priority_queue(const priority_queue&, const Alloc&);template<class Alloc> priority_queue(priority_queue&&, const Alloc&);template<class InputIter, class Alloc> priority_queue(InputIter, InputIter, const Alloc&);template<class InputIter, class Alloc> priority_queue(InputIter, InputIter, const Compare&, const Alloc&);template<class InputIter, class Alloc> priority_queue(InputIter, InputIter, const Compare&, const Container&, const Alloc&);template<class InputIter, class Alloc> priority_queue(InputIter, InputIter, const Compare&, Container&&, const Alloc&);template<container-compatible-range<T> R, class Alloc> priority_queue(from_range_t, R&& rg, const Compare&, const Alloc&);template<container-compatible-range<T> R, class Alloc> priority_queue(from_range_t, R&& rg, const Alloc&);   bool empty()const{return c.empty();} size_type size()const{return c.size();} const_reference top()const{return c.front();}void push(const value_type& x);void push(value_type&& x);template<container-compatible-range<T> R>void push_range(R&& rg);template<class... Args>void emplace(Args&&... args);void pop();void swap(priority_queue& q)noexcept( is_nothrow_swappable_v<Container>&& is_nothrow_swappable_v<Compare>){usingstd::swap; swap(c, q.c); swap(comp, q.comp);}};   template<class Compare, class Container> priority_queue(Compare, Container)-> priority_queue<typename Container::value_type, Container, Compare>;   template<class InputIter, class Compare = less</*iter-value-type*/<InputIter>>, class Container = vector</*iter-value-type*/<InputIter>>> priority_queue(InputIter, InputIter, Compare = Compare(), Container = Container())-> priority_queue</*iter-value-type*/<InputIter>, Container, Compare>;   template<ranges::input_range R, class Compare = less<ranges::range_value_t<R>>> priority_queue(from_range_t, R&&, Compare = Compare())-> priority_queue<ranges::range_value_t<R>, vector<ranges::range_value_t<R>>, Compare>;   template<class Compare, class Container, class Allocator> priority_queue(Compare, Container, Allocator)-> priority_queue<typename Container::value_type, Container, Compare>;   template<class InputIter, class Allocator> priority_queue(InputIter, InputIter, Allocator)-> priority_queue</*iter-value-type*/<InputIter>, vector</*iter-value-type*/<InputIter>, Allocator>, less</*iter-value-type*/<InputIter>>>;   template<class InputIter, class Compare, class Allocator> priority_queue(InputIter, InputIter, Compare, Allocator)-> priority_queue</*iter-value-type*/<InputIter>, vector</*iter-value-type*/<InputIter>, Allocator>, Compare>;   template<class InputIter, class Compare, class Container, class Allocator> priority_queue(InputIter, InputIter, Compare, Container, Allocator)-> priority_queue<typename Container::value_type, Container, Compare>;   template<ranges::input_range R, class Compare, class Allocator> priority_queue(from_range_t, R&&, Compare, Allocator)-> priority_queue<ranges::range_value_t<R>, vector<ranges::range_value_t<R>, Allocator>, Compare>;   template<ranges::input_range R, class Allocator> priority_queue(from_range_t, R&&, Allocator)-> priority_queue<ranges::range_value_t<R>, vector<ranges::range_value_t<R>, Allocator>>;   // no equality is provided   template<class T, class Container, class Compare, class Alloc>struct uses_allocator<priority_queue<T, Container, Compare>, Alloc>: uses_allocator<Container, Alloc>::type{};}