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 <meta> (C++26) <ratio> (C++11) <type_traits> (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)

Algorithms <algorithm> <numeric> Strings <cctype> <cstring> <cuchar> (C++11) <cwchar> <cwctype> <string_view> (C++17) <string> Text processing <clocale> <codecvt> (C++11/17/26*) <locale> <regex> (C++11) <text_encoding> (C++26)   Numerics <cfenv> (C++11) <cmath> <complex> <linalg> (C++26) <numbers> (C++20) <random> (C++11) <simd> (C++26) <stdckdint.h> (C++26) <valarray> Time <chrono> (C++11) <ctime> C compatibility <ccomplex> (C++11/17/20*) <ciso646> (until C++20) <cstdalign> (C++11/17/20*) <cstdbool> (C++11/17/20*) <ctgmath> (C++11/17/20*)

Input/output <cinttypes> (C++11) <cstdio> <filesystem> (C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print> (C++23) <spanstream> (C++23) <sstream> <streambuf> <strstream> (C++98/26*) <syncstream> (C++20) Concurrency support <atomic> (C++11) <barrier> (C++20) <condition_variable> (C++11) <future> (C++11) <hazard_pointer> (C++26) <latch> (C++20) <mutex> (C++11) <rcu> (C++26) <semaphore> (C++20) <shared_mutex> (C++14) <stdatomic.h> (C++23) <stop_token> (C++20) <thread> (C++11) Execution support <execution> (C++17)

 

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 queue
  template<class T, class Container = deque<T>> class queue;

  template<class T, class Container>
  constexpr bool operator==(const queue<T, Container>& x, const queue<T, Container>& y);
  template<class T, class Container>
  constexpr bool operator!=(const queue<T, Container>& x, const queue<T, Container>& y);
  template<class T, class Container>
  constexpr bool operator<(const queue<T, Container>& x, const queue<T, Container>& y);
  template<class T, class Container>
  constexpr bool operator>(const queue<T, Container>& x, const queue<T, Container>& y);
  template<class T, class Container>
  constexpr bool operator<=(const queue<T, Container>& x, const queue<T, Container>& y);
  template<class T, class Container>
  constexpr bool operator>=(const queue<T, Container>& x, const queue<T, Container>& y);
  template<class T, three_way_comparable Container>
  constexpr compare_three_way_result_t<Container> operator<=>(
    const queue<T, Container>& x, const queue<T, Container>& y);

  template<class T, class Container>
  constexpr 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 queue
  template<class CharT, class T, formattable<CharT> Container>
  struct formatter<queue<T, Container>, CharT>;

  template<class T, class Container>
  constexpr bool enable_nonlocking_formatter_optimization<queue<T, Container>> = false;

  // class template priority_queue
  template<class T,
           class Container = vector<T>,
           class Compare = less<typename Container::value_type>>
  class priority_queue;

  template<class T, class Container, class Compare>
  constexpr 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_queue
  template<class CharT, class T, formattable<CharT> Container, class Compare>
  struct formatter<priority_queue<T, Container, Compare>, CharT>;

  template<class T, class Container, class Compare>
  constexpr bool
    enable_nonlocking_formatter_optimization<priority_queue<T, Container, Compare>> =
      false;
}

Class template std::queue

namespace std {
  template<class T, class Container = deque<T>> class queue
  {
  public:
    using value_type = Container::value_type;
    using reference = Container::reference;
    using const_reference = Container::const_reference;
    using size_type = Container::size_type;
    using container_type = Container;

  protected:
    Container c;

  public:
    constexpr queue()
      : queue(Container())
    {
    }
    constexpr explicit queue(const Container&);
    constexpr explicit queue(Container&&);
    template<class InputIter> constexpr queue(InputIter first, InputIter last);
    template<container-compatible-range<T> R> constexpr queue(from_range_t, R&& rg);
    template<class Alloc> constexpr explicit queue(const Alloc&);
    template<class Alloc> constexpr queue(const Container&, const Alloc&);
    template<class Alloc> constexpr queue(Container&&, const Alloc&);
    template<class Alloc> constexpr queue(const queue&, const Alloc&);
    template<class Alloc> constexpr queue(queue&&, const Alloc&);
    template<class InputIter, class Alloc>
    constexpr queue(InputIter first, InputIter last, const Alloc&);
    template<container-compatible-range<T> R, class Alloc>
    constexpr queue(from_range_t, R&& rg, const Alloc&);

    constexpr bool empty() const { return c.empty(); }
    constexpr size_type size() const { return c.size(); }
    constexpr reference front() { return c.front(); }
    constexpr const_reference front() const { return c.front(); }
    constexpr reference back() { return c.back(); }
    constexpr const_reference back() const { return c.back(); }
    constexpr void push(const value_type& x) { c.push_back(x); }
    constexpr void push(value_type&& x) { c.push_back(std::move(x)); }
    template<container-compatible-range<T> R> constexpr void push_range(R&& rg);
    template<class... Args> constexpr decltype(auto) emplace(Args&&... args)
    {
      return c.emplace_back(std::forward<Args>(args)...);
    }
    constexpr void pop() { c.pop_front(); }
    constexpr void swap(queue& q) noexcept(is_nothrow_swappable_v<Container>)
    {
      using std::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 = Container::value_type;
    using reference = Container::reference;
    using const_reference = Container::const_reference;
    using size_type = Container::size_type;
    using container_type = Container;
    using value_compare = Compare;

  protected:
    Container c;
    Compare comp;

  public:
    constexpr priority_queue()
      : priority_queue(Compare())
    {
    }
    constexpr explicit priority_queue(const Compare& x)
      : priority_queue(x, Container())
    {
    }
    constexpr priority_queue(const Compare& x, const Container&);
    constexpr priority_queue(const Compare& x, Container&&);
    template<class InputIter>
    constexpr priority_queue(InputIter first,
                             InputIter last,
                             const Compare& x = Compare());
    template<class InputIter>
    constexpr priority_queue(InputIter first,
                             InputIter last,
                             const Compare& x,
                             const Container&);
    template<class InputIter>
    constexpr priority_queue(InputIter first,
                             InputIter last,
                             const Compare& x,
                             Container&&);
    template<container-compatible-range<T> R>
    constexpr priority_queue(from_range_t, R&& rg, const Compare& x = Compare());
    template<class Alloc> constexpr explicit priority_queue(const Alloc&);
    template<class Alloc> constexpr priority_queue(const Compare&, const Alloc&);
    template<class Alloc>
    constexpr priority_queue(const Compare&, const Container&, const Alloc&);
    template<class Alloc>
    constexpr priority_queue(const Compare&, Container&&, const Alloc&);
    template<class Alloc> constexpr priority_queue(const priority_queue&, const Alloc&);
    template<class Alloc> constexpr priority_queue(priority_queue&&, const Alloc&);
    template<class InputIter, class Alloc>
    constexpr priority_queue(InputIter, InputIter, const Alloc&);
    template<class InputIter, class Alloc>
    constexpr priority_queue(InputIter, InputIter, const Compare&, const Alloc&);
    template<class InputIter, class Alloc>
    constexpr priority_queue(
      InputIter, InputIter, const Compare&, const Container&, const Alloc&);
    template<class InputIter, class Alloc>
    constexpr priority_queue(
      InputIter, InputIter, const Compare&, Container&&, const Alloc&);
    template<container-compatible-range<T> R, class Alloc>
    constexpr priority_queue(from_range_t, R&& rg, const Compare&, const Alloc&);
    template<container-compatible-range<T> R, class Alloc>
    constexpr priority_queue(from_range_t, R&& rg, const Alloc&);

    constexpr bool empty() const { return c.empty(); }
    constexpr size_type size() const { return c.size(); }
    constexpr const_reference top() const { return c.front(); }
    constexpr void push(const value_type& x);
    constexpr void push(value_type&& x);
    template<container-compatible-range<T> R> constexpr void push_range(R&& rg);
    template<class... Args> constexpr void emplace(Args&&... args);
    constexpr void pop();
    constexpr void swap(priority_queue& q) noexcept(
      is_nothrow_swappable_v<Container>&& is_nothrow_swappable_v<Compare>)
    {
      using std::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
  {};
}