[priority.queue]

# 23 Containers library [[containers]](./#containers)

## 23.6 Container adaptors [[container.adaptors]](container.adaptors#priority.queue)

### 23.6.4 Class template priority_queue [priority.queue]

#### [23.6.4.1](#priqueue.overview) Overview [[priqueue.overview]](priqueue.overview)

[1](#priqueue.overview-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L15993)

Any sequence container with random access iterator and supporting operationsfront(),push_back() andpop_back() can be used to instantiatepriority_queue[.](#priqueue.overview-1.sentence-1)

In particular,<vector> and<deque> can be used[.](#priqueue.overview-1.sentence-2)

Instantiatingpriority_queue also involves supplying a function or function object for making
priority comparisons; the library assumes that the function or function
object defines a [strict weak ordering](alg.sorting "26.8 Sorting and related operations [alg.sorting]")[.](#priqueue.overview-1.sentence-3)

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: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 InputIterator>constexpr priority_queue(InputIterator first, InputIterator last, const Compare& x = Compare()); template<class InputIterator>constexpr priority_queue(InputIterator first, InputIterator last, const Compare& x, const Container&); template<class InputIterator>constexpr priority_queue(InputIterator first, InputIterator last, const Compare& x,
 Container&&); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<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 InputIterator, class Alloc>constexpr priority_queue(InputIterator, InputIterator, const Alloc&); template<class InputIterator, class Alloc>constexpr priority_queue(InputIterator, InputIterator, const Compare&, const Alloc&); template<class InputIterator, class Alloc>constexpr priority_queue(InputIterator, InputIterator, const Compare&, const Container&, const Alloc&); template<class InputIterator, class Alloc>constexpr priority_queue(InputIterator, InputIterator, const Compare&, Container&&, const Alloc&); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<T> R, class Alloc>constexpr priority_queue(from_range_t, R&& rg, const Compare&, const Alloc&); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<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*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<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 InputIterator, class Compare = less<*iter-value-type*<InputIterator>>, class Container = vector<*iter-value-type*<InputIterator>>> priority_queue(InputIterator, InputIterator, Compare = Compare(), Container = Container())-> priority_queue<*iter-value-type*<InputIterator>, Container, Compare>; template<ranges::[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") 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 InputIterator, class Allocator> priority_queue(InputIterator, InputIterator, Allocator)-> priority_queue<*iter-value-type*<InputIterator>,
 vector<*iter-value-type*<InputIterator>, Allocator>,
 less<*iter-value-type*<InputIterator>>>; template<class InputIterator, class Compare, class Allocator> priority_queue(InputIterator, InputIterator, Compare, Allocator)-> priority_queue<*iter-value-type*<InputIterator>,
 vector<*iter-value-type*<InputIterator>, Allocator>, Compare>; template<class InputIterator, class Compare, class Container, class Allocator> priority_queue(InputIterator, InputIterator, Compare, Container, Allocator)-> priority_queue<typename Container::value_type, Container, Compare>; template<ranges::[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") 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](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") 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 providedtemplate<class T, class Container, class Compare, class Alloc>struct uses_allocator<priority_queue<T, Container, Compare>, Alloc>: uses_allocator<Container, Alloc>::type { };}

#### [23.6.4.2](#priqueue.cons) Constructors [[priqueue.cons]](priqueue.cons)

[ð](#lib:priority_queue,constructor)

`constexpr priority_queue(const Compare& x, const Container& y);
constexpr priority_queue(const Compare& x, Container&& y);
`

[1](#priqueue.cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16141)

*Preconditions*: x defines a strict weak ordering ([[alg.sorting]](alg.sorting "26.8 Sorting and related operations"))[.](#priqueue.cons-1.sentence-1)

[2](#priqueue.cons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16145)

*Effects*: Initializescomp withx andc withy (copy constructing or move constructing as appropriate);
callsmake_heap(c.begin(), c.end(), comp)[.](#priqueue.cons-2.sentence-1)

[ð](#lib:priority_queue,constructor_)

`template<class InputIterator>
  constexpr priority_queue(InputIterator first, InputIterator last, const Compare& x = Compare());
`

[3](#priqueue.cons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16163)

*Preconditions*: x defines a strict weak ordering ([[alg.sorting]](alg.sorting "26.8 Sorting and related operations"))[.](#priqueue.cons-3.sentence-1)

[4](#priqueue.cons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16167)

*Effects*: Initializes c withfirst as the first argument andlast as the second argument, and
initializes comp with x;
then calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons-4.sentence-1)

[ð](#lib:priority_queue,constructor__)

`template<class InputIterator>
  constexpr priority_queue(InputIterator first, InputIterator last, const Compare& x,
                           const Container& y);
template<class InputIterator>
  constexpr priority_queue(InputIterator first, InputIterator last, const Compare& x,
                           Container&& y);
`

[5](#priqueue.cons-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16187)

*Preconditions*: x defines a strict weak ordering ([[alg.sorting]](alg.sorting "26.8 Sorting and related operations"))[.](#priqueue.cons-5.sentence-1)

[6](#priqueue.cons-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16191)

*Effects*: Initializescomp withx andc withy (copy constructing or move constructing as appropriate);
callsc.insert(c.end(), first, last);
and finally callsmake_heap(c.begin(), c.end(), comp)[.](#priqueue.cons-6.sentence-1)

[ð](#lib:priority_queue,constructor___)

`template<[container-compatible-range](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<T> R>
  constexpr priority_queue(from_range_t, R&& rg, const Compare& x = Compare());
`

[7](#priqueue.cons-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16211)

*Preconditions*: x defines a strict weak ordering ([[alg.sorting]](alg.sorting "26.8 Sorting and related operations"))[.](#priqueue.cons-7.sentence-1)

[8](#priqueue.cons-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16215)

*Effects*: Initializes comp with x andc with ranges​::​to<Container>(std​::​forward<R>(rg)) and
finally calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons-8.sentence-1)

#### [23.6.4.3](#priqueue.cons.alloc) Constructors with allocators [[priqueue.cons.alloc]](priqueue.cons.alloc)

[1](#priqueue.cons.alloc-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16224)

If uses_allocator_v<container_type, Alloc> is false the constructors in this subclause shall not participate in overload resolution[.](#priqueue.cons.alloc-1.sentence-1)

[ð](#lib:priority_queue,constructor____)

`template<class Alloc> constexpr explicit priority_queue(const Alloc& a);
`

[2](#priqueue.cons.alloc-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16234)

*Effects*: Initializes c with a and value-initializes comp[.](#priqueue.cons.alloc-2.sentence-1)

[ð](#lib:priority_queue,constructor_____)

`template<class Alloc> constexpr priority_queue(const Compare& compare, const Alloc& a);
`

[3](#priqueue.cons.alloc-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16245)

*Effects*: Initializes c with a and initializes comp with compare[.](#priqueue.cons.alloc-3.sentence-1)

[ð](#lib:priority_queue,constructor______)

`template<class Alloc>
  constexpr priority_queue(const Compare& compare, const Container& cont, const Alloc& a);
`

[4](#priqueue.cons.alloc-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16257)

*Effects*: Initializes c with cont as the first argument and a as the second
argument, and initializes comp with compare;
calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-4.sentence-1)

[ð](#lib:priority_queue,constructor_______)

`template<class Alloc>
  constexpr priority_queue(const Compare& compare, Container&& cont, const Alloc& a);
`

[5](#priqueue.cons.alloc-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16271)

*Effects*: Initializes c with std​::​move(cont) as the first argument and a as the second argument, and initializes comp with compare;
calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-5.sentence-1)

[ð](#lib:priority_queue,constructor________)

`template<class Alloc> constexpr priority_queue(const priority_queue& q, const Alloc& a);
`

[6](#priqueue.cons.alloc-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16284)

*Effects*: Initializes c with q.c as the first argument and a as
the second argument, and initializes comp with q.comp[.](#priqueue.cons.alloc-6.sentence-1)

[ð](#lib:priority_queue,constructor_________)

`template<class Alloc> constexpr priority_queue(priority_queue&& q, const Alloc& a);
`

[7](#priqueue.cons.alloc-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16296)

*Effects*: Initializes c with std​::​move(q.c) as the first argument and a as the second argument, and initializes comp with std​::​move(q.comp)[.](#priqueue.cons.alloc-7.sentence-1)

[ð](#lib:priority_queue,constructor__________)

`template<class InputIterator, class Alloc>
  constexpr priority_queue(InputIterator first, InputIterator last, const Alloc& a);
`

[8](#priqueue.cons.alloc-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16309)

*Effects*: Initializes c withfirst as the first argument,last as the second argument, anda as the third argument, and
value-initializes comp;
calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-8.sentence-1)

[ð](#lib:priority_queue,constructor___________)

`template<class InputIterator, class Alloc>
  constexpr priority_queue(InputIterator first, InputIterator last,
                           const Compare& compare, const Alloc& a);
`

[9](#priqueue.cons.alloc-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16327)

*Effects*: Initializes c withfirst as the first argument,last as the second argument, anda as the third argument, and
initializes comp with compare;
calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-9.sentence-1)

[ð](#lib:priority_queue,constructor____________)

`template<class InputIterator, class Alloc>
  constexpr priority_queue(InputIterator first, InputIterator last, const Compare& compare,
                           const Container& cont, const Alloc& a);
`

[10](#priqueue.cons.alloc-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16345)

*Effects*: Initializes c withcont as the first argument and a as the second argument, and
initializes comp with compare;
calls c.insert(c.end(), first, last); and
finally calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-10.sentence-1)

[ð](#lib:priority_queue,constructor_____________)

`template<class InputIterator, class Alloc>
  constexpr priority_queue(InputIterator first, InputIterator last, const Compare& compare,
                           Container&& cont, const Alloc& a);
`

[11](#priqueue.cons.alloc-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16362)

*Effects*: Initializes c withstd​::​move(cont) as the first argument anda as the second argument, and
initializes comp with compare;
calls c.insert(c.end(), first, last); and
finally calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-11.sentence-1)

[ð](#lib:priority_queue,constructor______________)

`template<[container-compatible-range](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<T> R, class Alloc>
  constexpr priority_queue(from_range_t, R&& rg, const Compare& compare, const Alloc& a);
`

[12](#priqueue.cons.alloc-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16379)

*Effects*: Initializes comp with compare andc with ranges​::​to<Container>(std​::​forward<R>(rg), a);
calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-12.sentence-1)

[ð](#lib:priority_queue,constructor_______________)

`template<[container-compatible-range](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<T> R, class Alloc>
  constexpr priority_queue(from_range_t, R&& rg, const Alloc& a);
`

[13](#priqueue.cons.alloc-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16393)

*Effects*: Initializesc with ranges​::​to<Container>(std​::​forward<R>(rg), a) and value-initializes comp;
calls make_heap(c.begin(), c.end(), comp)[.](#priqueue.cons.alloc-13.sentence-1)

#### [23.6.4.4](#priqueue.members) Members [[priqueue.members]](priqueue.members)

[ð](#lib:push,priority_queue)

`constexpr void push(const value_type& x);
`

[1](#priqueue.members-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16409)

*Effects*: As if by:c.push_back(x);
push_heap(c.begin(), c.end(), comp);

[ð](#lib:push,priority_queue_)

`constexpr void push(value_type&& x);
`

[2](#priqueue.members-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16424)

*Effects*: As if by:c.push_back(std::move(x));
push_heap(c.begin(), c.end(), comp);

[ð](#lib:push_range,priority_queue)

`template<[container-compatible-range](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<T> R>
  constexpr void push_range(R&& rg);
`

[3](#priqueue.members-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16440)

*Effects*: Inserts all elements of rg in c viac.append_range(std​::​forward<R>(rg)) if that is a valid expression, orranges​::​copy(rg, back_inserter(c)) otherwise[.](#priqueue.members-3.sentence-1)

Then restores the heap property as if bymake_heap(c.begin(), c.end(), comp)[.](#priqueue.members-3.sentence-2)

[4](#priqueue.members-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16448)

*Postconditions*: is_heap(c.begin(), c.end(), comp) is true[.](#priqueue.members-4.sentence-1)

[ð](#lib:emplace,priority_queue)

`template<class... Args> constexpr void emplace(Args&&... args);
`

[5](#priqueue.members-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16459)

*Effects*: As if by:c.emplace_back(std::forward<Args>(args)...);
push_heap(c.begin(), c.end(), comp);

[ð](#lib:pop,priority_queue)

`constexpr void pop();
`

[6](#priqueue.members-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16474)

*Effects*: As if by:pop_heap(c.begin(), c.end(), comp);
c.pop_back();

#### [23.6.4.5](#priqueue.special) Specialized algorithms [[priqueue.special]](priqueue.special)

[ð](#lib:swap,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)));
`

[1](#priqueue.special-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16493)

*Constraints*: is_swappable_v<Container> is true andis_swappable_v<Compare> is true[.](#priqueue.special-1.sentence-1)

[2](#priqueue.special-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L16498)

*Effects*: As if by x.swap(y)[.](#priqueue.special-2.sentence-1)
