std::priority_queue<T,Container,Compare>::priority_queue

`priority_queue() : priority_queue(Compare(), Container()) {}`	(1)	(since C++11)
`explicit priority_queue( const Compare& compare ) : priority_queue(compare, Container()) {}`	(2)	(since C++11)

	(3)
`explicit priority_queue( const Compare& compare = Compare(), const Container& cont = Container() );`			(until C++11)
`priority_queue( const Compare& compare, const Container& cont );`			(since C++11)

`priority_queue( const Compare& compare, Container&& cont );`		(4)	(since C++11)
`priority_queue( const priority_queue& other );`		(5)
`priority_queue( priority_queue&& other );`		(6)	(since C++11)
`template< class InputIt > priority_queue( InputIt first, InputIt last, const Compare& compare = Compare() );`		(7)	(since C++11)

		(8)
`template< class InputIt > priority_queue( InputIt first, InputIt last, const Compare& compare = Compare(), const Container& cont = Container() );`				(until C++11)
`template< class InputIt > priority_queue( InputIt first, InputIt last, const Compare& compare, const Container& cont );`				(since C++11)

`template< class InputIt > priority_queue( InputIt first, InputIt last, const Compare& compare, Container&& cont );`			(9)	(since C++11)
`template< class Alloc > explicit priority_queue( const Alloc& alloc );`			(10)	(since C++11)
`template< class Alloc > priority_queue( const Compare& compare, const Alloc& alloc );`			(11)	(since C++11)
`template< class Alloc > priority_queue( const Compare& compare, const Container& cont, const Alloc& alloc );`			(12)	(since C++11)
`template< class Alloc > priority_queue( const Compare& compare, Container&& cont, const Alloc& alloc );`			(13)	(since C++11)
`template< class Alloc > priority_queue( const priority_queue& other, const Alloc& alloc );`			(14)	(since C++11)
`template< class Alloc > priority_queue( priority_queue&& other, const Alloc& alloc );`			(15)	(since C++11)
`template< class InputIt, class Alloc > priority_queue( InputIt first, InputIt last, const Alloc& alloc );`			(16)	(since C++11)
`template< class InputIt, class Alloc > priority_queue( InputIt first, InputIt last, const Compare& compare, const Alloc& alloc );`			(17)	(since C++11)
`template< class InputIt, class Alloc > priority_queue( InputIt first, InputIt last, const Compare& compare, const Container& cont, const Alloc& alloc );`			(18)	(since C++11)
`template< class InputIt, class Alloc > priority_queue( InputIt first, InputIt last, const Compare& compare, Container&& cont, const Alloc& alloc );`			(19)	(since C++11)
`template< container-compatible-range<T> R > priority_queue( std::from_range_t, R&& rg, const Compare& compare = Compare() );`			(20)	(since C++23)
`template< container-compatible-range<T> R, class Alloc > priority_queue( std::from_range_t, R&& rg, const Compare& compare, const Alloc& alloc );`			(21)	(since C++23)
`template< container-compatible-range<T> R, class Alloc > priority_queue( std::from_range_t, R&& rg, const Alloc& alloc );`			(22)	(since C++23)

Constructs new underlying container of the container adaptor from a variety of data sources.

1) Default constructor. Value-initializes the comparator and the underlying container.

2) Copy-constructs the comparison functor comp with the contents of compare. Value-initializes the underlying container c.

3) Copy-constructs the underlying container c with the contents of cont. Copy-constructs the comparison functor comp with the contents of compare. Calls std::make_heap(c.begin(), c.end(), comp). This is also the default constructor.(until C++11)

4) Move-constructs the underlying container c with std::move(cont). Copy-constructs the comparison functor comp with compare. Calls std::make_heap(c.begin(), c.end(), comp).

5) Copy constructor. The underlying container is copy-constructed with other.c. The comparison functor is copy-constructed with other.comp. (implicitly declared)

6) Move constructor. The underlying container is constructed with std::move(other.c). The comparison functor is constructed with std::move(other.comp). (implicitly declared)

7-9) Iterator-pair constructors. These overloads participate in overload resolution only if InputIt satisfies LegacyInputIterator.

7) Constructs c as if by c(first, last) and comp from compare. Then calls std::make_heap(c.begin(), c.end(), comp);.

8) Copy-constructs c from cont and comp from compare. Then calls c.insert(c.end(), first, last);, and then calls std::make_heap(c.begin(), c.end(), comp);.

9) Move-constructs c from std::move(cont) and copy-constructs comp from compare. Then calls c.insert(c.end(), first, last);, and then calls std::make_heap(c.begin(), c.end(), comp);.

10-15) Allocator-extended constructors. These overloads participate in overload resolution only if std::uses_allocator<container_type, Alloc>::value is true, that is, if the underlying container is an allocator-aware container (true for all standard library containers).

10) Constructs the underlying container using alloc as allocator. Effectively calls c(alloc). comp is value-initialized.

11) Constructs the underlying container using alloc as allocator. Effectively calls c(alloc). Copy-constructs comp from compare.

12) Constructs the underlying container with the contents of cont and using alloc as allocator, as if by c(cont, alloc). Copy-constructs comp from compare. Then calls std::make_heap(c.begin(), c.end(), comp).

13) Constructs the underlying container with the contents of cont using move semantics while using alloc as allocator, as if by c(std::move(cont), alloc). Copy-constructs comp from compare. Then calls std::make_heap(c.begin(), c.end(), comp).

14) Constructs the underlying container with the contents of other.c and using alloc as allocator. Effectively calls c(other.c, alloc). Copy-constructs comp from other.comp.

15) Constructs the underlying container with the contents of other using move semantics while utilizing alloc as allocator. Effectively calls c(std::move(other.c), alloc). Move-constructs comp from other.comp.

16-19) Allocator-extended iterator-pair constructors. Same as (7-9), except that alloc is used for constructing the underlying container. These overloads participate in overload resolution only if std::uses_allocator<container_type, Alloc>::value is true and InputIt satisfies LegacyInputIterator.

20) Initializes comp with compare and c with ranges::to<Container>(std::forward<R>(rg)). Then calls std::make_heap(c.begin(), c.end(), comp).

21) Initializes comp with compare and c with ranges::to<Container>(std::forward<R>(rg), alloc). Then calls std::make_heap(c.begin(), c.end(), comp).

22) Initializes c with ranges::to<Container>(std::forward<R>(rg), alloc). Then calls std::make_heap(c.begin(), c.end(), comp).

Note that how an implementation checks whether a type satisfies LegacyInputIterator is unspecified, except that integral types are required to be rejected.

Parameters

alloc	-	allocator to use for all memory allocations of the underlying container
other	-	another container adaptor to be used as source to initialize the underlying container
cont	-	container to be used as source to initialize the underlying container
compare	-	the comparison function object to initialize the underlying comparison functor
first, last	-	the pair of iterators defining the range of elements to initialize with
rg	-	a container compatible range, that is, an `input_range` whose elements are convertible to `T`
Type requirements
- `Alloc` must meet the requirements of Allocator.
- `Compare` must meet the requirements of Compare.
- `Container` must meet the requirements of Container. The allocator-extended constructors are only defined if `Container` meets the requirements of AllocatorAwareContainer.
- `InputIt` must meet the requirements of LegacyInputIterator.

Complexity

1,2) Constant.

3,5,12)

O(N)

comparisons and

O(N)

calls to the constructor of value_type, where

N

is cont.size().

4)

O(N)

comparisons, where

N

is cont.size().

6) Constant.

7,16,17)

O(M)

comparisons, where

M

is std::distance(first, last).

8,18)

O(N + M)

comparisons and

O(N)

calls to the constructor of value_type, where

N

is cont.size() and

M

is std::distance(first, last).

9)

O(N + M)

comparisons, where

N

is cont.size() and

M

is std::distance(first, last).

10,11) Constant.

13)

O(N)

comparisons, where

N

is cont.size().

14) Linear in size of other.

15) Constant if Alloc compares equal to the allocator of other. Linear in size of other otherwise.

19)

O(N + M)

comparisons and possibly

O(N)

calls to the constructor of value_type (present if Alloc does not compare equal to the allocator of other), where

N

is cont.size() and

M

is std::distance(first, last).

20)

O(N)

comparisons and

O(N)

calls to the constructor of value_type, where

N

is ranges::distance(rg).

21,22)

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_containers_ranges`	`202202L`	(C++23)	Ranges-aware construction and insertion; overloads (20-22)

Example

Run this code

#include <complex>
#include <functional>
#include <iostream>
#include <queue>
#include <vector>

int main()
{
    std::priority_queue<int> pq1;
    pq1.push(5);
    std::cout << "pq1.size() = " << pq1.size() << '\n';

    std::priority_queue<int> pq2 {pq1};
    std::cout << "pq2.size() = " << pq2.size() << '\n';

    std::vector<int> vec {3, 1, 4, 1, 5};
    std::priority_queue<int> pq3 {std::less<int>(), vec};
    std::cout << "pq3.size() = " << pq3.size() << '\n';

    for (std::cout << "pq3 : "; !pq3.empty(); pq3.pop())
        std::cout << pq3.top() << ' ';
    std::cout << '\n';

    // Demo With Custom Comparator:

    using my_value_t = std::complex<double>;
    using my_container_t = std::vector<my_value_t>;

    auto my_comp = [](const my_value_t& z1, const my_value_t& z2)
    {
        return z2.real() < z1.real();
    };

    std::priority_queue<my_value_t,
                        my_container_t,
                        decltype(my_comp)> pq4{my_comp};

    using namespace std::complex_literals;
    pq4.push(5.0 + 1i);
    pq4.push(3.0 + 2i);
    pq4.push(7.0 + 3i);

    for (; !pq4.empty(); pq4.pop())
    {
        const auto& z = pq4.top();
        std::cout << "pq4.top() = " << z << '\n';
    }

    // TODO: C++23 range-aware ctors
}

Output:

pq1.size() = 1
pq2.size() = 1
pq3.size() = 5
pq3 : 5 4 3 1 1
pq4.top() = (3,2)
pq4.top() = (5,1)
pq4.top() = (7,3)

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
P0935R0	C++11	default constructor and constructor (4) were explicit	made implicit
LWG 3506	C++11	allocator-extended iterator-pair constructors were missing	added
LWG 3522	C++11	constraints on iterator-pair constructors were missing	added
LWG 3529	C++11	construction from a pair of iterators called `insert`	constructs the container from them

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priority_queue::priority_queue
priority_queue::~priority_queue
priority_queue::operator=
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priority_queue::push
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priority_queue::pop
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swap(std::priority_queue) (C++11)
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uses_allocator<std::priority_queue> (C++11)
formatter<std::priority_queue> (C++23)
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std::priority_queue<T,Container,Compare>::priority_queue

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