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

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C++
 
Containers library
 
std::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 - a range [first, last) 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)
This section is incomplete

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

See also

 assigns values to the container adaptor
(public member function)
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