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# std::priority_queue::priority_queue

From cppreference.com
< cpp‎ | container‎ | priority queue

| (1) |
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)
explicit priority_queue( const Compare& compare = Compare(), Container&& cont = Container() ); | (2) | (since C++11)
priority_queue( const priority_queue& other ); | (3) |
priority_queue( priority_queue&& other ); | (4) | (since C++11)
template< class Alloc > explicit priority_queue( const Alloc& alloc ); | (5) | (since C++11)
template< class Alloc > priority_queue( const Compare& compare, const Alloc& alloc ); | (6) | (since C++11)
template< class Alloc > priority_queue( const Compare& compare, const Container& cont, const Alloc& alloc ); | (7) | (since C++11)
template< class Alloc > priority_queue( const Compare& compare, Container&& cont, const Alloc& alloc ); | (8) | (since C++11)
template< class Alloc > priority_queue( const priority_queue& other, const Alloc& alloc ); | (9) | (since C++11)
template< class Alloc > priority_queue( priority_queue&& other, const Alloc& alloc ); | (10) | (since C++11)
template< class InputIt > priority_queue( InputIt first, InputIt last, const Compare& compare, const Container& cont ); | (11) | (since C++11)
template< class InputIt > priority_queue( InputIt first, InputIt last, const Compare& compare = Compare(), Container&& cont = Container() ); | (12) | (since C++11)

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

1) 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)
2) Move-constructs the underlying container `c` with std::move(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. (since C++11)
3) Copy constructor. The adaptor is copy-constructed with the contents of other.c. The comparison functor is constructed with std::move(other.comp). (implicitly declared)
4) Move constructor. The adaptor is constructed with std::move(other.c).The comparison functor is constructed with std::move(other.comp). (implicitly declared)
5-10) The following constructors are only defined if std::uses_allocator<container_type, Alloc>::value == true, that is, if the underlying container is an allocator-aware container (true for all standard library containers).
5) Constructs the underlying container using `alloc` as allocator. Effectively calls c(alloc). `comp` is value-initialized.
6) Constructs the underlying container using `alloc` as allocator. Effectively calls c(alloc). Copy-constructs `comp` from `compare`.
7) 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).
8) 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).
9) Constructs the adaptor with the contents of `other.c` and using `alloc` as allocator. Effectively calls c(other.c, alloc). Copy-constructs `comp` from `other.comp`.
10) Constructs the adaptor with the contents of `other` using move semantics while utilising `alloc` as allocator. Effectively calls c(std::move(other.c), alloc). Move-constructs `comp` from `other.comp`.
11) 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);.
12) Move-constructs `c` from `std::move(cont)` and `comp` from `std::move(compare)`. Then calls c.insert(c.end(), first, last);, and then calls std::make_heap(c.begin(), c.end(), comp);.

### [edit] 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 | - | range of elements to initialize with
Type requirements
- `Alloc` must meet the requirements of `Allocator`.
- `Container` must meet the requirements of `Container`. The constructors (5-10) are only defined if `Container` meets the requirements of `AllocatorAwareContainer`
- `InputIt` must meet the requirements of `InputIterator`.

### [edit] Complexity

1,3) O(N) comparisons, where N is cont.size().
Additionally, O(N) calls to the constructor of `value_type`, where N is cont.size().
2) O(N) comparisons, where N is cont.size().
4-6) Constant.
7) O(N) comparisons, where N is cont.size().
Additionally, O(N) calls to the constructor of `value_type`, where N is cont.size().
8) O(N) comparisons, where N is cont.size().
9) Linear in size of `other`.
10) Constant.
11) O(N) comparisons, where N is cont.size() + std::distance(first, last).
Additionally, O(N) calls to the constructor of `value_type`, where N is cont.size().
12) O(N) comparisons, where N is cont.size() + std::distance(first, last).

### [edit] Example

Run this code

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

    int main()
    {
        std::priority_queue<int> c1;
        c1.push(5);
        std::cout << c1.size() << '\n';

        std::priority_queue<int> c2(c1);
        std::cout << c2.size() << '\n';

        std::vector<int> vec={3, 1, 4, 1, 5};
        std::priority_queue<int> c3(std::less<int>(), vec);
        std::cout << c3.size() << '\n';
    }

Output:

    1
    1
    5

### [edit] Example With Custom Comparator

Run this code

    #include <iostream>
    #include <queue>
    #include <vector>
    #include <utility>

    using my_pair_t = std::pair<size_t,bool>;

    using my_container_t = std::vector<my_pair_t>;

    int main()
    {
        auto my_comp =
            [](const my_pair_t& e1, const my_pair_t& e2)
            { return e1.first > e2.first; };
        std::priority_queue<my_pair_t,
                            my_container_t,
                            decltype(my_comp)> queue(my_comp);
        queue.push(std::make_pair(5, true));
        queue.push(std::make_pair(3, false));
        queue.push(std::make_pair(7, true));
        std::cout << std::boolalpha;
        while(!queue.empty())
        {
            const auto& p = queue.top();
            std::cout << p.first << " " << p.second << "\n";
            queue.pop();
        }
    }

Output:

    3 false
    5 true
    7 true

### [edit] See also

operator= | assigns values to the container adaptor (public member function) [edit]

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