NAME

deductionguidesforstd::priority_queue - deductionguidesforstd::priority_queue

Synopsis

Defined in header <queue>
template <class Comp, class Container>

priority_queue(Comp, Container) (1) (since C++17)

-> priority_queue<typename Container::value_type, Container,
Comp>;
template<class InputIt,

class Comp = std::less</*iter-value-type*/<InputIt>>,
class Container = std::vector</*iter-value-type*/<InputIt>> (2) (since C++17)
priority_queue(InputIt, InputIt, Comp = Comp(), Container =
Container())

-> priority_queue</*iter-value-type*/<InputIt>, Container, Comp>;
template<class Comp, class Container, class Alloc>

priority_queue(Comp, Container, Alloc) (3) (since C++17)

-> priority_queue<typename Container::value_type, Container,
Comp>;
template<class InputIt, class Alloc>

priority_queue(InputIt, InputIt, Alloc)
-> priority_queue</*iter-value-type*/<InputIt>, (4) (since C++17)
std::vector</*iter-value-type*/<InputIt>, Alloc>,

std::less</*iter-value-type*/<InputIt>>>;
template<class InputIt, class Comp, class Alloc>

priority_queue(InputIt, InputIt, Comp, Alloc) (5) (since C++17)
-> priority_queue</*iter-value-type*/<InputIt>,

std::vector</*iter-value-type*/<InputIt>, Alloc>, Comp>;
template<class InputIt, class Comp, class Container, class Alloc>

priority_queue(InputIt, InputIt, Comp, Container, Alloc) (6) (since C++17)

-> priority_queue<typename Container::value_type, Container,
Comp>;

These deduction guides are provided for std::priority_queue to allow deduction from
underlying container type and from an iterator range. /*iter-value-type*/<It>
denotes typename std::iterator_traits<It>::value_type for any type It.

These overloads participate in overload resolution only if

* InputIt satisfies LegacyInputIterator,
* Comp does not satisfy Allocator,
* Container does not satisfy Allocator,
* for overloads (4) and (5),
(since C++23) Alloc satisfies Allocator, and
* for overloads (3) and (6), std::uses_allocator_v<Container, Alloc> is true.

Note: the extent to which the library determines that a type does not satisfy
LegacyInputIterator is unspecified, except that as a minimum integral types do not
qualify as input iterators. Likewise, the extent to which it determines that a type
does not satisfy Allocator is unspecified, except that as a minimum the member type
Alloc::value_type must exist and the expression
std::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as
an unevaluated operand.

Example

// Run this code

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

int main() {
const std::vector<int> v = {1,2,3,4};
std::priority_queue pq1{std::greater<int>{}, v}; // deduces std::priority_queue<
// int, std::vector<int>,
// std::greater<int>>
for (; !pq1.empty(); pq1.pop())
std::cout << pq1.top() << ' ';
std::cout << '\n';

std::priority_queue pq2{v.begin(), v.end()}; // deduces std::priority_queue<int>

for (; !pq2.empty(); pq2.pop())
std::cout << pq2.top() << ' ';
std::cout << '\n';
}

Output:

1 2 3 4
4 3 2 1

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 3506 C++17 deduction guides from iterator and allocator added
were missing