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

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>;
template< ranges::input_range R,

class Comp = std::less<ranges::range_value_t<R>> >
priority_queue( std::from_range_t, R&&, Comp = Comp() ) (7) (since C++23)
-> priority_queue<ranges::range_value_t<R>,

std::vector<ranges::range_value_t<R>>,
Comp>;
template< ranges::input_range R, class Comp, class Alloc >

priority_queue( std::from_range_t, R&&, Comp, Alloc )
-> priority_queue<ranges::range_value_t<R>, (8) (since C++23)

std::vector<ranges::range_value_t<R>,
Alloc>, Comp>;
template< ranges::input_range R, class Alloc >

priority_queue( std::from_range_t, R&&, Alloc )
-> priority_queue<ranges::range_value_t<R>, (9) (since C++23)

std::vector<ranges::range_value_t<R>,
Alloc>>;

The following deduction guides are provided for std::priority_queue:

1-6) 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.
7-9) Allow deduction from a std::from_range_t tag and an input_range.

These overloads participate in overload resolution only if

* InputIt satisfies LegacyInputIterator,
* Comp does not satisfy Allocator,
* Container does not satisfy Allocator,
* for overloads (4,5),
(since C++23) Alloc satisfies Allocator, and
* for overloads (3,6), 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.

Notes¶

Feature-test macro Value Std Feature
__cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion;
overloads (7-9)

Example¶

// Run this code

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

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