std::ranges::is_sorted_until
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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template< std::forward_iterator I, std::sentinel_for<I> S,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<I, Proj>> Comp = ranges::less >
constexpr I
is_sorted_until( I first, S last, Comp comp = {}, Proj proj = {} );
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(1) | (since C++20) |
template< std::forward_range R, class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<ranges::iterator_t<R>,
Proj>> Comp = ranges::less >
constexpr ranges::borrowed_iterator_t<R>
is_sorted_until( R&& r, Comp comp = {}, Proj proj = {} );
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(2) | (since C++20) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<I, Proj>> Comp = ranges::less >
I is_sorted_until( Ep&& policy, I first, S last,
Comp comp = {}, Proj proj = {} );
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(3) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<ranges::iterator_t<R>,
Proj>> Comp = ranges::less >
ranges::borrowed_iterator_t<R>
is_sorted_until( Ep&& policy, R&& r, Comp comp = {}, Proj proj = {} );
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(4) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
1,2) Examines the source range
[first, last) or r and finds the largest range which begins at first or ranges::begin(r) and is sorted with respect to the comparator comp and projection proj.3,4) Same as (1,2), but executed according to
policy.The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
Parameters
| first, last | - | the iterator-sentinel pair defining the source range |
| r | - | the source range |
| comp | - | the comparator to be applied to the (projected) elements |
| proj | - | the projection to be applied to the elements |
| policy | - | the execution policy to use |
Return value
The past-the-end iterator of the largest range found.
Complexity
Given N as ranges::distance(first, last) or ranges::distance(r):
1-4) 𝓞(N) applications of
comp, and twice as many applications of proj.Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
Notes
For empty ranges and ranges of length one, ranges::is_sorted_until returns its past-the-end iterator.
Possible implementation
struct is_sorted_until_fn
{
template<std::forward_iterator I, std::sentinel_for<I> S,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<I, Proj>> Comp = ranges::less>
constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
{
if (first == last)
return first;
for (auto next = first; ++next != last; first = next)
if (std::invoke(comp, std::invoke(proj, *next),
std::invoke(proj, *first)))
return next;
return first;
}
template<ranges::forward_range R, class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
constexpr ranges::borrowed_iterator_t<R>
operator()(R&& r, Comp comp = {}, Proj proj = {}) const
{
return (*this)(ranges::begin(r),
ranges::next(ranges::begin(r), ranges::end(r)),
std::ref(comp), std::ref(proj));
}
};
inline constexpr is_sorted_until_fn is_sorted_until;
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Example
Run this code
#include <array>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <random>
int main()
{
std::random_device rd;
std::mt19937 g{rd()};
std::array nums{3, 1, 4, 1, 5, 9};
constexpr int min_sorted_size = 4;
int sorted_size = 0;
do
{
std::ranges::shuffle(nums, g);
const auto sorted_end = std::ranges::is_sorted_until(nums);
sorted_size = std::ranges::distance(nums.begin(), sorted_end);
std::ranges::copy(nums, std::ostream_iterator<int>(std::cout, " "));
std::cout << ": " << sorted_size << " leading sorted element(s)\n";
}
while (sorted_size < min_sorted_size);
}
Possible output:
4 1 9 5 1 3 : 1 leading sorted element(s)
4 5 9 3 1 1 : 3 leading sorted element(s)
9 3 1 4 5 1 : 1 leading sorted element(s)
1 3 5 4 1 9 : 3 leading sorted element(s)
5 9 1 1 3 4 : 2 leading sorted element(s)
4 9 1 5 1 3 : 2 leading sorted element(s)
1 1 4 9 5 3 : 4 leading sorted element(s)