std::ranges::is_sorted
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 bool
is_sorted( I first, S last, Comp comp = {}, Proj proj = {} );
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(1) | (since C++20) |
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 bool
is_sorted( 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 >
bool is_sorted( 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 >
bool is_sorted( 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) Checks if all elements of the source range
[first, last) or r are 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
true if all elements of the source range are sorted, false otherwise.
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
ranges::is_sorted returns true for empty ranges and ranges of length one.
Possible implementation
struct is_sorted_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 bool operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
{
return ranges::is_sorted_until(first, last, comp, proj) == last;
}
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 bool 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_fn is_sorted;
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Example
Run this code
#include <algorithm>
#include <array>
#include <functional>
#include <iostream>
#include <iterator>
int main()
{
namespace ranges = std::ranges;
std::array digits{3, 1, 4, 1, 5};
ranges::copy(digits, std::ostream_iterator<int>(std::cout, " "));
ranges::is_sorted(digits)
? std::cout << ": sorted\n"
: std::cout << ": not sorted\n";
ranges::sort(digits);
ranges::copy(digits, std::ostream_iterator<int>(std::cout, " "));
ranges::is_sorted(ranges::begin(digits), ranges::end(digits))
? std::cout << ": sorted\n"
: std::cout << ": not sorted\n";
ranges::reverse(digits);
ranges::copy(digits, std::ostream_iterator<int>(std::cout, " "));
ranges::is_sorted(digits, ranges::greater{})
? std::cout << ": sorted (descending)\n"
: std::cout << ": not sorted\n";
}
Output:
3 1 4 1 5 : not sorted
1 1 3 4 5 : sorted
5 4 3 1 1 : sorted (descending)