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std::is_sorted_until(3) C++ Standard Libary std::is_sorted_until(3) NAME std::is_sorted_until - std::is_sorted_until Synopsis Defined in header <algorithm> template< class ForwardIt > (since C++11) ForwardIt is_sorted_until( ForwardIt first, (until C++20) ForwardIt last ); template< class ForwardIt > constexpr ForwardIt is_sorted_until( ForwardIt (since C++20) first, ForwardIt last ); template< class ExecutionPolicy, class ForwardIt > ForwardIt is_sorted_until( ExecutionPolicy&& (2) (since C++17) policy, ForwardIt first, ForwardIt last ); template< class ForwardIt, class Compare > ForwardIt is_sorted_until( ForwardIt first, (1) (since C++11) ForwardIt last, (until C++20) Compare comp ); template< class ForwardIt, class Compare > constexpr ForwardIt is_sorted_until( ForwardIt (since C++20) first, ForwardIt last, (3) Compare comp ); template< class ExecutionPolicy, class ForwardIt, class Compare > ForwardIt is_sorted_until( ExecutionPolicy&& (4) (since C++17) policy, ForwardIt first, ForwardIt last, Compare comp ); Examines the range [first, last) and finds the largest range begin- ning at first in which the elements are sorted in non-descending order. A sequence is sorted with respect to a comparator comp if for any iterator it pointing to the sequence and any non-negative integer n such that it + n is a valid iterator pointing to an element of the sequence, comp(*(it + n), *it) evaluates to false. 1) Elements are compared using operator<. 3) Elements are compared using the given binary comparison function comp. 2,4) Same as (1,3), but executed according to policy. These over- loads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> (until C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> (since C++20) is true. Parameters first, last - the range of elements to examine policy - the execution policy to use. See execution policy for details. comparison function object (i.e. an object that satis- fies the requirements of Compare) which returns true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1 &a, const Type2 &b); comp - While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 re- gardless of value category (thus, Type1 & is not allowed , nor is Type1 unless for Type1 a move is equivalent to a copy (since C++11)). The types Type1 and Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly con- verted to both of them. Type requirements - ForwardIt must meet the requirements of LegacyForwardIterator. Return value The upper bound of the largest range beginning at first in which the elements are sorted in ascending order. That is, the last iterator it for which range [first, it) is sorted. Complexity Linear in the distance between first and last. Exceptions The overloads with a template parameter named ExecutionPolicy report errors as follows: * If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::termi- nate is called. For any other ExecutionPolicy, the behavior is implementation- defined. * If the algorithm fails to allocate memory, std::bad_alloc is thrown. Possible implementation See also the implementations in libstdc++ and libc++. First version template<class ForwardIt> constexpr //< since C++20 ForwardIt is_sorted_until(ForwardIt first, ForwardIt last) { return std::is_sorted_until(first, last, std::less<>()); } Second version template <class ForwardIt, class Compare> constexpr //< since C++20 ForwardIt is_sorted_until(ForwardIt first, ForwardIt last, Compare comp) { if (first != last) { ForwardIt next = first; while (++next != last) { if (comp(*next, *first)) return next; first = next; } } return last; } Notes std::is_sorted_until returns last for empty ranges and ranges of length one. Example // Run this code #include <iostream> #include <algorithm> #include <iterator> #include <random> #include <string> #include <cassert> int main() { std::random_device rd; std::mt19937 g(rd()); const int N = 6; int nums[N] = {3, 1, 4, 1, 5, 9}; const int min_sorted_size = 4; for (int sorted_size = 0; sorted_size < min_sorted_size; ) { std::shuffle(nums, nums + N, g); int *const sorted_end = std::is_sorted_until(nums, nums + N); sorted_size = std::distance(nums, sorted_end); assert(sorted_size >= 1); for (auto i : nums) std::cout << i << ' '; std::cout << " : " << sorted_size << " initial sorted ele- ments\n" << std::string(sorted_size * 2 - 1, '^') << '\n'; } } Possible output: 4 1 9 5 1 3 : 1 initial sorted elements ^ 4 5 9 3 1 1 : 3 initial sorted elements ^^^^^ 9 3 1 4 5 1 : 1 initial sorted elements ^ 1 3 5 4 1 9 : 3 initial sorted elements ^^^^^ 5 9 1 1 3 4 : 2 initial sorted elements ^^^ 4 9 1 5 1 3 : 2 initial sorted elements ^^^ 1 1 4 9 5 3 : 4 initial sorted elements ^^^^^^^ See also is_sorted checks whether a range is sorted into as- cending order (C++11) (function template) ranges::is_sorted_until finds the largest sorted subrange (C++20) (niebloid) http://cppreference.com 2022.07.31 std::is_sorted_until(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Possible implementation | First version | Second version | Notes | Example | Possible output: | See also
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