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std::ranges...ition_point(3) C++ Standard Libary std::ranges...ition_point(3) NAME std::ranges::partition_point - std::ranges::partition_point Synopsis Defined in header <algorithm> Call signature template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> (1) (since C++20) Pred > constexpr I partition_point( I first, S last, Pred pred, Proj proj = {} ); template< ranges::forward_range R, class Proj = std::identity, std::indirect_unary_predicate< (2) (since C++20) std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_iterator_t<R> partition_point( R&& r, Pred pred, Proj proj = {} ); Examines the partitioned (as if by ranges::partition) range [first, last) or r and locates the end of the first partition, that is, the projected ele- ment that does not satisfy pred or last if all projected elements satisfy pred. The function-like entities described on this page are niebloids, that is: * Explicit template argument lists cannot be specified when call- ing 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 in- hibited. In practice, they may be implemented as function objects, or with special compiler extensions. Parameters first, last - iterator-sentinel defining the partially-ordered range to examine r - the partially-ordered range to examine pred - predicate to apply to the projected elements proj - projection to apply to the elements Return value The iterator past the end of the first partition within [first, last) or the iterator equal to last if all projected elements satisfy pred. Complexity Given N = ranges::distance(first, last), performs O(log N) applica- tions of the predicate pred and projection proj. However, if sentinels don't model std::sized_sentinel_for<I>, the number of iterator increments is O(N). Notes This algorithm is a more general form of ranges::lower_bound, which can be expressed in terms of ranges::partition_point with the predicate [&](auto const& e) { return std::invoke(pred, e, value); });. Example // Run this code #include <algorithm> #include <array> #include <iostream> #include <iterator> auto print_seq = [](auto rem, auto first, auto last) { for (std::cout << rem; first != last; std::cout << *first++ << ' ') {} std::cout << '\n'; }; int main() { std::array v {1, 2, 3, 4, 5, 6, 7, 8, 9}; auto is_even = [](int i) { return i % 2 == 0; }; std::ranges::partition(v, is_even); print_seq("After partitioning, v: ", v.cbegin(), v.cend()); const auto pp = std::ranges::partition_point(v, is_even); const auto i = std::ranges::distance(v.cbegin(), pp); std::cout << "Partition point is at " << i << "; v[" << i << "] = " << *pp << '\n'; print_seq("First partition (all even elements): ", v.cbegin(), pp); print_seq("Second partition (all odd elements): ", pp, v.cend()); } Possible output: After partitioning, v: 2 4 6 8 5 3 7 1 9 Partition point is at 4; v[4] = 5 First partition (all even elements): 2 4 6 8 Second partition (all odd elements): 5 3 7 1 9 See also ranges::is_sorted checks whether a range is sorted into ascending order (C++20) (niebloid) ranges::lower_bound returns an iterator to the first element not less than the given (C++20) value (niebloid) partition_point locates the partition point of a partitioned range (C++11) (function template) http://cppreference.com 2024.06.10 std::ranges...ition_point(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Example | Possible output: | See also
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