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std::ranges::search_n(3) C++ Standard Libary std::ranges::search_n(3) NAME std::ranges::search_n - std::ranges::search_n Synopsis Defined in header <algorithm> Call signature template< std::forward_iterator I, std::sentinel_for<I> S, class T, class Pred = ranges::equal_to, class Proj = std::identity > (since requires std::indirectly_comparable<I, const T*, Pred, Proj> C++20) constexpr ranges::subrange<I> (until search_n( I first, S last, std::iter_difference_t<I> C++26) count, const T& value, Pred pred = {}, Proj proj = {} ); template< std::forward_iterator I, std::sentinel_for<I> S, class Pred = ranges::equal_to, class Proj = std::identity, class T = std::projected_value_t<I, Proj> > requires std::indirectly_comparable<I, const T*, Pred, Proj> (since constexpr ranges::subrange<I> C++26) search_n( I first, S last, std::iter_difference_t<I> count, const T& value, Pred pred = {}, Proj proj = {} ); (1) template< ranges::forward_range R, class T, class Pred = ranges::equal_to, class Proj = std::identity > (since requires std::indirectly_comparable C++20) <ranges::iterator_t<R>, const T*, Pred, Proj> (until constexpr ranges::borrowed_subrange_t<R> C++26) search_n( R&& r, ranges::range_difference_t<R> count, const T& value, Pred pred = {}, Proj proj = {} ); template< ranges::forward_range R, (2) class Pred = ranges::equal_to, class Proj = std::identity, class T = std::projected_value_t<ranges::iterator_t<R>, Proj> > (since requires std::indirectly_comparable C++26) <ranges::iterator_t<R>, const T*, Pred, Proj> constexpr ranges::borrowed_subrange_t<R> search_n( R&& r, ranges::range_difference_t<R> count, const T& value, Pred pred = {}, Proj proj = {} ); 1) Searches the range [first, last) for the first sequence of count elements whose projected values are each equal to the given value according to the binary predicate pred. 2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last. 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 - the range of elements to examine (aka haystack) r - the range of elements to examine (aka haystack) count - the length of the sequence to search for value - the value to search for (aka needle) pred - the binary predicate that compares the projected ele- ments with value proj - the projection to apply to the elements of the range to examine Return value 1) Returns std::ranges::subrange object that contains a pair of it- erators in the range [first, last) that designate the found subsequence. If no such subsequence is found, returns std::ranges::subrange{last, last}. If count <= 0, returns std::ranges::subrange{first, first}. 2) Same as (1) but the return type is ranges::borrowed_sub- range_t<R>. Complexity Linear: at most ranges::distance(first, last) applications of the predicate and the projection. Notes An implementation can improve efficiency of the search in average if the iterators model std::random_access_iterator. Feature-test macro Value Std Feature __cpp_lib_algorithm_default_value_type 202403 (C++26) List-initial- ization for algorithms Possible implementation struct search_n_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Pred = ranges::equal_to, class Proj = std::iden- tity, class T = std::projected_value_t<I, Proj>> requires std::indirectly_comparable<I, const T*, Pred, Proj> constexpr ranges::subrange<I> operator()(I first, S last, std::iter_difference_t<I> count, const T& value, Pred pred = {}, Proj proj = {}) const { if (count <= 0) return {first, first}; for (; first != last; ++first) if (std::invoke(pred, std::invoke(proj, *first), value)) { I start = first; std::iter_difference_t<I> n{1}; for (;;) { if (n++ == count) return {start, std::next(first)}; // found if (++first == last) return {first, first}; // not found if (!std::invoke(pred, std::invoke(proj, *first), value)) break; // not equ to value } } return {first, first}; } template<ranges::forward_range R, class Pred = ranges::equal_to, class Proj = std::iden- tity, class T = std::projected_value_t<ranges::iterator_t<R>, Proj>> requires std::indirectly_comparable<ranges::iterator_t<R>, const T*, Pred, Proj> constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, ranges::range_difference_t<R> count, const T& value, Pred pred = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(count), value, std::move(pred), std::move(proj)); } }; inline constexpr search_n_fn search_n {}; Example // Run this code #include <algorithm> #include <cassert> #include <complex> #include <iomanip> #include <iostream> #include <iterator> #include <string> #include <vector> int main() { namespace ranges = std::ranges; static constexpr auto nums = {1, 2, 2, 3, 4, 1, 2, 2, 2, 1}; constexpr int count{3}; constexpr int value{2}; typedef int count_t, value_t; constexpr auto result1 = ranges::search_n ( nums.begin(), nums.end(), count, value ); static_assert // found ( result1.size() == count && std::distance(nums.begin(), result1.begin()) == 6 && std::distance(nums.begin(), result1.end()) == 9 ); constexpr auto result2 = ranges::search_n(nums, count, value); static_assert // found ( result2.size() == count && std::distance(nums.begin(), result2.begin()) == 6 && std::distance(nums.begin(), result2.end()) == 9 ); constexpr auto result3 = ranges::search_n(nums, count, value_t{5}); static_assert // not found ( result3.size() == 0 && result3.begin() == result3.end() && result3.end() == nums.end() ); constexpr auto result4 = ranges::search_n(nums, count_t{0}, value_t{1}); static_assert // not found ( result4.size() == 0 && result4.begin() == result4.end() && result4.end() == nums.begin() ); constexpr char symbol{'B'}; auto to_ascii = [](const int z) -> char { return 'A' + z - 1; }; auto is_equ = [](const char x, const char y) { return x == y; }; std::cout << "Find a sub-sequence " << std::string(count, symbol) << " in the "; std::ranges::transform(nums, std::ostream_itera- tor<char>(std::cout, ""), to_ascii); std::cout << '\n'; auto result5 = ranges::search_n(nums, count, symbol, is_equ, to_ascii); if (not result5.empty()) std::cout << "Found at position " << ranges::distance(nums.begin(), result5.begin()) << '\n'; std::vector<std::complex<double>> nums2{{4, 2}, {4, 2}, {1, 3}}; #ifdef __cpp_lib_algorithm_default_value_type auto it = ranges::search_n(nums2, 2, {4, 2}); #else auto it = ranges::search_n(nums2, 2, std::complex<double>{4, 2}); #endif assert(it.size() == 2); } Output: Find a sub-sequence BBB in the ABBCDABBBA Found at position 6 See also ranges::adjacent_find finds the first two adjacent items that are equal (or satisfy (C++20) a given predicate) (niebloid) ranges::find ranges::find_if ranges::find_if_not finds the first element satisfying specific criteria (C++20) (niebloid) (C++20) (C++20) ranges::find_end finds the last sequence of elements in a cer- tain range (C++20) (niebloid) ranges::find_first_of searches for any one of a set of elements (C++20) (niebloid) ranges::includes returns true if one sequence is a subsequence of another (C++20) (niebloid) ranges::mismatch finds the first position where two ranges dif- fer (C++20) (niebloid) ranges::search searches for a range of elements (C++20) (niebloid) searches a range for a number of consecutive copies of an search_n element (function template) http://cppreference.com 2024.06.10 std::ranges::search_n(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Possible implementation | Example | Output: | See also
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