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std::search_n(3) C++ Standard Libary std::search_n(3) NAME std::search_n - std::search_n Synopsis Defined in header <algorithm> template< class ForwardIt, class Size, class T > ForwardIt search_n( ForwardIt first, ForwardIt (until C++20) last, Size count, const T& value ); template< class ForwardIt, class Size, class T > constexpr ForwardIt search_n( ForwardIt first, (since C++20) ForwardIt last, Size count, const T& value ); template< class ExecutionPolicy, class ForwardIt, class Size, class T > ForwardIt search_n( ExecutionPolicy&& policy, (2) (since C++17) ForwardIt first, ForwardIt last, Size count, const T& value ); template< class ForwardIt, class Size, class T, class BinaryPredicate > (1) ForwardIt search_n( ForwardIt first, ForwardIt (until C++20) last, Size count, const T& value, BinaryPredicate p ); template< class ForwardIt, class Size, class T, class BinaryPredicate > constexpr ForwardIt search_n( ForwardIt first, (3) (since C++20) ForwardIt last, Size count, const T& value, BinaryPredicate p ); template< class ExecutionPolicy, class ForwardIt, class Size, class T, class BinaryPredicate > (4) (since C++17) ForwardIt search_n( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Size count, const T& value, BinaryPredicate p ); Searches the range [first, last) for the first sequence of count identical elements, each equal to the given value. 1) Elements are compared using operator==. 3) Elements are compared using the given binary predicate p. 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 count - the length of the sequence to search for value - the value of the elements to search for policy - the execution policy to use. See execution policy for details. binary predicate which returns true if the elements should be treated as equal. The signature of the predicate function should be equivalent to the following: bool pred(const Type1 &a, const Type2 &b); p - 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 type Type1 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to Type1. The type Type2 must be such that an object of type T can be implic- itly converted to Type2. Type requirements - ForwardIt must meet the requirements of LegacyForwardIterator. Return value Iterator to the beginning of the found sequence in the range [first, last). If no such sequence is found, last is returned. If count is zero or negative, first is returned. Complexity At most last - first applications of the predicate. 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 First version template<class ForwardIt, class Size, class T> ForwardIt search_n(ForwardIt first, ForwardIt last, Size count, const T& value) { if (count <= 0) { return first; } for(; first != last; ++first) { if (!(*first == value)) { continue; } ForwardIt candidate = first; Size cur_count = 0; while (true) { ++cur_count; if (cur_count >= count) { // success return candidate; } ++first; if (first == last) { // exhausted the list return last; } if (!(*first == value)) { // too few in a row break; } } } return last; } Second version template<class ForwardIt, class Size, class T, class BinaryPredi- cate> ForwardIt search_n(ForwardIt first, ForwardIt last, Size count, const T& value, BinaryPredicate p) { if (count <= 0) { return first; } for(; first != last; ++first) { if (!p(*first, value)) { continue; } ForwardIt candidate = first; Size cur_count = 0; while (true) { ++cur_count; if (cur_count >= count) { // success return candidate; } ++first; if (first == last) { // exhausted the list return last; } if (!p(*first, value)) { // too few in a row break; } } } return last; } Example // Run this code #include <iostream> #include <algorithm> #include <iterator> template <class Container, class Size, class T> bool consecutive_values(const Container& c, Size count, const T& v) { return std::search_n(std::begin(c),std::end(c),count,v) != std::end(c); } int main() { const char sequence[] = "1001010100010101001010101"; std::cout << std::boolalpha; std::cout << "Has 4 consecutive zeros: " << consecutive_values(sequence,4,'0') << '\n'; std::cout << "Has 3 consecutive zeros: " << consecutive_values(sequence,3,'0') << '\n'; } Output: Has 4 consecutive zeros: false Has 3 consecutive zeros: true See also find_end finds the last sequence of elements in a certain range (function template) find find_if finds the first element satisfying specific crite- ria find_if_not (function template) (C++11) search searches for a range of elements (function template) ranges::search_n searches for a number consecutive copies of an ele- ment in a range (C++20) (niebloid) http://cppreference.com 2022.07.31 std::search_n(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Possible implementation | First version | Second version | Example | Output: | See also
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