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std::search(3) C++ Standard Libary std::search(3) NAME std::search - std::search Synopsis Defined in header <algorithm> template< class ForwardIt1, class ForwardIt2 > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, (1) (const- expr since C++20) ForwardIt2 s_first, ForwardIt2 s_last ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt1 search( ExecutionPolicy&& policy, (2) (since C++17) ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); template< class ForwardIt1, class ForwardIt2, class BinaryPred > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, (3) (const- expr since C++20) ForwardIt2 s_first, ForwardIt2 s_last, BinaryPred p ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryPred > ForwardIt1 search( ExecutionPolicy&& policy, (4) (since C++17) ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPred p ); template< class ForwardIt, class Searcher > (since C++17) ForwardIt search( ForwardIt first, ForwardIt last, (5) (const- expr since C++20) const Searcher& searcher ); 1-4) Searches for the first occurrence of the sequence of elements [s_first, s_last) in the range [first, last). 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 overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. (until C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since C++20) 5) Searches the range [first, last) for the pattern specified in the constructor of searcher. The standard library provides the following searchers: default_searcher standard C++ library search algorithm (C++17) implementation (class template) boyer_moore_searcher Boyer-Moore search algorithm (since C++17) (C++17) implementation (class template) boyer_moore_horspool_searcher Boyer-Moore-Horspool search algorithm (C++17) implementation (class template) Parameters first, last - the range of elements to examine s_first, s_last - the range of elements to search for policy - the execution policy to use. See execution policy for details. searcher - the searcher encapsulating the search algorithm and the pattern to look for binary predicate which returns true if the ele- ments 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 regardless of value category (thus, Type1 & is not allowed , nor is Type1 unless for Type1 a move is equiva- lent to a copy (since C++11)). The types Type1 and Type2 must be such that ob- jects of types ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. Type requirements - ForwardIt1, ForwardIt2 must meet the requirements of LegacyFor- wardIterator. - BinaryPred must meet the requirements of BinaryPredicate. Return value 1-4) Iterator to the beginning of first occurrence of the sequence [s_first, s_last) in the range [first, last). If no such occurrence is found, last is returned. If [s_first, s_last) is empty, first is returned. 5) searcher(first, last).first. Complexity 1-4) Given \(\scriptsize N\)N as std::distance(first, last) and \(\scriptsize S\)S as std::distance(s_first, s_last): 1,2) At most \(\scriptsize N\cdot S\)NS comparisons using opera- tor==. 3,4) At most \(\scriptsize N\cdot S\)NS applications of the predi- cate p. 5) Depends on searcher. 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 search (1) template<class ForwardIt1, class ForwardIt2> constexpr //< since C++20 ForwardIt1 search(ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last) { while (true) { ForwardIt1 it = first; for (ForwardIt2 s_it = s_first; ; ++it, ++s_it) { if (s_it == s_last) return first; if (it == last) return last; if (!(*it == *s_it)) break; } ++first; } } search (3) template<class ForwardIt1, class ForwardIt2, class BinaryPred> constexpr //< since C++20 ForwardIt1 search(ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPred p) { while (true) { ForwardIt1 it = first; for (ForwardIt2 s_it = s_first; ; ++it, ++s_it) { if (s_it == s_last) return first; if (it == last) return last; if (!p(*it, *s_it)) break; } ++first; } } Example // Run this code #include <algorithm> #include <cassert> #include <functional> #include <iomanip> #include <iostream> #include <iterator> #include <string_view> #include <vector> using namespace std::literals; bool contains(const auto& cont, std::string_view s) { // str.find() (or str.contains(), since C++23) can be used as well return std::search(cont.begin(), cont.end(), s.begin(), s.end()) != cont.end(); } int main() { const auto str{"why waste time learning, when ignorance is instan- taneous?"sv}; assert(contains(str, "learning")); assert(not contains(str, "lemming")); const std::vector vec(str.begin(), str.end()); assert(contains(vec, "learning")); assert(not contains(vec, "leaning")); // The C++17 overload with searchers demo: constexpr auto quote { "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed " "do eiusmod tempor incididunt ut labore et dolore magna ali- qua"sv }; for (const auto word : {"pisci"sv, "Pisci"sv}) { std::cout << "The string " << std::quoted(word) << ' '; const std::boyer_moore_searcher searcher(word.begin(), word.end()); const auto it = std::search(quote.begin(), quote.end(), searcher); if (it == quote.end()) std::cout << "not found\n"; else std::cout << "found at offset " << std::distance(quote.be- gin(), it) << '\n'; } } Output: The string "pisci" found at offset 43 The string "Pisci" not found Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 1205 C++98 the return value was unclear if re- turns first in this [s_first, s_last) is empty case the resolution of LWG issue 1205 was LWG 1338 C++98 incorrectly applied, re- turns last in this making first to be returned if no case occurence is found LWG 2150 C++98 the condition of sequence occurence was cor- rected incorrect See also find_end finds the last sequence of elements in a certain range (function template) returns true if one sequence is a sub- sequence of includes another (function template) equal determines if two sets of elements are the same (function template) find find_if finds the first element satisfying specific criteria find_if_not (function template) (C++11) returns true if one range is lexico- graphically less lexicographical_compare than another (function template) mismatch finds the first position where two ranges differ (function template) searches a range for a number of con- secutive copies of search_n an element (function template) default_searcher standard C++ library search algorithm implementation (C++17) (class template) boyer_moore_searcher Boyer-Moore search algorithm implemen- tation (C++17) (class template) boyer_moore_horspool_searcher Boyer-Moore-Horspool search algorithm implementation (C++17) (class template) ranges::search searches for a range of elements (C++20) (niebloid) http://cppreference.com 2024.06.10 std::search(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Possible implementation | Example | Output: | See also
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