std::find,s...:find_if_not(3) C++ Standard Libary std::find,s...:find_if_not(3) NAME std::find,std::find_if,std::find_if_not - std::find,std::find_if,std::find_if_not Synopsis Defined in header <algorithm> template< class InputIt, class T > (constexpr since InputIt find( InputIt first, InputIt last, C++20) const T& value ); (until C++26) template< class InputIt, class T = typename std::iterator_traits (since C++26) <InputIt>::value_type > constexpr InputIt find( InputIt first, InputIt last, const T& value ); template< class ExecutionPolicy, class ForwardIt, class T > (since C++17) ForwardIt find( ExecutionPolicy&& policy, (un- til C++26) ForwardIt first, ForwardIt last, const T& value ); template< class ExecutionPolicy, class ForwardIt, class T = typename std::iterator_traits (since C++26) <ForwardIt>::value_type > ForwardIt find( ExecutionPolicy&& policy, (1) ForwardIt first, ForwardIt last, const T& value ); template< class InputIt, class UnaryPred > (constexpr since InputIt find_if( InputIt first, InputIt (3) C++20) last, UnaryPred p ); (2) template< class ExecutionPolicy, class ForwardIt, class UnaryPred > ForwardIt find_if( ExecutionPolicy&& (4) (since C++17) policy, ForwardIt first, ForwardIt last, UnaryPred p ); template< class InputIt, class UnaryPred > (since C++11) InputIt find_if_not( InputIt first, (5) (constexpr since InputIt last, UnaryPred q ); C++20) template< class ExecutionPolicy, class ForwardIt, class UnaryPred > ForwardIt find_if_not( ExecutionPolicy&& (6) (since C++17) policy, ForwardIt first, ForwardIt last, UnaryPred q ); Returns an iterator to the first element in the range [first, last) that satisfies specific criteria (or last if there is no such iterator). 1) find searches for an element equal to value (using operator==). 3) find_if searches for an element for which predicate p returns true. 5) find_if_not searches for an element for which predicate q returns false. 2,4,6) Same as (1,3,5), 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) Parameters first, last - the range of elements to examine value - value to compare the elements to policy - the execution policy to use. See execution policy for de- tails. unary predicate which returns true for the required ele- ment. The expression p(v) must be convertible to bool for every argument v p - of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT&is not allowed , nor is VT unless for VT a move is equivalent to a copy (since C++11). unary predicate which returns false for the required ele- ment. The expression q(v) must be convertible to bool for every argument v q - of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT&is not allowed , nor is VT unless for VT a move is equivalent to a copy (since C++11). Type requirements - InputIt must meet the requirements of LegacyInputIterator. - ForwardIt must meet the requirements of LegacyForwardIterator. - UnaryPredicate must meet the requirements of Predicate. Return value The first iterator it in the range [first, last) satisfying the follow- ing condition or last if there is no such iterator: 1,2) *it == value is true. 3,4) p(*it) is true. 5,6) q(*it) is false. Complexity Given \(\scriptsize N\)N as std::distance(first, last): 1,2) At most \(\scriptsize N\)N comparisons with value using operator==. 3,4) At most \(\scriptsize N\)N applications of the predicate p. 5,6) At most \(\scriptsize N\)N applications of the predicate q. Exceptions The overloads with a template parameter named ExecutionPolicy report er- rors 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::terminate is called. For any other ExecutionPolicy, the behavior is implementation-de- fined. * If the algorithm fails to allocate memory, std::bad_alloc is thrown. Possible implementation find template<class InputIt, class T = typename std::iterator_traits<In- putIt>::value_type> constexpr InputIt find(InputIt first, InputIt last, const T& value) { for (; first != last; ++first) if (*first == value) return first; return last; } find_if template<class InputIt, class UnaryPred> constexpr InputIt find_if(InputIt first, InputIt last, UnaryPred p) { for (; first != last; ++first) if (p(*first)) return first; return last; } find_if_not template<class InputIt, class UnaryPred> constexpr InputIt find_if_not(InputIt first, InputIt last, UnaryPred q) { for (; first != last; ++first) if (!q(*first)) return first; return last; } Notes If C++11 is not available, an equivalent to std::find_if_not is to use std::find_if with the negated predicate. template<class InputIt, class UnaryPred> InputIt find_if_not(InputIt first, InputIt last, UnaryPred q) { return std::find_if(first, last, std::not1(q)); } Feature-test macro Value Std Feature __cpp_lib_algorithm_default_value_type 202403 (C++26) List-initializa- tion for algorithms (1,2) Example The following example finds numbers in given sequences. // Run this code #include <algorithm> #include <array> #include <cassert> #include <complex> #include <iostream> #include <vector> int main() { const auto v = {1, 2, 3, 4}; for (const int n : {3, 5}) (std::find(v.begin(), v.end(), n) == std::end(v)) ? std::cout << "v does not contain " << n << '\n' : std::cout << "v contains " << n << '\n'; auto is_even = [](int i) { return i % 2 == 0; }; for (const auto& w : {std::array{3, 1, 4}, {1, 3, 5}}) if (auto it = std::find_if(begin(w), end(w), is_even); it != std::end(w)) std::cout << "w contains an even number " << *it << '\n'; else std::cout << "w does not contain even numbers\n"; std::vector<std::complex<double>> nums{{4, 2}}; #ifdef __cpp_lib_algorithm_default_value_type // T gets deduced making list-initialization possible const auto it = std::find(nums.begin(), nums.end(), {4, 2}); #else const auto it = std::find(nums.begin(), nums.end(), std::com- plex<double>{4, 2}); #endif assert(it == nums.begin()); } Output: v contains 3 v does not contain 5 w contains an even number 4 w does not contain even numbers 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 T was required to be EqualityComparable, LWG 283 C++98 but removed the requirement the value type of InputIt might not be T See also finds the first two adjacent items that are equal (or satisfy a adjacent_find given predicate) (function template) find_end finds the last sequence of elements in a certain range (function template) find_first_of searches for any one of a set of elements (function template) mismatch finds the first position where two ranges differ (function template) search searches for a range of elements (function template) ranges::find ranges::find_if ranges::find_if_not finds the first element satisfying specific criteria (C++20) (niebloid) (C++20) (C++20) http://cppreference.com 2024.06.10 std::find,s...:find_if_not(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Possible implementation | Notes | Example | Output: | See also
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