std::find, std::find_if, std::find_if_not

 

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Feature test macros(C++20)

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Ranges library(C++20)

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External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges(C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Defined in header <algorithm>
	(1)
template<class InputIt, class T > InputIt find( InputIt first, InputIt last, const T& value );			(constexpr since C++20) (until C++26)
template<class InputIt, class T =typenamestd::iterator_traits                                        <InputIt>::value_type> constexpr InputIt find( InputIt first, InputIt last, const T& value );			(since C++26)
		(2)
template<class ExecutionPolicy, class ForwardIt, class T > ForwardIt find( ExecutionPolicy&& policy,                 ForwardIt first, ForwardIt last, const T& value );				(since C++17) (until C++26)
template<class ExecutionPolicy,           class ForwardIt, class T =typenamestd::iterator_traits                                          <ForwardIt>::value_type> ForwardIt find( ExecutionPolicy&& policy,                 ForwardIt first, ForwardIt last, const T& value );				(since C++26)
template<class InputIt, class UnaryPred > InputIt find_if( InputIt first, InputIt last, UnaryPred p );			(3)	(constexpr since C++20)
template<class ExecutionPolicy, class ForwardIt, class UnaryPred > ForwardIt find_if( ExecutionPolicy&& policy,                    ForwardIt first, ForwardIt last, UnaryPred p );			(4)	(since C++17)
template<class InputIt, class UnaryPred > InputIt find_if_not( InputIt first, InputIt last, UnaryPred q );			(5)	(since C++11) (constexpr since C++20)
template<class ExecutionPolicy, class ForwardIt, class UnaryPred > ForwardIt find_if_not( ExecutionPolicy&& policy,                        ForwardIt first, ForwardIt last, UnaryPred q );			(6)	(since C++17)

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 all following conditions are satisfied:

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 pair of iterators defining the range of elements to examine
value	-	value to compare the elements to
policy	-	the execution policy to use
p	-	unary predicate which returns ​true for the required element. The expression p(v) must be convertible to bool for every argument v 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). ​
q	-	unary predicate which returns ​false for the required element. The expression q(v) must be convertible to bool for every argument v 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 following 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 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::terminate 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

find (1)
template<class InputIt, class T =typenamestd::iterator_traits<InputIt>::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 (3)
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 (5)
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-initialization 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 <initializer_list>#include <iostream>#include <vector>   bool is_even(int i){return i %2==0;}   void example_contains(){constauto haystack ={1, 2, 3, 4};   for(constint needle :{3, 5})if(std::find(haystack.begin(), haystack.end(), needle)== haystack.end())std::cout<<"haystack does not contain "<< needle <<'\n';elsestd::cout<<"haystack contains "<< needle <<'\n';}   void example_predicate(){for(constauto& haystack :{std::array{3, 1, 4}, {1, 3, 5}}){constauto it = std::find_if(haystack.begin(), haystack.end(), is_even);if(it != haystack.end())std::cout<<"haystack contains an even number "<<*it <<'\n';elsestd::cout<<"haystack does not contain even numbers\n";}}   void example_list_init(){std::vector<std::complex<double>> haystack{{4.0, 2.0}};#ifdef __cpp_lib_algorithm_default_value_type// T gets deduced making list-initialization possibleconstauto it = std::find(haystack.begin(), haystack.end(), {4.0, 2.0});#elseconstauto it = std::find(haystack.begin(), haystack.end(), std::complex{4.0, 2.0});#endifassert(it == haystack.begin());}   int main(){ example_contains(); example_predicate(); example_list_init();}

Output:

haystack contains 3 haystack does not contain 5 haystack contains an even number 4 haystack does not contain even numbers

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 283	C++98	T was required to be EqualityComparable, but the value type of InputIt might not be T	removed the requirement

See also

adjacent_find	finds the first two adjacent items that are equal (or satisfy a 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 the first occurrence of a range of elements (function template)
ranges::findranges::find_ifranges::find_if_not (C++20)(C++20)(C++20)	finds the first element satisfying specific criteria (algorithm function object)