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

 

C++

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Freestanding and hosted

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Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

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Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

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 );			(until C++20)
template< class InputIt, class T > constexpr InputIt find( InputIt first, InputIt last, const T& value );			(since C++20)
template< class ExecutionPolicy, class ForwardIt, class T > ForwardIt find( ExecutionPolicy&& policy,                 ForwardIt first, ForwardIt last, const T& value );		(2)	(since C++17)
		(3)
template< class InputIt, class UnaryPredicate > InputIt find_if( InputIt first, InputIt last, UnaryPredicate p );				(until C++20)
template< class InputIt, class UnaryPredicate > constexpr InputIt find_if( InputIt first, InputIt last, UnaryPredicate p );				(since C++20)
template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate > ForwardIt find_if( ExecutionPolicy&& policy,                    ForwardIt first, ForwardIt last, UnaryPredicate p );			(4)	(since C++17)
			(5)
template< class InputIt, class UnaryPredicate > InputIt find_if_not( InputIt first, InputIt last, UnaryPredicate q );					(since C++11) (until C++20)
template< class InputIt, class UnaryPredicate > constexpr InputIt find_if_not( InputIt first, InputIt last, UnaryPredicate q );					(since C++20)
template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate > ForwardIt find_if_not( ExecutionPolicy&& policy,                        ForwardIt first, ForwardIt last, UnaryPredicate 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

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 details.
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) != false is true

5,6) q(*it) == false is true

Complexity

Given N as std::distance(first, last):

1,2) at most N comparisons with value using operator==

3,4) at most N applications of the predicate p

5,6) at most 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
template<class InputIt, class T> 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 UnaryPredicate> constexpr InputIt find_if(InputIt first, InputIt last, UnaryPredicate p) { for (; first != last; ++first) if (p(*first)) return first;   return last; }
find_if_not
template<class InputIt, class UnaryPredicate> constexpr InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q) { for (; first != last; ++first) if (!q(*first)) return first;   return last; }

Notes

If you do not have C++11, an equivalent to std::find_if_not is to use std::find_if with the negated predicate.

template<class InputIt, class UnaryPredicate> InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q) { return std::find_if(first, last, std::not1(q)); }

Example

The following example finds integers in given vector.

Run this code

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> v {1, 2, 3, 4};
    int n1 = 3;
    int n2 = 5;
    auto is_even = [](int i){ return i % 2 == 0; };
 
    auto result1 = std::find(begin(v), end(v), n1);
    auto result2 = std::find(begin(v), end(v), n2);
    auto result3 = std::find_if(begin(v), end(v), is_even);
 
    (result1 != std::end(v))
        ? std::cout << "v contains " << n1 << '\n'
        : std::cout << "v does not contain " << n1 << '\n';
 
    (result2 != std::end(v))
        ? std::cout << "v contains " << n2 << '\n'
        : std::cout << "v does not contain " << n2 << '\n';
 
    (result3 != std::end(v))
        ? std::cout << "v contains an even number: " << *result3 << '\n'
        : std::cout << "v does not contain even numbers\n";
}

Output:

v contains 3
v does not contain 5
v contains an even number: 2

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 is not always 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 (niebloid)