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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

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

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

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
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	search search_n lexicographical_compare lexicographical_compare_three_way (C++20)	findfind_iffind_if_not (C++11) find_end find_first_of
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)
C library
qsort	bsearch

 

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 do not participate in overload resolution unless

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) is true

5,6) q(*it) is false

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 std::vector.

Run this code

#include <algorithm>
#include <array>
#include <iostream>
 
int main()
{
    const auto v = {1, 2, 3, 4};
 
    for (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 (auto const& 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";
}

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 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 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)