std::find_first_of

 

C++

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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)

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 ForwardIt > InputIt find_first_of( InputIt first, InputIt last,                        ForwardIt s_first, ForwardIt s_last );			(until C++20)
template< class InputIt, class ForwardIt > constexpr InputIt find_first_of( InputIt first, InputIt last,                                  ForwardIt s_first, ForwardIt s_last );			(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt1 find_first_of( ExecutionPolicy&& policy,                           ForwardIt1 first, ForwardIt1 last,                           ForwardIt2 s_first, ForwardIt2 s_last );		(2)	(since C++17)
		(3)
template< class InputIt, class ForwardIt, class BinaryPredicate > InputIt find_first_of( InputIt first, InputIt last,                        ForwardIt s_first, ForwardIt s_last,                        BinaryPredicate p );				(until C++20)
template< class InputIt, class ForwardIt, class BinaryPredicate > constexpr InputIt find_first_of( InputIt first, InputIt last,                                  ForwardIt s_first, ForwardIt s_last,                                  BinaryPredicate p );				(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,           class BinaryPredicate > ForwardIt1 find_first_of( ExecutionPolicy&& policy,                           ForwardIt1 first, ForwardIt last,                           ForwardIt2 s_first, ForwardIt2 s_last,                           BinaryPredicate p );			(4)	(since C++17)

Searches the range [first, last) for any of the elements in the range [s_first, s_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 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
s_first, s_last	-	the range of elements to search for
policy	-	the execution policy to use. See execution policy for details.
p	-	binary predicate which returns ​true if the elements 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); 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 equivalent to a copy (since C++11)). The types Type1 and Type2 must be such that objects of types ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. ​
Type requirements
- InputIt must meet the requirements of LegacyInputIterator.
- ForwardIt must meet the requirements of LegacyForwardIterator.
- ForwardIt1 must meet the requirements of LegacyForwardIterator.
- ForwardIt2 must meet the requirements of LegacyForwardIterator.
- BinaryPredicate must meet the requirements of BinaryPredicate.

Return value

Iterator to the first element in the range [first, last) that is equal to an element from the range [s_first, s_last). If no such element is found, last is returned.

Complexity

Given N as std::distance(first, last) and S as std::distance(s_first, s_last):

1,2) At most N·S comparisons using operator==

3,4) At most N·S applications of the predicate p

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_first_of (1)
template<class InputIt, class ForwardIt> InputIt find_first_of(InputIt first, InputIt last, ForwardIt s_first, ForwardIt s_last) { for (; first != last; ++first) for (ForwardIt it = s_first; it != s_last; ++it) if (*first == *it) return first; return last; }
find_first_of (3)
template<class InputIt, class ForwardIt, class BinaryPredicate> InputIt find_first_of(InputIt first, InputIt last, ForwardIt s_first, ForwardIt s_last, BinaryPredicate p) { for (; first != last; ++first) for (ForwardIt it = s_first; it != s_last; ++it) if (p(*first, *it)) return first; return last; }

Example

The following code searches for any of specified integers in a vector of integers:

Run this code

#include <algorithm>
#include <iostream>
#include <vector>
 
auto print_sequence = [](auto const id, auto const& seq, int pos = -1)
{
    std::cout << id << "{ ";
    for (int i{}; auto const& e : seq)
    {
        const bool mark{i == pos};
        std::cout << (i++ ? ", " : "");
        std::cout << (mark ? "[ " : "") << e << (mark ? " ]" : "");
    }
    std::cout << " }\n";
};
 
int main()
{
    const std::vector<int> v{0, 2, 3, 25, 5};
    const auto t1 = {19, 10, 3, 4};
    const auto t2 = {1, 6, 7, 9};
 
    auto find_any_of = [](const auto& v, const auto& t)
    {
        const auto result = std::find_first_of(v.begin(), v.end(),
                                               t.begin(), t.end());
        if (result == v.end())
        {
            std::cout << "No elements of v are equal to any element of ";
            print_sequence("t = ", t);
            print_sequence("v = ", v);
        }
        else
        {
            const auto pos = std::distance(v.begin(), result);
            std::cout << "Found a match (" << *result << ") at position " << pos;
            print_sequence(", where t = ", t);
            print_sequence("v = ", v, pos);
        }
    };
 
    find_any_of(v, t1);
    find_any_of(v, t2);
}

Output:

Found a match (3) at position 2, where t = { 19, 10, 3, 4 }
v = { 0, 2, [ 3 ], 25, 5 }
No elements of v are equal to any element of t = { 1, 6, 7, 9 }
v = { 0, 2, 3, 25, 5 }

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 576	C++98	first and last needed to be LegacyForwardIterators	they only need to be LegacyInputIterators

See also

findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template)
ranges::find_first_of (C++20)	searches for any one of a set of elements (niebloid)