std::find_first_of

 

C++

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Feature test macros (C++20)

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Ranges library (C++20)

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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>
template< class InputIt, class ForwardIt > InputIt find_first_of( InputIt first, InputIt last,                        ForwardIt s_first, ForwardIt s_last );	(1)	(constexpr 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)
template< class InputIt, class ForwardIt, class BinaryPred > InputIt find_first_of( InputIt first, InputIt last,                        ForwardIt s_first, ForwardIt s_last,                        BinaryPred p );	(3)	(constexpr since C++20)
template< class ExecutionPolicy,           class ForwardIt1, class ForwardIt2, class BinaryPred > ForwardIt1 find_first_of( ExecutionPolicy&& policy,                           ForwardIt1 first, ForwardIt last,                           ForwardIt2 s_first, ForwardIt2 s_last,                           BinaryPred 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 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
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.
- BinaryPred 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 [s_first, s_last) is empty or if no such element is found, last is returned.

Complexity

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

1,2) At most \(\scriptsize N\cdot S\)N·S comparisons using operator==.

3,4) At most \(\scriptsize N\cdot S\)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 BinaryPred> InputIt find_first_of(InputIt first, InputIt last, ForwardIt s_first, ForwardIt s_last, BinaryPred 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 = [](const auto id, const auto& 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
LWG 1205	C++98	the return value was unclear if [s_first, s_last) is empty	returns last in this case

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)