# std::find_end

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
| (1) |
template< class ForwardIt1, class ForwardIt2 > ForwardIt1 find_end( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); |  | (until C++20)
template< class ForwardIt1, class ForwardIt2 > constexpr ForwardIt1 find_end( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); |  | (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt1 find_end( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); | (2) | (since C++17)
| (3) |
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 find_end( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); |  | (until C++20)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > constexpr ForwardIt1 find_end( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); |  | (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 find_end( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); | (4) | (since C++17)

Searches for the last occurrence of the sequence `[`s_first`,` s_last`)` in the range `[`first`,` 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
- `ForwardIt1` must meet the requirements of LegacyForwardIterator.
- `ForwardIt2` must meet the requirements of LegacyForwardIterator.

### Return value

Iterator to the beginning of last occurrence of the sequence `[`s_first`,` s_last`)` in range `[`first`,` last`)`.

If `[`s_first`,` s_last`)` is empty or if no such sequence is found, last is returned.

### Complexity

Given \(\scriptsize N\)N as std::distance(first1, last1) and \(\scriptsize S\)S as std::distance(first2, last2):

1,2) At most \(\scriptsize S\cdot(N-S+1)\)S·(N-S+1) comparisons using operator==.
3,4) At most \(\scriptsize S\cdot(N-S+1)\)S·(N-S+1) 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_end (1)
    template<class ForwardIt1, class ForwardIt2>
    ForwardIt1 find_end(ForwardIt1 first, ForwardIt1 last,
                        ForwardIt2 s_first, ForwardIt2 s_last)
    {
        if (s_first == s_last)
            return last;
        ForwardIt1 result = last;
        while (true)
        {
            ForwardIt1 new_result = std::search(first, last, s_first, s_last);
            if (new_result == last)
                break;
            else
            {
                result = new_result;
                first = result;
                ++first;
            }
        }
        return result;
    }
find_end (3)
    template<class ForwardIt1, class ForwardIt2, class BinaryPredicate>
    ForwardIt1 find_end(ForwardIt1 first, ForwardIt1 last,
                        ForwardIt2 s_first, ForwardIt2 s_last,
                        BinaryPredicate p)
    {
        if (s_first == s_last)
            return last;
        ForwardIt1 result = last;
        while (true)
        {
            ForwardIt1 new_result = std::search(first, last, s_first, s_last, p);
            if (new_result == last)
                break;
            else
            {
                result = new_result;
                first = result;
                ++first;
            }
        }
        return result;
    }

### Example

Run this code

    #include <algorithm>
    #include <array>
    #include <cmath>
    #include <iostream>

    auto print_result = [](auto result, const auto& v)
    {
        result == v.end()
            ? std::cout << "Sequence not found\n"
            : std::cout << "Last occurrence is at: " << std::distance(v.begin(), result)
                        << '\n';
    };

    int main()
    {
        const auto v = {1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4};

        for (auto const& x : {std::array{1, 2, 3}, {4, 5, 6}})
        {
            auto iter = std::find_end(v.begin(), v.end(), x.begin(), x.end()); // overload (1)
            print_result(iter, v);
        }

        for (auto const& x : {std::array{-1, -2, -3}, {-4, -5, -6}})
        {
            auto iter = std::find_end(v.begin(), v.end(), x.begin(), x.end(), // overload (3)
                                      [](int x, int y)
                                      {
                                          return std::abs(x) == std::abs(y);
                                      });
            print_result(iter, v);
        }
    }

Output:

    Last occurrence is at: 8
    Sequence not found
    Last occurrence is at: 8
    Sequence not found

### 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 1205 | C++98 | the return value was unclear if `[`s_first`,` s_last`)` is empty | returns last in this case

### See also

search | searches for a range of elements (function template)
includes | returns true if one sequence is a subsequence of another (function template)
adjacent_find | finds the first two adjacent items that are equal (or satisfy a given predicate) (function template)
find find_if find_if_not (C++11) | finds the first element satisfying specific criteria (function template)
find_first_of | searches for any one of a set of elements (function template)
search_n | searches a range for a number of consecutive copies of an element (function template)
ranges::find_end (C++20) | finds the last sequence of elements in a certain range (niebloid)

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