# 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

### 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 no such sequence is found, `last` is returned. | (until C++11)
If `[s_first, s_last)` is empty or if no such sequence is found, `last` is returned. | (since C++11)

### Complexity

Does at most `S*(N-S+1)` comparisons where S = distance(s_first, s_last) and N = distance(first, last).

### 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

First version

    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;
    }

Second version

    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

The following code uses `find_end()` to search for two different sequences of numbers.

Run this code

    #include <algorithm>
    #include <iostream>
    #include <vector>

    int main()
    {
        std::vector<int> v{1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4};
        std::vector<int>::iterator result;

        std::vector<int> t1{1, 2, 3};

        result = std::find_end(v.begin(), v.end(), t1.begin(), t1.end());
        if (result == v.end()) {
            std::cout << "sequence not found\n";
        } else {
            std::cout << "last occurrence is at: "
                      << std::distance(v.begin(), result) << "\n";
        }

        std::vector<int> t2{4, 5, 6};
        result = std::find_end(v.begin(), v.end(), t2.begin(), t2.end());
        if (result == v.end()) {
            std::cout << "sequence not found\n";
        } else {
            std::cout << "last occurrence is at: "
                      << std::distance(v.begin(), result) << "\n";
        }
    }

Output:

    last occurrence is at: 8
    sequence not found

### See also

search | searches for a range of elements (function template)
includes | returns true if one set is a subset of another (function template)
adjacent_find | finds the first two adjacent items that are equal (or satisfy a given predicate) (function template)
findfind_iffind_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)

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