std::find_end - cppreference.com

Defined in header `<algorithm>`
template< class ForwardIt1, class ForwardIt2 > ForwardIt1 find_end( ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2 );	(1)	(constexpr since C++20)
template< class ForwardIt1, class ForwardIt2, class BinaryPred > ForwardIt1 find_end( ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2, BinaryPred p );	(2)	(constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt1 find_end( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2 );	(3)	(since C++17)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryPred > ForwardIt1 find_end( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2, BinaryPred p );	(4)	(since C++17)

Searches for the last occurrence of the target range [first2, last2) in the source range [first1, last1).

1) Elements are compared using operator==.

2) Elements are compared using the given binary predicate p.

3,4) Same as (1,2), but executed according to policy.

These overloads participate in overload resolution only if the value of the following expression is true:

`std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>`	(until C++20)
`std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>`	(since C++20)

Parameters

first1, last1	-	the pair of iterators defining the source range
first2, last2	-	the pair of iterators defining the target range
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.
policy	-	the execution policy to use
Type requirements
- `ForwardIt1` must meet the requirements of LegacyForwardIterator.
- `ForwardIt2` must meet the requirements of LegacyForwardIterator.

Return value

Iterator to the beginning of the last occurrence of the target range in source range.

If the target range is empty or it does not appear in the source range, last1 is returned.

Complexity

Given $\scriptsize N_1$ $N 1$ as std::distance(first1, last1) and $\scriptsize N_2$ $N 2$ as std::distance(first2, last2):

1) At most $\scriptsize N_2\cdot(N_1-N_2+1)$

N 2 \cdot(N 1 -N 2 +1)

comparisons using operator==.

2) At most $\scriptsize N_2\cdot(N_1-N_2+1)$

N 2 \cdot(N 1 -N 2 +1)

applications of p.

3) $\scriptsize \mathcal{O}(N_2\cdot(N_1-N_2+1))$

𝓞(N 2 \cdot(N 1 -N 2 +1))

comparisons using operator==.

4) $\scriptsize \mathcal{O}(N_2\cdot(N_1-N_2+1))$

𝓞(N 2 \cdot(N 1 -N 2 +1))

applications of p.

Exceptions

3,4) During the execution process:

If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

Possible implementation

find_end (1)

template<class ForwardIt1, class ForwardIt2>
constexpr //< since C++20
ForwardIt1 find_end(ForwardIt1 first1, ForwardIt1 last1,
                    ForwardIt2 first2, ForwardIt2 last2)
{
    if (first2 == last2)
        return last1;
    
    ForwardIt1 result = last1;
    while (true)
    {
        ForwardIt1 new_result = std::search(first1, last1, first2, last2);
        if (new_result == last1)
            break;
        else
        {
            result = new_result;
            first1 = result;
            ++first1;
        }
    }
    return result;
}

find_end (2)

template<class ForwardIt1, class ForwardIt2, class BinaryPred>
constexpr //< since C++20
ForwardIt1 find_end(ForwardIt1 first1, ForwardIt1 last1,
                    ForwardIt2 first2, ForwardIt2 last2, BinaryPred p)
{
    if (first2== last2)
        return last1;
    
    ForwardIt1 result = last1;
    while (true)
    {
        ForwardIt1 new_result = std::search(first1, last1, first2, first2, p);
        if (new_result == last1)
            break;
        else
        {
            result = new_result;
            first1 = result;
            ++first1;
        }
    }
    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 (const auto& 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 (const auto& 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 the target range is empty	returns `last1` in this case
LWG 2150	C++98	the condition of “occurence” was incorrect	corrected

Compiler support
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Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
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Numerics library
Date and time library
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Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Technical specifications
Symbols index
External libraries

ranges::find_end (C++20)	finds the last sequence of elements in a certain range (algorithm function object)[edit]
search	searches for the first occurrence of a range of elements (function template & algorithm function object)[edit]
ranges::search (C++20)
includes	determines if one sequence is a subsequence of another (function template & algorithm function object)[edit]
ranges::includes (C++20)
adjacent_find	finds the first two adjacent items that are equal (or satisfy a given predicate) (function template & algorithm function object)[edit]
ranges::adjacent_find (C++20)
findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template & algorithm function object)[edit]
ranges::findranges::find_ifranges::find_if_not (C++20)(C++20)(C++20)
find_first_of	searches for any one of a set of elements (function template & algorithm function object)[edit]
ranges::find_first_of (C++20)
search_n	searches for the first occurrence of a number consecutive copies of an element in a range (function template & algorithm function object)[edit]
ranges::search_n (C++20)