std::ranges::find_end - cppreference.com

Defined in header `<algorithm>`
Call signature
template< std::forward_iterator I1, std::sentinel_for<I1> S1, std::forward_iterator I2, std::sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = std::identity, class Proj2 = std::identity > requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2> constexpr ranges::subrange<I1> find_end( I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );	(1)	(since C++20)
template< ranges::forward_range R1, ranges::forward_range R2, class Pred = ranges::equal_to, class Proj1 = std::identity, class Proj2 = std::identity > requires std::indirectly_comparable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, Pred, Proj1, Proj2> constexpr ranges::borrowed_subrange_t<R1> find_end( R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );	(2)	(since C++20)
template< /execution-policy/ Ep, std::random_access_iterator I1, std::sized_sentinel_for<I1> S1, std::random_access_iterator I2, std::sized_sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity> requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2> ranges::subrange<I1> find_end( Ep&& policy, I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );	(3)	(since C++26)
template< /execution-policy/ Ep, /sized-random-access-range/ R1, /sized-random-access-range/ R2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity> requires std::indirectly_comparable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, Pred, Proj1, Proj2> ranges::borrowed_subrange_t<R1> find_end( Ep&& policy, R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );	(4)	(since C++26)

For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.

Searches for the last occurrence of the target range in the source range. The elements (projected by proj1 and proj2 respectively) are compared using the binary predicate pred.

1) The source range is [first1, last1), and the target range is [first2, last2).

2) The source range is r1, and the target range is r2.

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

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

Explicit template argument lists cannot be specified when calling any of them.
None of them are visible to argument-dependent lookup.
When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

Parameters

first1, last1	-	the iterator-sentinel pair defining the source range
first2, last2	-	the iterator-sentinel pair defining the target range
r1	-	the source range
r2	-	the target range
pred	-	the predicate to be applied to the (projected) elements
proj1	-	the projection to be applied to the elements in the source range
proj2	-	the projection to be applied to the elements in the target range
policy	-	the execution policy to use

Return value

A subrange corresponding to the last occurrence of the target range in the source range.

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

Complexity

Given N₁ as ranges::distance(first1, last1) or ranges::distance(r1), and N₂ as ranges::distance(first2, last2) or ranges::distance(r2):

1,2) At most N₂⋅(N₁-N₂+1) applications of pred and proj.

3,4) 𝓞(N₂⋅(N₁-N₂+1)) applications of pred and proj.

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).

Notes

An implementation can improve efficiency of the search if the iterator types model bidirectional_iterator by searching from the end towards the begin. Modelling random_access_iterator may improve the comparison speed. All this however does not change the theoretical complexity of the worst case.

Possible implementation

struct find_end_fn
{
    template<std::forward_iterator I1, std::sentinel_for<I1> S1,
             std::forward_iterator I2, std::sentinel_for<I2> S2,
             class Pred = ranges::equal_to,
             class Proj1 = std::identity, class Proj2 = std::identity>
        requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
    constexpr ranges::subrange<I1>
        operator()(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
                   Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        if (first2 == last2)
        {
            auto last_it = ranges::next(first1, last1);
            return {last_it, last_it};
        }
        auto result = ranges::search(std::move(first1), last1,
                                     first2, last2, pred, proj1, proj2);
        
        if (result.empty())
            return result;
        
        for (;;)
        {
            auto new_result = ranges::search(std::next(result.begin()), last1,
                                             first2, last2, pred, proj1, proj2);
            if (new_result.empty())
                return result;
            else
                result = std::move(new_result);
        }
    }
    
    template<ranges::forward_range R1, ranges::forward_range R2,
             class Pred = ranges::equal_to,
             class Proj1 = std::identity,
             class Proj2 = std::identity>
        requires std::indirectly_comparable<ranges::iterator_t<R1>,
                                            ranges::iterator_t<R2>,
                                            Pred, Proj1, Proj2>
    constexpr ranges::borrowed_subrange_t<R1>
        operator()(R1&& r1, R2&& r2, Pred pred = {},
                   Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (*this)(ranges::begin(r1),
                       ranges::next(ranges::begin(r1), ranges::end(r1)),
                       ranges::begin(r2),
                       ranges::next(ranges::begin(r2), ranges::end(r2)),
                       std::move(pred), std::move(proj1), std::move(proj2));
    }
};

inline constexpr find_end_fn find_end{};

Example

#include <algorithm>
#include <array>
#include <cctype>
#include <iostream>
#include <ranges>
#include <string_view>

void print(const auto haystack, const auto needle)
{
    const auto pos = std::distance(haystack.begin(), needle.begin());
    std::cout << "In \"";
    for (const auto c : haystack)
        std::cout << c;
    std::cout << "\" found \"";
    for (const auto c : needle)
        std::cout << c;
    std::cout << "\" at position [" << pos << ".." << pos + needle.size() << ")\n"
        << std::string(4 + pos, ' ') << std::string(needle.size(), '^') << '\n';
}

int main()
{
    using namespace std::literals;
    using std::ranges::find_end;
    
    constexpr auto secret{"password password word..."sv};
    constexpr auto wanted{"password"sv};
    
    constexpr auto found1 = find_end(secret.cbegin(), secret.cend(),
                                     wanted.cbegin(), wanted.cend());
    print(secret, found1);
    
    constexpr auto found2 = find_end(secret, "word"sv);
    print(secret, found2);
    
    const auto found3 = find_end(secret, "ORD"sv,
        [](const char x, const char y)
        { // uses a binary predicate
            return std::tolower(x) == std::tolower(y);
        });
    print(secret, found3);
    
    const auto found4 = find_end(secret, "SWORD"sv, {}, {},
        [](char c) { return std::tolower(c); }); // projects the 2nd range
    print(secret, found4);
    
    static_assert(find_end(secret, "PASS"sv).empty()); // => not found
}

Output:

In "password password word..." found "password" at position [9..17)
             ^^^^^^^^
In "password password word..." found "word" at position [18..22)
                      ^^^^
In "password password word..." found "ord" at position [19..22)
                       ^^^
In "password password word..." found "sword" at position [12..17)
                ^^^^^

find_end	finds the last sequence of elements in a certain range (function template) [edit]
ranges::find_lastranges::find_last_ifranges::find_last_if_not (C++23)(C++23)(C++23)	finds the last element satisfying specific criteria (algorithm function object)[edit]
ranges::findranges::find_ifranges::find_if_not (C++20)(C++20)(C++20)	finds the first element satisfying specific criteria (algorithm function object)[edit]
ranges::find_first_of (C++20)	searches for any one of a set of elements (algorithm function object)[edit]
ranges::adjacent_find (C++20)	finds the first two adjacent items that are equal (or satisfy a given predicate) (algorithm function object)[edit]
ranges::search (C++20)	searches for the first occurrence of a range of elements (algorithm function object)[edit]
ranges::search_n (C++20)	searches for the first occurrence of a number consecutive copies of an element in a range (algorithm function object)[edit]