std::ranges:: ends_with

From cppreference.com

Defined in header `<algorithm>`
Call signature
template < std:: input_iterator I1, std:: sentinel_for < I1 > S1, std:: input_iterator I2, std:: sentinel_for < I2 > S2, class Pred = ranges:: equal_to , class Proj1 = std:: identity , class Proj2 = std:: identity > requires ( std:: forward_iterator < I1 > \|\| std:: sized_sentinel_for < S1, I1 > ) && ( std:: forward_iterator < I2 > \|\| std:: sized_sentinel_for < S2, I2 > ) && std:: indirectly_comparable < I1, I2, Pred, Proj1, Proj2 > constexpr bool ends_with ( I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = { } , Proj1 proj1 = { } , Proj2 proj2 = { } ) ;	(1)	(since C++23)
template < ranges:: input_range R1, ranges:: input_range R2, class Pred = ranges:: equal_to , class Proj1 = std:: identity , class Proj2 = std:: identity > requires ( ranges:: forward_range < R1 > \|\| ranges:: sized_range < R1 > ) && ( ranges:: forward_range < R2 > \|\| ranges:: sized_range < R2 > ) && std:: indirectly_comparable < ranges:: iterator_t < R1 > , ranges:: iterator_t < R2 > , Pred, Proj1, Proj2 > constexpr bool ends_with ( R1 && r1, R2 && r2, Pred pred = { } , Proj1 proj1 = { } , Proj2 proj2 = { } ) ;	(2)	(since C++23)

Checks whether the second range matches the suffix of the first range.

1) Let N1 be ranges:: distance ( first1, last1 ) and N2 be ranges:: distance ( first2, last2 ) :

If N1 < N2 is true , returns false .
Otherwise, returns ranges:: equal ( std :: move ( first1 ) + ( N1 - N2 ) , last1,
std :: move ( first2 ) , last2, pred, proj1, proj2 ) .

2) Let N1 be ranges:: distance ( r1 ) and N2 be ranges:: distance ( r2 ) .

If N1 < N2 is true , returns false .
Otherwise, returns ranges:: equal ( views:: drop ( ranges:: ref_view ( r1 ) ,
N1 - static_cast < decltype ( N1 ) > ( N2 ) ) ,
r2, pred, proj1, proj2 ) .

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 range of elements to examine
r1	-	the range of elements to examine
first2, last2	-	the range of elements to be used as the suffix
r2	-	the range of elements to be used as the suffix
pred	-	the binary predicate that compares the projected elements
proj1	-	the projection to apply to the elements of the range to examine
proj2	-	the projection to apply to the elements of the range to be used as the suffix

Return value

true if the second range matches the suffix of the first range, false otherwise.

Complexity

Generally linear: at most $min(N1,N2)$ applications of the predicate and both projections. The predicate and both projections are not applied if N1 < N2 is true .

If both N1 and N2 can be calculated in constant time (i.e. both iterator-sentinel type pairs model sized_sentinel_for , or both range types model sized_range ) and N1 < N2 is true , the time complexity is constant.

Possible implementation

struct ends_with_fn
{
    template<std::input_iterator I1, std::sentinel_for<I1> S1,
             std::input_iterator I2, std::sentinel_for<I2> S2,
             class Pred = ranges::equal_to,
             class Proj1 = std::identity, class Proj2 = std::identity>
    requires (std::forward_iterator<I1> || std::sized_sentinel_for<S1, I1>) &&
             (std::forward_iterator<I2> || std::sized_sentinel_for<S2, I2>) &&
             std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
    constexpr bool operator()(I1 first1, S1 last1, I2 first2, S2 last2,
                              Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        const auto n1 = ranges::distance(first1, last1);
        const auto n2 = ranges::distance(first2, last2);
        if (n1 < n2)
            return false;
        ranges::advance(first1, n1 - n2);
        return ranges::equal(std::move(first1), last1,
                             std::move(first2), last2,
                             pred, proj1, proj2);
    }
 
    template<ranges::input_range R1, ranges::input_range R2,
             class Pred = ranges::equal_to,
             class Proj1 = std::identity, class Proj2 = std::identity>
    requires (ranges::forward_range<R1> || ranges::sized_range<R1>) &&
             (ranges::forward_range<R2> || ranges::sized_range<R2>) &&
             std::indirectly_comparable<ranges::iterator_t<R1>,
                                        ranges::iterator_t<R2>,
                                        Pred, Proj1, Proj2>
    constexpr bool operator()(R1&& r1, R2&& r2,
                              Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        const auto n1 = ranges::distance(r1);
        const auto n2 = ranges::distance(r2);
        if (n1 < n2)
            return false;
        return ranges::equal(views::drop(ranges::ref_view(r1),
                                         n1 - static_cast<decltype(n1)>(n2)),
                             r2, pred, proj1, proj2);
    }
};
 
inline constexpr ends_with_fn ends_with{};

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_ranges_starts_ends_with`	202106L	(C++23)	std::ranges::starts_with , `std::ranges::ends_with`

Example

Run this code

#include <algorithm>
#include <array>
 
static_assert
(
    ! std::ranges::ends_with("for", "cast") &&
    std::ranges::ends_with("dynamic_cast", "cast") &&
    ! std::ranges::ends_with("as_const", "cast") &&
    std::ranges::ends_with("bit_cast", "cast") &&
    ! std::ranges::ends_with("to_underlying", "cast") &&
    std::ranges::ends_with(std::array{1, 2, 3, 4}, std::array{3, 4}) &&
    ! std::ranges::ends_with(std::array{1, 2, 3, 4}, std::array{4, 5})
);
 
int main() {}

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 4105	C++23	overload ( 2 ) calculated the size difference by N1 - N2 ^[1]	changed to N1 - static_cast < decltype ( N1 ) > ( N2 )

↑ Its result might be of an integer-class type , in this case ranges::drop_view cannot be constructed.

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Technical specifications
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External libraries

ranges::starts_with (C++23)	checks whether a range starts with another range (algorithm function object)
ends_with (C++20)	checks if the string ends with the given suffix (public member function of `std::basic_string<CharT,Traits,Allocator>` )
ends_with (C++20)	checks if the string view ends with the given suffix (public member function of `std::basic_string_view<CharT,Traits>` )