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std::ranges::ends_with

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations Copy operations
(C++11)
(C++11)
Swap operations Transformation operations Generation operations Removing operations Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations Binary search operations
(on partitioned ranges) Set operations (on sorted ranges) Merge operations (on sorted ranges) Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations Permutation operations


C library
Numeric operations
 
Constrained algorithms
All names in this menu belong to namespace std::ranges
Non-modifying sequence operations
(C++23)
ends_with
(C++23)

Modifying sequence operations
Partitioning operations
Sorting operations
       
Binary search operations (on sorted ranges)
       
       
    
Set operations (on sorted ranges)
     
        
Heap operations
     
         
Minimum/maximum operations
       
       
Permutation operations
Fold operations
(C++23)
(C++23)  
(C++23)
(C++23)  
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:

Contents

[edit] Parameters

first1, last1 - the iterator-sentinel pair defining the range of elements to examine
r1 - the range of elements to examine
first2, last2 - the iterator-sentinel pair defining 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

[edit] Return value

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

[edit] Complexity

Generally linear: at most \(\scriptsize \min(N1,N2) \)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.

[edit] 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{};

[edit] Notes

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

[edit] 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() {}

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

[edit] See also

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

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