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最終更新日時: 2026年09月11日 13時06分31秒 (JST)
Akira Takahashi が更新

function template

std::ranges::ends_with(C++23)

namespace std::ranges {
  template <input_iterator I1,
            sentinel_for<I1> S1,
            input_iterator I2,
            sentinel_for<I2> S2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires (forward_iterator<I1> || sized_sentinel_for<S1, I1>) &&
             (forward_iterator<I2> || sized_sentinel_for<S2, I2>) &&
             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) C++23

  template <input_range R1,
            input_range R2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires (forward_range<R1> || sized_range<R1>) &&
             (forward_range<R2> || sized_range<R2>) &&
             indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr bool
    ends_with(R1&& r1,
              R2&& r2,
              Pred pred = {},
              Proj1 proj1 = {},
              Proj2 proj2 = {}); // (2) C++23

  template <execution-policy Ep,
            random_access_iterator I1,
            sized_sentinel_for<I1> S1,
            random_access_iterator I2,
            sized_sentinel_for<I2> S2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
  bool
    ends_with(Ep&& exec,
              I1 first1,
              S1 last1,
              I2 first2,
              S2 last2,
              Pred pred = {},
              Proj1 proj1 = {},
              Proj2 proj2 = {}); // (3) 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 indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  bool
    ends_with(Ep&& exec,
              R1&& r1,
              R2&& r2,
              Pred pred = {},
              Proj1 proj1 = {},
              Proj2 proj2 = {}); // (4) C++26
}

概要

シーケンスの末尾が指定されたシーケンスと一致するかを調べる

(1): イテレータ範囲を指定する
(2): Rangeを直接指定する
(3): (1)の並列アルゴリズム版。実行ポリシーを指定する
(4): (2)の並列アルゴリズム版。実行ポリシーを指定する

戻り値

(1):
- N1 = last1 - first1, N2 = last2 - first2 とする。
- N1 < N2 のとき、false
- それ以外のとき、ranges::equal(std::move(first1) + (N1 - N2), last1, std::move(first2), last2, pred, proj1, proj2)
(2):
- N1 = ranges::distance(r1), N2 = ranges::distance(r2) とする。
- N1 < N2 のとき、false
- それ以外のとき、ranges::equal(ranges::drop_view(ranges::ref_view(r1), N1 - static_cast<decltype(N1)>(N2)), r2, pred, proj1, proj2)

計算量

最大で N2 回の対応する述語が適用される。

例

基本的な使い方

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

int main() {
  const std::vector v  = { 1,2,3,4,5,6 };
  const std::vector v1 = { 1,2,3 };
  const std::vector v2 = { 4,5,6 };

  std::cout << std::ranges::ends_with(v1, v) << std::endl;
  std::cout << std::ranges::ends_with(v, v1) << std::endl;
  std::cout << std::ranges::ends_with(v, v2) << std::endl;
}

出力

0
0
1

並列アルゴリズムの例 (C++26)

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

int main() {
  std::vector<int> v = {1, 2, 3, 4, 5, 6};
  std::vector<int> suffix = {4, 5, 6};

  std::cout << std::boolalpha;

  // 並列に末尾が一致するかを判定
  bool result = std::ranges::ends_with(std::execution::par, v, suffix);
  std::cout << result << std::endl;
}

出力

true

実装例

struct ends_with_impl {
  template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
    requires (forward_iterator<I1> || sized_sentinel_for<S1, I1>) &&
             (forward_iterator<I2> || sized_sentinel_for<S2, I2>) &&
             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 = distance(first1, last1);
    const auto N2 = distance(first2, last2);
    return N1 < N2 ? false :
      equal(move(first1) + (N1 - N2), last1, move(first2), last2, pred, proj1, proj2);
  }

  template<input_range R1, input_range R2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
    requires (forward_range<R1> || sized_range<R1>) &&
             (forward_range<R2> || sized_range<R2>) &&
             indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr bool operator()(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const {
    const auto N1 = distance(r1);
    const auto N2 = distance(r2);
    return N1 < N2 ? false :
      equal(drop_view(ref_view(r1), N1 - N2), r2, pred, proj1, proj2);
  }
};

inline constexpr ends_with_impl ends_with;

バージョン

言語

C++23

処理系

Clang: ??
GCC: ??
Visual C++: ??

参照

N4950 27 Algorithms library
P3179R9 C++ parallel range algorithms
LWG Issue 4105. ranges::ends_with's Returns misses difference casting
- C++26で、範囲版の戻り値でN1 - N2がN1 - static_cast<decltype(N1)>(N2)に修正され、N1とN2の差分型が異なる場合にも正しく計算されるようになった

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