2. リファレンス
3. algorithm
4. copy_n

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

履歴 編集

std::ranges::copy_n(C++20)

namespace std::ranges {
  template <input_iterator I,
            weakly_incrementable O>
    requires indirectly_copyable<I, O>
  constexpr copy_n_result<I, O>
    copy_n(I first,
           iter_difference_t<I> n,
           O result);                // (1) C++20

  template <execution-policy Ep,
            random_access_iterator I,
            random_access_iterator O,
            sized_sentinel_for<O> OutS>
    requires indirectly_copyable<I, O>
  copy_n_result<I, O>
    copy_n(Ep&& exec,
           I first,
           iter_difference_t<I> n,
           O result,
           OutS result_last);        // (2) C++26
}

copy_n_result {
  .in  = first + n,
  .out = result + n,
}

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

int main() {
  std::vector<int> v = { 3, 1, 5, 2, 4 };
  std::ranges::copy_n(v.begin(), 5, std::ostream_iterator<int>(std::cout, "\n"));
}

3
1
5
2
4

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

int main() {
  std::vector<int> src = {1, 2, 3, 4, 5};
  std::vector<int> dst(5);

  // 並列に先頭3要素をコピー
  std::ranges::copy_n(std::execution::par, src.begin(), 3,
                      dst.begin(), dst.begin() + 3);

  for (int x : dst) {
    std::cout << x << ' ';
  }
  std::cout << std::endl;
}

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