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• ranges[meta header]
• std::ranges[meta namespace]
• subrange[meta class]
• function[meta id-type]
• cpp20[meta cpp]

[[nodiscard]]
constexpr subrange
  prev(iter_difference_t<I> n = 1) const
    requires bidirectional_iterator<I>;   // (1) C++20
constexpr subrange
  prev(iter_difference_t<I> n = 1) const
    requires bidirectional_iterator<I>;   // (1) C++26

• nodiscard[link /lang/cpp17/nodiscard.md]
• iter_difference_t[link /reference/iterator/iter_difference_t.md]
• bidirectional_iterator[link /reference/iterator/bidirectional_iterator.md]
• subrange[link ../subrange.md]

概要

先頭を後退させたsubrangeを得る。

効果

auto tmp = *this;
tmp.advance(-n);
return tmp;

• advance[link advance.md]

例

#include <ranges>
#include <iostream>

template<std::ranges::range R>
void print(const R& r) {
  for (int x : r) {
    std::cout << x << ',';
  }
  std::cout << '\n';
}

int main()
{
  constexpr int a[] = {1, 2, 3, 4, 5};
  std::ranges::subrange sub(a + 3, a + 4);

  print(sub);
  print(sub.prev());
  print(sub.prev().prev());
}

出力

4,
3,4,
2,3,4,

バージョン

言語

• C++20

処理系

• Clang: 13.0.0 [mark verified]
• GCC: 10.1.0 [mark verified]
• ICC: ?
• Visual C++: 2019 Update 10 [mark verified]

参照

• N4861 24 Ranges library
• C++20 ranges
• P2422R1 Remove nodiscard annotations from the standard library specification
  • C++26で[[nodiscard]]指定が削除された