op_minus.md

operator- (非メンバ関数)

• iterator[meta header]
• std[meta namespace]
• function template[meta id-type]
• cpp11[meta cpp]

namespace std {
  template <class Iterator>
  class move_iterator {

    template <sized_sentinel_for<Iterator> S>
    friend constexpr iter_difference_t<Iterator>
      operator-(const move_sentinel<S>& x, const move_iterator& y); // (1) C++20

    template <sized_sentinel_for<Iterator> S>
    friend constexpr iter_difference_t<Iterator>
      operator-(const move_iterator& x, const move_sentinel<S>& y); // (2) C++20
  };

  template <class Iterator1, class Iterator2>
  auto operator-(const move_iterator<Iterator1>& x,
                 const move_iterator<Iterator2>& y)
    -> decltype(x.base() - y.base());                               // (3) C++11

  template <class Iterator1, class Iterator2>
  constexpr auto operator-(const move_iterator<Iterator1>& x,
                           const move_iterator<Iterator2>& y)
    -> decltype(x.base() - y.base());                               // (3) C++17
}

• base[link /reference/iterator/move_iterator/base.md]
• sized_sentinel_for[link /reference/iterator/sized_sentinel_for.md]
• iter_difference_t[link /reference/iterator/iter_difference_t.md]
• move_sentinel[link /reference/iterator/move_sentinel.md]

概要

2つのイテレータの差を求める。

戻り値

return x.base() - y.base();

x.base()とy.base()はオーバーロードによって次のどちらか

• move_iterator::base()
• move_sentinel::base()

例

#include <iostream>
#include <vector>
#include <memory>
#include <iterator>

int main()
{
  std::vector<std::unique_ptr<int>> v;
  for (int i = 0; i < 5; ++i)
    v.emplace_back(new int(i));

  auto it1 = std::make_move_iterator(v.begin());
  auto it2 = std::make_move_iterator(v.end());

  std::ptrdiff_t result = it2 - it1;
  std::cout << result << std::endl;
}

• it2 - it1[color ff0000]
• v.emplace_back[link /reference/vector/vector/emplace_back.md]
• std::make_move_iterator[link /reference/iterator/make_move_iterator.md]

出力

5

バージョン

言語

• C++11

処理系

• Clang: ??
• GCC: 4.7.0 [mark verified]
• ICC: ??
• Visual C++: ??

参照

• LWG Issue 685. reverse_iterator/move_iterator difference has invalid signatures
• P0031R0 A Proposal to Add Constexpr Modifiers to reverse_iterator, move_iterator, array and Range Access
• P0896R4 The One Ranges Proposal (was Merging the Ranges TS)