op_minus.md

operator-

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

namespace std {
namespace chrono {
  // time_point - duration = time_point
  template <class Clock, class Duration1, class Rep2, class Period2>
  time_point<Clock, typename common_type<Duration1, duration<Rep2, Period2>>::type>
    operator-(const time_point<Clock, Duration1>& lhs,
              const duration<Rep2, Period2>& rhs);      // (1) C++11

  // time_point - duration = time_point
  template <class Clock, class Duration1, class Rep2, class Period2>
  constexpr time_point<Clock, typename common_type<Duration1, duration<Rep2, Period2>>::type>
    operator-(const time_point<Clock, Duration1>& lhs,
              const duration<Rep2, Period2>& rhs);      // (1) C++14

  // time_point - time_point = duration
  template <class Clock, class Duration1, class Duration2>
  typename common_type<Duration1, Duration2>::type
    operator-(const time_point<Clock, Duration1>& lhs,
              const time_point<Clock, Duration2>& rhs); // (2) C++11

  // time_point - time_point = duration
  template <class Clock, class Duration1, class Duration2>
  constexpr typename common_type<Duration1, Duration2>::type
    operator-(const time_point<Clock, Duration1>& lhs,
              const time_point<Clock, Duration2>& rhs); // (2) C++14
}}

• common_type[link /reference/chrono/common_type.md]

概要

time_pointの減算を行う。

• (1) : time_pointから時間間隔を減算する
• (2) : time_point同士の差を求める

戻り値

• (1)

return lhs + (-rhs);

• (2)

return lhs.time_since_epoch() - rhs.time_since_epoch();

• time_since_epoch[link time_since_epoch.md]

例

#include <iostream>
#include <chrono>

namespace chrono = std::chrono;

int main()
{
  using time_point = chrono::system_clock::time_point;

  time_point now = chrono::system_clock::now();

  // (1) 
  time_point tp1 = now - chrono::seconds{3};
  auto sec1 = chrono::duration_cast<chrono::seconds>(tp1.time_since_epoch());
  std::cout << sec1.count() << std::endl;

  // (2)
  auto sec2 = chrono::duration_cast<chrono::seconds>(now - tp1);
  std::cout << sec2.count() << std::endl;
}

• count()[link /reference/chrono/duration/count.md]
• chrono::system_clock[link /reference/chrono/system_clock.md]
• now()[link /reference/chrono/system_clock/now.md]
• time_since_epoch()[link time_since_epoch.md]

出力例

1572329112
3

バージョン

言語

• C++11

処理系

• Clang: 3.2
• GCC: 4.6.1
• Visual C++: 2012, 2013, 2015

参照

• N3469 Constexpr Library Additions: chrono, v3