27 Time library [time]

27.5 Class template duration [time.duration]

27.5.1 General [time.duration.general]

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A duration type measures time between two points in time (time_­points).
A duration has a representation which holds a count of ticks and a tick period.
The tick period is the amount of time which occurs from one tick to the next, in units of seconds.
It is expressed as a rational constant using the template ratio.
namespace std::chrono { template<class Rep, class Period = ratio<1>> class duration { public: using rep = Rep; using period = typename Period::type; private: rep rep_; // exposition only public: // [time.duration.cons], construct/copy/destroy constexpr duration() = default; template<class Rep2> constexpr explicit duration(const Rep2& r); template<class Rep2, class Period2> constexpr duration(const duration<Rep2, Period2>& d); ~duration() = default; duration(const duration&) = default; duration& operator=(const duration&) = default; // [time.duration.observer], observer constexpr rep count() const; // [time.duration.arithmetic], arithmetic constexpr common_type_t<duration> operator+() const; constexpr common_type_t<duration> operator-() const; constexpr duration& operator++(); constexpr duration operator++(int); constexpr duration& operator--(); constexpr duration operator--(int); constexpr duration& operator+=(const duration& d); constexpr duration& operator-=(const duration& d); constexpr duration& operator*=(const rep& rhs); constexpr duration& operator/=(const rep& rhs); constexpr duration& operator%=(const rep& rhs); constexpr duration& operator%=(const duration& rhs); // [time.duration.special], special values static constexpr duration zero() noexcept; static constexpr duration min() noexcept; static constexpr duration max() noexcept; }; }
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Rep shall be an arithmetic type or a class emulating an arithmetic type.
If duration is instantiated with a duration type as the argument for the template parameter Rep, the program is ill-formed.
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If Period is not a specialization of ratio, the program is ill-formed.
If Period​::​num is not positive, the program is ill-formed.
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Members of duration do not throw exceptions other than those thrown by the indicated operations on their representations.
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The defaulted copy constructor of duration shall be a constexpr function if and only if the required initialization of the member rep_­ for copy and move, respectively, would satisfy the requirements for a constexpr function.
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[Example 1: duration<long, ratio<60>> d0; // holds a count of minutes using a long duration<long long, milli> d1; // holds a count of milliseconds using a long long duration<double, ratio<1, 30>> d2; // holds a count with a tick period of of a second // (30 Hz) using a double — end example]