[time.duration]

# 30 Time library [[time]](./#time)

## 30.5 Class template duration [time.duration]

### [30.5.1](#general) General [[time.duration.general]](time.duration.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1238)

A duration type measures time between two points in time (time_points)[.](#general-1.sentence-1)

A duration has a representation which holds a count of ticks and a tick period[.](#general-1.sentence-2)

The tick period is the amount of time which occurs from one tick to the next, in units
of seconds[.](#general-1.sentence-3)

It is expressed as a rational constant using the template ratio[.](#general-1.sentence-4)

[🔗](#lib:duration)

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]](#cons "30.5.2 Constructors"), construct/copy/destroyconstexpr 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 "30.5.3 Observer"), observerconstexpr rep count() const; // [[time.duration.arithmetic]](#arithmetic "30.5.4 Arithmetic"), arithmeticconstexpr 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 "30.5.5 Special values"), special valuesstatic constexpr duration zero() noexcept; static constexpr duration min() noexcept; static constexpr duration max() noexcept; };}

[2](#general-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1294)

Rep shall be an arithmetic type or a class emulating an arithmetic type[.](#general-2.sentence-1)

If duration is instantiated with a duration type as the argument for the template
parameter Rep, the program is ill-formed[.](#general-2.sentence-2)

[3](#general-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1299)

If Period is not a specialization of ratio, the program is ill-formed[.](#general-3.sentence-1)

If Period​::​num is not positive, the program is ill-formed[.](#general-3.sentence-2)

[4](#general-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1303)

Members of duration do not throw exceptions other than
those thrown by the indicated operations on their representations[.](#general-4.sentence-1)

[5](#general-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1307)

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
be constexpr-suitable ([[dcl.constexpr]](dcl.constexpr "9.2.6 The constexpr and consteval specifiers"))[.](#general-5.sentence-1)

[6](#general-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1313)

[*Example [1](#general-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 130 of a second// (30 Hz) using a double — *end example*]

### [30.5.2](#cons) Constructors [[time.duration.cons]](time.duration.cons)

[🔗](#lib:duration,constructor)

`template<class Rep2>
  constexpr explicit duration(const Rep2& r);
`

[1](#cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1332)

*Constraints*: is_convertible_v<const Rep2&, rep> is true and

- [(1.1)](#cons-1.1)

treat_as_floating_point_v<rep> is true or

- [(1.2)](#cons-1.2)

treat_as_floating_point_v<Rep2> is false[.](#cons-1.sentence-1)

[*Example [1](#cons-example-1)*: duration<int, milli> d(3); // OK duration<int, milli> d2(3.5); // error — *end example*]

[2](#cons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1346)

*Effects*: Initializes rep_ with r[.](#cons-2.sentence-1)

[🔗](#lib:duration,constructor_)

`template<class Rep2, class Period2>
  constexpr duration(const duration<Rep2, Period2>& d);
`

[3](#cons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1358)

*Constraints*: No overflow is induced in the conversion andtreat_as_floating_point_v<rep> is true or bothratio_divide<Period2, period>​::​den is 1 andtreat_as_floating_point_v<Rep2> is false[.](#cons-3.sentence-1)

[*Note [1](#cons-note-1)*:

This
requirement prevents implicit truncation error when converting between
integral-based duration types[.](#cons-3.sentence-2)

Such a construction could easily lead to
confusion about the value of the duration[.](#cons-3.sentence-3)

— *end note*]

[*Example [2](#cons-example-2)*: duration<int, milli> ms(3);
duration<int, micro> us = ms; // OK duration<int, milli> ms2 = us; // error — *end example*]

[4](#cons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1378)

*Effects*: Initializes rep_ with duration_cast<duration>(d).count()[.](#cons-4.sentence-1)

### [30.5.3](#observer) Observer [[time.duration.observer]](time.duration.observer)

[🔗](#lib:count,duration)

`constexpr rep count() const;
`

[1](#observer-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1391)

*Returns*: rep_[.](#observer-1.sentence-1)

### [30.5.4](#arithmetic) Arithmetic [[time.duration.arithmetic]](time.duration.arithmetic)

[🔗](#lib:operator+,duration)

`constexpr common_type_t<duration> operator+() const;
`

[1](#arithmetic-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1404)

*Returns*: common_type_t<duration>(*this)[.](#arithmetic-1.sentence-1)

[🔗](#lib:operator-,duration)

`constexpr common_type_t<duration> operator-() const;
`

[2](#arithmetic-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1415)

*Returns*: common_type_t<duration>(-rep_)[.](#arithmetic-2.sentence-1)

[🔗](#lib:operator++,duration)

`constexpr duration& operator++();
`

[3](#arithmetic-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1426)

*Effects*: Equivalent to: ++rep_[.](#arithmetic-3.sentence-1)

[4](#arithmetic-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1430)

*Returns*: *this[.](#arithmetic-4.sentence-1)

[🔗](#lib:operator++,duration_)

`constexpr duration operator++(int);
`

[5](#arithmetic-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1441)

*Effects*: Equivalent to: return duration(rep_++);

[🔗](#lib:operator--,duration)

`constexpr duration& operator--();
`

[6](#arithmetic-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1452)

*Effects*: Equivalent to: --rep_[.](#arithmetic-6.sentence-1)

[7](#arithmetic-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1456)

*Returns*: *this[.](#arithmetic-7.sentence-1)

[🔗](#lib:operator--,duration_)

`constexpr duration operator--(int);
`

[8](#arithmetic-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1467)

*Effects*: Equivalent to: return duration(rep_--);

[🔗](#lib:operator+=,duration)

`constexpr duration& operator+=(const duration& d);
`

[9](#arithmetic-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1478)

*Effects*: Equivalent to: rep_ += d.count()[.](#arithmetic-9.sentence-1)

[10](#arithmetic-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1482)

*Returns*: *this[.](#arithmetic-10.sentence-1)

[🔗](#lib:operator-=,duration)

`constexpr duration& operator-=(const duration& d);
`

[11](#arithmetic-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1493)

*Effects*: Equivalent to: rep_ -= d.count()[.](#arithmetic-11.sentence-1)

[12](#arithmetic-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1497)

*Returns*: *this[.](#arithmetic-12.sentence-1)

[🔗](#lib:operator*=,duration)

`constexpr duration& operator*=(const rep& rhs);
`

[13](#arithmetic-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1508)

*Effects*: Equivalent to: rep_ *= rhs[.](#arithmetic-13.sentence-1)

[14](#arithmetic-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1512)

*Returns*: *this[.](#arithmetic-14.sentence-1)

[🔗](#lib:operator/=,duration)

`constexpr duration& operator/=(const rep& rhs);
`

[15](#arithmetic-15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1523)

*Effects*: Equivalent to: rep_ /= rhs[.](#arithmetic-15.sentence-1)

[16](#arithmetic-16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1527)

*Returns*: *this[.](#arithmetic-16.sentence-1)

[🔗](#lib:operator%25=,duration)

`constexpr duration& operator%=(const rep& rhs);
`

[17](#arithmetic-17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1538)

*Effects*: Equivalent to: rep_ %= rhs[.](#arithmetic-17.sentence-1)

[18](#arithmetic-18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1542)

*Returns*: *this[.](#arithmetic-18.sentence-1)

[🔗](#lib:operator%25=,duration_)

`constexpr duration& operator%=(const duration& rhs);
`

[19](#arithmetic-19)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1553)

*Effects*: Equivalent to: rep_ %= rhs.count()[.](#arithmetic-19.sentence-1)

[20](#arithmetic-20)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1557)

*Returns*: *this[.](#arithmetic-20.sentence-1)

### [30.5.5](#special) Special values [[time.duration.special]](time.duration.special)

[🔗](#lib:zero,duration)

`static constexpr duration zero() noexcept;
`

[1](#special-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1571)

*Returns*: duration(duration_values<rep>​::​zero())[.](#special-1.sentence-1)

[🔗](#lib:min,duration)

`static constexpr duration min() noexcept;
`

[2](#special-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1582)

*Returns*: duration(duration_values<rep>​::​min())[.](#special-2.sentence-1)

[🔗](#lib:max,duration)

`static constexpr duration max() noexcept;
`

[3](#special-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1593)

*Returns*: duration(duration_values<rep>​::​max())[.](#special-3.sentence-1)

### [30.5.6](#nonmember) Non-member arithmetic [[time.duration.nonmember]](time.duration.nonmember)

[1](#nonmember-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1600)

In the function descriptions that follow, unless stated otherwise,
let CD represent the return type of the function[.](#nonmember-1.sentence-1)

[🔗](#lib:operator+,duration_)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
    operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
`

[2](#nonmember-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1612)

*Returns*: CD(CD(lhs).count() + CD(rhs).count())[.](#nonmember-2.sentence-1)

[🔗](#lib:operator-,duration_)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
    operator-(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
`

[3](#nonmember-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1625)

*Returns*: CD(CD(lhs).count() - CD(rhs).count())[.](#nonmember-3.sentence-1)

[🔗](#lib:operator*,duration)

`template<class Rep1, class Period, class Rep2>
  constexpr duration<common_type_t<Rep1, Rep2>, Period>
    operator*(const duration<Rep1, Period>& d, const Rep2& s);
`

[4](#nonmember-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1638)

*Constraints*: is_convertible_v<const Rep2&, common_type_t<Rep1, Rep2>> is true[.](#nonmember-4.sentence-1)

[5](#nonmember-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1642)

*Returns*: CD(CD(d).count() * s)[.](#nonmember-5.sentence-1)

[🔗](#lib:operator*,duration_)

`template<class Rep1, class Rep2, class Period>
  constexpr duration<common_type_t<Rep1, Rep2>, Period>
    operator*(const Rep1& s, const duration<Rep2, Period>& d);
`

[6](#nonmember-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1655)

*Constraints*: is_convertible_v<const Rep1&, common_type_t<Rep1, Rep2>> is true[.](#nonmember-6.sentence-1)

[7](#nonmember-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1659)

*Returns*: d * s[.](#nonmember-7.sentence-1)

[🔗](#lib:operator/,duration)

`template<class Rep1, class Period, class Rep2>
  constexpr duration<common_type_t<Rep1, Rep2>, Period>
    operator/(const duration<Rep1, Period>& d, const Rep2& s);
`

[8](#nonmember-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1672)

*Constraints*: is_convertible_v<const Rep2&, common_type_t<Rep1, Rep2>> is true and Rep2 is not a specialization of duration[.](#nonmember-8.sentence-1)

[9](#nonmember-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1677)

*Returns*: CD(CD(d).count() / s)[.](#nonmember-9.sentence-1)

[🔗](#lib:operator/,duration_)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr common_type_t<Rep1, Rep2>
    operator/(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
`

[10](#nonmember-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1690)

Let CD becommon_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>[.](#nonmember-10.sentence-1)

[11](#nonmember-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1694)

*Returns*: CD(lhs).count() / CD(rhs).count()[.](#nonmember-11.sentence-1)

[🔗](#lib:operator%25,duration)

`template<class Rep1, class Period, class Rep2>
  constexpr duration<common_type_t<Rep1, Rep2>, Period>
    operator%(const duration<Rep1, Period>& d, const Rep2& s);
`

[12](#nonmember-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1707)

*Constraints*: is_convertible_v<const Rep2&, common_type_t<Rep1, Rep2>> is true andRep2 is not a specialization of duration[.](#nonmember-12.sentence-1)

[13](#nonmember-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1712)

*Returns*: CD(CD(d).count() % s)[.](#nonmember-13.sentence-1)

[🔗](#lib:operator%25,duration_)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
    operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
`

[14](#nonmember-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1725)

*Returns*: CD(CD(lhs).count() % CD(rhs).count())[.](#nonmember-14.sentence-1)

### [30.5.7](#comparisons) Comparisons [[time.duration.comparisons]](time.duration.comparisons)

[1](#comparisons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1733)

In the function descriptions that follow, CT representscommon_type_t<A, B>, where A and B are the types of
the two arguments to the function[.](#comparisons-1.sentence-1)

[🔗](#lib:operator==,duration)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator==(const duration<Rep1, Period1>& lhs,
                            const duration<Rep2, Period2>& rhs);
`

[2](#comparisons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1746)

*Returns*: CT(lhs).count() == CT(rhs).count()[.](#comparisons-2.sentence-1)

[🔗](#lib:operator%3c,duration)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator<(const duration<Rep1, Period1>& lhs,
                           const duration<Rep2, Period2>& rhs);
`

[3](#comparisons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1759)

*Returns*: CT(lhs).count() < CT(rhs).count()[.](#comparisons-3.sentence-1)

[🔗](#lib:operator%3e,duration)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator>(const duration<Rep1, Period1>& lhs,
                           const duration<Rep2, Period2>& rhs);
`

[4](#comparisons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1772)

*Returns*: rhs < lhs[.](#comparisons-4.sentence-1)

[🔗](#lib:operator%3c=,duration)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator<=(const duration<Rep1, Period1>& lhs,
                            const duration<Rep2, Period2>& rhs);
`

[5](#comparisons-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1785)

*Returns*: !(rhs < lhs)[.](#comparisons-5.sentence-1)

[🔗](#lib:operator%3e=,duration)

`template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator>=(const duration<Rep1, Period1>& lhs,
                            const duration<Rep2, Period2>& rhs);
`

[6](#comparisons-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1798)

*Returns*: !(lhs < rhs)[.](#comparisons-6.sentence-1)

[🔗](#lib:operator%3c=%3e,duration)

`template<class Rep1, class Period1, class Rep2, class Period2>
  requires [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<typename CT::rep>
  constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,
                             const duration<Rep2, Period2>& rhs);
`

[7](#comparisons-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1812)

*Returns*: CT(lhs).count() <=> CT(rhs).count()[.](#comparisons-7.sentence-1)

### [30.5.8](#cast) Conversions [[time.duration.cast]](time.duration.cast)

[🔗](#lib:duration,duration_cast)

`template<class ToDuration, class Rep, class Period>
  constexpr ToDuration duration_cast(const duration<Rep, Period>& d);
`

[1](#cast-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1827)

*Constraints*: ToDuration is a specialization of duration[.](#cast-1.sentence-1)

[2](#cast-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1831)

*Returns*: Let CF be ratio_divide<Period, typename ToDuration​::​period>, and CR be common_type<typename ToDuration​::​rep, Rep, intmax_t>​::​type[.](#cast-2.sentence-1)

- [(2.1)](#cast-2.1)

If CF​::​num == 1 and CF​::​den == 1, returnsToDuration(static_cast<typename ToDuration::rep>(d.count()))

- [(2.2)](#cast-2.2)

otherwise, if CF​::​num != 1 and CF​::​den == 1, returnsToDuration(static_cast<typename ToDuration::rep>(static_cast<CR>(d.count()) * static_cast<CR>(CF::num)))

- [(2.3)](#cast-2.3)

otherwise, if CF​::​num == 1 and CF​::​den != 1, returnsToDuration(static_cast<typename ToDuration::rep>(static_cast<CR>(d.count()) / static_cast<CR>(CF::den)))

- [(2.4)](#cast-2.4)

otherwise, returnsToDuration(static_cast<typename ToDuration::rep>(static_cast<CR>(d.count()) * static_cast<CR>(CF::num) / static_cast<CR>(CF::den)))

[3](#cast-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1861)

[*Note [1](#cast-note-1)*:

This function does not use any implicit conversions; all conversions
are done with static_cast[.](#cast-3.sentence-1)

It avoids multiplications and divisions when
it is known at compile time that one or more arguments is 1[.](#cast-3.sentence-2)

Intermediate
computations are carried out in the widest representation and only converted to
the destination representation at the final step[.](#cast-3.sentence-3)

— *end note*]

[🔗](#lib:floor,duration)

`template<class ToDuration, class Rep, class Period>
  constexpr ToDuration floor(const duration<Rep, Period>& d);
`

[4](#cast-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1878)

*Constraints*: ToDuration is a specialization of duration[.](#cast-4.sentence-1)

[5](#cast-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1882)

*Returns*: The greatest result t representable in ToDuration for which t <= d[.](#cast-5.sentence-1)

[🔗](#lib:ceil,duration)

`template<class ToDuration, class Rep, class Period>
  constexpr ToDuration ceil(const duration<Rep, Period>& d);
`

[6](#cast-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1895)

*Constraints*: ToDuration is a specialization of duration[.](#cast-6.sentence-1)

[7](#cast-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1899)

*Returns*: The least result t representable in ToDuration for which t >= d[.](#cast-7.sentence-1)

[🔗](#lib:round,duration)

`template<class ToDuration, class Rep, class Period>
  constexpr ToDuration round(const duration<Rep, Period>& d);
`

[8](#cast-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1912)

*Constraints*: ToDuration is a specialization of duration andtreat_as_floating_point_v<typename ToDuration​::​rep> is false[.](#cast-8.sentence-1)

[9](#cast-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1917)

*Returns*: The value of ToDuration that is closest to d[.](#cast-9.sentence-1)

If there are two closest values, then return the value t for which t % 2 == 0[.](#cast-9.sentence-2)

### [30.5.9](#literals) Suffixes for duration literals [[time.duration.literals]](time.duration.literals)

[1](#literals-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1926)

This subclause describes literal suffixes for constructing duration literals[.](#literals-1.sentence-1)

The
suffixes h, min, s, ms, us, ns denote duration values of the corresponding types hours, minutes,seconds, milliseconds, microseconds, and nanoseconds respectively if they are applied to [*integer-literal*](lex.icon#nt:integer-literal "5.13.2 Integer literals [lex.icon]")*s*[.](#literals-1.sentence-2)

[2](#literals-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1933)

If any of these suffixes are applied to a [*floating-point-literal*](lex.fcon#nt:floating-point-literal "5.13.4 Floating-point literals [lex.fcon]") the result is achrono​::​duration literal with an unspecified floating-point representation[.](#literals-2.sentence-1)

[3](#literals-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1938)

If any of these suffixes are applied to an [*integer-literal*](lex.icon#nt:integer-literal "5.13.2 Integer literals [lex.icon]") and the resultingchrono​::​duration value cannot be represented in the result type because
of overflow, the program is ill-formed[.](#literals-3.sentence-1)

[4](#literals-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1944)

[*Example [1](#literals-example-1)*:

The following code shows some duration literals[.](#literals-4.sentence-1)

using namespace std::chrono_literals;auto constexpr aday=24h;auto constexpr lesson=45min;auto constexpr halfanhour=0.5h; — *end example*]

[🔗](#lib:operator%22%22h,duration)

`constexpr chrono::hours                                 operator""h(unsigned long long hours);
constexpr chrono::duration<unspecified, ratio<3600, 1>> operator""h(long double hours);
`

[5](#literals-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1962)

*Returns*: A duration literal representing hours hours[.](#literals-5.sentence-1)

[🔗](#lib:operator%22%22min,duration)

`constexpr chrono::minutes                             operator""min(unsigned long long minutes);
constexpr chrono::duration<unspecified, ratio<60, 1>> operator""min(long double minutes);
`

[6](#literals-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1974)

*Returns*: A duration literal representing minutes minutes[.](#literals-6.sentence-1)

[🔗](#lib:operator%22%22s,duration)

`constexpr chrono::seconds               operator""s(unsigned long long sec);
constexpr chrono::duration<unspecified> operator""s(long double sec);
`

[7](#literals-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1986)

*Returns*: A duration literal representing sec seconds[.](#literals-7.sentence-1)

[8](#literals-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1990)

[*Note [1](#literals-note-1)*:

The same suffix s is used for basic_string but there is no
conflict, since duration suffixes apply to numbers and string literal suffixes
apply to character array literals[.](#literals-8.sentence-1)

— *end note*]

[🔗](#lib:operator%22%22ms,duration)

`constexpr chrono::milliseconds                 operator""ms(unsigned long long msec);
constexpr chrono::duration<unspecified, milli> operator""ms(long double msec);
`

[9](#literals-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2005)

*Returns*: A duration literal representing msec milliseconds[.](#literals-9.sentence-1)

[🔗](#lib:operator%22%22us,duration)

`constexpr chrono::microseconds                 operator""us(unsigned long long usec);
constexpr chrono::duration<unspecified, micro> operator""us(long double usec);
`

[10](#literals-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2017)

*Returns*: A duration literal representing usec microseconds[.](#literals-10.sentence-1)

[🔗](#lib:operator%22%22ns,duration)

`constexpr chrono::nanoseconds                 operator""ns(unsigned long long nsec);
constexpr chrono::duration<unspecified, nano> operator""ns(long double nsec);
`

[11](#literals-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2029)

*Returns*: A duration literal representing nsec nanoseconds[.](#literals-11.sentence-1)

### [30.5.10](#alg) Algorithms [[time.duration.alg]](time.duration.alg)

[🔗](#lib:abs,duration)

`template<class Rep, class Period>
  constexpr duration<Rep, Period> abs(duration<Rep, Period> d);
`

[1](#alg-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2043)

*Constraints*: numeric_limits<Rep>​::​is_signed is true[.](#alg-1.sentence-1)

[2](#alg-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2047)

*Returns*: If d >= d.zero(), return d,
otherwise return -d[.](#alg-2.sentence-1)

### [30.5.11](#io) I/O [[time.duration.io]](time.duration.io)

[🔗](#lib:operator%3c%3c,duration)

`template<class charT, class traits, class Rep, class Period>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const duration<Rep, Period>& d);
`

[1](#io-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2063)

*Effects*: Inserts the duration d onto the stream os as if it were implemented as follows:basic_ostringstream<charT, traits> s;
s.flags(os.flags());
s.imbue(os.getloc());
s.precision(os.precision());
s << d.count() << *units-suffix*;return os << s.str(); where *units-suffix* depends on the type Period​::​type as follows:

- [(1.1)](#io-1.1)

  If Period​::​type is atto,*units-suffix* is "as"[.](#io-1.1.sentence-1)

- [(1.2)](#io-1.2)

  Otherwise, if Period​::​type is femto,*units-suffix* is "fs"[.](#io-1.2.sentence-1)

- [(1.3)](#io-1.3)

  Otherwise, if Period​::​type is pico,*units-suffix* is "ps"[.](#io-1.3.sentence-1)

- [(1.4)](#io-1.4)

  Otherwise, if Period​::​type is nano,*units-suffix* is "ns"[.](#io-1.4.sentence-1)

- [(1.5)](#io-1.5)

  Otherwise, if Period​::​type is micro,
it isimplementation-defined
whether *units-suffix* is"μs" ("\u00b5\u0073") or"us"[.](#io-1.5.sentence-1)

- [(1.6)](#io-1.6)

  Otherwise, if Period​::​type is milli,*units-suffix* is "ms"[.](#io-1.6.sentence-1)

- [(1.7)](#io-1.7)

  Otherwise, if Period​::​type is centi,*units-suffix* is "cs"[.](#io-1.7.sentence-1)

- [(1.8)](#io-1.8)

  Otherwise, if Period​::​type is deci,*units-suffix* is "ds"[.](#io-1.8.sentence-1)

- [(1.9)](#io-1.9)

  Otherwise, if Period​::​type is ratio<1>,*units-suffix* is "s"[.](#io-1.9.sentence-1)

- [(1.10)](#io-1.10)

  Otherwise, if Period​::​type is deca,*units-suffix* is "das"[.](#io-1.10.sentence-1)

- [(1.11)](#io-1.11)

  Otherwise, if Period​::​type is hecto,*units-suffix* is "hs"[.](#io-1.11.sentence-1)

- [(1.12)](#io-1.12)

  Otherwise, if Period​::​type is kilo,*units-suffix* is "ks"[.](#io-1.12.sentence-1)

- [(1.13)](#io-1.13)

  Otherwise, if Period​::​type is mega,*units-suffix* is "Ms"[.](#io-1.13.sentence-1)

- [(1.14)](#io-1.14)

  Otherwise, if Period​::​type is giga,*units-suffix* is "Gs"[.](#io-1.14.sentence-1)

- [(1.15)](#io-1.15)

  Otherwise, if Period​::​type is tera,*units-suffix* is "Ts"[.](#io-1.15.sentence-1)

- [(1.16)](#io-1.16)

  Otherwise, if Period​::​type is peta,*units-suffix* is "Ps"[.](#io-1.16.sentence-1)

- [(1.17)](#io-1.17)

  Otherwise, if Period​::​type is exa,*units-suffix* is "Es"[.](#io-1.17.sentence-1)

- [(1.18)](#io-1.18)

  Otherwise, if Period​::​type is ratio<60>,*units-suffix* is "min"[.](#io-1.18.sentence-1)

- [(1.19)](#io-1.19)

  Otherwise, if Period​::​type is ratio<3600>,*units-suffix* is "h"[.](#io-1.19.sentence-1)

- [(1.20)](#io-1.20)

  Otherwise, if Period​::​type is ratio<86400>,*units-suffix* is "d"[.](#io-1.20.sentence-1)

- [(1.21)](#io-1.21)

  Otherwise, if Period​::​type​::​den == 1,*units-suffix* is "[*num*]s"[.](#io-1.21.sentence-1)

- [(1.22)](#io-1.22)

  Otherwise, *units-suffix* is"[*num*/*den*]s"[.](#io-1.22.sentence-1)

In the list above,
the use of *num* and *den* refers to the static data members of Period​::​type,
which are converted to arrays of charT using a decimal conversion with no leading zeroes[.](#io-1.sentence-2)

[2](#io-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2176)

*Returns*: os[.](#io-2.sentence-1)

[🔗](#lib:from_stream,duration)

`template<class charT, class traits, class Rep, class Period, class Alloc = allocator<charT>>
  basic_istream<charT, traits>&
    from_stream(basic_istream<charT, traits>& is, const charT* fmt,
                duration<Rep, Period>& d,
                basic_string<charT, traits, Alloc>* abbrev = nullptr,
                minutes* offset = nullptr);
`

[3](#io-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2192)

*Effects*: Attempts to parse the input stream is into the duration d using the format flags given in the NTCTS fmt as specified in [[time.parse]](time.parse "30.13 Parsing")[.](#io-3.sentence-1)

If the parse fails to decode a valid duration,is.setstate(ios_base​::​failbit) is called and d is not modified[.](#io-3.sentence-2)

If %Z is used and successfully parsed,
that value will be assigned to *abbrev if abbrev is non-null[.](#io-3.sentence-3)

If %z (or a modified variant) is used and successfully parsed,
that value will be assigned to *offset if offset is non-null[.](#io-3.sentence-4)

[4](#io-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L2205)

*Returns*: is[.](#io-4.sentence-1)