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[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)