29 Time library [time]

29.5 Class template duration [time.duration]

29.5.9 Suffixes for duration literals [time.duration.literals]

This subclause describes literal suffixes for constructing duration literals.
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-literals.
If any of these suffixes are applied to a floating-point-literal the result is a chrono​::​duration literal with an unspecified floating-point representation.
If any of these suffixes are applied to an integer-literal and the resulting chrono​::​duration value cannot be represented in the result type because of overflow, the program is ill-formed.
[Example 1: 
The following code shows some duration literals.
using namespace std::chrono_literals; auto constexpr aday=24h; auto constexpr lesson=45min; auto constexpr halfanhour=0.5h; — end example]
constexpr chrono::hours operator""h(unsigned long long hours); constexpr chrono::duration<unspecified, ratio<3600, 1>> operator""h(long double hours);
Returns: A duration literal representing hours hours.
constexpr chrono::minutes operator""min(unsigned long long minutes); constexpr chrono::duration<unspecified, ratio<60, 1>> operator""min(long double minutes);
Returns: A duration literal representing minutes minutes.
constexpr chrono::seconds operator""s(unsigned long long sec); constexpr chrono::duration<unspecified> operator""s(long double sec);
Returns: A duration literal representing sec seconds.
[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.
— end note]
constexpr chrono::milliseconds operator""ms(unsigned long long msec); constexpr chrono::duration<unspecified, milli> operator""ms(long double msec);
Returns: A duration literal representing msec milliseconds.
constexpr chrono::microseconds operator""us(unsigned long long usec); constexpr chrono::duration<unspecified, micro> operator""us(long double usec);
Returns: A duration literal representing usec microseconds.
constexpr chrono::nanoseconds operator""ns(unsigned long long nsec); constexpr chrono::duration<unspecified, nano> operator""ns(long double nsec);
Returns: A duration literal representing nsec nanoseconds.