27 Time library [time]

27.9 Class template hh_mm_ss [time.hms]

27.9.1 Overview [time.hms.overview]

namespace std::chrono { template<class Duration> class hh_mm_ss { public: static constexpr unsigned fractional_width = see below; using precision = see below; constexpr hh_mm_ss() noexcept : hh_mm_ss{Duration::zero()} {} constexpr explicit hh_mm_ss(Duration d); constexpr bool is_negative() const noexcept; constexpr chrono::hours hours() const noexcept; constexpr chrono::minutes minutes() const noexcept; constexpr chrono::seconds seconds() const noexcept; constexpr precision subseconds() const noexcept; constexpr explicit operator precision() const noexcept; constexpr precision to_duration() const noexcept; private: bool is_neg; // exposition only chrono::hours h; // exposition only chrono::minutes m; // exposition only chrono::seconds s; // exposition only precision ss; // exposition only }; }

The hh_mm_ss class template splits a duration into a multi-field time structure hours:minutes:seconds and possibly subseconds, where subseconds will be a duration unit based on a non-positive power of 10.

The Duration template parameter dictates the precision to which the time is split.

A hh_mm_ss models negative durations with a distinct is_negative getter that returns true when the input duration is negative.

The individual duration fields always return non-negative durations even when is_negative() indicates the structure is representing a negative duration.

If Duration is not an instance of duration, the program is ill-formed.

27.9.2 Members [time.hms.members]

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static constexpr unsigned fractional_width = see below;

fractional_width is the number of fractional decimal digits represented by precision.

fractional_width has the value of the smallest possible integer in the range [0, 18] such that precision will exactly represent all values of Duration.

If no such value of fractional_width exists, then fractional_width is 6.

[Example 1:

See Table 98 for some durations, the resulting fractional_width, and the formatted fractional second output of Duration{1}.

Table 98: Examples for fractional_width [tab:time.hms.width]

🔗	Duration	fractional_width	Formatted fractional second output
🔗	hours, minutes, and seconds	0
🔗	milliseconds	3	0.001
🔗	microseconds	6	0.000001
🔗	nanoseconds	9	0.000000001
🔗	duration<int, ratio<1, 2>>	1	0.5
🔗	duration<int, ratio<1, 3>>	6	0.333333
🔗	duration<int, ratio<1, 4>>	2	0.25
🔗	duration<int, ratio<1, 5>>	1	0.2
🔗	duration<int, ratio<1, 6>>	6	0.166666
🔗	duration<int, ratio<1, 7>>	6	0.142857
🔗	duration<int, ratio<1, 8>>	3	0.125
🔗	duration<int, ratio<1, 9>>	6	0.111111
🔗	duration<int, ratio<1, 10>>	1	0.1
🔗	duration<int, ratio<756, 625>>	4	0.2096

— end example]

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using precision = see below;

precision is duration<common_type_t<Duration::rep, seconds::rep>, ratio<1,

10fractional_width

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constexpr explicit hh_mm_ss(Duration d);

Effects: Constructs an object of type hh_mm_ss which represents the Duration d with precision precision.

(3.1)
Initializes is_neg with d < Duration::zero().
(3.2)
Initializes h with duration_cast<chrono::hours>(abs(d)).
(3.3)
Initializes m with duration_cast<chrono::minutes>(abs(d) - hours()).
(3.4)
Initializes s with duration_cast<chrono::seconds>(abs(d) - hours() - minutes()).
(3.5)
If treat_as_floating_point_v<precision::rep> is true, initializes ss with abs(d) - hours() - minutes() - seconds().

Otherwise, initializes ss with duration_cast<precision>(abs(d) - hours() - minutes() - seconds()).

[Note 1:

When precision::rep is integral and precision::period is ratio<1>, subseconds() always returns a value equal to 0s.

— end note]

Postconditions: If treat_as_floating_point_v<precision::rep> is true, to_duration() returns d, otherwise to_duration() returns duration_cast<precision>(d).

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constexpr bool is_negative() const noexcept;

Returns: is_neg.

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constexpr chrono::hours hours() const noexcept;

Returns: h.

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constexpr chrono::minutes minutes() const noexcept;

Returns: m.

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constexpr chrono::seconds seconds() const noexcept;

Returns: s.

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constexpr precision subseconds() const noexcept;

Returns: ss.

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constexpr precision to_duration() const noexcept;

Returns: If is_neg, returns -(h + m + s + ss), otherwise returns h + m + s + ss.

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constexpr explicit operator precision() const noexcept;

Returns: to_duration().

27.9.3 Non-members [time.hms.nonmembers]

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template<class charT, class traits, class Duration>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const hh_mm_ss<Duration>& hms);

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:%T}"), hms);

[Example 1: for (auto ms : {-4083007ms, 4083007ms, 65745123ms}) { hh_mm_ss hms{ms}; cout << hms << '\n'; } cout << hh_mm_ss{65745s} << '\n';