29 Time library [time]

29.9 Class template hh_mm_ss [time.hms]

29.9.1 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 a specialization of duration, the program is ill-formed.

29.9.2 Members [time.hms.members]

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 100 for some durations, the resulting fractional_width, and the formatted fractional second output of Duration{1}.
Table 100: 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]
using precision = see below;
precision is duration<common_type_t<Duration::rep, seconds::rep>, ratio<1, >>
constexpr explicit hh_mm_ss(Duration d);
Effects: Constructs an object of type hh_mm_ss which represents the Duration d with precision precision.
  • Initializes is_neg with d < Duration​::​zero().
  • Initializes h with duration_cast<chrono​::​hours>(abs(d)).
  • Initializes m with duration_cast<chrono​::​minutes>(abs(d) - hours()).
  • Initializes s with duration_cast<chrono​::​seconds>(abs(d) - hours() - minutes()).
  • 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).
constexpr bool is_negative() const noexcept;
Returns: is_neg.
constexpr chrono::hours hours() const noexcept;
Returns: h.
constexpr chrono::minutes minutes() const noexcept;
Returns: m.
constexpr chrono::seconds seconds() const noexcept;
Returns: s.
constexpr precision subseconds() const noexcept;
Returns: ss.
constexpr precision to_duration() const noexcept;
Returns: If is_neg, returns -(h + m + s + ss), otherwise returns h + m + s + ss.
constexpr explicit operator precision() const noexcept;
Returns: to_duration().

29.9.3 Non-members [time.hms.nonmembers]

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>("{:L%T}"), hms);
[Example 1: for (auto ms : {-4083007ms, 4083007ms, 65745123ms}) { hh_mm_ss hms{ms}; cout << hms << '\n'; } cout << hh_mm_ss{65745s} << '\n';
Produces the output (assuming the "C" locale): -01:08:03.007 01:08:03.007 18:15:45.123 18:15:45
— end example]