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Calendars and Timezones

Calendar

Chrono is extended to support calendars and timezones. Only Gregorian calendar is supported.

chrono::year_month_day date{2019y, September, 18d};
auto date = 2019y/September/18d; // 18d/September/2019y || September/18d/2019y
auto date = September/last/2019y;
auto date = 31d/October/2019;
if (!date.ok()) {
  date = chrono::sys_days{date};
}
auto date = Friday[2]/November/2019y;

New duration type aliases

  • days
  • weeks
  • months
  • years

New clocks

  • utc_clock represents Coordinated Universal Time (UTC), measures time since 00:00:00 UTC, Thursday, 1 January 1970, and includs leap seconds.

  • tai_clock represents International Atomic Time (TAI), measures time since 00:00:00, 1 January 1958, and was offseted 10 seconds ahead of UTC at that date, does not include leap seconds.

  • gps_clock represents Global Positioning System (GPS) time, measures time since 00:00:00, 6 January 1980 UTC, does not include leap seconds.

  • file_clock - alias for the clock used for filesystem::file_time_type::clock, epoch is unspecified.

New system_clock-related type aliases

template<class Duration>
using sys_time = chrono::time_point<chrono::system_clock, Duration>;

using sys_seconds = sys_time<chrono::seconds>;
using sys_days = sys_time<chrono::days>;
auto now = system_clock::now();

Date + Time

auto timestamp = sys_days{2019y/September/18d} + 9h + 35m + 10s; // 2019-09-18 09:35:10 UTC

Timezone conversion

  • Conver UTC to Denver time
auto now = system_clock::now();
zoned_time current{current_zone(), now};
zoned_time denver{"America/Denver", now};
  • Construct a localtime in Denver
auto denver = chrono::zoned_time{"America/Denver", chrono::local_days{Wednesday[3]/September/2019} + 9h};
  • Get current localtime
auto local = chrono::zoned_time{chrono::current_zone(), chrono::system_clock::now()};

Formating and parsing

C++20 chrono fully integrates into C++20 format

auto tp = system_clock::now();
auto tz = locale_zone("Europe/Berlin");
cout << format("{:%F %T %Z}\n", zoned_time{tz, tp});

>_ 2019-11-14 12:13:14.123456 CET

cout << format("{:%d.%m.%Y %T%z}\n", zoned_time{tz, tp});

>_ 14.11.2019 12:13:14.123556+0100

cout << format(locale("de_DE"), "{:%d.%m.%Y %T%z}\n", zoned_time{tz, tp});

>_ 14.11.2019 12:13:14,123656+0100

cout << format("{:%d.%m.%Y %T%z}\n", zoned_time{tz, floor<seconds>(tp)});

>_ 14.11.2019 12:13:14

If you can format it, you can chrono::parse it back in, usually with the same formatting string

system_clock::time_point tp;
cin >> parse("%d.%m.%Y %T%z", tp);
cout << tp << '\n';

>_

input: 14.11.2019 12:13:14.123556+0100
output: 2019-11-14 11:13:14.123556

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