Are leap seconds stored on Mac OS X anywhere?

Question

I ran find /usr/share/zoneinfo/ -type f -exec file {} \; |grep -v 'no leap' on my system and every single time zone file said it had no leap seconds. Are leap seconds stored anywhere on mac OS X that I can get to in a robust way? I'm writing a library that will need leap seconds so I'd rather not connect over the network, though making some kind of system call would be acceptable.

Answer 1

There is no leap second information stored in the IANA database on macOS: /usr/share/zoneinfo

If you are willing to use a 3rd party C++11 library, Howard Hinnant's time zone library gives you full functionality in dealing with leap seconds. This does require downloading the IANA database. But you can configure this library to either download it automatically, or you can download it manually, and the library will access that.

The documentation has this example:

#include "tz.h"
#include <iostream>

int
main()
{
    using namespace date;
    using namespace std::chrono_literals;
    auto start = to_utc_time(sys_days{2015_y/jul/1} - 500ms);
    auto end = start + 2s;
    for (auto utc = start; utc < end; utc += 100ms)
    {
        auto sys = to_sys_time(utc);
        auto tai = to_tai_time(utc);
        auto gps = to_gps_time(utc);
        std::cout << format("%F %T SYS  ==  ", sys)
                  << format("%F %T %Z  ==  ", utc)
                  << format("%F %T %Z  ==  ", tai)
                  << format("%F %T %Z\n", gps);
    }
}

This example iterates time near the Jun 2015 leap second insertion, comparing system time, UTC, TAI and GPS clock standards:

2015-06-30 23:59:59.500 SYS  ==  2015-06-30 23:59:59.500 UTC  ==  2015-07-01 00:00:34.500 TAI  ==  2015-07-01 00:00:15.500 GPS
2015-06-30 23:59:59.600 SYS  ==  2015-06-30 23:59:59.600 UTC  ==  2015-07-01 00:00:34.600 TAI  ==  2015-07-01 00:00:15.600 GPS
2015-06-30 23:59:59.700 SYS  ==  2015-06-30 23:59:59.700 UTC  ==  2015-07-01 00:00:34.700 TAI  ==  2015-07-01 00:00:15.700 GPS
2015-06-30 23:59:59.800 SYS  ==  2015-06-30 23:59:59.800 UTC  ==  2015-07-01 00:00:34.800 TAI  ==  2015-07-01 00:00:15.800 GPS
2015-06-30 23:59:59.900 SYS  ==  2015-06-30 23:59:59.900 UTC  ==  2015-07-01 00:00:34.900 TAI  ==  2015-07-01 00:00:15.900 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.000 UTC  ==  2015-07-01 00:00:35.000 TAI  ==  2015-07-01 00:00:16.000 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.100 UTC  ==  2015-07-01 00:00:35.100 TAI  ==  2015-07-01 00:00:16.100 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.200 UTC  ==  2015-07-01 00:00:35.200 TAI  ==  2015-07-01 00:00:16.200 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.300 UTC  ==  2015-07-01 00:00:35.300 TAI  ==  2015-07-01 00:00:16.300 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.400 UTC  ==  2015-07-01 00:00:35.400 TAI  ==  2015-07-01 00:00:16.400 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.500 UTC  ==  2015-07-01 00:00:35.500 TAI  ==  2015-07-01 00:00:16.500 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.600 UTC  ==  2015-07-01 00:00:35.600 TAI  ==  2015-07-01 00:00:16.600 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.700 UTC  ==  2015-07-01 00:00:35.700 TAI  ==  2015-07-01 00:00:16.700 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.800 UTC  ==  2015-07-01 00:00:35.800 TAI  ==  2015-07-01 00:00:16.800 GPS
2015-06-30 23:59:59.999 SYS  ==  2015-06-30 23:59:60.900 UTC  ==  2015-07-01 00:00:35.900 TAI  ==  2015-07-01 00:00:16.900 GPS
2015-07-01 00:00:00.000 SYS  ==  2015-07-01 00:00:00.000 UTC  ==  2015-07-01 00:00:36.000 TAI  ==  2015-07-01 00:00:17.000 GPS
2015-07-01 00:00:00.100 SYS  ==  2015-07-01 00:00:00.100 UTC  ==  2015-07-01 00:00:36.100 TAI  ==  2015-07-01 00:00:17.100 GPS
2015-07-01 00:00:00.200 SYS  ==  2015-07-01 00:00:00.200 UTC  ==  2015-07-01 00:00:36.200 TAI  ==  2015-07-01 00:00:17.200 GPS
2015-07-01 00:00:00.300 SYS  ==  2015-07-01 00:00:00.300 UTC  ==  2015-07-01 00:00:36.300 TAI  ==  2015-07-01 00:00:17.300 GPS
2015-07-01 00:00:00.400 SYS  ==  2015-07-01 00:00:00.400 UTC  ==  2015-07-01 00:00:36.400 TAI  ==  2015-07-01 00:00:17.400 GPS