# Seconds Since Epoch

Example of calculating seconds elapsed since epoch (1970-Jan-1) using local_date_time.

      /* This example demonstrates the use of the time zone database and
       * local time to calculate the number of seconds since the UTC
       * time_t epoch 1970-01-01 00:00:00.  Note that the selected timezone
       * could be any timezone supported in the time zone database file which
       * can be modified and updated as needed by the user.
       *
       * To solve this problem the following steps are required:
       * 1) Get a timezone from the tz database for the local time
       * 2) Construct a local time using the timezone
       * 3) Construct a posix_time::ptime for the time_t epoch time
       * 4) Convert the local_time to utc and subtract the epoch time
       *
       */

      #include "boost/date_time/local_time/local_time.hpp"
      #include <iostream>

      int main()
      {
        using namespace boost::gregorian;
        using namespace boost::local_time;
        using namespace boost::posix_time;

        tz_database tz_db;
        try {
          tz_db.load_from_file("../data/date_time_zonespec.csv");
        }catch(data_not_accessible dna) {
          std::cerr << "Error with time zone data file: " << dna.what() << std::endl;
          exit(EXIT_FAILURE);
        }catch(bad_field_count bfc) {
          std::cerr << "Error with time zone data file: " << bfc.what() << std::endl;
          exit(EXIT_FAILURE);
        }

        time_zone_ptr nyc_tz = tz_db.time_zone_from_region("America/New_York");
        date in_date(2004,10,04);
        time_duration td(12,14,32);
        // construct with local time value
        // create not-a-date-time if invalid (eg: in dst transition)
        local_date_time nyc_time(in_date,
                                 td,
                                 nyc_tz,
                                 local_date_time::NOT_DATE_TIME_ON_ERROR);

        std::cout << nyc_time << std::endl;

        ptime time_t_epoch(date(1970,1,1));
        std::cout << time_t_epoch << std::endl;

        // first convert nyc_time to utc via the utc_time()
        // call and subtract the ptime.
        time_duration diff = nyc_time.utc_time() - time_t_epoch;

        //Expected 1096906472
        std::cout << "Seconds diff: " << diff.total_seconds() << std::endl;

      }