# Local to UTC Conversion

Demonstrate utc to local and local to utc calculations including dst.

      /* Demonstrate conversions between a local time and utc
       * Output:
       *
       * UTC <--> New York while DST is NOT active (5 hours)
       * 2001-Dec-31 19:00:00 in New York is 2002-Jan-01 00:00:00 UTC time
       * 2002-Jan-01 00:00:00 UTC is 2001-Dec-31 19:00:00 New York time
       *
       * UTC <--> New York while DST is active (4 hours)
       * 2002-May-31 20:00:00 in New York is 2002-Jun-01 00:00:00 UTC time
       * 2002-Jun-01 00:00:00 UTC is 2002-May-31 20:00:00 New York time
       *
       * UTC <--> Arizona (7 hours)
       * 2002-May-31 17:00:00 in Arizona is 2002-Jun-01 00:00:00 UTC time
       */

      #include "boost/date_time/posix_time/posix_time.hpp"
      #include "boost/date_time/local_time_adjustor.hpp"
      #include "boost/date_time/c_local_time_adjustor.hpp"
      #include <iostream>

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

        //This local adjustor depends on the machine TZ settings-- highly dangerous!
        typedef boost::date_time::c_local_adjustor<ptime> local_adj;
        ptime t10(date(2002,Jan,1), hours(7));
        ptime t11 = local_adj::utc_to_local(t10);
        std::cout << "UTC <--> Zone base on TZ setting" << std::endl;
        std::cout << to_simple_string(t11) << " in your TZ is "
                  << to_simple_string(t10) << " UTC time "
                  << std::endl;
        time_duration td = t11 - t10;
        std::cout << "A difference of: "
                  << to_simple_string(td) << std::endl;

        //eastern timezone is utc-5
        typedef boost::date_time::local_adjustor<ptime, -5, us_dst> us_eastern;

        ptime t1(date(2001,Dec,31), hours(19)); //5 hours b/f midnight NY time

        std::cout << "\nUTC <--> New York while DST is NOT active (5 hours)"
                  << std::endl;
        ptime t2 =  us_eastern::local_to_utc(t1);
        std::cout << to_simple_string(t1) << " in New York is "
                  << to_simple_string(t2) << " UTC time "
                  << std::endl;

        ptime t3 = us_eastern::utc_to_local(t2);//back should be the same
        std::cout << to_simple_string(t2) << " UTC is "
                  << to_simple_string(t3) << " New York time "
                  << "\n\n";

        ptime t4(date(2002,May,31), hours(20)); //4 hours b/f midnight NY time
        std::cout << "UTC <--> New York while DST is active (4 hours)" << std::endl;
        ptime t5 = us_eastern::local_to_utc(t4);
        std::cout << to_simple_string(t4) << " in New York is "
                  << to_simple_string(t5) << " UTC time "
                  << std::endl;

        ptime t6 = us_eastern::utc_to_local(t5);//back should be the same
        std::cout << to_simple_string(t5) << " UTC is "
                  << to_simple_string(t6) << " New York time "
                  << "\n" << std::endl;

        //Arizona timezone is utc-7 with no dst
        typedef boost::date_time::local_adjustor<ptime, -7, no_dst> us_arizona;

        ptime t7(date(2002,May,31), hours(17));
        std::cout << "UTC <--> Arizona (7 hours)" << std::endl;
        ptime t8 = us_arizona::local_to_utc(t7);
        std::cout << to_simple_string(t7) << " in Arizona is "
                  << to_simple_string(t8) << " UTC time "
                  << std::endl;

        return 0;
      }