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## Examples

### Dates as Strings

Various parsing and output of strings.

      /* The following is a simple example that shows conversion of dates
       * to and from a std::string.
       *
       * Expected output:
       * 2001-Oct-09
       * 2001-10-09
       * Tuesday October 9, 2001
       * An expected exception is next:
       * Exception: Month number is out of range 1..12
       */

      #include "boost/date_time/gregorian/gregorian.hpp"
      #include <iostream>
      #include <string>

      int
      main()
      {

        using namespace boost::gregorian;

        try {
          // The following date is in ISO 8601 extended format (CCYY-MM-DD)
          std::string s("2001-10-9"); //2001-October-09
          date d(from_simple_string(s));
          std::cout << to_simple_string(d) << std::endl;

          //Read ISO Standard(CCYYMMDD) and output ISO Extended
          std::string ud("20011009"); //2001-Oct-09
          date d1(from_undelimited_string(ud));
          std::cout << to_iso_extended_string(d1) << std::endl;

          //Output the parts of the date - Tuesday October 9, 2001
          date::ymd_type ymd = d1.year_month_day();
          greg_weekday wd = d1.day_of_week();
          std::cout << wd.as_long_string() << " "
                    << ymd.month.as_long_string() << " "
                    << ymd.day << ", " << ymd.year
                    << std::endl;

          //Let's send in month 25 by accident and create an exception
          std::string bad_date("20012509"); //2001-??-09
          std::cout << "An expected exception is next: " << std::endl;
          date wont_construct(from_undelimited_string(bad_date));
          //use wont_construct so compiler doesn't complain, but you wont get here!
          std::cout << "oh oh, you shouldn't reach this line: "
                    << to_iso_string(wont_construct) << std::endl;
        }
        catch(std::exception& e) {
          std::cout << "  Exception: " <<  e.what() << std::endl;
        }

        return 0;
      }

### Days Alive

Calculate the number of days you have been living using durations and dates.

    /* Short example that calculates the number of days since user was born.
     * Demonstrates comparisons of durations, use of the day_clock,
     * and parsing a date from a string.
     */

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

    int
    main()
    {

      using namespace boost::gregorian;
      std::string s;
      std::cout << "Enter birth day YYYY-MM-DD (eg: 2002-02-01): ";
      std::cin >> s;
      try {
        date birthday(from_simple_string(s));
        date today = day_clock::local_day();
        days days_alive = today - birthday;
        days one_day(1);
        if (days_alive == one_day) {
          std::cout << "Born yesterday, very funny" << std::endl;
        }
        else if (days_alive < days(0)) {
          std::cout << "Not born yet, hmm: " << days_alive.days()
                    << " days" <<std::endl;
        }
        else {
          std::cout << "Days alive: " << days_alive.days() << std::endl;
        }

      }
      catch(...) {
        std::cout << "Bad date entered: " << s << std::endl;
      }
      return 0;
    }

### Days Between New Years

Calculate the number of days till new years

      /* Provides a simple example of using a date_generator, and simple
       * mathematical operatorations, to calculate the days since
       * New Years day of this year, and days until next New Years day.
       *
       * Expected results:
       * Adding together both durations will produce 366 (365 in a leap year).
       */
      #include <iostream>
      #include "boost/date_time/gregorian/gregorian.hpp"

      int
      main()
      {

        using namespace boost::gregorian;

        date today = day_clock::local_day();
        partial_date new_years_day(1,Jan);
        //Subtract two dates to get a duration
        days days_since_year_start = today - new_years_day.get_date(today.year());
        std::cout << "Days since Jan 1: " << days_since_year_start.days()
                  << std::endl;

        days days_until_year_start = new_years_day.get_date(today.year()+1) - today;
        std::cout << "Days until next Jan 1: " << days_until_year_start.days()
                  << std::endl;
        return 0;
      };

### Last Day of the Months

Example that gets a month and a year from the user and finds the last day of each remaining month of that year.

      /* Simple program that finds the last day of the given month,
       * then displays the last day of every month left in the given year.
       */

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

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

        greg_year year(1400);
        greg_month month(1);

        // get a month and a year from the user
        try {
          int y, m;
          std::cout << "   Enter Year(ex: 2002): ";
          std::cin >> y;
          year = greg_year(y);
          std::cout << "   Enter Month(1..12): ";
          std::cin >> m;
          month = greg_month(m);
        }
        catch(bad_year by) {
          std::cout << "Invalid Year Entered: " << by.what() << '\n'
            << "Using minimum values for month and year." << std::endl;
        }
        catch(bad_month bm) {
          std::cout << "Invalid Month Entered" << bm.what() << '\n'
            << "Using minimum value for month. " << std::endl;
        }

        date start_of_next_year(year+1, Jan, 1);
        date d(year, month, 1);

        // add another month to d until we enter the next year.
        while (d < start_of_next_year){
          std::cout << to_simple_string(d.end_of_month()) << std::endl;
          d += months(1);
        }

        return 0;
      }

### Localization Demonstration

The boost::date_time library provides the ability to create customized locale facets. Date ordering, language, seperators, and abbreviations can be customized.

      /* The following shows the creation of a facet for the output of
       * dates in German (please forgive me for any errors in my German --
       * I'm not a native speaker).
       */

      #include "boost/date_time/gregorian/gregorian.hpp"
      #include <iostream>
      #include <algorithm>

      /* Define a series of char arrays for short and long name strings
       * to be associated with German date output (US names will be
       * retrieved from the locale). */
      const char* const de_short_month_names[] =
      {
        "Jan", "Feb", "Mar", "Apr", "Mai", "Jun",
        "Jul", "Aug", "Sep", "Okt", "Nov", "Dez", "NAM"
      };
      const char* const de_long_month_names[] =
      {
        "Januar", "Februar", "Marz", "April", "Mai",
        "Juni", "Juli", "August", "September", "Oktober",
        "November", "Dezember", "NichtDerMonat"
      };
      const char* const de_long_weekday_names[] =
      {
        "Sonntag", "Montag", "Dienstag", "Mittwoch",
        "Donnerstag", "Freitag", "Samstag"
      };
      const char* const de_short_weekday_names[] =
      {
        "Son", "Mon", "Die","Mit", "Don", "Fre", "Sam"
      };

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

        // create some gregorian objects to output
        date d1(2002, Oct, 1);
        greg_month m = d1.month();
        greg_weekday wd = d1.day_of_week();

        // create a facet and a locale for German dates
        date_facet* german_facet = new date_facet();
        std::cout.imbue(std::locale(std::locale::classic(), german_facet));

        // create the German name collections
        date_facet::input_collection_type short_months, long_months,
                                          short_weekdays, long_weekdays;
        std::copy(&de_short_month_names[0], &de_short_month_names[11],
                  std::back_inserter(short_months));
        std::copy(&de_long_month_names[0], &de_long_month_names[11],
                  std::back_inserter(long_months));
        std::copy(&de_short_weekday_names[0], &de_short_weekday_names[6],
                  std::back_inserter(short_weekdays));
        std::copy(&de_long_weekday_names[0], &de_long_weekday_names[6],
                  std::back_inserter(long_weekdays));

        // replace the default names with ours
        // NOTE: date_generators and special_values were not replaced as
        // they are not used in this example
        german_facet->short_month_names(short_months);
        german_facet->long_month_names(long_months);
        german_facet->short_weekday_names(short_weekdays);
        german_facet->long_weekday_names(long_weekdays);

        // output the date in German using short month names
        german_facet->format("%d.%m.%Y");
        std::cout << d1 << std::endl; //01.10.2002

        german_facet->month_format("%B");
        std::cout << m << std::endl; //Oktober

        german_facet->weekday_format("%A");
        std::cout << wd << std::endl; //Dienstag

        // Output the same gregorian objects using US names
        date_facet* us_facet = new date_facet();
        std::cout.imbue(std::locale(std::locale::classic(), us_facet));

        us_facet->format("%m/%d/%Y");
        std::cout << d1 << std::endl; //  10/01/2002

        // English names, iso order (year-month-day), '-' separator
        us_facet->format("%Y-%b-%d");
        std::cout << d1 << std::endl; //  2002-Oct-01

        return 0;

      }

### Date Period Calculations

Calculates if a date is in an 'irregular' collection of periods using period calculation functions.

      /*
      This example demonstrates a simple use of periods for the calculation
      of date information.

      The example calculates if a given date is a weekend or holiday
      given an exclusion set.  That is, each weekend or holiday is
      entered into the set as a time interval.  Then if a given date
      is contained within any of the intervals it is considered to
      be within the exclusion set and hence is a offtime.

      Output:
      Number Excluded Periods: 5
      20020202/20020203
      20020209/20020210
      20020212/20020212
      20020216/20020217
      In Exclusion Period: 20020216 --> 20020216/20020217
      20020223/20020224

      */

      #include "boost/date_time/gregorian/gregorian.hpp"
      #include <set>
      #include <algorithm>
      #include <iostream>

      typedef std::set<boost::gregorian::date_period> date_period_set;

      //Simple population of the exclusion set
      date_period_set
      generateExclusion()
      {
        using namespace boost::gregorian;
        date_period periods_array[] =
          { date_period(date(2002,Feb,2), date(2002,Feb,4)),//weekend of 2nd-3rd
            date_period(date(2002,Feb,9), date(2002,Feb,11)),
            date_period(date(2002,Feb,16), date(2002,Feb,18)),
            date_period(date(2002,Feb,23), date(2002,Feb,25)),
            date_period(date(2002,Feb,12), date(2002,Feb,13))//a random holiday 2-12
          };
        const int num_periods = sizeof(periods_array)/sizeof(date_period);

        date_period_set ps;
        //insert the periods in the set
        std::insert_iterator<date_period_set> itr(ps, ps.begin());
        std::copy(periods_array, periods_array+num_periods, itr );
        return ps;

      }

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

        date_period_set ps = generateExclusion();
        std::cout << "Number Excluded Periods: "  << ps.size() << std::endl;

        date d(2002,Feb,16);
        date_period_set::const_iterator i = ps.begin();
        //print the periods, check for containment
        for (;i != ps.end(); i++) {
          std::cout << to_iso_string(*i) << std::endl;
          //if date is in exclusion period then print it
          if (i->contains(d)) {
            std::cout << "In Exclusion Period: "
                << to_iso_string(d) << " --> " << to_iso_string(*i)
                << std::endl;
          }
        }

        return 0;

      }

### Print Holidays

This is an example of using functors to define a holiday schedule

      /* Generate a set of dates using a collection of date generators
       * Output looks like:
       * Enter Year: 2002
       * 2002-Jan-01 [Tue]
       * 2002-Jan-21 [Mon]
       * 2002-Feb-12 [Tue]
       * 2002-Jul-04 [Thu]
       * 2002-Sep-02 [Mon]
       * 2002-Nov-28 [Thu]
       * 2002-Dec-25 [Wed]
       * Number Holidays: 7
       */

      #include "boost/date_time/gregorian/gregorian.hpp"
      #include <algorithm>
      #include <functional>
      #include <vector>
      #include <iostream>
      #include <set>

      void
      print_date(boost::gregorian::date d)
      {
        using namespace boost::gregorian;
      #if defined(BOOST_DATE_TIME_NO_LOCALE)
        std::cout << to_simple_string(d) << " [" << d.day_of_week() << "]\n";
      #else
        std::cout << d << " [" << d.day_of_week() << "]\n";
      #endif
      }

      int
      main() {

        std::cout << "Enter Year: ";
        int year;
        std::cin >> year;

        using namespace boost::gregorian;

        //define a collection of holidays fixed by month and day
        std::vector<year_based_generator*> holidays;
        holidays.push_back(new partial_date(1,Jan)); //Western New Year
        holidays.push_back(new partial_date(4,Jul)); //US Independence Day
        holidays.push_back(new partial_date(25, Dec));//Christmas day

        //define a shorthand for the nth_day_of_the_week_in_month function object
        typedef nth_day_of_the_week_in_month nth_dow;

        //US labor day
        holidays.push_back(new nth_dow(nth_dow::first,  Monday,   Sep));
        //MLK Day
        holidays.push_back(new nth_dow(nth_dow::third,  Monday,   Jan));
        //Pres day
        holidays.push_back(new nth_dow(nth_dow::second, Tuesday,  Feb));
        //Thanksgiving
        holidays.push_back(new nth_dow(nth_dow::fourth, Thursday, Nov));

        typedef std::set<date> date_set;
        date_set all_holidays;

        for(std::vector<year_based_generator*>::iterator it = holidays.begin();
            it != holidays.end(); ++it)
        {
          all_holidays.insert((*it)->get_date(year));
        }

        //print the holidays to the screen
        std::for_each(all_holidays.begin(), all_holidays.end(), print_date);
        std::cout << "Number Holidays: " << all_holidays.size() << std::endl;

        return 0;
      }

### Print Month

Simple utility to print out days of the month with the days of a month. Demontstrates date iteration (date_time::date_itr).

      /* This example prints all the dates in a month. It demonstrates
       * the use of iterators as well as functions of the gregorian_calendar
       *
       * Output:
       * Enter Year: 2002
       * Enter Month(1..12): 2
       * 2002-Feb-01 [Fri]
       * 2002-Feb-02 [Sat]
       * 2002-Feb-03 [Sun]
       * 2002-Feb-04 [Mon]
       * 2002-Feb-05 [Tue]
       * 2002-Feb-06 [Wed]
       * 2002-Feb-07 [Thu]
       */

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

      int
      main()
      {
        std::cout << "Enter Year: ";
        int year, month;
        std::cin >> year;
        std::cout << "Enter Month(1..12): ";
        std::cin >> month;

        using namespace boost::gregorian;
        try {
          //Use the calendar to get the last day of the month
          int eom_day = gregorian_calendar::end_of_month_day(year,month);
          date endOfMonth(year,month,eom_day);

          //construct an iterator starting with firt day of the month
          day_iterator ditr(date(year,month,1));
          //loop thru the days and print each one
          for (; ditr <= endOfMonth; ++ditr) {
      #if defined(BOOST_DATE_TIME_NO_LOCALE)
            std::cout << to_simple_string(*ditr) << " ["
      #else
            std::cout << *ditr << " ["
      #endif
                      << ditr->day_of_week() << "]"
                      << std::endl;
          }
        }
        catch(std::exception& e) {

          std::cout << "Error bad date, check your entry: \n"
                    << "  Details: " << e.what() << std::endl;
        }
        return 0;
      }

### Month Adding

Adding a month to a day without the use of iterators.

      /* Simple program that uses the gregorian calendar to progress by exactly
       * one month, irregardless of how many days are in that month.
       *
       * This method can be used as an alternative to iterators
       */

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

      int
      main()
      {

        using namespace boost::gregorian;

        date d = day_clock::local_day();
        add_month mf(1);
        date d2 = d + mf.get_offset(d);
        std::cout << "Today is: " << to_simple_string(d) << ".\n"
          << "One month from today will be: " << to_simple_string(d2)
          << std::endl;

        return 0;
      }

### Time Math

Various types of calculations with times and time durations.

      /* Some simple examples of constructing and calculating with times
       * Output:
       * 2002-Feb-01 00:00:00 - 2002-Feb-01 05:04:02.001000000 = -5:04:02.001000000
       */

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

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

        date d(2002,Feb,1); //an arbitrary date
        //construct a time by adding up some durations durations
        ptime t1(d, hours(5)+minutes(4)+seconds(2)+millisec(1));
        //construct a new time by subtracting some times
        ptime t2 = t1 - hours(5)- minutes(4)- seconds(2)- millisec(1);
        //construct a duration by taking the difference between times
        time_duration td = t2 - t1;

        std::cout << to_simple_string(t2) << " - "
                  << to_simple_string(t1) << " = "
                  << to_simple_string(td) << std::endl;

        return 0;
      }

### Print Hours

Demonstrate time iteration, clock retrieval, and simple calculation.

      /* Print the remaining hours of the day
       * Uses the clock to get the local time
       * Use an iterator to iterate over the remaining hours
       * Retrieve the date part from a time
       *
       * Expected Output something like:
       *
       * 2002-Mar-08 16:30:59
       * 2002-Mar-08 17:30:59
       * 2002-Mar-08 18:30:59
       * 2002-Mar-08 19:30:59
       * 2002-Mar-08 20:30:59
       * 2002-Mar-08 21:30:59
       * 2002-Mar-08 22:30:59
       * 2002-Mar-08 23:30:59
       * Time left till midnight: 07:29:01
       */

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

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

        //get the current time from the clock -- one second resolution
        ptime now = second_clock::local_time();
        //Get the date part out of the time
        date today = now.date();
        date tommorrow = today + days(1);
        ptime tommorrow_start(tommorrow); //midnight

        //iterator adds by one hour
        time_iterator titr(now,hours(1));
        for (; titr < tommorrow_start; ++titr) {
          std::cout << to_simple_string(*titr) << std::endl;
        }

        time_duration remaining = tommorrow_start - now;
        std::cout << "Time left till midnight: "
                  << to_simple_string(remaining) << std::endl;
        return 0;
      }

### 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;
      }

### Time Periods

Demonstrate some simple uses of time periods.

      /* Some simple examples of constructing and calculating with times
       * Returns:
       * [2002-Feb-01 00:00:00/2002-Feb-01 23:59:59.999999999]
       * contains 2002-Feb-01 03:00:05
       * [2002-Feb-01 00:00:00/2002-Feb-01 23:59:59.999999999]
       * intersected with
       * [2002-Feb-01 00:00:00/2002-Feb-01 03:00:04.999999999]
       * is
       * [2002-Feb-01 00:00:00/2002-Feb-01 03:00:04.999999999]
       */

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

      using namespace boost::posix_time;
      using namespace boost::gregorian;

      //Create a simple period class to contain all the times in a day
      class day_period : public time_period
      {
      public:
        day_period(date d) : time_period(ptime(d),//midnight
                                         ptime(d,hours(24)))
        {}

      };

      int
      main()
      {

        date d(2002,Feb,1); //an arbitrary date
        //a period that represents a day
        day_period dp(d);
        ptime t(d, hours(3)+seconds(5)); //an arbitray time on that day
        if (dp.contains(t)) {
          std::cout << to_simple_string(dp) << " contains "
                    << to_simple_string(t)  << std::endl;
        }
        //a period that represents part of the day
        time_period part_of_day(ptime(d, hours(0)), t);
        //intersect the 2 periods and print the results
        if (part_of_day.intersects(dp)) {
          time_period result = part_of_day.intersection(dp);
          std::cout << to_simple_string(dp) << " intersected with\n"
                    << to_simple_string(part_of_day) << " is \n"
                    << to_simple_string(result) << std::endl;
        }

        return 0;
      }

### Simple Time Zones

Example usage of custom_time_zone as well as posix_time_zone.

      /* A simple example for using a custom_time_zone and a posix_time_zone.
       */

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

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

        /***** custom_time_zone *****/

        // create the dependent objects for a custom_time_zone
        time_zone_names tzn("Eastern Standard Time", "EST",
                            "Eastern Daylight Time", "EDT");
        time_duration utc_offset(-5,0,0);
        dst_adjustment_offsets adj_offsets(time_duration(1,0,0),
                                           time_duration(2,0,0),
                                           time_duration(2,0,0));
        // rules for this zone are:
        // start on first Sunday of April at 2 am
        // end on last Sunday of October at 2 am
        // so we use a first_last_dst_rule
        first_day_of_the_week_in_month start_rule(Sunday, Apr);
        last_day_of_the_week_in_month    end_rule(Sunday, Oct);
        shared_ptr<dst_calc_rule> nyc_rules(new first_last_dst_rule(start_rule,
                                                                    end_rule));
        // create more dependent objects for a non-dst custom_time_zone
        time_zone_names tzn2("Mountain Standard Time", "MST",
                             "", ""); // no dst means empty dst strings
        time_duration utc_offset2(-7,0,0);
        dst_adjustment_offsets adj_offsets2(time_duration(0,0,0),
                                            time_duration(0,0,0),
                                            time_duration(0,0,0));
        // no dst means we need a null pointer to the rules
        shared_ptr<dst_calc_rule> phx_rules;

        // create the custom_time_zones
        time_zone_ptr nyc_1(new custom_time_zone(tzn, utc_offset,
                                                 adj_offsets, nyc_rules));
        time_zone_ptr phx_1(new custom_time_zone(tzn2, utc_offset2,
                                                 adj_offsets2, phx_rules));

        /***** posix_time_zone *****/

        // create posix_time_zones that are the duplicates of the
        // custom_time_zones created above. See posix_time_zone documentation
        // for details on full zone names.
        std::string nyc_string, phx_string;
        nyc_string = "EST-05:00:00EDT+01:00:00,M4.1.0/02:00:00,M10.5.0/02:00:00";
        // nyc_string = "EST-05EDT,M4.1.0,M10.5.0"; // shorter when defaults used
        phx_string = "MST-07"; // no-dst
        time_zone_ptr nyc_2(new posix_time_zone(nyc_string));
        time_zone_ptr phx_2(new posix_time_zone(phx_string));

        /***** show the sets are equal *****/

        std::cout << "The first zone is in daylight savings from:\n "
          << nyc_1->dst_local_start_time(2004) << " through "
          << nyc_1->dst_local_end_time(2004) << std::endl;

        std::cout << "The second zone is in daylight savings from:\n "
          << nyc_2->dst_local_start_time(2004) << " through "
          << nyc_2->dst_local_end_time(2004) << std::endl;

        std::cout << "The third zone (no daylight savings):\n "
          << phx_1->std_zone_abbrev() << " and "
          << phx_1->base_utc_offset() << std::endl;

        std::cout << "The fourth zone (no daylight savings):\n "
          << phx_2->std_zone_abbrev() << " and "
          << phx_2->base_utc_offset() << std::endl;

        return 0;
      }

### Daylight Savings Calc Rules

Example of creating various Daylight Savings Calc Rule objects.

      /* A simple example for creating various dst_calc_rule instances
       */

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

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

        /***** create the necessary date_generator objects *****/
        // starting generators
        first_day_of_the_week_in_month fd_start(Sunday, May);
        last_day_of_the_week_in_month ld_start(Sunday, May);
        nth_day_of_the_week_in_month nkd_start(nth_day_of_the_week_in_month::third,
                                               Sunday, May);
        partial_date pd_start(1, May);
        // ending generators
        first_day_of_the_week_in_month fd_end(Sunday, Oct);
        last_day_of_the_week_in_month ld_end(Sunday, Oct);
        nth_day_of_the_week_in_month nkd_end(nth_day_of_the_week_in_month::third,
                                             Sunday, Oct);
        partial_date pd_end(31, Oct);

        /***** create the various dst_calc_rule objects *****/
        dst_calc_rule_ptr pdr(new partial_date_dst_rule(pd_start, pd_end));
        dst_calc_rule_ptr flr(new first_last_dst_rule(fd_start, ld_end));
        dst_calc_rule_ptr llr(new last_last_dst_rule(ld_start, ld_end));
        dst_calc_rule_ptr nlr(new nth_last_dst_rule(nkd_start, ld_end));
        dst_calc_rule_ptr ndr(new nth_day_of_the_week_in_month_dst_rule(nkd_start,
                                                                        nkd_end));

        return 0;
      }

### Flight Time Example

This example shows a program that calculates the arrival time of a plane that flys from Phoenix to New York. During the flight New York shifts into daylight savings time (Phoenix doesn't because Arizona doesn't use dst).

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

    /* This example shows a program that calculates the arrival time of a plane
     * that flys from Phoenix to New York.  During the flight New York shifts
     * into daylight savings time (Phoenix doesn't because Arizona doesn't use
     * dst).
     *
     *
     */

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

      //setup some timezones for creating and adjusting local times
      //This user editable file can be found in libs/date_time/data.
      tz_database tz_db;
      tz_db.load_from_file("date_time_zonespec.csv");
      time_zone_ptr nyc_tz = tz_db.time_zone_from_region("America/New_York");
      //Use a
      time_zone_ptr phx_tz(new posix_time_zone("MST-07:00:00"));

      //local departure time in phoenix is 11 pm on april 2 2005
      // (ny changes to dst on apr 3 at 2 am)
      local_date_time phx_departure(date(2005, Apr, 2), hours(23),
                                    phx_tz,
                                    local_date_time::NOT_DATE_TIME_ON_ERROR);

      time_duration flight_length = hours(4) + minutes(30);
      local_date_time phx_arrival = phx_departure + flight_length;
      local_date_time nyc_arrival = phx_arrival.local_time_in(nyc_tz);

      std::cout << "departure phx time: " << phx_departure << std::endl;
      std::cout << "arrival phx time:   " << phx_arrival << std::endl;
      std::cout << "arrival nyc time:   " << nyc_arrival << std::endl;

    }

### 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;

      }