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Struct template us_dst_trait

boost::date_time::us_dst_trait — Specification for daylight savings start rules in US.


// In header: <boost/date_time/local_timezone_defs.hpp>

template<typename date_type> 
struct us_dst_trait {
  // types
  typedef date_type::day_of_week_type                 day_of_week_type;          
  typedef date_type::month_type                       month_type;                
  typedef date_type::year_type                        year_type;                 
  typedef date_time::nth_kday_of_month< date_type >   start_rule_functor;        
  typedef date_time::first_kday_of_month< date_type > end_rule_functor;          
  typedef date_time::first_kday_of_month< date_type > start_rule_functor_pre2007;
  typedef date_time::last_kday_of_month< date_type >  end_rule_functor_pre2007;  

  // public static functions
  static day_of_week_type start_day(year_type);
  static month_type start_month(year_type);
  static day_of_week_type end_day(year_type);
  static month_type end_month(year_type);
  static date_type local_dst_start_day(year_type);
  static date_type local_dst_end_day(year_type);
  static int dst_start_offset_minutes();
  static int dst_end_offset_minutes();
  static int dst_shift_length_minutes();


This class is used to configure dst_calc_engine template typically as follows:

using namespace boost::gregorian;
using namespace boost::posix_time;
typedef us_dst_trait<date> us_dst_traits;
typedef boost::date_time::dst_calc_engine<date, time_duration, 
//calculate the 2002 transition day of USA April 7 2002
date dst_start = us_dst_calc::local_dst_start_day(2002); 

//calculate the 2002 transition day of USA Oct 27 2002
date dst_end = us_dst_calc::local_dst_end_day(2002); 
//check if a local time is in dst or not -- posible answers
//are yes, no, invalid time label, ambiguous
ptime t(...some time...);  
if (us_dst::local_is_dst(, t.time_of_day()) 
    == boost::date_time::is_not_in_dst) 


This generates a type suitable for the calculation of dst transitions for the United States. Of course other templates can be used for other locales.

us_dst_trait public static functions

  1. static day_of_week_type start_day(year_type);
  2. static month_type start_month(year_type y);
  3. static day_of_week_type end_day(year_type);
  4. static month_type end_month(year_type y);
  5. static date_type local_dst_start_day(year_type year);
  6. static date_type local_dst_end_day(year_type year);
  7. static int dst_start_offset_minutes();
  8. static int dst_end_offset_minutes();
  9. static int dst_shift_length_minutes();