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Calculates the start and end of summer time in the specified year and region.

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Interface

#include <codecogs/units/time/summertime.h>

using namespace Units::Time;

void summerTime(int Year, double &StartDate, double &EndDate, summerTimeRegion Region)
bool summerTime(double nDate, summerTimeRegion Region)

Overview

\copydoc summerTimeRegion

FUNCTION

summerTime

Calculates the start and end dates for summer time in the region specified. This information can be used to adjust the local time by adding 1hr to the local time during their summer. The majority of the calculations assume that switch over between summer and winter time occurs at mid-night (12am), unless otherwise specified (see summerTimeRegion). This function returns a real number that represents the exact date and time of the switch-over, with the date represented by a serial number of Julian days with time added using a fraction of a day, i.e

$date = Julian\ Days + \frac{3600 hours + 60 minutes + seconds}{24 *3600}$

(1)

References

www.webexhibits.org/daylightsaving

Example 1

#include <stdio.h>
#include <codecogs/units/time/summertime.h>
#include <codecogs/units/time/hour.h>
#include <codecogs/units/time/minute.h>
#include <codecogs/units/date/month_str.h>
#include <codecogs/units/date/month.h>
#include <codecogs/units/date/day.h>
#include <codecogs/units/date/date.h>

using namespace Units::Time;
using namespace Units::Date;
int main()
{
  for(int i=2004;i<2006;i++)
  {
    printf("\n In year %d",i);
    double start,end;
    summerTime(i, start, end, st_UK);
    printf("\n         UK Summer time runs from %2d %s\t%2d:%02d", day(int(start)), month_str(month(int(start))), hour(start), minute(start));
    printf(" to %2d %s\t%2d:%02d", day(int(end)), month_str(month(int(end))), hour(end), minute(end));
    
    summerTime(i, start, end, st_Canada);
    printf("\n   Canadian Summer time runs from %2d %s\t%2d:%02d", day(int(start)), month_str(month(int(start))), hour(start), minute(start));
    printf(" to %2d %s\t%2d:%02d", day(int(end)), month_str(month(int(end))), hour(end), minute(end));
  }
  return 0;
}

Output:

In year 2004
UK Summer time runs from 28 March	 1:00 to 31 October	 1:00
Canadian Summer time runs from  4 April	 0:00 to 31 October	 0:00
In year 2005
UK Summer time runs from 27 March	 1:00 to 30 October	 1:00
Canadian Summer time runs from  3 April	 0:00 to 30 October	 0:00

Parameters

Year

is a 4 digit Gregorian year.

StartDate

is a location (passed by reference) into which is placed the start date and time when summer time within Year occurs - the point when everyone adds 1hr to the times shown on their clocks.

EndDate

is a location (passed by reference) into which is placed the end date and time for summer time - the point when everyone subtracts 1hr from the times shown on their clocks.

In the northern hemisphere the EndDate > StartDate. In the southern hemisphere, summertime crosses the new year, so EndDate < StartDate. For this reason if you want to check if your current date is in summer time, you must simply check the relative order of StartDate and EndDate.

Author

Will Bateman (Nov 2004)

FUNCTION

summerTime

Calculates if the provided date occurs in summer time. You might use the result from this function to add 1 hour to nDate in order to factor in Summer time variations. Summer time is always applied some time between midnight (12am) and 3am, with this time being repeated twice during the transition from summer to winter time. To capture the transition correctly, it is important that nDate represents local time without summer time, such that the addition of 1hr is only added to during the summer. For example:

if(summerTime(somedate, st_UK)) somedate+=1/24.0;

N.B. You should not subtract 1hr from a summer time value in order to obtain standard time for the winter months, as this will yield slightly incorrect times at the transition from winter to summer (the changeover occurring 1 hour early).

Example 1

#include <stdio.h>
#include <codecogs/units/time/summertime.h>
#include <codecogs/units/date/day.h>
#include <codecogs/units/time/hour.h>
#include <codecogs/units/time/minute.h>

void main()
{
  double nDate=date("30 oct 2004");
  for(double i=22/24.0;i<26/24.0;i+=1/48.0)
  {
    double a=nDate+i;
    bool summer=summerTime(a, st_UK);
    a+=summer* 1/24.0;
    printf("\n %s day=%d time=%2d:%02d", summer?"Summer":"Winter", day(int(a)), hour(a), minute(a));
  }
}

Output:

Summer day=30 time=23:00
Summer day=30 time=23:30
Summer day=31 time= 0:00
Summer day=31 time= 0:30
Summer day=31 time= 1:00
Summer day=31 time= 1:30
Winter day=31 time= 1:00
Winter day=31 time= 1:30
Winter day=31 time= 2:00

Parameters

nDate

is a serial number of days from 24 November 4714 BC (1 January 4713BC in the Julian Calendar) - also known as the Julian Period. Time during the day is representing using a fraction of the day, i.e. 1hr=1/24.0.

Author

Will Bateman (Nov 2004)