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summertime

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

Controller: CodeCogs

Contents

Interface
SummerTime
SummerTime
Page Comments

Dependents

Interface

C++

Overview

Most countries that observe daylight saving time are listed in the table below. They all save one hour in the summer and change their clocks some time between midnight and 3 am.


Continent	Code	Country	Beginning and ending days
Africa	st_Egypt	Egypt	Start: Last Friday in April End: Last Thursday in September
	st_Namibia	Namibia	Start: First Sunday in September End: First Sunday in April
Asia	st_FormerUSSR	Most states of the Former USSR.	Start: Last Sunday in March End: Last Sunday in October
	st_Iraq	Iraq	Start: April 1 End: October 1
	st_Israel	Israel (an approximation)	(Estimate, Israel decides the dates every year) Start: First Friday in April End: First Friday in September
	st_Lebanon st_Kirgizstan	Lebanon, Kirgizstan	Start: Last Sunday in March End: Last Sunday in October
	st_Palestine	Palestine (an approximation)	Start: First Friday on or after 15 April End: First Friday on or after 15 October
	st_Syria	Syria	Start: April 1 End: October 1
	st_Iran	Iran	Start: the first day of Farvardin End: the first day of Mehr
Australasia	st_Australia	Australia - South Australia, Victoria, Australian Capital Territory, New South Wales, Lord Howe Island	Start: Last Sunday in October End: Last Sunday in March
	st_Tasmania	Australia - Tasmania	Start: First Sunday in October End: Last Sunday in March
	st_NewZealand st_Chatham	New Zealand, Chatham	Start: First Sunday in October End: Third Sunday in March
	st_Tonga	Tonga	Start: First Sunday in November End: Last Sunday in January
Europe	st_EU	European Union UK	Start: Last Sunday in March at 1 am UTC End: Last Sunday in October at 1 am UTC
	st_Russia	Russia	Start: Last Sunday in March at 2 am local time End: Last Sunday in October at 2 am local time
North America	st_USA st_Canada st_Mexico st_Bahamas	United States, Canada, Mexico St. Johns, Bahamas, Turks and Caicos	Start: Second Sunday in March End: First Sunday in November (Post 2007 - no longer implemented) Start: First Sunday in April End: Last Sunday in October
	st_Cuba	Cuba	Start: April 1 End: Last Sunday in October
	st_Greenland	Greenland	Same as EU
South America	st_Brazil	Brazil (rules vary from year to year - and equatorial Brazil does not observe DST)	Start: First Sunday in November End: Third Sunday in February
	st_Chile	Chile	Start: Second Saturday of October End: Second Saturday of March
	st_Falklands	Falklands	Start: First Sunday on or after 8 September End: First Sunday on or after 6 April
	st_Paraquay	Paraguay	Start: First Sunday in September End: First Sunday in April

SummerTime

voidsummerTime(	int	`Year`
	double&	`StartDate`
	double&	`EndDate`
	summerTimeRegion	`Region`	)

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

Note

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.

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.

Authors

Will Bateman (Nov 2004)

Source Code

Source code is available when you agree to a GP Licence or buy a Commercial Licence.

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SummerTime

boolsummerTime(	double	`nDate`
	summerTimeRegion	`Region`	)

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 2

#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