我正在使用Arduino和实时时钟芯片。芯片可以补偿闰年等，所以它总是有正确的日期，但它不处理夏令时，我想是由于地区的复杂性。时钟可以告诉我日、月、年(以1为基础)和星期几(星期日= 0到星期六= 6)。
因为我需要与用户输入的日期和时间进行比较，所以我需要知道为夏令时调整的日期和时间。如果当前日期是夏令时，我可以简单地从时钟上添加一个小时的时间，我就有了我需要的时间。
困难的部分是确定我是否在夏令时，因为它每年都在变化。我只关心它在我的位置(山地时间)工作。在我的平台上似乎没有任何全面的日期库，而且我觉得这样做太过分了。是否有一个简单的公式来确定我是否在夏令时?
这实际上看起来很简单。这里有一些事实可以帮助我们:
- 在美国大部分地区，夏令时从3月的第二个星期日开始，到11月的第一个星期日结束，两个时间都是凌晨2点。
- 3月的第二个星期天总是在8号到14号之间。
- 11月的第一个星期天总是在1号到7号之间。
- 星期几编号是非常方便的，因为星期几会给你上一个星期日。
public bool IsDST(int day, int month, int dow)
{
//January, february, and december are out.
if (month < 3 || month > 11) { return false; }
//April to October are in
if (month > 3 && month < 11) { return true; }
int previousSunday = day - dow;
//In march, we are DST if our previous sunday was on or after the 8th.
if (month == 3) { return previousSunday >= 8; }
//In november we must be before the first sunday to be dst.
//That means the previous sunday must be before the 1st.
return previousSunday <= 0;
}
事实证明，你甚至不需要知道年份，只要你相信你的星期几值就可以了。
我写了一个快速的单元测试，并验证了这段代码在1800到2200的所有日期与TimeZone.IsDayLightSavingsTime()一致。我没有考虑到凌晨2点的规则，但你可以很容易地检查一周中的一天是星期日，日期是在8到14(3月)之间还是1到7(11月)之间。
中欧代码(2014-3000年范围内每天测试)
public static bool IsDst(int day, int month, int dow)
{
if (month < 3 || month > 10) return false;
if (month > 3 && month < 10) return true;
int previousSunday = day - dow;
if (month == 3) return previousSunday >= 25;
if (month == 10) return previousSunday < 25;
return false; // this line never gonna happend
}
测试函数
static void Main(string[] args)
{
TimeZoneInfo tzf2 = TimeZoneInfo.FindSystemTimeZoneById("Central Europe Standard Time");
var date = new DateTime(2014, 01, 1, 5, 0,0);
bool wasSummer = false;
while (date <= new DateTime(3000,1,1))
{
var dow = (int) date.DayOfWeek;
var isDst = IsDst(date.Day, date.Month, dow);
DateTime f2 = TimeZoneInfo.ConvertTime(date, tzf2);
var isSummer = f2.IsDaylightSavingTime();
if (isSummer != isDst)
{
Console.WriteLine("ERROR");
Console.WriteLine(date);
}
if (isSummer != wasSummer)
{
Console.WriteLine(date.AddDays(-1).ToShortDateString());
}
date = date.AddDays(1);
wasSummer = isSummer;
}
Console.ReadKey();
}
虽然在当前规则下计算特定地点的特定日期是否在夏时制中很容易，但请注意夏时制是由政治家们一时心血潮决定的，并且可能在任何时候改变。我有一个2007年以前生产的时钟，它会自动调整夏令时，现在我必须一年修改它四次:两次当实际发生变化时，两次当它现在在旧日期不正确地改变自己时。
在这种情况下，您可以通过让用户在输入日期和时间的同时输入时区这一简单的权术来完全忽略DST。或者你可以像大多数消费类设备一样，让用户每年两次将时间调整到当地时区。
但是如果你真的需要处理DST并且真的想把事情做好，使用zoneinfo数据库并确保它可以以某种方式更新。如果由于某些原因不能这样做，至少允许用户重写规则。如果连这都太难的话，至少给用户提供关闭自动调节的选项(不像我那愚蠢的闹钟)。
这段代码使用mktime获取一周中的一天。它使用一周中的一天来计算夏令时。如果不想使用mktime，可以使用程序second_sunday。从2007年3月14日开始，也就是星期三。2004年以后，每隔一年，星期几将提前1天，每隔闰年，星期几将提前2天。
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <sys/timeb.h>
int isDst(int month, int dayOfMonth, int hour, int dayOfWeek);
int main(int argc, char *argv[])
{
int isdst, dayOfWeek;
char buf[80];
struct tm tmData;
if( argc == 1 )
{
printf("nsyntax: %s mm/dd/yyyy_hh:mm:00", argv[0]);
return -1;
}
// 0123456789A12
// 03/12/2018_12
strcpy(buf, argv[1]);
tmData.tm_mon = atoi(&buf[0]) - 1; //month -1
tmData.tm_mday = atoi(&buf[3]); //day of month
tmData.tm_year = atoi(&buf[6]) - 1900; // year - 1900
tmData.tm_hour = atoi(&buf[11]); // hour
tmData.tm_min = 0; //minutes (not used)
tmData.tm_sec = 0; //seconds (not used)
//tmData.tm_min = atoi(&buf[14]);
//tmData.tm_sec = atoi(&buf[27]);
//day light saving time variable.
//NOT used in this calculation.
//Tells mktime the input date is in day light saving time
tmData.tm_isdst = 0; //
mktime(&tmData);
dayOfWeek = tmData.tm_wday;
printf("%02d/%02d/%2d_%02d dayWk=%d ",
tmData.tm_mon+1, tmData.tm_mday, tmData.tm_year, tmData.tm_hour, dayOfWeek);
isdst = isDst(tmData.tm_mon+1, tmData.tm_mday, tmData.tm_hour, dayOfWeek);
printf("isdst=%dn", isdst);
return 0;
}
int isDst(int month, int dayOfMonth, int hour, int dayOfWeek)
{
int second_sunday, first_sunday;
if( month > 3 && month < 11 ) return 1; //4,5,6,7,8,9,10
if( month < 3 || month == 12 ) return 0; //1, 2 or 12
if( month == 3 )
{
//The 2nd Sunday in March is 8,9,10,11,12,13,14
if( dayOfMonth < 8 ) return 0;
if( dayOfMonth > 14 ) return 1;
//To get here dayOfMonth >= 8 && dayOfMonth <= 14
second_sunday = dayOfMonth - dayOfWeek;
if( second_sunday < 8 ) second_sunday += 7;
printf("2nd_Sunday=%2d ", second_sunday);
if( dayOfMonth > second_sunday ) return 1;
if( dayOfMonth < second_sunday ) return 0;
//To get here dayOfMonth = second_sunday
if( hour >= 2 ) return 1;
else return 0;
}
if( month == 11 )
{
//The 1st Sunday in Nov is 1,2,3,4,5,6,7
if( dayOfMonth > 7 ) return 0;
//To get here dayOfMonth >= 1 && dayOfMonth <= 7
first_sunday = dayOfMonth - dayOfWeek;
if( first_sunday < 1 ) first_sunday += 7;
printf("1st_Sunday=%2d ", first_sunday);
if( dayOfMonth > first_sunday ) return 0;
if( dayOfMonth < first_sunday ) return 1;
//To get here dayOfMonth = first_sunday
if( hour >= 2 ) return 0;
else return 1;
}
return -1;
}
/**************
Compile via cl.exe isDst.c
Begin and End dates for day light saving time
03/11/2007_01:00:00 11/04/2007_01:00:00
03/09/2008_01:00:00 11/02/2008_01:00:00
03/08/2009_01:00:00 11/01/2009_01:00:00
03/14/2010_01:00:00 11/07/2010_01:00:00
03/13/2011_01:00:00 11/06/2011_01:00:00
03/11/2012_01:00:00 11/04/2012_01:00:00
03/10/2013_01:00:00 11/03/2013_01:00:00
03/09/2014_01:00:00 11/02/2014_01:00:00
03/08/2015_01:00:00 11/01/2015_01:00:00
03/13/2016_01:00:00 11/06/2016_01:00:00
03/12/2017_01:00:00 11/05/2017_01:00:00
03/11/2018_01:00:00 11/04/2018_01:00:00
03/10/2019_01:00:00 11/03/2019_01:00:00
03/08/2020_01:00:00 11/01/2020_01:00:00
03/14/2021_01:00:00 11/07/2021_01:00:00
03/13/2022_01:00:00 11/06/2022_01:00:00
03/12/2023_01:00:00 11/05/2023_01:00:00
03/10/2024_01:00:00 11/03/2024_01:00:00
03/09/2025_01:00:00 11/02/2025_01:00:00
03/08/2026_01:00:00 11/01/2026_01:00:00
03/14/2027_01:00:00 11/07/2027_01:00:00
03/12/2028_01:00:00 11/05/2028_01:00:00
03/11/2029_01:00:00 11/04/2029_01:00:00
03/10/2030_01:00:00 11/03/2030_01:00:00
03/09/2031_01:00:00 11/02/2031_01:00:00
03/14/2032_01:00:00 11/07/2032_01:00:00
isDst.exe 03/11/2007_02:00:00 >> dst.txt
isDst.exe 03/09/2008_02:00:00 >> dst.txt
isDst.exe 03/08/2009_02:00:00 >> dst.txt
isDst.exe 03/14/2010_02:00:00 >> dst.txt
isDst.exe 03/13/2011_02:00:00 >> dst.txt
isDst.exe 03/11/2012_02:00:00 >> dst.txt
isDst.exe 03/10/2013_02:00:00 >> dst.txt
isDst.exe 03/09/2014_02:00:00 >> dst.txt
isDst.exe 03/08/2015_02:00:00 >> dst.txt
isDst.exe 03/13/2016_02:00:00 >> dst.txt
isDst.exe 03/12/2017_02:00:00 >> dst.txt
isDst.exe 03/11/2018_02:00:00 >> dst.txt
isDst.exe 03/10/2019_02:00:00 >> dst.txt
isDst.exe 03/08/2020_02:00:00 >> dst.txt
isDst.exe 03/14/2021_02:00:00 >> dst.txt
isDst.exe 03/13/2022_02:00:00 >> dst.txt
isDst.exe 03/12/2023_02:00:00 >> dst.txt
isDst.exe 03/10/2024_02:00:00 >> dst.txt
isDst.exe 03/09/2025_02:00:00 >> dst.txt
isDst.exe 03/08/2026_02:00:00 >> dst.txt
isDst.exe 03/14/2027_02:00:00 >> dst.txt
isDst.exe 03/12/2028_02:00:00 >> dst.txt
isDst.exe 03/11/2029_02:00:00 >> dst.txt
isDst.exe 03/10/2030_02:00:00 >> dst.txt
isDst.exe 03/09/2031_02:00:00 >> dst.txt
isDst.exe 03/14/2032_02:00:00 >> dst.txt
isDst.exe 11/04/2007_02:00:00 >> dst.txt
isDst.exe 11/02/2008_02:00:00 >> dst.txt
isDst.exe 11/01/2009_02:00:00 >> dst.txt
isDst.exe 11/07/2010_02:00:00 >> dst.txt
isDst.exe 11/06/2011_02:00:00 >> dst.txt
isDst.exe 11/04/2012_02:00:00 >> dst.txt
isDst.exe 11/03/2013_02:00:00 >> dst.txt
isDst.exe 11/02/2014_02:00:00 >> dst.txt
isDst.exe 11/01/2015_02:00:00 >> dst.txt
isDst.exe 11/06/2016_02:00:00 >> dst.txt
isDst.exe 11/05/2017_02:00:00 >> dst.txt
isDst.exe 11/04/2018_02:00:00 >> dst.txt
isDst.exe 11/03/2019_02:00:00 >> dst.txt
isDst.exe 11/01/2020_02:00:00 >> dst.txt
isDst.exe 11/07/2021_02:00:00 >> dst.txt
isDst.exe 11/06/2022_02:00:00 >> dst.txt
isDst.exe 11/05/2023_02:00:00 >> dst.txt
isDst.exe 11/03/2024_02:00:00 >> dst.txt
isDst.exe 11/02/2025_02:00:00 >> dst.txt
isDst.exe 11/01/2026_02:00:00 >> dst.txt
isDst.exe 11/07/2027_02:00:00 >> dst.txt
isDst.exe 11/05/2028_02:00:00 >> dst.txt
isDst.exe 11/04/2029_02:00:00 >> dst.txt
isDst.exe 11/03/2030_02:00:00 >> dst.txt
isDst.exe 11/02/2031_02:00:00 >> dst.txt
isDst.exe 11/07/2032_02:00:00 >> dst.txt
https://stackoverflow.com/questions/5590429/calculating-daylight-saving-time-from-only-date
***************/
/*****
The previous programs used mktime to compute day_of_week.
It used day_of_week to compute 2nd_sunday in march and
1st_sunday in Nov.
If you don't want to use mktime, you can use this program to
compute 2nd_sunday. The same technique will compute 1st_sunday.
On 03/14/2007, the day of the week is Wed, or 3.
Every year after 2007, the day of the week advances 1 day.
on leap years, the day of the week advances 2 days.
Must include the no. of leap years sinc 2004.
******/
#include <stdio.h>
#include <string.h>
#include <time.h>
int secondSunday(year);
int main(int argc, char *argv[])
{
int year, second_sunday;
if( argc == 1 )
{
printf("nsyntax: %s year, with year >= 2007.n", argv[0]);
return -1;
}
year = atoi(argv[1]);
if( year < 2007 )
{
printf("nsyntax: %s year, with year >= 2007.n", argv[0]);
return -1;
}
second_sunday = secondSunday(year);
printf("second_sunday=%dn", second_sunday);
return 0;
}
int secondSunday(year)
{
//On 03/14/2007, the day of the week is Wed, or 3.
int no_years, no_leaps, day_of_week, second_sunday;
no_years = year - 2007;
no_leaps = (year - 2004)/4;
day_of_week = 3 + (no_years + no_leaps) % 7;
second_sunday = 14 - day_of_week;
if( second_sunday < 8 ) second_sunday += 7;
//printf("no_years=%d,no_leaps=%d,day_of_week=%d, second_sunday=%dn",
//no_years, no_leaps, day_of_week, second_sunday);
return second_sunday;
}
/**************
Compile via cl.exe second_sunday.c
second_sunday.exe 2007
second_sunday.exe 2008
second_sunday.exe 2009
second_sunday.exe 2010
second_sunday.exe 2011
second_sunday.exe 2012
second_sunday.exe 2013
second_sunday.exe 2014
second_sunday.exe 2015
second_sunday.exe 2016
second_sunday.exe 2017
second_sunday.exe 2018
second_sunday.exe 2019
second_sunday.exe 2020
second_sunday.exe 2021
second_sunday.exe 2022
second_sunday.exe 2023
second_sunday.exe 2024
second_sunday.exe 2025
second_sunday.exe 2026
second_sunday.exe 2027
second_sunday.exe 2028
second_sunday.exe 2029
second_sunday.exe 2030
second_sunday.exe 2031
second_sunday.exe 2032
***************/
3月14日和11月7日一直是美国实行夏令时的一周的一部分。它们可能是星期天、星期六，也可能是中间的某一天，但它们总是那一周的一部分。下面的代码将查找这两个日期是所讨论的日期所在年份的一部分的星期日。然后在这个日期上加上2个小时，得到实际发生夏令时的时间。然后将所讨论的日期与夏令时的开始和结束日期进行比较，并根据GMT偏移量调整时间。这一过程也适用于其他国家的开始和结束日期。您可以设置一个表，其中包含每个国家代码和邮政编码，以及夏令时结束和开始日期以及两个时间段的GMT偏移量。日期将是7日，14日，21日和28日，为一个月的第一个到第四个星期日。你可以在9月30日或10月31日以外的最后一个星期日输入最多的一天。
三月第二个星期日:
cdate("3/14/" & format(now(),"yyyy"))-format(cdate("3/14/" & format(now(),"yyyy")),"W")+1+2/24
11月1日星期日:
cdate("11/7/" & format(now(),"yyyy"))-format(cdate("11/7/" & format(now(),"yyyy")),"W")+1+2/24
。
If(now() < cdate("3/14/" & format(now(),"yyyy"))-format(cdate("3/14/" & format(now(),"yyyy")),"W")+1+2/24, dateadd("H",-5,now()), if(now() < cdate("11/7/" & format(now(),"yyyy"))-format(cdate("11/7/" & format(now(),"yyyy")),"W")+1+2/24, dateadd("H",-6,now()), dateadd("H",-5,now())))
t_SQL例子
CASE WHEN [date2check] <DATEADD(hh,>
我正在尝试这种方法，我认为它简单而准确:
//表示3月的第一个星期日，如果DoW = 1表示星期日If (month==3 &&> = 8天,,日<=14 &&DoW=1)返回True
//11月的第二个星期日，如果DoW = 1If (month==11 &&天> = 1,,日<=7 &&
这是我的答案，欢迎任何更正。假定年份在2000年至2099年之间。详情请参阅参考链接。
int timezone = 0; // Set to correct initial value depending on where you are (or via GPS if you like).
// Calculate day of week for Daylight savings time.
int day_of_week = (day_of_month + int(2.6 * (((month + 12 - 3) % 12) + 1) - 0.2) - 40 +
(month < 3 ? year-1 : year) + int((month < 3 ? year-1 : year)/4) + 5) % 7;
// Adjust timezone based on Daylight savings time for northern hemisphere, USA
if ((month > 3 && month < 11 ) ||
(month == 3 && day_of_month >= 8 && day_of_week == 0 && hour >= 2) || // DST starts 2nd Sunday of March; 2am
(month == 11 && day_of_month < 8 && day_of_week > 0) ||
(month == 11 && day_of_month < 8 && day_of_week == 0 && hour < 2)) { // DST ends 1st Sunday of November; 2am
timezone++;
}
星期计算参考:给定月、日、年，如何确定星期几
DST测试参考是通过这篇由captncraig回答的文章以及我自己对他的回答的推理和解释。
我发现这些都很有帮助。巴西有一些特殊的问题，南半球，有时狂欢节与秋天的变化日期重叠。
在这些情况下，立法机构将夏令时推迟一周。美国海军天文台的计算可以找到复活节(在http://aa.usno.navy.mil/faq/docs/easter.php，检索日期为2017年1月3日)，而狂欢节是提前几天的确切日期，即灰星期三之前的周末(Mardi Gras意为"油腻的星期二")。
那么，在C中:
static const uint8_t carnival[] = {
0x04, 0x24, 0x24, 0x21, // 2000... 2031
0x01, 0x09, 0x48, 0x09, // 2032... 2063
0x4a, 0x40, 0x4a, 0x52, // 2064... 2095
0x02, 0x90, 0x12, 0x94 // 2096... 2127
}
/* Returns the current time offset. */
int dst(struct tm *tm_ptr)
{
int st = 0;
int dst = 60;
int mon = tm_ptr->tm_mon;
int mday, previous_sunday;
int gmt_offset = tm_ptr->gmt_offset;
// If not Brasilia or Amazon time, no DST.
if(gmt_offset != -240 && gmt_offset != -300)
return st;
if(NOV < mon || FEB > mon) // Summer?
return dst;
else if(NOV > mon && FEB < mon) // Winter?
return st;
mday = tm_ptr->tm_mday;
previous_sunday = mday - tm_ptr->tm_wday;
// Begin DST on first Sunday of November.
if(NOV == mon) // If it's November... i.e. spring, so forward
{
if(previous_sunday < 1) // Before Sunday, week 1?
{
return st;
} else { // After or during Sunday, week 1
return dst;
}
// End DST in February, accounting for Carnival.
} else { // It has to be February, i.e. fall, so backward.
int year, week_start;
year = tm_ptr->tm_year;
if(0 == (carnival[year/8] & (1 << (year%8))))
week_start = 15; // 3rd Sunday is not in Carnival.
else
week_start = 22; // Use 4th Sunday, 1 week after Carnival.
if(previous_sunday < (week_start-1))
return dst;
if(previous_sunday < week_start) {
if(tm_ptr->tm_isdst == st) // if it already fell backward, stay.
return st;
return dst;
}
// On or after the correct Sunday?
return st;
}
}
如果有人在python中寻找这个，这里有一篇很棒的文章:http://code.activestate.com/recipes/425607-findng-the-xth-day-in-a-month/
包含以下代码:
from calendar import monthrange
def dow_date_finder(which_weekday_in_month=FIRST,day=MONDAY,month=JANUARY,year=2000):
bom, days = monthrange(year, month)
firstmatch = (day - bom) % 7 + 1
return xrange(firstmatch, days+1, 7)[which_weekday_in_month]
请记住，您需要在上面链接的页面顶部显示所有变量，以使其更加用户友好。
以下内容适用于2007年或以后的任何年份:
def find_dt_of_daylight_savings_time(yr=date.today().year):
dst = {}
spring = dow_date_finder(SECOND, SUNDAY, MARCH, yr)
spring_dt = datetime(int(yr), 3, spring, 3, 0)
dst['spring'] = spring_dt
fall = dow_date_finder(FIRST, SUNDAY, NOVEMBER, yr)
fall_dt = datetime(int(yr), 11, fall, 3, 0)
dst['fall'] = fall_dt
return dst