Datetime 仅从日期计算夏令时

我正在使用Arduino和实时时钟芯片。芯片补偿闰年等，所以它总是有正确的日期，但它不处理夏令时，我认为由于地区复杂。时钟可以告诉我日期、月份和年份（以1为基础）以及一周中的哪一天（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，我只需在时钟上加一个小时，我就有了所需的时间

---

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（山区时间）起作用。对于我的平台，似乎没有任何全面的日期库，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DST中？

这实际上很简单。有几个事实可以帮助我们：

在美国大部分地区，DST从3月的第二个星期日开始，到11月的第一个星期日结束，两次都是凌晨2点

三月的第二个星期日总是在8号和14号之间，包括8号和14号

11月的第一个星期日总是在1号和7号之间，包括1号和7号

星期几的编号非常方便，因为星期几将为您提供上一个星期日

这些事实导致了以下代码（C#，但可移植到您的平台）：

public bool IsDST（整数日、整数月、整数道指）
{
//一月、二月和十二月已经过去了。
如果（月<3 | |月>11）{返回false；}
//4月到10月是一段时间
如果（月>3&&month<11）{return true；}
int previousSunday=日-道指；
//在三月份，如果我们的上一个周日是在8号或之后，我们就是DST。
如果（月==3）{返回上一个星期日>=8；}
//在11月，我们必须赶在第一个周日之前进行dst。
//这意味着前一个星期日必须在第一个星期日之前。
return previousSunday虽然根据当前规则很容易计算特定日期是否在特定地点的DST中，但请注意DST是政客们一时兴起的，随时可能发生变化。我有一个2007年之前制造的时钟，可以自动调整夏令时，现在我必须将其更改为ur一年两次：实际变化发生时两次，现在在旧日期错误地变化时两次

在这种情况下，您可以通过简单的权宜之计完全忽略DST，即让用户输入时区以及日期和时间。或者您也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本地时区

但是，如果你真的需要处理DST，并且真的想把事情做好，请使用，并确保它可以以某种方式更新。如果你因为某种原因不能做到这一点，至少允许用户覆盖规则。如果这太难，至少给用户关闭自动调整的选项（不像我愚蠢的闹钟）.
中欧代码（2014-3000年期间每天测试）

公共静态bool IsDst（整数日、整数月、整数道指）
{
如果（月<3 | |月>10）返回false；
如果（月份>3和月份<10）返回true；
int previousSunday=日-道指；
如果（月==3）返回上一个星期日>=25；
如果（月==10）返回上一个星期日<25；
return false；//这行永远不会发生
}

测试功能

    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();

static void Main（字符串[]args）
{
TimeZoneInfo tzf2=TimeZoneInfo.FindSystemTimeZoneById（“中欧标准时间”）；
var日期=新的日期时间（2014,01,1,5,0,0）；
bool wassammer=false；
虽然（日期在美国，3月14日和11月7日始终是日间储蓄发生的一周的一部分。它们可能是星期日或星期六或一周中的一天，但它们始终是该周的一部分。下面的代码将发现这两个日期的星期日是该日期发生年份的一部分n、 然后在此日期上再加上2小时，以获得夏令时实际发生的时间。然后，您将讨论中的日期与夏令时开始和结束日期进行比较，并通过gmt偏移量调整时间。此过程可用于其他国家/地区的开始和结束日期。您可以设置一个包含每个国家/地区代码和p的表其中的ostal代码包含夏时制结束和开始日期以及这两个期间的gmt偏移量。对于一个月的第一个到第四个星期日，日期为第7、14、21和28日。您可以输入该月最后一个星期日（9月30日或10月31日）的最大天数

三月的第二个星期日：

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

前

If（now（）

t_SQL示例

当[date2check]cdate("3/14/" & format(now(),"yyyy"))-format(cdate("3/14/" & format(now(),"yyyy")),"W")+1+2/24

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())))

  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++;
  }

#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=%d\n", 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=%d\n", 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=%d\n",
   //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
***************/

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]

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