How can I convert a DateTime to the number of seconds since 1970

Question

I m trying to convert a C  DateTime variable to Unix time  ie  the number of seconds since Jan 1st  1970   It looks like a DateTime is actually implemented as the number of  ticks  since Jan 1st  0001   My current thought is to subtract Jan 1st  1970 from my DateTime like this   TimeSpan span  DateTime Now Subtract new DateTime 1970 1 1 0 0 0    return span TotalSeconds    Is there a better way

User · Answer

That approach will be good if the date-time in question is in UTC  or represents local time in an area that has never observed daylight saving time   The DateTime difference routines do not take into account Daylight Saving Time  and consequently will regard midnight June 1 as being a multiple of 24 hours after midnight January 1   I m unaware of anything in Windows that reports historical daylight-saving rules for the current locale  so I don t think there s any good way to correctly handle any time prior to the most recent daylight-saving rule change

User · Answer

You probably want to use DateTime UtcNow to avoid timezone issue  TimeSpan span  DateTime UtcNow Subtract new DateTime 1970 1 1 0 0 0

User · Answer

You can create a startTime and endTime of DateTime  then do endTime Subtract startTime   Then output your span Seconds   I think that should work

User · Answer

That s basically it   These are the methods I use to convert to and from Unix epoch time   public static DateTime ConvertFromUnixTimestamp double timestamp        DateTime origin   new DateTime 1970  1  1  0  0  0  0  DateTimeKind Utc       return origin AddSeconds timestamp      public static double ConvertToUnixTimestamp DateTime date        DateTime origin   new DateTime 1970  1  1  0  0  0  0  DateTimeKind Utc       TimeSpan diff   date ToUniversalTime   - origin      return Math Floor diff TotalSeconds       Update  As of  Net Core 2 1 and  Net Standard 2 1 a DateTime equal to the Unix Epoch can be obtained from the static DateTime UnixEpoch

User · Answer

I use year 2000 instead of Epoch Time in my calculus  Working with smaller numbers is easy to store and transport and is JSON friendly      Year 2000 was at second 946684800 of epoch time       Year 2000 was at second 63082281600 from 1-st of Jan 0001       DateTime UtcNow Ticks starts from 1-st of Jan 0001   Seconds from year 2000   DateTime UtcNow Ticks 10000000-63082281600   Seconds from Unix Time   DateTime UtcNow Ticks 10000000-946684800   For example year 2020 is    var year2020    new DateTime    AddYears 2019  Ticks     Because DateTime starts already at year 1  637134336000000000 Ticks since 1-st of Jan 0001  63713433600 Seconds since 1-st of Jan 0001  1577836800 Seconds since Epoch Time  631152000 Seconds since year 2000  References   Epoch Time converter  https   www epochconverter com  Year 1 converter  https   www epochconverter com seconds-days-since-y0

User · Answer

If the rest of your system is OK with DateTimeOffset instead of DateTime  there s a really convenient feature   long unixSeconds   DateTimeOffset Now ToUnixTimeSeconds

User · Answer

The only thing I see is that it s supposed to be since Midnight Jan 1  1970 UTC  TimeSpan span  DateTime Now Subtract new DateTime 1970 1 1 0 0 0  DateTimeKind Utc    return span TotalSeconds

[c#] How can I convert a DateTime to the number of seconds since 1970?

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