How to get the unix timestamp in C

Question

I have had look around stackoverflow  and even looked at some of the suggested questions and none seem to answer  how do you get a unix timestamp in C

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I ve spliced together the most elegant approaches to this utility method   public static class Ux       public static decimal ToUnixTimestampSecs this DateTime date    gt  ToUnixTimestampTicks date     decimal  TimeSpan TicksPerSecond      public static long ToUnixTimestampTicks this DateTime date    gt  date ToUniversalTime   Ticks - UnixEpochTicks      private static readonly long UnixEpochTicks   new DateTime 1970  1  1  0  0  0  DateTimeKind Utc  Ticks

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When you subtract 1970 from the current time  be aware that the timespan will most often have a non zero milliseconds field  If for some reason you are interested in the milliseconds  keep this in mind   Here s what I did to get around this issue    DateTime now   UtcNow         milliseconds Not included   DateTime nowToTheSecond   new DateTime now Year now Month now Day now Hour now Minute now Second      TimeSpan span    date - new DateTime 1970  1  1  0  0  0  0      Assert That span Milliseconds  Is EqualTo 0       passes

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Below is a 2-way extension class that supports    Timezone localization Input output in seconds or milliseconds    In OP s case  usage is   DateTime Now ToUnixtime      or  DateTime UtcNow ToUnixtime      Even though a direct answer exists  I believe using a generic approach is better  Especially because it s most likely a project that needs a conversion like this  will also need these extensions anyway  so it s better to use the same tool for all       public static class UnixtimeExtensions               public static readonly DateTime UNIXTIME ZERO POINT   new DateTime 1970  1  1  0  0 0  DateTimeKind Utc                 lt summary gt              Converts a Unix timestamp  UTC timezone by definition  into a DateTime object              lt  summary gt               lt param name  value  gt An input of Unix timestamp in seconds or milliseconds format lt  param gt               lt param name  localize  gt should output be localized or remain in UTC timezone  lt  param gt               lt param name  isInMilliseconds  gt Is input in milliseconds or seconds  lt  param gt               lt returns gt  lt  returns gt          public static DateTime FromUnixtime this long value  bool localize   false  bool isInMilliseconds   true                        DateTime result               if  isInMilliseconds                                result   UNIXTIME ZERO POINT AddMilliseconds value                             else                               result   UNIXTIME ZERO POINT AddSeconds value                              if  localize                  return result ToLocalTime                else                 return result                          lt summary gt              Converts a DateTime object into a Unix time stamp              lt  summary gt               lt param name  value  gt any DateTime object as input lt  param gt               lt param name  isInMilliseconds  gt Should output be in milliseconds or seconds  lt  param gt               lt returns gt  lt  returns gt          public static long ToUnixtime this DateTime value  bool isInMilliseconds   true                        if  isInMilliseconds                                return  long value ToUniversalTime   Subtract UNIXTIME ZERO POINT  TotalMilliseconds                            else                               return  long value ToUniversalTime   Subtract UNIXTIME ZERO POINT  TotalSeconds

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As of  NET 4 6  there is DateTimeOffset ToUnixTimeSeconds   This is an instance method  so you are expected to call it on an instance of DateTimeOffset  You can also cast any instance of DateTime  though beware the timezone  To get the current timestamp  DateTimeOffset Now ToUnixTimeSeconds    To get the timestamp from a DateTime  DateTime foo   DateTime Now  long unixTime     DateTimeOffset foo  ToUnixTimeSeconds

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This solution helped in my situation      public class DateHelper        public static double DateTimeToUnixTimestamp DateTime dateTime                                      return  TimeZoneInfo ConvertTimeToUtc dateTime  -                              new DateTime 1970  1  1  0  0  0  0  System DateTimeKind Utc   TotalSeconds                          using helper in code    double ret   DateHelper DateTimeToUnixTimestamp DateTime Now

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This is what I use   public long UnixTimeNow         var timeSpan    DateTime UtcNow - new DateTime 1970  1  1  0  0  0        return  long timeSpan TotalSeconds      Keep in mind that this method will return the time as Coordinated Univeral Time  UTC

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This is what I use    public class TimeStamp               public Int32 UnixTimeStampUTC                         Int32 unixTimeStamp              DateTime currentTime   DateTime Now              DateTime zuluTime   currentTime ToUniversalTime                DateTime unixEpoch   new DateTime 1970  1  1               unixTimeStamp    Int32  zuluTime Subtract unixEpoch   TotalSeconds              return unixTimeStamp

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The simple code that I am using    public static long CurrentTimestamp        return  long  DateTime UtcNow Subtract new DateTime 1970  1  1   TotalSeconds   1000       This code is giving unix timestamp  total milliseconds from 1970-01-01 to now

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There is a ToUnixTimeMilliseconds for DateTimeOffset in System  You can write similar method for DateTime   public static long ToUnixTimeSeconds this DateTime value        return value Ticks   10000000L - 62135596800L      10000000L - converting ticks to seconds  62135596800L - converting 01 01 01 to 01 01 1978   There is no problem with Utc and leaks

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You get a unix timestamp in C  by using DateTime UtcNow and subtracting the epoch time of 1970-01-01   e g   Int32 unixTimestamp    Int32  DateTime UtcNow Subtract new DateTime 1970  1  1    TotalSeconds    DateTime UtcNow can be replaced with any DateTime object that you would like to get the unix timestamp for   There is also a field  DateTime UnixEpoch  which is very poorly documented by MSFT  but may be a substitute for new DateTime 1970  1  1

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Updated code from Brad with few things  You don t need Math truncate  conversion to int or long automatically truncates the value  In my version I am using long instead of int  We will run out of 32 bit signed integers in 2038 year   Also  added timestamp parsing  public static class DateTimeHelper            lt summary gt           Converts a given DateTime into a Unix timestamp           lt  summary gt            lt param name  quot value quot  gt Any DateTime lt  param gt            lt returns gt The given DateTime in Unix timestamp format lt  returns gt      public static long ToUnixTimestamp this DateTime value                return  long  value ToUniversalTime   Subtract new DateTime 1970  1  1    TotalSeconds                  lt summary gt          Gets a Unix timestamp representing the current moment          lt  summary gt           lt param name  quot ignored quot  gt Parameter ignored lt  param gt           lt returns gt Now expressed as a Unix timestamp lt  returns gt      public static long UnixTimestamp this DateTime ignored                return  long  DateTime UtcNow Subtract new DateTime 1970  1  1    TotalSeconds                  lt summary gt          Returns a local DateTime based on provided unix timestamp          lt  summary gt           lt param name  quot timestamp quot  gt Unix posix timestamp lt  param gt           lt returns gt Local datetime lt  returns gt      public static DateTime ParseUnixTimestamp long timestamp                return  new DateTime 1970  1  1   AddSeconds timestamp  ToLocalTime

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I used this after struggling for a while  it caters to the timezone offset as well        public double Convert DatTime To UNIXDATETIME DateTime dt                System DateTime from date   new DateTime 1970  1  1  0  0  0  0  System DateTimeKind Utc           double unix time since   dt Subtract from date  TotalMilliseconds           TimeSpan ts offset   TimeZoneInfo Local GetUtcOffset DateTime UtcNow            double offset   ts offset TotalMilliseconds           return unix time since - offset

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You can also use Ticks  I m coding for Windows Mobile so don t have the full set of methods  TotalSeconds is not available to me   long epochTicks   new DateTime 1970  1  1  Ticks  long unixTime     DateTime UtcNow Ticks - epochTicks    TimeSpan TicksPerSecond     or  TimeSpan epochTicks   new TimeSpan new DateTime 1970  1  1  Ticks   TimeSpan unixTicks   new TimeSpan DateTime UtcNow Ticks  - epochTicks  double unixTime   unixTicks TotalSeconds

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Truncating  TotalSeconds is important since it s defined as the value of the current System TimeSpan structure expressed in whole fractional seconds   And how about an extension for DateTime  The second one is probably more confusing that it s worth until property extensions exist        lt summary gt      Converts a given DateTime into a Unix timestamp      lt  summary gt       lt param name  value  gt Any DateTime lt  param gt       lt returns gt The given DateTime in Unix timestamp format lt  returns gt  public static int ToUnixTimestamp this DateTime value        return  int Math Truncate  value ToUniversalTime   Subtract new DateTime 1970  1  1    TotalSeconds           lt summary gt      Gets a Unix timestamp representing the current moment      lt  summary gt       lt param name  ignored  gt Parameter ignored lt  param gt       lt returns gt Now expressed as a Unix timestamp lt  returns gt  public static int UnixTimestamp this DateTime ignored        return  int Math Truncate  DateTime UtcNow Subtract new DateTime 1970  1  1    TotalSeconds

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