Difference between System DateTime Now and System DateTime Today

Question

Can anyone explain the difference between System DateTime Now and System DateTime Today in C  NET  Pros and cons of each if possible

User · Answer

I thought of Adding these links -

A brief History of DateTime - By Anthony Moore by BCL team
Choosing between Datetime and DateTime Offset - by MSDN
Do not forget SQL server 2008 onwards has a new Datatype as DateTimeOffset
The .NET Framework includes the DateTime, DateTimeOffset, and TimeZoneInfo types, all of which can be used to build applications that work with dates and times.
Performing Arithmetic Operations with Dates and Times-MSDN

Coming back to original question , Using Reflector i have explained the difference in code

 public static DateTime Today
    {
      get
      {
        return DateTime.Now.Date;   // It returns the date part of Now

        //Date Property
       // returns same date as this instance, and the time value set to 12:00:00 midnight (00:00:00) 
      }
    }


    private const long TicksPerMillisecond = 10000L;
    private const long TicksPerDay = 864000000000L;
    private const int MillisPerDay = 86400000;

    public DateTime Date
    {
       get
      {
        long internalTicks = this.InternalTicks; // Date this instance is converted to Ticks 
        return new DateTime((ulong) (internalTicks - internalTicks % 864000000000L) | this.InternalKind);  
// Modulo of TicksPerDay is subtracted - which brings the time to Midnight time 
      }
    }


     public static DateTime Now
        {
          get
          {
           /* this is why I guess Jon Skeet is recommending to use  UtcNow as you can see in one of the above comment*/
            DateTime utcNow = DateTime.UtcNow;


            /* After this i guess it is Timezone conversion */
            bool isAmbiguousLocalDst = false;
            long ticks1 = TimeZoneInfo.GetDateTimeNowUtcOffsetFromUtc(utcNow, out isAmbiguousLocalDst).Ticks;
            long ticks2 = utcNow.Ticks + ticks1;
            if (ticks2 > 3155378975999999999L)
              return new DateTime(3155378975999999999L, DateTimeKind.Local);
            if (ticks2 < 0L)
              return new DateTime(0L, DateTimeKind.Local);
            else
              return new DateTime(ticks2, DateTimeKind.Local, isAmbiguousLocalDst);
          }
        }

User · Answer

The DateTime Now property returns the current date and time  for example 2011-07-01 10 09 45310   The DateTime Today property returns the current date with the time compnents set to zero  for example 2011-07-01 00 00 00000   The DateTime Today property actually is implemented to return DateTime Now Date   public static DateTime Today     get       DateTime now   DateTime Now      return now Date

User · Answer

DateTime Today represents the current system date with the time part set to 00 00 00  and  DateTime Now represents the current system date and time

User · Answer

DateTime dt   new DateTime      gives 01 01 0001 12 00 00 AM DateTime dt   DateTime Now    gives today date with current time DateTime dt   DateTime Today    gives today date and 12 00 00 AM time

User · Answer

DateTime Today is DateTime Now with time set to zero   It is important to note that there is a difference between a DateTime value  which represents the number of ticks that have elapsed since midnight of January 1  0000  and the string representation of that DateTime value  which expresses a date and time value in a culture-specific-specific format   https   msdn microsoft com en-us library system datetime now 28v vs 110 29 aspx  DateTime Now Ticks is the actual time stored by  net  essentially UTC time   the rest are just representations  which are important for display purposes    If the Kind property is DateTimeKind Local it implicitly includes the time zone information of the local computer  When sending over a  net web service  DateTime values are by default serialized with time zone information included  e g  2008-10-31T15 07 38 6875000-05 00  and a computer in another time zone can still exactly know what time is being referred to   So  using DateTime Now and DateTime Today is perfectly OK   You usually start running into trouble when you begin confusing the string representation with the actual value and try to  fix  the DateTime  when it isn t broken

User · Answer

DateTime Now ToShortDateString   will display only the date part

User · Answer

Time   Now includes the 09 23 12 or whatever   Today is the date-part only   at 00 00 00 on that day    So use  Now if you want to include the time  and  Today if you just want the date    Today is essentially the same as  Now Date

User · Answer

DateTime Now returns a DateTime value that consists of the local date and time of the computer where the code is running   It has DateTimeKind Local assigned to its Kind property   It is equivalent to calling  any of the following    DateTime UtcNow ToLocalTime   DateTimeOffset UtcNow LocalDateTime DateTimeOffset Now LocalDateTime TimeZoneInfo ConvertTime DateTime UtcNow  TimeZoneInfo Local  TimeZoneInfo ConvertTimeFromUtc DateTime UtcNow  TimeZoneInfo Local    DateTime Today returns a DateTime value that has the same year  month  and day components as any of the above expressions  but with the time components set to zero   It also has DateTimeKind Local in its Kind property   It is equivalent to any of the following    DateTime Now Date DateTime UtcNow ToLocalTime   Date DateTimeOffset UtcNow LocalDateTime Date DateTimeOffset Now LocalDateTime Date TimeZoneInfo ConvertTime DateTime UtcNow  TimeZoneInfo Local  Date TimeZoneInfo ConvertTimeFromUtc DateTime UtcNow  TimeZoneInfo Local  Date   Note that internally  the system clock is in terms of UTC  so when you call DateTime Now it first gets the UTC time  via the GetSystemTimeAsFileTime function in the Win32 API  and then it converts the value to the local time zone    Therefore DateTime Now ToUniversalTime   is more expensive than DateTime UtcNow    Also note that DateTimeOffset Now DateTime will have similar values to DateTime Now  but it will have DateTimeKind Unspecified rather than DateTimeKind Local - which could lead to other errors depending on what you do with it   So  the simple answer is that DateTime Today is equivalent to DateTime Now Date  But IMHO - You shouldn t use either one of these  or any of the above equivalents   When you ask for DateTime Now  you are asking for the value of the local calendar clock of the computer that the code is running on   But what you get back does not have any information about that clock   The best that you get is that DateTime Now Kind    DateTimeKind Local   But whose local is it   That information gets lost as soon as you do anything with the value  such as store it in a database  display it on screen  or transmit it using a web service   If your local time zone follows any daylight savings rules  you do not get that information back from DateTime Now   In ambiguous times  such as during a  fall-back  transition  you won t know which of the two possible moments correspond to the value you retrieved with DateTime Now   For example  say your system time zone is set to Mountain Time  US  amp  Canada  and you ask for DateTime Now in the early hours of November 3rd  2013   What does the result 2013-11-03 01 00 00 mean   There are two moments of instantaneous time represented by this same calendar datetime   If I were to send this value to someone else  they would have no idea which one I meant   Especially if they are in a time zone where the rules are different   The best thing you could do would be to use DateTimeOffset instead      This will always be unambiguous  DateTimeOffset now   DateTimeOffset Now    Now for the same scenario I described above  I get the value 2013-11-03 01 00 00 -0600 before the transition  or 2013-11-03 01 00 00 -0700 after the transition   Anyone looking at these values can tell what I meant   I wrote a blog post on this very subject   Please read - The Case Against DateTime Now   Also  there are some places in this world  such as Brazil  where the  spring-forward  transition happens exactly at Midnight   The clocks go from 23 59 to 01 00   This means that the value you get for DateTime Today on that date  does not exist   Even if you use DateTimeOffset Now Date  you are getting the same result  and you still have this problem   It is because traditionally  there has been no such thing as a Date object in  Net   So regardless of how you obtain the value  once you strip off the time - you have to remember that it doesn t really represent  midnight   even though that s the value you re working with   If you really want a fully correct solution to this problem  the best approach is to use NodaTime   The LocalDate class properly represents a date without a time   You can get the current date for any time zone  including the local system time zone   using NodaTime       Instant now   SystemClock Instance Now   DateTimeZone zone1   DateTimeZoneProviders Tzdb GetSystemDefault    LocalDate todayInTheSystemZone   now InZone zone1  Date   DateTimeZone zone2   DateTimeZoneProviders Tzdb  America New York    LocalDate todayInTheOtherZone   now InZone zone2  Date    If you don t want to use Noda Time  there is now another option   I ve contributed an implementation of a date-only object to the  Net CoreFX Lab project   You can find the System Time package object in their MyGet feed   Once added to your project  you will find you can do any of the following   using System       Date localDate   Date Today   Date utcDate   Date UtcToday   Date tzSpecificDate   Date TodayInTimeZone anyTimeZoneInfoObject

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