System.DateTime (struct)

An instance of the System.DateTime represents

a point in time between 0001-01-01 and 9999-12-31
with an accuracy of 100 nanoseconds
without a reference to a time zone.

Each of these possible point in times is assigned a 64-bit number, called tick, which represents the number of 100-nonosecond intervals between Midnight January 1, 0001 and the point in time the instance of the struct represents.

In PowerShell, the current date-time is returned by the get-date cmdLet.

Creating a DateTime object in PowerShell

A DateTime object can be created in PowerShell like so:

$dt = new-object dateTime 2020,03,15 , 14,53,18

It is also possible to crete a DateTime object with the System.Convert.ToDatetime() method.

String-formatting a DateTime

The ToString() method takes a format string that allows to format the value of a DateTime object.

The following C# example shows a few format strings that are culture-independent:

using System;

class C {

   private static void printFormat(String format) {
      Console.WriteLine("{0,-20}: {1}", format, DateTime.Now.ToString(format));
   }

   static void Main() {
      printFormat("yyyy-MM-dd");   
      printFormat("HH:mm:ss"  );   
      printFormat("r"         ); // RFC 1123
      printFormat("s"         ); // sortable
      printFormat("U"         ); // universal
   }
}
//   possible Output:
//
//   yyyy-MM-dd          : 2019-11-09
//   HH:mm:ss            : 20:28:53
//   r                   : Sat, 09 Nov 2019 20:28:53 GMT
//   s                   : 2019-11-09T20:28:53
//   u                   : 2019-11-09 20:28:53Z

Github repository .NET-API, path: /System/DateTime/ToString.cs

In PowerShell,it is possible to format a DateTime object with the -f operator.

$dt = new-object dateTime 2020,08,28 , 22,23,24

write-host "created date time refers to $('{0:yyyy-MM-dd HH:mm:ss}' -f $dt)"

Github repository .NET-API, path: /System/DateTime/format.ps1

Converting a UTC string to a local time

In PowerShell, a string that describes a point in time in UTC format can be converted to a local time like so:

$utc   =  '2021-10-25T13:23:08.0966497Z'
$local = ([dateTime] $utc).ToLocalTime()

write-host $local

Relation to file times

Ticks that are used in System.DateTime are related to another Microsoft specific representation of point in times: file times.

A file time measures a point in time as the number of 100-nanosecond intervals («ticks») that have elapsed since midnight, January 1601, UTC (as opposed to counting such intervals starting in the Year 1).

System.DateTime offers four methods to convert between file times and DateTimes.

Removing time information from a DateTime object

With .NET 6, time related information (hours, minutes, seconds) can be «removed» from a DateTime object:

var dt = DateOnly.FromDateTime(dt_hms);

Fields, properties and methods

`Add()`
`AddDays()`
`AddHours()`
`AddMilliseconds()`
`AddMinutes()`
`AddMonths()`
`AddSeconds()`
`AddTicks()`
`AddYears()`
`Compare()`
`CompareTo()`
`Date`
`Day`
`DayOfWeek`
`DayOfYear`
`DaysInMonth()`
`Equals()`
`FromBinary()`
`FromFileTime()`
`FromFileTimeUtc()`
`FromOADate()`
`GetDateTimeFormats()`
`GetHashCode()`
`GetTypeCode()`
`Hour`
`IsDaylightSavingTime()`
`IsLeapYear()`
`Kind`	indicates whether the time represented by this instance is based on local time, UTC or neither.
`MaxValue`	one of the three fields
`Millisecond`
`Minute`
`MinValue`	one of the three fields
`Month`
`Now`
`Parse()`
`ParseExact()`
`Second`
`SpecifyKind()`
`Subtract()`
`Ticks`
`TimeOfDay`
`ToBinary()`
`Today`	A static property that evaluates to a `DateTime` that represents today.
`ToFileTime()`
`ToFileTimeUtc()`
`ToLocalTime()`
`ToLongDateString()`
`ToLongTimeString()`
`ToOADate()`
`ToShortDateString()`
`ToShortTimeString()`
`ToString()`
`ToUniversalTime()`
`TryFormat()`
`TryParse()`
`TryParseExact()`
`UnixEpoch`	one of the three fields
`UtcNow`
`Year`