Choose between DateTime, DateOnly, DateTimeOffset, TimeSpan, TimeOnly, and TimeZoneInfo
.NET applications can use date and time information in several ways. The more common uses of date and time information include:
- To reflect a date only, so that time information is not important.
- To reflect a time only, so that date information is not important.
- To reflect an abstract date and time that's not tied to a specific time and place (for example, most stores in an international chain open on weekdays at 9:00 A.M.).
- To retrieve date and time information from sources outside of .NET, typically where date and time information is stored in a simple data type.
- To uniquely and unambiguously identify a single point in time. Some applications require that a date and time be unambiguous only on the host system. Other apps require that it be unambiguous across systems (that is, a date serialized on one system can be meaningfully deserialized and used on another system anywhere in the world).
- To preserve multiple related times (such as the requester's local time and the server's time of receipt for a web request).
- To perform date and time arithmetic, possibly with a result that uniquely and unambiguously identifies a single point in time.
.NET includes the DateTime, DateOnly, DateTimeOffset, TimeSpan, TimeOnly, and TimeZoneInfo types, all of which can be used to build applications that work with dates and times.
Note
This article doesn't discuss TimeZone because its functionality is almost entirely incorporated in the TimeZoneInfo class. Whenever possible, use the TimeZoneInfo class instead of the TimeZone class.
The DateTimeOffset structure
The DateTimeOffset structure represents a date and time value, together with an offset that indicates how much that value differs from UTC. Thus, the value always unambiguously identifies a single point in time.
The DateTimeOffset type includes all of the functionality of the DateTime type along with time zone awareness. This makes it suitable for applications that:
- Uniquely and unambiguously identify a single point in time. The DateTimeOffset type can be used to unambiguously define the meaning of "now", to log transaction times, to log the times of system or application events, and to record file creation and modification times.
- Perform general date and time arithmetic.
- Preserve multiple related times, as long as those times are stored as two separate values or as two members of a structure.
Note
These uses for DateTimeOffset values are much more common than those for DateTime values. As a result, consider DateTimeOffset as the default date and time type for application development.
A DateTimeOffset value isn't tied to a particular time zone, but can originate from a variety of time zones. The following example lists the time zones to which a number of DateTimeOffset values (including a local Pacific Standard Time) can belong.
using System;
using System.Collections.ObjectModel;
public class TimeOffsets
{
public static void Main()
{
DateTime thisDate = new DateTime(2007, 3, 10, 0, 0, 0);
DateTime dstDate = new DateTime(2007, 6, 10, 0, 0, 0);
DateTimeOffset thisTime;
thisTime = new DateTimeOffset(dstDate, new TimeSpan(-7, 0, 0));
ShowPossibleTimeZones(thisTime);
thisTime = new DateTimeOffset(thisDate, new TimeSpan(-6, 0, 0));
ShowPossibleTimeZones(thisTime);
thisTime = new DateTimeOffset(thisDate, new TimeSpan(+1, 0, 0));
ShowPossibleTimeZones(thisTime);
}
private static void ShowPossibleTimeZones(DateTimeOffset offsetTime)
{
TimeSpan offset = offsetTime.Offset;
ReadOnlyCollection<TimeZoneInfo> timeZones;
Console.WriteLine("{0} could belong to the following time zones:",
offsetTime.ToString());
// Get all time zones defined on local system
timeZones = TimeZoneInfo.GetSystemTimeZones();
// Iterate time zones
foreach (TimeZoneInfo timeZone in timeZones)
{
// Compare offset with offset for that date in that time zone
if (timeZone.GetUtcOffset(offsetTime.DateTime).Equals(offset))
Console.WriteLine(" {0}", timeZone.DisplayName);
}
Console.WriteLine();
}
}
// This example displays the following output to the console:
// 6/10/2007 12:00:00 AM -07:00 could belong to the following time zones:
// (GMT-07:00) Arizona
// (GMT-08:00) Pacific Time (US & Canada)
// (GMT-08:00) Tijuana, Baja California
//
// 3/10/2007 12:00:00 AM -06:00 could belong to the following time zones:
// (GMT-06:00) Central America
// (GMT-06:00) Central Time (US & Canada)
// (GMT-06:00) Guadalajara, Mexico City, Monterrey - New
// (GMT-06:00) Guadalajara, Mexico City, Monterrey - Old
// (GMT-06:00) Saskatchewan
//
// 3/10/2007 12:00:00 AM +01:00 could belong to the following time zones:
// (GMT+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna
// (GMT+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague
// (GMT+01:00) Brussels, Copenhagen, Madrid, Paris
// (GMT+01:00) Sarajevo, Skopje, Warsaw, Zagreb
// (GMT+01:00) West Central Africa
Imports System.Collections.ObjectModel
Module TimeOffsets
Public Sub Main()
Dim thisTime As DateTimeOffset
thisTime = New DateTimeOffset(#06/10/2007#, New TimeSpan(-7, 0, 0))
ShowPossibleTimeZones(thisTime)
thisTime = New DateTimeOffset(#03/10/2007#, New TimeSpan(-6, 0, 0))
ShowPossibleTimeZones(thisTime)
thisTime = New DateTimeOffset(#03/10/2007#, New TimeSpan(+1, 0, 0))
ShowPossibleTimeZones(thisTime)
End Sub
Private Sub ShowPossibleTimeZones(offsetTime As DateTimeOffset)
Dim offset As TimeSpan = offsetTime.Offset
Dim timeZones As ReadOnlyCollection(Of TimeZoneInfo)
Console.WriteLine("{0} could belong to the following time zones:", _
offsetTime.ToString())
' Get all time zones defined on local system
timeZones = TimeZoneInfo.GetSystemTimeZones()
' Iterate time zones
For Each timeZone As TimeZoneInfo In timeZones
' Compare offset with offset for that date in that time zone
If timeZone.GetUtcOffset(offsetTime.DateTime).Equals(offset) Then
Console.WriteLine(" {0}", timeZone.DisplayName)
End If
Next
Console.WriteLine()
End Sub
End Module
' This example displays the following output to the console:
' 6/10/2007 12:00:00 AM -07:00 could belong to the following time zones:
' (GMT-07:00) Arizona
' (GMT-08:00) Pacific Time (US & Canada)
' (GMT-08:00) Tijuana, Baja California
'
' 3/10/2007 12:00:00 AM -06:00 could belong to the following time zones:
' (GMT-06:00) Central America
' (GMT-06:00) Central Time (US & Canada)
' (GMT-06:00) Guadalajara, Mexico City, Monterrey - New
' (GMT-06:00) Guadalajara, Mexico City, Monterrey - Old
' (GMT-06:00) Saskatchewan
'
' 3/10/2007 12:00:00 AM +01:00 could belong to the following time zones:
' (GMT+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna
' (GMT+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague
' (GMT+01:00) Brussels, Copenhagen, Madrid, Paris
' (GMT+01:00) Sarajevo, Skopje, Warsaw, Zagreb
' (GMT+01:00) West Central Africa
The output shows that each date and time value in this example can belong to at least three different time zones. The DateTimeOffset value of 6/10/2007 shows that if a date and time value represents a daylight saving time, its offset from UTC doesn't even necessarily correspond to the originating time zone's base UTC offset or to the offset from UTC found in its display name. Because a single DateTimeOffset value isn't tightly coupled with its time zone, it can't reflect a time zone's transition to and from daylight saving time. This can be problematic when date and time arithmetic is used to manipulate a DateTimeOffset value. For a discussion of how to perform date and time arithmetic in a way that takes account of a time zone's adjustment rules, see Performing arithmetic operations with dates and times.
The DateTime structure
A DateTime value defines a particular date and time. It includes a Kind property that provides limited information about the time zone to which that date and time belongs. The DateTimeKind value returned by the Kind property indicates whether the DateTime value represents the local time (DateTimeKind.Local), Coordinated Universal Time (UTC) (DateTimeKind.Utc), or an unspecified time (DateTimeKind.Unspecified).
The DateTime structure is suitable for applications with one or more of the following characteristics:
- Work with abstract dates and times.
- Work with dates and times for which time zone information is missing.
- Work with UTC dates and times only.
- Perform date and time arithmetic, but are concerned with general results. For example, in an addition operation that adds six months to a particular date and time, it is often not important whether the result is adjusted for daylight saving time.
Unless a particular DateTime value represents UTC, that date and time value is often ambiguous or limited in its portability. For example, if a DateTime value represents the local time, it's portable within that local time zone (that is, if the value is deserialized on another system in the same time zone, that value still unambiguously identifies a single point in time). Outside the local time zone, that DateTime value can have multiple interpretations. If the value's Kind property is DateTimeKind.Unspecified, it's even less portable: it is now ambiguous within the same time zone and possibly even on the same system where it was first serialized. Only if a DateTime value represents UTC does that value unambiguously identify a single point in time regardless of the system or time zone in which the value is used.
Important
When saving or sharing DateTime data, use UTC and set the DateTime value's Kind property to DateTimeKind.Utc.
The DateOnly structure
The DateOnly structure represents a specific date, without time. Since it has no time component, it represents a date from the start of the day to the end of the day. This structure is ideal for storing specific dates, such as a birth date, an anniversary date, a holiday, or a business-related date.
Although you could use DateTime while ignoring the time component, there are a few benefits to using DateOnly over DateTime:
- The
DateTimestructure may roll into the previous or next day if it's offset by a time zone.DateOnlycan't be offset by a time zone, and it always represents the date that was set. - Serializing a
DateTimestructure includes the time component, which may obscure the intent of the data. Also,DateOnlyserializes less data. - When code interacts with a database, such as SQL Server, whole dates are generally stored as the
datedata type, which doesn't include a time.DateOnlymatches the database type better.
For more information about DateOnly, see How to use the DateOnly and TimeOnly structures.
Important
DateOnly isn't available in .NET Framework.
The TimeSpan structure
The TimeSpan structure represents a time interval. Its two typical uses are:
- Reflecting the time interval between two date and time values. For example, subtracting one DateTime value from another returns a TimeSpan value.
- Measuring elapsed time. For example, the Stopwatch.Elapsed property returns a TimeSpan value that reflects the time interval that has elapsed since the call to one of the Stopwatch methods that begins to measure elapsed time.
A TimeSpan value can also be used as a replacement for a DateTime value when that value reflects a time without reference to a particular day. This usage is similar to the DateTime.TimeOfDay and DateTimeOffset.TimeOfDay properties, which return a TimeSpan value that represents the time without reference to a date. For example, the TimeSpan structure can be used to reflect a store's daily opening or closing time, or it can be used to represent the time at which any regular event occurs.
The following example defines a StoreInfo structure that includes TimeSpan objects for store opening and closing times, as well as a TimeZoneInfo object that represents the store's time zone. The structure also includes two methods, IsOpenNow and IsOpenAt, that indicates whether the store is open at a time specified by the user, who is assumed to be in the local time zone.
using System;
public struct StoreInfo
{
public String store;
public TimeZoneInfo tz;
public TimeSpan open;
public TimeSpan close;
public bool IsOpenNow()
{
return IsOpenAt(DateTime.Now.TimeOfDay);
}
public bool IsOpenAt(TimeSpan time)
{
TimeZoneInfo local = TimeZoneInfo.Local;
TimeSpan offset = TimeZoneInfo.Local.BaseUtcOffset;
// Is the store in the same time zone?
if (tz.Equals(local)) {
return time >= open & time <= close;
}
else {
TimeSpan delta = TimeSpan.Zero;
TimeSpan storeDelta = TimeSpan.Zero;
// Is it daylight saving time in either time zone?
if (local.IsDaylightSavingTime(DateTime.Now.Date + time))
delta = local.GetAdjustmentRules()[local.GetAdjustmentRules().Length - 1].DaylightDelta;
if (tz.IsDaylightSavingTime(TimeZoneInfo.ConvertTime(DateTime.Now.Date + time, local, tz)))
storeDelta = tz.GetAdjustmentRules()[tz.GetAdjustmentRules().Length - 1].DaylightDelta;
TimeSpan comparisonTime = time + (offset - tz.BaseUtcOffset).Negate() + (delta - storeDelta).Negate();
return comparisonTime >= open && comparisonTime <= close;
}
}
}
Public Structure StoreInfo
Dim store As String
Dim tz As TimeZoneInfo
Dim open As TimeSpan
Dim close As TimeSpan
Public Function IsOpenNow() As Boolean
Return IsOpenAt(Date.Now.TimeOfDay)
End Function
Public Function IsOpenAt(time As TimeSpan) As Boolean
Dim local As TimeZoneInfo = TimeZoneInfo.Local
Dim offset As TimeSpan = TimeZoneInfo.Local.BaseUtcOffset
' Is the store in the same time zone?
If tz.Equals(local) Then
Return time >= open AndAlso time <= close
Else
Dim delta As TimeSpan = TimeSpan.Zero
Dim storeDelta As TimeSpan = TimeSpan.Zero
' Is it daylight saving time in either time zone?
If local.IsDaylightSavingTime(Date.Now.Date + time) Then
delta = local.GetAdjustmentRules(local.GetAdjustmentRules().Length - 1).DaylightDelta
End If
If tz.IsDaylightSavingTime(TimeZoneInfo.ConvertTime(Date.Now.Date + time, local, tz))
storeDelta = tz.GetAdjustmentRules(tz.GetAdjustmentRules().Length - 1).DaylightDelta
End If
Dim comparisonTime As TimeSpan = time + (offset - tz.BaseUtcOffset).Negate() + (delta - storeDelta).Negate
Return (comparisonTime >= open AndAlso comparisonTime <= close)
End If
End Function
End Structure
The StoreInfo structure can then be used by client code like the following.
public class Example
{
public static void Main()
{
// Instantiate a StoreInfo object.
var store103 = new StoreInfo();
store103.store = "Store #103";
store103.tz = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
// Store opens at 8:00.
store103.open = new TimeSpan(8, 0, 0);
// Store closes at 9:30.
store103.close = new TimeSpan(21, 30, 0);
Console.WriteLine("Store is open now at {0}: {1}",
DateTime.Now.TimeOfDay, store103.IsOpenNow());
TimeSpan[] times = { new TimeSpan(8, 0, 0), new TimeSpan(21, 0, 0),
new TimeSpan(4, 59, 0), new TimeSpan(18, 31, 0) };
foreach (var time in times)
Console.WriteLine("Store is open at {0}: {1}",
time, store103.IsOpenAt(time));
}
}
// The example displays the following output:
// Store is open now at 15:29:01.6129911: True
// Store is open at 08:00:00: True
// Store is open at 21:00:00: True
// Store is open at 04:59:00: False
// Store is open at 18:31:00: True
Module Example
Public Sub Main()
' Instantiate a StoreInfo object.
Dim store103 As New StoreInfo()
store103.store = "Store #103"
store103.tz = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time")
' Store opens at 8:00.
store103.open = new TimeSpan(8, 0, 0)
' Store closes at 9:30.
store103.close = new TimeSpan(21, 30, 0)
Console.WriteLine("Store is open now at {0}: {1}",
Date.Now.TimeOfDay, store103.IsOpenNow())
Dim times() As TimeSpan = {New TimeSpan(8, 0, 0),
New TimeSpan(21, 0, 0),
New TimeSpan(4, 59, 0),
New TimeSpan(18, 31, 0)}
For Each time In times
Console.WriteLine("Store is open at {0}: {1}",
time, store103.IsOpenAt(time))
Next
End Sub
End Module
' The example displays the following output:
' Store is open now at 15:29:01.6129911: True
' Store is open at 08:00:00: True
' Store is open at 21:00:00: False
' Store is open at 04:59:00: False
' Store is open at 18:31:00: False
The TimeOnly structure
The TimeOnly structure represents a time-of-day value, such as a daily alarm clock or what time you eat lunch each day. TimeOnly is limited to the range of 00:00:00.0000000 - 23:59:59.9999999, a specific time of day.
Prior to the TimeOnly type being introduced, programmers typically used either the DateTime type or the TimeSpan type to represent a specific time. However, using these structures to simulate a time without a date may introduce some problems, which TimeOnly solves:
TimeSpanrepresents elapsed time, such as time measured with a stopwatch. The upper range is more than 29,000 years, and its value can be negative to indicate moving backwards in time. A negativeTimeSpandoesn't indicate a specific time of the day.- If
TimeSpanis used as a time of day, there's a risk that it could be manipulated to a value outside of the 24-hour day.TimeOnlydoesn't have this risk. For example, if an employee's work shift starts at 18:00 and lasts for 8 hours, adding 8 hours to theTimeOnlystructure rolls over to 2:00. - Using
DateTimefor a time of day requires that an arbitrary date be associated with the time, and then later disregarded. It's common practice to chooseDateTime.MinValue(0001-01-01) as the date, however, if hours are subtracted from theDateTimevalue, anOutOfRangeexception might occur.TimeOnlydoesn't have this problem as the time rolls forwards and backwards around the 24-hour timeframe. - Serializing a
DateTimestructure includes the date component, which may obscure the intent of the data. Also,TimeOnlyserializes less data.
For more information about TimeOnly, see How to use the DateOnly and TimeOnly structures.
Important
TimeOnly isn't available in .NET Framework.
The TimeZoneInfo class
The TimeZoneInfo class represents any of the Earth's time zones, and enables the conversion of any date and time in one time zone to its equivalent in another time zone. The TimeZoneInfo class makes it possible to work with dates and times so that any date and time value unambiguously identifies a single point in time. The TimeZoneInfo class is also extensible. Although it depends on time zone information provided for Windows systems and defined in the registry, it supports the creation of custom time zones. It also supports the serialization and deserialization of time zone information.
In some cases, taking full advantage of the TimeZoneInfo class may require further development work. If date and time values are not tightly coupled with the time zones to which they belong, further work is required. Unless your application provides some mechanism for linking a date and time with its associated time zone, it's easy for a particular date and time value to become disassociated from its time zone. One method of linking this information is to define a class or structure that contains both the date and time value and its associated time zone object.
To take advantage of time zone support in .NET, you must know the time zone to which a date and time value belongs when that date and time object is instantiated. The time zone is often not known, particularly in web or network apps.
