Microsoft Developer Network
 IsDaylightSavingTime Method (DateTime)
.NET Framework Class Library
TimeZone..::.IsDaylightSavingTime Method (DateTime)

Returns a value indicating whether the specified date and time is within a daylight saving time period.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
Visual Basic (Declaration)
Public Overridable Function IsDaylightSavingTime ( _
    time As DateTime _
) As Boolean
Visual Basic (Usage)
Dim instance As TimeZone
Dim time As DateTime
Dim returnValue As Boolean

returnValue = instance.IsDaylightSavingTime(time)
C#
public virtual bool IsDaylightSavingTime(
    DateTime time
)
Visual C++
public:
virtual bool IsDaylightSavingTime(
    DateTime time
)
JScript
public function IsDaylightSavingTime(
    time : DateTime
) : boolean

Parameters

time
Type: System..::.DateTime
A date and time.

Return Value

Type: System..::.Boolean
true if time is in a daylight saving time period; otherwise, false.

The year to which the daylight saving time period applies is derived from the time parameter.

Because the TimeZone class supports a single daylight saving time adjustment rule, the IsDaylightSavingTime(DateTime) method applies the current adjustment rule to any date, regardless of whether the adjustment rule was in effect on that date. Assuming that the operating system itself has accurate historic daylight saving time data, a more accurate result is available by using the TimeZoneInfo..::.IsDaylightSavingTime method.

The following example uses the IsDaylightSavingTime method to determine whether selected dates are within daylight saving time for any year.

Visual Basic
' Example of the TimeZone.IsDaylightSavingTime( DateTime ),
' TimeZone.IsDaylightSavingTime( DateTime, DaylightTime ), and 
' TimeZone.ToUniversalTime( DateTime ) methods.
Imports System
Imports System.Globalization
Imports Microsoft.VisualBasic

Module DaylightTimeDemo

    Sub Main( )

        Const headFmt As String = "{0,-22}{1,-10}{2,-10}{3,-10}{4}"

        ' Get the local time zone and a base local time.
        Dim localZone As TimeZone = TimeZone.CurrentTimeZone
        Dim localTime As DateTime = new DateTime( 2001, 1, 1 )

        Console.WriteLine( "This example of " & vbCrLf & _
            "   TimeZone.IsDaylightSavingTime( DateTime ), " & _
            vbCrLf & "   TimeZone.IsDaylightSavingTime( " & _
            "DateTime, DaylightTime ), and " & vbCrLf & _
            "   TimeZone.ToUniversalTime( DateTime )" & vbCrLf & _
            "generates the following output, which varies " & _
            "depending on the " & vbCrLf & "time zone in which " & _
            "it is run." & vbCrLf )
        Console.WriteLine( "The example creates " & _
            "several local times and the corresponding " & vbCrLf & _
            "Coordinated Universal Times (UTC) and shows if " & _
            "they occur in " & vbCrLf & "daylight saving time " & _
            "(DST), both for specified years and for " & vbCrLf & _
            "any year." & vbCrLf )
        Console.WriteLine( "Local time: {0}" & vbCrLf, _
            localZone.StandardName )

        Console.WriteLine( headFmt, "Local Date and Time", _
            "2001 DST?", "2002 DST?", "Any DST?", "Corresponding UTC" )
        Console.WriteLine( headFmt, "-------------------", _
            "---------", "---------", "--------", "-----------------" )

        ' Create DaylightTime objects for specific years.
        Dim daylight2001 As DaylightTime = _
            localZone.GetDaylightChanges( 2001 )
        Dim daylight2002 As DaylightTime = _
            localZone.GetDaylightChanges( 2002 )

        ' Generate several local times.
        Dim loopX As Integer
        For loopX = 0 to 10

            ' Calculate the corresponding UTC.
            Dim utcTime As DateTime = _
                localZone.ToUniversalTime( localTime )

            ' Show if dates and times occur in daylight saving 
            ' time, for specified years and for any year.
            Console.WriteLine( "{0,-22:yyyy-MM-dd HH:mm}" & _
                "{1,-10}{2,-10}{3,-10}{4:yyyy-MM-dd HH:mm}", _
                localTime, _
                TimeZone.IsDaylightSavingTime( _
                    localTime, daylight2001 ), _
                TimeZone.IsDaylightSavingTime( _
                    localTime, daylight2002 ), _
                localZone.IsDaylightSavingTime( localTime ), _
                utcTime )

            ' Advance to another local time.
            localTime = localTime.AddDays( 109.1 )
        Next loopX
    End Sub
End Module 

' This example of
'    TimeZone.IsDaylightSavingTime( DateTime ),
'    TimeZone.IsDaylightSavingTime( DateTime, DaylightTime ), and
'    TimeZone.ToUniversalTime( DateTime )
' generates the following output, which varies depending on the
' time zone in which it is run.
' 
' The example creates several local times and the corresponding
' Coordinated Universal Times (UTC) and shows if they occur in
' daylight saving time (DST), both for specified years and for
' any year.
' 
' Local time: Pacific Standard Time
' 
' Local Date and Time   2001 DST? 2002 DST? Any DST?  Corresponding UTC
' -------------------   --------- --------- --------  -----------------
' 2001-01-01 00:00      False     False     False     2001-01-01 08:00
' 2001-04-20 02:24      True      False     True      2001-04-20 09:24
' 2001-08-07 04:48      True      False     True      2001-08-07 11:48
' 2001-11-24 07:12      False     False     False     2001-11-24 15:12
' 2002-03-13 09:36      False     False     False     2002-03-13 17:36
' 2002-06-30 12:00      False     True      True      2002-06-30 19:00
' 2002-10-17 14:24      False     True      True      2002-10-17 21:24
' 2003-02-03 16:48      False     False     False     2003-02-04 00:48
' 2003-05-23 19:12      False     False     True      2003-05-24 02:12
' 2003-09-09 21:36      False     False     True      2003-09-10 04:36
' 2003-12-28 00:00      False     False     False     2003-12-28 08:00
C#
// Example of the TimeZone.IsDaylightSavingTime( DateTime ),
// TimeZone.IsDaylightSavingTime( DateTime, DaylightTime ), and 
// TimeZone.ToUniversalTime( DateTime ) methods.
using System;
using System.Globalization;

class DaylightTimeDemo
{
    static void Main( )
    {
        const string headFmt = "{0,-22}{1,-10}{2,-10}{3,-10}{4}";

        // Get the local time zone and a base local time.
        TimeZone localZone = TimeZone.CurrentTimeZone;
        DateTime localTime = new DateTime( 2001, 1, 1 );

        Console.WriteLine( "This example of \n" +
            "   TimeZone.IsDaylightSavingTime( DateTime ), \n" +
            "   TimeZone.IsDaylightSavingTime( " +
            "DateTime, DaylightTime ), and \n" +
            "   TimeZone.ToUniversalTime( DateTime )\n" +
            "generates the following output, which varies " +
            "depending on the \ntime zone in which it is run.\n" );
        Console.WriteLine( "The example creates several local " +
            "times and the corresponding \nCoordinated Universal " +
            "Times (UTC) and shows if they occur in \ndaylight " +
            "saving time (DST), both for specified years " +
            "and for \nany year.\n" );
        Console.WriteLine( "Local time: {0}\n", 
            localZone.StandardName );

        Console.WriteLine( headFmt, "Local Date and Time", "2001 DST?", 
            "2002 DST?", "Any DST?", "Corresponding UTC" );
        Console.WriteLine( headFmt, "-------------------", "---------", 
            "---------", "--------", "-----------------" );

        // Create DaylightTime objects for specific years.
        DaylightTime daylight2001 = 
            localZone.GetDaylightChanges( 2001 );
        DaylightTime daylight2002 = 
            localZone.GetDaylightChanges( 2002 );

        // Generate several local times.
        for( int loopX = 0; loopX <= 10; loopX++ )
        {
            // Calculate the corresponding UTC.
            DateTime utcTime = 
                localZone.ToUniversalTime( localTime );

            // Show if dates and times occur in daylight saving 
            // time, for specified years and for any year.
            Console.WriteLine( "{0,-22:yyyy-MM-dd HH:mm}" +
                "{1,-10}{2,-10}{3,-10}{4:yyyy-MM-dd HH:mm}", 
                localTime, 
                TimeZone.IsDaylightSavingTime( 
                    localTime, daylight2001 ), 
                TimeZone.IsDaylightSavingTime( 
                    localTime, daylight2002 ), 
                localZone.IsDaylightSavingTime( localTime ), 
                utcTime );

            // Advance to another local time.
            localTime = localTime.AddDays( 109.1 );
        }
    } 
} 

/*
This example of
   TimeZone.IsDaylightSavingTime( DateTime ),
   TimeZone.IsDaylightSavingTime( DateTime, DaylightTime ), and
   TimeZone.ToUniversalTime( DateTime )
generates the following output, which varies depending on the
time zone in which it is run.

The example creates several local times and the corresponding
Coordinated Universal Times (UTC) and shows if they occur in
daylight saving time (DST), both for specified years and for
any year.

Local time: Pacific Standard Time

Local Date and Time   2001 DST? 2002 DST? Any DST?  Corresponding UTC
-------------------   --------- --------- --------  -----------------
2001-01-01 00:00      False     False     False     2001-01-01 08:00
2001-04-20 02:24      True      False     True      2001-04-20 09:24
2001-08-07 04:48      True      False     True      2001-08-07 11:48
2001-11-24 07:12      False     False     False     2001-11-24 15:12
2002-03-13 09:36      False     False     False     2002-03-13 17:36
2002-06-30 12:00      False     True      True      2002-06-30 19:00
2002-10-17 14:24      False     True      True      2002-10-17 21:24
2003-02-03 16:48      False     False     False     2003-02-04 00:48
2003-05-23 19:12      False     False     True      2003-05-24 02:12
2003-09-09 21:36      False     False     True      2003-09-10 04:36
2003-12-28 00:00      False     False     False     2003-12-28 08:00
*/
Visual C++
// Example of the TimeZone::IsDaylightSavingTime( DateTime ),
// TimeZone::IsDaylightSavingTime( DateTime, DaylightTime ), and 
// TimeZone::ToUniversalTime( DateTime ) methods.
using namespace System;
using namespace System::Globalization;
int main()
{
   String^ headFmt = "{0,-22}{1,-10}{2,-10}{3,-10}{4}";

   // Get the local time zone and a base local time.
   TimeZone^ localZone = TimeZone::CurrentTimeZone;
   DateTime localTime = DateTime(2001,1,1);
   Console::WriteLine( "This example of \n"
   "   TimeZone::IsDaylightSavingTime( DateTime ), \n"
   "   TimeZone::IsDaylightSavingTime( "
   "DateTime, DaylightTime* ), and \n"
   "   TimeZone::ToUniversalTime( DateTime )\n"
   "generates the following output, which varies "
   "depending on the \ntime zone in which it is run.\n" );
   Console::WriteLine( "The example creates several local "
   "times and the corresponding \nCoordinated Universal "
   "Times (UTC) and shows if they occur in \ndaylight "
   "saving time (DST), both for specified years "
   "and for \nany year.\n" );
   Console::WriteLine( "Local time: {0}\n", localZone->StandardName );
   Console::WriteLine( headFmt, "Local Date and Time", "2001 DST?", "2002 DST?", "Any DST?", "Corresponding UTC" );
   Console::WriteLine( headFmt, "-------------------", "---------", "---------", "--------", "-----------------" );

   // Create DaylightTime objects for specific years.
   DaylightTime^ daylight2001 = localZone->GetDaylightChanges( 2001 );
   DaylightTime^ daylight2002 = localZone->GetDaylightChanges( 2002 );

   // Generate several local times.
   for ( int loopX = 0; loopX <= 10; loopX++ )
   {

      // Calculate the corresponding UTC.
      DateTime utcTime = localZone->ToUniversalTime( localTime );

      // Show if dates and times occur in daylight saving 
      // time, for specified years and for any year.
      Console::WriteLine( "{0,-22:yyyy-MM-dd HH:mm}"
      "{1,-10}{2,-10}{3,-10}{4:yyyy-MM-dd HH:mm}", localTime, TimeZone::IsDaylightSavingTime( localTime, daylight2001 ), TimeZone::IsDaylightSavingTime( localTime, daylight2002 ), localZone->IsDaylightSavingTime( localTime ), utcTime );

      // Advance to another local time.
      localTime = localTime.AddDays( 109.1 );

   }
}

/*
This example of
   TimeZone::IsDaylightSavingTime( DateTime ),
   TimeZone::IsDaylightSavingTime( DateTime, DaylightTime* ), and
   TimeZone::ToUniversalTime( DateTime )
generates the following output, which varies depending on the
time zone in which it is run.

The example creates several local times and the corresponding
Coordinated Universal Times (UTC) and shows if they occur in
daylight saving time (DST), both for specified years and for
any year.

Local time: Pacific Standard Time

Local Date and Time   2001 DST? 2002 DST? Any DST?  Corresponding UTC
-------------------   --------- --------- --------  -----------------
2001-01-01 00:00      False     False     False     2001-01-01 08:00
2001-04-20 02:24      True      False     True      2001-04-20 09:24
2001-08-07 04:48      True      False     True      2001-08-07 11:48
2001-11-24 07:12      False     False     False     2001-11-24 15:12
2002-03-13 09:36      False     False     False     2002-03-13 17:36
2002-06-30 12:00      False     True      True      2002-06-30 19:00
2002-10-17 14:24      False     True      True      2002-10-17 21:24
2003-02-03 16:48      False     False     False     2003-02-04 00:48
2003-05-23 19:12      False     False     True      2003-05-24 02:12
2003-09-09 21:36      False     False     True      2003-09-10 04:36
2003-12-28 00:00      False     False     False     2003-12-28 08:00
*/

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
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