Calendar.GetWeekOfYear(DateTime, CalendarWeekRule, DayOfWeek) Method

Definition

Namespace:

System.Globalization

Assembly:

System.Runtime.dll

Source:

Calendar.cs

Returns the week of the year that includes the date in the specified DateTime value.

public:
 virtual int GetWeekOfYear(DateTime time, System::Globalization::CalendarWeekRule rule, DayOfWeek firstDayOfWeek);

public virtual int GetWeekOfYear (DateTime time, System.Globalization.CalendarWeekRule rule, DayOfWeek firstDayOfWeek);

abstract member GetWeekOfYear : DateTime * System.Globalization.CalendarWeekRule * DayOfWeek -> int
override this.GetWeekOfYear : DateTime * System.Globalization.CalendarWeekRule * DayOfWeek -> int

Public Overridable Function GetWeekOfYear (time As DateTime, rule As CalendarWeekRule, firstDayOfWeek As DayOfWeek) As Integer

Parameters

time

DateTime

A date and time value.

rule

CalendarWeekRule

An enumeration value that defines a calendar week.

firstDayOfWeek

DayOfWeek

An enumeration value that represents the first day of the week.

Returns

Int32

A positive integer that represents the week of the year that includes the date in the time parameter.

Exceptions

ArgumentOutOfRangeException

time is earlier than MinSupportedDateTime or later than MaxSupportedDateTime.

-or-

firstDayOfWeek is not a valid DayOfWeek value.

-or-

rule is not a valid CalendarWeekRule value.

Examples

The following code example shows how the result of GetWeekOfYear varies depending on the FirstDayOfWeek and the CalendarWeekRule used. If the specified date is the last day of the year, GetWeekOfYear returns the total number of weeks in that year.

using namespace System;
using namespace System::Globalization;
int main()
{
   
   // Gets the Calendar instance associated with a CultureInfo.
   CultureInfo^ myCI = gcnew CultureInfo( "en-US" );
   Calendar^ myCal = myCI->Calendar;
   
   // Gets the DTFI properties required by GetWeekOfYear.
   CalendarWeekRule myCWR = myCI->DateTimeFormat->CalendarWeekRule;
   DayOfWeek myFirstDOW = myCI->DateTimeFormat->FirstDayOfWeek;
   
   // Displays the number of the current week relative to the beginning of the year.
   Console::WriteLine( "The CalendarWeekRule used for the en-US culture is {0}.", myCWR );
   Console::WriteLine( "The FirstDayOfWeek used for the en-US culture is {0}.", myFirstDOW );
   Console::WriteLine( "Therefore, the current week is Week {0} of the current year.", myCal->GetWeekOfYear( DateTime::Now, myCWR, myFirstDOW ) );
   
   // Displays the total number of weeks in the current year.
   DateTime LastDay = System::DateTime( DateTime::Now.Year, 12, 31 );
   Console::WriteLine( "There are {0} weeks in the current year ( {1}).", myCal->GetWeekOfYear( LastDay, myCWR, myFirstDOW ), LastDay.Year );
}

/*
This code produces the following output.  Results vary depending on the system date.

The CalendarWeekRule used for the en-US culture is FirstDay.
The FirstDayOfWeek used for the en-US culture is Sunday.
Therefore, the current week is Week 1 of the current year.
There are 53 weeks in the current year (2001).
*/

using System;
using System.Globalization;

public class SamplesCalendar  {

   public static void Main()  {

      // Gets the Calendar instance associated with a CultureInfo.
      CultureInfo myCI = new CultureInfo("en-US");
      Calendar myCal = myCI.Calendar;

      // Gets the DTFI properties required by GetWeekOfYear.
      CalendarWeekRule myCWR = myCI.DateTimeFormat.CalendarWeekRule;
      DayOfWeek myFirstDOW = myCI.DateTimeFormat.FirstDayOfWeek;

      // Displays the number of the current week relative to the beginning of the year.
      Console.WriteLine( "The CalendarWeekRule used for the en-US culture is {0}.", myCWR );
      Console.WriteLine( "The FirstDayOfWeek used for the en-US culture is {0}.", myFirstDOW );
      Console.WriteLine( "Therefore, the current week is Week {0} of the current year.", myCal.GetWeekOfYear( DateTime.Now, myCWR, myFirstDOW ));

      // Displays the total number of weeks in the current year.
      DateTime LastDay = new System.DateTime( DateTime.Now.Year, 12, 31 );
      Console.WriteLine( "There are {0} weeks in the current year ({1}).", myCal.GetWeekOfYear( LastDay, myCWR, myFirstDOW ), LastDay.Year );
   }
}

/*
This code produces the following output.  Results vary depending on the system date.

The CalendarWeekRule used for the en-US culture is FirstDay.
The FirstDayOfWeek used for the en-US culture is Sunday.
Therefore, the current week is Week 1 of the current year.
There are 53 weeks in the current year (2001).

*/

Imports System.Globalization

Public Class SamplesCalendar

   Public Shared Sub Main()
      
      ' Gets the Calendar instance associated with a CultureInfo.
      Dim myCI As New CultureInfo("en-US")
      Dim myCal As Calendar = myCI.Calendar
      
      ' Gets the DTFI properties required by GetWeekOfYear.
      Dim myCWR As CalendarWeekRule = myCI.DateTimeFormat.CalendarWeekRule
      Dim myFirstDOW As DayOfWeek = myCI.DateTimeFormat.FirstDayOfWeek
      
      ' Displays the number of the current week relative to the beginning of the year.
      Console.WriteLine("The CalendarWeekRule used for the en-US culture is {0}.", myCWR)
      Console.WriteLine("The FirstDayOfWeek used for the en-US culture is {0}.", myFirstDOW)
      Console.WriteLine("Therefore, the current week is Week {0} of the current year.", myCal.GetWeekOfYear(DateTime.Now, myCWR, myFirstDOW))
      
      ' Displays the total number of weeks in the current year.
      Dim LastDay = New System.DateTime(DateTime.Now.Year, 12, 31)
      Console.WriteLine("There are {0} weeks in the current year ({1}).", myCal.GetWeekOfYear(LastDay, myCWR, myFirstDOW), LastDay.Year)
   End Sub
End Class


'This code produces the following output.  Results vary depending on the system date.
'
'The CalendarWeekRule used for the en-US culture is FirstDay.
'The FirstDayOfWeek used for the en-US culture is Sunday.
'Therefore, the current week is Week 1 of the current year.
'There are 53 weeks in the current year (2001).

Remarks

This method can be used to determine the number of weeks in the year by setting time to the last day of the year.

The DateTimeFormatInfo object for a particular culture that uses the calendar indicated by the DateTimeFormatInfo.Calendar property includes the following culture-specific values that can be used for the rule and firstDayOfWeek parameters:

• The DateTimeFormatInfo.FirstDayOfWeek property contains the default first day of the week that can be used for the firstDayOfWeek parameter.

• The DateTimeFormatInfo.CalendarWeekRule property contains the default calendar week rule that can be used for the rule parameter.

Note

This does not map exactly to ISO 8601. The differences are discussed in the blog entry ISO 8601 Week of Year format in Microsoft .NET. Starting with .NET Core 3.0, ISOWeek.GetYear and ISOWeek.GetWeekOfYear solve this problem.

The following example uses the current culture's DateTimeFormatInfo object to determine that January 1, 2011 is in the first week of the year in the Gregorian calendar.

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
      DateTime date1 = new DateTime(2011, 1, 1);
      Calendar cal = dfi.Calendar;

      Console.WriteLine("{0:d}: Week {1} ({2})", date1,
                        cal.GetWeekOfYear(date1, dfi.CalendarWeekRule,
                                          dfi.FirstDayOfWeek),
                        cal.ToString().Substring(cal.ToString().LastIndexOf(".") + 1));
   }
}
// The example displays the following output:
//       1/1/2011: Week 1 (GregorianCalendar)

Imports System.Globalization

Module Example
   Public Sub Main()
      Dim dfi As DateTimeFormatInfo = DateTimeFormatInfo.CurrentInfo
      Dim date1 As Date = #1/1/2011#
      Dim cal As Calendar = dfi.Calendar
      
      Console.WriteLine("{0:d}: Week {1} ({2})", date1, 
                        cal.GetWeekOfYear(date1, dfi.CalendarWeekRule, 
                                          dfi.FirstDayOfWeek),
                        cal.ToString().Substring(cal.ToString().LastIndexOf(".") + 1))       
   End Sub
End Module
' The example displays the following output:
'       1/1/2011: Week 1 (GregorianCalendar)

For some calendars, a call to the GetWeekOfYear method throws an ArgumentOutOfRangeException for particular combinations of rule and firstDayOfWeek values even if time is greater than the date returned by that calendar's MinSupportedDateTime property. The following table lists the affected calendars, the specific rule values, and the range of the earliest supported time values. The specific minimum DateTime value depends on the value of the firstDayOfWeek parameter.

Calendar	CalendarWeekRule value	Gregorian date (M/dd/yyyy)	Date in calendar (M/dd/yyyy)
ChineseLunisolarCalendar	FirstFullWeek	2/19/1901 to 2/25/1901	1/1/1901 to 1/7/1901
ChineseLunisolarCalendar	FirstFourDayWeek	2/19/1901 to 2/22/1901	1/01/1901 to 1/04/1901
HebrewCalendar	FirstDay	9/17/1583	1/01/5344
HebrewCalendar	FirstFullWeek	9/17/1583 to 9/23/1583	1/01/5344 to 1/07/5344
HebrewCalendar	FirstFourDayWeek	9/17/1583 to 9/20/1583	1/01/5344 to 1/04/5344
HijriCalendar	FirstFullWeek	7/18/0622 to 7/24/0622	1/01/0001 to 1/07/0001
HijriCalendar	FirstFourDayWeek	7/18/0622 to 7/21/0622	1/01/0001 to 1/04/0001
JapaneseLunisolarCalendar	FirstFullWeek	1/28/1960 to 2/03/1960	1/01/35 to 1/07/0035
JapaneseLunisolarCalendar	FirstFourDayWeek	1/28/1960 to 1/31/1960	1/01/0035 to 1/04/0035
JulianCalendar	FirstFullWeek	1/01/0001 to 1/05/0001	1/03/0001 to 1/07/0001
JulianCalendar	FirstFourDayWeek	1/01/0001 to 1/02/0001	1/03/0001 to 1/04/0001
KoreanLunisolarCalendar	FirstFullWeek	2/14/0918 to 2/20/0918	1/01/0918 to 1/07/0918
KoreanLunisolarCalendar	FirstFourDayWeek	2/14/0918 to 2/17/0918	1/01/0918 to 1/04/0918
PersianCalendar	FirstFullWeek	3/21/0622 to 3/27/0622	1/01/0001 to 1/07/0001
PersianCalendar	FirstFourDayWeek	3/21/0622 to 3/24/0622	1/01/0001 to 1/04/0001
TaiwanLunisolarCalendar	FirstFullWeek	2/18/1912 to 2/24/1912	1/01/0001 to 1/07/0001
TaiwanLunisolarCalendar	FirstFourDayWeek	2/18/1912 to 2/21/1912	1/01/0001 to 1/04/0001
UmAlQuraCalendar	FirstFullWeek	4/30/1900 to 5/06/1900	1/01/1318 to 1/07/1318
UmAlQuraCalendar	FirstFourDayWeek	4/30/1900 to 5/03/1900	1/01/1318 to 1/04/1318

See also

• DateTime
• CalendarWeekRule
• DayOfWeek
• GetEra(DateTime)
• GetYear(DateTime)
• GetMonth(DateTime)
• GetDayOfYear(DateTime)
• GetDayOfMonth(DateTime)
• GetDayOfWeek(DateTime)
• GetHour(DateTime)
• GetMinute(DateTime)
• GetSecond(DateTime)
• GetMilliseconds(DateTime)