Calendar.GetWeekOfYear Method

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

Namespace:  System.Globalization
Assembly:  mscorlib (in mscorlib.dll)

public virtual int GetWeekOfYear(
	DateTime time,
	CalendarWeekRule rule,
	DayOfWeek firstDayOfWeek
)

Parameters

time
Type: System.DateTime

A date and time value.

rule
Type: System.Globalization.CalendarWeekRule

An enumeration value that defines a calendar week.

firstDayOfWeek
Type: System.DayOfWeek

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

Return Value

Type: System.Int32
A positive integer that represents the week of the year that includes the date in the time parameter.

ExceptionCondition
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.

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 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)

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

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 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).

*/

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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