CalendarWeekRule Enumeration
Updated: May 2012
Defines different rules for determining the first week of the year.
Assembly: mscorlib (in mscorlib.dll)
| Member name | Description | |
|---|---|---|
![]() ![]() | FirstDay | Indicates that the first week of the year starts on the first day of the year and ends before the following designated first day of the week. The value is 0. |
![]() ![]() | FirstFullWeek | Indicates that the first week of the year begins on the first occurrence of the designated first day of the week on or after the first day of the year. The value is 1. |
![]() ![]() | FirstFourDayWeek | Indicates that the first week of the year is the first week with four or more days before the designated first day of the week. The value is 2. |
A member of the CalendarWeekRule enumeration is returned by the DateTimeFormatInfo::CalendarWeekRule property and is used by the culture's current calendar to determine the calendar week rule. The enumeration value is also used as a parameter to the Calendar::GetWeekOfYear method.
Calendar week rules depend on the System::DayOfWeek value that indicates the first day of the week. The DateTimeFormatInfo::FirstDayOfWeek property provides the default value for a culture, but any DayOfWeek value can be specified as the first day of the week in the Calendar::GetWeekOfYear method.
The first week based on the FirstDay value can have one to seven days. The first week based on the FirstFullWeek value always has seven days. The first week based on the FirstFourDayWeek value can have four to seven days.
For example, in the Gregorian calendar, suppose that the first day of the year (January 1) falls on a Tuesday and the designated first day of the week is Sunday. Selecting FirstFullWeek defines the first Sunday (January 6) as the beginning of the first week of the year. The first five days of the year are considered part of the last week of the previous year. In contrast, selecting FirstFourDayWeek defines the first day of the year (January 1) as the beginning of the first week of the year because there are more than four days from January 1 to the day before the following Sunday.
Date | FirstDay | FirstFullWeek | FirstFourDayWeek |
|---|---|---|---|
Dec 31 Mon | Last week of the previous year | Last week of the previous year | Last week of the previous year |
Jan 1 Tue | Week 1 | Last week of the previous year | Week 1 |
Jan 2 Wed | Week 1 | Last week of the previous year | Week 1 |
Jan 3 Thu | Week 1 | Last week of the previous year | Week 1 |
Jan 4 Fri | Week 1 | Last week of the previous year | Week 1 |
Jan 5 Sat | Week 1 | Last week of the previous year | Week 1 |
Jan 6 Sun | Week 2 | Week 1 | Week 2 |
Jan 7 Mon | Week 2 | Week 1 | Week 2 |
Jan 8 Tue | Week 2 | Week 1 | Week 2 |
Jan 9 Wed | Week 2 | Week 1 | Week 2 |
Jan 10 Thu | Week 2 | Week 1 | Week 2 |
Jan 11 Fri | Week 2 | Week 1 | Week 2 |
Jan 12 Sat | Week 2 | Week 1 | Week 2 |
Suppose the first day of the year (January 1) falls on a Friday and the designated first day of the week is Sunday. Selecting FirstFourDayWeek defines the first Sunday (January 3) as the beginning of the first week of the year because there are fewer than four days from January 1 to the day before the following Sunday.
Date | FirstDay | FirstFullWeek | FirstFourDayWeek |
|---|---|---|---|
Dec 31 Thu | Last week of the previous year | Last week of the previous year | Last week of the previous year |
Jan 1 Fri | Week 1 | Last week of the previous year | Last week of the previous year |
Jan 2 Sat | Week 1 | Last week of the previous year | Last week of the previous year |
Jan 3 Sun | Week 2 | Week 1 | Week 1 |
Jan 4 Mon | Week 2 | Week 1 | Week 1 |
Jan 5 Tue | Week 2 | Week 1 | Week 1 |
Jan 6 Wed | Week 2 | Week 1 | Week 1 |
Jan 7 Thu | Week 2 | Week 1 | Week 1 |
Jan 8 Fri | Week 2 | Week 1 | Week 1 |
Jan 9 Sat | Week 2 | Week 1 | Week 1 |
The following example illustrates how the CalendarWeekRule and System::DayOfWeek values are used together to determine how weeks are assigned. In the Gregorian calendar, the first day of the year (January 1) in 2013 falls on a Tuesday. If the designated first day of the week is Sunday, the first Sunday (January 6) is the first day of the first week of the year, and Saturday (January 5) belongs to the fifty-third week of the previous year. Changing the calendar week rule to CalendarWeekRule::FirstFourDayWeek defines Tuesday (January 1) as the beginning of the first week of the year, because there are more than four days between Tuesday, January 1, and Sunday, January 6. Using this rule, January 5 belongs to the first week of the year. For 2010, a year in which January 1 falls on a Friday, applying the CalendarWeekRule::FirstFourDayWeek rule with DayOfWeek::Sunday as the first day of the week makes Sunday, January 3 the beginning of the first week of the year, because the first week in 2010 that has more than four days is January 3 through 9.
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. |
Each CultureInfo object supports a set of calendars. The Calendar property returns the default calendar for the culture, and the OptionalCalendars property returns an array containing all the calendars supported by the culture. To change the calendar used by a CultureInfo, the application should set the Calendar property of CultureInfo::DateTimeFormat to a new Calendar.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
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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