Week numbers in .NET (Legacy)
To get the current ISO 8601 week number in .NET (Legacy), use the following code snippet:
CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
DateTime.Now,
CalendarWeekRule.FirstFourDayWeek,
DayOfWeek.Monday
);
* Ensure your system or application regional settings are set to follow ISO 8601 standards (weeks start on Monday) if the output varies.
Instructions étape par étape
- Get the current culture's calendar via CultureInfo.CurrentCulture.Calendar.
- Call GetWeekOfYear with CalendarWeekRule.FirstFourDayWeek and DayOfWeek.Monday.
- The parameters approximate ISO 8601 numbering on legacy .NET Framework.
Bon à savoir
This legacy approach can return week 53 for the Monday-Wednesday before an ISO week 1 (a documented .NET Framework quirk). If you can target .NET Core 3.0+, use System.Globalization.ISOWeek instead.