如该MSDN页面中所述，ISO8601周和.Net周编号之间存在细微差异。
您可以在MSDN博客中参考本文以获得更好的解释：“ Microsoft .Net中的ISO 8601年度格式 ”
简而言之，.Net允许将数年的时间分成数年，而ISO标准则不允许。在文章中，还有一个简单的函数可以为一年的最后一周获取正确的ISO 8601周编号。
以下方法实际上返回1，2012-12-31在ISO 8601中该值是正确的（例如德国）。
// This presumes that weeks start with Monday.
// Week 1 is the 1st week of the year with a Thursday in it.
public static int GetIso8601WeekOfYear(DateTime time)
{
// SerIoUsly cheat. If its Monday, Tuesday or Wednesday, then it'll
// be the same week# as whatever Thursday, Friday or Saturday are,
// and we always get those right
DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
{
time = time.AddDays(3);
}
// Return the week of our adjusted day
return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}
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