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POIs .NET giving me the wrong week number for Dec. 29th 2008?
 

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  1. POIs .NET giving me the wrong week number for Dec. 29th 2008?
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    <p>According to the <a href="http://www.timeanddate.com/calendar/custom.html?year=2008&amp;country=22&amp;month=12&amp;typ=2&amp;months=2&amp;display=0&amp;space=0&amp;fdow=1&amp;wno=1&amp;hol=" rel="noreferrer">official (gregorian) calendar</a>, the week number for 29/12/2008 is 1, because after the last day of week 52 (i.e. 28/12) there are three or less days left in the year. Kinda weird, but OK, rules are rules.</p> <p>So according to this calendar, we have these boundary values for 2008/2009</p> <ul> <li>28/12 is week 52</li> <li>29/12 is week 1</li> <li>1/1 is week 1</li> <li>8/1 is week 2</li> </ul> <p>C# offers a GregorianCalendar class, that has a function <code>GetWeekOfYear(date, rule, firstDayOfWeek)</code>. </p> <p>The parameter <code>rule</code> is an enumeration with 3 possible values: <code>FirstDay, FirstFourWeekDay, FirstFullWeek</code>. From what I've understood I should go for the <code>FirstFourWeekDay</code> rule, but I tried all of them just in case.</p> <p>The last parameter informs which week day should be considered the first day of the week, according to that calendar it's Monday so Monday it is.</p> <p>So I fired up a quick and dirty console app to test this:</p> <pre><code>using System; using System.Globalization; namespace CalendarTest { class Program { static void Main(string[] args) { var cal = new GregorianCalendar(); var firstWeekDay = DayOfWeek.Monday; var twentyEighth = new DateTime(2008, 12, 28); var twentyNinth = new DateTime(2008, 12, 29); var firstJan = new DateTime(2009, 1, 1); var eightJan = new DateTime(2009, 1, 8); PrintWeekDays(cal, twentyEighth, firstWeekDay); PrintWeekDays(cal, twentyNinth, firstWeekDay); PrintWeekDays(cal, firstJan, firstWeekDay); PrintWeekDays(cal, eightJan, firstWeekDay); Console.ReadKey(); } private static void PrintWeekDays(Calendar cal, DateTime dt, DayOfWeek firstWeekDay) { Console.WriteLine("Testing for " + dt.ToShortDateString()); Console.WriteLine("--------------------------------------------"); Console.Write(CalendarWeekRule.FirstDay.ToString() + "\t\t"); Console.WriteLine(cal.GetWeekOfYear(dt, CalendarWeekRule.FirstDay, firstWeekDay)); Console.Write(CalendarWeekRule.FirstFourDayWeek.ToString() + "\t"); Console.WriteLine(cal.GetWeekOfYear(dt, CalendarWeekRule.FirstFourDayWeek, firstWeekDay)); Console.Write(CalendarWeekRule.FirstFullWeek.ToString() + "\t\t"); Console.WriteLine(cal.GetWeekOfYear(dt, CalendarWeekRule.FirstFullWeek, firstWeekDay)); Console.WriteLine("--------------------------------------------"); } } } </code></pre> <p>... and this what I get</p> <pre><code>Testing for 28.12.2008 -------------------------------------------- FirstDay 52 FirstFourDayWeek 52 FirstFullWeek 51 -------------------------------------------- Testing for 29.12.2008 -------------------------------------------- FirstDay 53 FirstFourDayWeek 53 FirstFullWeek 52 -------------------------------------------- Testing for 01.01.2009 -------------------------------------------- FirstDay 1 FirstFourDayWeek 1 FirstFullWeek 52 -------------------------------------------- Testing for 08.01.2009 -------------------------------------------- FirstDay 2 FirstFourDayWeek 2 FirstFullWeek 1 -------------------------------------------- </code></pre> <p>So as we see, none of the combinations above matches the official calendar (if you are in a hurry, just see that 29/12 never gets week #1).</p> <p>What am I getting wrong here? Maybe there's something glaring that I am missing? (it's Friday and late work hours here in Belgium, bear with me ;))</p> <p>Edit: Maybe I should explain: what I need is a function that works for any year, returning the same results as the gregorian calendar I linked. So no special workarounds for 2008. </p>
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