There are 52.17 weeks in a year. How do I compute current week in C#?

Question

I am saving data into a circular log with designated byte multiples (dataSlots), and I'm calculating the week number based on the days that pass from a reference date.

 DateTime startDate = DateTime.UtcNow;
 for (int ii = 0; ii < 900; ii++)
 {
    currentDate = startDate + new TimeSpan(7 * ii, 1, 1, 1, 1)
    DateTime globalStartReference = new DateTime(2011, 12, 1, 0, 0, 0, DateTimeKind.Utc);
    var span = currentDate - globalStartReference ;
    int dataSlot = 0;
    dataSlot = (span.Days * 7) / 52;
    Console.WriteLine(dataSlot);
 }

My hope is that dataSlot will be an ever-increasing number based upon the current week, however it isn't. I get duplicate entries (and therefore overwrite my data) on these weeks

Why am I getting duplicate weeks and how do I account for this? My guess is that there is a fractional number of weeks in a year...

score 5 · Answer 1 · answered Dec 06 '11 at 04:30

5

The Calendar.GetWeekOfYear method may be helpful. It doesn't allow for an arbitrary reference date, however you could adjust for that yourself.

answered Dec 06 '11 at 04:30

Lance U. Matthews

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score 1 · Answer 2 · answered Dec 06 '11 at 04:23

1

Are you trying to get the current week for any given year? It looks like from some pre-defined start date ad infinitum. Using the appropriate calendar, and methods it it, you can get a given week of the year based on a particular date, but not x weeks from any arbitrary date.

Plus you need to account for leap years, partial weeks, etc.

answered Dec 06 '11 at 04:23

Jared Peless

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What methods are available to determine week of year? I don't see them under DateTime. I need to get the sum of all weeks from a given start date (fixed, system defined or not), to a user supplied end date. – makerofthings7 Dec 06 '11 at 04:28
Well, it would probably involve the Calendar class... but have you also checked out http://stackoverflow.com/questions/1083955/how-to-get-difference-between-two-dates-in-year-month-week-day – Jared Peless Dec 06 '11 at 04:36

score 0 · Answer 3 · answered Dec 06 '11 at 04:47

If you're just worried about weeks from baseline, years don't enter into it - it's just 7-day increments.

Otherwise you have year and week-of-year; @BACON's answer is probably right for this. You'll get a bit of overlap - Y2W1 may share the same calendar week as Y1W52. Dunno if you'll just add and make that Week 53 but this gets problematic the longer you go.

There are 52.17 weeks in a year. How do I compute current week in C#?

3 Answers3