Get Date Range by week number c#

c# .net datetime date calendar

19,460

Solution 1

Note

I appear to have missed bug. The current code have been updated as of 2012-01-30 to account for this fact and we now derive the daysOffset based on Tuesday which according to Mikael Svenson appears to solve the problem.

These ISO8601 week date calculations are a bit wonky, but this is how you do it:

DateTime jan1 = new DateTime(yyyy, 1, 1); 

int daysOffset = DayOfWeek.Tuesday - jan1.DayOfWeek; 

DateTime firstMonday = jan1.AddDays(daysOffset); 

var cal = CultureInfo.CurrentCulture.Calendar; 

int firstWeek = cal.GetWeekOfYear(jan1, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);

var weekNum = ww;

if (firstWeek <= 1) 
{ 
    weekNum -= 1; 
}

var result = firstMonday.AddDays(weekNum * 7 + d - 1);

return result;

Basically calculate a reference point, then add days, the hard stuff has to do with the fact that week 53 can sometimes occur in January and week 1 can sometimes occur in December. You need to adjust for that and this is one way to do that.

The above code calculates the date off a year (yyyy) and week number (ww) and day of week (d).

Solution 2

Find out which day of the week was the first January of the year (e.g. in 2011 it was Saturday)
Add the necessary count of days to become the next monday (2 days)
From this day on, add (Number of weeks - 1) * 7 days to get the first day of the week you are interested in -Display this day plus the next days to get the whole week

19,460

Author by

Wesley

Updated on June 13, 2022

Comments

Wesley almost 2 years
Possible Duplicate:
In .net, knowing the week number how can I get the weekdays date?

Hello,

I've got a question for ya'll. How do i get the date range of a given week number.

For example: If I enter week 12 the output should be:
```
21-03-2011
22-03-2011
23-03-2011
24-03-2011
25-03-2011
26-03-2011
27-03-2011
```
I really hope you guys can help me out, i just cant find the awnser anywhere!

Thanks in advance.
Martin Milan about 13 years

Won't downvote - but John's solution below is correct. This is all laid out in ISO stuff...
John Leidegren about 13 years

Yes, this is too simplistic and occasionally computes the wrong date.
Mikael Svenson about 12 years

If I enter yyyy=2012, ww=1 and d=Monday(1), your code returns Jan 9th and not Jan 2nd which would be correct.
Mikael Svenson about 12 years

See my answer here: stackoverflow.com/a/9064954/153390
John Leidegren about 12 years

That's unfortunate, I do remember reworking this code and creating a lot of test but this is older and obviously not right, your small change however seem to work and I don't have the ability to test this more thoroughly, so I'm gonna believe that you did that yourself and correct my own answer ;)
Mikael Svenson about 12 years

Tested it for every day from 1900-1-1 to 3000-12-31 :)