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I recently found myself having a DateTime value and needing to calculate the date of the first day in the week that my known date was in using C#. While this is one of those things that are pretty simple to do once you know the solution it did take me a couple of hours to get it right. It turns out that something as simple as calculating a the first day of a week is trickier than one might expect, at least if we want a solution that works for all cultures.
My first instinct was to calculate the first day of a week by subtracting dayInWeek.DayOfWeek - firstDayInWeek days from dayInWeek where dayInWeek is a DateTime specifying a date in the week. That worked fine as long as I did the calculations in an environment where the culture was English, where the first day of the week is Sunday which is enumerated as 0 in DayOfWeek (against international standards which says the first day of the week is monday). As I shifted to using a Swedish culture it broke down and I had to find a better solution.
Heres what I finally came up with:
using System;
using System.Globalization;
public static class FirstDayOfWeekUtility
{
/// <summary>
/// Returns the first day of the week that the specified
/// date is in using the current culture.
/// </summary>
public static DateTime GetFirstDayOfWeek(DateTime dayInWeek)
{
CultureInfo defaultCultureInfo = CultureInfo.CurrentCulture;
return GetFirstDateOfWeek(dayInWeek, defaultCultureInfo);
}
/// <summary>
/// Returns the first day of the week that the specified date
/// is in.
/// </summary>
public static DateTime GetFirstDayOfWeek(DateTime dayInWeek, CultureInfo cultureInfo)
{
DayOfWeek firstDay = cultureInfo.DateTimeFormat.FirstDayOfWeek;
DateTime firstDayInWeek = dayInWeek.Date;
while (firstDayInWeek.DayOfWeek != firstDay)
firstDayInWeek = firstDayInWeek.AddDays(-1);
return firstDayInWeek;
}
}
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Comments
colin 2 years ago
This works... it deals with "less than zero values" by doing the (+7)%7 method. it also lets the programmer decide if he's going to override the culture's first day of week with an evil Business Rule.
******
public static DateTime GetFirstDayInWeek(DateTime dayInWeek, DayOfWeek firstDay) {
int difference = ((int)dayInWeek.DayOfWeek) - ((int)firstDay);
difference = (7 + difference) % 7;
return dayInWeek.AddDays(-difference).Date;
}
******
public static DateTime GetFirstDayInWeek(DateTime dayInWeek) {
return GetFirstDayInWeek(dayInWeek, CultureInfo.CurrentCulture);
}
public static DateTime GetFirstDayInWeek(DateTime dayInWeek, CultureInfo cultureInfo) {
return GetFirstDayInWeek(dayInWeek, cultureInfo.DateTimeFormat.FirstDayOfWeek);
}
Andrea 1 years ago
I think this is better:
DateTime aday = new DateTime(2010,04,09).DayOfWeek;
DateTime firstDate = aday.AddDays(-(int)aday.DayOfWeek);
Joel Abrahamsson 1 years ago
Andrea, the problem with that approach is that it doesn't work for all cultures as DayOfWeek is an enum that says that Sunday is the first day of the week. So while that approach works in cultures where Sunday is the first day of the week it doesn't for cultures where it isn't.
Jimmy 1 years ago
Nice post but not really what I needed. I want to know if a specific date is a weekday or weekend day. In other words I want to know if a date is a sunday/saturday and since we work in sweden its not as easy as specifying that a day should start with S (Saturday in sweden is named Lördag, no S there)
Do you have any idé on how to do this?
Riverama 11 months ago
first of all, the second function in the code should be named GetFirstDateOfWeek.
to Jimmy: DateTime.Today.DayOfWeek.ToString();
Alex 11 months ago
Thank you very much! Works great!
Mark Beale 10 months ago
Nice solution, I changed it slightly so the user can choose whether to pass in the first day of the week or not:
public static DateTime GetFirstDayOfWeek(DateTime dayInWeek) { CultureInfo defaultCultureInfo = CultureInfo.CurrentCulture; DayOfWeek firstDay = defaultCultureInfo.DateTimeFormat.FirstDayOfWeek; return GetFirstDateOfWeek(dayInWeek, firstDay); } public static DateTime GetFirstDateOfWeek(DateTime dayInWeek, DayOfWeek firstDay) { DateTime firstDayInWeek = dayInWeek.Date; while (firstDayInWeek.DayOfWeek != firstDay) firstDayInWeek = firstDayInWeek.AddDays(-1); return firstDayInWeek; }Vijay 10 months ago
Refer the below weblink.
http://epandu.wordpress.com/2011/03/29/get-first-and-last-date-of-the-current-week/
mrblackman 8 months ago
Thanks, a lot...
Ashok 7 months ago
how to get first day and date of week in grid view header in asp.net c#
Kostiantyn 6 months ago
This does the job a bit more straightforward and basically with less calculations:
var today = DateTime.Now.Date;
int difference = (int) today.DayOfWeek - (int) CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;
if (difference
Kostiantyn 6 months ago
This does the job a bit more straightforward and basically with less calculations:
Just to give you the idea.
muthu 5 months ago
I want to get month name when I write month no. for eg. when i type 2 it should come feb...lik tat
Mark 4 months ago
Would be nice if there was a version (if you cant use an enum due to the culture issue, perhaps a boolean) that lets you choose between a business week (5 days) and the standard 7 day week.