Do the .NET libraries have an easy way of returning the week number for a given date? For example, input of Year = 2010, Month = 1, Day = 25, should output 5 for the week number.
Closest I found was Calendar.GetWeekOfYear, which is almost there.
Java has a date string format "W" which returns week in month but I can't see anything equivalent in .NET.
There is no direct built-in way to do this, but it can be done quite easily. Here is an extension method which can be used to easily get the year-based week number of a date:
public static int GetWeekNumber(this DateTime date)
{
return GetWeekNumber(date, CultureInfo.CurrentCulture);
}
public static int GetWeekNumber(this DateTime date, CultureInfo culture)
{
return culture.Calendar.GetWeekOfYear(date,
culture.DateTimeFormat.CalendarWeekRule,
culture.DateTimeFormat.FirstDayOfWeek);
}
We can then use that to calculate the month-based week number, kind of like Jason shows. A culture friendly version could look something like this:
public static int GetWeekNumberOfMonth(this DateTime date)
{
return GetWeekNumberOfMonth(date, CultureInfo.CurrentCulture);
}
public static int GetWeekNumberOfMonth(this DateTime date, CultureInfo culture)
{
return date.GetWeekNumber(culture)
- new DateTime(date.Year, date.Month, 1).GetWeekNumber(culture)
+ 1; // Or skip +1 if you want the first week to be 0.
}