DateTimeFormatInfo string format for day of week. Thursday becomes Th

Question

Is there a DateTimeFormatInfo format pattern to convert a day of week to two characters? For example Tuesday becomes Tu, Wednesday becomes We. The format string needs to conform to the DateTimeFormatInfo for date formats.

Addition:

Maybe I am looking for a solution to extend DateTimeFormatInfo to include custom formats?

Answer 1

You need to get the DateTimeFormatInfo of the culture you're working with, then modify the array of strings called AbbreviatedDayNames. After that, ddd will return Th for you.

http://msdn.microsoft.com/en-us/library/system.globalization.datetimeformatinfo.abbreviateddaynames(VS.71).aspx

DateTimeFormatInfo.AbbreviatedDayNames
Gets or sets a one-dimensional array of type String containing the culture-specific abbreviated names of the days of the week.

Here's a sample of how to do it:

class Program
{
    static void Main()
    {
        var dtInfo = new System.Globalization.DateTimeFormatInfo();            
        Console.WriteLine("Old array of abbreviated dates:");
        var dt = DateTime.Today;
        for (int i = 0; i < 7; i++)
        {
            Console.WriteLine(dt.AddDays(i).ToString("ddd", dtInfo));
        }

        // change the short weekday names array
        var newWeekDays = 
            new string[] { "Su", "Mo", "Tu", "We", "Th", "Fr", "Sa" };
        dtInfo.AbbreviatedDayNames = newWeekDays;

        Console.WriteLine("New array of abbreviated dates:");
        for (int i = 0; i < 7; i++)
        {
            Console.WriteLine(dt.AddDays(i).ToString("ddd", dtInfo));
        }

        Console.ReadLine();
    }
}

One more note: of course, if you are constrained from providing the IFormatProvider, then you can override the current thread's CultureInfo, for example:

CultureInfo customCulture = CultureInfo.CreateSpecificCulture("en-US");
// ... set up the DateTimeFormatInfo, etc...

System.Threading.Thread.CurrentThread.CurrentCulture = customCulture;

More on CurrentCulture:

http://msdn.microsoft.com/en-us/library/system.threading.thread.currentuiculture.aspx

Thread.CurrentUICulture Property
Gets or sets the current culture used by the Resource Manager to look up culture-specific resources at run time.

Answer 2

The closes you can get is the "ddd" custom format specifier - this produces three lettered abbreviations, so not exactly what you want. There is nothing built in that does exactly what you want.

You can always take the first two characters of that:

DateTime.Now.ToString("ddd").Substring(0,2);

Unfortunately you can't extend DateTimeFormatInfo since it is declared as sealed.