How to create .NET CultureInfo with Dateformat ISO 8601?

Question

Is it possible to make .NET create the following output?

DateTime.UtcNow.ToString() --> "2017-11-07T00:40:00.123456Z"

Of course there is always the possibility to use ToString("s") or ToString("yyyy-MM-ddTHH:mm:ss.fffffffK"). But is there a way to adjust the default-behaviour for the parameterless ToString-Method to the desired output?

I tried changing the CurrentCulture. But the best I got was "2017-11-07 00:40:00.123456Z". I did not find a way to change the separator between the date and the time from a space to "T".

Answer 1

It is possible, but only by accessing an internal field via reflection, which is not guaranteed to work in all cases.

var culture = (CultureInfo) CultureInfo.InvariantCulture.Clone();
var field = typeof(DateTimeFormatInfo).GetField("generalLongTimePattern",
                                           BindingFlags.NonPublic | BindingFlags.Instance);
if (field != null)
{
    // we found the internal field, set it
    field.SetValue(culture.DateTimeFormat, "yyyy-MM-dd'T'HH:mm:ss.FFFFFFFK");
}
else
{
    // fallback to setting the separate date and time patterns
    culture.DateTimeFormat.ShortDatePattern = "yyyy-MM-dd";
    culture.DateTimeFormat.LongTimePattern = "HH:mm:ss.FFFFFFFK";
}
CultureInfo.CurrentCulture = culture;

Console.WriteLine(DateTime.UtcNow);  // "2017-11-07T00:53:36.6922843Z"

Note that the ISO 8601 spec does allow a space to be used instead of a T. It's just preferable to use the T.