.NET datetime Millisecond precision issue when converting from string to datetime

Question

Hi. I am trying to convert an incoming datetime value that comes to our system in a string format. It seems that when the precision of milliseconds is higher than 7, the datetime parsing in .NET does not seem to like the value and cannot convert/parse the value. I am a bit stuck on what to do for this? My only current thought is there is a limit on the millisecond size and that anymore precision is not possible? But I want to confirm this is the case rather than assume. Example:

string candidateDateTimeString = "2017-12-08T15:14:38.123456789Z";
if (!success)
        {
            success = DateTime.TryParseExact(trayportDateTimeString, "yyyy-
MM-dd'T'HH:mm:ss.fffffffff'Z'",
                CultureInfo.InvariantCulture, dateTimeStyles, out dateTime);
        }

If I reduce the 'f' values down to just 7, then date time parsing works fine. Is there a limit? Or am I doing something obvious wrong?

Answer 1

According to Custom Date and Time Format Strings docs, 7 is maximum supported digits of second fraction.

Answer 2

Internally, all DateTime values are represented as the number of ticks (the number of 100-nanosecond intervals) that have elapsed since 12:00:00 midnight, January 1, 0001.

https://msdn.microsoft.com/en-us/library/system.datetime(v=vs.110).aspx

see also: https://docs.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings