how to C# convert ulong to DateTime?

Question

In my C# program I'm receiving datetime from a PLC. It is sending data in "ulong" format. How can I convert ulong to DateTime format? for example I am receiving:

ulong timeN = 99844490909448899;//time in nanoseconds

then I need to convert it into DateTime ("MM/dd/yyyy hh:mm:ss") format.

How can I solve this?

Brazier

What time is 99844490909448899? – Burmeister

Is it a unix date? See here – Burmeister

Thanks for the comment. no, it is Distributed Clock System Time (known as DC Time for short) in the form of a linear, 64-bit unsigned integer value. The time is expressed in nanoseconds. – Brazier

@user2964067: Duration can be expressed in nanoseconds. Absolute time can not. What is your point of reference? – Fairy

You have to add that to your question. If that value can be transformed to 100-nanosecond intervals that have elapsed since January 1, 0001 at 00:00:00.000 in the Gregorian calendar. you can use this DateTime constructors that takes a long. – Burmeister

As of this page (german), the point of reference is 2000/01/01 00:00 UTC. – Tetrode

Dear Gene, yes you are true. So how can I convert that in c# to DateTime? – Brazier

DateTime does not have the resolution to support nanoseconds, you have to work with ticks (a tick is 100 nanoseconds). – Commandment

@user2964067: Do var d = new DateTime(timeN/100). (Because ticks is in 100 nanoseconds interval). – Thierry

@Thierry That gives the wrong date because DateTime(long) has a different reference date. The best way to solve it is probably to create a datetime for the reference date, then a timespan with timeN/100, then add the timespan to the reference datetime. – Commandment

Dear PMF, DateTime has no constructor for ulong. – Brazier

@user2964067: There is one for Int64 ("signed long"). Shouldn't matter. But I was really overlooking the fact that the reference time is different. See the answer below. – Thierry

Answer 1

static DateTime GetDTCTime(ulong nanoseconds, ulong ticksPerNanosecond)
{
    DateTime pointOfReference = new DateTime(2000, 1, 1, 0, 0, 0, DateTimeKind.Utc);
    long ticks = (long)(nanoseconds / ticksPerNanosecond);
    return pointOfReference.AddTicks(ticks);
}

static DateTime GetDTCTime(ulong nanoseconds)
{
    return GetDTCTime(nanoseconds, 100);
}

This gives a date time of: 01 March 2003 14:34:50 using the following call:

ulong timeN = 99844490909448899;//time in nanoseconds
var theDate = GetDTCTime(timeN);

Duren

Since the point of reference is in UTC, it may be desirable to explicitly set the Kind to UTC (e.g., pointOfReference = new DateTime(2000,1,1,0,0,0,DateTimeKind.Utc)), particularly if conversions to and from local time are needed. – Singapore

Thanks to David and drf – Brazier