Develop Reference

Timezone StartOfDay

Hi i receice some random datetimeoffset utc my point is
1 - turn it into chicago time
2- Define the chicago startOfDay
3-finaly convert chicago startOfDay back to an utc datetimeOffset.
(this process is needed to query an utc api)
i writed this that seem do what i want but realy not sure it will always do the job with day saving light etc..
someone can tell or improve the code?
var UTCDate = DateTimeOffset.UtcNow; //<----------Some random utc dateTimeOffset
TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
DateTimeOffset CSTDate = GetZoneDatetimeOffset(UTCDate, zone);
Console.WriteLine("Utc : {0} Chicago: {1} local : {2}", UTCDate, CSTDate, UTCDate.ToLocalTime());
Console.WriteLine(" Chicago StartOfDay: {0} Chicago StartOfDay To UTC : {1}", CSTDate.Date, CSTDate.Date.ToUniversalTime());
public DateTimeOffset GetZoneDatetimeOffset(DateTimeOffset someUTCDate , TimeZoneInfo destZone)
{
DateTimeOffset ZoneDateTimeOffset = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(someUTCDate.DateTime , TimeZoneInfo.Utc.Id, destZone.Id);
return ZoneDateTimeOffset;
}

You have a few bugs in your code:
You call TimeZoneInfo.ConvertTimeBySystemTimeZoneId and pass a DateTime value. The result will thus also be a DateTime. The Kind of that result will be Unspecified. Assigning it to a DateTimeOffset thus will perform an implicit cast operation from DateTime to DateTimeOffset, which will use the computer's local time zone - not the time zone you are working with.
Both DateTimeOffset.Date and DateTimeOffset.DateTime also return a DateTime whose Kind is Unspecified. Thus when you call ToLocalTime or ToUniversalTime, you are again using your the computer's local time zone.
Determining the start of the day in a specific time zone can be tricky. Though it doesn't happen in Chicago (or anywhere in the USA), some time zones of the world have DST transitions that occur immediately at the start of the day. Thus 00:00 might not be the first moment of the day, or it might occur twice. Your code doesn't account for that.
A good example is Cuba, where DST next starts on 2022-03-13 at midnight, and thus the start of that day in Cuba is 2022-03-13T01:00.
You can use the GetStartOfDay method I already provided in this answer to handle these edge cases.
Putting it all together:
// Input values
DateTimeOffset utc = DateTimeOffset.UtcNow;
TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
// Convert with full fidelity using only DateTimeOffset values
DateTimeOffset converted = TimeZoneInfo.ConvertTime(utc, zone);
// Get the start of day using the method from https://stackoverflow.com/a/49988688
DateTimeOffset startOfDay = GetStartOfDay(converted.DateTime, zone);
// Output the results
Console.WriteLine("Original values:");
Console.WriteLine("Chicago: {0:o} UTC: {1:o} Local: {2:o}", converted, utc, utc.ToLocalTime());
Console.WriteLine();
Console.WriteLine("At start of day in Chicago:");
Console.WriteLine("Chicago: {0:o} UTC: {1:o} Local: {2:o}", startOfDay, startOfDay.ToUniversalTime(), startOfDay.ToLocalTime());
Example output (local time zone is US Pacific Time in this example):
Original values:
Chicago: 2022-03-10T10:58:47.8164830-06:00 UTC: 2022-03-10T16:58:47.8164830+00:00 Local: 2022-03-10T08:58:47.8164830-08:00
At start of day in Chicago:
Chicago: 2022-03-10T00:00:00.0000000-06:00 UTC: 2022-03-10T06:00:00.0000000+00:00 Local: 2022-03-09T22:00:00.0000000-08:00
See also the working .NET Fiddle here.

Parse String into DateTimeOffset While Assuming TimeZone

Probably a super simple solution but I'm clearly missing something.
I have a string object with value "2020/07/29 13:30:00".
How can I parse that into a DateTimeOffset object and make the assumption that the time zone of that parsed time is "GMT Standard Time" for example, or any TimeZoneInfo I wish to specify preferably?
How can I then take that DateTimeOffset, and return its Utc time but to any specified time zone of my choice?
Many thanks

The easiest I could find is something like this.
I couldn't find any methods to parse a DateTimeOffset in a particular given timezone, but you can parse your string as a DateTime (with a Kind of Unspecified, which just acts as a container for the bits of information in the string, without trying to apply timezone knowledge to it).
Then you can ask a TimeZoneInfo for the UTC offset in a given timezone at the given local time, and apply this to the DateTime to create a DateTimeOffset.
Once you've got your DateTimeOffset, you can work with it using its ToOffset method, and TimeZoneInfo.ConvertTime.
string input = "2020/07/29 13:30:00";
var timezone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
// DateTime.Parse creates a DateTime with Kind == Unspecified
var dateTime = DateTime.Parse(input);
Console.WriteLine(dateTime); // 7/29/2020 1:30:00 PM
// Since Kind == Unspecified, timezone.GetUtcOffset will give us the UTC offset in effect at
// the given local time in timezone
var dateTimeOffset = new DateTimeOffset(dateTime, timezone.GetUtcOffset(dateTime));
Console.WriteLine(dateTimeOffset); // 7/29/2020 1:30:00 PM +01:00
// Convert to UTC
Console.WriteLine(dateTimeOffset.UtcDateTime); // 7/29/2020 12:30:00 PM
Console.WriteLine(dateTimeOffset.ToOffset(TimeSpan.Zero)); // 7/29/2020 12:30:00 PM +00:00
// Convert to another timezone
var cst = TimeZoneInfo.FindSystemTimeZoneById("Central America Standard Time");
Console.WriteLine(TimeZoneInfo.ConvertTime(dateTimeOffset, cst)); // 7/29/2020 6:30:00 AM -06:00

Try the DateTimeOffset.ParseExact overload that accepts a DateTimeStyles parameter.
This code:
var dt=DateTimeOffset.ParseExact("2020/07/29 13:30:00","yyyy/MM/dd HH:mm:ss",
CultureInfo.InvariantCulture,DateTimeStyles.AssumeUniversal);
Returns 2020-07-29T13:30:00.0000000+00:00
There's no GMT Standard Time, that's a very unfortunate name used in Windows that somehow manages to mix up British and UTC time to the point that no-one knows what it means without looking at the docs. This was thoroughly discussed and explained in this question: Difference between UTC and GMT Standard Time in .NET. As one of the answers explains :
The names GMT Standard Time and GMT Daylight Time are unknown outside of Redmond. They are mythical animals that appear only in the bestiary called the Windows Registry.
If you wanted to assume British time and your machine uses a British timezone, you can use DateTimeStyles.AssumeLocal

This function should convert your date time string (with assumption this is GMT Standard Time) to any other timezone:
public static DateTime? ToUTCTimeZone(string sDate, string timeZone)
{
DateTime utcDate = DateTime.Parse(sDate);
DateTimeOffset localServerTime = DateTimeOffset.Now;
utcDate = DateTime.SpecifyKind(utcDate, DateTimeKind.Utc);
TimeZoneInfo cstZone = TimeZoneInfo.FindSystemTimeZoneById(timeZone);
if (cstZone == null)
return null;
return TimeZoneInfo.ConvertTimeFromUtc(utcDate, cstZone);
}//ToUTCTimeZone

c# Converting UTC time to Central including timezone in DateTime object

I'm converting the UTC time, taken from my local Server time to Central standard time. I have this running on a server in Germany.
Converting the time and date works, but when a library i have converts it to a string it has a wrong Timezone offset.
It comes out as 2019-05-11T14:44:09+02:00
when i need it to be 2019-05-11T14:44:09-06:00
TimeZoneInfo CRtimezone = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, CRtimezone);
The +02:00 is the UTCoffset for Germany, which i don't want, even the the time and date are correctly in Central Time.
Is there a way to pass or include the offset in the DateTime object?

Is there a way to pass or include the offset in the DateTime object?
No, DateTime structure does not have UTC Offset but DateTimeOffset has. If you really wanna keep your UTC Offset value in your code, I suggest you to work with DateTimeOffset instead of DateTime.
Since it doesn't keep UTC Offset value, when you get it's textual (aka string) representation, you still get the offset value of your server in Germany (includes K, z, zz and zzz specifiers by the way). TimeZoneInfo.ConvertTimeFromUtc method returns a DateTime instance, the offset value you might wanna represent depends on how you want to show it.
One option might be that you might wanna concatenate The Sortable ("s") Format Specifier representation of your DateTime and your TimeZoneInfo.BaseUtcOffset value.
TimeZoneInfo CRtimezone = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
$"{TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, CRtimezone).ToString("s")}{CRtimezone.BaseUtcOffset}".Dump();

convert datetime string to Utc

how to convert datetime string to utc time format in GMT.
var x = "02/01/2017 10:00";
var z = DateTime.ParseExact(x, "ddd, dd MMM yyyy HH:mm:ss 'GMT'", CultureInfo.InvariantCulture);

Actually the thing you have tried is wrong, what you can do is, get the DateTime value equivalent to the given date and then convert them to the UTC time, try something like the following:
string inputDateStr = "02/01/2017 10:00";
DateTime inputDate;
if (DateTime.TryParseExact(inputDateStr, "MM/dd/yyyy HH:mm", CultureInfo.InvariantCulture, DateTimeStyles.None, out inputDate))
{
Console.WriteLine("Date time Now : {0} ", inputDate);
Console.WriteLine("Date time UTC : {0} ", inputDate.ToUniversalTime().ToString("ddd, dd MMM yyyy HH:mm:ss 'GMT'"));
}
Working Example

I am not sure what you wanted to do. But, Universal Time, Zulu time, and UTC are effectively modern names for Greenwich Mean Time (GMT). So both the times will be same. You can use the DateTime.ToUniversalTime() or DateTime.UtcNow method to get the UTC time.

It's not completely clear what you are asking... UTC isn't a format, it's a timezone, equivalent to GMT (well, actually that isn't strictly true, but for the purposes of this question it should be ok.
What point in time is your string representing? Is it UTC? Or is it the local time in Moscow? You need to have the answer to that, because they are completely different times.
If the string represents a UTC time, then you can do something like this:
// first parse it to a DateTime object. Notice that the format string corresponds with the string you have - in your code, they were completely different.
var dateTimeWithUnspecifiedKind = DateTime.ParseExact(x, "dd/MM/yyyy HH:mm", CultureInfo.InvariantCulture);
So how you have a datetime object. It has a "Kind" property of Unspecified. So it isn't storing any information to specify that it's supposed to be UTC, rather than Moscow or New York time.
// so we do this...
var dateTimeAsUtc = DateTime.SpecifyKind(dateTimeWithUnspecifiedKind, DateTimeKind.Utc);
That means, "keep the numbers the same, but make a note that the datetime is to be interpreted as a UTC datetime".
Then, if you want to convert it back into a string, you can do something like:
var s = dateTimeAsUtc.ToString("O");
Which will give you a nice representation:
2017-01-02T10:00:00.0000000Z
You are lucky you are interested in UTC. The datetime class can only do UTC, "local" (whatever that is), or "Unspecified". It's not super useful for this sort of thing. DateTimeOffset is a bit better - it's basically a DateTime but it also stores the difference between UTC and the offset that's in force at the time.
That may be all you need. If you ever need real clarity around this stuff though, take a look at Noda time - an alternative set of date and time classes for .NET.

Converting Local Time To UTC

I'm up against an issue storing datetimes as UTC and confused why this does not yield the same result when changing timezones:
var dt = DateTime.Parse("1/1/2013");
MessageBox.Show(TimeZoneInfo.ConvertTimeToUtc(dt, TimeZoneInfo.Local).ToString());
I am manually switching my local time zone on the machine between eastern and central.
Central yields 1/1/2013 6:00:00 AM, and Eastern yields 1/1/2013 5:00:00 AM. What am I missing here? They should be the same regardless of the time zone, correct?
Thanks so much in advance!

I think what you are missing is that the DateTime returned by your DateTime.Parse() statement doesn't come with a time zone. It's just a date and time that can be in any time zone. When you call TimeZoneInfo.ConvertTimeToUtc(dt, TimeZoneInfo.Local), you are telling it which time zone it starts in. So if you start in Central, you will get one answer, whereas if you start in Eastern, you will get an answer that is an hour earlier, UTC. Indeed, this is what your code shows.

There is a .ToUniversalTime() method for DateTime class

This is midnight
var dt = DateTime.Parse("1/1/2013");
Midnight in eastern and central is not the same absolute time.
That is the whole purpose of time zones.

You can use NodaTime :
static string LocalTimeToUTC(string timeZone, string localDateTime)
{
var pattern = LocalDateTimePattern.CreateWithInvariantCulture("dd/MM/yyyy HH:mm:ss");
LocalDateTime ldt = pattern.Parse(localDateTime).Value;
ZonedDateTime zdt = ldt.InZoneLeniently(DateTimeZoneProviders.Tzdb[timeZone]);
Instant instant = zdt.ToInstant();
ZonedDateTime utc = instant.InUtc();
string output = utc.ToString("dd/MM/yyyy HH:mm:ss", CultureInfo.InvariantCulture);
return output;
}

When you have trouble with converting to local time to UTC then just remove the last keyword of index and then convert to UtcDateTime
NewsDate = DateTimeOffset.Parse(data.NewsDate.Remove(data.NewsDate.LastIndexOf("IST"))).UtcDateTime;