Develop Reference

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

I want to specify a TimeZone as GMT but create a DateTime that is local (EST);

I want to specify a time in GMT timezone, and then convert it to the local TimeZone which is EST.
This appears to do what I want, but seems a long way to get there!
Is there a simpler way to achieve this:
public static TimeZoneInfo edtZone = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
public static TimeZoneInfo gmtZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
public static CultureInfo ci = CultureInfo.InvariantCulture;
DateTime edtStartDT = TimeZoneInfo.ConvertTime(DateTime.SpecifyKind(DateTime.Now.Date.Add(new TimeSpan(18, 00, 00)), DateTimeKind.Unspecified), gmtZone, edtZone);

This is probably what you are looking for:
// A timespan isn't really a time-of-day, but we'll let that slide for now.
TimeSpan time = new TimeSpan(18, 00, 00);
// Use the current utc date, at that time.
DateTime utcDateTime = DateTime.UtcNow.Date.Add(time);
// Convert to the US Eastern time zone.
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
DateTime easternDateTime = TimeZoneInfo.ConvertTimeFromUtc(utcDateTime, tz);
Note that we're pairing the current UTC date with the time you provided. Since US Eastern time is either 5 or 4 hours behind UTC, with 18:00 you will always get the same date. But if you were using a different time, such as 00:00, you would find that the resulting Eastern time was on the prior day. This is normal.
A couple of notes about your previous code:
The Windows Time Zone ID "Eastern Standard Time" refers to both EST and EDT. It really should have been called "Eastern Time". Don't let the name confuse the issue.
GMT and UTC are mostly the same for all modern usage. Unless you are referring to the time zone used in London, you should prefer the term UTC.
The Windows Time Zone ID "GMT Standard Time" is not actually for GMT/UTC. It is specifically the time zone used in London, which alternates between GMT (UTC+00:00) and BST (UTC+01:00). If you want a TimeZoneInfo representing UTC, the ID is just "UTC". (However, you don't really need that in this case.)
Your original code assumed used DateTime.Now.Date, which would assume the date in the computer's local time zone - which might not be either UTC or Eastern.
If you find yourself using DateTime.SpecifyKind, in most situations, you're probably doing something wrong. (The exception would be when loading or deserializing.)
Regarding my note about a TimeSpan not being a true time-of-day, this is how .NET would have you handle that:
DateTime time = DateTime.Parse("18:00:00", CultureInfo.InvariantCulture);
DateTime utcDateTime = DateTime.UtcNow.Date.Add(time.TimeOfDay);
Or even uglier in one line:
DateTime utcDateTime = DateTime.Parse("18:00:00", CultureInfo.InvariantCulture,
DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal);
Personally, I would rather use Noda Time, which has a separate LocalTime type explicitly for a time-of-day that's not bound to a specific date. I'm also working to get System.TimeOfDate and System.Date types added to the CoreCLR.

Convert American datetime to EU datetime in computer located in EU?

I get some datetime (ExactDate) from a db. These time are in US timezone, I need to convert them in EU TimeZone.
However if I use :
ExactDate = (DateTime)dr["CREATE_DATE"];
// change exact date to european time
TimeZoneInfo info;
info = TimeZoneInfo.FindSystemTimeZoneById("US Mountain Standard Time");
ExactDate = TimeZoneInfo.ConvertTime(ExactDate,info);
The dates are not converted properly because my computer is seeing the ExactDate as an European date.
Do you know how I can solve this ?

Try converting the date from the other TimeZone to UTC
like
ExactDate = TimeZoneInfo.ConvertTimeToUtc(ExactDate,info);
Once you have the corresponding UTC time you can get the European one later on using .ToLocal
Hope this is what you want.

Display current time in this format: HH:mm:ss

I'm having some trouble displaying the time in this format: HH:mm:ss.
No matter what i try, i never get it in that format.
I want the time in the culture of the Netherlands which is "nl-NL".
This was one of my (although i forgot to keep the count) 1000th try:
CultureInfo ci = new CultureInfo("nl-NL");
string s = DateTime.Now.TimeOfDay.ToString("HH:mm:ss", ci);
What am i doing wrong?

string s = DateTime.Now.ToString("HH:mm:ss");

You need to use the TimeZoneInfo class, here's how to show the current time in the Eastern Standard Time time zone in HH:mm:ss format:
var timeZone = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
string s = TimeZoneInfo.ConvertTime(DateTime.Now, timeZone).ToString("HH:mm:ss");
To find all the timezones available, you can use
TimeZoneInfo.GetSystemTimeZones();
Looking through the returned value from the above, the Id for the time zone you need (Amsterdam I assume) is called W. Europe Standard Time:
var timeZone = TimeZoneInfo.FindSystemTimeZoneById("W. Europe Standard Time");
string s = TimeZoneInfo.ConvertTime(DateTime.Now, timeZone).ToString("HH:mm:ss");

TimeOfDay is a TimeSpan, which has only one ToString() without parameters.
Use Darin's solution or a sample from MSDN documentation for TimeSpan.ToString()

convert from EST/EDT to GMT

How do I convert a DateTime from EST/EDT to GMT but I don't know where the code will be ran (unknown local time zone) and also account for time savings...

You want TimeZoneInfo.ConvertTimeToUtc(), which allows you to pass the source time zone info as a parameter. For example:
TimeZoneInfo est = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
DateTime someDateTimeInUtc = TimeZoneInfo.ConvertTimeToUtc(someDateTime, est);
I think this will automatically handle daylight-saving time, but you'll want to test it to be sure.

Take a look at the TimeZoneInfo class.