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.Net C# DateTime on Mac OSX vs Debian Linux

I have code that converts long numbers to dates.
DateTimeOffset value =
DateTimeOffset.FromUnixTimeSeconds(1597325462);
DateTime showTime = value.DateTime;
string easternZoneId = "America/New_York";
TimeZoneInfo easternZone =
TimeZoneInfo.FindSystemTimeZoneById(easternZoneId);
DateTime targetTime =
TimeZoneInfo.ConvertTime(showTime, easternZone);
Console.WriteLine("DateTime is {0}", targetTime);
On my Mac, the output is "DateTime is 8/13/2020 6:31:02 AM"
On my server the output is "DateTime is 8/13/2020 9:31:02 AM"
Identical code on both.
The Linux box value is accurate. How can I get the same result on my Mac?

The overload of TimeZone.ConvertTime you're using takes a DateTime value and a destination TimeZoneInfo. There's no mention of the source time zone, so it is infered from the .Kind property of the DateTime being passed in.
In your case, that is DateTimeKind.Unspecified, because the .DateTime property of a DateTimeOffset always returns unspecified, regardless of what the offset is.
In the ConvertTime call, if the kind is DateTimeKind.Unspecified, it is assumed to be local time (as if it were DateTimeKind.Local). (Scroll down to the Remarks section in the docs here.) Thus, you are converting as if the Unix timestamp were local-time based, rather than the actuality that it is UTC based. You get different results between your workstation and server because they have different system-local time zones - not because they are running different operating systems.
There are a number of different ways to rewrite this to address the problem. I will give you a few to choose from, in order of my preference:
You could leave everything as a DateTimeOffset throughout the conversion process:
DateTimeOffset value = DateTimeOffset.FromUnixTimeSeconds(1597325462);
string easternZoneId = "America/New_York";
TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById(easternZoneId);
DateTimeOffset targetTime = TimeZoneInfo.ConvertTime(value, easternZone);
You could use the .UtcDateTime property instead of the .DateTime property:
DateTimeOffset value = DateTimeOffset.FromUnixTimeSeconds(1597325462);
DateTime showTime = value.UtcDateTime;
string easternZoneId = "America/New_York";
TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById(easternZoneId);
DateTime targetTime = TimeZoneInfo.ConvertTime(showTime, easternZone);
You could use ConvertTimeFromUtc instead of ConvertTime:
DateTimeOffset value = DateTimeOffset.FromUnixTimeSeconds(1597325462);
DateTime showTime = value.DateTime;
string easternZoneId = "America/New_York";
TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById(easternZoneId);
DateTime targetTime = TimeZoneInfo.ConvertTimeFromUtc(showTime, easternZone);
You could specify UTC as the source time zone in the ConvertTime call:
DateTimeOffset value = DateTimeOffset.FromUnixTimeSeconds(1597325462);
DateTime showTime = value.DateTime;
string easternZoneId = "America/New_York";
TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById(easternZoneId);
DateTime targetTime = TimeZoneInfo.ConvertTime(showTime, TimeZoneInfo.Utc, easternZone);
There are a few other options, such as explicitly setting the kind, but I think the above gives you enough to go on.
If in doubt, pick the first option. DateTimeOffset is much easier to rationalize than DateTime in most cases.

The issue seems to be that there is not such a timezone I'd in the ICU library that both OS look into.
Check the example in the Microsoft docs:
https://learn.microsoft.com/en-us/dotnet/api/system.timezoneinfo.converttimebysystemtimezoneid?view=netcore-3.1
DateTime currentTime = DateTime.Now;
Console.WriteLine("New York: {0}",
TimeZoneInfo.ConvertTimeBySystemTimeZoneId(currentTime, TimeZoneInfo.Local.Id, "Eastern Standard Time"));
So it looks like the id you should look for is ""Eastern Standard Time"
If you can't find it then run the following code to check the available timezones on your pc
foreach (TimeZoneInfo z in TimeZoneInfo.GetSystemTimeZones())
Console.WriteLine(z.Id);
The destinationTimeZoneId parameter must correspond exactly to the time zone's identifier in length, but not in case, for a successful match to occur; that is, the comparison of destinationTimeZoneId with time zone identifiers is case-insensitive.
So check the timezones and copy the correct string to use based on what exists on the machine.

Check if daylight savings is in effect?

How to check if in Denmark daylight time savings has taken effect, if so, then add 1 hour to my data, else not?
I have a xml file:
<day = "1"
month = "5"
sunrise ="06:30"
sunset ="21:30"
/>

Think you need convert this xml to DateTime and then use TimeZoneInfo class.
If Denmark your local time:
DateTime thisTime = DateTime.Now;
bool isDaylight = TimeZoneInfo.Local.IsDaylightSavingTime(thisTime);
Else you need to get Denmark TimeZone:
DateTime thisTime = DateTime.Now;
// get Denmark Standard Time zone - not sure about that
TimeZoneInfo tst = TimeZoneInfo.FindSystemTimeZoneById("Denmark Standard Time");
bool isDaylight = tst.IsDaylightSavingTime(thisTime);

When I coded as above - for New-York, I found in the debugger that the time was set correctly (including DST)
TimeZoneInfo nyTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
DateTime nyTime = GetLocalDateTime(DateTime.UtcNow, nyTimeZone);
if (nyTimeZone.IsDaylightSavingTime(nyTime))
nyTime = nyTime.AddHours(1);
public static DateTime GetLocalDateTime(DateTime utcDateTime, TimeZoneInfo timeZone)
{
utcDateTime = DateTime.SpecifyKind(utcDateTime, DateTimeKind.Utc);
DateTime time = TimeZoneInfo.ConvertTime(utcDateTime, timeZone);
return time;
}

You can use TimeZoneInfo.IsDaylightSavingTime
DateTime theDate = new DateTime(2012, 5, 1); // may 1st
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("Central European Standard Time");
bool isCurrentlyDaylightSavings = tzi.IsDaylightSavingTime(theDate);

Here is a generic test and happy to be corrected if my math is incorrect. In my case I just needed to get the GMT offset for the timezone regardless of where it was in the world.
int timezone;
TimeZoneInfo localZone = TimeZoneInfo.Local;
DateTime myTime = DateTime.Now;
bool isDayLight = TimeZoneInfo.Local.IsDaylightSavingTime(myTime);
if (isDayLight)
timezone = Math.Abs(localZone.BaseUtcOffset.Hours) + 1;
else
timezone = Math.Abs(localZone.BaseUtcOffset.Hours);
Debug.WriteLine("timezone is " + timezone);
I simply found the current time and if it was in Day Light Savings period added +1 to the GMT offset.
This works with Visual Studio Express 2013.

You need to do two things:
call IsAmbiguous
List item IsDaylightSavingTime.
if (TimeZoneInfo.Local.IsAmbiguousTime(unclearDate) ||
TimeZoneInfo.Local.IsDaylightSavingTime(unclearDate))
Console.WriteLine("{0} may be daylight saving time in {1}.", unclearDate, TimeZoneInfo.Local.DisplayName);
https://msdn.microsoft.com/en-us/library/bb460642(v=vs.110).aspx

this is my short solution which can be using in all timezones:
DateTime utcTime = DateTime.Parse("30.10.2018 18:21:34")
DateTime localtime = ConvertUTCToLocalTime(utcTime);
public static DateTime ConvertUTCToLocalTime(DateTime UTCTime)
{
var localZone = TimeZone.CurrentTimeZone;
var offset = localZone.GetUtcOffset(UTCTime);
var localTime = UTCTime.AddHours(offset.Hours);
return localTime;
}

Important
myDateTime.IsDaylightSavingTime DOES return the proper value... but... it is accurate down to at least the hour of the day, just passing the date alone isn't enough.
For instance this year (2019) 3/10/2019 02:00:00 passed as myDateTime will return false, but 3/10/2019 03:00:00 will return true.

Based on other codes provided above, I made a complete code to run and make tests. The variable cityTz is receiving an IANA timezone name example. IANA timezone pattern is used in Mac and Linux (Windows uses different timezone style). In 2020, daylight-saving (DST) in New York ends on November 01. If you test the code below, the return will be FALSE, because "theDate" is November 02, the next day after the end of DST. But if you change the line commented and set theDate to November 01 (last DST date in NY), the return will be TRUE.
You can compile this program in Mac or Linux terminal typing:
csc testDST.cs
To run your program:
mono testDST.exe
Complete code:
using System;
using System.Collections.Generic;
using System.Linq;
class Program{
static void Main(string[] args)
{
string cityTz;
//cityTz = "America/Sao_Paulo";
cityTz = "America/New_York";
//DateTime theDate = new DateTime(2020, 11, 1); //returns TRUE
DateTime theDate = new DateTime(2020, 11, 2); //returns FALSE
Console.WriteLine("Data: "+theDate);
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById(cityTz);
bool isDaylight = tzi.IsDaylightSavingTime(theDate);
Console.WriteLine("isDaylight this date in "+ cityTz +"?: "+ isDaylight);
}
}

Save the Datetime in UTC in database

I am facing problem with saving date time in UTC.
I amtaking datetime as input from user after that I want to save that datetime's UTC value in database.
I am using one text box(for taking the exact date) and one dropdownlist(for taking the hours of that date)to get the datetime input values from user.
below is my code to get the exact input datetime from user after combinending both controls value.
like:25/12/2011 as date and 10 hours as hours after combinding both values the date values is 25/12/2011 10:00 AM
fort his calculation I am using below code:
string[] dateArray = HdnDPC_date1.Value.Split('/');
string dtt = dateArray[1] + "/" + dateArray[0] + "/" + dateArray[2];
var fdate = Convert.ToDateTime(dtt);
DateTime dadate = new DateTime(Convert.ToInt32(dateArray[2]), Convert.ToInt32(dateArray[1]), Convert.ToInt32(dateArray[0]));
dadate = Convert.ToDateTime(fdate).AddHours(deadlineHr);
below code is used to convert the date time value in UTC
DateTime DeadLine = TimeZoneInfo.ConvertTimeToUtc(dadate);
but code is not converting the input datetime according to the Time zone, it is always convert according to the "Central Time Zone, USA & Canada"
But I want to convert that datetime according to the user's Timezone.
Please help me to identify this problem why this happened.

You can try using the ToUniversalTime function
DateTime univDateTime = DateTime.Now.ToUniversalTime();
More on ToUniveralTime here

You need to specify the user's timezone. For example:
TimeZoneInfo.ConvertTimeToUtc(dadate,
TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time"));

Set your thread's current culture to the user's culture like:
Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture(selectedLanguage);
Thread.CurrentThread.CurrentUICulture = new CultureInfo(selectedLanguage);
See http://msdn.microsoft.com/en-us/library/bz9tc508.aspx

Get origin time from a datetime string with offset

If I run:
// 7:10 am at a location which has a +2 offset from UTC
string timeString = "2011-06-15T07:10:25.894+02:00";
DateTime time = DateTime.Parse(timeString);
It gives me time = 6/14/2011 10:10:25 PM. This is the local time where I am at (Pacific time i.e. UTC -7).
Is there an elegant way of getting the local time at the origin i.e. 6/15/2011 07:10:25 AM?

You can use TimeZoneInfo:
DateTime localTime = DateTime.Now;
TimeZoneInfo targetTimeZone =
TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
DateTime targetTime = TimeZoneInfo.ConvertTime(localTime, targetTimeZone);
Actually, the ConvertTimeBySystemTimeZoneId method would be even more succinct:
DateTime targetTime =
TimeZoneInfo.ConvertTimeBySystemTimeZoneId(localTime, "Eastern Standard Time");
You can get information for time zones available using TimeZoneInfo.GetSystemTimeZones().

The DateTimeOffset structure seems to be built to specifically handle timezones. It includes most of the functionality of the DateTime type.
string timeString = "2011-06-15T07:10:25.894+02:00";
DateTimeOffset time = DateTimeOffset.Parse(timeString);
As this article illustrates, you should DateTimeOffset instead of DateTime whenever you need to unambiguously identify a single point in time.

Lock into using TimeZoneInfo - http://msdn.microsoft.com/en-us/library/system.timezoneinfo.aspx to do conversions. FindSystemTimeZoneById and ConvertTimeFromUtc should be enough. You may need to convert your local DateTime to UTC first with DateTime.ToUniversalTime.

You can format the way DateTime is Parse.
For example, if I want the DateTime to be format in french Canadian format :
IFormatProvider culture = new CultureInfo("fr-CA", true);
DateTime dt = DateTime.ParseExact(dateString, "dd-MM-yyyy", culture);
You can do it the same way for a en-US culture and add the time format to specify the format you want ...

How to represent the current UK time?

I'm facing an issue while converting dates between my server and client where both is running in Germany. The Regional settings on the client machines could be set to both UK or Germany.I recieve a date from the server which is CET format, and I need to represent this time on UI as UK time. For example a time recieved from server like say, 01/07/2010 01:00:00 should be represented on the UI as 01/07/2010 00:00:00. I have written a converter for this purpose, however while running it 'am getting a time difference of 2 hours.Below is the code, please can you help?
public class LocalToGmtConverter : IDateConverter
{
private readonly TimeZoneInfo timeZoneInfo;
public LocalToGmtConverter()
: this(TimeZoneInfo.Local)
{
}
public LocalToGmtConverter(TimeZoneInfo timeZoneInfo)
{
this.timeZoneInfo = timeZoneInfo;
}
public DateTime Convert(DateTime localDate)
{
var utcKind = DateTime.SpecifyKind(localDate, DateTimeKind.Utc);
return utcKind;
}
public DateTime ConvertBack(object fromServer)
{
DateTime serverDate = (DateTime)fromServer;
var utcOffset = timeZoneInfo.GetUtcOffset(serverDate);
var uiTime = serverDate- utcOffset;
return uiTime;
}
}

I think you're converting to UTC (instead of UK) time. Since there is still summer time in Central Europe (event if the temperatures say otherwise), the difference is +2 hours until October, 31st.
If you know that you're converting from Germany to UK (i.e. CEST to BST in summer and CET to GMT in winter), why you don't just subtract 1 hour?
If you want the time zone information for UK, you can construct it using
var britishZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
Then you could convert the date using
var newDate = TimeZoneInfo.ConvertTime(serverDate, TimeZoneInfo.Local, britishZone);

This is what I do:
var BritishZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
DateTime dt = DateTime.SpecifyKind(DateTime.UtcNow, DateTimeKind.Unspecified);
DateTime DateTimeInBritishLocal = TimeZoneInfo.ConvertTime(dt, TimeZoneInfo.Utc, BritishZone);
I needed to add the SpecifyKind part or the ConvertTime throws an exception

Use TimeZoneInfo.ConvertTime to convert original input timezone (CET) to target timezone (UK).
public static DateTime ConvertTime(
DateTime dateTime,
TimeZoneInfo sourceTimeZone,
TimeZoneInfo destinationTimeZone
)
Full guidance on MSDN here:
Converting Times Between Time Zones
Modified code sample from MSDN:
DateTime ceTime = new DateTime(2007, 02, 01, 08, 00, 00);
try
{
TimeZoneInfo ceZone = TimeZoneInfo.FindSystemTimeZoneById("Central Europe Standard Time");
TimeZoneInfo gmtZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
Console.WriteLine("{0} {1} is {2} GMT time.",
ceTime,
ceZone.IsDaylightSavingTime(ceTime) ? ceZone.DaylightName : ceZone.StandardName,
TimeZoneInfo.ConvertTime(ceTime, ceZone, gmtZone));
}
catch (TimeZoneNotFoundException)
{
Console.WriteLine("The registry does not define the required timezones.");
}
catch (InvalidTimeZoneException)
{
Console.WriteLine("Registry data on the required timezones has been corrupted.");
}

The better approach to deal with local times is store them in unified representation such as UTC.
So you can convert all input times to UTC (via .ToUniversalTime()), and store (or transmit) its value. When you need to show it just convert back by using .ToLocalTime().
So you avoid rquirements to know which time zone was original value and can easily show stored value in different timezones.
Also you can avoid incoming troubles where you have to write specific logic for processing time in next timezone trying to figure out how to convert them amongs all available.

I realize the question is for C#, but if all you want to do is a single conversion you can do this from the PowerShell command line:
$d = [DateTime]::Parse("04/02/2014 17:00:00")
$gmt = [TimeZoneInfo]::FindSystemTimeZoneById("GMT Standard Time");
[TimeZoneInfo]::ConvertTime($d, $gmt, [TimeZoneInfo]::Local)
This script would convert 17:00 UK time into your local time zone.
For me, that would be CST. It's interesting to note that if I had set the date to 03/27/2014, the result would be different because the UK daylight saving time kicks in on different dates that the US.