Develop Reference

Reading the installation date of the C# OS

With the C# Core 3.1 WinForms application, the first installation date of the operating system cannot be read through regedit. It gives different results than the date given by "SystemInfo" command with CMD.
CMD "System Info":
CMD Image
Original Install Date: 11/26/2022, 1:08:26 PM
C# Read a "Regedit InstallDate(DWord)":
Regedit Image
Date: "1.01.1601 00:02:46"
C# Read a Date
RegistryKey key = RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, computerName);
key = key.OpenSubKey(#"SOFTWARE\Microsoft\Windows NT\CurrentVersion", false);
if (key != null)
{
DateTime installDate =
DateTime.FromFileTimeUtc(
Convert.ToInt64(
key.GetValue("InstallDate").ToString()));
return installDate;
}
return DateTime.MinValue;

The value in InstallDate is not a FILETIME value, but a Unix Time (seconds since 1970-01-01).
You can use
var installDate = DateTimeOffset.FromUnixTimeSeconds(regValue);
to convert to a DateTimeOffset.
For other conversion methods see How do you convert epoch time in C#?

#KlausGutter's answer is spot on, the value in the registry is a Unix time. If you want to convert it to a DateTime rather than a DateTimeOffset, then you could use something like
var installDate = DateTime.UnixEpoch.AddSeconds(regValue)

You can use this method for Converting UnixTime or whatever it is :
public static DateTime FromDate(string SerialDate)
{
var year = Convert.ToInt32(SerialDate.Substring(0, 4));
var mon = Convert.ToInt32(SerialDate[4].ToString() + SerialDate[5].ToString());
var day = Convert.ToInt32(SerialDate[6].ToString() + SerialDate[7].ToString());
try
{
var date = new DateTime(year, mon, day);
return date;
}
catch(Exception ss)
{
return DateTime.Now;
}
}

Convert time duration from String to TimeSpan

I have a string that contains day of the week, time and duration. E.g. Monday,10:00 AM,45m
The duration could be in either of the following formats:
45m
1h45m
1h
Now I need to convert this into a date with time for both the start of the event and end of the event based on the duration.
I managed to convert this piece "Monday,10:00 AM" into the upcoming date and time for whatever the day of the week is so now I have a datetime as let's say "05/30/2022 10:00:00 AM".
Now I need to create a datetime object for the end time of the event by adding e.g. "45m" to the previous datetime. I don't know the format of the duration piece but it will be one of three from the list above.
How do I convert this into a standard timespan to add to the previous time? Is the above format a standard format that perhaps has a built in way to parse? It's coming from an API.
I have tried this and it works but I'm not sure how to detect and handle the formats.
\\split the original string so now I have duration
\\when I have just the hour duraton e.g. 1h
t = TimeSpan.ParseExact(durationString, "h\\h", CultureInfo.InvariantCulture);
var finalDate = dt.Add(t);
\\when I have just the minute format e.g. 45m
t = TimeSpan.ParseExact(durationString, "m\\m", CultureInfo.InvariantCulture);

Use a ParseExact method overload that accepts an array of formats.
var values = new string[] { "45m", "1h45m", "1h" };
var formats = new string[] { #"m\m", #"h\hm\m", #"h\h" };
foreach (var value in values)
{
var ts = TimeSpan.ParseExact(value, formats, CultureInfo.InvariantCulture);
Console.WriteLine(ts);
}

You can use REGEX to check for matching patterns:
using System.Text.RegularExpressions;
Regex HourOnly = new Regex("^[0-9]+h$");
Regex MinuteOnly = new Regex("^[[0-9]+m");
Regex HourAndMinute = new Regex("^[0-9]+h[0-9]+m$");
List<string> conditions = new List<string>();
string Condition1 = "Monday,10:00 AM,45m";
string Condition2 = "Monday,10:00 AM,1h45m";
string Condition3 = "Monday,10:00 AM,1h";
conditions.Add(Condition1);
conditions.Add(Condition2);
conditions.Add(Condition3);
foreach(string condition in conditions)
{
if (HourOnly.IsMatch(condition.Split(',').Last()))
{
Console.WriteLine($"Hour only: {condition}");
}
else if (HourAndMinute.IsMatch(condition.Split(',').Last()))
{
Console.WriteLine($"Hour and minute: {condition}");
}
else if (MinuteOnly.IsMatch(condition.Split(',').Last()))
{
Console.WriteLine($"Minute only: {condition}");
}
}
Granted users can enter 99999h99999m but if you are reasonably sure that won't happen the above regex should suit you just fine.
Here is some additional documentation to aid you on your quest: https://learn.microsoft.com/en-us/dotnet/standard/base-types/regular-expression-language-quick-reference

Comparing two different timezone timespans using NodaTime

I have a requirement which I'm getting a little confused about. I started using NodaTime which I think is the best way to go.
I have two users, User1 and User2 both in two different timezones. They are available to meet between 2pm and 5pm for example, in their local timezones. If User2 has an offset of +2 hours from User1, then the overlap is just 1 hour. What I want to get the number of hours overlap (the actual time for User1 and User2 would be a bonus.)
All I have got so far is:
var user1TimeZone = DateTimeZoneProviders.Tzdb.GetZoneOrNull(user1timezone);
var user2TimeZone = DateTimeZoneProviders.Tzdb.GetZoneOrNull(user2timeZone);
Any thoughts on how I should even start tackling this problem?
Thanks,

Firstly, be aware that it could change each day: don't treat a time zone as a fixed offset.
Secondly, be aware that the local time specified (for each of start/end) may not even happen, or may happen twice. Work out how you want to handle ambiguous and skipped times.
For any particular day, I would just convert they users' start/end times to Instant (via ZonedDateTime) and then you can find the overlap. This does assume that any overlap happens on the same day, however... that isn't the case in reality. I'm having a meeting soon where one of the attendees is in New Zealand - it's March 14th here, but March 15th there. Accounting for that is rather trickier...
Here's code for the relatively simple case though:
using NodaTime;
using System;
class Test
{
static void Main()
{
// My availability: 4pm-7pm in London
var jon = new Availability(
DateTimeZoneProviders.Tzdb["Europe/London"],
new LocalTime(16, 0, 0),
new LocalTime(19, 0, 0));
// My friend Richard's availability: 12pm-4pm in New York
var richard = new Availability(
DateTimeZoneProviders.Tzdb["America/New_York"],
new LocalTime(12, 0, 0),
new LocalTime(16, 0, 0));
// Let's look through all of March 2017...
var startDate = new LocalDate(2017, 3, 1);
var endDate = new LocalDate(2017, 4, 1);
for (LocalDate date = startDate; date < endDate; date = date.PlusDays(1))
{
var overlap = GetAvailableOverlap(date, jon, richard);
Console.WriteLine($"{date:yyyy-MM-dd}: {overlap:HH:mm}");
}
}
static Duration GetAvailableOverlap(
LocalDate date,
Availability avail1,
Availability avail2)
{
// TODO: Check that the rules of InZoneLeniently are what you want.
// Be careful, as you could end up with an end before a start...
var start1 = (date + avail1.Start).InZoneLeniently(avail1.Zone);
var end1 = (date + avail1.End).InZoneLeniently(avail1.Zone);
var start2 = (date + avail2.Start).InZoneLeniently(avail2.Zone);
var end2 = (date + avail2.End).InZoneLeniently(avail2.Zone);
var latestStart = Instant.Max(start1.ToInstant(), start2.ToInstant());
var earliestEnd = Instant.Min(end1.ToInstant(), end2.ToInstant());
// Never return a negative duration... return zero of there's no overlap.
// Noda Time should have Duration.Max really...
var overlap = earliestEnd - latestStart;
return overlap < Duration.Zero ? Duration.Zero : overlap;
}
}
public sealed class Availability
{
public DateTimeZone Zone { get; }
public LocalTime Start { get; }
public LocalTime End { get; }
public Availability(DateTimeZone zone, LocalTime start, LocalTime end)
{
Zone = zone;
Start = start;
End = end;
}
}

If you have a server where you do that, you have to send UTC and then compare it. When you get the time on the client side you have to convert it into local. It means, that when first user wants to arrange a meeting, he sends his time into UTC to server, then when second user gets this time, he will convert it into his local time.
// First user sends UTC.
DateTime firstUserTime = DateTime.UtcNow;
// Second user gets time in his time zone.
DateTime secondUserTime = firstUserTime.ToLocalTime();

TimeZone conversion displaying EDT instead of EST

I am using this piece of code to convert "Eastern Time Zone" to "EST". Now it is showing "EDT". You dont see that abbr that often in places and would like to stick to "EST". How do I do this with NodaTime?
public static string GetTimeZoneAbbr(string timeZone)
{
var timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById(timeZone);
if (timeZoneInfo != null)
{
var dateTime = DateTime.UtcNow;
var instant = Instant.FromDateTimeUtc(dateTime);
var tzdbSource = TzdbDateTimeZoneSource.Default;
var tzid = tzdbSource.MapTimeZoneId(timeZoneInfo);
var dateTimeZone = DateTimeZoneProviders.Tzdb[tzid];
var zoneInterval = dateTimeZone.GetZoneInterval(instant);
return zoneInterval.Name;
}
return string.Empty;
}

UPDATE
The answer below described how to parse and use the CLDR data. This is fine, but I've made it much easier by encompassing this all in a library. See this StackOverflow answer, read my blog post, and take a look at the TimeZoneNames library. Using this library is much easier than parsing the CLDR data yourself.
// You can pass either type of time zone identifier:
var tz = "America/New_York"; // IANA
var tz = "Eastern Standard Time"; // Windows
// You can get names or abbreviations for any language or locale
var names = TZNames.GetNamesForTimeZone(tz, "en-US");
var abbreviations = TZNames.GetAbbreviationsForTimeZone(tz, "en-US");
names.Generic == "Eastern Time"
names.Standard == "Eastern Standard Time"
names.Daylight == "Eastern Daylight Time"
abbreviations.Generic == "ET"
abbreviations.Standard == "EST"
abbreviations.Daylight == "EDT"
ORIGINAL ANSWER
I've written a bit in the question comments about why it's perfectly valid to show the abbreviated form, but allow me to also answer the question as it was asked.
Reiterating your question another way, you wish to start with a Microsoft Windows time zone id, and end up with a human-readable string that represents the entire time zone, and not just the time zone segment that is in effect.
You could just give them the TimeZoneInfo.DisplayName, but that isn't always going to be appropriate. For the US, you might get a display name back of "(UTC-05:00) Eastern Time (US & Canada), and you could strip off the leading offset and parenthesis to just give back "Eastern Time (US & Canada)". But that's not going to work for all time zones, since many just have display names that list cities, such as "(UTC-04:00) Georgetown, La Paz, Manaus, San Juan".
A better approach would be to use the data from the Unicode CLDR Project. Noda Time has a portion of this data, but not everything you need for this particular problem. So I can't give you a code example that uses Noda Time. However, you can use the following steps against the raw CLDR data to achieve your goal:
Find the IANA time zone ID corresponding to the Windows time zone, such as you've already done in the code above, or using the CLDR Windows time zone mappings directly.
Lookup the IANA time zone in the CLDR MetaZones file.
Lookup the MetaZone in one of the CLDR translation data files, or charts such as this one. Use the "generic-long" or "generic-short" pattern, and the language of your choice, such as "en" for English.
So, in your case, starting with the Windows TimeZoneInfo.Id of "Eastern Standard Time":
IANA Zone = "America/New_York"
CLDR MetaZone = "America_Eastern"
generic-long [en] = "Eastern Time"
generic-short [en] = "ET"
Note that not every Windows time zone is mappable to an IANA zone, not every meta zone has a short name, and some zones that have never followed daylight saving time will only have a standard name instead of a generic name.
Here is some C# code that shows how to traverse the CLDR's XML data to get the generic long names for the TimeZoneInfo objects. It assumes you have access to the CLDR data at the path specified. Download the latest core.zip and extract, then point the basePath at that folder.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Xml.Linq;
using System.Xml.XPath;
static Dictionary<TimeZoneInfo, string> GetCldrGenericLongNames(string basePath, string language)
{
// Set some file paths
string winZonePath = basePath + #"\common\supplemental\windowsZones.xml";
string metaZonePath = basePath + #"\common\supplemental\metaZones.xml";
string langDataPath = basePath + #"\common\main\" + language + ".xml";
// Make sure the files exist
if (!File.Exists(winZonePath) || !File.Exists(metaZonePath) || !File.Exists(langDataPath))
{
throw new FileNotFoundException("Could not find CLDR files with language '" + language + "'.");
}
// Load the data files
var xmlWinZones = XDocument.Load(winZonePath);
var xmlMetaZones = XDocument.Load(metaZonePath);
var xmlLangData = XDocument.Load(langDataPath);
// Prepare the results dictionary
var results = new Dictionary<TimeZoneInfo, string>();
// Loop for each Windows time zone
foreach (var timeZoneInfo in TimeZoneInfo.GetSystemTimeZones())
{
// Get the IANA zone from the Windows zone
string pathToMapZone = "/supplementalData/windowsZones/mapTimezones/mapZone" +
"[#territory='001' and #other='" + timeZoneInfo.Id + "']";
var mapZoneNode = xmlWinZones.XPathSelectElement(pathToMapZone);
if (mapZoneNode == null) continue;
string primaryIanaZone = mapZoneNode.Attribute("type").Value;
// Get the MetaZone from the IANA zone
string pathToMetaZone = "/supplementalData/metaZones/metazoneInfo/timezone[#type='" + primaryIanaZone + "']/usesMetazone";
var metaZoneNode = xmlMetaZones.XPathSelectElements(pathToMetaZone).LastOrDefault();
if (metaZoneNode == null) continue;
string metaZone = metaZoneNode.Attribute("mzone").Value;
// Get the generic name for the MetaZone
string pathToNames = "/ldml/dates/timeZoneNames/metazone[#type='" + metaZone + "']/long";
var nameNodes = xmlLangData.XPathSelectElement(pathToNames);
var genericNameNode = nameNodes.Element("generic");
var standardNameNode = nameNodes.Element("standard");
string name = genericNameNode != null
? genericNameNode.Value
: standardNameNode != null
? standardNameNode.Value
: null;
// If we have valid results, add to the dictionary
if (name != null)
{
results.Add(timeZoneInfo, name);
}
}
return results;
}
Calling this will get you a dictionary which you can then use for lookups. Example:
// load the data once an cache it in a static variable
const string basePath = #"C:\path\to\extracted\cldr\core";
private static readonly Dictionary<TimeZoneInfo, string> timeZoneNames =
GetCldrGenericLongNames(basePath, "en");
// then later access it like this
string tzname = timeZoneNames[yourTimeZoneInfoObject];

How to get current user timezone in c#

I am building an application in MVC3 and when a user comes into my site I want to know that user's timezone. I want to know how to do this in c# not in javaScript?

As has been mentioned, you need your client to tell your ASP.Net server details about which timezone they're in.
Here's an example.
I have an Angular controller, which loads a list of records from my SQL Server database in JSON format. The problem is, the DateTime values in these records are in the UTC timezone, and I want to show the user the date/times in their local timezone.
I determine the user's timezone (in minutes) using the JavaScript "getTimezoneOffset()" function, then append this value to the URL of the JSON service I'm trying to call:
$scope.loadSomeDatabaseRecords = function () {
var d = new Date()
var timezoneOffset = d.getTimezoneOffset();
return $http({
url: '/JSON/LoadSomeJSONRecords.aspx?timezoneOffset=' + timezoneOffset,
method: 'GET',
async: true,
cache: false,
headers: { 'Accept': 'application/json', 'Pragma': 'no-cache' }
}).success(function (data) {
$scope.listScheduleLog = data.Results;
});
}
In my ASP.Net code, I extract the timezoneOffset parameter...
int timezoneOffset = 0;
string timezoneStr = Request["timezoneOffset"];
if (!string.IsNullOrEmpty(timezoneStr))
int.TryParse(timezoneStr, out timezoneOffset);
LoadDatabaseRecords(timezoneOffset);
... and pass it to my function which loads the records from the database.
It's a bit messy as I want to call my C# FromUTCData function on each record from the database, but LINQ to SQL can't combine raw SQL with C# functions.
The solution is to read in the records first, then iterate through them, applying the timezone offset to the DateTime fields in each record.
public var LoadDatabaseRecords(int timezoneOffset)
{
MyDatabaseDataContext dc = new MyDatabaseDataContext();
List<MyDatabaseRecords> ListOfRecords = dc.MyDatabaseRecords.ToList();
var results = (from OneRecord in ListOfRecords
select new
{
ID = OneRecord.Log_ID,
Message = OneRecord.Log_Message,
StartTime = FromUTCData(OneRecord.Log_Start_Time, timezoneOffset),
EndTime = FromUTCData(OneRecord.Log_End_Time, timezoneOffset)
}).ToList();
return results;
}
public static DateTime? FromUTCData(DateTime? dt, int timezoneOffset)
{
// Convert a DateTime (which might be null) from UTC timezone
// into the user's timezone.
if (dt == null)
return null;
DateTime newDate = dt.Value - new TimeSpan(timezoneOffset / 60, timezoneOffset % 60, 0);
return newDate;
}
It works nicely though, and this code is really useful when writing a web service to display date/times to users in different parts of the world.
Right now, I'm writing this article at 11am Zurich time, but if you were reading it in Los Angeles, you'd see that I edited it at 2am (your local time). Using code like this, you can get your webpages to show date times that make sense to international users of your website.
Phew.
Hope this helps.

This isn't possible server side unless you assume it via the users ip address or get the user to set it in some form of a profile. You could get the clients time via javascript.
See here for the javacript solution: Getting the client's timezone in JavaScript

You will need to use both client-side and server-side technologies.
On the client side:
(pick one)
This works in most modern browsers:
Intl.DateTimeFormat().resolvedOptions().timeZone
There is also jsTimeZoneDetect's jstz.determine(), or Moment-Timezone's moment.tz.guess() function for older browsers, thought these libraries are generally only used in older applications.
The result from either will be an IANA time zone identifier, such as America/New_York. Send that result to the server by any means you like.
On the server side:
(pick one)
Using TimeZoneInfo (on. NET 6+ on any OS, or older on non-Windows systems only):
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");
Using TimeZoneConverter (on any OS):
TimeZoneInfo tzi = TZConvert.GetTimeZoneInfo("America/New_York");
Using NodaTime (on any OS):
DateTimeZone tz = DateTimeZoneProviders.Tzdb["America/New_York"];

I got the same issue , Unfortunately there is no way for the server to know the client timezone .
If you want you can send client timezone as header while making ajax call .
In-case if you want more info on adding the header this post may help how to add header to request : How can I add a custom HTTP header to ajax request with js or jQuery?
new Date().getTimezoneOffset();//gets the timezone offset
If you don't want to add header every time , you can think of setting a cookie since cookie is sent with all httpRequest you can process the cookie to get client timezone on server side . But i don't prefer adding cookies , for the same reason they sent with all http requests.
Thanks.

For Dot Net version 3.5 and higher you can use :
TimeZoneInfo.Local.GetUtcOffset(DateTime.UtcNow);
but for Dot Net lower than version 3.5 you can handle it manually via this way :
first, get Offset from the client and store it in the cookie
function setTimezoneCookie(){
var timezone_cookie = "timezoneoffset";
// if the timezone cookie does not exist create one.
if (!$.cookie(timezone_cookie)) {
// check if the browser supports cookie
var test_cookie = 'test cookie';
$.cookie(test_cookie, true);
// browser supports cookie
if ($.cookie(test_cookie)) {
// delete the test cookie
$.cookie(test_cookie, null);
// create a new cookie
$.cookie(timezone_cookie, new Date().getTimezoneOffset());
// re-load the page
location.reload();
}
}
// if the current timezone and the one stored in cookie are different
// then store the new timezone in the cookie and refresh the page.
else {
var storedOffset = parseInt($.cookie(timezone_cookie));
var currentOffset = new Date().getTimezoneOffset();
// user may have changed the timezone
if (storedOffset !== currentOffset) {
$.cookie(timezone_cookie, new Date().getTimezoneOffset());
location.reload();
}
}
}
after that you can use a cookie in backend code like that :
public static string ToClientTime(this DateTime dt)
{
// read the value from session
var timeOffSet = HttpContext.Current.Session["timezoneoffset"];
if (timeOffSet != null)
{
var offset = int.Parse(timeOffSet.ToString());
dt = dt.AddMinutes(-1 * offset);
return dt.ToString();
}
// if there is no offset in session return the datetime in server timezone
return dt.ToLocalTime().ToString();
}

I know the user asked about a non-javascript solution, but I wanted to post a javascript solution that I came up with. I found some js libraries (jsTimezoneDetect, momentjs), but their output was an IANA code, which didn't seem to help me with getting a TimeZoneInfo object in C#. I borrowed ideas from jsTimezoneDetect. In javascript, I get the BaseUtcOffset and the first day of DST and send to server. The server then converts this to a TimeZoneInfo object.
Right now I don't care if the client Time Zone is chosen as "Pacific Time (US)" or "Baja California" for example, as either will create the correct time conversions (I think). If I find multiple matches, I currently just pick the first found TimeZoneInfo match.
I can then convert my UTC dates from the database to local time:
DateTime clientDate = TimeZoneInfo.ConvertTimeFromUtc(utcDate, timeZoneInfo);
Javascript
// Time zone. Sets two form values:
// tzBaseUtcOffset: minutes from UTC (non-DST)
// tzDstDayOffset: number of days from 1/1/2016 until first day of DST ; 0 = no DST
var form = document.forms[0];
var janOffset = -new Date(2016, 0, 1).getTimezoneOffset(); // Jan
var julOffset = -new Date(2016, 6, 1).getTimezoneOffset(); // Jul
var baseUtcOffset = Math.min(janOffset, julOffset); // non DST offset (winter offset)
form.elements["tzBaseUtcOffset"].value = baseUtcOffset;
// Find first day of DST (from 1/1/2016)
var dstDayOffset = 0;
if (janOffset != julOffset) {
var startDay = janOffset > baseUtcOffset ? 180 : 0; // if southern hemisphere, start 180 days into year
for (var day = startDay; day < 365; day++) if (-new Date(2016, 0, day + 1, 12).getTimezoneOffset() > baseUtcOffset) { dstDayOffset = day; break; } // noon
}
form.elements["tzDstDayOffset"].value = dstDayOffset;
C#
private TimeZoneInfo GetTimeZoneInfo(int baseUtcOffset, int dstDayOffset) {
// Converts client/browser data to TimeZoneInfo
// baseUtcOffset: minutes from UTC (non-DST)
// dstDayOffset: number of days from 1/1/2016 until first day of DST ; 0 = no DST
// Returns first zone info that matches input, or server zone if none found
List<TimeZoneInfo> zoneInfoArray = new List<TimeZoneInfo>(); // hold multiple matches
TimeSpan timeSpan = new TimeSpan(baseUtcOffset / 60, baseUtcOffset % 60, 0);
bool supportsDst = dstDayOffset != 0;
foreach (TimeZoneInfo zoneInfo in TimeZoneInfo.GetSystemTimeZones()) {
if (zoneInfo.BaseUtcOffset.Equals(timeSpan) && zoneInfo.SupportsDaylightSavingTime == supportsDst) {
if (!supportsDst) zoneInfoArray.Add(zoneInfo);
else {
// Has DST. Find first day of DST and test for match with sent value. Day = day offset into year
int foundDay = 0;
DateTime janDate = new DateTime(2016, 1, 1, 12, 0, 0); // noon
int startDay = zoneInfo.IsDaylightSavingTime(janDate) ? 180 : 0; // if southern hemsphere, start 180 days into year
for (int day = startDay; day < 365; day++) if (zoneInfo.IsDaylightSavingTime(janDate.AddDays(day))) { foundDay = day; break; }
if (foundDay == dstDayOffset) zoneInfoArray.Add(zoneInfo);
}
}
}
if (zoneInfoArray.Count == 0) return TimeZoneInfo.Local;
else return zoneInfoArray[0];
}

You can get this information from client to server (any web API call)
var timezoneOffset = new Date().getTimezoneOffset();
With the help of timezoneoffset details you can achieve the same. Here in my case i converted UTC DateTime to my client local datetime in Server side.
DateTime clientDateTime = DateTime.UtcNow - new TimeSpan(timezoneOffset / 60, timezoneOffset % 60, 0);
Click for code example

Take a look at this asp.net c# solution
TimeZoneInfo mytzone = TimeZoneInfo.Local;

System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_TIMEZONE"] ;