The thing I want to do is quite simple:
private static TimeZoneInfo Tzi = // ... custom timeZone I've set;
public static DateTime ToTimeZone(DateTime dateTime, TimeZoneInfo target)
{
return TimeZoneInfo.ConvertTime(dateTime, Tzi, target);
}
Idea is - all dates that come to the server are automatically converted to certain TimeZone and saved like that to DB (UTC, Central US, Pacific US, whatever).
And this works quite well as long as timezone set on the server is same as Tzi. However, when that's not true, conversion fails - when creating DateTime instance .NET sets it to TimeZone of the machine and then TimeZoneInfo.ConvertTime(dateTime, Tzi, target) processes my request in a funky way. For example, let's say that Server TimeZone is Pacific (UTC -8), I set Tzi to Central (UTC -6), and I target Singapure (UTC +8).
Now when I call TimeZoneInfo.ConvertTime(dateTime, Tzi, target) first "converts" dateTime from UTC -8 to UTC -6 (Tzi time zone), adding 2 hours... and only then from Tzi to target.
Is there a way to signal to TimeZoneInfo.ConvertTime that dateTime I am sending is in TimeZone I am passing in as from parameter, and not in the TimeZone of server?
EDIT:
OK, both answers are great recommendations, but it seems I have different kind of trouble. TimeZoneInfo.ConvertTime(dateTime, Tzi, target) seems to be working correctly, and the real culprit is actually:
return Json(new {data}, JsonRequestBehavior.AllowGet);
that outputs dates like: "Created":"/Date(1346810072950)/". I've confirmed that sent date is different depending on TimeZone on the server (AppPool restart is needed after changing server's TimeZone). Anyone have experience with this and suggestion on how to influence the way ASP.NET MVC outputs dates in JSON that's sent back to client?
ConvertTime should do the job. Maybe your issue is the DateTime.Kind.
See the following example:
// Gets current local date
// Returns 04/09/12 11:30 in my case
var date = DateTime.Now;
// Sets DateTime as Unspecified kind (not local nor UTC)
// Returns same date as before, but the date is not tagged as "local"
date = DateTime.SpecifyKind(date, DateTimeKind.Unspecified);
// Converts the current date, specified as UTC+12, into a date specified as UTC-11
// Returns 03/09/12 12:30 in my case, which is the expected result
// (23 hours between previous date and result)
var zz = TimeZoneInfo.ConvertTime(
date,
TimeZoneInfo.FindSystemTimeZoneById("UTC+12"),
TimeZoneInfo.FindSystemTimeZoneById("UTC-11"));
You can use DateTimeOffset instead of DateTime - this structure includes a timezone offset property, so when creating instances of it you should specify what offset to use.
Related
Given the 11:00 PM, and knowing that the server is running using UTC time, I need to take that time parse it into a DateTimeOffset from a specific TimeZone.
For example if the docker container's time running the server is 2:00 AM 6/3/2022, I need to be able to check if current date time now in 'Eastern Standard Time' zone, is past 6/2/2022 11:00 PM or before.
To get localized DateTime now I have the following code which works as expected:
TimeZoneInfo tzInfo = TimeZoneInfo.FindSystemTimeZoneById(zoneId);
DateTime nowLocalTime = TimeZoneInfo.ConvertTime(DateTime.Now, tzInfo);
DateTimeOffset targetDateTimeOffset =
new DateTimeOffset(nowLocalTime,
tzInfo.GetUtcOffset
(
DateTime.SpecifyKind(nowLocalTime, DateTimeKind.Local)
));
I thought I had it figured out for parsing the time into DateTime and then getting the specific DateTimeOffset object, until it hit past midnight on the server. Since the server's time is now 12:01 AM 6/3/2022 when I run the following code:
string timeOfDay = "11:00 AM";
TimeZoneInfo tzInfo = TimeZoneInfo.FindSystemTimeZoneById(zoneId);
DateTime.TryParse(timeOfDay, out DateTime dateTime);
DateTimeOffset targetDateTimeOffset =
new DateTimeOffset
(
dateTime,
tzInfo.GetUtcOffset
(
DateTime.SpecifyKind(dateTime,
DateTimeKind.Local)
)
);
This now returns 6/3/2022 11:00PM. This makes sense but I need to get DateTimeOffset parsed into the specified TimeZone. Because right now in 'Eastern Standard Time' zone it is 6/2/2022 not 6/3/2022. So basically I need to take 11:00 PM parse it into DateTimeOffset of the provided TimeZone, is that possible?
The .net DateTime type was designed before the age of cloud computing. Where you only had to worry about the machine's .Local time or .Utc. IMHO DateTimeKind.Unspecified should be marked [Obsolete] and any API behaviour which relies on it should instead throw an exception.
TimeZoneInfo.ConvertTime(DateTime, TimeZoneInfo) is a particularly strange function. If you pass a DateTimeKind.Unspecified, or a TimeZoneInfo other than TimeZoneInfo.Local or TimeZoneInfo.Utc, the result is essentially unusable.
IMHO you're better off pushing the problem of parsing and displaying date / time values to the client. Force the client to parse any date time strings in their local timezone. Then either use UTC everywhere, or use DateTimeOffset to store the timezone explicitly.
It's easy enough to get the current time in a specific timezone;
TimeZoneInfo tzInfo = TimeZoneInfo.FindSystemTimeZoneById(zoneId);
DateTimeOffset tzLocalTime = TimeZoneInfo.ConvertTime(DateTimeOffset.UtcNow, tzInfo);
Unfortunately while you can parse a string and .AssumeLocal or .AssumeUniversal, anything else is barely supported or documented. While you can provide a CultureInfo for parsing non-gregorian calendars, there's no DateTimeOffset.Parse which takes a default TimeZoneInfo parameter. The closest I've found is to check if the string contains an offset, based on this question.
static DateTimeOffset ParseAsDateTimeOffset(string s, TimeZoneInfo defaultTimeZone, CultureInfo culture = null)
{
if (Regex.IsMatch(s, #"(Z|[+-]\d{2}:\d{2})$"))
return DateTimeOffset.Parse(s, culture ?? CultureInfo.InvariantCulture);
var dt = DateTime.Parse(s, culture ?? CultureInfo.InvariantCulture);
return new DateTimeOffset(dt, defaultTimeZone.GetUtcOffset(dt));
}
While this works for most of the year, I'm not certain if it works properly for time values around DST adjustments. But without an explicit offset, those values are going to be wrong anyway.
All of our date/time data in our database is stored in UTC time. I'm trying to write a function to convert that UTC time into the user's preferred time zone (they can select their timezone in their profile so it has NOTHING to do with local settings on their computer and everything to do with which timezone they have selected from a dropdown of available choices.
This function is in the context of a DevExpress AspxGridView event (the third party control is not relevant to the question but I thought I'd mention it):
DateTimeOffset utcTime = (DateTimeOffset)e.Value;
TimeZoneInfo destTimeZone = Helper.GetTimeZoneInfo();
DateTime modifiedDate = TimeZoneInfo
.ConvertTimeFromUtc(utcTime.DateTime, destTimeZone);
e.DisplayText = String.Format("{0} {1}",
modifiedDate.ToString("g"),
destTimeZone.Abbreviation());
Helper.GetTimeZoneInfo() simply returns a TimeZoneInfo class that corresponds to the one the user selected, or defaults to "Pacific Standard Time" if they have not chosen one.
This generally works fine until I switch my system clock (which this server is running on) from today (which is Oct. 14, a DST date) to something like January 11, which is NOT DST.
The time seems to always be displayed in DST (i.e. always a 7 hour offset). No matter what I do with my system clock, I can't get the time to adjust for the extra hour.
For example, when I have my timezone set to Pacific Standard Time, for UTC time 10-10-2011 20:00:00, it is always displaying this time:
10-10-2011 13:00:00 (the DST time, offset of -7).
During non-Daylight Savings dates (standard), the time should be:
10-10-2011 12:00:00 (offset of -8).
What am I missing?
The converted local time of a UTC time is always based on the time zone info for that UTC time... not for whatever the current time happens to be.
That is, the PST offset on Oct 10, 2011 UTC is always -7. It doesn't matter what date you are doing the conversion on.
...Or am I misunderstanding what you are asking?
You might have a look at the e.Value.
Is the DateTimeKind for it set to DateTimeKind.Utc or is it DateTimeKind.Unspecified
If it is Unspecified, the conversion will not work correctly.
One cannot set the Kind directly. The best I have come up with is something along the lines of
// the value off the DB, but Kind is unspecified
var fromDb = new DateTime(1999,31,12)
// convert it to a Utc version of the same date
var fromDbInUtc = new DateTime(fromDb.Ticks, DateTimeKind.Utc)
var destTimeZone = Helper.GetTimeZoneInfo();
var local = TimeZoneInfo.ConvertFromUtc(fromDbInUtc, destTimeZone);
Hope this helps,
Alan.
I'm stuck with a problem around parsing date and time:
I'm trying to parse a datetime string extracted from a german website. It is given in the format 'day.month.year 24hours:minutes', like:
01.01.2011 17:00
And it is always in the german timezone. But here comes the problem:
'01.01.2011 17:00' should be parsed to a DateTime struct with '01.01.2011 16:00' in UTC (here, the timezone is CET, without daylight saving time)
while '01.06.2011 17:00' should be parsed to a DateTime struct with '01.01.2011 15:00' in UTC (here, the timezone is CEST, with daylight saving time)
I have no clue how to achieve this. If I set my local clock to the german timezone, and I parse with DateTime.ParseExact and the flag DateTimeStyles.AssumeLocal and DateTimeStyles.AdjustToUniversal it is parsed correctly. However, I want any client to parse it independently from their local clock and timezone. Also, I dont want to do the timezone offset myself, because it depends on the date (summer: -2 / winter: -1).
Once I have the datetime in UTC it would be easy to convert it to any local timezone.
It sounds like you know what time zone you should be parsing it with. Assuming .NET 3.5 (and thus TimeZoneInfo) you should logically:
Parse it as a "local" time (not time zone specific)
Convert that local time to a UTC time
Unfortunately DateTime makes that slightly tricky. EDIT: I thought you'd want to convert parse it using DateTimeStyles.AssumeUniversal - but that ends up returning a local DateTime, annoyingly. Basically you want to end up with a DateTime with the right time so that you can use:
parsed = DateTime.SpecifyKind(parsed, DateTimeKind.Unspecified);
You can then get a UTC value with:
DateTime utc = TimeZoneInfo.ConvertTimeToUtc(parsed, germanTimeZone);
Note that you really want an "unspecified" date time first, so that you can convert it to UTC in an arbitrary time zone. You should also remember the possibility that a local time is ambiguous (occurs twice) or impossible (doesn't occur at all) due to DST changes.
And yes, this will be a lot easier in Noda Time when it's finished :)
After having seen that the task can not be archieved with the help of the WP7/Silverlight framework, I wrote a small helper that does the job:
public static class DateTimeHelper
{
/// <summary>
/// Tries to parse the given datetime string that is not annotated with a timezone
/// information but known to be in the CET/CEST zone and returns a DateTime struct
/// in UTC (so it can be converted to the devices local time). If it could not be
/// parsed, result contains the current date/time in UTC.
/// </summary>
public static bool TryParseCetCest(string s, string format, IFormatProvider provider, DateTimeStyles style, out DateTime result)
{
// Parse datetime, knowing it is in CET/CEST timezone. Parse as universal as we fix it afterwards
if (!DateTime.TryParseExact(s, format, provider, style, out result))
{
result = DateTime.UtcNow;
return false;
}
result = DateTime.SpecifyKind(result, DateTimeKind.Utc);
// The boundaries of the daylight saving time period in CET and CEST (_not_ in UTC!)
// Both DateTime structs are of kind 'Utc', to be able to compare them with the parsing result
DateTime DstStart = LastSundayOf(result.Year, 3).AddHours(2);
DateTime DstEnd = LastSundayOf(result.Year, 10).AddHours(3);
// Are we inside the daylight saving time period?
if (DstStart.CompareTo(result) <= 0 && result.CompareTo(DstEnd) < 0)
result = result.AddHours(-2); // CEST = UTC+2h
else
result = result.AddHours(-1); // CET = UTC+1h
return true;
}
/// <summary>
/// Returns the last sunday of the given month and year in UTC
/// </summary>
private static DateTime LastSundayOf(int year, int month)
{
DateTime firstOfNextMonth = new DateTime(year, month + 1, 1, 0, 0, 0, DateTimeKind.Utc);
return firstOfNextMonth.AddDays(firstOfNextMonth.DayOfWeek == DayOfWeek.Sunday ? -7 :
(-1 * (int)firstOfNextMonth.DayOfWeek));
}
}
The trick was to parse it without the DateTimeStyles.AssumeUniversal flag (this makes TryParseExact assume the date is UTC and returning the date converted/adjusted to local), respecifying it as UTC and then manually adjusting it to the actual UTC equivalent.
It follows the DST rules that can be found here. I tested it with all 4 boundary cases just before/after the start/end of the daylight saving time. That showed again the importance of testing: I had to change the < operator in DstStart.CompareTo(result) < 0 to <= to make it produce the correct result.
I had the feeling that I am reinventing the wheel here (which I hate to do), but did not want to use a dedicated library for this simple job. I had a look at Noda Time which is a great project, but I think its not necessary for this.
I hope I can save someone a little time with this small helper. It is intentionally not generic for all time zones (if you need this use a lib like Noda Time instead), but for these cases in which you just have one fixed single time zone, like in my case.
Can anyone explain the difference between System.DateTime.Now and System.DateTime.Today in C#.NET? Pros and cons of each if possible.
DateTime.Now returns a DateTime value that consists of the local date and time of the computer where the code is running. It has DateTimeKind.Local assigned to its Kind property. It is equivalent to calling any of the following:
DateTime.UtcNow.ToLocalTime()
DateTimeOffset.UtcNow.LocalDateTime
DateTimeOffset.Now.LocalDateTime
TimeZoneInfo.ConvertTime(DateTime.UtcNow, TimeZoneInfo.Local)
TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, TimeZoneInfo.Local)
DateTime.Today returns a DateTime value that has the same year, month, and day components as any of the above expressions, but with the time components set to zero. It also has DateTimeKind.Local in its Kind property. It is equivalent to any of the following:
DateTime.Now.Date
DateTime.UtcNow.ToLocalTime().Date
DateTimeOffset.UtcNow.LocalDateTime.Date
DateTimeOffset.Now.LocalDateTime.Date
TimeZoneInfo.ConvertTime(DateTime.UtcNow, TimeZoneInfo.Local).Date
TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, TimeZoneInfo.Local).Date
Note that internally, the system clock is in terms of UTC, so when you call DateTime.Now it first gets the UTC time (via the GetSystemTimeAsFileTime function in the Win32 API) and then it converts the value to the local time zone. (Therefore DateTime.Now.ToUniversalTime() is more expensive than DateTime.UtcNow.)
Also note that DateTimeOffset.Now.DateTime will have similar values to DateTime.Now, but it will have DateTimeKind.Unspecified rather than DateTimeKind.Local - which could lead to other errors depending on what you do with it.
So, the simple answer is that DateTime.Today is equivalent to DateTime.Now.Date.
But IMHO - You shouldn't use either one of these, or any of the above equivalents.
When you ask for DateTime.Now, you are asking for the value of the local calendar clock of the computer that the code is running on. But what you get back does not have any information about that clock! The best that you get is that DateTime.Now.Kind == DateTimeKind.Local. But whose local is it? That information gets lost as soon as you do anything with the value, such as store it in a database, display it on screen, or transmit it using a web service.
If your local time zone follows any daylight savings rules, you do not get that information back from DateTime.Now. In ambiguous times, such as during a "fall-back" transition, you won't know which of the two possible moments correspond to the value you retrieved with DateTime.Now. For example, say your system time zone is set to Mountain Time (US & Canada) and you ask for DateTime.Now in the early hours of November 3rd, 2013. What does the result 2013-11-03 01:00:00 mean? There are two moments of instantaneous time represented by this same calendar datetime. If I were to send this value to someone else, they would have no idea which one I meant. Especially if they are in a time zone where the rules are different.
The best thing you could do would be to use DateTimeOffset instead:
// This will always be unambiguous.
DateTimeOffset now = DateTimeOffset.Now;
Now for the same scenario I described above, I get the value 2013-11-03 01:00:00 -0600 before the transition, or 2013-11-03 01:00:00 -0700 after the transition. Anyone looking at these values can tell what I meant.
I wrote a blog post on this very subject. Please read - The Case Against DateTime.Now.
Also, there are some places in this world (such as Brazil) where the "spring-forward" transition happens exactly at Midnight. The clocks go from 23:59 to 01:00. This means that the value you get for DateTime.Today on that date, does not exist! Even if you use DateTimeOffset.Now.Date, you are getting the same result, and you still have this problem. It is because traditionally, there has been no such thing as a Date object in .Net. So regardless of how you obtain the value, once you strip off the time - you have to remember that it doesn't really represent "midnight", even though that's the value you're working with.
If you really want a fully correct solution to this problem, the best approach is to use NodaTime. The LocalDate class properly represents a date without a time. You can get the current date for any time zone, including the local system time zone:
using NodaTime;
...
Instant now = SystemClock.Instance.Now;
DateTimeZone zone1 = DateTimeZoneProviders.Tzdb.GetSystemDefault();
LocalDate todayInTheSystemZone = now.InZone(zone1).Date;
DateTimeZone zone2 = DateTimeZoneProviders.Tzdb["America/New_York"];
LocalDate todayInTheOtherZone = now.InZone(zone2).Date;
If you don't want to use Noda Time, there is now another option. I've contributed an implementation of a date-only object to the .Net CoreFX Lab project. You can find the System.Time package object in their MyGet feed. Once added to your project, you will find you can do any of the following:
using System;
...
Date localDate = Date.Today;
Date utcDate = Date.UtcToday;
Date tzSpecificDate = Date.TodayInTimeZone(anyTimeZoneInfoObject);
Time. .Now includes the 09:23:12 or whatever; .Today is the date-part only (at 00:00:00 on that day).
So use .Now if you want to include the time, and .Today if you just want the date!
.Today is essentially the same as .Now.Date
The DateTime.Now property returns the current date and time, for example 2011-07-01 10:09.45310.
The DateTime.Today property returns the current date with the time compnents set to zero, for example 2011-07-01 00:00.00000.
The DateTime.Today property actually is implemented to return DateTime.Now.Date:
public static DateTime Today {
get {
DateTime now = DateTime.Now;
return now.Date;
}
}
DateTime.Today represents the current system date with the time part set to 00:00:00
and
DateTime.Now represents the current system date and time
I thought of Adding these links -
A brief History of DateTime - By Anthony Moore by BCL team
Choosing between Datetime and DateTime Offset - by MSDN
Do not forget SQL server 2008 onwards has a new Datatype as DateTimeOffset
The .NET Framework includes the DateTime, DateTimeOffset, and
TimeZoneInfo types, all of which can be used to build applications
that work with dates and times.
Performing Arithmetic Operations with Dates and Times-MSDN
Coming back to original question , Using Reflector i have explained the difference in code
public static DateTime Today
{
get
{
return DateTime.Now.Date; // It returns the date part of Now
//Date Property
// returns same date as this instance, and the time value set to 12:00:00 midnight (00:00:00)
}
}
private const long TicksPerMillisecond = 10000L;
private const long TicksPerDay = 864000000000L;
private const int MillisPerDay = 86400000;
public DateTime Date
{
get
{
long internalTicks = this.InternalTicks; // Date this instance is converted to Ticks
return new DateTime((ulong) (internalTicks - internalTicks % 864000000000L) | this.InternalKind);
// Modulo of TicksPerDay is subtracted - which brings the time to Midnight time
}
}
public static DateTime Now
{
get
{
/* this is why I guess Jon Skeet is recommending to use UtcNow as you can see in one of the above comment*/
DateTime utcNow = DateTime.UtcNow;
/* After this i guess it is Timezone conversion */
bool isAmbiguousLocalDst = false;
long ticks1 = TimeZoneInfo.GetDateTimeNowUtcOffsetFromUtc(utcNow, out isAmbiguousLocalDst).Ticks;
long ticks2 = utcNow.Ticks + ticks1;
if (ticks2 > 3155378975999999999L)
return new DateTime(3155378975999999999L, DateTimeKind.Local);
if (ticks2 < 0L)
return new DateTime(0L, DateTimeKind.Local);
else
return new DateTime(ticks2, DateTimeKind.Local, isAmbiguousLocalDst);
}
}
DateTime dt = new DateTime();// gives 01/01/0001 12:00:00 AM
DateTime dt = DateTime.Now;// gives today date with current time
DateTime dt = DateTime.Today;// gives today date and 12:00:00 AM time
DateTime.Today is DateTime.Now with time set to zero.
It is important to note that there is a difference between a DateTime value, which represents the number of ticks that have elapsed since midnight of January 1, 0000, and the string representation of that DateTime value, which expresses a date and time value in a culture-specific-specific format:
https://msdn.microsoft.com/en-us/library/system.datetime.now%28v=vs.110%29.aspx
DateTime.Now.Ticks is the actual time stored by .net (essentially UTC time), the rest are just representations (which are important for display purposes).
If the Kind property is DateTimeKind.Local it implicitly includes the time zone information of the local computer. When sending over a .net web service, DateTime values are by default serialized with time zone information included, e.g. 2008-10-31T15:07:38.6875000-05:00, and a computer in another time zone can still exactly know what time is being referred to.
So, using DateTime.Now and DateTime.Today is perfectly OK.
You usually start running into trouble when you begin confusing the string representation with the actual value and try to "fix" the DateTime, when it isn't broken.
DateTime.Now.ToShortDateString() will display only the date part
I am storing information in a database and setting my POCO's property to DateTime.Now.
When this value is displayed it is appearing as the PST time. I would like it to to display as GMT time.
Do I do something like this to display/store it or is there a better way?
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("GMT");
var GMTTime = TimeZoneInfo.ConvertTimeToUtc(DateTime.Now, tz));
Also it needs to consider Daylight Savings as UK changes its clocks at different times in the year than USA:
UPDATE: I have found that in the TimeZone setting you can pass either GMT Standard Time or Greenwich Mean Time, the first taking into account DST
Store it as UTC. It's designed for universal timezone-independent time.
DateTime currentUtcTime = DateTime.UtcNow;
DateTime localTime = currentUtcTime.ToLocalTime();
DateTime backToUtcAgain = localTime.ToUniversalTime();
Whether a given DateTime is already UTC or local time is determined by DateTime.Kind. You have to keep this in mind when serializing/deserializing DateTime values (e.g from a database) because this information is often not stored and when you get your DateTime back, it will most of the time have the value DateTimeKind.Unspecified, which may cause issues with conversion methods. I just make sure to force DateTimeKind.Utc when I load something in from a persistent data store.
there's DateTime.UtcNow if that meets your needs.
Have a look at DateTimeOffset.
I'd propose to change your DateTime property to this type
MSDN
DateTime vs. DateTimeOffSet
You could add it into an extension method to make it nicer
public static DateTime ConvertToGreenwichMeanTime(this DateTime utcDateTime)
{
return TimeZoneInfo.ConvertTimeFromUtc(utcDateTime, TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time"));
}
Then just call it
DateTime.UtcNow.ConvertToGreenwichMeanTime();