I try to insert local time in MongoDB
var time = DateTime.Now; // 03.05.2014 18:30:30
var query = new QueryDocument
{
{ "time", nowTime}
};
collection3.Insert(query);
But in database I see ISODate("2014-05-03T15:30:30.170Z"),
that must be ISODate("2014-05-03T18:30:30.300Z").
Please help me!
I think you're getting confused by time zones. The Z at the end of the string indicates that it's in UTC. When you posted this question, it was just after 15:30 UTC.
I strongly suspect that the correct instant in time is being recorded - but it's being recorded as an instant in time without reference to a particular time zone. You can then convert that to whatever time zone you want later on, but recording the UTC time is almost always the correct approach.
As an aside, you can make this clearer by using UtcNow to start with. That way it's more obvious that you're not trying to obtain a "local" time.
Looking at the MongoDB documentation, it seems that the internal representation is simply a number of milliseconds since the Unix epoch - so again, that has no indication of time zone or an offset between UTC and local time. If you want to store a value which can be converted back to the local time you saw when it was recorded (even if you're now in a different time zone) you should store a time zone ID and/or the UTC offset as a separate value. That's not needed terribly often, but it's an option.
The MongoDB driver is converting your DateTime to UTC.
If you don't want to bother with time zones, you could change the kind to UTC:
time = DateTime.SpecifyKind(time, DateTimeKind.Utc);
I would not recommed this because the database will store a "wrong" Date, but it will show you ISODate("2014-05-03T18:30:30.170Z").
Just define the "Kind" of the DateTime by the "BsonDateTimeOptions" attribute and set it to local:
[BsonDateTimeOptions(Kind = DateTimeKind.Local)]
public DateTime SomeDateProperty {get;set;}
It could work with:
DateTime t = DateTime.Now;
var update = Builders<BsonDocument>.Update
.Set("key1", t.ToUniversalTime())
.CurrentDate("key_updatetime");
Related
I'm working with an ASP.Net backend. I'm saving all my dates from the client side to the database in UTC time.
I have a function in the backend that exports some records and I would like to convert the dates extracted, from UTC time to the user's local time before displaying them.
I have tried tons of solutions proposed here on StackOverflow, but none of them seem to convert the date to local time, even though this works when displaying some of these dates on the client.I suspect the server already thinks the date is in local time, but I'm not sure how else to solve it.
Below are the different solutions I have tried:
//1.
var alertTime = record.TimeRecorded.GetValueOrDefault().ToLocalTime().ToString("hh:mm tt");
// 2.
var alertTime = record.TimeRecorded;
if (alertTime.HasValue)
{
var timeInUtc = TimeZoneInfo.ConvertTimeToUtc(alertTime.Value);
string alertTimeToLocalTime = timeInUtc.ToLocalTime().ToString("hh:mm tt");
}
//alertTimeToLocalTime is still in UTC time here
// 3.
if (alertTime.HasValue)
{
var localTime = TimeZoneInfo.ConvertTimeFromUtc(timeInUtc, TimeZoneInfo.Local);
string alertTimeToLocalTime = localTime.ToString("hh:mm tt");
}
None of these have managed to convert the alertTime to local time.
Am I missing something?
EDIT
//4. Another approach I had already tried which didn't work as well
var alertTime = DateTime.SpecifyKind(record.TimeRecorded.GetValueOrDefault(), DateTimeKind.Utc);
alertTimeToLocalTime = alertTime.ToLocalTime().ToString("hh:mm tt");
You said:
... from UTC time to the user's local time ...
Nothing in ASP.Net will tell you the user's local time zone. Calling ToLocalTime will convert from UTC to the server's time zone (unless the .Kind is already DateTimeKind.Local).
In many cases, the best practice of setting the server's time zone to UTC will mean that you will see no change with ToLocalTime or ToUniversalTime, other than the kind. And since the server's time zone is irrelevant in most cases, this is not the correct approach.
Instead, you either need to know the user's time zone through some other mechanism (such as them selecting it in your application) so you can use the TimeZoneInfo.ConvertTime (or Noda Time) to convert server-side, or you need to send UTC time down to the client and do the utc-to-local in JavaScript (since the browser is running in the user's time zone).
In general, any use of "local time" in a server application (such as ASP.NET) should be avoided. This includes ToLocalTime, ToUniversalTime, DateTimeKind.Local, TimeZoneInfo.Local, DateTime.Now, and a few other miscellaneous things.
It's because your DateTime's Kind is either Local or Unspecified. See the documentation for ToLocalTime():
Starting with the .NET Framework version 2.0, the value returned by the ToLocalTime method is determined by the Kind property of the current DateTime object. The following table describes the possible results.
Utc - This instance of DateTime is converted to local time.
Local - No conversion is performed.
Unspecified - This instance of DateTime is assumed to be a UTC time, and the conversion is performed as if Kind were Utc.
You can use the SpecifyKind method to set the Kind prior to doing the conversion.
I want to convert my time to universal time when I store date time in database and convert back to system time when I retrieve from the database.
Both of them I have done it success fully by creating functions ConvertToLocalTime()
and ConvertToUniversalTime().
The code for convert to local time is given below:
public void ConvertToLocalTime()
{
string szTimezoneinfoid = TimeZoneInfo.Local.Id.ToString();
TimeZoneInfo tzInfo = TimeZoneInfo.FindSystemTimeZoneById(szTimezoneinfoid);
this.m_dtCreatedDate = TimeZoneInfo.ConvertTimeFromUtc(m_dtCreatedDate, tzInfo);
}
When I call a function Shipment.ConvertToLocalTime() it changes the shipment created date to local time till this it works fine.
Now if I call the Shipment.ConvertToLocalTime() again then it consider the local time again as UTC and convert it to local time.
Is there any way to block the conversion to local time if it is already in local time?
Does there any way that we can get the time zone of the datetime?
The result of TimeZoneInfo.ConvertTimeFromUtc is a DateTime with a Kind of Unspecified, unless the time zone itself is UTC.
When you pass that result into TimeZoneInfo.ConvertTimeFromUtc, it will assume you understand it to be UTC DateTime - otherwise you wouldn't be calling ConvertTimeFromUtc...
Basically, DateTime.Kind is a hack to try to work around the problem that DateTime tries to represent too many different things. Your method starts with potentially ambiguous data, and ends up with ambiguous data... which doesn't bode well.
Either you could just make sure you always know what you're doing, and avoid calling your method with its own result, or you could consider using Noda Time, my alternative .NET date/time API which avoids this sort of thing by having different data types to represent different kinds of data.
I'm not sure exactly what's going wrong in your example, but if you simply want to get a date/time you know to be UTC from the database and convert it to local time, you can do the following:
var dbTime = //whatever, from database.
var utcTime = DateTime.SpecifyKind(dbTime, DateTimeKind.Utc);
var localTime = utcTime.ToLocalTime();
In my own project, I check dbTime.Kind != DateTimeKind.Local first, jut in case my data reader has decided to start performing the conversion for me.
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 all my dates in UTC format in my database. I ask the user for their timezone and I want to use their time zone plus what I am guessing is the server time to figure out the UTC for them.
Once I have that I want to do a search to see what the range is in the database using their newly converted UTC date.
But I always get this exception.
System.ArgumentException was unhandled by user code
Message="The conversion could not be completed because the
supplied DateTime did not have the Kind property set correctly.
For example, when the Kind property is DateTimeKind.Local,
the source time zone must be TimeZoneInfo.Local.
Parameter name: sourceTimeZone"
I don't know why I am getting this.
I tried 2 ways
TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById(id);
// I also tried DateTime.UtcNow
DateTime now = DateTime.SpecifyKind(DateTime.Now, DateTimeKind.Local);
var utc = TimeZoneInfo.ConvertTimeToUtc(now , zone );
This failed so I tried
DateTime now = DateTime.SpecifyKind(DateTime.Now, DateTimeKind.Local);
var utc = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(now,
ZoneId, TimeZoneInfo.Utc.Id);
This also failed with the same error. What am I doing wrong?
Edit Would this work?
DateTime localServerTime = DateTime.SpecifyKind(DateTime.Now, DateTimeKind.Local);
TimeZoneInfo info = TimeZoneInfo.FindSystemTimeZoneById(id);
var usersTime = TimeZoneInfo.ConvertTime(localServerTime, info);
var utc = TimeZoneInfo.ConvertTimeToUtc(usersTime, userInfo);
Edit 2 # Jon Skeet
Yes, I was just thinking about that I might not even need to do all this. Time stuff confuses me right now so thats why the post may not be as clear as it should be. I never know what the heck DateTime.Now is getting (I tried to change my Timezone to another timezone and it kept getting my local time).
This is what I wanted to achieve: User comes to the site, adds some alert and it gets saved as utc (prior it was DateTime.Now, then someone suggested to store everything UTC).
So before a user would come to my site and depending where my hosting server was it could be like on the next day. So if the alert was said to be shown on August 30th (their time) but with the time difference of the server they could come on August 29th and the alert would be shown.
So I wanted to deal with that. So now I am not sure should I just store their local time then use this offset stuff? Or just store UTC time. With just storing UTC time it still might be wrong since the user still probably would be thinking in local time and I am not sure how UTC really works. It still could end up in a difference of time.
Edit3
var info = TimeZoneInfo.FindSystemTimeZoneById(id)
DateTimeOffset usersTime = TimeZoneInfo.ConvertTime(DataBaseUTCDate,
TimeZoneInfo.Utc, info);
You need to set the Kind to Unspecified, like this:
DateTime now = DateTime.SpecifyKind(DateTime.Now, DateTimeKind.Unspecified);
var utc = TimeZoneInfo.ConvertTimeToUtc(now , zone);
DateTimeKind.Local means the in local time zone, and not any other time zone. That's why you were getting the error.
The DateTime structure supports only two timezones:
The local timezone the machine is running in.
and UTC.
Have a look at the DateTimeOffset structure.
var info = TimeZoneInfo.FindSystemTimeZoneById("Tokyo Standard Time");
DateTimeOffset localServerTime = DateTimeOffset.Now;
DateTimeOffset usersTime = TimeZoneInfo.ConvertTime(localServerTime, info);
DateTimeOffset utc = localServerTime.ToUniversalTime();
Console.WriteLine("Local Time: {0}", localServerTime);
Console.WriteLine("User's Time: {0}", usersTime);
Console.WriteLine("UTC: {0}", utc);
Output:
Local Time: 30.08.2009 20:48:17 +02:00
User's Time: 31.08.2009 03:48:17 +09:00
UTC: 30.08.2009 18:48:17 +00:00
Everyone else's answer seems overly complex. I had a specific requirement and this worked fine for me:
void Main()
{
var startDate = DateTime.Today;
var StartDateUtc = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(DateTime.SpecifyKind(startDate.Date, DateTimeKind.Unspecified), "Eastern Standard Time", "UTC");
startDate.Dump();
StartDateUtc.Dump();
}
Which outputs (from linqpad) what I expected:
12/20/2013 12:00:00 AM
12/20/2013 5:00:00 AM
Props to Slaks for the Unspecified kind tip. That's what I was missing. But all the talk about there being only two kinds of dates (local and UTC) just muddled the issue for me.
FYI -- the machine I ran this on was in Central Time Zone and DST was not in effect.
As dtb says, you should use DateTimeOffset if you want to store a date/time with a specific time zone.
However, it's not at all clear from your post that you really need to. You only give examples using DateTime.Now and you say you're guessing that you're using the server time. What time do you actually want? If you just want the current time in UTC, use DateTime.UtcNow or DateTimeOffset.UtcNow. You don't need to know the time zone to know the current UTC time, precisely because it's universal.
If you're getting a date/time from the user in some other way, please give more information - that way we'll be able to work out what you need to do. Otherwise we're just guessing.
UTC is just a time zone that everyone agreed on as the standard time zone. Specifically, it's a time zone that contains London, England. EDIT: Note that it's not the exact same time zone; for example, UTC has no DST. (Thanks, Jon Skeet)
The only special thing about UTC is that it's much easier to use in .Net than any other time zone (DateTime.UtcNow, DateTime.ToUniversalTime, and other members).
Therefore, as others have mentioned, the best thing for you to do is store all dates in UTC within your database, then convert to the user's local time (by writing TimeZoneInfo.ConvertTime(time, usersTimeZone) before displaying.
If you want to be fancier, you can geolocate your users' IP addresses to automatically guess their time zones.
We are developing a C# application for a web-service client. This will run on Windows XP PC's.
One of the fields returned by the web service is a DateTime field. The server returns a field in GMT format i.e. with a "Z" at the end.
However, we found that .NET seems to do some kind of implicit conversion and the time was always 12 hours out.
The following code sample resolves this to some extent in that the 12 hour difference has gone but it makes no allowance for NZ daylight saving.
CultureInfo ci = new CultureInfo("en-NZ");
string date = "Web service date".ToString("R", ci);
DateTime convertedDate = DateTime.Parse(date);
As per this date site:
UTC/GMT Offset
Standard time zone: UTC/GMT +12 hours
Daylight saving time: +1 hour
Current time zone offset: UTC/GMT +13 hours
How do we adjust for the extra hour? Can this be done programmatically or is this some kind of setting on the PC's?
For strings such as 2012-09-19 01:27:30.000, DateTime.Parse cannot tell what time zone the date and time are from.
DateTime has a Kind property, which can have one of three time zone options:
Unspecified
Local
Utc
NOTE If you are wishing to represent a date/time other than UTC or your local time zone, then you should use DateTimeOffset.
So for the code in your question:
DateTime convertedDate = DateTime.Parse(dateStr);
var kind = convertedDate.Kind; // will equal DateTimeKind.Unspecified
You say you know what kind it is, so tell it.
DateTime convertedDate = DateTime.SpecifyKind(
DateTime.Parse(dateStr),
DateTimeKind.Utc);
var kind = convertedDate.Kind; // will equal DateTimeKind.Utc
Now, once the system knows its in UTC time, you can just call ToLocalTime:
DateTime dt = convertedDate.ToLocalTime();
This will give you the result you require.
I'd look into using the System.TimeZoneInfo class if you are in .NET 3.5. See http://msdn.microsoft.com/en-us/library/system.timezoneinfo.aspx. This should take into account the daylight savings changes correctly.
// Coordinated Universal Time string from
// DateTime.Now.ToUniversalTime().ToString("u");
string date = "2009-02-25 16:13:00Z";
// Local .NET timeZone.
DateTime localDateTime = DateTime.Parse(date);
DateTime utcDateTime = localDateTime.ToUniversalTime();
// ID from:
// "HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Time Zone"
// See http://msdn.microsoft.com/en-us/library/system.timezoneinfo.id.aspx
string nzTimeZoneKey = "New Zealand Standard Time";
TimeZoneInfo nzTimeZone = TimeZoneInfo.FindSystemTimeZoneById(nzTimeZoneKey);
DateTime nzDateTime = TimeZoneInfo.ConvertTimeFromUtc(utcDateTime, nzTimeZone);
TimeZone.CurrentTimeZone.ToLocalTime(date);
DateTime objects have the Kind of Unspecified by default, which for the purposes of ToLocalTime is assumed to be UTC.
To get the local time of an Unspecified DateTime object, you therefore just need to do this:
convertedDate.ToLocalTime();
The step of changing the Kind of the DateTime from Unspecified to UTC is unnecessary. Unspecified is assumed to be UTC for the purposes of ToLocalTime: http://msdn.microsoft.com/en-us/library/system.datetime.tolocaltime.aspx
I know this is an older question, but I ran into a similar situation, and I wanted to share what I had found for future searchers, possibly including myself :).
DateTime.Parse() can be tricky -- see here for example.
If the DateTime is coming from a Web service or some other source with a known format, you might want to consider something like
DateTime.ParseExact(dateString,
"MM/dd/yyyy HH:mm:ss",
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal)
or, even better,
DateTime.TryParseExact(...)
The AssumeUniversal flag tells the parser that the date/time is already UTC; the combination of AssumeUniversal and AdjustToUniversal tells it not to convert the result to "local" time, which it will try to do by default. (I personally try to deal exclusively with UTC in the business / application / service layer(s) anyway. But bypassing the conversion to local time also speeds things up -- by 50% or more in my tests, see below.)
Here's what we were doing before:
DateTime.Parse(dateString, new CultureInfo("en-US"))
We had profiled the app and found that the DateTime.Parse represented a significant percentage of CPU usage. (Incidentally, the CultureInfo constructor was not a significant contributor to CPU usage.)
So I set up a console app to parse a date/time string 10000 times in a variety of ways. Bottom line:
Parse() 10 sec
ParseExact() (converting to local) 20-45 ms
ParseExact() (not converting to local) 10-15 ms
... and yes, the results for Parse() are in seconds, whereas the others are in milliseconds.
I'd just like to add a general note of caution.
If all you are doing is getting the current time from the computer's internal clock to put a date/time on the display or a report, then all is well. But if you are saving the date/time information for later reference or are computing date/times, beware!
Let's say you determine that a cruise ship arrived in Honolulu on 20 Dec 2007 at 15:00 UTC. And you want to know what local time that was.
1. There are probably at least three 'locals' involved. Local may mean Honolulu, or it may mean where your computer is located, or it may mean the location where your customer is located.
2. If you use the built-in functions to do the conversion, it will probably be wrong. This is because daylight savings time is (probably) currently in effect on your computer, but was NOT in effect in December. But Windows does not know this... all it has is one flag to determine if daylight savings time is currently in effect. And if it is currently in effect, then it will happily add an hour even to a date in December.
3. Daylight savings time is implemented differently (or not at all) in various political subdivisions. Don't think that just because your country changes on a specific date, that other countries will too.
#TimeZoneInfo.ConvertTimeFromUtc(timeUtc, TimeZoneInfo.Local)
Don't forget if you already have a DateTime object and are not sure if it's UTC or Local, it's easy enough to use the methods on the object directly:
DateTime convertedDate = DateTime.Parse(date);
DateTime localDate = convertedDate.ToLocalTime();
How do we adjust for the extra hour?
Unless specified .net will use the local pc settings. I'd have a read of: http://msdn.microsoft.com/en-us/library/system.globalization.daylighttime.aspx
By the looks the code might look something like:
DaylightTime daylight = TimeZone.CurrentTimeZone.GetDaylightChanges( year );
And as mentioned above double check what timezone setting your server is on. There are articles on the net for how to safely affect the changes in IIS.
In answer to Dana's suggestion:
The code sample now looks like:
string date = "Web service date"..ToString("R", ci);
DateTime convertedDate = DateTime.Parse(date);
DateTime dt = TimeZone.CurrentTimeZone.ToLocalTime(convertedDate);
The original date was 20/08/08; the kind was UTC.
Both "convertedDate" and "dt" are the same:
21/08/08 10:00:26; the kind was local
I had the problem with it being in a data set being pushed across the wire (webservice to client) that it would automatically change because the DataColumn's DateType field was set to local. Make sure you check what the DateType is if your pushing DataSets across.
If you don't want it to change, set it to Unspecified
I came across this question as I was having a problem with the UTC dates you get back through the twitter API (created_at field on a status); I need to convert them to DateTime. None of the answers/ code samples in the answers on this page were sufficient to stop me getting a "String was not recognized as a valid DateTime" error (but it's the closest I have got to finding the correct answer on SO)
Posting this link here in case this helps someone else - the answer I needed was found on this blog post: http://www.wduffy.co.uk/blog/parsing-dates-when-aspnets-datetimeparse-doesnt-work/ - basically use DateTime.ParseExact with a format string instead of DateTime.Parse
This code block uses universal time to convert current DateTime object then converts it back to local DateTime. Works perfect for me I hope it helps!
CreatedDate.ToUniversalTime().ToLocalTime();