How can I change only the time in my DateTime variable "s"?
DateTime s = some datetime;
399
votes
28 Answers
655
votes
You can't change a DateTime value - it's immutable. However, you can change the variable to have a new value. The easiest way of doing that to change just the time is to create a TimeSpan with the relevant time, and use the DateTime.Date property:
DateTime s = ...;
TimeSpan ts = new TimeSpan(10, 30, 0);
s = s.Date + ts;
s will now be the same date, but at 10.30am.
Note that DateTime disregards daylight saving time transitions, representing "naive" Gregorian time in both directions (see Remarks section in the DateTime docs). The only exceptions are .Now and .Today: they retrieve current system time which reflects these events as they occur.
This is the kind of thing which motivated me to start the Noda Time project, which is now production-ready. Its ZonedDateTime type is made "aware" by linking it to a tz database entry.
118
votes
Alright I'm diving in with my suggestion, an extension method:
public static DateTime ChangeTime(this DateTime dateTime, int hours, int minutes, int seconds, int milliseconds)
{
return new DateTime(
dateTime.Year,
dateTime.Month,
dateTime.Day,
hours,
minutes,
seconds,
milliseconds,
dateTime.Kind);
}
Then call:
DateTime myDate = DateTime.Now.ChangeTime(10,10,10,0);
It's important to note that this extension returns a new date object, so you can't do this:
DateTime myDate = DateTime.Now;
myDate.ChangeTime(10,10,10,0);
But you can do this:
DateTime myDate = DateTime.Now;
myDate = myDate.ChangeTime(10,10,10,0);
73
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45
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22
votes
DateTime is an immutable type, so you can't change it.
However, you can create a new DateTime instance based on your previous instance. In your case, it sounds like you need the Date property, and you can then add a TimeSpan that represents the time of day.
Something like this:
var newDt = s.Date + TimeSpan.FromHours(2);
19
votes
If you already have the time stored in another DateTime object you can use the Add method.
DateTime dateToUse = DateTime.Now();
DateTime timeToUse = new DateTime(2012, 2, 4, 10, 15, 30); //10:15:30 AM
DateTime dateWithRightTime = dateToUse.Date.Add(timeToUse.TimeOfDay);
The TimeOfDay property is a TimeSpan object and can be passed to the Add method. And since we use the Date property of the dateToUse variable we get just the date and add the time span.
18
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11
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9
votes
You can assign an initial value to a new DateTime value in many different ways:
- Extension Method
Extension method DateTime
public static DateTime ChangeTime(this DateTime dateTime, int hours, int minutes, int seconds = default, int milliseconds = default)
{
return new DateTime(dateTime.Year, dateTime.Month, dateTime.Day, hours, minutes, seconds, milliseconds, dateTime.Kind);
}
then using ChangeTime:
DateTime datetime = DateTime.Now; //Your DateTime
datetime = datetime.ChangeTime(12, 20, 10);
using the Add methods
DateTime datetime = DateTime.Now; //Your DateTime datetime = datetime.Date.AddHours(12).AddMinutes(20).AddSeconds(10);using the Timespan
DateTime datetime = DateTime.Now; //Your DateTime datetime = datetime.Date.Add(new TimeSpan(12, 20, 10));using initial value
DateTime datetime = DateTime.Now; datetime = new DateTime(datetime.Year, datetime.Month, datetime.Day, 12, 20, 10);
8
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4
votes
Since DateTime is immutable, a new instance has to be created when a date component needs to be changed. Unfortunately, there is no built-in functionality to set individual components of a DateTime instance.
Using the following extension methods
public static DateTime SetPart(this DateTime dateTime, int? year, int? month, int? day, int? hour, int? minute, int? second)
{
return new DateTime(
year ?? dateTime.Year,
month ?? dateTime.Month,
day ?? dateTime.Day,
hour ?? dateTime.Hour,
minute ?? dateTime.Minute,
second ?? dateTime.Second
);
}
public static DateTime SetYear(this DateTime dateTime, int year)
{
return dateTime.SetPart(year, null, null, null, null, null);
}
public static DateTime SetMonth(this DateTime dateTime, int month)
{
return dateTime.SetPart(null, month, null, null, null, null);
}
public static DateTime SetDay(this DateTime dateTime, int day)
{
return dateTime.SetPart(null, null, day, null, null, null);
}
public static DateTime SetHour(this DateTime dateTime, int hour)
{
return dateTime.SetPart(null, null, null, hour, null, null);
}
public static DateTime SetMinute(this DateTime dateTime, int minute)
{
return dateTime.SetPart(null, null, null, null, minute, null);
}
public static DateTime SetSecond(this DateTime dateTime, int second)
{
return dateTime.SetPart(null, null, null, null, null, second);
}
you can set individual DateTime components like
var now = DateTime.Now;
now.SetSecond(0);
4
votes
Adding .Date to your date sets it to midnight (00:00).
MyDate.Date
Note The equivavalent SQL is CONVERT(DATETIME, CONVERT(DATE, @MyDate))
What makes this method so good is that it's both quick to type and easy to read. A bonus is that there is no conversion from strings.
I.e. To set today's date to 23:30, use:
DateTime.Now.Date.AddHours(23).AddMinutes(30)
You can of course replace DateTime.Now or MyDate with any date of your choice.
3
votes
3
votes
In fact, you can't change the time once it's created. But you can create it easily with many constructors: https://docs.microsoft.com/en-us/dotnet/api/system.datetime.-ctor?view=netframework-4.7.2
For example, if you want to create a DateTime changing Seconds, you can just do this:
DateTime now = DateTime.Now;
DateTime secondschanged = new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute, yourseconds);
2
votes
When you construct your DateTime object, use a constructor that allows you to specify time:
var myDateTime = new DateTime(2000, 01, 01, 13, 37, 42); // 2000-01-01 13:37:42
If you already have a DateTime object and wish to change the time, uou can add minutes, hours or seconds to your DateTime using simple methods:
var myDateTime = new DateTime(2000, 01, 01); // 2000-01-01 00:00:00
myDateTime = myDateTime.AddHours(13); // 2000-01-01 13:00:00
myDateTime = myDateTime.AddMinutes(37); // 2000-01-01 13:37:00
myDateTime = myDateTime.AddSecounds(42); // 2000-01-01 13:37:42
Notice how we have to "save" the result from each method call to the myDateTime variable. This is because the DateTime is immutable, and its methods simply create new instances with the extra hours/minutes/seconds added.
If you need to add both hours and minutes (and/or seconds) and the same time, you can simplify the code by adding a TimeSpan to the original DateTime instead:
var myDateTime = new DateTime(2000, 01, 01); // 2000-01-01 00:00:00
myDateTime += new TimeSpan(13, 37, 42); // 2000-01-01 13:37:42
If you want to set absolute hours/minues/seconds, rather than adding to the existing values, you can use the aforementioned DateTime constructor, and reuse values for year/month/day from earlier:
myDateTime = new DateTime(myDateTime.Year, myDateTime.Month, myDateTime.Day,
20, 33, 19) // 2000-01-01 20:33:19
2
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2
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1
votes
Here is a method you could use to do it for you, use it like this
DateTime newDataTime = ChangeDateTimePart(oldDateTime, DateTimePart.Seconds, 0);
Here is the method, there is probably a better way, but I just whipped this up:
public enum DateTimePart { Years, Months, Days, Hours, Minutes, Seconds };
public DateTime ChangeDateTimePart(DateTime dt, DateTimePart part, int newValue)
{
return new DateTime(
part == DateTimePart.Years ? newValue : dt.Year,
part == DateTimePart.Months ? newValue : dt.Month,
part == DateTimePart.Days ? newValue : dt.Day,
part == DateTimePart.Hours ? newValue : dt.Hour,
part == DateTimePart.Minutes ? newValue : dt.Minute,
part == DateTimePart.Seconds ? newValue : dt.Second
);
}
1
votes
I have just come across this post because I had a similar issue whereby I wanted to set the time for an Entity Framework object in MVC that gets the date from a view (datepicker) so the time component is 00:00:00 but I need it to be the current time. Based on the answers in this post I came up with:
myEntity.FromDate += DateTime.Now.TimeOfDay;
1
votes
//The fastest way to copy time
DateTime justDate = new DateTime(2011, 1, 1); // 1/1/2011 12:00:00AM the date you will be adding time to, time ticks = 0
DateTime timeSource = new DateTime(1999, 2, 4, 10, 15, 30); // 2/4/1999 10:15:30AM - time tick = x
justDate = new DateTime(justDate.Date.Ticks + timeSource.TimeOfDay.Ticks);
Console.WriteLine(justDate); // 1/1/2011 10:15:30AM
Console.Read();
0
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0
votes
Using an extencion to DateTime:
public enum eTimeFragment
{
hours,
minutes,
seconds,
milliseconds
}
public static DateTime ClearTimeFrom(this DateTime dateToClear, eTimeFragment etf)
{
DateTime dtRet = dateToClear;
switch (etf)
{
case eTimeFragment.hours:
dtRet = dateToClear.Date;
break;
case eTimeFragment.minutes:
dtRet = dateToClear.AddMinutes(dateToClear.Minute * -1);
dtRet = dtRet.ClearTimeFrom(eTimeFragment.seconds);
break;
case eTimeFragment.seconds:
dtRet = dateToClear.AddSeconds(dateToClear.Second * -1);
dtRet = dtRet.ClearTimeFrom(eTimeFragment.milliseconds);
break;
case eTimeFragment.milliseconds:
dtRet = dateToClear.AddMilliseconds(dateToClear.Millisecond * -1);
break;
}
return dtRet;
}
Use like this:
Console.WriteLine (DateTime.Now.ClearTimeFrom(eTimeFragment.hours))
this has to return: 2016-06-06 00:00:00.000
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