Adding a TimeSpan to a given DateTime
Solution 1
DateTime values are immutable. The Add method returns a new DateTime value with the TimeSpan added.
This works:
Console.WriteLine("A day after the day: " + date.Add(t).ToString());
Solution 2
You need to change a line:
date = date.Add(t);
Solution 3
dtb is right about DateTime
being immutable. Think of it this way: a DateTime
is a value type, which puts it in the same category as int
or double
. Instances of these structures cannot be modified; they can only be evaluated and copied.
Consider this code:
int i = 4;
i + 2; // does not compile, but what if it did?
// would i become 6? clearly not --
// i + 2 expresses a NEW value, which can
// be copied somewhere
i = i + 2; // there we go -- that's better
This is analogous to:
DateTime d = DateTime.Now;
TimeSpan t = TimeSpan.FromDays(1.0);
d.Add(t); // compiles (because AddDays is a function),
// but is really the same as i + 2 above
d = d.Add(t); // that's better
By the way, one thing that might help make this clearer is realizing that the above line, d = d.Add(t)
, is the same as d = d + t
. And you wouldn't write d + t
on its own line, just like you wouldn't write i + 2
on its own line.
Solution 4
A DateTime is immutable, but the Add and Subtract functions return new DateTimes for you to use.
DateTime tomorrow = DateTime.Now.AddDays(1);
Solution 5
What is wrong with just doing date = date.AddDays(1)
?
Amokrane Chentir
Updated on June 14, 2020Comments
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Amokrane Chentir almost 4 years
I just want to add 1 day to a
DateTime
. So I wrote:DateTime date = new DateTime(2010, 4, 29, 10, 25, 00); TimeSpan t = new TimeSpan(1, 0, 0, 0); date.Add(t); Console.WriteLine("A day after the day: " + date.ToString());
I thought the result would be:
2010 04 30- 10:25:00
but I'm still getting the initial date.What's wrong?
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BlueRaja - Danny Pflughoeft about 14 yearsStill has the same problem - DateTimes are immutable :)
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Amokrane Chentir about 14 yearsMy Delta Time is a TimeSpan. So I can't use AddDays which takes an integer as a parameter.
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Klaus Byskov Pedersen about 14 years@Amokrane, if your delta is a timespan I think you should rephrase the question title.
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Anthony Pegram about 14 years@Amokrane, the larger point remains. .Add(...) returns a new date, it doesn't modify the existing date. You still would use
date = date.Add(...
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KyleMit about 6 yearsThe real answer is always in the comments