CODEWITHSUNDEEP
c#visual-studio-2010datetime
Sas Gabriel
Sas Gabriel

Reputation: 1556

DateTime.AddDays() not working as expected

I have this simple program:

        DateTime aux = new DateTime(2012, 6, 12, 12, 24, 0);
        DateTime aux2 = new DateTime(2012, 6, 12, 13, 24, 0);
        aux2.AddDays(1);

       Console.WriteLine((aux2 - aux).TotalHours.ToString());

        Console.ReadLine();

I debugged this and found aux2.AddDays(1); doesn't seem to work, what am I missing here? it should return 25 but the answer is one.

What is the problem?

also AddHours doesn't work, I guess that the others aren't working too.

Upvotes: 24

Views: 36833

Answers (3)

Neil Meyer
Neil Meyer

Reputation: 591

You are working with immutable functions.

The DateTime function is immutable, once you set variable equal to it, it cannot change, you can though set new variables equal to a working of the function. The AddDay function takes the variable you put into it, but it does not change the original variable, that remains immutable. So you need to set a new variable equall to the original variable + a day.

So all you really need to do is change

aux2.AddDays(1);

to

aux2 = aux2.Adddays(1);

and then the rest of your comparison functions should work

Upvotes: 1

Jodrell
Jodrell

Reputation: 35696

It does work but you don't do anything with the return value, try

aux2 = aux2.AddDays(1);

DateTimes share this facet of immutability with Strings.

EDIT

There is a little paragraph about it on MSDN

This method does not change the value of this DateTime. Instead, it returns a new DateTime whose value is the result of this operation.

Upvotes: 66

Zbigniew
Zbigniew

Reputation: 27584

DateTime.AddDays returns new DateTime that adds specified number of days. You need to assign it to your variable:

aux2 = aux2.AddDays(1);

Upvotes: 5

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