CODEWITHSUNDEEP
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Peyman Zehtab-Fard
Peyman Zehtab-Fard

Reputation: 85

DateTime and duration add

Consider the following code:

void main() {

  var duration = new Duration(days : 1);
  print ("duration " + duration.toString());

  var d1 = new DateTime(2014, 10, 26);
  print ("d1 " + d1.toString());

  d1 = d1.add(duration);
  print ("d1 + duration " + d1.toString());


  var d2 = new DateTime(2014, 10, 20);
  print ("d2 " + d2.toString());

  d2 = d2.add(duration);
  print ("d2 + duration " + d2.toString());

}

and the output:

duration 24:00:00.000000
d1 2014-10-26 00:00:00.000
d1 + duration 2014-10-26 23:00:00.000
d2 2014-10-20 00:00:00.000
d2 + duration 2014-10-21 00:00:00.000

Why does October 20 and 26 behave differently. I have checked the same code for every day of the year and every year has one day in which the date + 1 day equals the same date. Every year the date seems to be in October between 25/10 and 30/10.

Is this a bug or have I missed something?

Regards Peyman

Upvotes: 5

Views: 9315

Answers (3)

JackMag
JackMag

Reputation: 53

Just to expand on Александр Бабич answer - you don't have to care about the range of the days in the month when creating the DateTime in constructor. For example

DateTime(2014, 9, 57)

will correctly return 2014-10-27 and will not introduce any daylight saving shifts. Negative numbers work as well, but are offset by 1, because 0 also works e.g.

DateTime(2014, 9, 0) DateTime(2014, 9, -1)

will yield 2014-08-31 and 2014-08-30 respectively

Upvotes: 0

Олександр Бабіч
Олександр Бабіч

Reputation: 1452

As per Günter Zöchbauer answer - it is due daylight saving time.

To properly add day you may use the following:

var d1 = new DateTime(2014, 10, 26);
var d1 = new DateTime(d1.year, d1.month, d1.day + 1);

Upvotes: 8

Günter Zöchbauer
Günter Zöchbauer

Reputation: 657476

I guess the Oct 26. (and the other days between 25/10 and 30/10 is due to daylight saving period ending. The difference of 1h (23:00:00.000) indicates this as the cause.

Upvotes: 4

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