DateTime and duration add

Question

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

Answer 1

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);

Answer 2

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.