Determine if a time is daylight savings

[Dustin Norlander]

I want to find out whether a time is in dst for Location "America/New_York".

Looking at the code, this is what I want, but this func is not visible:

_, _, isDST, _, _ := nycLocation.lookup(mytime.Unix())

is there any way to do this?

Thanks much,

Dustin

[Ian Lance Taylor]

Doesn't look like it. Please file an issue for this. Thanks.

Ian

[Russ Cox]

If you specifically care about America/New_York, you can check whether Zone() returns "EST" or "EDT".

Russ

[Tor Langballe]

What if you created a location using:

location := FixedZone("FixedNew_York", -5)

and set it to the same time (using date/hour, minute, seconds) and also with the normal America/New_York location.

If there is a time-difference between the two times, it's daylight savings.

tor 

[Tor Langballe]

Actually, my original post only works for a known location.

How about this (semi real code):

_, timeOffset := time.Zone() //with time already in correct myLocation

_, winterOffset := time.Time(1, jan, 2013, 0, 0, 0).In(myLocation).Zone()

_, summerOffset := time.Time(1, july, 2013, 0, 0, 0).In(myLocation).Zone()

if winterOffset != summerOffset { // the location has daylight saving

  if timeOffset != winterOffset {

    fmt.Println("Daylight Saving")

  }

}

Can be made better by using year of time you are checking.

On Wednesday, February 13, 2013 12:29:41 AM UTC+1, Dustin Norlander wrote:

[Kyle Lemons]

This assumes that January is not in daylight saving time and that july is.  That might seem like a safe assumption now, but so does assuming that a week has 7 days and that a day has 24 hours.  (Time is hard)

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[Kyle Lemons]

On Wed, Feb 13, 2013 at 8:25 AM, Kyle Lemons <kev...@google.com> wrote:

This assumes that January is not in daylight saving time and that july is.

er, the reverse, but you get the idea.

[Dustin Norlander]

Using Russ's suggestion seems to work:

var USEast, err = time.LoadLocation("America/New_York")

func IsEasternDayLight(time time.Time) bool {

    t := time.In(USEast)

    zone, _ := t.Zone()

    if zone == "EDT" {

        return true

    }

    return false;

}

Thanks!

[Tor Langballe]

Kyle wrote: This assumes that January is not in daylight saving time and that july is.

-Good point, I guess that's the case in the southern hemisphere. 

[Dan Kortschak]

That's exactly how it is here. Time is hard.

[Peter Kleiweg]

Op woensdag 13 februari 2013 15:17:40 UTC+1 schreef Tor Langballe het volgende:

Actually, my original post only works for a known location.

How about this (semi real code):

_, timeOffset := time.Zone() //with time already in correct myLocation

_, winterOffset := time.Time(1, jan, 2013, 0, 0, 0).In(myLocation).Zone()

_, summerOffset := time.Time(1, july, 2013, 0, 0, 0).In(myLocation).Zone()

if winterOffset != summerOffset { // the location has daylight saving

  if timeOffset != winterOffset {

    fmt.Println("Daylight Saving")

  }

}

Full working example: http://play.golang.org/p/JvHUk1NjO5

(Well, it works at home, not on the playground)

[Tor Langballe]

Nice, good check for winterOffset > summerOffset.