In Go, how can I extract the value of my current local time offset?

Question

I'm a Go newbie, and I'm struggling a bit trying to format and display some IBM mainframe TOD clock data. I want to format the data in both GMT and local time (as the default -- otherwise in the zone the user specifies).

For this, I need to get the value of the local time offset from GMT as a signed integer number of seconds.

In zoneinfo.go (which I confess I don't fully understand), I can see

// A zone represents a single time zone such as CEST or CET.
type zone struct {
    name   string // abbreviated name, "CET"
    offset int    // seconds east of UTC
    isDST  bool   // is this zone Daylight Savings Time?
}

but this is not, I think, exported, so this code doesn't work:

package main
import ( "time"; "fmt" )

func main() {
    l, _ := time.LoadLocation("Local")
    fmt.Printf("%v\n", l.zone.offset)
}

Is there a simple way to get this information?

Answer 1

You can use the Zone() method on the time type:

package main

import (
    "fmt"
    "time"
)

func main() {
    t := time.Now()
    zone, offset := t.Zone()
    fmt.Println(zone, offset)
}

Zone computes the time zone in effect at time t, returning the abbreviated name of the zone (such as "CET") and its offset in seconds east of UTC.

Answer 2

Package time

func (Time) Local

func (t Time) Local() Time

Local returns t with the location set to local time.

func (Time) Zone

func (t Time) Zone() (name string, offset int)

Zone computes the time zone in effect at time t, returning the abbreviated name of the zone (such as "CET") and its offset in seconds east of UTC.

type Location

type Location struct {
        // contains filtered or unexported fields
}

A Location maps time instants to the zone in use at that time. Typically, the Location represents the collection of time offsets in use in a geographical area, such as CEST and CET for central Europe.

var Local *Location = &localLoc

Local represents the system's local time zone.

var UTC *Location = &utcLoc

UTC represents Universal Coordinated Time (UTC).

func (Time) In

func (t Time) In(loc *Location) Time

In returns t with the location information set to loc.

In panics if loc is nil.

For example,

package main

import (
    "fmt"
    "time"
)

func main() {
    t := time.Now()

    // For a time t, offset in seconds east of UTC (GMT)
    _, offset := t.Local().Zone()
    fmt.Println(offset)

    // For a time t, format and display as UTC (GMT) and local times.
    fmt.Println(t.In(time.UTC))
    fmt.Println(t.In(time.Local))
}

Output:

-18000
2016-01-24 16:48:32.852638798 +0000 UTC
2016-01-24 11:48:32.852638798 -0500 EST

Answer 3

I don't think it makes sense to manually convert time to another TZ. Use time.Time.In function:

package main

import (
    "fmt"
    "time"
)

func printTime(t time.Time) {
    zone, offset := t.Zone()
    fmt.Println(t.Format(time.Kitchen), "Zone:", zone, "Offset UTC:", offset)
}

func main() {
    printTime(time.Now())
    printTime(time.Now().UTC())

    loc, _ := time.LoadLocation("America/New_York")
    printTime(time.Now().In(loc))
}