How can I extract the value of my current local time offset?

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?

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.

> 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

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))
}