continue executing loop when exception happens

Question

During first execution of the loop in the code snippet,an exception throws.my question is how to continue executing next iteration of the loop when panic happens.like try catch mechanism in java,the loop will continue executing next iteration of the loop.

package main

import (
        "fmt"
)

func main() {
        var arr []int = []int{5, 6, 7, 8, 9}
        fmt.Println(arr)
        for i := 6; i < 10; i++ {
                defer func() {
                        fmt.Println("aaa")
                        if err := recover(); err != nil {
                                fmt.Printf("error is %v\n", err)
                        }
                }()
                arr[i] = i

        }

}

1. The execution wont be in the loop after defer execution., 2. You need to set atleast 10 as the capacity of slice arr — Sarath Sadasivan Pillai
– Sarath Sadasivan Pillai, Commented May 4, 2017 at 17:34
Panics are not exceptions. It is a common mistake for programmers used to other languages to treat them a such, but it doesn't work well at all! If you have a panic in Go, then this usually means you've made a programming mistake that needs to be corrected, rather than "handles" by "catching" the panic (like you tried to do here). — Martin Tournoij
– Martin Tournoij, Commented May 4, 2017 at 17:34
my question is how to continue executing next iteration of the loop when panic happens,thanks.like try catch mechanism in java,the loop will continue executing next iteration of the loop. — witrus
– witrus, Commented May 4, 2017 at 23:47

dave · Accepted Answer · 2017-05-04 16:27:42Z

4

The issue is that your slice has a length and capacity of 5,

https://play.golang.org/p/7wy91PTPum

and you are trying to add something to the 6th position.

You need to either set a fixed size that you know will hold everything you want to put into it:

var arr [10]int = [10]int{5, 6, 7, 8, 9}

https://play.golang.org/p/GSNDXGt1Jp

Or use append and change

arr[i] = i

to

arr = append(arr, i)

https://play.golang.org/p/kHNsFpcjVx

answered May 4, 2017 at 16:27

dave

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2 Comments

witrus Over a year ago

my question is how to continue executing next iteration of the loop when panic happens,thanks.like try catch mechanism in java,the loop will continue executing next iteration of the loop.

Martin Tournoij Over a year ago

Go is not Java @witrus. It doesn't really have such a mechanism. The way to deal with this is to make sure the panic doesn't happen, either with the suggestions in this answer, or by guarding the assignment with something like if i > len(arr) {... }.

Hepri · Accepted Answer · 2017-05-05 08:58:24Z

1

You could wrap all work inside some func, and call defer with recover inside it

package main

import (
        "fmt"
)

func doSmth(arr []int, idx int) {
    defer func() {
        if err := recover(); err != nil {
            fmt.Printf("error is %v\n", err)
        }
    }()
    arr[idx] = idx
}

func main() {
    var arr []int = []int{5, 6, 7, 8, 9}
    fmt.Println(arr)
    for i := 6; i < 10; i++ {
        doSmth(arr, i)
    }
}

answered May 5, 2017 at 8:58

Hepri

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