CODEWITHSUNDEEP
go
user51
user51

Reputation: 10153

how to copy contents of one slice to another slice in go

I'm doing below exercise in go.

Create a slice with four elements. Create a new slice and copy the third and fourth elements only into it.

I have return the below program

    package main

    import "fmt"

    func main() {
        var elements = make([]string, 4)
        elements[0] = "1"
        elements[1] = "2"
        elements[2] = "3"
        elements[3] = "4"
        fmt.Println(elements)

        var newElements = make([]string, 2)
        newElements = append(elements[:0], elements[:2]...)
        fmt.Println(newElements)
    }

output of my program is. But I want the newElements slice to be [3 4]-

[1 2 3 4]
[1 2]

What is wrong in my program.

Upvotes: 2

Views: 4862

Answers (2)

Thundercat
Thundercat

Reputation: 120941

Use the built-in copy function to copy elements from one slice to another.

var newElements = make([]string, 2)
copy(newElements, elements[2:])

Run it on the playground

Use slices.Clone to create the slice and copy the elements in a single statement:

newElements := slices.Clone(elements[2:])

Run it on the playground

In versions of Go before 1.21, use append to create the slice and copy the elements in a single statement:

newElements := append([]string(nil), elements[2:4]...)

Run it on the playground.

Upvotes: 13

nightfury1204
nightfury1204

Reputation: 4654

Problem is in the line newElements = append(elements[:0], elements[:2]...). Here elements[:2] means elements elements[0], elements[1]. That's why your output is [1,2]. For third and fourth elements use this elements[2:4].

package main

import "fmt"

func main() {
    var elements = make([]string, 4)
    elements[0] = "1"
    elements[1] = "2"
    elements[2] = "3"
    elements[3] = "4"
    fmt.Println(elements)

    var newElements = make([]string, 2)
    newElements = append(elements[:0], elements[2:4]...)
    fmt.Println(newElements)
}

Upvotes: 2

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