如何将一个切片的内容复制到另一个切片中

Question

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.

Answer 1

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

You can use append to create the slice and copy the elements in a single statement, but the code is not as obvious as using copy.

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

Run it on the playground .

Answer 2

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)
}