如果切片的大小超过数组的大小，切片的元素将存储在哪里？

Question

I create a slice from the array OrgArray as follows

orgArray:=[3] string{"00","01","02"}
s := orgArray[:2]
s = append(s,"03")
s = append(s,"04")

Where 's' is my slice I built up on the array 'orgArray'

If I print the size of the s and orgArray

fmt.Println(s) //[00 01 03 04]
fmt.Println(len(s),cap(s)) //4 6
fmt.Println(len(orgArray),cap(orgArray)) //3 3

len(s) is 4 but len(orgArray) is only 3 why?

Where is the extra elements of slice is storing while appending?

Answer 1

The Go Programming Language Specification

Appending to and copying slices

If the capacity of s is not large enough to fit the additional values, append allocates a new, sufficiently large underlying array that fits both the existing slice elements and the additional values. Otherwise, append re-uses the underlying array.

For additional details on how the append built-in function works, read this blog post:

Arrays, slices (and strings): The mechanics of 'append'

Also, see this StackOverflow answer, which illustrates the reallocation capacity calculation:

append complexity

For example,

package main

import "fmt"

func main() {
    orgArray := [3]string{"00", "01", "02"}
    fmt.Println("orgArray:", &orgArray[0], len(orgArray), orgArray)
    s := orgArray[:2]
    fmt.Println("       s:", &s[0], len(s), cap(s), s)
    s = append(s, "03")
    fmt.Println("       s:", &s[0], len(s), cap(s), s)
    s = append(s, "04")
    fmt.Println("       s:", &s[0], len(s), cap(s), s)
    fmt.Println("orgArray:", &orgArray[0], len(orgArray), orgArray)
}

Output:

orgArray: 0x1052f2c0 3 [00 01 02]
       s: 0x1052f2c0 2 3 [00 01]
       s: 0x1052f2c0 3 3 [00 01 03]
       s: 0x1051a120 4 6 [00 01 03 04]
orgArray: 0x1052f2c0 3 [00 01 03]