go-切片的追加
// The append built-in function appends elements to the end of a slice. If
// it has sufficient capacity, the destination is resliced to accommodate the
// new elements. If it does not, a new underlying array will be allocated.
// Append returns the updated slice. It is therefore necessary to store the
// result of append, often in the variable holding the slice itself:
// slice = append(slice, elem1, elem2)
// slice = append(slice, anotherSlice...)
// As a special case, it is legal to append a string to a byte slice, like this:
// slice = append([]byte("hello "), "world"...)
func append(slice []Type, elems ...Type) []Type
- 该函数的作用是追加元素到切片slice的末尾。
- 如果slice还有剩余的容量，则该切片被允许容纳新的元素；如果没有剩余容量，一个新的底层数组将会创建。
- 该函数返回更新的切片，因此新的切片必须存储追加结果，通常更新的切片也包含原切片本身。
package test
import (
"fmt"
"testing"
)
func TestSize(t *testing.T) {
a := []int{1, 2, 3, 4, 5, 6}
fmt.Printf("aaaa 的地址: %p ,长度 :%d %#v\n", a, len(a), a)
for i := 0; i < len(a); i++ {
fmt.Printf("a[%d] 的地址: %p \n", i, &a[i])
}
// b 引用a索引为 2的元素
b := a[2:3]
fmt.Printf("bbbb 的地址: %p ,长度 :%d %#v\n", b, len(b), b)
for i := 0; i < 16; i++ {
b = append(b, 30)
fmt.Printf("b----b 的地址: %p ,长度 :%d %#v\n", b, len(b), b)
//fmt.Printf("a----a 的地址: %p ,长度 :%d %#v\n", a, len(a), a)
}
}
=== RUN TestSize
aaaa 的地址: 0xc000020420 ,长度 :6 []int{1, 2, 3, 4, 5, 6}
a[0] 的地址: 0xc000020420
a[1] 的地址: 0xc000020428
a[2] 的地址: 0xc000020430 // b 的引用地址
a[3] 的地址: 0xc000020438
a[4] 的地址: 0xc000020440
a[5] 的地址: 0xc000020448
b 的地址: 0xc000020430 ,容量： 4,长度 :1 []int{3}
b 的地址: 0xc000020430 ,容量： 4,长度 :2 []int{3, 30}
b 的地址: 0xc000020430 ,容量： 4,长度 :3 []int{3, 30, 30}
b 的地址: 0xc000020430 ,容量： 4,长度 :4 []int{3, 30, 30, 30}
//扩容后,地址改变
b 的地址: 0xc00001a280 ,容量： 8,长度 :5 []int{3, 30, 30, 30, 30}
b 的地址: 0xc00001a280 ,容量： 8,长度 :6 []int{3, 30, 30, 30, 30, 30}
b 的地址: 0xc00001a280 ,容量： 8,长度 :7 []int{3, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00001a280 ,容量： 8,长度 :8 []int{3, 30, 30, 30, 30, 30, 30, 30}
//扩容后,地址改变
b 的地址: 0xc000116180 ,容量： 16,长度 :9 []int{3, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :10 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :11 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :12 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :13 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :14 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :15 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc000116180 ,容量： 16,长度 :16 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
//扩容后,地址改变
b 的地址: 0xc00000a700 ,容量： 32,长度 :17 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :18 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :19 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :20 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :21 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :22 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :23 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :24 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :25 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :26 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :27 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :28 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :29 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :30 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :31 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00000a700 ,容量： 32,长度 :32 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
//扩容后,地址改变
b 的地址: 0xc00014e000 ,容量： 64,长度 :33 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :34 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :35 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :36 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :37 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :38 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :39 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :40 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
b 的地址: 0xc00014e000 ,容量： 64,长度 :41 []int{3, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30}
--- PASS: TestSize (0.00s)
PASS
Process finished with the exit code 0
从上面程序的输出可以看出
- 向 b 中追加数据会覆盖 a 中的数据。
- 当切片b的长度超过数组a固有长度时,b 的地址改变了。
- 当切片容量被用完时，如果继续追加，则切片扩容后的大小为切片当前大小2 倍。
