# Go語言切片

Go切片(Slice)是Go數組的一個抽象。 由於Go數組允許定義類型的變量，可以容納相同數據類型的幾個數據項，但它不提供任何內置的方法來動態增加其大小或獲取自己的子數組。切片就沒有這樣的限制。 它提供了數組所需的許多實用功能，並廣泛用於Go編程。

## 定義切片

var numbers []int /* a slice of unspecified size */
/* numbers == []int{0,0,0,0,0}*/
numbers = make([]int,5,5) /* a slice of length 5 and capacity 5*/

### len() 和 cap()函數

package main

import "fmt"

func main() {
var numbers = make([]int,3,5)

printSlice(numbers)
}

func printSlice(x []int){
fmt.Printf("len=%d cap=%d slice=%v\n",len(x),cap(x),x)
}

len=3 cap=5 slice=[0 0 0]

### Nil切片

package main

import "fmt"

func main() {
var numbers []int

printSlice(numbers)

if(numbers == nil){
fmt.Printf("slice is nil")
}
}

func printSlice(x []int){
fmt.Printf("len=%d cap=%d slice=%v\n",len(x),cap(x),x)
}

len=0 cap=0 slice=[]
slice is nil

### 子切片

package main

import "fmt"

func main() {
/* create a slice */
numbers := []int{0,1,2,3,4,5,6,7,8}
printSlice(numbers)

/* print the original slice */
fmt.Println("numbers ==", numbers)

/* print the sub slice starting from index 1(included) to index 4(excluded)*/
fmt.Println("numbers[1:4] ==", numbers[1:4])

/* missing lower bound implies 0*/
fmt.Println("numbers[:3] ==", numbers[:3])

/* missing upper bound implies len(s)*/
fmt.Println("numbers[4:] ==", numbers[4:])

numbers1 := make([]int,0,5)
printSlice(numbers1)

/* print the sub slice starting from index 0(included) to index 2(excluded) */
number2 := numbers[:2]
printSlice(number2)

/* print the sub slice starting from index 2(included) to index 5(excluded) */
number3 := numbers[2:5]
printSlice(number3)

}

func printSlice(x []int){
fmt.Printf("len=%d cap=%d slice=%v\n",len(x),cap(x),x)
}

len=9 cap=9 slice=[0 1 2 3 4 5 6 7 8]
numbers == [0 1 2 3 4 5 6 7 8]
numbers[1:4] == [1 2 3]
numbers[:3] == [0 1 2]
numbers[4:] == [4 5 6 7 8]
len=0 cap=5 slice=[]
len=2 cap=9 slice=[0 1]
len=3 cap=7 slice=[2 3 4]

### append()和copy()函數

package main

import "fmt"

func main() {
var numbers []int
printSlice(numbers)

/* append allows nil slice */
numbers = append(numbers, 0)
printSlice(numbers)

/* add one element to slice*/
numbers = append(numbers, 1)
printSlice(numbers)

/* add more than one element at a time*/
numbers = append(numbers, 2,3,4)
printSlice(numbers)

/* create a slice numbers1 with double the capacity of earlier slice*/
numbers1 := make([]int, len(numbers), (cap(numbers))*2)

/* copy content of numbers to numbers1 */
copy(numbers1,numbers)
printSlice(numbers1)
}

func printSlice(x []int){
fmt.Printf("len=%d cap=%d slice=%v\n",len(x),cap(x),x)
}

len=0 cap=0 slice=[]
len=1 cap=2 slice=[0]
len=2 cap=2 slice=[0 1]
len=5 cap=8 slice=[0 1 2 3 4]
len=5 cap=16 slice=[0 1 2 3 4]