Go - 切片
Go Slice 是 Go Array 的抽象。Go Array 允许您定义可以保存多个同类数据项的变量，但它不提供任何内置方法来动态增加其大小或获取自己的子数组。切片克服了这个限制。它提供了Array所需的许多实用函数，并广泛用于Go编程中。
定义切片
要定义切片，您可以将其声明为数组而不指定其大小。或者，您可以使用make函数来创建切片。
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() 函数
切片是数组的抽象。它实际上使用数组作为底层结构。len ()函数返回切片中存在的元素，其中cap()函数返回切片的容量（即，它可以容纳多少个元素）。以下示例解释了切片的用法 -
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)
}
当上面的代码被编译并执行时，它会产生以下结果 -
len = 3 cap = 5 slice = [0 0 0]
零切片
如果声明的切片没有输入，则默认情况下它会被初始化为 nil。它的长度和容量为零。例如 -
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)
}
当上面的代码被编译并执行时，它会产生以下结果 -
len = 0 cap = 0 slice = [] slice is nil
子切片
切片允许指定下限和上限，以使用[lower-bound:upper-bound]获取其子切片。例如 -
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)
}
当上面的代码被编译并执行时，它会产生以下结果 -
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() 函数
可以使用append()函数增加切片的容量。使用copy()函数，将源切片的内容复制到目标切片。例如 -
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)
}
当上面的代码被编译并执行时，它会产生以下结果 -
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]