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  Go语言 切片

  • 切片

    Go Slice（切片）是Go 数组的抽象。Go Array（数组）允许您定义可容纳相同种类的多个数据项的变量，但是它不提供任何内置方法来动态增加其大小或获取其自身的子数组。切片克服了此限制。它提供了Array所需的许多实用程序功能，并广泛用于Go编程中。

  • 定义切片

    要定义切片，可以将其声明为数组，而无需指定其大小。另外，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()函数返回切中的元素，cap()函数返回切片的容量(它可以容纳多少元素)。下面的例子说明切片的用法 
    
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)
}
    尝试一下
    编译并执行上述代码后，将产生以下结果- 
    
len = 3 cap = 5 slice = [0 0 0]

  • nil 切片

    如果声明没有任何输入的切片，则默认情况下将其初始化为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)
}
    尝试一下
    编译并执行上述代码后，将产生以下结果- 
    
len = 0 cap = 0 slice = []
slice is nil

  • 子切片

    Slice允许使用[lower-bound：upper-bound]指定下限和上限，以获取其子切片。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)
}
    尝试一下

  • append()和copy()函数

    可以使用append()函数来增加切片的容量。使用copy()函数，源切片的内容被复制到目标切片。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)
}
    尝试一下
    编译并执行上述代码后，将产生以下结果- 
    
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]
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