深入理解Go语言中的数组和切片

　　一、类型

　　数组是值类型，将一个数组赋值给另一个数组时，传递的是一份拷贝。

　　切片是引用类型，切片包装的数组称为该切片的底层数组。

　　我们来看一段代码

　　 //a是一个数组，注意数组是一个固定长度的，初始化时候必须要指定长度，不指定长度的话就是切片了 a := [3]int{1, 2, 3} //b是数组，是a的一份拷贝 b := a //c是切片，是引用类型，底层数组是a c := a[:] for i := 0; i < len(a); i++ { a[i] = a[i] + 1 } //改变a的值后，b是a的拷贝，b不变，c是引用，c的值改变 fmt.Println(a) //[2,3,4] fmt.Println(b) //[1 2 3] fmt.Println(c) //[2,3,4]

　　二、make

　　make 只能用于slice, map 和 channel, 所以下面一段代码生成了一个slice，是引用类型

　　 s1 := make([]int, 0, 3) for i := 0; i < cap(s1); i++ { s1 = append(s1, i) } s2 := s1 for i := 0; i < len(a); i++ { s1[i] = s1[i] + 1 } fmt.Println(s1) //[1 2 3] fmt.Println(s2) //[1 2 3]

　　三、当对slice append 超出底层数组的界限时

　　 //n1是n2的底层数组 n1 := [3]int{1, 2, 3} n2 := n1[0:3] fmt.Println(address of items in n1: ) for i := 0; i < len(n1); i++ { fmt.Printf(%p\n, &n1[i]) } //address of items in n1: //0xc20801e160 //0xc20801e168 //0xc20801e170 fmt.Println(address of items in n2: ) for i := 0; i < len(n2); i++ { fmt.Printf(%p\n, &n2[i]) } //address of items in n2: //0xc20801e160 //0xc20801e168 //0xc20801e170 //对n2执行append操作后，n2超出了底层数组n1的j n2 = append(n2, 1) fmt.Println(address of items in n1: ) for i := 0; i < len(n1); i++ { fmt.Printf(%p\n, &n1[i]) } //address of items in n1: //0xc20801e160 //0xc20801e168 //0xc20801e170 fmt.Println(address of items in n2: ) for i := 0; i < len(n2); i++ { fmt.Printf(%p\n, &n2[i]) } //address of items in n2: //0xc20803a2d0 //0xc20803a2d8 //0xc20803a2e0 //0xc20803a2e8

　　四、引用“失效”

　　实现了删除slice最后一个item的函数

　　 func rmLast(a []int) { fmt.Printf([rmlast] the address of a is %p, a) a = a[:len(a)-1] fmt.Printf([rmlast] after remove, the address of a is %p, a) }

　　调用此函数后，发现原来的slice并没有改变

　　 func main() { xyz := []int{1, 2, 3, 4, 5, 6, 7, 8, 9} fmt.Printf([main] the address of xyz is %p\n, xyz) rmLast(xyz) fmt.Printf([main] after remove, the address of xyz is %p\n, xyz) fmt.Printf(%v, xyz) //[1 2 3 4 5 6 7 8 9] }

　　打印出来的结果如下：

　　 [main] the address of xyz is 0xc2080365f0 [rmlast] the address of a is 0xc2080365f0 [rmlast] after remove, the address of a is 0xc2080365f0 [main] after remove, the address of xyz is 0xc2080365f0 [1 2 3 4 5 6 7 8 9]

　　这里直接打印了slice的指针值，因为slice是引用类型，所以指针值都是相同的，我们换成打印slice的地址看下

　　 func rmLast(a []int) { fmt.Printf([rmlast] the address of a is %p, &a) a = a[:len(a)-1] fmt.Printf([rmlast] after remove, the address of a is %p, &a) } func main() { xyz := []int{1, 2, 3, 4, 5, 6, 7, 8, 9} fmt.Printf([main] the address of xyz is %p\n, &xyz) rmLast(xyz) fmt.Printf([main] after remove, the address of xyz is %p\n, &xyz) fmt.Printf(%v, xyz) //[1 2 3 4 5 6 7 8 9] }

　　结果：

　　 [main] the address of xyz is 0xc20801e1e0 [rmlast] the address of a is 0xc20801e200 [rmlast] after remove, the address of a is 0xc20801e200 [main] after remove, the address of xyz is 0xc20801e1e0 [1 2 3 4 5 6 7 8 9]

　　这次可以看到slice作为函数参数传入函数时，实际上也是拷贝了一份slice，因为slice本身是个指针，所以从现象来看，slice是引用类型

　　总结

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