Go语言

分别观察一下f1和f2函数的输出，f1函数里的是直接开辟了一块新的内存去存储，f2函数里的是先在原基础上上写的

f1中ia2 := ia[1:3]后cap(ia2)的长度是4，因为ia2 = append(ia2, 6,7,8,9)，会超出4，所以直接分配一块内存，在新的内存上写

f2中ia2 := ia[1:3]后cap(ia2)的长度是4，因为逐个写的，第一次append(ia2, i)之后，没有超出4，第二次操作也没有，所以改动了原来的ia，第三次的时候，超出了4，就重新分配一个块cap(ia2)为8的内存上，并把值拷贝过去

```go func f2() { ia := [...]int{1, 2, 3, 4, 5} ia2 := ia[1:3] fmt.Printf("len: %d, cap: %d\n",len(ia2), cap(ia2)) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[0]), unsafe.Pointer(&ia2[0])) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[1]), unsafe.Pointer(&ia2[1])) fmt.Printf("%v\n", unsafe.Pointer(&ia[2])) fmt.Printf("%v\n", unsafe.Pointer(&ia[3])) fmt.Printf("%v\n", unsafe.Pointer(&ia[4])) for i := 6; i < 10; i++ { fmt.Println("------------") ia2 = append(ia2, i) fmt.Printf("len: %d, cap: %d\n",len(ia2), cap(ia2)) fmt.Printf("%v %v\n", unsafe.Pointer(&ia), unsafe.Pointer(&ia2)) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[1]), unsafe.Pointer(&ia2[1])) if len(ia2) < 3 { fmt.Printf("%v\n", unsafe.Pointer(&ia[2])) } else { fmt.Printf("%v %v\n", unsafe.Pointer(&ia[2]), unsafe.Pointer(&ia2[2])) } if len(ia2) < 4 { fmt.Printf("%v\n", unsafe.Pointer(&ia[3])) } else { fmt.Printf("%v %v\n", unsafe.Pointer(&ia[3]), unsafe.Pointer(&ia2[3])) } if len(ia2) < 5 { fmt.Printf("%v\n", unsafe.Pointer(&ia[4])) } else { fmt.Printf("%v %v\n", unsafe.Pointer(&ia[4]), unsafe.Pointer(&ia2[4])) } if len(ia2) == 6 { fmt.Printf("%v\n", unsafe.Pointer(&ia2[5])) } } fmt.Println(ia, ia2) }

func f1() { ia := [...]int{1, 2, 3, 4, 5} ia2 := ia[1:3] fmt.Printf("%v %v\n", unsafe.Pointer(&ia), unsafe.Pointer(&ia2)) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[0]), unsafe.Pointer(&ia2[0])) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[1]), unsafe.Pointer(&ia2[1])) fmt.Printf("%v\n", unsafe.Pointer(&ia[2])) fmt.Printf("%v\n", unsafe.Pointer(&ia[3])) fmt.Printf("%v\n", unsafe.Pointer(&ia[4])) fmt.Println("------------") ia2 = append(ia2, 6,7,8,9) fmt.Printf("%v %v\n", unsafe.Pointer(&ia), unsafe.Pointer(&ia2)) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[0]), unsafe.Pointer(&ia2[0])) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[1]), unsafe.Pointer(&ia2[1])) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[2]), unsafe.Pointer(&ia2[2])) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[3]), unsafe.Pointer(&ia2[3])) fmt.Printf("%v %v\n", unsafe.Pointer(&ia[4]), unsafe.Pointer(&ia2[4])) fmt.Printf("%v\n", unsafe.Pointer(&ia2[5])) fmt.Println(ia, ia2) } ```