转指针到指针(双指针)
先决条件:围棋指针
Go 编程语言或 Golang 中的指针是一个变量，用于存储另一个变量的内存地址。指针是一种特殊的变量，因此它可以指向任何类型的变量，甚至指针。基本上，这看起来像一个指针链。当我们定义一个指向指针的指针时，第一个指针用来存储第二个指针的地址。这个概念有时被称为双指针。
如何在 Golang 中将指针声明为指针？ 声明指针指向指针类似于在 Go 中声明指针。不同的是，我们必须在指针名称的名称前附加一个' * '。这通常是在我们使用 var 关键字和类型一起声明指针变量时完成的。下面的例子和图片将更好地解释这个概念。
例 1: 在下面的程序中，指针 pt2 存储 pt1 指针的地址。取消引用 pt2 即 pt2* 会给出变量 v 的地址，也可以说指针 pt1 的值。如果您尝试 pt2 ，那么这将给出变量 v 的值，即 100。
// Go program to illustrate the
// concept of the Pointer to Pointer
package main
import "fmt"
// Main Function
func main() {
// taking a variable
// of integer type
var V int = 100
// taking a pointer
// of integer type
var pt1 *int = &V
// taking pointer to
// pointer to pt1
// storing the address
// of pt1 into pt2
var pt2 **int = &pt1
fmt.Println("The Value of Variable V is = ", V)
fmt.Println("Address of variable V is = ", &V)
fmt.Println("The Value of pt1 is = ", pt1)
fmt.Println("Address of pt1 is = ", &pt1)
fmt.Println("The value of pt2 is = ", pt2)
// Dereferencing the
// pointer to pointer
fmt.Println("Value at the address of pt2 is or *pt2 = ", *pt2)
// double pointer will give the value of variable V
fmt.Println("*(Value at the address of pt2 is) or **pt2 = ", **pt2)
}
输出:
The Value of Variable V is = 100
Address of variable V is = 0x414020
The Value of pt1 is = 0x414020
Address of pt1 is = 0x40c128
The value of pt2 is = 0x40c128
Value at the address of pt2 is or *pt2 = 0x414020
*(Value at the address of pt2 is) or **pt2 = 100
例 2: 我们对上面的程序做一些修改。通过使用如下所示的取消引用来更改指针的值，从而为指针分配一些新值:
// Go program to illustrate the
// concept of the Pointer to Pointer
package main
import "fmt"
// Main Function
func main() {
// taking a variable
// of integer type
var v int = 100
// taking a pointer
// of integer type
var pt1 *int = &v
// taking pointer to
// pointer to pt1
// storing the address
// of pt1 into pt2
var pt2 **int = &pt1
fmt.Println("The Value of Variable v is = ", v)
// changing the value of v by assigning
// the new value to the pointer pt1
*pt1 = 200
fmt.Println("Value stored in v after changing pt1 = ", v)
// changing the value of v by assigning
// the new value to the pointer pt2
**pt2 = 300
fmt.Println("Value stored in v after changing pt2 = ", v)
}
输出:
The Value of Variable v is = 100
Value stored in v after changing pt1 = 200
Value stored in v after changing pt2 = 300
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