转指针到指针（双指针）

先决条件：Go 中的指针

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，甚至可以指向指针。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，第一个指针用于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 中声明一个指向指针的指针？
声明指向指针的指针类似于在 Go 中声明指针。不同之处在于我们必须在指针名称之前放置一个额外的“*”。这通常在我们使用 var 关键字和类型声明指针变量时完成。下面的示例和图像将以更好的方式解释这个概念。

例 1：在下面的程序中，指针pt2存储了pt1指针的地址。取消引用pt2即*pt2将给出变量v的地址，或者您也可以说出指针pt1的值。如果你尝试**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

示例 2：让我们对上述程序进行一些更改。通过使用取消引用更改指针的值来为指针分配一些新值，如下所示：

// 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