Pointer to Pointer 顧名思義就是指標的指標~

它可能是一個變數的地址的地址~

我們要在function間~傳遞Pointer的時候~ 會用到Pointer to Pointer~

學習目標: Pointer to Pointer的概念及實務

學習難度: ☆☆★

Pointer函式傳輸parameter沒side effect

#include <iostream>

using namespace std;

int value1 = 5;

void changePtr (int *valuepointer)
{
    valuepointer = &value1;
}

int main ()
{
    int value2 = 10;
    
    int *value2Ptr = &value2;
    
    changePtr (value2Ptr);//因為這裡還是copy的概念....類似call by value
    
    printf ("%d\n", *value2Ptr); //will print 10
    
    return 0;
}

Pointer Pointer函式傳輸parameter有side effect

#include <iostream>

using namespace std;

int value1 = 0;

void changePtr (int **valuepointer) //value2指標的地址
{
    *valuepointer = &value1; //value2指標= value1地址
}

int main ()
{
    int value2 = 1; //value2整數
    
    int *value2Ptr = &value2; //value2指標
    
    changePtr (&value2Ptr); //取value2指標的地址丟去函式
    
    printf ("%d\n", *value2Ptr);///will print 5
    
    return 0;
}

參考資料:

http://low-understated.blogspot.com/2009/04/pointer-to-pointer.html