【C++】Pointer to Pointer

Pointer to Pointer 顾名思义就是指标的指标~

它可能是一个变数的地址的地址~

我们要在function间~传递Pointer的时候~ 会用到Pointer to Pointer~

学习目标: Pointer to Pointer的概念及实务

学习难度: ☆☆★

Pointer函式传输parameter没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);//因为这里还是copy的概念....类似call by value
    
    printf ("%d\n", *value2Ptr); //will print 10
    
    return 0;
}

Pointer Pointer函式传输parameter有side effect

#include <iostream>

using namespace std;

int value1 = 0;

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

int main ()
{
    int value2 = 1; //value2整数
    
    int *value2Ptr = &value2; //value2指标
    
    changePtr (&value2Ptr); //取value2指标的地址丢去函式
    
    printf ("%d\n", *value2Ptr);///will print 5
    
    return 0;
}

参考资料:

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