c++中指针,指针的引用,指针的指针的区别(转)

看例子和结果:

#include "stdafx.h"
#include <iostream>
using namespace std;
void FreePtr1(int* ptr1)
{
    delete ptr1; 
    ptr1 = NULL;
}

void FreePtr2(int*& ptr2)
{
    delete ptr2; 
    ptr2 = NULL;
}
void FreePtr3(int **ptr3)
{
    delete *ptr3;
*ptr3 = NULL;
}

void main()
{
    cout<<"---------------------------------------"<<endl;
int *p1 = new int;
*p1 = 1;
    cout<<"*p1="<<*p1<<endl;
    FreePtr1(p1);
    cout<<"after call freePtr1"<<endl;
if(p1 != NULL)
{
        cout<<"p1 is not null"<<endl;
        cout<<"*p1="<<(*p1)<<endl;
    }
    cout<<"---------------------------------------"<<endl;
int *p2 = new int;
*p2 = 2;
    cout<<"*p2="<<*p2<<endl;
    FreePtr2(p2);
    cout<<"after call freePtr2"<<endl;
if(p2 != NULL)
{       
        cout<<"*p2="<<*p2<<endl;
    }
else
{
        cout<<"the p2 is null"<<endl;
    }
    cout<<"---------------------------------------"<<endl;
int *p3 ;
    p3 = new int(3);
    cout<<"*p3="<<*p3<<endl;
    FreePtr3(&p3);
    cout<<"after call freePtr3"<<endl;
if(p3 != NULL)
{       
        cout<<"*p3="<<*p3<<endl;
    }
else
{
        cout<<"the p3 is null"<<endl;
    }
    cout<<"---------------------------------------"<<endl;
    system("pause");

}

结果:

comments:
对p1指针:
cout<<"---------------------------------------"<<endl;
int *p1 = new int;
*p1 = 1;
cout<<"*p1="<<*p1<<endl;

// FreePtr1(p1);
void FreePtr1(int* ptr1)
{

delete ptr1; 

ptr1 = NULL;

}

cout<<"after call freePtr1"<<endl;
if(p1 != NULL)
{
  cout<<"p1 is not null"<<endl;
  cout<<"*p1="<<(*p1)<<endl;
}
cout<<"---------------------------------------"<<endl;
而p2为:
调用前:

调用后:

注意:函数的参数进行值拷贝,即使传的是指针,也的对指针(即指针里存的地址)的拷贝, 可不是指针里地址所指的值的拷贝啊!