c++中指针,指针的引用,指针的指针的区别
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!
#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!
本文转自Work Hard Work Smart博客园博客，原文链接：http://www.cnblogs.com/linlf03/archive/2011/11/19/2255173.html，如需转载请自行联系原作者
