VC6.0中友元函数无法访问类私有成员的解决办法(VC6.0的bug)

举个例子: 

#include<iostream> using namespace std; class cylinder { friend istream operator>>(istream& is,cylinder &cy); public: inline double square() { return length*(width+height)*2+width*height*2; } inline double volume() { return length*width*height; } private: double length; double width; double height; }; istream operator>>(istream is,cylinder &cy) { cout<<"input length:"<<endl; is>>cy.length; cout<<"input width:"<<endl; is>>cy.width; cout<<"input height:"<<endl; is>>cy.height; return is; } int main() { cylinder first; cin>>first; cout<<first.square()<<endl; cout<<first.volume()<<endl; return 0; }
这些代码在VC6.0中不能被编译通过:提示不能访问私有成员,没有这个访问权限

改成这样就可以了,代码如下: 

#include<iostream> using std::cin; using std::endl; using std::cout; using std::ostream; using std::istream; using std::ostream; class cylinder { friend istream operator>>(istream& is,cylinder &cy); public: inline double square() { return length*(width+height)*2+width*height*2; } inline double volume() { return length*width*height; } private: double length; double width; double height; }; istream operator>>(istream is,cylinder &cy) { cout<<"input length:"<<endl; is>>cy.length; cout<<"input width:"<<endl; is>>cy.width; cout<<"input height:"<<endl; is>>cy.height; return is; } int main() { cylinder first; cin>>first; cout<<first.square()<<endl; cout<<first.volume()<<endl; return 0; }

原因:

这据说是VC的一个经典BUG。和namespace也有关.

只要含有using namespace std; 就会提示友员函数没有访问私有成员的权限。

解决方法：去掉using namespace std;换成更小的名字空间。

例如:

含有#include <string>就要加上using std::string

含有#include <fstream>就要加上using std::fstream

含有#include <iostream>就要加上using std::cin; using std::cout; using std::ostream; using std::istream; using std::endl; 等等,需要什么即可通过using声明什么.

 

下面给出流浪给的解决办法:

//方法一：

//提前声明

class cylinder; istream &operator>>(istream& is,cylinder &cy);

//方法二：

//不用命名空间 或者 像晨雨那样写

#include<iostream.h>

 

 

//方法三：

class cylinder { friend istream &operator>>(istream& is,cylinder &cy)//写在类里面 { cout<<"input length:"<<endl; is>>cy.length; cout<<"input width:"<<endl; is>>cy.width; cout<<"input height:"<<endl; is>>cy.height; return is; }

//方法四：打SP6补丁，貌似不好使。。。(呵呵,是貌似也没用)

 

//方法五：换别的对标准C++支持好的编译器，如DEV C++/。。。(呵呵)