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举个例子：
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#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:
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#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;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:
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//方法一：//提前声明class cylinder;istream &operator>>(istream& is,cylinder &cy);//方法二：//不用命名空间#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; } |
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原文地址：http://www.cnblogs.com/Macchiato1988-10-17/p/4707255.html
