VC6_0中友元函数无法访问类私有成员的解决办法VC6_0的经典bug(转)

转自（http://hi.baidu.com/zgjxwl/blog/item/f0382a6e4ea08ddc80cb4a3d.html）

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 "<<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 "<<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,需要什么即可包含什么.