c++,vc6.0,中友元函数,无法访问私有字段(private)的问题(problem),cannot access private member declared in class 'Date'

c++,vc6.0,中友元函数,无法访问私有字段(private)的问题(problem),cannot access private member declared in class 'Date'

代码如下：

#ifndef _DATE_H_#define _DATE_H_#include<iostream>using namespace std;class Date{public:Date();Date(int y,int m,int d);void printOn();private:int _year;int _mounth;int _day;friend const ostream& operator<<(ostream & out,Date d);};Date::Date():_year(0),_mounth(0),_day(0){}Date::Date(int y,int m,int d):_year(y),_mounth(m),_day(d){}void Date::printOn(){ cout<<*this; }const ostream& operator<<(ostream & out,Date d){out<<d._year<<d._mounth<<d._day<<endl;return out;}#endif

错误提示如下图：

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.

更正后如下：

#ifndef _DATE_H_#define _DATE_H_#include<iostream>//using namespace std;using std::cin;using std::endl; using std::cout;using std::ostream;using std::istream;class Date{public:Date();Date(int y,int m,int d);void printOn();private:int _year;int _mounth;int _day;friend const ostream& operator<<(ostream & out,Date d);};Date::Date():_year(0),_mounth(0),_day(0){}Date::Date(int y,int m,int d):_year(y),_mounth(m),_day(d){}void Date::printOn(){ cout<<*this; } const ostream& operator<<(ostream & out,Date d){out<<d._year<<d._mounth<<d._day<<endl;return out;}#endif

 

或者更改如下：

#include<iostream.h>