C++基础(十三)友元

背景：在类中 私有成员变量无法被类外访问 

1.全局函数做友元

实例代码如下：

#include <iostream>
using namespace std;class Person 
{//友元friend void showDetial(Person* p);public:Person(): m_Age(10), m_Name(20){}
public:int m_Age;
private:int m_Name;
};void showDetial(Person *p) 
{cout << "age :" << p->m_Age << endl;cout << "name :" << p->m_Name << endl;
}int main()
{return 0;
}

2.友元类 

示例代码如下

#include <iostream>
using namespace std;
#include <string>class Build;class Friend 
{
public :Friend();Build *bui;void visit();
};class Build 
{//友元类friend class Friend;
public:Build();string m_Name;
private:string m_Age;
};//这里仅仅使用类外定义的使用
Build::Build(): m_Name("godv"), m_Age("抱金砖")
{}Friend::Friend()
{bui = new Build();
}void Friend::visit() 
{cout << bui->m_Name << endl;cout << bui->m_Age << endl;
}int main() 
{Friend f;f.visit();system("pause");return 0;
}

3.友元函数

示例代码如下;

#include <iostream>
using namespace std;
#include <string>class Builds;class Friends
{
public:Friends();Builds* b;void visit();
};class Builds 
{friend void Friends::visit();	
public:Builds();string m_Name;
private:string m_Age;
};void Friends::visit() 
{cout << b->m_Name << endl;cout << b->m_Age << endl;
}Builds::Builds():m_Name("godv"), m_Age("666")
{}Friends::Friends():b(new Builds())
{}int main() 
{Friends fs;fs.visit();return 0;
}