《Essential C++》系列笔记之第四章(基于对象的编程风格)之第七节(合作关系必须建立在友谊的基础上)

代码实践

• Building.h

  #pragma once
  #include 
  using namespace std;
  
  class Building
  {
  	friend class Goodgay; //这个类做了友元,那么这个类的所有member function都是friend
  	friend void visit_building(Building* b);
  public:
  	Building(string ke = "客厅", string wo = "卧室")
  		:_keting(ke), _woshi(wo)
  	{}
  	string _keting;
  private:
  	string _woshi;
  };
  

• main.cpp

  #include 
  #include "Building.h"
  #include "Goodgay.h"
  #include 
  using namespace std;
  
  void visit_building(Building* b)
  {
  	;
  	cout << "好朋友正在参观你的: " << b->_keting << endl;
  	cout << "好朋友正在参观你的: " << b->_woshi << endl; //在没有建立友元时,全局函数无法访问私有成员
  }
  
  void demo_1()
  {
  	Building B;            //这里没有括号!
  	visit_building(&B);
  }
  
  void demo_2()
  {
  	Goodgay gg;
  	gg.visit();
  }
  
  
  int main()
  {
  	//全局函数做友元
  	//demo_1();
  
  	//友元类 
  	demo_2();
  
  
  	system("pause");
  	return 0;
  }
  

• Goodgay.h

  #pragma once
  #include "Building.h"
  class Goodgay
  {
  public:
  	Goodgay();
  	void visit();
  
  private:
  	Building* _Building;
  };
  

• Goodgay.cpp

  #include "Goodgay.h"
  
  Goodgay::Goodgay()
  {
  	this->_Building = new Building;
  }
  
  void Goodgay::visit()
  {
  	cout << "Good gay正在访问你的:" << this->_Building->_keting << endl;
  	cout << "Good gay正在访问你的:" << this->_Building->_woshi << endl;
  	//没有把goodgay类作为building类的友元就无法访问卧室  
  }
  

今天是20200325 记得是同类无私处,异类有友元^ _ ^