8. 상속과 다형성

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출처: 윤성우 열혈강의 C++ 예제코드

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8.1. 객체 포인터의 참조관계

• Base Class형 변수로 Derived Class 객체 다루기

#include <iostream>
using namespace std;

class Person
{
public:
	void Sleep() { cout<<"Sleep"<<endl; }
};

class Student : public Person
{
public:
	void Study() { cout<<"Study"<<endl; }
};

class PartTimeStudent : public Student
{
public:
	void Work() { cout<<"Work"<<endl; }
};

int main(void)
{
	Person * ptr1=new Student();
	Person * ptr2=new PartTimeStudent();
	Student * ptr3=new PartTimeStudent();
	ptr1->Sleep();
	ptr2->Sleep();
	ptr3->Study();
	delete ptr1; delete ptr2; delete ptr3;
	return 0;
}

8.2. 가상함수(Vitual Function)

• 가상함수를 이용하여 override한 함수 호출하기(포인터)

#include <iostream>
#include <cstring>
using namespace std;

class Employee
{
private:
	char name[100];
public:
	Employee(char * name)
	{
		strcpy(this->name, name);
	}
	void ShowYourName() const
	{
		cout<<"name: "<<name<<endl;
	}
	virtual int GetPay() const
	{
		return 0;
	}
	virtual void ShowSalaryInfo() const
	{  }
};

class PermanentWorker : public Employee
{
private:
	int salary;
public:
	PermanentWorker(char * name, int money)
		: Employee(name), salary(money)
	{  }
	int GetPay() const
	{
		return salary;
	}
	void ShowSalaryInfo() const
	{
		ShowYourName();
		cout<<"salary: "<<GetPay()<<endl<<endl;
	}
};

class TemporaryWorker : public Employee
{
private:
	int workTime;
	int payPerHour;
public:
	TemporaryWorker(char * name, int pay)
		: Employee(name), workTime(0), payPerHour(pay)
	{  }
	void AddWorkTime(int time)
	{
		workTime+=time;
	}
	int GetPay() const
	{
		return workTime*payPerHour;
	}
	void ShowSalaryInfo() const
	{
		ShowYourName();
		cout<<"salary: "<<GetPay()<<endl<<endl;
	}
};

class SalesWorker : public PermanentWorker
{
private:
	int salesResult;    // 월 판매실적
	double bonusRatio;    // 상여금 비율 
public:
	SalesWorker(char * name, int money, double ratio)
		: PermanentWorker(name, money), salesResult(0), bonusRatio(ratio)
	{  }
	void AddSalesResult(int value)
	{
		salesResult+=value;
	}
	int GetPay() const
	{
		return PermanentWorker::GetPay()  
					+ (int)(salesResult*bonusRatio);
	}
	void ShowSalaryInfo() const
	{
		ShowYourName();
		cout<<"salary: "<<GetPay()<<endl<<endl;
	}
};

class EmployeeHandler
{
private:
	Employee* empList[50];
	int empNum;
public:
	EmployeeHandler() : empNum(0) 
	{ }
	void AddEmployee(Employee* emp)
	{
		empList[empNum++]=emp;
	}
	void ShowAllSalaryInfo() const
	{
		
		for(int i=0; i<empNum; i++)
			empList[i]->ShowSalaryInfo();
		
	}
	void ShowTotalSalary() const
	{
		int sum=0;
		
		for(int i=0; i<empNum; i++)
			sum+=empList[i]->GetPay();
		
		cout<<"salary sum: "<<sum<<endl;
	}
	~EmployeeHandler()
	{
		for(int i=0; i<empNum; i++)
			delete empList[i];
	}
};

int main(void)
{
	// 직원관리를 목적으로 설계된 컨트롤 클래스의 객체생성
	EmployeeHandler handler;

	// 정규직 등록
	handler.AddEmployee(new PermanentWorker("KIM", 1000));
	handler.AddEmployee(new PermanentWorker("LEE", 1500));

	// 임시직 등록
	TemporaryWorker * alba=new TemporaryWorker("Jung", 700);
	alba->AddWorkTime(5);	// 5시간 일한결과 등록
	handler.AddEmployee(alba);

	// 영업직 등록
	SalesWorker * seller=new SalesWorker("Hong", 1000, 0.1);
	seller->AddSalesResult(7000);	// 영업실적 7000
	handler.AddEmployee(seller);

	// 이번 달에 지불해야 할 급여의 정보
	handler.ShowAllSalaryInfo();	

	// 이번 달에 지불해야 할 급여의 총합
	handler.ShowTotalSalary();
	return 0;
}

8.3. 가상 소멸자와 참조자의 참조 가능성

• 가상 소멸자 이용하기

#include <iostream>
using namespace std;

class First
{
private:
	char * strOne;
public:
	First(char * str)
	{
		strOne=new char[strlen(str)+1];
	}
	virtual ~First()
	{
		cout<<"~First()"<<endl;
		delete []strOne;
	}
};
   
class Second: public First
{
private:
	char * strTwo;
public:
	Second(char * str1, char * str2) : First(str1)
	{
		strTwo=new char[strlen(str2)+1];
	}
	virtual ~Second()
	{
		cout<<"~Second()"<<endl;
		delete []strTwo;
	}
};

int main(void)
{
	First * ptr=new Second("simple", "complex");
	delete ptr;
	return 0;
}

• 가상함수를 이용하여 override한 함수 호출하기(참조자)

#include <iostream>
using namespace std;

class First
{
public:
	void FirstFunc()
	{
		cout<<"FirstFunc()"<<endl;
	}
	virtual void SimpleFunc()
	{
		cout<<"First's SimpleFunc()"<<endl;
	}
};
   
class Second: public First
{
public:
	void SecondFunc()
	{
		cout<<"SecondFunc()"<<endl;
	}
	virtual void SimpleFunc()
	{
		cout<<"Second's SimpleFunc()"<<endl;
	}
};

class Third: public Second
{
public:
	void ThirdFunc()
	{
		cout<<"ThirdFunc()"<<endl;
	}
	virtual void SimpleFunc()
	{
		cout<<"Third's SimpleFunc()"<<endl;
	}
};

int main(void)
{
	Third obj;
	obj.FirstFunc();
	obj.SecondFunc();
	obj.ThirdFunc();
	obj.SimpleFunc();

	Second & sref=obj;
	sref.FirstFunc();
	sref.SecondFunc();
	sref.SimpleFunc();

	First & fref=obj;
	fref.FirstFunc();
	fref.SimpleFunc();
	return 0;
}