C++之類的繼承和多態

#include <iostream>

using namespace std;

class CPeople
{
public:
	void do_Thing1(){cout<<"CPeople do_thing1!"<<endl;};
	virtual void do_Thing2(){cout<<"CPeople do_thing2!"<<endl;};
	//virtual void do_Thing() = 0;  //帶純虛函數的類叫做純虛類，純虛類不可實例化，其派生類若不實現該虛函數則仍爲虛類
	static void pr(){cout<<"CPeople static!"<<endl;};
	static int sex;
	void People(){
		cout<<"people"<<age<<endl;};

	void func(){cout<<"void func() CPeople"<<endl;};
private:
	
protected:
	int age;
};

class CStudent:public CPeople
{
public:
	void do_Thing1(){cout<<"CStudent do_thing1!"<<endl;};
	void do_Thing2(){cout<<"CStudent do_thing2!"<<endl;};
	//static void pr(){cout<<"CStudent static pr!"<<endl;};   //允許聲明定義，表面CStudent類有自己的static pr()
	void pr(){cout<<"CStudent pr!"<<endl;};   //允許聲明定義，表面CStudent類有自己的非staitc pr(),覆蓋基類static void pr()
	void Student(){
		cout<<"student"<<age<<num<<endl;};

	void set_param(int _age, int _num)
	{
		age = _age;
		num = _num;
	}
	void func(int a){cout<<"void func(int a) CStudent"<<endl;};
protected:
	int num;
};

class CGrade:public CStudent
{
public:
	void do_Thing1(){cout<<"CGrade do_thing1!"<<endl;};
	void do_Thing2(){cout<<"CGrade do_thing2!"<<endl;};
	void Grade(){
		sex = 3;
		cout<<"grade"<<age<<num<<grade<<endl;};
	void set_param(int _age, int _num, int _grade)
	{
		age = _age;
		num = _num;
		grade = _grade;
	}
private:
	int grade;
};

int CPeople::sex = 2;  
//int CStudent::sex = 2;  //可在派生類初始化，但是編譯器警告

int main(int argc, char* argv[])
{
	CGrade *gd = NULL;
	CPeople *pp = NULL;
	CStudent* sd = new CStudent();

	gd = static_cast<CGrade*>(sd);
	pp = static_cast<CPeople*>(sd);	
	
	sd->set_param(2,2);
	gd->set_param(1,2,3);
	sd->Student();		//輸出student12 說明gd指針指向CStduent對象空間
	//sd->func();		//error:如果派生類重定義了重載成員，則通過派生類型只能訪問派生類中重定義的那些成員。
	sd->func(1);

	gd->People();		//派生類指針接收基類對象指針，可以訪問基類方法
	gd->do_Thing1();	//能調用CGrade的do_thing1 ?
	//gd->do_Thing2();  //將出錯，CGrade的do_thing2未實現
	gd->Grade();		//能調用Grade()？爲什麼？  這一段函數的空間哪裏來的？

	//pp->Student();	//基類指針接收派生類對象指針，無法訪問派生類方法？ “Student”: 不是“CPeople”的成員
	pp->do_Thing1();    //調用CPeople的do_Thing1();
	pp->do_Thing2();    //仍然調用CStudent的do_thing2，虛函數的調用之和new處理的對象有關，new出來的是誰的對象就調用誰的方法

	sd->People();		//調用繼承過來的方法
	sd->Student();

	CPeople::pr();
	//CStudent::pr();
	sd->pr();

	CPeople* pp1 = new CGrade();
	pp1->do_Thing1();    // 非虛函數，調用接收指針的類方法  CPeople::do_Thing1()
	pp1->do_Thing2();    // 虛函數，調用new對象的方法

	CStudent* dg2 = new CGrade();
	dg2->do_Thing1();    // 非虛函數，調用接收指針的類方法  CStudent::do_Thing1()
	dg2->do_Thing2();    // 虛函數，調用new對象的方法

	return 0;
}

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