c++249多态 - 技术栈

cpp 复制代码

#include<iostream>
using namespace std;
class Parent
{
public:
	Parent(int a)
	{
		this->a = a;
		cout << " Parent" << a << endl;
	}
public:
	virtual void print()//在子类里面可写可不写 
	{
		cout << "Parent" <<a<< endl;
	}
protected:
private:
	int a;
};

class Child:public Parent 
{
public:
	Child(int b):Parent(10)
	{
		this->b = b;
		cout << " Child b" << b << endl;
	}
public:
	void print()
	{
		cout << "Child" <<b<< endl;
	}
protected:
private:
	int b;

};


void main()
{
	//可以把子类的对象赋值给指针
	Parent* base = NULL;
	Parent p1(20);
	Child c1(30);
	base = &p1;
	base->print();//父类
	base = &c1;
	base->print();//执行谁的 ->面向对象新需求



	  
	return;
}

多态如何演变：

cpp 复制代码

#include<iostream>
using namespace std;

class HeroFighter
{
public:
	virtual int power()
	{
		return 10;
	}
};

class EncmyFighter
{
public:
	int attact()
	{
		return 15;
	}
};

class AdvHeroFighter :public HeroFighter
{
public:
	virtual  int power()
	{
		return 10;
	}
};

//


class AdvAdvHeroFighter :public HeroFighter
{
public:
	virtual int power()
	{
		return 30;
	}
};
void play(HeroFighter *hf, EncmyFighter *ef)
{
	//多态场景
	if (hf->power() > ef->attact())//hf->power() 会有多态发生
	{
		cout << "hero win" << endl;
	}
	else
	{
		cout << "hero faule" << endl;
	}
	
}
void main()
{
	HeroFighter hf;
	EncmyFighter ef;
	AdvHeroFighter advhf;

	//

	AdvAdvHeroFighter advadvhf;

	play(&hf, &ef);
	play(&advhf, &ef);
	//
	play(&advadvhf, &ef);//这个框架能把后来写的代码调用起来

 }
//多态框架
//play 给对象搭建舞台 看成一个框架 
//封装：突破函数 用类做函数参数时候 可以使用对象的属性和对象的方法
//继承： A B代码复用
//多态：可以使用未来  
//实现多态的三个条件：1.要有继承 2.要有函数重写3.父类指针指向子类对象


//void main01()
//{
//	HeroFighter hf;
//	EncmyFighter ef;
//	AdvHeroFighter advhf;
//	if (hf.power() > ef.attact())
//	{
//		cout << "hero win" << endl;
//	}
//	else
//	{
//		cout << "hero faule" << endl;
//	}
//	if (advhf.power() > ef.attact())
//	{
//		cout << "hero win" << endl;
//	}
//	else
//	{
//		cout << "hero faule" << endl;
//	}
//	return;
//}

虚析构

cpp 复制代码

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
class A
{
public:
	A()
	{
		p = new char[20];
		strcpy(p, "obja");
		cout << "a" << endl;
	}
	virtual ~A()
	{
		delete[] p;
		cout << "~a" << endl;
	}

	protected:
	private:
		char* p;
};

class B  :public A
{
public:
	B()
	{
		p = new char[20];
		strcpy(p, "obja");
		cout << "b" << endl;
	}
	~B()
	{
		delete[] p;
		cout << "~b" << endl;
	}

protected:
private:
	char* p;
};
class C :public B
{
public:
	C()
	{
		p = new char[20];
		strcpy(p, "obja");
		cout << "c" << endl;

	}
	~C()
	{
		delete[] p;
		cout << " ~`c" << endl;
	}

protected:
private:
	char* p;
};
//只执行了父类的析构 
//通过父类指针把子类的析构函数都执行一遍
//释放所有的子类资源 只能用virtual
void howtodelete(A *base)
{
	delete base;//不会表现成多态
}

void main()
{
	C* myc = new C;//how delete 匹配  new会自动调用~函数 
	howtodelete(myc);



	return;
}

调用a进去把a的地址赋值给指针

1.补充：一个函数在不同类中穿梭（动态）

c++提前vptr指针找到虚化列表找到函数指针进行动态绑定

子类和父类步长：

步长问题：

子类跳到下一个单元父类跳两个元素

子类和父类指针步长不一样

多态时用父类指针指向对象父类步长加加是两个概念

cpp 复制代码

#include<iostream>
using namespace std;


//构造函数中调用虚函数能发生多态吗
class Parent
{
public:
	Parent(int a = 0)
	{
		this->a = a;
		print();
	}
	virtual void print()
	{
		cout << "我是爹" << endl;
	}
	virtual void print2()
	{
		cout << "我是爹" << endl;
	}
private:
	int a;
};



class Child:public Parent
{
public:
	/*Child(int a=0,int b = 0):Parent(a)
	{
		this->b = b;
	}*/
	Child(int b = 0) :Parent(0)
	{
		this->b = b;
		print();
	}
	virtual void print()
	{
		cout << "我是son" << endl;
	}
	virtual void print2()
	{
		cout << "我是son" << endl;
	}
private:
	int b;
};

void HowtoPlay(Parent* base)
{
	base->print();//有多态
}




void main()
{
	Child c1;//定义一个子类对象 在这个过程中构造函数调用虚函数print 能发生多态吗

	Parent* pP = NULL;
	Child* pC = NULL;



	Child array[] = { Child(1),Child(2),Child(3) };
   
	pP = array;
	pC = array;
	//访问
	pP->print();
	pC->print();


	pP++;
	pC++;


	pP->print();
	pC->print();
	return;
}

没添加属性和方法子类和父类指针步长一样