c++249多态

#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：
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#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;
//}

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虚析构

#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;
}

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调用a进去把a的地址赋值给指针

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1.
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：

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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

#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;
}