类型转换规则

父类定义的指针可以指向子类对象；


指针会误以为，他们指向的对象是Base1类型，导致错误；

虚函数定义

多态

如何实现多态：
1.创建类的继承关系图
2.所以类对象都可以调用的这个函数
3.创建父类指针数组
4.子类的地址赋给父类指针
5.指针调用虚函数

动态绑定

和多态其实是一个概念

动态绑定我们是无法在运行之前，事先知道运行的结果是不知道的；

不仅是指针，引用也可以！

指针和引用可以，但最后一种情况无法实现多态

虚析构函数

创建的时候是先创建base再创建derived的；这个时候，不加virtual 的话会导致，只delete了base，但没有delete掉derived；
建议所有析构函数都加virtual
只有用new去创建的时候，才有可能出现这种错误。

纯虚函数与抽象类

对于暂时无法实现的函数，我们可以定义为纯虚函数，留给派生类去实现；
定义了纯虚函数的类叫抽象类；
抽象类只能作为基类来使用；
构造函数不能是虚函数，析构函数可以是虚函数；

为什么需要抽象类

抽象类的特点

作业

main.cpp

#include "shape.h"
#include "circle.h"
#include "rectangle.h"
#include "roundrectangle.h" 
#include <iostream>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(void) {
	shape *ptrShape[6];
	circle circle1;
	circle circle2("red",2);
	Rectangle Rectangle1,Rectangle2("green",2,3);
	RoundRectangle RoundRectangle1,RoundRectangle2("yelow",2,3,1);
	ptrShape[0] = &circle1;
	ptrShape[1] = &circle2;
	ptrShape[2] = &Rectangle1;
	ptrShape[3] = &Rectangle2;
	ptrShape[4] = &RoundRectangle1;
	ptrShape[5] = &RoundRectangle2;
	
//	ptrShape[0] = new circle;
//	ptrShape[1] = new Rectangle;
//	ptrShape[2] = new RoundRectangle;
//	ptrShape[3] = new circle("red",2);
//	ptrShape[4] = new Rectangle("red",2,3);
//	ptrShape[5] = new RoundRectangle("red",2,3,1);
	for(int i=0;i<6;i++){
		cout<<"该图形面积为："<<ptrShape[i]->getArea()<<endl;
	}
	return 0;
}

shape.cpp

#include "shape.h"
#include <iostream>
using namespace std;		
	shape::shape():color("white"){
		cout<<"无参创建shape"<<endl;
	}
	shape::shape(string color){
		this->color = color;
		cout<<"有参创建shape"<<endl;
	}
	shape::~shape(){
		cout<<"消亡shape"<<endl;
	}
	string shape::getColor(){
		return this->color;
	}
	void shape::setColor(char color){
		this->color = color;
	}
	void shape::display(){
		cout<<"color:"<<getColor()<<endl;
	}

shape.h

#ifndef SHAPE_H
#define SHAPE_H
#include <string>
#include <iostream>
using namespace std;
class shape{
	private:
		string color;
	public:
		shape();
		shape(string color);
		virtual ~shape();			//析构函数＋virtual 
		string getColor();
		void setColor(char color);
		void display();
		virtual double getArea()=0; //纯虚函数，变成抽象类 
};

#endif

circle.cpp

#include "circle.h"
#include "shape.h"
#include <iostream>
	const double pi = 3.14;
	circle::circle(){
		radius = 1;
		cout<<"无参创建circle"<<endl;
	}
	circle::circle(string color,double radius):shape(color){
		this->radius = radius;
		cout<<"有参创建circle"<<endl;
	}
	circle::~circle(){
		cout<<"消亡circle"<<endl;
	}
	double circle::getRadius(){
		return this->radius;
	}
	void circle::setradius(double radius){
		this->radius = radius;	
	}
	double circle::getArea(){
		return pi*radius*radius;
	}
	void circle::display(){
		shape::display();
		cout<<"R="<<getRadius()<<","<<"Area="<<getArea()<<endl;
	}

circle.h

#ifndef CIRCLE_H
#define CIRCLE_H
#include <string>
#include "shape.h"

class circle:public shape{
	private:
		double radius;
	public:
		circle();
		circle(string color,double radius);
		virtual ~circle();
		void setradius(double radius);
		double getRadius();
		double getArea();
		void display();
};



#endif

rectangle.cpp

#include "rectangle.h"
#include "shape.h"
#include <iostream>

	Rectangle::Rectangle(){
		width = 1;
		height = 1;
		cout<<"无参创建Rectangle"<<endl;
	}
	Rectangle::Rectangle(string color,double width,double height):shape(color){
		this->width = width;
		this->height = height;
		cout<<"有参创建Rectangle"<<endl; 
	}
	Rectangle::~Rectangle(){
		cout<<"消亡Rectangle"<<endl;
	}
	double Rectangle::getWidth(){
		return width; 
	}
	double Rectangle::getHeight(){
		return height;
	}
	void Rectangle::setWidth(double width){
		this->width = width;
	}
	void Rectangle::setHeight(double height){
		this->height = height;
	}
	double Rectangle::getArea(){
		return width*height;
	}
	void Rectangle::display(){
		shape::display();
		cout<<"width="<<getWidth()<<","<<"Height="<<getHeight()<<","<<"Area="<<getArea()<<endl;
	}

rectangle.h

#ifndef RECTANGLE_H
#define RECTANGLE_H
#include <string>
#include "shape.h"

class Rectangle:public shape{
	private:
		double width;
		double height;
	public:
		Rectangle();
		Rectangle(string color,double width,double height);
		virtual ~Rectangle();
		void setWidth(double width);
		void setHeight(double height);
		double getWidth();
		double getHeight();
		double getArea();
		void display();
};


#endif

roundrectangle.cpp

#include "roundrectangle.h"
#include "rectangle.h"
#include"shape.h"
#include <iostream>
	RoundRectangle::RoundRectangle(){
		this->roundRadius = 1;
		cout<<"无参创建RoundRectangle"<<endl; 
	}
	RoundRectangle::RoundRectangle(string color,double width,double height,double roundRadius):Rectangle(color,width,height){
		this->roundRadius = roundRadius;
		cout<<"有参创建RoundRectangle"<<endl;
	}
	RoundRectangle::~RoundRectangle(){
		cout<<"消亡RoundRectangle"<<endl; 
	}
	double RoundRectangle::getRoundradius(){
		return roundRadius;
	}
	void RoundRectangle::setRoundradius(double roundRadius){
		this->roundRadius = roundRadius;
	}
	double RoundRectangle::getArea(){
		return Rectangle::getWidth()*Rectangle::getHeight()+(3.14*roundRadius*roundRadius)/2;
	}
	void RoundRectangle::display(){
		shape::display();
		cout<<"width="<<Rectangle::getWidth()<<","<<"Height="<<Rectangle::getHeight()<<","<<"Area="<<getArea()<<endl;
	}

roundrectangle.h

#ifndef ROUNDRECTANGLE_H
#define ROUNDRECTANGLE_H
#include <string>
#include "rectangle.h"

class RoundRectangle:public Rectangle{
	private:
		double roundRadius;
	public:
		RoundRectangle();
		RoundRectangle(string color,double width,double height,double roundRadius);
		virtual ~RoundRectangle();
		void setRoundradius(double roundRadius);
		double getRoundradius();
		double getArea();
		void display();
};


#endif

（1）必须要定义，因为getArea（）是纯虚函数，派生类必须补全他的函数实现，否则Circle也会变成抽象类，无法创建对象
（2）不会，因为它可以调用他的父类Rectangle类的getArea（），编译不出错，但内容是错误的
（3）可以。但

#include "shape.h"
#include "circle.h"
#include "rectangle.h"
#include "roundrectangle.h" 
#include <iostream>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

double sumArea(shape* shapes[],int n){
	double sum = 0;
	for(int i = 0 ;i<n;i++){
		sum += shapes[i]->getArea();
	}
}

int main(void) {
	shape *ptrShape[6];
	circle circle1;
	circle circle2("red",2);
	Rectangle Rectangle1,Rectangle2("green",2,3);
	RoundRectangle RoundRectangle1,RoundRectangle2("yelow",2,3,1);
	ptrShape[0] = &circle1;
	ptrShape[1] = &circle2;
	ptrShape[2] = &Rectangle1;
	ptrShape[3] = &Rectangle2;
	ptrShape[4] = &RoundRectangle1;
	ptrShape[5] = &RoundRectangle2;
	
//	ptrShape[0] = new circle;
//	ptrShape[1] = new Rectangle;
//	ptrShape[2] = new RoundRectangle;
//	ptrShape[3] = new circle("red",2);
//	ptrShape[4] = new Rectangle("red",2,3);
//	ptrShape[5] = new RoundRectangle("red",2,3,1);
	for(int i=0;i<6;i++){
		cout<<"该图形面积为："<<ptrShape[i]->getArea()<<endl;
	}
	cout<<"总面积"<<sumArea(ptrShape,6)<<endl;
	return 0;
}