dynamic_cast.cpp

动态映射             安全类型向下映射

#include <iostream>
#include <stdlib.h>
#include <time.h>
#include <vector>


using namespace std;


class shape{

	public:
		shape() { count++; }
		virtual ~shape() { count--; }
		virtual void draw() const = 0;
		static int quantity() { return count; }
	protected:
		static int count;
};

int shape::count = 0;

class rectangle:public shape{
	void operator=(rectangle&);
	protected:
		static int count;
	public:
		rectangle() { count++; }
		rectangle(const rectangle&){ count++; }
		~rectangle() { count--; }
		void draw() const {
			cout<<"rectangle::draw()"<<endl;
		}
		static int quantity() { return count; }
};

int rectangle::count = 0;

class ellipse:public shape{
	void operator=(ellipse&);
	protected:
		static int count;
	public:
		ellipse() { count++; }
		ellipse(const ellipse&){ count++; }
		~ellipse() { count--; }
		void draw() const{
			cout<<"ellipse::draw()"<<endl;
		}
		static int quantity() { return count; }
};

int ellipse::count = 0;

class circle:public shape{
	void operator=(circle&);
	protected:
		static int count;
	public:
		circle() { count++; }
		circle(const circle&){ count++; }
		~circle(){ count--; }
		void draw() const{
			cout<<"circle::darw()"<<endl;
		}
		static int quantity() { return count; }
};

int circle::count = 0;

int main()
{
	vector<shape*> shapes;

	time_t t;
	
	srand((unsigned int)time(&t));
	const int mod = 12;
	for(int i=0; i<rand()%mod; ++i)
		shapes.push_back(new rectangle);
	for(int i=0; i<rand()%mod; ++i)
		shapes.push_back(new circle);
	for(int i=0; i<rand()%mod; ++i)
		shapes.push_back(new ellipse);

	int Ncircles = 0;
	int Nellipses = 0;
	int Nrects = 0;
	int Nshapes = 0;
	for(int i=0; i<shapes.size(); ++i)
	{
		shapes[i]->draw();
		if(dynamic_cast<circle*>(shapes[i]))
			Ncircles++;
		if(dynamic_cast<ellipse*>(shapes[i]))
			Nellipses++;
		if(dynamic_cast<rectangle*>(shapes[i]))
			Nrects++;

		if(dynamic_cast<shape*>(shapes[i]))
			Nshapes++;
		cout<<"dynamic_cast:"<<Nshapes<<endl;
	}

	cout<<endl<<endl
		<<"circles="<<Ncircles<<endl
		<<"ellipse = "<<Nellipses<<endl
		<<"rectangles = "<<Nrects<<endl
		<<"shapes = "<<Nshapes<<endl
		<<endl
		<<"circle::quantity()="<<circle::quantity()<<endl
		<<"ellipse::quantity = "<<ellipse::quantity()<<endl
		<<"rectangle::quantity()="<<rectangle::quantity()<<endl
		<<"shape::quantity()="<<shape::quantity()<<endl;

	for(int i=0; i<shapes.size(); ++i)
		delete shapes[i];

	circle * ptemp = new circle;
	delete ptemp;

	return 0;
}