（10）C++智能指针---shared_ptr,dynamic_pointer_cast

#include <iostream>
#include <thread>
#include <memory> //智能指针所在头文件
using namespace std;
class BaseClass
{
public:
	BaseClass(){}
	~BaseClass(){}
	virtual void print()
	{
		cout << "this is base class" << endl;
	}
protected:
	string _name;
	int _key;



};

class DerivedClass :public BaseClass
{
public:
	DerivedClass() {}
	~DerivedClass(){}
	void print() 
	{
		cout << "this is derived class" << endl;
	}

};
int main()
{
	BaseClass *base = new DerivedClass(); //基类指针可以指向派生类对象

	base->print();  //这里调用print函数是直接调用的派生类的print函数，如果print函数没有加virtual关键字，则会调用基类的print函数
	//DerivedClass *derived = new BaseClass();//这里报错，派生类指针不能指向基类对象

	DerivedClass *de = dynamic_cast<DerivedClass*>(base); //把基类指针所指的对象转换为具体的派生类对象,要能实现这个多态的转换，基类必须要有函数添加关键字virtual
	de->print();

	//智能指针
	cout << "shared pointer" << endl;
	shared_ptr<BaseClass> shared_base = make_shared<DerivedClass>();
	shared_base->print();
	//智能指针基类强转为派生类
	shared_ptr<DerivedClass> shared_de = dynamic_pointer_cast<DerivedClass>(shared_base);
	shared_de->print();

	//由普通指针构造智能指针
	shared_ptr<BaseClass>shared_ba(base);//base 是上面用过的指向派生类的普通指针类型，通过构造函数直接构造智能指针
	shared_ba->print();
	//由智能指针构造普通指针

	BaseClass *common_base;
	common_base = shared_ba.get();
	common_base->print();

	system("pause");

	return 0;
}