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工厂模式与shared_ptr_shared_ptr c++ 工厂模式

作者：编程谜题解决者 | 2024-01-31 18:49:09

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shared_ptr c++ 工厂模式

文章目录

工厂模式图

在这里插入图片描述

c++为什么涉及到虚函数时要将基类的析构函数设计为虚函数

要回答这个问题，首先需要弄清楚的问题是，在C++中类的构造函数、析构函数的调用次序是什么？

这里指假设基类和派生类的成员中，包含其他类的对象。

在C++中，构造函数的调用次序是：

基类的成员->基类的构造函数体->派生类的成员->派生类的构造函数体

析构函数的调用次序是：

派生类的析构函数->派生类的成员析构->基类的析构函数->基类的成员析构

#include <iostream>
using namespace std;
 
class AA
{
public:
    AA()
    {
        cout<<"AA Construct"<<endl;
    }
 
    ~AA()
    {
        cout<<"AA Destroy"<<endl;
    }
};
 
class BB
{
public:
    BB()
    {
        cout<<"BB Construct"<<endl;
    }
 
    ~BB()
    {
        cout<<"BB Destroy"<<endl;
    }
};
 
class Base
{
public:
    Base()
    {
        cout<<"Base Construct"<<endl;
    }
 
    ~Base()
    {
        cout<<"Base Destroy"<<endl;
    }
private:
    AA aa;
};
 
class Derive: public Base
{
public:
    Derive()
    {
        cout<<"Derive Construct"<<endl;
    }
    
    ~Derive()
    {
        cout<<"Derive Destroy"<<endl;
    }
private:
    BB bb;
};
 
int main()
{
    Base *p = new Derive;
    delete p;
    /*运行结果
    AA Construct
    Base Construct
    BB Construct
    Derive Construct
    Base Destroy
    AA Destroy
    */
}

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从程序的运行情况来看，我们不难发现，在最后释放指针p所指向的对象时，只释放了基类的部分，没有释放派生类的部分。这是因为，指针p声明时是基类的指针，而基类的析构函数不是虚函数，所以调用那个析构函数是在编译时确定的。如果要执行正确的析构顺序，需要将基类的析构函数定义为 virtual， 这样派生类的析构函数就自动是virtual的了，在最后释放指针p时，按照RTTI，执行p所指真实对象的析构函数

工厂模式代码

//当类里面没有数据只有纯虚方法时称之为接口
class Shape // 接口
{
public:
	Shape() { cout << "Shape" << endl; }
	virtual ~Shape() { cout << "~Shape" << endl; }
	virtual void draw() = 0;
	virtual void erase() = 0;
};

class Circle : public Shape
{
public:
	Circle() { cout << "Circle" << endl; }
	virtual ~Circle() { cout << "~Circle" << endl; }
	void draw() { cout << "circle::draw" << endl; }
	void erase() { cout << "circle::erase" << endl; }
};

class Square : public Shape
{
public:
	Square() { cout << "Square" << endl; }
	virtual ~Square() { cout << "~Square" << endl; }
	void draw() { cout << "Square::draw" << endl; }
	void erase() { cout << "Square::erase" << endl; }
};


class ShapeFactory//工厂
{
public:
	ShapeFactory() { cout << "ShapeFactory" << endl; }
	virtual ~ShapeFactory() { cout << "~ShapeFactory" << endl; }

	virtual Shape* create() = 0;
};
class CircleFactory : public  ShapeFactory
{
public:
	CircleFactory() { cout << "CircleFactory" << endl; }
	~CircleFactory() { cout << "~CircleFactory" << endl; }
	virtual Shape* create()
	{
		return new Circle();
	}
};

class SquareFactory : public  ShapeFactory
{
public:
	SquareFactory() { cout << "SquareFactory" << endl; }
	~SquareFactory() { cout << "~SquareFactory" << endl; }
	virtual Shape* create()
	{
		return new Square();
	}
};

int main()
{
	ShapeFactory* factory = new SquareFactory();
	Shape* shape = factory->create();
	shape->draw();
	shape->erase();

	factory = new CircleFactory();
	shape = factory->create();
	shape->draw();
	shape->erase();
	return 0;
}

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在这里插入图片描述

#include<iostream>
#include<atomic>
#include<string>
#include<map>
//key_value键值对，和值
using namespace std;
//当类里面没有数据只有纯虚方法时称之为接口
class Shape // 接口
{
public:
	Shape() { cout << "Shape" << endl; }
	virtual ~Shape() { cout << "~Shape" << endl; }
	virtual void draw() = 0;
	virtual void erase() = 0;
};

class Circle : public Shape
{
public:
	Circle() { cout << "Circle" << endl; }
	virtual ~Circle() { cout << "~Circle" << endl; }
	void draw() { cout << "circle::draw" << endl; }
	void erase() { cout << "circle::erase" << endl; }
};

class Square : public Shape
{
public:
	Square() { cout << "Square" << endl; }
	virtual ~Square() { cout << "~Square" << endl; }
	void draw() { cout << "Square::draw" << endl; }
	void erase() { cout << "Square::erase" << endl; }
};


class ShapeFactory//工厂
{
public:
	ShapeFactory() { cout << "ShapeFactory" << endl; }
	virtual ~ShapeFactory() { cout << "~ShapeFactory" << endl; }
	virtual Shape* create() = 0;
public:
	static std::map<string, ShapeFactory*> factories;
	//              key       value
	//             ShapeName; 
	static Shape* createShape(const string& id)
	{
		if (factories.find(id) != factories.end())
		{
			return factories[id]->create();
		}
		else
		{
			return nullptr;
		}
	}
};
//静态成员的初始化
std::map<string, ShapeFactory*> ShapeFactory::factories;

class CircleFactroy : public  ShapeFactory
{
public:
	CircleFactroy() { cout << "CircleFactroy" << endl; }
	~CircleFactroy() { cout << "~CircleFactroy" << endl; }
	virtual Shape* create()
	{
		return new Circle();
	}
};

class SquareFactroy : public  ShapeFactory
{
public:
	SquareFactroy() { cout << "SquareFactroy" << endl; }
	~SquareFactroy() { cout << "~SquareFactroy" << endl; }
	virtual Shape* create()
	{
		return new Square();
	}
};
//形状工厂的初始化，主要负责初始map
class ShapeFactoryInitializer
{//不能在类里面定义一个类型成员会无限递归下去，使用static
	static ShapeFactoryInitializer si;
	ShapeFactoryInitializer()
	{
		// key  value ShapeFactroy *                            
		ShapeFactory::factories["Circle"] = new CircleFactroy();
		ShapeFactory::factories["Square"] = new SquareFactroy();
	}
};
//下面这行代码会在主函数之前生成CircleFactroy和SquareFactroy对象
ShapeFactoryInitializer ShapeFactoryInitializer::si;

// Client
int main()
{
	Shape* shape = ShapeFactory::createShape("Circle");

	shape->draw();
	shape->erase();

	shape = ShapeFactory::createShape("Square");

	shape->draw();
	shape->erase();


	return 0;
} 

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在这里插入图片描述

#include<iostream>
#include<atomic>
#include<string>
#include<map>
#include<memory>
//当类里面没有数据只有纯虚方法时称之为接口
class Shape // 接口
{
public:
	Shape() { cout << "Shape" << endl; }
	virtual ~Shape() { cout << "~Shape" << endl; }
	virtual void draw() = 0;
	virtual void erase() = 0;
};

class Circle : public Shape
{
public:
	Circle() { cout << "Circle" << endl; }
	virtual ~Circle() { cout << "~Circle" << endl; }
	void draw() { cout << "circle::draw" << endl; }
	void erase() { cout << "circle::erase" << endl; }
};

class Square : public Shape
{
public:
	Square() { cout << "Square" << endl; }
	virtual ~Square() { cout << "~Square" << endl; }
	void draw() { cout << "Square::draw" << endl; }
	void erase() { cout << "Square::erase" << endl; }
};


class ShapeFactory//工厂
{
public:
	ShapeFactory() { cout << "ShapeFactory" << endl; }
	virtual ~ShapeFactory() { cout << "~ShapeFactory" << endl; }
	virtual std::shared_ptr<Shape> create() = 0;
public:
	static std::map<string, std::shared_ptr<ShapeFactory>> factories;
	//              key       value
	//             ShapeName; 
	static std::shared_ptr<Shape> createShape(const string& id)
	{
		if (factories.find(id) != factories.end())
		{
			return factories[id]->create();
		}
		else
		{
			return nullptr;
		}
	}
};
//静态成员的初始化
std::map<string, std::shared_ptr<ShapeFactory>> ShapeFactory::factories;

class CircleFactroy : public  ShapeFactory
{
public:
	CircleFactroy() { cout << "CircleFactroy" << endl; }
	~CircleFactroy() { cout << "~CircleFactroy" << endl; }
	virtual std::shared_ptr<Shape> create()
	{
		return std::make_shared<Circle>();
	}
};

class SquareFactroy : public  ShapeFactory
{
public:
	SquareFactroy() { cout << "SquareFactroy" << endl; }
	~SquareFactroy() { cout << "~SquareFactroy" << endl; }
	virtual std::shared_ptr<Shape> create()
	{
		return std::make_shared<Square>();
	}
};
//形状工厂的初始化，主要负责初始map
class ShapeFactoryInitializer
{//不能在类里面定义一个类型成员会无限递归下去，使用static
	static ShapeFactoryInitializer si;
	ShapeFactoryInitializer()
	{
		// key  value ShapeFactroy *                            
		ShapeFactory::factories["Circle"] = std::make_shared<CircleFactroy>();//new CircleFactroy();
		ShapeFactory::factories["Square"] = std::make_shared<SquareFactroy>();//new SquareFactroy();
	}
};
//下面这行代码会在主函数之前生成CircleFactroy和SquareFactroy对象
ShapeFactoryInitializer ShapeFactoryInitializer::si;

// Client
int main()
{
	std::shared_ptr<Shape> shape = ShapeFactory::createShape("Circle");

	shape->draw();
	shape->erase();

	shape = ShapeFactory::createShape("Square");

	shape->draw();
	shape->erase();

	return 0;
} 

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shared_ptr对象创建方法的讨论

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标题make_share的好处

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make_share的坏处

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