Virtual and pure virtual destructors and their implementation in c++

Virtual deconstruction and pure virtual deconstruction -----> Solve the problem that the subclass destructor cannot be called

In the use of polymorphism , If there are attributes in the subclass that go to the heap , Then the parent class child needle cannot call the destructor code of the child class when it is released
Solution ： Change the destructor in the parent class to virtual or pure virtual destructor

Destructions and pure virtual destructions have something in common ：

1、 Can solve the parent class pointer to release the child class object
2、 Need to have specific function implementation

difference ：

If it's pure virtual deconstruction , This class belongs to the abstract class , Cannot instantiate object

class Animal{
public:
    Animal(){
        printf(" Animal class constructor !\n");
    }

    //  Virtual destructions can be used to solve the problem that the parent class pointer releases unclean subclass objects 
//    virtual ~Animal(){
//        cout<<" Animal destructors "<<endl;
//    }
    
    //  Pure virtual destructors   Required declaration , It also needs to be realized 
    //  With pure virtual destructor   This class is also an abstract class , Cannot instantiate object 
    virtual ~Animal() =0;

    //
    virtual void speak(){
        cout<<"hello"<<endl;
    }
};




//  Implementation of pure virtual destructor , You can release variables opened by the parent class in the heap area 
Animal::~Animal(){
    cout<<" Animal destructors , Here, release the variables opened by the parent class in the heap ！"<<endl;
}




class Dog:public Animal{
public:
    string *m_Name;
    Dog(string name){
        //  Subclasses have attributes that open up to the heap 
        m_Name = new string(name);
        cout<<" Subclass "<<*m_Name<<" Constructors !\n";
    }
    
    ~Dog(){
        cout<<" Dog destructor "<<endl;
        if (m_Name!=NULL) {
            delete m_Name;
            m_Name = NULL;
        }
    }
    
    void speak(){
        cout<<" Wang Wang Wang "<<endl;
    };
};




void demo(){
//    Animal an; //  Unable to instantiate the object 
    Animal *animal = new Dog(" rhubarb ");
    //  When the parent class pointer is destructed , The destructor of the subclass will not be called , As a result, if the subclass has attributes in the heap , There is a memory leak 
    animal->speak();
    delete animal;
}




int main(int argc, const char * argv[]) {
    demo();
    return 0;
}

summary

1、 Virtual destructors and pure virtual destructors are used to release subclass objects through parent class pointers
2、 If there is no heap data in the subclass , There is no need for virtual fiction and pure virtual deconstruction
3、 Classes with pure virtual destructors also belong to abstract classes