c++ How to access derived class custom unordered_map from base class pointer pointing to derived class object with out using casting

Question

I have designed my classes like the below.. I am trying to access unordered_map of derived class from base class pointer pointing to derived class instance... I know I cant do this because of Object Slicing...

I know I can access derived class map after static_casting / dynamic_casting.... --> I am not interested in this approach.

But I am looking for approach in the form of creating abstract base class containing one pure virtual function and defining it in derived class so that it returns a pointer to its map...

I tried using static_cast and dynamic_cast concept It is working but i dont want to do like this.

My Code:

class Base{

    public:

    Base(string key, string type){

        this->key = key;
        this->key_Type = type;
    }

    protected:
        string key;
        string key_Type;
};

class Derived : public Base{    

    public:
        Derived(string k, string t) : Base(k,t){}

    protected:
        unordered_map<string, Base*> my_Map;

};

int main(){

    Derived *d1 = new Derived("Id","Integer");

    Base* b = d1;

    Derived *d2 = new Derived("Name","String");

    b->my_Map.insert({"Name",d2});

        return 0;

}

My expected outcome is somehow i need access to that derived class map so that I can insert values into it like:

my_Map.insert({"Name",PointerobjectofDerivedclass})

EDIT:1-----------------------------

I tried using pure virtual functions, but I am not so clear on how to use this..SO I ended up with a lot of errors..

My code:

class Base{

public:

Base(string key, string type){

    this->key = key;
    this->key_Type = type;
}

virtual void insertmap()=0;

protected:
    string key;
    string key_Type;

};

class Derived : public Base{

public:
    Derived(string k, string t) : Base(k,t){}

    virtual void insertmap(string n , Base* obj){

        this->my_Map.insert({n,obj});

    }

protected:
    unordered_map<string, Base*> my_Map;

};

int main(){

Derived *d1 = new Derived("Id","Integer");

Base* b = d1;

Derived *d2 = new Derived("Name","String");

b->insertmap("Name",d2);

return 0;

}

My compiler errors: In function 'int main()': error: invalid new-expression of abstract class type 'Derived' Derived *d1 = new Derived("Id","Integer"); ^ note: because the following virtual functions are pure within 'Derived': class Derived : public Base{ ^ note: virtual void Base::insertmap() virtual void insertmap()=0; ^ error: invalid new-expression of abstract class type 'Derived' Derived d2 = new Derived("Name","String"); ^ error: no matching function for call to 'Base::insertmap(const char [5], Derived&)' b->insertmap("Name",d2); ^ note: candidate is: note: virtual void Base::insertmap() virtual void insertmap()=0; ^ note: candidate expects 0 arguments, 2 provided

LoneWolf97 LoneWolf97 · Accepted Answer · 2019-05-13T06:00:22

After going through a lot of similar question answers I was able to clear the errors and had implemented successfully...

My Final working code:

class Base{

public:

Base(string key, string type){

    this->key = key;
    this->key_Type = type;
}

virtual void insertmap(string n, Base* obj)=0;

protected:
    string key;
    string key_Type;

};

class Derived : public Base{

public:
    Derived(string k, string t) : Base(k,t){}

     void insertmap(string n , Base* obj){

        this->my_Map.insert({n,obj});

    }

    void getdetails(){

        for(auto itr = my_Map.begin();itr!=my_Map.end();++itr){

        cout<<itr->first << '\n'; 
    }
    }
protected:
    unordered_map<string, Base*> my_Map;

};

int main(){

Derived *d1 = new Derived("Id","Integer");

Base* b = d1;

Derived *d2 = new Derived("Name","String");

b->insertmap("Name",d2);

d1->getdetails();

return 0;

}

Output: Name

c++ How to access derived class custom unordered_map from base class pointer pointing to derived class object with out using casting

1 Answers