Store abstract derived class objects in base class vector

Question

I've learned to store derived class pointers in base class vectors by storing base class pointers:

vector<base*> base_vector;
base_vector.push_back(new derived());
// free memory at the end

But if I have an abstract base class:

class interface {
public:
    virtual interface(){} 
    virtual ~interface(){}
};

From which two more abstract classes are derived.

class abstract_derived_1 : virtual public interface 
{ 
public:
    virtual abstract_derived_1(){} 
    virtual ~abstract_derived_1(){}
};

class abstract_derived_2 : virtual public interface 
{ 
public:
    virtual abstract_derived_2(){} 
    virtual ~abstract_derived_2(){}
};

And several other derived classes from the secondary abstract classes:

class derived_1 : virtual public interface, virtual public abstract_derived_1
{
private:
    double value;
public:
    derived_1(){value=0;}
    derived_1(const double val1, const double val2) { value = val1+val2; }
    ~derived_1(){}
};


class derived_2 : virtual public interface, virtual public abstract_derived_2
{
private:
    string name;
public:
    derived_2(){name="";}
    derived_2(string my_str) { name = my_str; }
};

Is it possible to store all of them in a polymorphic vector? As usual, I did the following:

vector<abstract_derived_1*> abs1;
vector<abstract_derived_2*> abs2;
abs1.push_back(new derived_1(1,2));
abs2.push_back(new derived_2("polymorphism"));

But how do I store the two polymorphic vectors in a base class vector?

vector</* What should I put in here? */> interface_vector;

Why are your constructors virtual and how do you manage to assign derived_2 * to abstract_derived_1 *? — Killzone Kid
I used virtual so that i have them as pure abstract classes. I’ve made a typo there I’ve now corrected it:) — Ret
Have you tried to compile your code or no need because you just confident that you can have virtual constructors? ideone.com/C8Ii77 — Killzone Kid
@KillzoneKid I’ve compiled my codes (similar to the simplified example i used above), and everything worked fine, i was able to print out information. But I’m a bit confused about how to store data in polymorphic arrays/vectors :) — Ret
@Z.Yang "I used virtual so that i have them as pure abstract classes" - what you have are not abstract classes. That requires methods be declared with not only virtual but also = 0 as well, eg: virtual void doSomething() = 0;. And constructors can't be virtual, but destructors can (and should be, in a base class) — Remy Lebeau

tangoal tangoal · Accepted Answer · 2018-04-07T14:39:42

There is no problem to just push_back new instances of derived_1 and derived_2 to a generic vector vector<interface*>, because they have the interface class as ancestor.

By the way: you don't need the derived_1 class and derived_2 class to inherit from interface again. This is a uncommon and I am quite sure that this may lead to other problems.

Store abstract derived class objects in base class vector

2 Answers