Vector of objects from different classes

Question

I'm trying to create a vector containing objects from different classes, derived from a base class. Following answers to this question I've the following code which tries four different ways (commented out below); none of which will compile:

class observable {

    public:
    virtual void observe(alglib::complex_1d_array)=0;

    observable() {

    }
};

class Energy : public observable {

    public:
    void observe(alglib::complex_1d_array);

    Energy() {

    }
};

class ObservableCollection {

    private:
    int no_obs;
    vector<observable*> obs;

    public:

    ObservableCollection(vector<string> obs) {
        no_obs=obs.size();
        for(int i=0;i<no_obs;i++) {
            if(!strcmp(obs[i].c_str(), "energy")) {
                // option 1:
                // Energy E();
                // obs.push_back(E);

                // option 2:
                // obs.push_back<std::shared_ptr<observable>(new Energy())>;

                // option 3:
                // obs.push_back(new Energy());

                // option 4:
                // observable *E=new Energy();
                // obs.push_back(E);
            }
        }
    }


};

Any ideas?

Answer 1

Option 1 cannot work because obs is a vector<observable*>^. You cannot push a object of type observable because you can only store pointers (observable*) in it. You could store such objects in a vector<observable> but you cannot store Energy objects in such vector.

Option 2 cannot work because ecause obs is a vector<observable*>^. You cannot push a object of type std::shared_ptr<observable> because you can only store raw pointers (observable*) in it. To store shared pointers, the vector must be of type vector<shared_ptr<observable>>.

Option 3 is effectively same as option 4. They would work if you actually tried to push into the member variable obj. However, you've hidden that variable by declaring a local variable by the same name (the function parameter). You cannot push observable* into a vector of strings. The compilation error should be clear about this. If you inteded to push into the member variable, you can use this->obs instead, or even better, use different name for the local variable.

^Assuming you were actually pushing into this->obs rather than the local variable.

Answer 2

You are passing vector obs (called the same as member) and you are trying to push your class to it. If you want to push to the member, use this.obs.push_back().