create an array based on size from derived class

Question

So i have an abstract class named Matrice containing a matrix of complex numbers

class Matrice {
    Complex** v;      //matrix
public:
    Matrice() {
        v = new Complex * [//lin];    //use size here, without declaring it here
        for (int i = 0; i < //lin; i++) {
            v[i] = new Complex[//col];
            for (int j = 0; j < //col; j++)
                cin >> v[i][j];
        }
    }
    virtual void afisare(int lin, int col) {
        for (int i = 0; i < lin; i++) {
            for (int j = 0; j < col; j++)
                cout << v[i][j] << " ";
            cout << endl;
        }
    }
};

and it's derived class

class Matrice_oarecare :Matrice {
    int lin, col;    //the size i want to use
public:
    Matrice_oarecare();
    ~Matrice_oarecare() {

    }
    void afisare() { Matrice::afisare(lin, col); }
};

the question is how do i dynamically allocate my matrix using the size specified in my derived class Matrice_oarecare, sorry for the dumb question but i'm new to this inheritance thing

Answer 1

If Matrice_oarecare inherits from Matrice, it has visibility on all protected attributes of Matrice class.

If you want to have access to Complex**v from the derived class then Complex**v should protected in the base class.

and to allocate in Matrice_oarecare:

v = new Complex*[lin];
for(int i = 0; i < lin; ++i)
   v[i] = new Complex[col];

Alternative

You can have a function called allocatein the base class that allocates the Complex** array like so :

class Matrice{
    void allocate(int rows, int cols){
           v = new Complex*[rows];
           for(int i = 0; i < rows; ++i)
                v[i] = new Complex[cols];
    }
}

and call it from the constructor of the derived class. So you will have

class Matrice_oarecare :Matrice {
    int lin, col;   
public:
    Matrice_oarecare(int rows, int cols):lin(rows),col(cols){
          Matrice::allocate(lin, col);
    }
    ~Matrice_oarecare() {

    }
    void afisare() { Matrice::afisare(lin, col); }
};

also you can have linand col taken as parameters to the contructor of Matrice