create an array based on size from derived class - c++

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

Answer 2

Why not just overload the constructor?
You can pass the parameters of the derived constructor to the base_class constructor and than use those parameters as you see fit.
class Matrice {
Complex** v; //matrix
public:
Matrice(int lin, int cols) {
v = new Complex * [lin]; //use size here, without declaring it here
for (int i = 0; i < lin; i++) {
v[i] = new Complex[cols];
for (int j = 0; j < cols; 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;
}
}
};
class Matrice_oarecare :Matrice {
int lin, col; //the size i want to use
public:
Matrice_oarecare():
Matrice(lin, col) {};
~Matrice_oarecare() {}
void afisare() { Matrice::afisare(lin, col); }
};