C++ : Get a child member from the Father class - c++

Question

I recently asked a question related to the accessibility of a child member from a parent class using the cout method . But this time what if I want to use a get method instead of cout ? Will this change the idea ?
Assuming I have a class called CArray :
class CArray
{
public:
CArray();
private:
std::vector<CPerson *>Persons;
};
Where CPerson a parent class :
class CPerson
{
public:
CPerson();
virtual void Print()
{
std::cout << Name << "\n";
}
protected:
std::string Name;
};
and CStudent the child of Person
class CStudent : public CPerson
{
public:
CStudent();
private:
int MatriculationNr;
};
Let's assume that we loaded the private members of CStudent and CPerson as follows :
if (condition)
{
CStudent *S1 = new CStudent();
S1->load(src); //Load function is missing in class but ignore it
Persons.push_back(S1);
}
I recently learned how to access the private member of CStudent and CPerson with the use of the virtual method and exactly by adding to CStudent class this function below :
void Print()
{
CPerson::Print();
std::cout << MatriculationNr << "\n";
}
Now moving on to my class CArray . I wrote a print method to print the elements of Persons :
I just have to write Persons[i]->Print(); which will call Print() from all Persons .
The question now what If I want to get the MatriculationNr from the first element of Persons (as an example)?
cout << Persons[i]->getMatrikulNr();is not valid since we're trying here to get a function from a child class which is not possible this way .
I wanted to apply the same behavior that I did with print() but this is not possible due to the return parameter that I will have with the get method .

Answer 1

what If I want to get the MatriculationNr from the first element of Persons (as an example)?
You won't be able to. Not with the code you have shown, anyway. MatriculationNr exists only in CStudent, and it is private at that, so only CStudent can access it.
cout << Persons[i]->getMatrikulNr(); is not valid since we're trying here to get a function from a child class which is not possible this way . I wanted to apply the same behavior that I did with print() but this is not possible due to the return paramater that I will have with the get method .
You would have to either:
add a public virtual getMatrikulNr() method to CPerson which CStudent can then override, eg:
class CPerson
{
public:
...
virtual int getMatrikulNr() const
{
return 0;
}
...
};
class CStudent : public CPerson
{
public:
...
int getMatrikulNr() const override
{
return MatriculationNr;
}
private:
int MatriculationNr;
};
And then you can use Persons[i]->getMatrikulNr() as needed.
add a public getMatrikulNr() method to CStudent, and then dynamic_cast each CPerson* pointer to see if it is pointing at a CStudent object or not, eg:
class CStudent : public CPerson
{
public:
...
int getMatrikulNr() const
{
return MatriculationNr;
}
private:
int MatriculationNr;
};
CStudent *student = dynamic_cast<CStudent*>(Persons[i]);
if (student) {
// use student->getMatrikulNr() as needed...
}