Base class with a vector<int> member - c++

Question

I'm trying to create an abstract base class that I intend the derive classes to implement a vector<int> member. My problem is if I try to do this:
class BaseClass
{
public:
virtual int GetCount() = 0;
virtual vector<int> ChildData;
}
class CID1 : public BaseClass
{
public:
int GetCount()
{
return 3;
}
//and so on.....
}
I get
'virtual' not permitted on data declarations
'virtual' is not allowed.
What I'm trying to do is:
make my child classes override the vector because they will contain different number of the vector elements
To be able to loop through an array of BaseClass* containing addresses of declared child classes, and the second loop for the data of the vectors.
Am I doing it the right way? Thanks in advance!
Note: I have no prior experience in coding in C++.

Answer 1

Am I doing it the right way?
No.
As the compiler lets you know, you can have virtual member functions but not virtual member variables.
Change the member variables to member functions and make sure you implement them properly in the derived classes.
class BaseClass
{
public:
virtual int GetCount() = 0;
virtual vector<int>& GetChildData() = 0;
}
class CID1 : public BaseClass
{
public:
// virtual keyword is not necessary here
// but helps with understanding code.
virtual int GetCount()
{
return 3;
}
virtual vector<int>& GetChildData()
{
return data;
}
private:
vector<int> data;
}