I am not very experienced with the OO side of C++ and I'm trying to port some code across and brush up my knowledge but I'm having an issue. I have a class defined like this:

```

class ExtendedKalmanFilter
{
private:

    double dt;

public:
    ExtendedKalmanFilter(int states);

    virtual VectorXd f(VectorXd x, VectorXd u);
    virtual MatrixXd F(VectorXd x);
    virtual VectorXd h(VectorXd x);
    virtual MatrixXd H(VectorXd x);

    ~ExtendedKalmanFilter();
};

```

I have another class which inherits `ExtendedKalmanFilter` and implements the virtual functions:

```

class KineticEnergyEKF : public ExtendedKalmanFilter {
public:
    KineticEnergyEKF(int nstates) : ExtendedKalmanFilter(nstates)
    {}

    VectorXd f(VectorXd x, VectorXd u)
    {
        this->dt = 1.0; //ERROR: Apparently I have no access to dt
    }
    MatrixXd F(VectorXd x);
    VectorXd h(VectorXd x);
    MatrixXd H(VectorXd x);
};

```

Visual Studio is showing that I can't access `dt`, but I can access the other functions defined in the `ExtendedKalmanFilter`. How do I access `dt`?