An alternative would be to put the data members in a 'protected' section.

class Employee
{
protected:  // Derived classes can access protected members
  string name;     // For other code, protected is like private
  double salary;
public:
  Employee(const string& nm, double sal) 
        : name(nm), salary(sal) {}
  string getName() const { return name; }
  double getSalary() const { return salary; }
  virtual double getBonus() const;
};