How to use Virtual functions?

[Jake123456]

I am unfamiliar with using virtual functions and was wondering how I would implement them correctly. I have a class called 'car' and an abstract class called 'Carbon Footprint' and want to have a one pure virtual function called
getCarbonFootprint(). I am trying to get the 'car' class to inherit this getCarbonFootprint() function. Cheers to anyone that can lend a hand

[AbstractionAnon]

Not sure why getCarbonFootprint() needs to be virtual (other than perhaps that's your assignment). From your limited description, getCarbonFootprint() could just as easily be a non-virtual member of CarbonFootPrint.

The purpose of virtual functions is to exhibit different behavior in different derived classes. A classic example is a base class of Shape. Square, Circle and Triangle all derive from Shape. Shape has a pure virtual member Area(). Area() has no meaning for the base class, each derived class calculates area differently. Yet, you can call shape->area() and invoke the Area() function for the appropriate derived class.

Since you haven't fully described your assignment, I've made the assumption that the base class has a member m_cfp that's accessible from its derived classes.

class CarbonFootPrint 
{
protected:
    int     m_cfp;    //  Or whatever you're measuring
    
public:
    CarbonFootPrint (int cfp)
    {  m_cfp = cfp;
    }
    
    virtual ~CarbonFootPrint ()
    {}

    virtual int getCarbonFootprint () const = 0;    
};

class Car : public CarbonFootPrint
{
public:
    Car () : CarbonFootPrint (50)   //  Assume a car has a CFP of 50
    {}
    
    int getCarbonFootprint () const
    {   return m_cfp;
    }
};

[gunnerfunner]

@AbstractionAnon: how'd you explain public inheritance of Car from CarbonFootPrint? What sort of relationship would that entail b/w the two classes? Admittedly private/protected inheritance (as CarbonFootPrint <- Car should be) support virtual functions but the only query on these lines that I found did not really have any good answers as to why virtual functions might be necessary in non-public inheritance with some of the replies sceptical about having virtual functions under such inheritance
http://stackoverflow.com/questions/2157854/virtual-function-in-private-or-protected-inheritance