C++ knowledge

**indranilmuk** · 08-21-2002

Tell me what is the basic difference between a virtual base class and an abstract base class.

**Ruski** · 08-21-2002

Never heard of it

**SilentStrike** · 08-21-2002

A virtual class is a class with a virtual function. An abstract class is a class that has a pure virtual function. One cannot create abstract classes (only subclasses of abstract classes). However, non-abstract virtual classes can be instantiated. Confusing enough?

.

Code:

class virtualClass {
public:
    virtual void someVirtualFunc();
};

class abstractClass {
public:
     virtual void pureVirtualFunc()=0;
};

**Ruski** · 08-21-2002

Yea, that IS confusing...

**face_master** · 08-21-2002

>> Yea, that IS confusing...

Well, not really. Its actually quite logical.

eg.

Code:

class Teacher
{
public:
    virtual void Teacher();

    char fname[256];
    char sname[256];
    
    virtual void TeachClass();
}

In the above class we have an abstract class called teacher. It has its contructor and a pure virtual function called 'TeachClass()'. Obviously this function would be differernt according to each different type of teacher (eg. Science teacher). The science teacher would be a subclass of Teacher and it would overload the pure virtual functions with their own version of them like the following.

Code:

class ScienceTeacher : public Teacher
{
    void TeachClass()
    {
        // do special science stuff
    }
}

Its not that confusing after all

**Ruski** · 08-21-2002

You're wrong... it's SO Confusing!!

**BMJ** · 08-21-2002

Don't fret... it'll just take some time to 'click' with you I guess... It makes sense though!

In face_master's example, TeachClass() is virtual function member of Teacher, which means that when you derive a class from Teacher (excuse the terminology

) TeachClass() can be redefined to fit that class if it chooses not to use the default from Teacher if it's defined

**BMJ** · 08-21-2002

I just read what I posted and I think I probably confused you more

Look at some tutorials...

One other thing... you cannot create instances of abstract classes; remember this.

Code:

abstractClass ac;

Cannot be done

**Prelude** · 08-21-2002

>Confusing enough?

.
Only to those who do not already understand it. This seems to be the case with almost everything in C++.

-Prelude

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