Thread: Why did I get this question wrong?

ok. First of all, there can be only one anwser to this question. The quesiton is.

Question from my test.

The reason for declaring a pure virtual function is:

A. The function will always exsist in each of the derived classes.

B. Each copy of the function is completely different in each of the derived classes.

C. There is no common denominator between versions of the function in the derived classes.

D. All of the above.

E. None of the above.

The anwser was D. I said B. I missed this because I was confused about A.

Is it true, that if you don't overide the pure virtual function in a derived class, this class will just become abstract itself? Then you could derive other classes from this abstract and maybe enhance it with other pure virtual functions? Maybe I am wrong but I would like to argue this one because it cost me an A on the test.

I also agree that the correct answer should have been A.
B and C do not hold for all virtual functions.Sometimes those conditions are met and sometimes they are not.

What is a virtual function?

>A. The function will always exsist in each of the derived classes.
Yes

>B. Each copy of the function is completely different in each of the derived classes.
Sometimes, but not always

>C. There is no common denominator between versions of the function in the derived classes.
More or less, this could be worded better

>D. All of the above.
I can see how this would be the answer, but it's not wholely correct.

A virtual function allows derived classes to replace the implementation provided by the base class. The compiler makes sure the replacement is always called whenever the object in question is actually of the derived class, even if the object is accessed by a base pointer rather than a derived pointer. This allows algorithms in the base class to be replaced in the derived class, even if users don't know about the derived class.

The derived class can either fully replace ("override") the base class member function, or the derived class can partially replace ("augment") the base class member function. The latter is accomplished by having the derived class member function call the base class member function, if desired.

-Prelude