🚀 go-pugleaf

fischer@Informatik.RWTH-Aachen.DE (Rainer Fischer) wrote:

>In "Bjarne Stroustrup, The C++ programming language (german translation)"
>I found an example, which looks like this:

>struct base {
>  base *next;
>  static base *list;

>  base() {next = list; list = this};

>  virtual void function() = 0;
>  // ...
>};

>class derived : public base {
>  // ...
>public:
>  void function();
>  // ...
>};


>Two questions:

>1)  Does function() in class derived really override function() in base?
>    Does the declaration in derived really say that function is not pure
>    virtual and not virtual at all? I get a linker error-message, when I
>    use such a construction without defining the overriding function, but
>    neither a compiler error nor a warning. Is this correct?

I'm not totally sure what you are asking here, but it all looks OK.

The virtualness of function is inherited from base. It perhaps  makes
the code easier to understand if the virtual keyword is added to
derived.

>2)  What happens, when the very first object is created with a class
>    derived from base? The constructor of base assignes list to next, but
>    list is not yet initialized; so rubbish may be assigned to next. Is
>    there no need to initialize list first, e.g. base *base::list = 0; some-
>    where outside of base? I get a compiler error, if I don't do it.

You should get a linker error rather than a compiler error if you
don't.

>Thanks in advance for any help,

>Rainer Fischer.
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