In article <9314101.17440@mulga.cs.mu.OZ.AU> fjh@munta.cs.mu.OZ.AU (Fergus James HENDERSON) writes:
>MeKeNkAmP@STPC.WI.LeidenUniv.NL (Leo Mekenkamp) writes:
>
>>class derived_obj : obj {
>
>In C++, inheritance is private inheritance by default.

...when the derived class is declared as a class.  Inheritance is
public by default when the derived class is declared as a struct.

ARM, section 11.2, page 242.

--steve

Steve Vinoski  (508)436-5904   vinoski@apollo.hp.com
Distributed Object Computing Program
Hewlett-Packard, Chelmsford, MA 01824       These are my opinions.

Hello C++ Wizards!

While doing our first C++ project, we stumbeled onto two Q's:

In OO Turbo Pascal it is possible to do the following:

type
   tobj = object
      {...}
   end;
   pobj = ^tobj;

   tderived_obj = object( tobj )
      {...}
   end;
   pderived_obj = ^tderived_obj;

procedure do_something( an_obj : pobj );
begin
{...}
end;

var
   an_obj : pobj;
   a_derived_obj : pderived_obj;

begin
   do_something( an_obj );
   do_something( a_derived_obj );
end.


This compiles and executes just like you expected it to do.
But when we try this in Borland C++ 3.1

class obj {
// ...
};

class derived_obj : obj {
// ...
};

void do_something( obj* );

// ...


int main( void ) {

   obj *an_obj;
   derived_obj *a_derived_obj;

   do_something( an_obj );
   do_something( a_derived_obj ); // does not compile
}

it does not compile. Something about not being able to convert
'derived_obj*' to 'obj*'. I don't see why it can't be done; both pointers
should have the same size...

Anyway, is there a way to hack around this without having to typecast?
(do_something( (obj*) a_derived_obj);) It looks so dirty.

Second question: is there a standard way to work with 'va_start' when you
don't have any fixed parameters? i.e. how to work with va_start in a
function like

void f( ... );

We now do something like
void f( int dummy, ... ) {
//...
va_start( ap, dummy );

We would really appreciate if someone could help us out on these two.
Reply via e-mail would be much appreciated.

Celine Koster & Leo Mekenkamp.

MeKeNkAmP@STPC.WI.LeidenUniv.NL (Leo Mekenkamp) writes:

>class derived_obj : obj {

In C++, inheritance is private inheritance by default.
You need to explicitly specify "public" to get public inheritance.

 class derived_obj : public obj {
 ...

>Second question: is there a standard way to work with 'va_start' when you
>don't have any fixed parameters?

No. There is no portable method.

--
Fergus Henderson                     This .signature virus might be
fjh@munta.cs.mu.OZ.AU                getting old, but you still can't
                                     consistently believe it unless you
Linux: Choice of a GNU Generation    copy it to your own .signature file!