great c++ question

[Amar Kumar Dubedy]

implement a c++ class such that it allows us
to add data members at runtime.

[John Harrison]

Amar Kumar Dubedy wrote:

implement a c++ class such that it allows us
to add data members at runtime.

Here's a great answer, impossible.
I think Coplien has some code that *simulates* this in 'Advanced C++
Programming Styles and Idioms'.

john

[Ulterior]

On Jun 21, 6:48 am, Amar Kumar Dubedy <adub...@yahoo. co.inwrote:

implement a c++ class such that it allows us
to add data members at runtime.

Who in the world would want that?

[amarkrdubedy]

On Jun 21, 10:50 am, John Harrison <john_androni.. [e-mail]>
wrote:

Amar Kumar Dubedy wrote:

implement a c++ class such that it allows us
to add data members at runtime.

Here's a great answer, impossible.

I think Coplien has some code that *simulates* this in 'Advanced C++
Programming Styles and Idioms'.

john

I thought that it was impossible too. But its a question asked in
Yahoo Interview. So i thought i wud put it up.

[John Harrison]

am**********@ya hoo.co.in wrote:

On Jun 21, 10:50 am, John Harrison <john_androni.. [e-mail]>
wrote:

>Amar Kumar Dubedy wrote:

>>implement a c++ class such that it allows us
to add data members at runtime.

Here's a great answer, impossible.

I think Coplien has some code that *simulates* this in 'Advanced C++
Programming Styles and Idioms'.

john

I thought that it was impossible too. But its a question asked in
Yahoo Interview. So i thought i wud put it up.

Sounds like a trick question.

[Bobba Dobba]

Amar Kumar Dubedy wrote:

implement a c++ class such that it allows us
to add data members at runtime.

sure it's possible, still you need to access them, and know their types. all
feasible.
a void pointer kan be used, or if you know the type you can make an abstract
base class and inherit classes from that. save in whatever for later
access. Still, as I see it there needs to be some kind of "known" interface
that you can use for accessing.

[John Harrison]

Bobba Dobba wrote:

Amar Kumar Dubedy wrote:

>implement a c++ class such that it allows us
to add data members at runtime.

sure it's possible, still you need to access them, and know their types. all
feasible.
a void pointer kan be used, or if you know the type you can make an abstract
base class and inherit classes from that. save in whatever for later
access. Still, as I see it there needs to be some kind of "known" interface
that you can use for accessing.

Show us some code. I don't see how anything you've said above relates to
adding data members at runtime.

john

[Bobba Dobba]

John Harrison wrote:

Bobba Dobba wrote:

>Amar Kumar Dubedy wrote:

>>implement a c++ class such that it allows us
to add data members at runtime.

sure it's possible, still you need to access them, and know their types.
all feasible.
a void pointer kan be used, or if you know the type you can make an
abstract base class and inherit classes from that. save in whatever for
later access. Still, as I see it there needs to be some kind of "known"
interface that you can use for accessing.

Show us some code. I don't see how anything you've said above relates to
adding data members at runtime.

john

depends on where you save them, stack, list, vector. a data member can also
be embedded in a abstract class, which you derive a specialised class from.
so, my idea is that the cotnainer used for storing the dynamic data members
would be "compiled in". but the contents would not. well, try it*S*

[John Harrison]

John Harrison wrote:

Bobba Dobba wrote:

>Amar Kumar Dubedy wrote:

>>implement a c++ class such that it allows us
to add data members at runtime.

sure it's possible, still you need to access them, and know their
types. all
feasible.
a void pointer kan be used, or if you know the type you can make an
abstract
base class and inherit classes from that. save in whatever for later
access. Still, as I see it there needs to be some kind of "known"
interface
that you can use for accessing.

Show us some code. I don't see how anything you've said above relates to
adding data members at runtime.

Data members have a type, and a name, they are accessed with a
particular syntax. All of these are features of source code, not of a
running program. The question doesn't amke sense unless it is a trick
question.

Of course of the question had been, 'write a class so that you can add
arbitrary data at runtime' it would be much easier. But the question
said data members, not data.

[John Harrison]

Bobba Dobba wrote:

John Harrison wrote:

>Bobba Dobba wrote:

>>Amar Kumar Dubedy wrote:

implement a c++ class such that it allows us
to add data members at runtime.
sure it's possible, still you need to access them, and know their types.
all feasible.
a void pointer kan be used, or if you know the type you can make an
abstract base class and inherit classes from that. save in whatever for
later access. Still, as I see it there needs to be some kind of "known"
interface that you can use for accessing.

Show us some code. I don't see how anything you've said above relates to
adding data members at runtime.

john

depends on where you save them, stack, list, vector. a data member can also
be embedded in a abstract class, which you derive a specialised class from.
so, my idea is that the cotnainer used for storing the dynamic data members
would be "compiled in". but the contents would not. well, try it*S*

Add data to a vector is adding data to an object. It is not the same
thing at all as adding a data member to a class. For instance if you add
a data member to a class, then ALL objects of that class get the new
data member.

class X
{
int d;
};

d is a data member, now how at runtime do I change the code so that X
becomes

class X
{
int d;
int d2;
};

The obvious problem is that X only exists in the source code of the
program. This is not true of all programming languages, but it is true
of C++.