Re: great c++ question

From:

shadowman <shadowman@noemail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 21 Jun 2007 10:51:17 -0400

Message-ID:

<f5e39c$df6$1@aioe.org>

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.

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.

>
> #include <iostream>
> #include <vector>
> class AbstrBase
> {
> public:
> virtual void run()=0;
> };
> class Int:public AbstrBase
> {
> int m_i;
> public:
> void setI(int i)
> {
> m_i = i;
> };
> const int& getI()const
> {
> return m_i;
> };
> void run()
> {
> std::cout << "Value is of type integer" << std::endl;
> std::cout << "Value is=" << m_i << std::endl;
> };
>
> };
> class Str:public AbstrBase
> {
> std::string m_s;
> public:
> void setS(const std::string s)
> {
> m_s = s;
> };
> const std::string& getS()const
> {
> return m_s;
> };
> void run()
> {
> std::cout << "Value is of type string" << std::endl;
> std::cout << "Value is=" << m_s << std::endl;
> };
> };
> class Container:public std::vector<AbstrBase*>
> {
> };
> int main(void)
> {
> Container c;
> Int * a = new Int;
> a->setI(1);
> Str * b = new Str;
> b->setS(std::string("hello world!"));
> c.push_back(a);
> c.push_back(b);
> std::vector<AbstrBase*>::iterator it = c.begin();
> while(it != c.end() )
> {
> (*it)->run();
> it++;
> }
> return 0;
> }

OK, but all you have shown here is an example of polymorphism and
dynamic binding. Both of these are well-known and basic OO concepts
that can be implemented in C++. If the question really was about this,
than it's not a very interesting or "great c++ question," as the OP stated.

However, the question explicitly asked about adding data _members_ at
runtime. That is something entirely different from what you are doing here.