Re: create an object with variable CLASS

[Axel Freyn <axel-freyn at gmx dot de>]

Hi Mohsen,
On Tue, Oct 27, 2009 at 07:40:45AM +0330, Mohsen Pahlevanzadeh wrote:
> Suppose following code:
> ////////////
> char *var;
> var = "class1"
> ////////////
> So, I don't know name of class1, but i have varibale var.How can i
> create an object from class1 by this variavble?
Sorry, now I understand the question:-)
Well - I think the best way is the one proposed by Andrew: You first
have to some kind of dictionary, which maps the names to the classes -
this dictionary can't be created automatically in C++, but you have to
write it yourself. And in addition, you have to supply a common
base-class for all your classes. The following example (untested...) 
should explain the procedure:

#include <iostream>
#include <cstring>
#include <cstdlib>
class Base{
  public:
    virtual void DoSomething() = 0;
};
class A:public Base{
  public:
    void DoSomething(){std::cout << "A" << std::endl;}
};
class B:public Base{
  public:
    void DoSomething(){std::cout << "B" << std::endl;}
};
Base *Create(const char *name){
  if (strcmp(name, "A")==0)
    return new A;
  if (strcmp(name, "B")==0)
    return new B;
  exit(1);
}
int main(){
  Base *base;
  base = Create("A");
  base->DoSomething();
  delete base;
  base = Create("B");
  base->DoSomething();
  delete base;
}

Axel

> 
> 
> On Mon, 2009-10-26 at 10:55 +0100, Axel Freyn wrote:
> > Hi,
> > On Tue, Oct 27, 2009 at 12:31:05AM +0330, Mohsen Pahlevanzadeh wrote:
> > > Oh, I forgot that i say i need to variable name of objects.same classes.
> > > Therefor i need to variable name of objects & variable name of classes.
> > > On Mon, 2009-10-26 at 23:42 +0330, Mohsen Pahlevanzadeh wrote:
> > > > Dear all,
> > > > We know that we can create an object with following code:
> > > > /////////////////////////////////////////////////
> > > > class_name *object_name = new() class_name;
> > > > ///////////////////////////////////////////////
> > > > So, i have a class pool,I wanna create Object with a variable name that
> > > > variable is my class.Same:
> > > > var *obj = new() var;
> > > > var is a variable that contains a my class's name.
> > > > How can i implement it?
> > Well, I'm not sure I understand correctly, but I think the solution is
> > derivation:
> > class Base{};
> > class A:public Base{};
> > class B:public Base{};
> > ...
> > 
> > 
> > Then you can do:
> > Base *var;
> > var = new A;
> > delete var;
> > var = new B;
> > delete B;
> > 
> > All functions, which you want to call by accessing "var" (e.g.
> > var->Function()) have to be defined as virtual function in class Base.
> > 
> > Does that solve your problem?
> > 
> > Axel
>