RE: [Dev-C++] Help with creating objects dynamically

[Per W. <pw...@ia...>]

No, there are no Class.forname.

But if you register all your classes into a map, you could create one
yourself:

#include <map>
#include <string>

class Base {
    public:
        virtual void Something() {}
};

typedef Base* (*PeopleFactory)();

class PeopleTypes {
    protected:
        std::map<std::string,PeopleFactory> factories;
    public:
        void Register(const char *type,Base* (*factory)());
        Base* Allocate(const char *type);
};

extern PeopleTypes people_types;

class Student : public Base {
    protected:
        static Base* Factory() { return new Student; }
        class RegisterStudent {
            public:
                RegisterStudent() {
                    people_types.Register("Student",Student::Factory);
                }
        }
        static RegisterStudent register;

    public:
        ...
};

Student::RegisterStudent Student::register; // Register "Student" factory


PeopleTypes people_types;                   // Keep map of factories

int main() {
    Base *p = people_types.Allocate("Student");
    p->Somethong();
    delete p;
    return 0;
}

/Per W


On Tue, 22 Jul 2003, Somanathan Kaimal wrote:

> Hi Marc,
>
>  Thanks for the suggestion. The switch statement is the one I want to
> avoid in real time. As when the type of message (worker,clerk etc here)
> more and more switch statements needs to be added. If you know the
> working of Class.forname, you will get to know what I mean. One way I
> can achieve this is by pooling the object(this is how normally people
> does for real time saving) but would like to know there is an equivalent
> to Class.forname. I will rewrite your code if C++ has Class.forname
>
> #define PERSON_WORKER 1
> #define PERSON_CLERK 2
> #define PERSON_MANAGER 3
> base* NewPerson(int nType)
> {
>    return(base*) Class.forname(person_types[i];// person_types has array
> of
>                          //strings, say "worker, clerk etc. Please note
> that 						//as and when the number
> of types
> //increased this line of code won't be
> //changed but only the array index needs
> //to be created
> }
>
> And then your function becomes:
>
> some_func(int i)
> {
> 	base *b = NewPerson(i);
> 	b->any_common_func();
> }
>
> Does it makes any sense?
>
> somanathan
>
> -----Original Message-----
> From: Marc Heiligers [mailto:ma...@e-...]
> Sent: Tuesday, July 22, 2003 1:42 PM
> To: Somanathan Kaimal; dev...@li...
> Subject: RE: [Dev-C++] Help with creating objects dynamically
>
> Hi Somanathan,
>
> There's probably a million different ways of doing this. I would
> probably
> start by creating a NewPerson method defined something like (and
> defines):
>
> #define PERSON_WORKER 1
> #define PERSON_CLERK 2
> #define PERSON_MANAGER 3
> base* NewPerson(int nType)
> {
> 	switch(nType)
> 	{
> 		case PERSON_WORKER:
> 			return (base*) new worker;
> 		case PERSON_CLERK:
> 			return (base*) new clerk;
> 		case PERSON_MANAGER:
> 			return (base*) new manager;
> 		default:
> 			return (base*) NULL;
> 	}
> }
>
> And then your function becomes:
>
> some_func(int i)
> {
> 	base *b = NewPerson(i);
> 	b->any_common_func();
> }
>
> Then you only have to maintain the switch in NewPerson().
> __________________________________
> Marc Heiligers
>
>
> -----Original Message-----
> From: Somanathan Kaimal [mailto:som...@wi...]
>
>
>
> Hi Gurus,
>
> I would like to take this discussion to another turn,
>
> Say if I have requirement like creating an object dynamically, means not
> the
> object name but the class definition needs to be dynamically chosen, for
> eg:- let me talk in C++ language
>
> Class worker : public base
> {
> }
> class clerk : public base
> {
> }
> class manager : public base
> {
> }
> // create an array of string
> string emp[3] = {"worker","clerk","manager"};
>
> some_func(int i)
> {
>   base b* = new emp[i];
>   b->any_common_func();
> }
>
> --------------
> This avoids lots of case statements, makes it easy to maintain and
> extend.
> Any body has any idea how to implement it in C++(equivalent to
> Class.forname
> in JAVA) If you have any other idea to accomplish this, also welcome.
>
> Let me know if things are not clear.
>
> Thanks
> Somanathan
>
>
>
>
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