C++ Classes.

hello experts,
i have created the following empty class (i mean without any member data and member functions) , Even an object can be created and the class can be inherited also.
class temp
//Nothing Here.
} object1;

class child_temp : public temp
//Nothing Here either
} object2;

Experts, Please tell me what is the fun of creating such an empty class. what purpose it can serve. Any appllication or use of it?
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There isn't much fun in creating such a class. The things you can accomplish thereby can be covered in various other ways that are at least as intuitive.

But if you're just looking for any application at all, sure there are some. The class still has an attribute: its type; and the object has its identity: the address. These can be utilized in application.

In function/operator overloading, you can use the type to resolve the ambiguity and achieve different functionalities (here illustrated on the constructor of a class):

class Graph
  class Directed { };
  class Symmetric{ };
  Graph(Directed) { /* Whatever implementation... */ }
  Graph(Symmetric) { /* Whatever implementation... */ }
  /* Whatever remaining implementation... */

In a small game, you can keep track of the active player using the address of objects (null meaning the game is over):

class Player { } one,two;
Player *active=&one;
    // Handle player 1...
    // Handle player 2...

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Regarding inheritance, common base classes in class hierarchies are sometimes empty/abstract classes (no members, no implementation of methods) since these enter at a certain level of specialization only.
well sandeep...right question!!

so you created an empty class; try out for some fun too.

check out this:

cout << "size of temp" << sizeof(temp) << endl;
cout << "size of child_temp " << sizeof(child_temp) << endl;

what do ya guess the answer is? 0? wrong!!!
it's 1; just think of why

make the dtor of the class temp as virtual and check the size again. Find out the justification for the answers you're getting.

Sometimes you may need to have an emply class with a virtual dtor...just come back again if you still have any doubts.

Virtual classes are of huge importance.

Imagine you are creating a billing system for a communications company.
They provide Phone, Email, and Cellular communications.

So you create a general class that is virtual called Communications.
Then you create the Phone, Email and Cellular classes and have them extended to the virtual class.

Now you can pass any one of the three types as Communications.
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