Object creation

[Guriks]

HI,
When can i use aggregation and composition. I mean

Class A{

};

Class B{

private:
A a;
A* a;
}

In the abovecode. When can i use A a and A* a?

Regards

[Mike Wahler]

"Guriks" <ms*******@gmail.com> wrote in message
news:b4*************************@posting.google.co m...

HI,
When can i use aggregation and composition.
Whenever you like. :-)
I mean

Class A{

};

Class B{

private:
A a;
A* a;
You can't have two data members with the same name.
}
};

In the abovecode. When can i use A a and A* a?

Private members of a class are only accessible by
member functions of the same class, and by friends
of that class.

Which C++ book(s) are you reading?

-Mike

[Ivan Vecerina]

"Guriks" <ms*******@gmail.com> wrote in message
news:b4*************************@posting.google.co m...

HI,
When can i use aggregation and composition. I mean

Class A{

};

Class B{

private:
A a;
A* a;
}

In the abovecode. When can i use A a and A* a?

You should use a direct data member ( A a ), unless
there is a good reason to use a pointer (e.g. the
member is not always present, or is polymorphic,
or you want to implement a special C++ idiom such
as the 'pimpl'/implementation hiding).

When a pointer/indirection is needed, not that in
most cases a smart pointer (std::auto_ptr<A> or other)
will be preferred to a naked pointer (A*).
This helps ensure proper resource management.

hth,
Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
Brainbench MVP for C++ <> http://www.brainbench.com

[EventHelix.com]

I assume you are asking if A should be contained or referenced as a
pointer.

Directly adding "a" as a member variable makes the design simple as
you do not need to worry about allocating memory for a, it is allocated
within b.
The disadvantage here is that you have anybody using the class B has to
directly or indirectly include the header file containing class A.

Deepa
--
http://www.EventHelix.com/EventStudio
EventStudio 2.5 - Automate sequence diagram generation