inheritance

[jalalsad]

this is a complicate situation:
i have A class by type

Base
{
Btype* m_b;
};

and a class

DerivBtype:public Btype
{
..
}

and this class

class derived :public base
{
}
and i want to behave m_b as a derived class
i used this approach
m_b=new derived ;
and cast m_ b to derived where is neede is ther a simplere way to do this?

[dkalita]

I didn't get what u are trying to do. But let me explain a bit of inheritance

class Base
{
/*members*/
};

class Derived:public Base
{
/*members*/
};

Base *bptr = new Derived();
/*or if u need only base object*/
bptr = new Base();

But using bptr u wont' be able to access the mebers of Derived class untill and unless they are declared in the Base class as virtual and overridden in the derived class.

Read on inheritance.

[jalalsad]

themethod can be defined virtual but is there a way to declare data member not function virtual?this is my problem.

[dkalita]

the data variables can be defined virtual but is there a way to declare dat member not function virtual?this is my problem.

If u dont declare them as virtual and u try to access the derived class member then it will invoke the base class member only.
e.g.

class base
{
public:
   virtual void fun()
   {
         /*do something*/
   }
};
class derived:public base
{
public:
   void fun()
   {
    /*do something else*/
   }
};

base *bptr = new derived();
bptr->fun();
/*this will invoke the derived class member.(derived::fun())*/
/*But if u remove the keyword virtual in base class, it will invoke the base class member(base::fun()).*/

[jalalsad]

thanks for yor replies
excuse me .maybe i cant describe it well. i mean if i have a variable not a function in the base class. and then if i want to use a derived instance of that variable not method in the derived class whts the best way ?
i use these method but i amnot sure

class ClassVar
{
...........
}
class DerivedClassVar:public ClassVar
{
.........
}
class BaseContainer
{

ClassVar* m_meber;//variable

}
and i want to treat in below class as derived class with this meber

class DerivedBaseContainer:public BaseContainer
{

DerivedBaseContainer()
{
//my soloution::
m_meber=new DerivedClassVar;
DerivedClassVar* m_CastMem=dynamic_cast< DerivedClassVar *>(m_member)

m_CastMem->......................

}

}

thanks

{

}