confusion in understanding the inheritance concept!

[gaurav#]

#include<iostream>
using namespace std;
class A {
protected:
  int i;
public:
  void  fun(int p)	
	{
		i=p;	
		cout<<"i= "<<i<<"p= "<<p<<endl;
	}
};


class B: public A
   {
	public: 
	void function()
		{
			cout<<i<<endl;	
		}
   };
int main()
	{
		A obj;
		obj.fun(123);
		B object;
		object.function();
		return 0;
	}

The output of this code is:
123 123
##GARBAGE VALUE##

why is it happening? At the time when I passed 123 to p & then 'i' copied the value 123 into it, I thought it must have stored 123 into the memory space allocated to it, but after inheriting it 'function()' in class B is not printing the value. WHY?

[Salem]

obj and object are two different instances of things.
Simply storing 123 in obj has NO possible relationship to the data you see in object.

> class B: public A
This means B contains it's own copy of an A

It does not mean, go looking through the code for other declarations of A (like on line 25) and hijack them into B.

It would help if your example at least had default constructors for everything.

[gaurav#]

So the memory has nothing to do with that! What good would default constructor do?

[whiteflags]

What good would default constructor do?

You have no way to set A::i currently, using default constructors would give you one.

[Salem]

> What good would default constructor do?
Well if you had a default contructor in A that assigned the value say 42 to i, then you'd get a more consistent answer.

Further, if you put a cout statement in both default constructors, you would see two instances of A being created.
One of them would be the standalone instance of A
The other would be an inherited instance within B

Finally, having default constructors which initialise all the members (well all the Plain-Old-Data members) is a good thing.