asked on

assigning a child class its parent

Hi

I have a class hierarchy as follows:
A (parent)->B(child)

I create an object A. A a=new A();

Somewhere, later in the code, I want to create an object B, called b, and want to specifically assign the object a as its parent. Is there a way to do this in C++?

Normally, I would do something like this:
B b=new B();

B's constructor would make a call to A's constructor
B::B()
:A(){
}

But if i have a parent object already instantiated, is there a way to assign that particular object as a child object's parent at the time the child is instantiated?

thanks

jkr

There seems to be a misconception. A statement like

B::B()
:A(){
}

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only a base class' constructor. That is not related to storing a reference to a specific instance to the base class. If you want to create a relation between two instances of A and B, pass an instance of A to one of B's constructors, e.g.

class B {

public:

  // default constructor
  B() : parent(A()) {
  }
  // constructor that implicitly takes an instance of 'A'
  B(A& a) : parent(a) {
  }

private:

  A& parent;
};

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If you need to have to option to instantiate B without a parent, you have to use pointers, since references can't be 'NULL', e.g. like

class B {

public:

  // default constructor
  B() : parent(NULL) {
  }
  // constructor that implicitly takes an instance of 'A'
  B(A* a) : parent(a) {
  }

private:

  A* parent;
};

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LuckyLucks

ASKER

In the solution you gave, A and B do not have a base class-derived class relationship. B just keeps a member variable of A.

B cannot use a function defined in A as would be possible using rules of inheritance (searching the parent class when child class does not have that function).

I am looking for a way where B can be a derived class of A , but as A is already instantiated in earlier code, if i can get an association with that particular instance of A.

SOLUTION

jkr

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ASKER CERTIFIED SOLUTION

sarabande

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