Re: reference member variable question

"Jim Langston" <>
Sat, 5 May 2007 13:50:27 -0700
"Bart Simpson" <> wrote in message

Salt_Peter wrote:

On May 3, 7:35 pm, Bart Simpson <> wrote:

If a class has a member variable that is a reference. What happens to
teh class that is being referenced, when the containing class is


Class A{ };

class A { };

Class B

class B



   B(const A& a):m_a(a){}
   A& m_a ;


int main()
   A a;
   B * b = new B(a);
   delete b ; // is a deleted also at this point ?


No, the instance 'a' dies at the end of the scope its in, namely - the
closing brace of int main() in this case. In other words: an instance
of class B does not 'own' the instance of type A. If you require 'a'
to die with the deallocation of *b, you'ld probably want a member of
type A in class B.

class B
  A a;
  B() : a() {}
  B( const A& r_a ) : a( r_a ) {}

And nothing stops you from declaring and defining a member reference
to private member 'a'.

Class B contains a reference to class A. since a reference IS the object
itself, I dont understand how come A is not destroyed when B is
destroyed - unless some kind of "reference counting" is employed "under
the hood" ?. BTW this is the desired behaviour - I just dont understand
how or why it works though ... and am seeking more of an insight to
explain this (maybe someone has a copy of the language reference)?

I like to call a reference a "pointer on steroids". If it was a pointer
A*m_a ;
you could see how it's possible for the pointer to go out of scope and leave
what it was pointing to untouched. A pointer going out of scope does not
call the destructor on what the pointer was pointing to, only the pointer

Same with a reference. A reference points to another variable somewhere.
When the reference goes out of scope, it gets deleted, not what it was
pointing to.

If, in this context, you think of a reference as simply a pointer you don't
have to derefernce (dont' have to use -> but can use . Don't have to use *
but the reference naem itself, etc...) then it should become clearer, as
long as you understand pointers.

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