Question

I have structure aa and I’m trying to run such code:

aa * b = new aa;
aa * c = new aa;
c=b;
delete (b);
c.useSomeFunction

Can I use the object pointed to by c after destruction of b?

The same question in case of:

aa * b = new aa;
aa * c ;
c=b;
delete (b);
c.useSomeFunction

Answer 1

The title of the question is misleading, because you don’t use an operator=() in your code. You only assign pointers which are built-in types.

As pointed out before:

In your first example, the pointer assignment yields a memory leak, as the object (*c) can no longer be deleted. Also you cannot call a function of (*b) (even if pointed to by c after deleting object (*b).

In your second example you don’t get the memory leak. Note that in production code you should initialise every pointer with nullptr. Also here you cannot access a function of (*b) after deleting the object.

the call to the function must be c->useSomeFunction() in order to by syntactically correct.

What you probably want (and is suggested by the title) is to create a new object and assign the content of the old one to it. Something like:

struct aa {
  aa():x(0),y(0){}
  aa& operator=(const aa& rhs);
  int foo(){return x-y;}
  int x;
  int y;
};

aa& aa::operator=(const aa& rhs){
  if (this == &rhs) {return *this;}
  x = rhs.x; 
  y = rhs.y;
  return *this;
}

int main(){
  aa *b = new aa();
  aa *c = new aa();
  *c = *b;
  delete(b);
  c->foo();
  delete(c);
  return 0;
}