Question

I have some library code (I cannot not change the source code) that returns a pointer to an object (B). I would like to store this pointer as shared_ptr under a class with this type of constructor:

class A
{
  public:
   A(boost::shared_ptr<B> val);
   ...
  private:
   boost::shared_ptr<B> _val;
   ...
};

int main()
{
   B *b = SomeLib();
   A a(b); //??
   delete b;
   ...
} 

That is, I would like to make a deep-copy of b and control its life-time under a (even if original b is deleted (delete b), I still have an exact copy under a).

I’m new to this, sorry if it seems trivial…

Answer 1

As you say, you have to copy them not just copy a pointer. So either B already has implemented ‘clone’ method or you have to implement some external B* copy(B* b) which will create new B with same state.

In case B has implemented copy constructor you can implement copy as just

B* copyOf(B* b)
{
    return new B(*b);
}

In case B has implemented clone method or similar you can implement copy as

B* copyOf(B* b)
{
    return b->clone();
}

and then your code will look like

int main()
{
   B *b = SomeLib();
   A a(copyOf(b));
   delete b;
   ...
}