Question

Is there a standard way of maintaining a weak pointer to a parent (which is created using a shared pointer) in a child object in C++?

Essentially, I need to implement something on the lines of the following:

Class B;

Class A
{

...
private:
B m_b;
};

Class B
{
....
public:
void SetParentPtr(const boost::shared_ptr<A>& a)
{
m_parentPtr = a;
}
private:
boost::weak_ptr<A> m_parentPtr;
};

In the above all instances of class B need to hold a weak pointer to their parent (i.e object of class A). Class A objects are instantiated using a shared_ptr. I can think of a solution that uses a null deleter. But is that a standard way of doing something like this?

Answer 1

There is an implicit conversion to weak_ptr, so you can use

void SetParentPtr(boost::weak_ptr<A> a) { }

directly.

check also boost::shared_from_this so the parent can give a pointer to himself without storing a weak_ptr explicitly.

Otherwise, this seems like a normal way to have a back-pointer. Just check whether there is a real added value in using back-pointers.