How to delete pointer only once?

enum Reaction{single,chain};

class X
{
X* parent_;
X* left_;
X* right_;
Reaction* reaction_;//this pointer p开发者_如何学运维oints from every obj to the same place, cannot be static
};

The Q is: how to design destructor in order to delete reaction_ only once?

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Three immediate ideas:

1) Must reaction_ be owned by an instance of class X? Can't it be owned by an external entity, so that no X::~X will ever need to delete it?

2) Use boost::shared_ptr

3) Implement your own reference counting using a static int. Remember locking if you're multithreaded.

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What is problem with this:

~X()
{
   delete reaction_;
}

Or, maybe I didn't understand your question completely!

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Use boost::shared_ptr<Reaction> in your objects

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Use a boost::shared_ptr or a std::shared_ptr (c++0x). It will count references and call delete when needed only.