Making a hash table of iterators in C++

Use the address of the element that the iterator refers to.

struct list_iterator_hash {
    size_t operator()(const list<int>::iterator &i) const {
        return hash<int*>()(&*i);
    }
};

But this will only work for dereferenceable iterators, not end() or list<int>::iterator().

You can use pointers to the element in place of iterators. Let's say you had a list of structs MyStruct. You can use

unordered_set<MyStruct*> myhashset;

and the C++ standard library already implements std::hash for any pointer.

So if you ever need to insert or search listIt then use &(*listIt) which will get the pointer of type MyStruct*.

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