Question

I’m writing some C++ code that manipulates a bunch of vectors that are changing in size and are thus being reallocated constantly.

I would like to get a ‘pointer’ into these vectors that remains valid even after reallocation of the vector. More specifically, I just want these ‘pointers’ to remember which vector they point into and the index to which they point. When I dereference them using the standard (*ptr) syntax, I just want them to do the obvious lookup.

Obviously, actual pointers will not be valid after reallocation, and my understanding is that iterators aren’t valid after reallocation either. Note also that I don’t care if elements are inserted before my objects, so these ‘pointers’ really don’t have to remember anything but a vector and an index.

Now, I could easily write such a class myself. Has anyone (Boost? STL?) done it for me already?

Edit: The answers don’t address my question. I asked if this functionality is any standard library. I take the responses as a ‘no’?

Answer 1

Try a std::pair< vector*, int>, as neither the position of the vector nor the index of the element changes.
Or, as a class:

template<class T> class VectorElementPointer {   vector<T>& vectorref;   typename vector<T>::size_type index; public:   VectorElementPointer(vector<T>& vref, typename vector<T>::size_type index):vectorref(vref),index(index){}   T& operator*() const {return vectorref[index];}   T* operator->() const {return &vectorref[index];} }; 

This is the easiest solution that comes to my mind, as neither the STL nor Boost contains anything to do it easier.