unresolved external symbol when implementing memory management template class

Question

I'm trying to create a pool to manage the allocation and so on of little game objects that will die and reborn quickly.

For it I have created a Pool:

template <class T>
class Pool {

public:

    T* obtain()
    {
        T* obj = 0;

        if (_avaibles.size() > 0)
        {
            std::vector<T*>::iterator it = _avaibles.begin();
            obj = *it;
            _avaibles.erase(it);
        }
        else
            obj = new T();

        return obj;
    }

    void free(T* obj)
    {
        _avaibles.push_back(obj);
    }

    void clear()
    {
        std::vector<T*>::iterator it = _avaibles.begin();

        while (it != _avaibles.end())
        {
            T act = *it;
            delete act;
            ++it;
        }
    }

private:

    std::vector<T*> _avaibles;

};

The problem is I'm getting unresolved external symbols. The pool is placed as a static member of a class:

 static Pool<Ship> _shipPool;

Here is the error:

Error   16  error LNK2001: unresolved external symbol "private: 
static class Pool<class Ship> Asdf::_shipPool"  
(?_shipPool@Asdf@@0V?$Pool@VShip@@@@A)  C:\-\Asdf.obj

Please provide the exact wording of the error message you are getting (if it is a stack/core dump, we just need the relevant bits). — Robert Harvey, Feb 16 '14 at 16:40
the title of the question and the issue raised are very different from each other... — UmNyobe, Feb 17 '14 at 07:44

score 2 · Answer 1 · edited May 23 '17 at 12:03

2

You can't split up a template like that. Put the implementation into the .hpp file and everything's shiny.

Refer to Why can templates only be implemented in the header file? for futher information.

edited May 23 '17 at 12:03

Community

1
1

answered Feb 16 '14 at 16:42

filmor

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You are right. Now is giving me this: cannot convert from Ship** to Ship* – Frion3L Feb 16 '14 at 16:46
That's because you're interface is not right. As an exercise, do the template instantiation once on paper to see which types you have for your variables. Hint: `new T` is `new Ship*` in your case. You might also want to head over to http://codereview.stackexchange.com since there are more flaws in your implementation. – filmor Feb 16 '14 at 16:50
@filmor: Code Review will only work when the code functions. – Robert Harvey Feb 16 '14 at 16:58
Thanks again. I fixed that but still, now it cannot resolve the "external symbol private: static class Pool ..." – Frion3L Feb 16 '14 at 16:59
What did you fix? You have moved the whole implementation into the header file? Would you please refresh the question or post a new one with your current code? – filmor Feb 16 '14 at 17:07
Ah, well now you have the problem the other way round. If you have a static member of a class you have to *define* it in exactly one implementation file. So in `asdf.cpp` add a line `static Pool Asdf::_shipPool;`. – filmor Feb 16 '14 at 17:45

unresolved external symbol when implementing memory management template class

1 Answers1