Question

Consider a class like so:

template < class T >
class MyClass
{
  private:
    static T staticObject;
    static T * staticPointerObject;
};
...
template < class T >
T MyClass<T>::staticObject; // <-- works
...
template < class T >
T * MyClass<T>::staticPointerObject = NULL; // <-- cannot find symbol staticPointerObject.

I am having trouble figuring out why I cannot successfully create that pointer object.

The above code is all specified in the header, and the issue I mentioned is an error in the link step, so it is not finding the specific symbol.

Answer 1

I have found two solutions. Neither of them are 100% what I was hoping for.

1. Explicitely initialize the specific instance, e.g.

   int * MyClass<int>::staticPointerObject = NULL;

This is not convinient especially when I have a lot of different types.

2. Wrap the pointer inside the class, e.g.

    template < class T >   
    class MyClass   
    {   
      private:   
        struct PointerWrapper   
        {   
          T * pointer;   
          PointerWrapper( void )   
            : pointer( NULL )   
          { }   
        };   
        T staticObject;   
        PointerWrapper staticPointerObject;   
    };   
    ...   
    template < class T >   
    T MyClass<T>::staticObject; // <-- works fine.   
    ...   
    template < class T >   
    MyClass<T>::PointerWrapper MyClass<T>::staticPointerObject; // <-- works fine.

This is a bit of a hassle, but at least usable. Why is it I can instansiate a variable object but not a pointer to a variable object? If anything I would think I’d have more problems the other way around (the compiler knows ahead of time what a pointer looks like, but not what my object looks like).

If someone has a better answer I’d love to see it!