static array of enclosing type in class template

Question

I'm attempting to compile the following:

template<typename T>
class Foo {
protected:
   static Foo<T>* pool[5];
public:
   static Foo* Bar() {
      pool[1] = new Foo();
   }
};

int main() {
   Foo<int>* b = new Foo<int>();
   b->Bar();
}

I get the error:

 undefined reference to `Foo<int>::pool'

How to I cause the pool array to be defined?

Asked every day, has nothing to do with templates, and is covered in the FAQ. Should be covered in your book, too. Static members must be defined. — Lightness Races in Orbit, Sep 07 '16 at 00:47

score 2 · Accepted Answer · answered Sep 07 '16 at 00:17

2

You can define a static member of a templated class outside of the class like this.

// for generic T
template<typename T>
Foo<T>* Foo<T>::pool[5] = {0, 0, 0, 0, 0};

// specifically for int
template<>
Foo<int>* Foo<int>::pool[5] = {0, 0, 0, 0, 0};

answered Sep 07 '16 at 00:17

Robert Prévost

1,667
16
22

static array of enclosing type in class template

1 Answers1