Static const getter file giving me an error [duplicate]

Item.h:

class Item { private: static const int price = 5; public: static const int& getPrice(); }; 

Item.cpp:

const int& Item::getPrice(){ return price; } 

main.cpp:

 int main() { Item item; cout << item.getPrice() << endl; } 

Error: undefined reference to 'Item::price'

Why is this?