Unresolved external symbol symbol "public __cdecl DoubleLinkedList(void)" ... referenced in function main

Question

My main function:

#include "DoubleLinkedList.h"

int main()
{
    DoubleLinkedList<double> d;

    return 0;
}

DoubleLinkedList.h:

template <class T>
class DoubleLinkedList{

public:
    DoubleLinkedList();
};

DoubleLinkedList.cpp:

#include "DoubleLinkedList.h"

template <class T>
DoubleLinkedList<T>::DoubleLinkedList() {}

I really don't know what is wrong with my code...