1. A class template can declare static data members. Each instantiation of the class template has its own set of static data members.
  2. The template definition of a static data member must appear outside the class template definition.
  3. The static data member definitions are added to a header file. These definitions must be included in the files in which instantiations of the static data members are used.
  4. A static data member is instantiated from the template definition only if it is used in a program.
  5. The template definition for the static data member does not cause any memory to be allocated. Memory is only allocated for particular instantiations of the static data member. 
     #include <iostream>
    
 template <class T>
 class MyClass{
 public:
    MyClass(int m) : _m(m){}
    
    // do not allocate memory for static member at this line
    static int counter;
 private:
    T _m;
 };
    
 // allocate memory for static member at this line when MyClass is instantiated
 template<class T>
 int MyClass<T>::counter = 2;
    
 int main(){
    
    // No additional memory allocated for static member
    MyClass<int> obj(1);
    MyClass<float> objf(1);
    
    std::cout << MyClass<int>::counter << "\n";
    std::cout << MyClass<float>::counter << "\n";
    
    MyClass<float>::counter = 3;
    
    std::cout << MyClass<int>::counter << "\n";
    std::cout << MyClass<float>::counter << "\n";
    
    return 0;
 }