访问模板化 class 的非模板基的 static 数据

Question

A template class is derived from non-template class that has static data member. Why can't I access that without specifying the template arguments? Actually, can I access any method or data in a template class without template arguments?

class CNonTemplateBase{

public:
    static int some_data;

};

int CNonTemplateBase::some_data = 10;

template<typename T> class CTemplateClass : public CNonTemplateBase{};

...
...

int a = CTemplateClass<int>::some_data;    //OK
int b = CTemplateClass::some_data;         //ERROR

Answer 1

It's because CTemplateClass doesn't exist on it's own. Template class must be generated with provided template argument first.

Answer 2

Why can't I access that without specifying the template arguments?

Because it's possible to write CTemplateClass so that it inherits from CNonTemplateBase only for some specific values of the template parameters.

Actually, can I access any method or data in a template class without template arguments?

No, because they could depend on the template parameters.

---

In the end, this is simply how the langauge works. I assume it would be possible to change the language to permit the syntax you want under certain conditions, but it'd make C++ even more complex without a good reason.

Answer 3

The compiler does not generate code to a template class without instantiation (of a type). Therefore, you cannot access a static member of an instantiation template class.