模板参数和模板参数

Question

I am relatively new to C++(14) . And i am working on enhancing my current knowledge by reading through the official documentation from cpprefernce . I have some questions about template declaration : This page gives the following possible parameters(non-type template parameter) in the declarations for a class template .

type name(optional) // (1)

My question is :
1.)What is meant by type name ? I am sure it is not same as typename mentioned here .

Further on the same page , i see the example :

// simple non-type template parameter
template<int N>
struct S { int a[N]; };

However from //1 , i see the type name is optional , so i hypothesis the below should work but it does not:(Indeed i see the below declaration template<N> can be seen as template argument with type param.) \\

// simple non-type template parameter
template<N>
struct S { int a[N]; };

So where is my understanding/reading of official docs is going wrong ?

Edit :

I tried the following :

template< int>
struct S { int a[N]; };

which does not compile with the error 'N' was not declared in the scope .

Answer 1

For that to work, N would need to be a type.

Templates only accept a type followed by an optional name for that type. So for instance this might work (though I haven't tried it):

template <int> // ...

But note that N is not declared. If you want to use N in your template, you will need to declare N like this:

template <int N> // ...

Here, N is declared as an int , so you can use it just as you would an int .

---

Note: You also have the option of something like this:

template <class N> // ...

Here N becomes a template replacement for a type. It isn't an int as above.

Of course, that's probably not what you want.