how to declare template of template class

How can declare template of a template class?? see below code:

File: A.h
class A
{
    ...
    ...
};

File: B.h
template <typename U>
class B
{
    ...
    ...
};

File C.h
temp开发者_运维技巧late <class T>
class C
{
    ...
    ...
};

File C.cpp
//In this file I am able to write template declaration for class A(non-template class)
#include "A.h"
template C<A>; //this works fine. 

How can I write the same for class B(which is a template class.)
#include "B.h"
template C<What should I write here for class B?>;

If you want to use B as type argument to C class template, then you can write this:

template class C<B<int> >; //i.e provide the some type B template class
       //^^^^ this is needed for explicit instantiation!

C<B<A> >  variable;
C<B<short> >  *pointer = new C<B<short> >();

The C template expects a non-template type so that it can generate a class. That's why C<A> works: A is not a template. However, C<B> doesn't work, since B is only a template for a type itself. You need to have some type to instantiate the B template.

For instance, this could work:

C<B<A> > x;

You can just write it like this:

C< B< A > > c;

If you find that confusing then you can use a typedef:

typedef B<A> MyB;
C<MyB> c;

Well, B is also a template, so something like C<B<A>> would work.

Note that some compilers see >> as a shift operator, and requires C<B<A> >.