[C/C++] Simple example of using 'typename'

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We can use 'typename' in template class.

template
class C
{
    typename T::bT* a;
}

But, keyword 'typename' cannot be used outside template. So, following is incorrect syntax.

class A;
class B
{
    A*     a;
    typename A::bT* b; // error here!
};

So, in this case, class A's definition should be included before definition of class B.

It's just small information about using 'typename'.