Still a template issue! !! !

661193

c ++ primer 4th p553

template <class T> class A;

template <class T> class B
{
   friend class A <T>;
   friend class E <T>;
};

If the compiler is not told that the friend is a template, the compiler considers the friend to be a normal non-template class or non-template function.

What I want to ask is, how does the compiler treat E as a normal non-template class?

verance

If you write:
template <class T> class B
{
friend class A;
};

Then the compiler thinks that there is a common class called A. If you do not define such a class, then you should encounter a compilation error.
You defined A <T> and it didn't work either

boxer2005

What you write here is friend class E <T> ;, this means that E must be a template class, and the friend relationship between E and A is bound, that is, E and A corresponding to each T It is a friend relationship, and E and A corresponding to different T are not friend relationships.

PS: Friends and templates are troublesome. There are some syntaxes that are interpreted differently between compilers, and they seem to be a lot worse, so don't take it too seriously, otherwise you will be horny.

superandy

Searchable "Befriending Templates" by herb sutter