c++ - C++ 中的内部类会自动成为 friend 吗？

Question

如果我在 C++ 中定义了一个内部类，它会自动成为包含它的类的 friend 吗？例如，这是否合法:

class Outer {
public:
    class Inner {
    public:
        void mutateOuter(Outer& o);
    };

private:
    int value;
};

void Outer::Inner::mutateOuter(Outer& o) {
    o.value ++; // Legal?  Or not?
}

我之所以问，是因为在我尝试过的某些编译器 (VS2003) 上，此代码不起作用，但我至少听说过它确实适用于某些编译器。我在 C++ 规范中找不到关于此的相关部分，如果有人能引用一些具体的内容来说明它是否合法，那就太好了。

Answer 1

在问过或多或少相同的问题后here我自己，我想分享 C++11 的(显然)更新的答案:

引自 https://stackoverflow.com/a/14759027/1984137 :

standard $11.7.1

"A nested class is a member and as such has the same access rights as any other member. The members of an enclosing class have no special access to members of a nested class; the usual access rules shall be obeyed"

and the usual access rules specify that:

"A member of a class can also access all the names to which the class has access..."

specific examples has been given in the standard:

class E {
    int x;
    class B { };

    class I {
        B b; // OK: E::I can access E::B
        int y;
        void f(E* p, int i) {
            p->x = i; // OK: E::I can access E::x
        }
    };
}