Re: Friends and Visual C++ Express 2005

"t" <tmt513@Yahoo.com> wrote in message
news:1190444162.041907.187660@r29g2000hsg.googlegroups.com...
: Lippman's C++ Primer, 4th ed., p575 says:
:
: Friendship is not inherited. Friends of the base class have no
: special access to members of its derived class. If a base class is
: granted friendship, only the base has special access. Classes derived
: from that base have no access to the class granting friendship.
:
: I tried this in Visual C++ 2005 Express, and it seems to only
: implement half of the friendship rules above.
:
: Example code:
:
: =================================================
:
:
:
: class A2;
:
: class A
: {
: friend class B;
: friend void g(A, A2);
: private:
: int x;
: };
:
: class A2 : public A
: {
: private:
: int x2;
: };
:
: class B
: {
: public:
: void f(A a) { a.x; }
:
: void f2(A2 a2) { a2.x; a2.x2;}
: // a2.x compiles, but a2.x2 gives compile error
: // both statements in f2 should be compile errors ???
a2.x is ok, without "inheritance of friendship":
A is a *public* base class of A2, so a2 can be used
as an object of type A (without friendship). And
because B is a friend of A, B::f2 has access to A::x.

: };
:
: class B2 : public B
: {
: public:
: // void f(A a) { a.x; } // gives compile error, as it should
Right: this is what demonstrates the limitation
described in Lippman's paragraph quoted above.

: };
:
: void g(A a, A2 a2)
: {
: a.x; // compiles
: a2.x; // compiles, but shouldn't ?
Again: seeing that a2 is of type A does not require friendship,
because A is a public base class of A2.

: a2.x2; // doesn't compile
: }
:
: int main()
: {
: }
:
: =================================================
:
: Is Visual C++ 2005 Express not implementing friendship rules
correctly?

The above code at least seems to be handled correctly.

hth -Ivan
--
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