Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!SABER.TERA.COM!fred
From: fred@SABER.TERA.COM
Newsgroups: gnu.g++.bug
Subject: Error not produced correctly on incorrect access of private data.
Message-ID: <8912220335.AA12109@saber.tera.com>
Date: 22 Dec 89 03:34:59 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 50

The GNU C++ compiler appears to allow access to data which violates C++
protection rules.  The following two examples will illustrate the problem.
These examples are taken from the Unix System V, AT&T C++ Language
System Release 2.0 Selected Readings Manual, Chapter 7.

	class B
	{
	    friend void f1();
	  public:
	    int a;
	}; 

	class C : private B
	{
	    friend void f2();
	};

	class D : public C{};
	
	void f1()
	{
	    D* p1;
	    p1->a=1;  // This should be an error.
	}

Since f1 is referencing 'a' from a pointer to a D object which is
derived from a public C which is derived from a private B.  This means
that B::a is a private member of the derived class C.  Only friends and
members of C should have access to B::a in the derived class C. 

	class B
	{
	    int i;
	    friend class D;
    	};

	class C : private B {};

	class D : public C
	{
	    void f()
	    {
		int fi1=i;  // This should be an error.
	    }
	};

Again B::i is a private member of class C.  Only public and protected
members of the base class C are avaible to members and friends of the
derived class D.