Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!pasteur!helios.ee.lbl.gov!ux1.lbl.gov!beard
From: beard@ux1.lbl.gov (Patrick C Beard)
Newsgroups: comp.lang.c++
Subject: Re: Private base class
Summary: you need a public or protected in your inherited decl.
Message-ID: <4604@helios.ee.lbl.gov>
Date: 11 Jan 90 02:15:58 GMT
References: <1533@castle.ed.ac.uk>
Sender: usenet@helios.ee.lbl.gov
Reply-To: beard@ux1.lbl.gov (Patrick C Beard)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 57
X-Local-Date: 10 Jan 90 18:15:58 PST

In article <1533@castle.ed.ac.uk> sam@lfcs.ed.ac.uk (S. Manoharan) writes:
#
#Yet another What's-wrong-with-my-code question:
#
#	 1  class base {
#	 2  public:
#	 3     int a;
#	 4     void f()     {}
#	 5  };
#	 6
#	 7  class derived: base {
#	 8  public:
#	 9     base::a;
#	10     base::f;
#	11  };
#	12
#	13
#	14  void main()
#	15  {
#	16     derived x;
#	17
#	18     x.a = 0;
#	19     x.f();
#	20  }
#
#
#Compiling this with CC (cfront version 1.2.1) gives the following
#errors:
#CC  test.c:
#"test.c", line 18: error:  a is from private base class
#"test.c", line 19: error:  f is from private base class
#2 errors

As it should, you have inherited the base class privately.  In other
words, all members, public, protected, or private, are inaccessible
to the derived class.  The fix is to declare derived like so:

derived : public base {...};

#
#BS says "It is possible to declare some, not all, of the public
#members of a base class public memberes of a derived class."
#(page 196)   Where have I gone wrong then? Could someone help me?
#

Redeclaring the members a and f can only make the visibility MORE strict,
not less.  From the AT&T C++ reference manual (pp. 70-71):  "If a class
is declared to be a base class for another class using the private access
specifier, the public and protected members of the base class are private
members of the derived class."  By not specifying the access in the declaration
of the derived class, base is by default private.

Hope that helps.
-------------------------------------------------------------------------------
-  Patrick Beard, Macintosh Programmer                        (beard@lbl.gov) -
-  Berkeley Systems, Inc.  ".......<dead air>.......Good day!" - Paul Harvey  -
-------------------------------------------------------------------------------