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From: peter@mit-amt.MEDIA.MIT.EDU (Peter Schroeder)
Newsgroups: comp.lang.c++
Subject: question regarding derivation
Keywords: derivation,public/protected/private
Message-ID: <681@mit-amt.MEDIA.MIT.EDU>
Date: 8 Sep 89 19:09:20 GMT
Organization: MIT Media Lab, Cambridge, MA
Lines: 50

Consider the following example of derivation.

I was under the impression that `val' would be visible to member functions
of the derived class cvect because it is protected in vect.

Sure enough cfront 1.2 does compile it as expected, however to get it
to compile under g++ (1.35.1-vax) I need to insert the commented out lines
in the derived class. Who is correct?

class vect{
protected:
   double val;
public:
   vect() { val = 0; }
   vect( double d ) { val = d; }
   vect( vect& a ) { val = a.val; }

   vect&   operator=( vect& a ) { val = a.val; return *this; }

   vect    operator+( vect& a ) { return vect( val + a.val ); }
};

class cvect : private vect{
private:
   cvect( vect& v ) : ( v.val ) {}
// uncommenting the following two lines makes things work under g++
// protected:
//    vect::val;
public:
   cvect() : () {}
   cvect( double d ) : ( d ) {}
   cvect( cvect& cv ) : ( cv ) {}

   cvect&  operator=( cvect& cv ) { return vect::operator=( cv ); }

   cvect   operator+( cvect& cv ) { return vect::operator+( cv ); }
};

main()
{
   cvect v0, v1( 2 );

   v0 = v0 + v1;
}

Your comments would be much appreciated!

Peter

peter@media-lab.media.mit.edu