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From: jon@oddhack.caltech.edu (Jon Leech)
Newsgroups: comp.lang.c++
Subject: Re: Function Arguments
Message-ID: <2882@cit-vax.Caltech.Edu>
Date: Sat, 30-May-87 18:42:01 EDT
Article-I.D.: cit-vax.2882
Posted: Sat May 30 18:42:01 1987
Date-Received: Mon, 1-Jun-87 06:46:21 EDT
References: <31900002@boning>
Sender: news@cit-vax.Caltech.Edu
Reply-To: jon@oddhack.Caltech.EDU (Jon Leech)
Organization: Caltech Odd Hack Committee
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In article <31900002@boning> boning@boning.applicon.UUCP writes:
>Is there any way to use a derived class as an argument to a base class?
>I don't want to use a void pointer and lose type checking.
>
>The example I'm thinking of is a base class 'geometry' which has
>derived classes 'edges' and 'polygons'.  I want to have a function
>'get_edges' under 'geometry' which will find the edges belonging to
>a piece of geometry, ie

    Easily, in the same way you would declare mutually-referential
structures in C:

    class edges;		    // Let compiler know this class exists

    class geometry {
	...
	void get_edges(edges &e);   // I like references more than pointers
    };

    class edges : public geometry { // Define the class
	...
    };

    What you probably want to do, however, is make get_edges() a
member function of class edges taking an argument which is a geometry:

    class geometry {
	...
    };

    class edges : public geometry { // Define the class
	...
	void get_edges(geometry &g);
    };

    Remember that an edges contains all the information of a geometry,
so you may not need the 'g' argument, which is part of the idea behind
member functions (I can't tell from your example if this is the case).

--
    Jon Leech (jon@csvax.caltech.edu || ...seismo!cit-vax!jon)
    Caltech Computer Science Graphics Group
    __@/

``There is only one spacefaring nation today. And it's not the United
    States, comrade!''