NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/lang/cplus/18882

Text File | 1993-01-09 | 2.5 KB | 72 lines

Newsgroups: comp.lang.c++
Path: sparky!uunet!munnari.oz.au!metro!extro.ucc.su.OZ.AU!maxtal
From: [e-mail] (John MAX Skaller)
Subject: Re: Passing 2-d arrys to functions
Message-ID: <[e-mail]>
Sender: [e-mail]
Nntp-Posting-Host: extro.ucc.su.oz.au
Organization: MAXTAL P/L C/- University Computing Centre, Sydney
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Sat, 9 Jan 1993 16:10:19 GMT
Lines: 59

In article <[e-mail]> [e-mail] writes:
>In article <[e-mail]> [e-mail] (Nikki Locke) writes:
>
>I happen to be of this opinion.  I believe that a well-designed array
>class is essential, and should be part of the C++ Standard Library.
>(Actually, make that several well-designed array classes; probably the
>right solution is to have one class for one-dimensional arrays, and
>another for multi-dimensional arrays.)  Now that templates are part of
>the language, this is more practical than it used to be.

    Not that simple! Even for 1-dimensional arrays,
several classes might be needed.

>
>I've written my own array classes (I imagine that we all have), but it
>would be nice if I could count on arrays being there in every
>implementation.

    What we need standardised most is an ABSTRACT array class.

    template<class T>
    class Array<T> {
    public:
        virtual T& operator[](int)=0;
        virtual const T& operator[](int)const =0;
        virtual int count()const=0;
        int operator+()const{return count();}
        virtual ~Array(){}
    };

Thats mine. A 'simulation' of unsafe C like arrays:

    template<class T, int len>
    class CArray : public virtual  Array<T> {
        T data[len];
        virtual void check(int)const{}
    public:
        T& operator[](int i){check(i); return data[i];}
        const T& operator[](int i)const {check(i); return data[i];}
        int count()const{return len;}
    };

Note the rare private virtual function 'check'.
And a safe one:

    template<class T, int len>
    class CheckedCArray : public virtual CArray<T,len> {
        void check(int i)const{assert(i<count());}
    };

Now do it all over again, but use a pointer to a 'new'ed
array instead of 'data'. (In preparation for
deriving arrays of variable length)

--
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        JOHN (MAX) SKALLER,         [e-mail]
    Maxtal Pty Ltd, 6 MacKay St ASHFIELD, NSW 2131, AUSTRALIA
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