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From: beard@ux1.lbl.gov (Patrick C Beard)
Newsgroups: comp.lang.c++
Subject: Virtual Memory from C++.
Summary: Overloading [] two ways.
Message-ID: <1054@helios.ee.lbl.gov>
Date: 4 Oct 88 07:47:32 GMT
Sender: usenet@helios.ee.lbl.gov
Reply-To: beard@ux1.lbl.gov (Patrick C Beard)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 38

Hello.  I am still getting my bearings in C++ and decided that as a first
attempt at class construction I would write a file class of a slightly
different flavor than the ostream model presented in Stroustrap's book.
My model is that of an array of bytes:

#include <stdio.h>
#include <stream.h>

class file {
	FILE *f;		// pointer to a file variable
	char buf[BUFSIZ];
	char opened;	// has file been opened?
	long _where;
	int error;
  public:
	file(char*, char*);
	~file(void);
	char& operator[](long);
	char operator=(char);
};

I can get to byte n of the file by specifying:
	file f("foo","r+");	/* fopen style call */
	long n=100000;
	char c=f[n];

Now, what if I want to set the value of byte n?  i.e.,
	f[n]=c;

Do I make operator[] a friend of class file and write two versions,
one with class file as first argument, and one with second?  Can what
I want to do be done?

Thanks,

Patrick Beard
Lawrence Berkeley Laboratory
beard@ux1.lbl.gov