Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!decwrl!megatest!djones
From: djones@megatest.UUCP (Dave Jones)
Newsgroups: comp.lang.c
Subject: Re: magic cookies given back by ftell, and used in fseek
Message-ID: <572@goofy.megatest.UUCP>
Date: 26 May 88 06:58:40 GMT
References: <129@lakart.UUCP>
Organization: Megatest Corporation, San Jose, Ca
Lines: 22

in article <129@lakart.UUCP>, dg@lakart.UUCP (David Goodenough) says:
> 
> There has been much discussion in this group on the fact that on certain
> systems (VMS I believe), ftell & fseek use magic cookies to tell about
> file position. I have my asbestos suit ready if this suggestion is out of
> line, but have the ANSI comittee considered providing some means to convert
> from cookie format to and from character position in file.

The problem is that some operating systems have file-format built into
them :-(, whereas UNIX has unformated byte-streams :-).

One example is to store "lines" in variable length records, prefixed by a 
line-length number. So now if the devil chooses a byte-count offset x, and 
says fseek(x), you've got to do some pretty fancy stepping to find the
correct record and offset into it.  For such a file, ftell would
presumably return a magic cookie which codes for record number and
offset.

Sigh.


		-- Dave J.