Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!munnari.oz.au!comp.vuw.ac.nz!canterbury!cctr132
From: cctr132@csc.canterbury.ac.nz (Nick FitzGerald, CSC, Uni. of Canterbury, NZ)
Newsgroups: comp.lang.pascal
Subject: Re: string ghosts
Message-ID: <1991Feb28.180622.137@csc.canterbury.ac.nz>
Date: 28 Feb 91 05:18:17 GMT
References: <26159@adm.brl.mil>
Organization: University of Canterbury, Christchurch, New Zealand
Lines: 42

In article <26159@adm.brl.mil>, STANKULI%UWF.BITNET@cunyvm.cuny.edu
( stan kulikowski ii) writes:
> (*
>   i was having some strange behavior in one of my TP 5.5 programs...
>   a string variable was behaving as if it still had the contents of previous
>   assignments after it had been nulled.  even the turbo debugger saw
>   that the string had null value, but it still operated as if the ghost
>   of its previous assignment was still there...
> *)
> 
>[demo code deleted] 
> 
> (*
>   is this the way pascal is supposed to run?

Dunno.  Are strings part of standard Pascal?? - They seem to be implemented in
so many different ways I always assumed the answer (to my question) was "No".

>   if so, this is very counterintuitive. when i null out a string,
>   i obviously intend that all of its contents should be likewise null.
>   surely any reference to a zero-length null string returns nil value.
> 
>     my understanding of fregean compositionality requires that
>[stuff deleted]

What's Fregean logic got to do with compiler implementation?  8-)

>     am i missing something important here?  this is elementary logic which
>   was worked out in the 1920's.

Is it relevant to programming, as opposed to "natural", languages?

I though it was common knowledge that nulling a string in TP simply reset the
index byte (AnyString(0)) to zero, and that to actually null out the contents
you had to do that "manually".

That is:    AnyString:='';             is equivalent to
            AnyString(0):=char(0);     not to
            for I:=length(AnyString) down to 0 do
                AnyString(I):=char(0);

Nick.