Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!haven!uvaarpa!virginia!scl
From: scl@virginia.acc.virginia.edu (Steve Losen)
Newsgroups: comp.lang.pascal
Subject: Re: file windows (was Re: Standard Pascal)
Message-ID: <2929@virginia.acc.virginia.edu>
Date: 24 Jul 89 21:18:23 GMT
References: <8616@pyr.gatech.EDU> <18965@paris.ics.uci.edu> <SCHWARTZ.89Jul12023301@shire.cs.psu.edu> <4623@freja.diku.dk>
Reply-To: scl@virginia.acc.Virginia.EDU (Steve Losen)
Organization: University of Va., Charlottesville, VA
Lines: 58

In article <4623@freja.diku.dk> dat0@rimfaxe.diku.dk (Dat-0 undervisningsassistent) writes:
>schwartz@shire.cs.psu.edu (Scott Schwartz) writes:
>>Alastair Milne writes:
>>| >	while (input^ in [space, tab, newline, cr, formfeed]) do
>>| >		get (input)
>>| 
>>|     How does this constitute not commiting to read the file variable?  You are
>>|     doing exactly that when you dereference the file variable to get its
>>|     window.
>>I didn't say you don't commit to reading the the window variable.  The
>>thing you don't commit to is advancing the file pointer: commiting to
>>read from the FILE.
>
>As somebody already have pointed out, "read(input, ch)" is exactly 
>equivalent to "ch:=input^;get(input)" (by definition of the ISO standard).
>
>The interesting thing about this is (IMHO) that using the filewindow you 
>can check what you are about to read, not just what you have already read.
>I have seen a couple of examples, where this saves you a lot of trouble.
>
>
...
>
>Kristian Damm Jensen 
>(dat0@diku.dk)
>Institute of datalogi, University of Copenhagen (DIKU)

Here's a good example of how convenient the file buffer variable is:

Suppose you want to allow the user to input a bunch of integers, separated
by any sequence of non-numeric characters.  For example, the following
atrocity is legal input:

,,100 ,20,
,

   30
40,, 5050
,,,

The program should process the integers 100, 20, 30, 40, and 5050.
Here is a trivial piece of Standard Pascal that does the job correctly.

while not eof do begin
	if (input^ >= '0') and (input^ <= '9') then begin
		read(number);
		process(number);
	end
	else
		get(input);
end

I admit that for most programming languages it is possible to come up
with simple and elegant solutions to selected bizarre problems.  Too
bad there isn't one language that is universally applicable.
-- 
Steve Losen     scl@virginia.edu
University of Virginia Academic Computing Center