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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: while loop vs do while loop reading from the file issue
Date: Sat, 10 Dec 2016 16:08:33 -0800
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BartC <bc@freeuk.com> writes:
> On 10/12/2016 21:11, Ben Bacarisse wrote:
[...]
>> (Have you got an example of a loop that's simpler with pre-EOF testing
>> yet?  I don't want that interesting point to slip away.)
>
> This is just going to be your opinion versus mine. Last time this was 
> discussed, you favoured putting as much as possible into a while 
> condition; I preferred keeping the conditional minimal, except in the 
> simplest case (reading a character at a time).
>
> To me, divorcing the eof check and the main loop terminating logic from 
> the actual processing that is done, is a benefit:
>
>   while (!eof(f)) {
>     read stuff...
>   }

I think that's to general to be a useful example.

> I can see at a glance that this is probably iterating over a file. I can 
> see that it will definitely end as soon eof() returns true.
>
> It's just an idiom I use a lot (in fact I could go through a pile of 
> code looking for such while loops, in a way I couldn't do if the loop 
> condition was always different).

As I recall, your eof() function attempts to read a character, and the
pushes it back with ungetc() if it was able to do so.  I haven't tried
it, but I believe it would cause problems with interactive input.  I
remember that being a serious problem with Pascal's input handling.

If you don't like putting complex expressions into a while condition, as
in the common C idiom:

    int c;
    while ((c = getchar()) != EOF) {
        /* do something with c */
    }

then you can separate it:

    while (1) {
        int c = getchar();
        if (c == EOF) break;
        /* do something with c */
    }

It's less than ideal in that the condition that terinates the loop is in
the body of the loop rather than at the top (which is why I prefer the
usual idiom).

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"