Re: While or if: function to get next operator or operand

From	Tim Rentsch <txr@alumni.caltech.edu>
Newsgroups	comp.lang.c
Subject	Re: While or if: function to get next operator or operand
Date	2015-11-27 13:32 -0800
Organization	A noiseless patient Spider
Message-ID	<kfnsi3ryvpi.fsf@x-alumni2.alumni.caltech.edu> (permalink)
References	(1 earlier) <564F5520.8050503@verizon.net> <kfnsi409zwa.fsf@x-alumni2.alumni.caltech.edu> <MPG.30bc214448c35f27a4@news.eternal-september.org> <kfna8q44snw.fsf@x-alumni2.alumni.caltech.edu> <MPG.30bdb356bb72ffb9a7@news.eternal-september.org>

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Philip Lantz <prl@canterey.us> writes:

> Tim Rentsch wrote:
>
>> Philip Lantz <prl@canterey.us> writes:
>>
>>> Tim Rentsch wrote:
>>>> James Kuyper writes:
>>>>> Alla _ wrote:
>>>>>> QUOTE:
>>>>>> Lines like while ((s[0] = c = getch()) == ' ' || c == '\t'); make me wanna weep. - ammoQ
>>>>>>
>>>>>> @ammoQ Indeed.  And then people still recommend K&R, I have
>>>>>> absolutely no idea why.  Look at this horrible code, it is not
>>>>>> written by the OP, it is written by K&R!  Had any rookie
>>>>>> programmer written code like this today, he would have been
>>>>>> immediately fired. - Lundin
>>>>>>
>>>>>> UNQUOTE
>>>>>>
>>>>>> Function: 
>>>>>>
>>>>>> /* getop:  get next character or numeric operand */
>>>>>> int getop(char s[])
>>>>>> {
>>>>>>     int i, c;
>>>>>> /* the below while loop */
>>>>>>     while ((s[0] = c = getch()) == ' ' || c == '\t')
>>>>>>         ;
>>>>>
>>>>> I disagree with ammoQ.  Once you've learned enough about C, such
>>>>> code should be quite clear.  [...]
>>>>
>>>> For people who think this code snippet is clear - did you spot
>>>> the subtle bug?
>>>
>>> Are you referring to the possibility that (char)EOF could equal ' '
>>> or '\t', which would result in an infinite loop?
>>
>> Yes that's it.
>>
>> Note by the way that the claim that this situation can occur only
>> if CHAR_MAX > INT_MAX isn't right.  It can occur if char is
>> unsigned and EOF has one of the appropriate negative values,
>> or if char is signed and EOF has a value less than CHAR_MIN.
>>
>> To me the code has a bug not because either of those situations
>> is likely (which they aren't) but because it has an unobvious
>> implementation dependency which could cause erroneous behavior.
>> Also the problem is easy to code around --
>>
>>     while (  s[0] = c = getch(),  c == ' ' || c == '\t'  ) ...
>>
>> Now what happens with the value of the assignment to s[0] doesn't
>> matter, and pretty obviously doesn't matter.
>
> Or even better,
>     while (c = getch(), c == ' ' || c == '\t');
>     s[0] = c;
>
> Since the assignment to s[0] has no business being inside the loop
> anyway.

Yes, I saw that idea in another posting.  I didn't bring it up
because my point was only about the expression, not about the
loop as a whole.  For didactic reasons I try avoid muddying
the waters.

Thread

While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 08:06 -0800
  Re: While or if: function to get next operator or operand Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-20 08:17 -0800
    Re: While or if: function to get next operator or operand Richard Heathfield <rjh@cpax.org.uk> - 2015-11-20 16:44 +0000
  Re: While or if: function to get next operator or operand Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-20 11:23 -0500
    Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 08:39 -0800
      Re: While or if: function to get next operator or operand Richard Heathfield <rjh@cpax.org.uk> - 2015-11-20 16:47 +0000
      Re: While or if: function to get next operator or operand Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-20 11:54 -0500
        Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 09:13 -0800
        Re: While or if: function to get next operator or operand David Thompson <dave.thompson2@verizon.net> - 2015-12-06 08:04 -0500
      Re: While or if: function to get next operator or operand James Kuyper <jameskuyper@verizon.net> - 2015-11-20 12:02 -0500
  Re: While or if: function to get next operator or operand Richard Heathfield <rjh@cpax.org.uk> - 2015-11-20 16:41 +0000
    Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 09:11 -0800
      Re: While or if: function to get next operator or operand Richard Heathfield <rjh@cpax.org.uk> - 2015-11-20 17:39 +0000
        Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 10:42 -0800
        Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-21 14:58 -0500
          Re: While or if: function to get next operator or operand Richard Heathfield <rjh@cpax.org.uk> - 2015-11-23 12:21 +0000
        Re: While or if: function to get next operator or operand Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-21 21:29 +0000
          Re: While or if: function to get next operator or operand BartC <bc@freeuk.com> - 2015-11-21 22:31 +0000
            Re: While or if: function to get next operator or operand BartC <bc@freeuk.com> - 2015-11-22 10:57 +0000
              Re: While or if: function to get next operator or operand Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-22 13:45 +0000
          Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-22 01:31 -0500
          Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 04:33 -0800
            Re: While or if: function to get next operator or operand Philip Lantz <prl@canterey.us> - 2015-11-23 23:44 -0800
        Re: While or if: function to get next operator or operand Rosario19 <Ros@invalid.invalid> - 2015-11-22 09:39 +0100
          Re: While or if: function to get next operator or operand Rosario19 <Ros@invalid.invalid> - 2015-11-22 09:49 +0100
            Re: While or if: function to get next operator or operand asetofsymbols@gmail.com - 2015-11-22 02:27 -0800
              Re: While or if: function to get next operator or operand asetofsymbols@gmail.com - 2015-11-22 02:32 -0800
        Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-22 10:02 -0500
          Re: While or if: function to get next operator or operand Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-23 17:23 +0000
            Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-23 12:31 -0500
              Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-23 13:02 -0500
        Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-22 07:06 -0800
          Re: While or if: function to get next operator or operand Barry Schwarz <schwarzb@dqel.com> - 2015-11-22 11:43 -0800
            Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-24 02:03 -0800
            Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-24 02:11 -0800
              Re: While or if: function to get next operator or operand James Kuyper <jameskuyper@verizon.net> - 2015-11-24 07:09 -0500
          Re: While or if: function to get next operator or operand Richard Heathfield <rjh@cpax.org.uk> - 2015-11-23 12:26 +0000
            Re: While or if: function to get next operator or operand raltbos@xs4all.nl (Richard Bos) - 2015-11-23 13:26 +0000
        Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-22 07:17 -0800
  Re: While or if: function to get next operator or operand James Kuyper <jameskuyper@verizon.net> - 2015-11-20 12:15 -0500
    Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 10:44 -0800
    Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-20 12:31 -0800
      Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-20 15:38 -0500
        Re: While or if: function to get next operator or operand James Kuyper <jameskuyper@verizon.net> - 2015-11-20 16:14 -0500
          Re: While or if: function to get next operator or operand Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-20 16:55 -0500
            Re: While or if: function to get next operator or operand Geoff <geoff@invalid.invalid> - 2015-11-20 15:04 -0800
        Re: While or if: function to get next operator or operand Barry Schwarz <schwarzb@dqel.com> - 2015-11-20 20:59 -0800
        Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 23:50 -0800
          Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-21 00:18 -0800
        Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 14:10 -0800
      Re: While or if: function to get next operator or operand Philip Lantz <prl@canterey.us> - 2015-11-22 19:00 -0800
        Re: While or if: function to get next operator or operand James Kuyper <jameskuyper@verizon.net> - 2015-11-23 06:57 -0500
          Re: While or if: function to get next operator or operand Philip Lantz <prl@canterey.us> - 2015-11-23 23:49 -0800
            Re: While or if: function to get next operator or operand James Kuyper <jameskuyper@verizon.net> - 2015-11-24 07:13 -0500
        Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 07:55 -0800
          Re: While or if: function to get next operator or operand Philip Lantz <prl@canterey.us> - 2015-11-23 23:36 -0800
            Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 13:32 -0800
    Re: While or if: function to get next operator or operand Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-20 16:13 -0500
      Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 13:54 -0800
  Re: While or if: function to get next operator or operand Geoff <geoff@invalid.invalid> - 2015-11-20 12:19 -0800
  Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-20 15:32 -0800
    Re: While or if: function to get next operator or operand Chad <cdalten@gmail.com> - 2015-11-20 18:38 -0800
      Re: While or if: function to get next operator or operand Keith Thompson <kst-u@mib.org> - 2015-11-20 19:45 -0800
        Re: While or if: function to get next operator or operand Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-20 20:12 -0800
      Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 20:45 -0800
        Re: While or if: function to get next operator or operand Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-20 21:04 -0800
      Re: While or if: function to get next operator or operand Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 13:57 -0800
    Re: While or if: function to get next operator or operand Alla _ <modelling.data@gmail.com> - 2015-11-20 20:43 -0800

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