Re: solved Re: writing a c program to substitute text

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: solved Re: writing a c program to substitute text
Date	2017-03-02 23:55 +0000
Organization	A noiseless patient Spider
Message-ID	<87r32fkze2.fsf@bsb.me.uk> (permalink)
References	(2 earlier) <ehiij4Ffgn1U1@mid.individual.net> <aa13d6d7-7cdf-4001-84fa-782ae8764b83@googlegroups.com> <ehq6ohF195iU1@mid.individual.net> <87fuiwlzjd.fsf@bsb.me.uk> <549192cf-828c-43a7-8a32-f6b9e93dd794@googlegroups.com>

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John Bode <jfbode1029@gmail.com> writes:

> On Thursday, March 2, 2017 at 4:54:26 AM UTC-6, Ben Bacarisse wrote:
>> fred flintstone <fred@server.invalid> writes:
>> <snip>
>> 
>> There's a bug in the code, so I'll mention a couple of other things that
>> are not very important since I posting about something that does matter.
>> 
>
> In my defense, I tossed this off in about 15 minutes without putting too
> much thought into it, so I'm not surprised there are problems.  Like I
> said, this ain't professional-quality code.

It's always grim posting code to comp.lang.c since so many eyes see it,
but it's good for the soul and good for the group so thanks.

>> <snip>
>> > /**
>> >  * Read the next token from the input stream.  In this program,
>> >  * tokens are either sequences of alphanumeric characters, or individual
>> >  * non-alphanumeric characters.  Both are saved as strings to buf.
>> >  *
>> >  * For example, the input ">>text3.txt" would be tokenized as ">", ">",
>> >  * "text3", ".", "txt".
>> >  */
>> > int getNextSym( FILE *stream, char **buf, size_t *bufsize )
>> 
>> I would consider returning the number of characters read here.  It's
>> always a shame to return 0/1 when you have a potentially useful
>> alternative.  You might not need it now, but getNextSym is a potentially
>> reusable function.
>
> Wouldn't that be covered by calling strlen on the target buffer?

Oh sure, but since this function calculates the length of the token as
it goes, I'd be tempted to return it.  0 still means no token and != 0
still means OK, but the caller can immediately look at tok[len-1] when
that's useful.  Not a big deal but I dislike throwing information away.

<snip>
>> >       if ( charsRead < *bufsize || expand( buf, bufsize ) )
>> 
>> I think you need <= here or you can overflow the buffer when it gets
>> zero terminated.
>
> Hmm. Acutally, I think it needs to be "charsRead < *bufsize - 1" (or
> "charsRead + 1 < *bufsize").  Oh well.

Yes, I didn't think enough about the correction.  I think I had a
similar bug recently where the fix was to include equality and I just
trotted that out.

<snip>
>> What I do in these cases in to start by setting buffer = 0 and
>> bufsize = 0 so the first character triggers and expand operation.  You
>> need to make the expand work correctly with a zero size so you can do
>> 
>>   new_size = size * 2 + 80;
>> 
>> or
>> 
>>   new_size = size ? 80 : size * 2;
>> 
>> but that avoids duplicating allocation code and checks.
>
> OTOH, setting the initial buffer size to something that handles most input
> cases means you don't have to worry about reallocating most of the
> time.

I don't get that.  You have to allocate at least once no matter how you
do it.  My preference is to keep all the allocation in one place.  The
cost is either a test or an addition that is not strictly needed on
every allocation.

<snip>
>> >     if ( strcmp( buffer, sym1 ) == 0 )
>> >       fprintf( output, "%s", sym2 );
>> >     else
>> >       fprintf( output, "%s", buffer );
>> >   }
>> 
>> Again I favour conditional expressions for cases like this:
>> 
>>   fputs(strcmp( buffer, sym1 ) == 0 ? sym2 : buffer, output);
>
> Doesn't fputs automatically append a newline?

No, that's just puts.  I suspect a lot of people are put off using fputs
because of this historical hang-over.

<snip>
-- 
Ben.

Thread

writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-02-26 04:14 -0800
  Re: writing a c program to substitute text fir <profesor.fir@gmail.com> - 2017-02-26 04:55 -0800
  Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-26 14:28 +0100
    Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-02-27 03:58 -0800
      Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-27 13:11 +0000
        Re: writing a c program to substitute text BartC <bc@freeuk.com> - 2017-02-27 13:33 +0000
          Re: writing a c program to substitute text scott@slp53.sl.home (Scott Lurndal) - 2017-02-27 17:12 +0000
            Re: writing a c program to substitute text BartC <bc@freeuk.com> - 2017-02-27 17:59 +0000
              Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 19:05 +0100
              Re: writing a c program to substitute text scott@slp53.sl.home (Scott Lurndal) - 2017-02-27 18:37 +0000
                Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-27 11:40 -0800
        Re: writing a c program to substitute text Manfred <noname@invalid.add> - 2017-02-27 16:03 +0100
        Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-03-01 05:33 -0800
          Re: writing a c program to substitute text "D. Aaron Sawyer" <aaron@110.net> - 2017-03-01 10:32 -0400
            Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-03-01 06:59 -0800
              Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-03-01 15:24 +0000
                Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-03-02 01:47 -0800
                Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-03-02 11:05 +0000
      Re: writing a c program to substitute text jt@toerring.de (Jens Thoms Toerring) - 2017-02-27 13:33 +0000
        Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-27 09:10 -0800
          Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 19:07 +0100
            Re: writing a c program to substitute text jt@toerring.de (Jens Thoms Toerring) - 2017-02-27 18:23 +0000
      Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 14:46 +0100
        Re: writing a c program to substitute text James Kuyper <jameskuyper@verizon.net> - 2017-02-27 09:27 -0500
          Re: writing a c program to substitute text GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-27 15:28 +0100
            Re: writing a c program to substitute text James Kuyper <jameskuyper@verizon.net> - 2017-02-27 09:38 -0500
          Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 15:44 +0100
            Re: writing a c program to substitute text James Kuyper <jameskuyper@verizon.net> - 2017-02-27 10:36 -0500
            Re: writing a c program to substitute text Anglican <h.toms@qmul.ac.uk> - 2017-02-27 15:50 +0000
              Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 17:13 +0100
              Re: writing a c program to substitute text Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-27 16:30 -0800
          Re: writing a c program to substitute text fir <profesor.fir@gmail.com> - 2017-02-27 07:08 -0800
            Re: writing a c program to substitute text fir <profesor.fir@gmail.com> - 2017-02-27 07:20 -0800
              Re: writing a c program to substitute text fir <profesor.fir@gmail.com> - 2017-02-27 07:24 -0800
        Re: writing a c program to substitute text Manfred <noname@invalid.add> - 2017-02-27 16:00 +0100
        Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-27 09:22 -0800
          Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 19:11 +0100
      Re: writing a c program to substitute text John Bode <jfbode1029@gmail.com> - 2017-02-28 15:41 -0800
        solved Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-03-02 01:25 -0800
          Re: solved Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-03-02 11:28 +0100
          Re: solved Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-03-02 10:54 +0000
            Re: solved Re: writing a c program to substitute text Manfred <noname@invalid.add> - 2017-03-02 15:28 +0100
              Re: solved Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-03-02 14:51 +0000
            Re: solved Re: writing a c program to substitute text John Bode <jfbode1029@gmail.com> - 2017-03-02 14:18 -0800
              Re: solved Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-03-02 23:55 +0000
                Re: solved Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-03-14 18:32 -0700
        Re: writing a c program to substitute text Tim Rentsch <txr@alumni.caltech.edu> - 2017-04-17 07:04 -0700
    Re: writing a c program to substitute text jladasky@itu.edu - 2017-02-27 13:48 -0800
      Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-02-27 14:16 -0800
        Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-28 08:47 +0100
          Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-02-28 01:59 -0800
            Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-28 11:39 +0100
            Re: writing a c program to substitute text Richard Heathfield <rjh@cpax.org.uk> - 2017-02-28 12:03 +0000
              Re: writing a c program to substitute text BartC <bc@freeuk.com> - 2017-02-28 13:33 +0000
                Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-28 14:43 +0100
                Re: writing a c program to substitute text BartC <bc@freeuk.com> - 2017-02-28 13:59 +0000
                Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-03-01 04:26 -0800
      Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 23:29 +0100
      Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-27 15:10 -0800
  Re: writing a c program to substitute text Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-26 06:42 -0800
    Re: writing a c program to substitute text Richard Heathfield <rjh@cpax.org.uk> - 2017-02-26 16:54 +0000
      [OT] "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2017-02-27 00:56 +0800
    Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-26 13:36 -0800
      Re: writing a c program to substitute text Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-26 14:53 -0800
        Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 00:53 +0100
          Re: writing a c program to substitute text Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-26 17:30 -0800
            Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-26 17:44 -0800
            Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-27 01:46 +0000
              Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 09:29 +0100
                Re: writing a c program to substitute text Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-27 02:12 -0800
                Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-27 13:11 +0100
    Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-02-27 04:41 -0800
      Re: writing a c program to substitute text Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-27 05:04 -0800
        Re: writing a c program to substitute text Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-27 13:25 +0000
        Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-27 09:56 -0800
  Re: writing a c program to substitute text "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2017-02-27 01:00 +0800
  Re: writing a c program to substitute text "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-26 18:55 -0500
    Re: writing a c program to substitute text fred flintstone <fred@server.invalid> - 2017-02-28 04:20 -0800
      Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-28 14:38 +0100
        Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-28 08:33 -0800
          Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-28 19:38 +0100
            Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-28 11:40 -0800
              Re: writing a c program to substitute text David Brown <david.brown@hesbynett.no> - 2017-02-28 21:03 +0100
            Re: gcc optimization levels Noob <root@127.0.0.1> - 2017-02-28 22:55 +0100
      Re: writing a c program to substitute text "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-28 11:43 -0500
      Re: writing a c program to substitute text Keith Thompson <kst-u@mib.org> - 2017-02-28 08:46 -0800

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