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Re: Return value for strcat and similar functions

From glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups comp.lang.c
Subject Re: Return value for strcat and similar functions
Date 2015-05-07 18:02 +0000
Organization Aioe.org NNTP Server
Message-ID <mig9bu$gdh$1@speranza.aioe.org> (permalink)
References <michpc$2b0$1@dont-email.me> <87r3qtlmtn.fsf@kst-u.example.com> <mif75a$gr6$1@dont-email.me> <mifosp$4gu$1@speranza.aioe.org> <mifsh9$udt$1@dont-email.me>

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David Brown <david.brown@hesbynett.no> wrote:

(snip, regarding strcat, then I wrote)

>> C originated on small machines. Seems to me that they didn't think
>> about how it would scale to really large machines. Pretty much no-one
>> at the time thought about what you would do with gigabytes of RAM,
>> or even gigabytes of disk. 
 
>> A big disk at the time was 100MB, but they might have had a 5MB disk.
 
> I work mostly with small machines, with fewer resources than the
> earliest C targets.  Re-scanning strings unnecessarily to find their
> ends is a waste of resources no matter what size of system you have, and
> it would not have been difficult to avoid when strcat, etc., were first
> specified.

Yes. But note that a strcat() loop is O(N**2) in time, and the 
reasonable size for N increases with memory size.  

I once ran into this with real data. Someone had written a program
to read in DNA sequence data, with strcat() in a loop. Sometime later,
we noticed that part was unusually slow. It was reading in megabytes
of data 60 bytes per line. On a PDP-11, you might read in kilobytes
that way, but not megabytes.

I changed the loop to remember where the previous read ended, and
strcpy() the new data in. Not much harder, but O(N).

-- glen

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Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-06 10:02 +0200
  Re: Return value for strcat and similar functions Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2015-05-06 10:34 +0200
  Re: Return value for strcat and similar functions Lőrinczy Zsigmond <zsiga@nospam.for.me> - 2015-05-06 16:51 +0200
  Re: Return value for strcat and similar functions Keith Thompson <kst-u@mib.org> - 2015-05-06 08:58 -0700
    Re: Return value for strcat and similar functions Richard Heathfield <rjh@cpax.org.uk> - 2015-05-06 17:07 +0100
      Re: Return value for strcat and similar functions Morris Dovey <mrdovey@iedu.com> - 2015-05-06 12:01 -0500
    Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-07 10:19 +0200
      Re: Return value for strcat and similar functions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-07 13:21 +0000
        Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-07 16:24 +0200
          Re: Return value for strcat and similar functions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-07 18:02 +0000
      Re: Return value for strcat and similar functions Morris Dovey <mrdovey@iedu.com> - 2015-05-07 10:17 -0500
        Re: Return value for strcat and similar functions Morris Dovey <mrdovey@iedu.com> - 2015-05-07 10:56 -0500
          Re: Return value for strcat and similar functions asetofsymbols@gmail.com - 2015-05-07 11:00 -0700
            Re: Return value for strcat and similar functions Morris Dovey <mrdovey@iedu.com> - 2015-05-07 14:28 -0500
              Re: Return value for strcat and similar functions asetofsymbols@gmail.com - 2015-05-07 12:47 -0700
          Re: Return value for strcat and similar functions Nathan Wagner <nw@hydaspes.if.org> - 2015-05-08 09:31 +0000
        Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-07 15:55 -0700
        Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-08 11:03 +0200
          Re: Return value for strcat and similar functions Morris Dovey <mrdovey@iedu.com> - 2015-05-08 05:07 -0500
  Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-06 18:25 -0700
    Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-07 10:22 +0200
      Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-07 15:39 -0700
        Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-08 11:09 +0200
          Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-10 08:44 -0700
            Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-10 21:30 +0200
              Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-11 20:42 -0700
                Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-12 09:52 +0200
                Re: Return value for strcat and similar functions Bartc <bc@freeuk.com> - 2015-05-12 13:33 +0100
                Re: Return value for strcat and similar functions Ike Naar <ike@iceland.freeshell.org> - 2015-05-14 20:15 +0000
                Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-14 23:06 +0200
                Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-20 11:08 -0700
                Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-21 10:55 +0200
                Re: Return value for strcat and similar functions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-21 13:05 +0000
                Re: Return value for strcat and similar functions David Brown <david.brown@hesbynett.no> - 2015-05-21 20:42 +0200
                Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-10 10:40 -0700
    Re: Return value for strcat and similar functions raltbos@xs4all.nl (Richard Bos) - 2015-05-08 21:56 +0000
      Re: Return value for strcat and similar functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-10 09:07 -0700
  Re: Return value for strcat and similar functions Bartc <bc@freeuk.com> - 2015-05-07 10:11 +0100

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