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Re: Pointer to structure

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BartC <bc@freeuk.com> wrote:

> On 21/12/2014 18:01, Richard Bos wrote:
> > BartC <bc@freeuk.com> wrote:
> >
> >> How do you copy one pstring to another? The first byte will give the
> >> current length, but not the maximum that has been allocated; how will it
> >> know how much to copy?
> >
> > You don't. _It_ does, underneath the hood. Remember that this is not a
> > Standard Pascal feature; it's a common but not completely standardised
> > extension.
> 
> I was commenting about this:
> 
>   unsigned char pstring[];
> 
> which looks nearer C than Pascal! The original Pascal will know the 
> maximum length as it's part of the type (so is implicit in the 
> underlying data structure). The C version won't have that, so can only 
> work if the maximum length is a constant value throughout the program, 
> or is added as part of the code that works with these arrays.

Exactly. So this is an inferior solution, and the OP should learn to
work with real C strings already.

> > (It may have made it into Pascal Extended; I never looked
> > enough into that /contradictio in terminis/ to know or care.) Some
> > implementations may have had yet a third member; some may have just
> > crashed if you cross the borders. In any case, length-indicated strings
> > are a Wrong Idea all 'round.
> 
> (No, they're a good idea in the right language, with several advantages. 
> But I admit they are a bit of a pain in C.)

They have a built-in limit to the string length, and require extra
behind-the-scenes bookkeeping from the compiler _even though_ you're
expected to do the other half of it yourself. That's not a good idea in
any language.

Richard

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Pointer to structure Dexterr <dejangru@gmail.com> - 2014-12-21 03:16 -0800
  Re: Pointer to structure BartC <bc@freeuk.com> - 2014-12-21 12:09 +0000
    Re: Pointer to structure Siri Crews <chine.bleu@yahoo.com> - 2014-12-21 04:39 -0800
      Re: Pointer to structure BartC <bc@freeuk.com> - 2014-12-21 12:59 +0000
        Re: Pointer to structure Siri Crews <chine.bleu@yahoo.com> - 2014-12-21 05:05 -0800
          Re: Pointer to structure BartC <bc@freeuk.com> - 2014-12-21 13:12 +0000
            Re: Pointer to structure Siri Crews <chine.bleu@yahoo.com> - 2014-12-21 05:55 -0800
              Re: Pointer to structure BartC <bc@freeuk.com> - 2014-12-21 14:31 +0000
                Re: Pointer to structure Siri Crews <chine.bleu@yahoo.com> - 2014-12-21 06:47 -0800
                Re: Pointer to structure BartC <bc@freeuk.com> - 2014-12-21 20:10 +0000
                Re: Pointer to structure Geoff <geoff@invalid.invalid> - 2014-12-21 10:00 -0800
                Re: Pointer to structure Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-21 22:44 +0000
                Re: Pointer to structure raltbos@xs4all.nl (Richard Bos) - 2014-12-21 18:01 +0000
                Re: Pointer to structure BartC <bc@freeuk.com> - 2014-12-21 21:21 +0000
                Re: Pointer to structure raltbos@xs4all.nl (Richard Bos) - 2014-12-22 12:11 +0000
                Re: Pointer to structure Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-21 22:36 +0000
              Re: Pointer to structure Stephen Sprunk <stephen@sprunk.org> - 2014-12-27 17:56 -0600
                Re: Pointer to structure Siri Crews <chine.bleu@yahoo.com> - 2014-12-27 16:33 -0800
                Re: Pointer to structure Stephen Sprunk <stephen@sprunk.org> - 2015-01-15 12:29 -0600
            Re: Pointer to structure glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-22 00:50 +0000
              Re: Pointer to structure Richard Damon <Richard@Damon-Family.org> - 2014-12-21 20:19 -0500
                Re: Pointer to structure glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-22 06:23 +0000
                Re: Pointer to structure gazelle@shell.xmission.com (Kenny McCormack) - 2014-12-22 12:03 +0000
          Re: Pointer to structure gazelle@shell.xmission.com (Kenny McCormack) - 2014-12-21 13:20 +0000
            Re: Pointer to structure Siri Crews <chine.bleu@yahoo.com> - 2014-12-21 05:40 -0800
  Re: Pointer to structure Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-21 13:16 +0000
  Re: Pointer to structure Barry Schwarz <schwarzb@dqel.com> - 2014-12-21 10:02 -0800
  Re: Pointer to structure Keith Thompson <kst-u@mib.org> - 2014-12-21 12:25 -0800
    Re: Pointer to structure Dexterr <dejangru@gmail.com> - 2014-12-21 15:07 -0800

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