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Re: Arrays Vs Pointers

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Keith Thompson wrote:
) Willem <willem@toad.stack.nl> writes:
)> peter wrote:
)> ) I am currently exploring the world of pointers and have encounter some
)> ) inconsistent information regarding the best way to reference an
)> ) array: array[1]   OR    *(array +1).
)> )
)> ) One book says that you should not use the syntax array[1] because
)> ) of performance reason.
)>
)> That book is completely and utterly wrong.
)> In C, "array[index]" is *exactly the same* as "*(array + index)"
)> I would go so far as to call it syntactic sugar.
)> Hell, it's even commutative.  "array[index]" means the same as "index[array]" !
) [...]
)
) Yes, but I doubt that that's what the book actually said.

Granted.

) I'm only
) guessing, but the book was probably advocating code like this:
)
)     void func(char *s) {
)         while (*s != '\0') {
)             do_something_with(*s);
)             s++;
)         }
)     }
)
) over this:
)
)     void func(char *s) {
)         size_t i = 0;
)         while (s[i] != '\0') {
)             do_something_with(s[i]);
)             i++;
)         }
)     }
)
) The former, by updating the pointer on each iteration, avoids
) redoing the index calculation, which might be moderately expenstive,
) especially for arrays of something bigger than char.

Or which might not be expensive at all, especially given special indexing
instructions such as those on the x86.  Also for types bigger than char.

A long time ago, I did some speed tests on an x86 machine, and it turned
out that there was no speed difference whatsoever between an indexed loop
and a pointer loop.


SaSW, Willem
-- 
Disclaimer: I am in no way responsible for any of the statements
            made in the above text. For all I know I might be
            drugged or something..
            No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

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Arrays Vs Pointers peter <pc722@nospam.mail.com.br> - 2012-02-07 21:28 +0000
  Re: Arrays Vs Pointers William Ahern <william@wilbur.25thandClement.com> - 2012-02-07 13:50 -0800
  Re: Arrays Vs Pointers James Kuyper <jameskuyper@verizon.net> - 2012-02-07 17:13 -0500
  Re: Arrays Vs Pointers Stephen Sprunk <stephen@sprunk.org> - 2012-02-07 16:38 -0600
    Re: Arrays Vs Pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-07 23:09 +0000
  Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-07 14:41 -0800
    Re: Arrays Vs Pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-07 23:07 +0000
      Re: Arrays Vs Pointers James Kuyper <jameskuyper@verizon.net> - 2012-02-07 19:14 -0500
    Re: Arrays Vs Pointers Shao Miller <sha0.miller@gmail.com> - 2012-02-07 18:21 -0500
      Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-07 16:25 -0800
        Re: Arrays Vs Pointers Shao Miller <sha0.miller@gmail.com> - 2012-02-07 20:31 -0500
    Re: Arrays Vs Pointers Ike Naar <ike@sverige.freeshell.org> - 2012-02-07 23:36 +0000
      Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-07 16:26 -0800
    Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-07 16:24 -0800
  Re: Arrays Vs Pointers Paul N <gw7rib@aol.com> - 2012-02-07 14:55 -0800
  Re: Arrays Vs Pointers Shao Miller <sha0.miller@gmail.com> - 2012-02-07 18:11 -0500
  Re: Arrays Vs Pointers John Bode <jfbode1029@gmail.com> - 2012-02-08 16:06 -0800
    Re: Arrays Vs Pointers Philip Lantz <prl@canterey.us> - 2012-02-08 23:25 -0800
      Re: Arrays Vs Pointers John Bode <jfbode1029@gmail.com> - 2012-02-09 05:34 -0800
        Re: Arrays Vs Pointers Philip Lantz <prl@canterey.us> - 2012-02-10 01:04 -0800
  Re: Arrays Vs Pointers Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-09 00:20 -0800
    Re: Arrays Vs Pointers 88888 Dihedral <dihedral88888@googlemail.com> - 2012-02-09 23:42 -0800
    Re: Arrays Vs Pointers gwowen <gwowen@gmail.com> - 2012-02-10 01:20 -0800
    Re: Arrays Vs Pointers David Thompson <dave.thompson2@verizon.net> - 2012-02-18 23:12 -0500
      Re: Arrays Vs Pointers Kaz Kylheku <kaz@kylheku.com> - 2012-02-19 05:53 +0000
        Re: Arrays Vs Pointers Markus Wichmann <nullplan@gmx.net> - 2012-02-19 18:54 +0100
          Re: Arrays Vs Pointers Willem <willem@toad.stack.nl> - 2012-02-19 18:51 +0000
          Re: Arrays Vs Pointers "io_x" <a@b.c.invalid> - 2012-02-19 21:29 +0100
          Re: Arrays Vs Pointers Markus Wichmann <nullplan@gmx.net> - 2012-02-20 11:24 +0100
          Re: Arrays Vs Pointers gwowen <gwowen@gmail.com> - 2012-02-21 01:51 -0800
  Re: Arrays Vs Pointers Willem <willem@toad.stack.nl> - 2012-02-19 12:32 +0000
    Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-19 12:21 -0800
      Re: Arrays Vs Pointers Willem <willem@toad.stack.nl> - 2012-02-19 21:00 +0000
        Re: Arrays Vs Pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-19 21:42 +0000
      Re: Arrays Vs Pointers pete <pfiland@mindspring.com> - 2012-02-20 17:32 -0500
        Re: Arrays Vs Pointers James Kuyper <jameskuyper@verizon.net> - 2012-02-20 17:56 -0500
        Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-20 15:19 -0800
          Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-20 16:35 -0800
            Re: Arrays Vs Pointers pete <pfiland@mindspring.com> - 2012-02-20 22:53 -0500
              Re: Arrays Vs Pointers Keith Thompson <kst-u@mib.org> - 2012-02-20 21:16 -0800
            Re: Arrays Vs Pointers Richard Sanders <lnr729@gmail.com> - 2012-02-21 00:26 -0800
              Re: Arrays Vs Pointers pete <pfiland@mindspring.com> - 2012-02-21 11:46 -0500

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