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| From | Stephen Sprunk <stephen@sprunk.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Issue on assigning address to pointers |
| Date | 2015-11-17 12:17 -0600 |
| Organization | A noiseless patient Spider |
| Message-ID | <n2fqsd$7jp$1@dont-email.me> (permalink) |
| References | <dc62f43a-1725-496b-b36a-c3e196015b7d@googlegroups.com> |
On 17-Nov-15 10:49, Alla _ wrote: > I have seen many times the following declaration of pointers to > arrays, advised without any caveats: > > int numbers[8]; > int *ptr; > > ptr = numbers + 8; // to point at a value stored at numbers[8] > > Please, take a look at a paragraph from K&R, stating that this method > doesn't work on "multi-tasking machines". Given K&R was published in > 1999, I wonder if that statement still holds. It might have been in K&R1, published in 1978, but that has been obsolete since ANSI C in 1989; it's not in K&R2, published in 1999. > The code above sets the array arrayname to zero. This method of > getting at array data is not recommended by this author except in > very simple computer environments. If a program is running on a > normal microcomputer, then there should be few problems with this > alternative method of handling arrays. On the hand, if the > microcomputer is multi-tasking, or the program is running on a larger > system which has a limited manager, then memory ceases to be > something which can be thought of as a sequence of boxes standing > next to one another. Standard C _guarantees_ that, as far as the program can tell, elements of an array _are_ contiguous in (virtual) memory. It's entirely possible that, under the hood, the array spans a page boundary and those pages are not contiguous in (physical) memory, but it must _appear to the program_ as if they were contiguous, using whatever mechanisms are necessary for that to occur. > So ptr = arrayname + 5; might not be a pointer to the fifth character > in a character array. This could be found instead using the '&' > operator. A pointer to the fifth element can be reliably found with: > ptr = &(arrayname[5]); > Be warned! > END OF QUOTE Standard C _defines_ arrayname+5 to be identical to &arrayname[5]; use whichever more clearly expresses your intent to human readers. S -- Stephen Sprunk "God does not play dice." --Albert Einstein CCIE #3723 "God is an inveterate gambler, and He throws the K5SSS dice at every possible opportunity." --Stephen Hawking
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Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 08:49 -0800
Re: Issue on assigning address to pointers James Kuyper <jameskuyper@verizon.net> - 2015-11-17 12:36 -0500
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 17:47 +0000
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:34 -0800
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-17 12:16 -0800
Re: Issue on assigning address to pointers James Kuyper <jameskuyper@verizon.net> - 2015-11-17 15:23 -0500
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:33 -0800
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-17 09:41 -0800
Re: Issue on assigning address to pointers Geoff <geoff@invalid.invalid> - 2015-11-17 10:03 -0800
Re: Issue on assigning address to pointers glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-17 20:31 +0000
Re: Issue on assigning address to pointers Geoff <geoff@invalid.invalid> - 2015-11-17 12:53 -0800
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:32 -0800
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 18:45 +0000
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:53 -0800
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-17 15:05 -0800
Re: Issue on assigning address to pointers Philip Lantz <prl@canterey.us> - 2015-11-19 21:16 -0800
Re: Issue on assigning address to pointers Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2015-11-17 15:47 -0800
Re: Issue on assigning address to pointers Barry Schwarz <schwarzb@dqel.com> - 2015-11-17 15:53 -0800
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-18 04:05 +0000
Re: Issue on assigning address to pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 19:41 +0000
Re: Issue on assigning address to pointers Stephen Sprunk <stephen@sprunk.org> - 2015-11-17 12:17 -0600
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 18:21 +0000
Re: Issue on assigning address to pointers Geoff <geoff@invalid.invalid> - 2015-11-17 10:36 -0800
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 18:46 +0000
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:49 -0800
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:47 -0800
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 18:51 +0000
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:55 -0800
Re: Issue on assigning address to pointers Geoff <geoff@invalid.invalid> - 2015-11-17 11:59 -0800
Re: Issue on assigning address to pointers Stephen Sprunk <stephen@sprunk.org> - 2015-11-17 12:58 -0600
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 19:12 +0000
Re: Issue on assigning address to pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 19:33 +0000
Re: Issue on assigning address to pointers Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-11-17 13:25 -0500
Re: Issue on assigning address to pointers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-17 18:31 +0000
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:39 -0800
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-17 10:40 -0800
Re: Issue on assigning address to pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 19:40 +0000
Re: Issue on assigning address to pointers Geoff <geoff@invalid.invalid> - 2015-11-17 11:15 -0800
Re: Issue on assigning address to pointers James Kuyper <jameskuyper@verizon.net> - 2015-11-17 15:32 -0500
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-17 15:09 -0800
Re: Issue on assigning address to pointers supercat@casperkitty.com - 2015-11-17 15:41 -0800
Re: Issue on assigning address to pointers Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-17 21:28 -0800
Re: Issue on assigning address to pointers supercat@casperkitty.com - 2015-11-17 23:18 -0800
Re: Issue on assigning address to pointers Geoff <geoff@invalid.invalid> - 2015-11-17 17:18 -0800
Re: Issue on assigning address to pointers James Kuyper <jameskuyper@verizon.net> - 2015-11-17 22:37 -0500
Re: Issue on assigning address to pointers Lőrinczy Zsigmond <zsiga@nospam.for.me> - 2015-11-18 11:27 +0100
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-18 06:13 -0800
Re: Issue on assigning address to pointers guinness.tony@gmail.com - 2015-11-24 02:46 -0800
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-24 09:21 -0800
Re: Issue on assigning address to pointers John Bode <jfbode1029@gmail.com> - 2015-11-24 05:01 -0800
Re: Issue on assigning address to pointers Keith Thompson <kst-u@mib.org> - 2015-11-24 09:22 -0800
Re: Issue on assigning address to pointers John Bode <jfbode1029@gmail.com> - 2015-11-24 06:47 -0800
Re: Issue on assigning address to pointers Alla _ <modelling.data@gmail.com> - 2015-11-25 06:44 -0800
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