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Groups > comp.lang.c > #138082
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Pointer conversion and alignment |
| Date | 2018-11-17 21:01 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87r2fjl8pl.fsf@bsb.me.uk> (permalink) |
| References | <20181117143819.43938ee34006bbcc1826bf0c@gmail.com> <20181117173706.aa796408d8f064693c860302@gmail.com> |
Anton Shepelev <anton.txt@gmail.com> writes:
> I wrote:
>
>> By way of exercise, I am writing a small dynamic array
>> library that makes dynamic arrays appear and behave as if
>> they were pointers to allocated objects of the
>> corresponding type, so that they can be substituded for
>> such pointers without rewriting the code. The following
>> sample (without error handling for simplicity):
>>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <string.h>
>> #include "dynarray.h"
>> /* ... */
>> int *a, v, i, l;
>> void* vP;
>>
>> da_new ( &a, sizeof( int ) );
>> da_setlen( &a, 2 );
>>
>> a[0] = 0;
>> a[1] = 1;
>> da_setlen( &a, 4 );
>> a[2] = 2;
>> a[3] = 3;
>>
>> v = 4;
>> da_add( &a, &v );
>>
>> v = 5;
>> da_addemp( &a, &vP );
>> memcpy( vP, &v, sizeof( int ) );
This use confuses me. It may be linked to what you say below. What's
going on here?
>> l = da_len( &a );
>> for( i = 0; i < l; i++ )
>> { printf("%i ", a[i]); }
>>
>> da_free( &a );
>>
>> prints: "0 1 2 3 4 5 ", but in order to make sure that my
>> implementation works not by coincidence but by design
>
> It works by coincidence, because Standard C has no generic
> pointer-to-pointer, and I shall have to work around that.
Can you elaborate on what you see as the problem there? C has a generic
pointer-to-object, and there's nothing stopping that object from holding
a pointer. What do you want a generic pointer-to-pointer to be able to
do?
You need to be very strict with this sort of interface. The fact that
the array is represented by a pointer to the data is very handy, but it
invites dangerous uses such as
int *save = a;
After that, any use of &a that causes the data to move will invalidate
the saved pointer.
<snip>
--
Ben.
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Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-17 14:38 +0300
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-17 17:37 +0300
Re: Pointer conversion and alignment Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-17 21:01 +0000
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 00:43 +0300
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 01:20 +0300
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-17 18:12 -0500
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 02:32 +0300
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-17 18:59 -0500
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 12:40 +0300
Re: Pointer conversion and alignment Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-18 02:14 +0000
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 13:23 +0300
Re: Pointer conversion and alignment Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-18 11:28 +0000
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 15:31 +0300
Re: Pointer conversion and alignment Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-18 15:03 +0000
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 23:00 +0300
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 00:49 +0300
Re: Pointer conversion and alignment Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-11-17 06:52 -0800
Re: Pointer conversion and alignment Ian Collins <ian-news@hotmail.com> - 2018-11-18 09:18 +1300
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-17 13:49 -0800
Re: Pointer conversion and alignment Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-11-17 13:57 -0800
Re: Pointer conversion and alignment Ian Collins <ian-news@hotmail.com> - 2018-11-18 11:08 +1300
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 01:13 +0300
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-17 18:37 -0800
Re: Pointer conversion and alignment Philipp Klaus Krause <pkk@spth.de> - 2018-11-18 14:14 +0100
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-17 10:05 -0500
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 01:08 +0300
Re: Pointer conversion and alignment "Chris M. Thomasson" <invalid_chris_thomasson@invalid.invalid> - 2018-11-17 14:31 -0800
Re: Pointer conversion and alignment "Chris M. Thomasson" <invalid_chris_thomasson@invalid.invalid> - 2018-11-17 16:10 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-18 15:01 +0300
Re: Pointer conversion and alignment James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-18 07:25 -0500
Re: Pointer conversion and alignment "Chris M. Thomasson" <invalid_chris_thomasson@invalid.invalid> - 2018-11-19 21:30 -0800
Re: Pointer conversion and alignment "Chris M. Thomasson" <invalid_chris_thomasson@invalid.invalid> - 2018-11-20 14:20 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-17 18:04 -0500
Re: Pointer conversion and alignment Philipp Klaus Krause <pkk@spth.de> - 2018-11-18 14:18 +0100
Re: Pointer conversion and alignment scott@slp53.sl.home (Scott Lurndal) - 2018-11-18 19:49 +0000
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-11-23 18:27 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-23 21:59 -0500
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-11-24 00:32 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-24 08:17 -0500
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-11-29 09:55 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-29 21:48 -0500
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-12-05 04:14 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-12-05 08:14 -0500
Re: Pointer conversion and alignment Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-12-05 05:29 -0800
Re: Pointer conversion and alignment David Brown <david.brown@hesbynett.no> - 2018-12-05 14:44 +0100
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-12-05 21:58 -0500
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-12-05 16:38 +0300
Re: Pointer conversion and alignment scott@slp53.sl.home (Scott Lurndal) - 2018-12-05 14:23 +0000
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-12-05 14:35 -0800
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-12-08 19:28 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-12-09 08:18 -0500
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-12-09 14:35 -0500
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-12-09 14:04 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-12-09 20:40 -0500
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-12-17 07:18 -0800
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-12-17 12:35 -0800
Re: Pointer conversion and alignment Tim Rentsch <txr@alumni.caltech.edu> - 2018-12-17 12:48 -0800
Re: Pointer conversion and alignment "Chris M. Thomasson" <invalid_chris_thomasson@invalid.invalid> - 2018-11-24 18:33 -0800
My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-19 02:26 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-19 11:08 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-19 15:37 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-19 15:39 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-19 15:07 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-19 22:24 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-19 12:33 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-20 00:34 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-19 14:38 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-20 00:43 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-19 21:44 -0500
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jadill33@gmail.com - 2018-11-20 07:11 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] bart4858@gmail.com - 2018-11-20 10:02 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-19 22:20 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-20 14:01 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Melzzzzz <Melzzzzz@zzzzz.com> - 2018-11-20 11:07 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-20 15:12 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-20 08:15 -0500
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-20 23:08 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-20 14:13 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-21 16:38 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-21 09:05 -0500
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-21 20:28 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-21 12:58 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-22 01:47 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-21 15:50 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-24 19:37 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-21 21:22 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-21 01:15 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-19 15:06 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] mark.bluemel@gmail.com - 2018-11-19 08:05 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] scott@slp53.sl.home (Scott Lurndal) - 2018-11-19 16:49 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-19 10:35 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-20 00:45 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-19 14:24 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-20 15:05 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-20 08:31 -0500
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Richard Damon <Richard@Damon-Family.org> - 2018-11-20 20:02 -0500
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-21 22:47 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] jameskuyper@alumni.caltech.edu - 2018-11-21 13:08 -0800
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-22 00:31 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-21 21:36 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-19 16:04 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-19 14:56 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-24 19:24 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-24 21:31 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-24 21:46 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-25 01:12 +0300
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-11-25 01:39 +0000
Re: My dynamic arrays module [was:Re: Pointer conversion and alignment] Anton Shepelev <anton.txt@gmail.com> - 2018-11-25 14:19 +0300
Re: Pointer conversion and alignment jadill33@gmail.com - 2018-11-19 08:44 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-20 00:02 +0300
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-19 13:51 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-20 01:08 +0300
Re: Pointer conversion and alignment jameskuyper@alumni.caltech.edu - 2018-11-19 14:31 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-20 15:21 +0300
Re: Pointer conversion and alignment James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-20 08:59 -0500
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-20 11:06 -0800
Re: Pointer conversion and alignment jameskuyper@alumni.caltech.edu - 2018-11-20 12:43 -0800
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-20 14:33 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-21 14:33 +0300
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-21 07:49 -0500
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-21 12:42 -0800
Re: Pointer conversion and alignment James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-21 08:41 -0500
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-25 15:06 +0300
Re: Pointer conversion and alignment James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-11-25 10:47 -0500
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-11-26 12:42 +0300
Re: Pointer conversion and alignment Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-11-26 03:07 -0800
Re: Pointer conversion and alignment Keith Thompson <kst-u@mib.org> - 2018-11-26 12:56 -0800
Re: Pointer conversion and alignment Richard Damon <Richard@Damon-Family.org> - 2018-11-26 18:17 -0500
Re: Pointer conversion and alignment jameskuyper@alumni.caltech.edu - 2018-11-26 09:06 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-26 23:52 +0300
Re: Pointer conversion and alignment jameskuyper@alumni.caltech.edu - 2018-11-26 13:13 -0800
Re: Pointer conversion and alignment Anton Shepelev <anton.txt@gmail.com> - 2018-11-27 00:31 +0300
Re: Pointer conversion and alignment jameskuyper@alumni.caltech.edu - 2018-11-26 14:15 -0800
Re: Pointer conversion and alignment jadill33@gmail.com - 2018-11-19 14:33 -0800
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