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Groups > comp.lang.c > #138094

Re: Pointer conversion and alignment

From Anton Shepelev <anton.txt@gmail.com>
Newsgroups comp.lang.c
Subject Re: Pointer conversion and alignment
Date 2018-11-18 02:32 +0300
Organization A noiseless patient Spider
Message-ID <20181118023201.abbbb1298a7119348f5ba624@gmail.com> (permalink)
References (1 earlier) <20181117173706.aa796408d8f064693c860302@gmail.com> <87r2fjl8pl.fsf@bsb.me.uk> <20181118004332.f3bbecb2e75db48245ac0cf9@gmail.com> <20181118012013.517a9036400f34fb8590bd22@gmail.com> <Bf1ID.1386784$YL3.227668@fx48.iad>

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Richard Damon:

> When using a void * pointer to pass an address, you ALWAYS
> need to convert it into the right type of pointer before
> using it to write into the memory it points to. In some
> cases, like memcpy, it can use a generic char type, but if
> you are passing the address of a pointer, in general, to
> write to that pointer, you will need to know the type of
> the pointer. On some machines the representation of a
> char* pointer (and void *) is different than other
> pointers (it might not even be the same size),

Thanks for the explanation, Richard.  Since the Standard
defines pointer casts as conversions, the size of different
pointer types does not matter.  For example, char* may be of
a size different from that of int*, yet it is required to be
convertible from int* and any pointer type.  What is
important is that the Standard does not guarantee that
void** can be converted to char** (unless the underlying
object is indeed of type char).

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Thread

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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