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Re: Aliasing through a union pointer

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From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Aliasing through a union pointer
Date Tue, 24 Nov 2015 21:52:24 -0800
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supercat@casperkitty.com writes:
> On Tuesday, November 24, 2015 at 1:51:52 PM UTC-6, Keith Thompson wrote:
>> If gcc knows that it's accessing a member of a packed struct, it will do
>> whatever is necessary, perhaps generating code to access it a byte at a
>> time.  Problems occur only when you take the address of a member.
>
> Many compilers (I believe gcc is among them) have distinct types for "packed"
> and "unpacked" pointers; problems arise when storing a value of a "packed"
> pointer type into a variable of a "normal" pointer type.
[...]

As far as I know, gcc doesn't support "packed" pointers.

If it did, they would be relevant to this question on Stack Overflow:
    http://stackoverflow.com/q/8568432/827263
and nobody has commented on such a thing in the 4 years since I
posted it.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Aliasing through a union pointer Ian Pilcher <arequipeno@gmail.com> - 2015-11-23 10:14 -0600
  Re: Aliasing through a union pointer Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-23 11:43 -0500
    Re: Aliasing through a union pointer Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-23 11:49 -0500
    Re: Aliasing through a union pointer Ian Pilcher <arequipeno@gmail.com> - 2015-11-23 13:22 -0600
      Re: Aliasing through a union pointer Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-23 14:38 -0500
        Re: Aliasing through a union pointer Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-25 10:38 -0800
          Re: Aliasing through a union pointer Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-25 14:17 -0500
            Re: Aliasing through a union pointer Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 13:16 -0800
      Re: Aliasing through a union pointer David Brown <david.brown@hesbynett.no> - 2015-11-23 21:46 +0100
        Re: Aliasing through a union pointer Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-23 22:20 +0000
          Re: Aliasing through a union pointer Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 16:52 -0600
            Re: Aliasing through a union pointer Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-23 23:10 +0000
              Re: Aliasing through a union pointer Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 19:05 -0600
          Re: Aliasing through a union pointer Nick Bowler <nbowler@draconx.ca> - 2015-11-23 22:51 +0000
          Re: Aliasing through a union pointer Keith Thompson <kst-u@mib.org> - 2015-11-23 15:49 -0800
            Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-23 16:01 -0800
          Re: Aliasing through a union pointer David Brown <david.brown@hesbynett.no> - 2015-11-24 09:55 +0100
            Re: Aliasing through a union pointer Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-24 14:29 +0000
              Re: Aliasing through a union pointer David Brown <david.brown@hesbynett.no> - 2015-11-24 22:58 +0100
                Re: Aliasing through a union pointer Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-24 17:30 -0500
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-24 15:27 -0800
                Re: Aliasing through a union pointer Ian Collins <ian-news@hotmail.com> - 2015-11-25 12:57 +1300
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-24 16:31 -0800
                Re: Aliasing through a union pointer Ian Collins <ian-news@hotmail.com> - 2015-11-25 18:28 +1300
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-25 06:54 -0800
                Re: Aliasing through a union pointer Ian Collins <ian-news@hotmail.com> - 2015-11-26 08:59 +1300
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-25 13:01 -0800
                Re: Aliasing through a union pointer Ian Collins <ian-news@hotmail.com> - 2015-11-26 12:58 +1300
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-25 16:44 -0800
                Re: Aliasing through a union pointer Ian Collins <ian-news@hotmail.com> - 2015-11-26 14:12 +1300
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-25 21:34 -0800
                Re: Aliasing through a union pointer Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-25 21:55 -0800
                Re: Aliasing through a union pointer Ian Collins <ian-news@hotmail.com> - 2015-11-26 20:51 +1300
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-26 11:39 -0800
                Re: Aliasing through a union pointer Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-26 00:06 +0000
            Re: Aliasing through a union pointer Keith Thompson <kst-u@mib.org> - 2015-11-24 11:51 -0800
              Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-24 12:20 -0800
                Re: Aliasing through a union pointer Keith Thompson <kst-u@mib.org> - 2015-11-24 21:52 -0800
                Re: Aliasing through a union pointer supercat@casperkitty.com - 2015-11-25 08:30 -0800
              Re: Aliasing through a union pointer David Brown <david.brown@hesbynett.no> - 2015-11-24 23:04 +0100
  Re: Aliasing through a union pointer Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-25 10:10 -0800
    Re: Aliasing through a union pointer Richard Damon <Richard@Damon-Family.org> - 2015-11-25 11:02 -0800
      Re: Aliasing through a union pointer Philip Lantz <prl@canterey.us> - 2015-11-26 13:06 -0800
        Re: Aliasing through a union pointer Richard Damon <Richard@Damon-Family.org> - 2015-11-26 13:09 -0800
      Re: Aliasing through a union pointer Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 13:08 -0800

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