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Re: unions

From Vaclav Haisman <v.haisman@sh.cvut.cz>
Newsgroups comp.lang.c++
Subject Re: unions
Date 2011-06-04 20:13 +0200
Organization Czech Technical University
Message-ID <4DEA75DF.6010402@sh.cvut.cz> (permalink)
References <iscfn1$keo$8@reader1.panix.com> <isdrr3$urc$1@node2.news.atman.pl>

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Edek wrote, On 4.6.2011 19:59:
>   Am I missing something about them?  I
>> started to have deep doubts about what I thought I knew.
>>
> 
> Other things aside, by the standard unions are the only
> possibility to alias two non-char types without breaking
> optimisations. Maybe void* is another and a couple of
> other strange cases. Don't ask me about where it is in the
> standard; I just know that it is a pain to find bugs
> caused by wrong casting coupled with unpredictable optimisation
> results (UB caused by casts really, unions are safe).
Unions are not safe. You cannot write using one union member and read using
another. It is only GCC extension that it works but the standard does not
allow it, AFAIK.

-- 
VH

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unions Ruben Safir <ruben@mrbrklyn.com> - 2011-06-04 05:26 +0000
  Re: unions Ian Collins <ian-news@hotmail.com> - 2011-06-04 17:38 +1200
    Re: unions Ruben Safir <ruben@mrbrklyn.com> - 2011-06-04 05:45 +0000
      Re: unions Ian Collins <ian-news@hotmail.com> - 2011-06-04 18:04 +1200
        Re: unions Ruben Safir <ruben@mrbrklyn.com> - 2011-06-04 06:13 +0000
  Re: unions Öö Tiib <ootiib@hot.ee> - 2011-06-04 04:54 -0700
  Re: unions Edek <edek.pienkowski@gmail.com> - 2011-06-04 19:59 +0200
    Re: unions Vaclav Haisman <v.haisman@sh.cvut.cz> - 2011-06-04 20:13 +0200
      Re: unions Edek <edek.pienkowski@gmail.com> - 2011-06-04 22:34 +0200
        Re: unions Vaclav Haisman <v.haisman@sh.cvut.cz> - 2011-06-05 07:29 +0200
  Re: unions Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-06-09 09:19 +0000
  Re: unions Keith <kbelder@gmail.com> - 2011-06-09 11:17 -0700
    Re: unions Victor Bazarov <v.bazarov@comcast.invalid> - 2011-06-09 14:29 -0400
    Re: unions Edek <edek.pienkowski@gmail.com> - 2011-06-10 13:16 +0200

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