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Groups > comp.lang.c > #14525

Re: Repeated types in union

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Am 12/12/2011 09:09 PM, schrieb Edward Rutherford:

> Thanks for the explanation, Eric.
> 
> Does that mean the "It's Legal" brigade would say it's always legal to 
> read an unsigned char from an union, whatever was previously stored in 
> it, on the grounds that an unsigned char cannot contain a trap 
> representation?

One thing is sure, the standard explicitly mandates to copy any object
(with memcpy) to an array of `unsigned char`. This is even the way the
term object representation is introduced.

So first of all this means that we are allowed to read all the bytes of
a union. Second it means that all bytes of of the object representation
can be interpreted as unsigned char.

Jens

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Repeated types in union Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-12-10 22:06 +0000
  Re: Repeated types in union Jens Gustedt <jens.gustedt@loria.fr> - 2011-12-11 00:11 +0100
  Re: Repeated types in union Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-10 18:14 -0500
    Re: Repeated types in union Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-12-12 20:09 +0000
      Re: Repeated types in union Jens Gustedt <jens.gustedt@loria.fr> - 2011-12-12 23:45 +0100
      Re: Repeated types in union Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-12 19:48 -0500
        Re: Repeated types in union "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-12-13 15:17 -0800
          Re: Repeated types in union Keith Thompson <kst-u@mib.org> - 2011-12-13 15:29 -0800
          Re: Repeated types in union James Kuyper <jameskuyper@verizon.net> - 2011-12-13 18:30 -0500
          Re: Repeated types in union Noob <root@127.0.0.1> - 2011-12-14 17:40 +0100
          Re: Repeated types in union Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 13:28 -0800
        Re: Repeated types in union Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 15:04 -0800
    Re: Repeated types in union ralph <nt_consulting64@yahoo.net> - 2011-12-12 14:50 -0600
    Re: Repeated types in union Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 14:53 -0800
  Re: Repeated types in union Barry Schwarz <schwarzb@dqel.com> - 2011-12-10 22:04 -0800
    Re: Repeated types in union "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-12-12 09:49 -0800
      Re: Repeated types in union Jens Gustedt <jens.gustedt@loria.fr> - 2011-12-12 20:09 +0100
        Re: Repeated types in union "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-12-13 15:10 -0800
          Re: Repeated types in union Jens Gustedt <jens.gustedt@loria.fr> - 2011-12-14 00:24 +0100
          Re: Repeated types in union Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 13:46 -0800
      Re: Repeated types in union Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 13:42 -0800
    Re: Repeated types in union Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 13:36 -0800

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