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Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type?

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On 05/03/2012 03:05 PM, Jens Gustedt wrote:
> Am 05/03/2012 08:45 PM, schrieb John Reye:
>> On May 3, 8:14 pm, Nobody wrote:
>>> The compiler is free to lose track of that information during
>>> optimisation, and may well do so.
>>
>> char a;
>> char *p = &a;
>>
>> a = 1;
>> *p = 2;
>> printf("%d\n", a);
>>
>> Does the C standard guarantee, that the value 2 will get printed in
>> the above code??
> 
> no

Why not? In the abstract machine those statements must be executed in
sequence. There's a sequence point at the end of each statement, which
means that side effects such as the change in value of a in the second
statement, must be complete by the time the value of 'a' is read by the
third statement.

> for that you'd have to declare them
> 
> char volatile a;
> char volatile *p = &a;

Why should that be necessary?

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Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-02 09:06 -0700
  Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? "In a very dark China Blue, China Blue condition." <chine.bleu@yahoo.com> - 2012-05-02 09:33 -0700
  Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-02 12:36 -0400
    Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-02 10:04 -0700
      Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-02 13:23 -0400
    Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 09:20 -0700
      Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 09:25 -0700
        Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 10:16 -0700
        Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 11:05 -0700
        Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-03 15:21 -0400
      Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 09:46 -0700
      Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Nobody <nobody@nowhere.com> - 2012-05-03 19:14 +0100
        Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 11:45 -0700
          Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Jens Gustedt <jens.gustedt@loria.fr> - 2012-05-03 21:05 +0200
            Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 12:14 -0700
            Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-03 15:16 -0400
              Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Lanarcam <lanarcam1@yahoo.fr> - 2012-05-03 21:56 +0200
                Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-03 16:12 -0400
                Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 13:45 -0700
                Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Nobody <nobody@nowhere.com> - 2012-05-04 01:34 +0100
              Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Jens Gustedt <jens.gustedt@loria.fr> - 2012-05-03 22:32 +0200
            Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 12:10 -0700
              Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Keith Thompson <kst-u@mib.org> - 2012-05-03 16:14 -0700
            Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Tim Rentsch <txr@alumni.caltech.edu> - 2012-05-07 17:24 -0700
          Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-03 15:19 -0400
            Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? John Reye <jononanon@googlemail.com> - 2012-05-03 12:25 -0700
      Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-03 17:44 -0400
  Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Barry Schwarz <schwarzb@dqel.com> - 2012-05-02 12:35 -0700
    Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-05-02 14:40 -0700
    Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? James Kuyper <jameskuyper@verizon.net> - 2012-05-02 17:51 -0400
    Re: Can *common* struct-members of 2 different struct-types, that are the same for the first common members, be accessed via pointer cast to either struct-type? Tim Rentsch <txr@alumni.caltech.edu> - 2012-05-07 17:16 -0700

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