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Re: Strict aliasing and buffer handling

From "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com>
Newsgroups comp.lang.c++
Subject Re: Strict aliasing and buffer handling
Date 2011-06-20 23:27 +0200
Organization A noiseless patient Spider
Message-ID <itodld$67u$1@dont-email.me> (permalink)
References (2 earlier) <50d78ca6-6153-40c1-85c2-fde0d3d83707@l18g2000yql.googlegroups.com> <UPidnUow18I4BmLQnZ2dnUVZ7oednZ2d@giganews.com> <59682659-868a-4498-b5bc-ef53f6a74105@k6g2000yqc.googlegroups.com> <ito9h7$6jr$1@dont-email.me> <5fa0718f-c308-450c-ac3b-b71c0638dc1e@r14g2000yqr.googlegroups.com>

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* Francois Duranleau, on 20.06.2011 22:29:
> On Jun 20, 4:16 pm, "Alf P. Steinbach /Usenet"<alf.p.steinbach
> +use...@gmail.com>  wrote:
>>
>> Strict aliasing is a g++ thing, not a standard C++ thing: the standard is The
>> Wrong Place to look for info about strict aliasing, it's not there.
>
> Quoting 3.10-15 from the C++ standard (2003):
>
> "If a program attempts to access the stored value of an object through
> an lvalue of other than one of the following
> types the behavior is undefined):
> — the dynamic type of the object,
> — a cv-qualified version of the dynamic type of the object,
> — a type that is the signed or unsigned type corresponding to the
> dynamic type of the object,
> — a type that is the signed or unsigned type corresponding to a cv-
> qualified version of the dynamic type of the object,
> — an aggregate or union type that includes one of the aforementioned
> types among its members (including, recursively, a member of a
> subaggregate or contained union),
> — a type that is a (possibly cv-qualified) base class type of the
> dynamic type of the object,
> — a char or unsigned char type."
>
> So what I am reading here?

A flawed attempt at enumerating the ways, which attempt was/is presumably the 
perceived rationale for g++ "strict aliasing".


>> Standard C++ does however have rules about alignment.
>>
>> As a practical matter, if you break your system's alignment rules, then in
>> practice you get extreme inefficiency or a program crash.
>
> Of course.

Well, that's all, if your data is correct representation of the object.

Just tell g++ to shut up. :-)


Cheers & hth.,

- Alf

-- 
blog at <url: http://alfps.wordpress.com>

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Thread

Strict aliasing and buffer handling Francois Duranleau <xiao.bai.xiong@gmail.com> - 2011-06-20 09:59 -0700
  Re: Strict aliasing and buffer handling "Paul" <pchristor@yahoo.co.uk> - 2011-06-20 19:39 +0100
    Re: Strict aliasing and buffer handling Francois Duranleau <xiao.bai.xiong@gmail.com> - 2011-06-20 11:56 -0700
      Re: Strict aliasing and buffer handling Leigh Johnston <leigh@i42.co.uk> - 2011-06-20 20:12 +0100
        Re: Strict aliasing and buffer handling Francois Duranleau <xiao.bai.xiong@gmail.com> - 2011-06-20 12:39 -0700
          Re: Strict aliasing and buffer handling Leigh Johnston <leigh@i42.co.uk> - 2011-06-20 20:49 +0100
            Re: Strict aliasing and buffer handling "Paul" <pchristor@yahoo.co.uk> - 2011-06-20 21:12 +0100
              Re: Strict aliasing and buffer handling Leigh Johnston <leigh@i42.co.uk> - 2011-06-20 21:20 +0100
                Re: Strict aliasing and buffer handling "Paul" <pchristor@yahoo.co.uk> - 2011-06-21 10:35 +0100
                Re: Strict aliasing and buffer handling Leigh Johnston <leigh@i42.co.uk> - 2011-06-21 12:35 +0100
                Re: Strict aliasing and buffer handling "Paul" <pchristor@yahoo.co.uk> - 2011-06-21 12:37 +0100
          Re: Strict aliasing and buffer handling "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-06-20 22:16 +0200
            Re: Strict aliasing and buffer handling Francois Duranleau <xiao.bai.xiong@gmail.com> - 2011-06-20 13:29 -0700
              Re: Strict aliasing and buffer handling "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-06-20 23:27 +0200
                Re: Strict aliasing and buffer handling Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-20 14:37 -0700
                Re: Strict aliasing and buffer handling "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-06-21 00:31 +0200
                Re: Strict aliasing and buffer handling Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-20 19:37 -0700
                Re: Strict aliasing and buffer handling Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-06-20 23:38 +0200
                Re: Strict aliasing and buffer handling "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-06-21 00:46 +0200
                Re: Strict aliasing and buffer handling Francois Duranleau <xiao.bai.xiong@gmail.com> - 2011-06-21 05:03 -0700
                Re: Strict aliasing and buffer handling "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-06-21 16:19 +0200
                Re: Strict aliasing and buffer handling Francois Duranleau <xiao.bai.xiong@gmail.com> - 2011-06-21 09:08 -0700
                Re: Strict aliasing and buffer handling "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-06-22 01:43 +0200
  Re: Strict aliasing and buffer handling Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-20 14:49 -0700
  Re: Strict aliasing and buffer handling "io_x" <a@b.c.invalid> - 2011-06-21 09:12 +0200
    Re: Strict aliasing and buffer handling Ian Collins <ian-news@hotmail.com> - 2011-06-21 20:14 +1200

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