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NNTP-Posting-Date: Sun, 02 Dec 2012 17:50:49 -0600
Message-ID: <50BBE95D.268A@mindspring.com>
Date: Sun, 02 Dec 2012 18:50:53 -0500
From: pete <pfiland@mindspring.com>
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Subject: Re: Casts on lvalues
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Eric Sosman wrote:
> 
> On 12/2/2012 4:21 PM, pete wrote:
> > Keith Thompson wrote:
> >
> >> The result of a cast is not an lvalue.
> >
> > I don't think that the standard explicitly states this;
> 
>      It's in a footnote to 6.5.4p5.  Footnotes are non-normative,
> but then there's the definition of lvalue in 6.3.2.1p1:
> 
>         "An lvalue is an expression [...] that potentially
>         designates an object [...]"
> 
> There is no cast that produces an object designator,[*] hence
> there is no cast that produces an lvalue.
> 
>      [*] You can (sometimes) derive an lvalue from the result
> of a cast by applying an operator to it, as in
> 
>         * (unsigned char*)&foo = 42;
> 
> or
>         ((struct baz*)&foo) -> mumble = 17;
> 
> > but as far as I can tell,
> > the result of any conversion of the type of any expression,
> > is not an lvalue.
> 
>      Even a non-conversion is not an lvalue:
> 
>         double trouble;
>         (double)trouble = 3.14;  // BZZZT!

The other type conversion that I was thinking of,
was the implicit conversion of an array type.

-- 
pete