Re: "Not really an lvalue" warnings
Re: "Not really an lvalue" warnings
- Subject: Re: "Not really an lvalue" warnings
- From: "Clark Cox" <email@hidden>
- Date: Fri, 6 Apr 2007 15:40:51 -0700
On 4/6/07, Mark Wagner <email@hidden> wrote:
On 4/6/07, Marshall Clow <email@hidden> wrote:
> At 2:48 PM -0700 4/6/07, Mark Wagner wrote:
> >The following code produces a warning from GCC about "target of
> >assignment not really an lvalue; this will be a hard error in the
> >future". What's going wrong, and how do I fix it?
> >
> > char *typeOfQ = NULL;
> > static_cast<const char *>(typeOfQ) =
> >handle.FirstChildElement("fieldlabel").Element()->NextSiblingElement("fieldentry")->GetText();
>
> GCC is telling you that there is a problem in your code (hence the
> warning), and telling you that future versions of the compiler will
> flag this as an error rather than a warning.
>
> This expression:
> static_cast<const char *>(typeOfQ)
> is not a variable, it is a expression.
>
> Think of the difference between 'x' and '3' - one can be assigned to,
> the other cannot )
> Googling for "rvalue" and "lvalue" will give more general information.
I know the difference between an lvalue and an rvalue. My
understanding is that "static_cast<const char *>(typeOfQ)" is
functionally and semantically equivalent to "(const char *)typeOfQ"
with the addition of compile-time checking to make sure the conversion
is defined.
Yes, those two are equivalent in this case. And neither of them yields
an lvalue. The code is just as broken whether you use C-style casts or
C++-style casts.
--
Clark S. Cox III
email@hidden
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