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From: joerg.barfurth@attglobal.net (Joerg Barfurth)
Newsgroups: comp.std.c++
Subject: Re: Are literals const?
Date: Thu, 23 Aug 2001 00:14:33 GMT
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Peter Dimov <pdimov@mmltd.net> wrote:

> What do you think about this piece of code:
>=20
> int main()
> {
>   int const & r =3D 5;
>   const_cast<int &>(r) =3D 6;
> }
>=20
> Is this legal? I think that it is. Literals aren't const (they are
> about 90% const, but not 100% const.)

IMO this is not legal.=20

The literal is not const, but it is an rvalue. (Note: rvalues of builtin
types are never const.) According to 8.5.3/5 (last bullet) a temporary
of type 'const int' is created and the reference is bound to this
temporary.

As the temporary is const (100% :-o), the const_cast + modification
invokes undefined behavior.

> Similarly:
>=20
> int f();

> int main()
> {
>   int const & r =3D f();
>   const_cast<int &>(r) =3D 6;
> }
>=20
> Do we _really_ need non-const literals and rvalues (of built-in
> types)?

I don't think it matters (afaict you can't exploit the non-constness).

BTW: The only literals that are lvalues are string literals (5.1/2).
Those are const to begin with.

Regards, Joerg

--=20
J=F6rg Barfurth                         joerg.barfurth@attglobal.net
<<<<<<<<<<<<< using std::disclaimer;  <<<<<<<<<<<<<<<<<<<<<<<<<<<<
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