Subject: Re: __UNCONST(a)
From: David Laight <firstname.lastname@example.org>
Date: 07/04/2004 16:38:46
On Sat, Jul 03, 2004 at 03:28:47PM -0400, James K. Lowden wrote:
> On Thu, 1 Jul 2004 Christos Zoulas wrote:
> > On Jul 2, 10:06am, email@example.com (YAMAMOTO Takashi) wrote:
> > | > Why cast to a specific type? We could do the same, but it seems
> > | > gratuitous.
> > |
> > | because it's only sane way without typeof().
> > Why, (void *) matches everything.
> You want to defeat the whole type system, merely to quell compiler
> wchar_t *ws;
> const char s = "hello";
> ws = __UNCONST(s);
> This is good? I realize that's not the intended context, but there's
> nothing except vigilance to prevent it from being used that way, and
> vigilance breaks down in complex situations.
> C++ uses const_cast<>, providing a type. Seems a like a good model to
Providing the required type doesn't help - the compiler still can't
check that you aren't changing the type of the data.
This is one reason why I dislike using casts to remove compiler/lint
warnings - it can hide a real error.
Of course you can do things like:
#define __U(s) ((void *)(uintptr_t)(s))
#define __UNCONST(type,s) (((type)(s) - s) + (type)__U(s))
Which (probably) checks that 's' is of the require basic type.
David Laight: firstname.lastname@example.org