Date: Tue, 22 Jul 2003 13:54:32 +0200 From: Marc Olzheim <marcolz@stack.nl> To: Tim Kientzle <kientzle@acm.org> Cc: Chad David <davidc@issci.ca> Subject: Re: Correct way to call execve? Message-ID: <20030722115432.GA36870@stack.nl> In-Reply-To: <3F1C2FEB.4070801@acm.org> References: <3F1B0610.90803@acm.org> <20030720225041.GA26277@ussenterprise.ufp.org> <3F1C0C91.6050203@acm.org> <20030721165735.GA56766@ussenterprise.ufp.org> <20030721171538.GA21656@colnta.acns.ab.ca> <20030721172321.GA57666@ussenterprise.ufp.org> <20030721174206.GA21892@colnta.acns.ab.ca> <3F1C2FEB.4070801@acm.org>
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On Mon, Jul 21, 2003 at 11:24:43AM -0700, Tim Kientzle wrote:
> Chad David wrote:
> >I assumed it was obvious that you could copy the data, but I believe
> >the intent of the original question was to find an alternative. As
> >far as I know there isn't one. A const is a const, except in C++.
>
> Yes, the intent was to find a way to avoid copying the data.
>
> I was hoping that someone knew a standard way to
> say "yes, I really do mean to cast away that const,"
> akin to C++ const_cast.
>
> As far as I can tell, the POSIX-mandated declaration
> of execvp is simply wrong. (SUSv3 even has a comment
> that essentially admits this fact and then vainly tries
> to rationalize it. <sigh>)
I mailed this a long time ago:
char *
func(void)
{
char *foo;
const char *cfoo = "bar";
/* From http://www.eskimo.com/~scs/C-faq/q11.10.html:
*
* References: ANSI Sec. 3.1.2.6, Sec. 3.3.16.1, Sec. 3.5.3
* ISO Sec. 6.1.2.6, Sec. 6.3.16.1, Sec. 6.5.3
* H&S Sec. 7.9.1 pp. 221-2
*
* Use -Wcast-qual with gcc.
* gcc 2.7.2.3 ok, gcc 2.95.2 not ok.
*/
foo = *((char *const *) &cfoo);
return (foo);
}
But that doesn't work after 2.7.2
What does work, except with 2.95 is this:
foo = *((char **)((void *)&cfoo)));
Then again: you can always use the union trick:
union
{
void *nonconst;
const void *constant;
} hack;
hack.constant = cfoo;
foo = hack.nonconst;
Zlo
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