Re: Compiling GCC With a C++ Compiler (g++)

[Geoffrey Keating <geoffk at apple dot com>]

On 14/10/2004, at 5:33 AM, Dave Korn wrote:

> [ Phil Edwards snecked from Cc: line in accordance with his wish to 
> escape
> "this eternal thread"! ]
>
> > -----Original Message-----
> > From: Geoffrey Keating
> > Sent: 13 October 2004 20:42
>
> > On 13/10/2004, at 8:23 AM, Dave Korn wrote:
>
> > >   Huh?  Are you saying that in:
> > >
> > > typedef struct { const char x } AA;
> > >
> > > AA *py1, py2;
> > > AA y1 = { z };
> > >
> > >   py1 = malloc (sizeof *py2);
> > >   py2 = &y1;
> > >
> > > it is valid to say
> > >
> > >   *(char *)(&py1->x) = '?';
> > >
> > > but not valid to say
> > >
> > >   *(char *)(&py2->x) = '?';
> >
> > Yes, that sounds right.
>
>
>   Wow, we really seem to me to be entering the realm of the bizarre 
> here.
> What about this function: is it valid, conformant C?
>
> void fubar (const char *x)
> {
>     *(char *)x = '?';
> }

It can be part of a conforming program, yes.

>   Is it not implicit from what you've just told me that the answer to 
> the
> question of whether or not that function is valid conformant C depends 
> on
> whether the value of the pointer you pass into it was originally 
> derived
> from a call to malloc (valid) or by taking the address-of a local or 
> static
> variable (not valid)?  Does this still make sense?  It's making my mind
> boggle in several directions at once.

Yes, it matters what value 'x' has.  For instance, consider

int main(void)
{
  fubar(NULL);
  return 0;
}

Obviously that program is not conforming, whether or not 'x' is const.

Attachment: smime.p7s
Description: S/MIME cryptographic signature