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

[Gabriel Dos Reis <gdr at cs dot tamu dot edu>]

"Dave Korn" <dk@artimi.com> writes:

| [ 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.

Yep.

| What about this function: is it valid, conformant C?
| 
| void fubar (const char *x)
| {
|     *(char *)x = '?';
| }

It is valid C and C++, if only if the object pointed to by x is const.

|   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)?

If you remove the argument about malloc(), I agree.

|  Does this still make sense?  It's making my mind
| boggle in several directions at once.

I think there is a hole in the argument about allocating object
with malloc().  The key is to understand what the effective type of
the object is.

-- Gaby