Re: [PATCH] warnkill trivia 2/2

[Tomas Szepe <szepe@pinerecords.com>]

>    From: Tomas Szepe <szepe@pinerecords.com>
>    Date: Sun, 1 Sep 2002 14:10:53 +0200
> 
>    > Let's keep the sparc atomic_read() how it is so more bugs
>    > like this can be found.
>    
>    I don't know, though... scratching my head here -- Is GCC actually
>    able to distinguish between 'const int *a' and 'int const *a'?
>    
> No I don't mean this in a "C" sense, I mean conceptually that marking
> an object const which has members which are volatile and updated
> asynchronously makes zero sense.

True.

I've been playing a bit with how gcc handles the const qualifiers
and made an interesting discovery:

Trying to compile

typedef int *p_int;
void a(const p_int t) { *t = 0; }
void b(const p_int t) { t = (int *) 0; }
void c(const int *t) { *t = 0; }
void d(const int *t) { t = (int *) 0; }
void e(int const *t) { *t = 0; }
void f(int const *t) { t = (int *) 0; }

will give 'assignment of read-only location' warnings for
b(), c() and e(), i.e. it's impossible to have a constant
pointer to a non-constant value w/o using a qualified
typedef.

W/o a typedef, gcc seems unable to tell the difference
between 'const int *' and 'int const *' altogether. In case
one needs a constant pointer to a constant value, something
like this should do:

typedef const int *p_int;
void f(const p_int a);

Usable? I don't quite think so.

T.