Re: Strict aliasing and pointers to functions

[Andrew Haley <aph at redhat dot com>]

malc writes:
 > On Sun, 26 Nov 2006, Andrew Haley wrote:
 > 
 > 
 > [..snip..]
 > 
 > > Are we talking ISO C or GNU C here?  This is OK for GNU C, and I think
 > > for POSIX.
 > 
 > You mentioned ISO C a few times. So i'd guess we are talking c89.

OK.  I don't think it matters: the rules of C89 and C99 are not
substantially different in this area.

 > > > However i'm not targetting standard C
 > >
 > > So why are you using -pedantic?  -pedantic is only for strict ISO C.
 > 
 > Because i happen to compile with 5-6 versions of gcc on different 
 > platforms with different ideas of what -W[xxx] turns on and throwing
 > `-pedantic' into the mix generally turns on more.

Sure, it does, but why do you want them?  They're not going to make
your programs any better.

 > [..snip..]
 > 
 > > ...
 > > * The cast below is the correct way to handle the problem.
 > > * The (void *) cast is to avoid a GCC warning like:
 > > * "warning: dereferencing type-punned pointer will break \
 > > * strict-aliasing rules"
 > > * which is wrong this code. (void *) introduces a compatible
 > > * intermediate type in the cast list.
 > > */
 > > count -= got, *(char **)(void *)&buffer += size * got;
 > >
 > > I'm not convinced this hackery is correct by my reading of ISO C, and
 > > in any case it's pointless.  It could be replaced by:
 > >
 > > count -= got, buffer = (char*)buffer + (size * got);
 > 
 > That's not for me to decide, not a language layer by any stretch of
 > imagination.

I don't understand this remark.

Andrew.