-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 06/17/11 08:12, Zdenek Dvorak wrote:
>>> if we do, we definitely should not -- the only point of such a construction >>> is >>> to bypass the pointer arithmetics restrictions, >> >> Ok, we don't. Where does the C standard say that NULL + 0 is undefined? > > I don't think it explicitly states that it is undefined. But 6.5.6 #7 and #8 > only > give semantics for pointers to objects, Right. I think we need to review the standard closely, but IIRC pointers are allowed to be NULL, point into an object or point to one element beyond an object. If that's correct P+C could only result in a NULL value if P was one element beyond the end of an object and C happened to be the exact magic value to wrap P to zero. I have a hard time seeing how code could which did that (and relied upon it) could ever be standard conforming. Closely related, given P+C where the result is a pointer ought to tells us that P is non-null since the only way it could be null would be if C was the exact magic constant to make the result point to a valid object. Jeff -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJN+5ZSAAoJEBRtltQi2kC7H34H/RG+9VrV6RqeolgSIqjyLsUf WbJwl2AWo3xIMt/8OKpWG5zzhgJk67tW+PpSHhzs615kjRPryOiiNq+GBIelteKT ho3mgbBeU5qJsPLU6j2feBR4+OEdo/oJZxHm/m8zUwWcGuZtazNGtoiuq7rlNr52 PDl7DM7ZWK731nFZfKYPq/fYMgNxWhxTBo9ucH3s9yXKJ6LYbUGHpKNyP14nB3n3 bJhdPF8A365uLYz5xCmP0QOKInbzNclN+gbTVZXc+NxtOYNUM16NalsxWhHSALCB U0S9hpDMDznWWEwPDNdNN2oRphSGmIB0oYxeuaga5RgviNiPNVgEzANkGIv7OEo= =z8kH -----END PGP SIGNATURE-----
