From: rminnich@sarnoff.com (Ron G. Minnich) Subject: Re: strlen on a NULL 14 May 1998 00:02:42 -0700 Message-ID: References: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII To: Kjeld.F.Christensen@dxd.ericsson.se Cc: ian@kiwiplan.co.nz, gnu-win32@cygnus.com On Tue, 12 May 1998 Kjeld.F.Christensen@dxd.ericsson.se wrote: > > If I do a strlen on a NULL pointer I get a coredump. > > I have the same code running on a few *other* Unix machines with > > exhibiting this behaviour. > > OK, so I could tidy it up, but I wondered is this an oversight or the > > correct behaviour? > > I just observed the same problem. > The differnce lies in where the core is located. A UNIX core starts from > ZERO, and thus you are allowed to read from a NULL pointer on UNIX, as > You read from your code. > > On NT your process may lie anywhere, but never in ZERO, Thus you are not > permitted to read from adress NULL. (You are not allowed to snoop around > in the interrupt vetors!) > > So this is the explanation! > > Kjeld This is quite wrong for most unixes. cat test.c main() { char *c = (char *) 0; char d; d = *c; } bash$ cc test.c bash$ ./a.out Segmentation fault (core dumped) on FreeBSD, linux, solaris, sunos ... Anyway, check the kernel source, and see the part where they make page 0 unreadable and unwriteable. Stupid exceptions: some SvR4 implementations, and of course stupid old AIX. ron - For help on using this list (especially unsubscribing), send a message to "gnu-win32-request@cygnus.com" with one line of text: "help".