From: utzoo!decvax!decwrl!sun!megatest!fortune!hpda!hplabs!sri-unix!chris.umcp-cs@UDel-Relay
Newsgroups: net.unix-wizards
Title: Re:  Questions about nil-pointer dereferences (the "plague")
Article-I.D.: sri-arpa.754
Posted: Fri Mar  4 18:07:06 1983
Received: Fri Apr  1 05:57:04 1983

From:  Chris Torek <chris.umcp-cs@UDel-Relay>

Actually, in Vax virtual memory you always have something at 0;
you have the stuff that is in /lib/crt0.o (or /lib/mcrt0.o if you
compiled with -p) but it isn't necessarily zero.  However, you
should never trust to *(int *)0 being legal -- it's not on a large
number of machines (e.g. Codatas).  This seems to be a common
"berkeleyism" (assuming that *(int *)0 is legal).  If you have
a pointer which could be nil, then you should always check it
first, before following it.

	if (p == (int *) 0 || *p == 0) {
		some code...
	}

or something like that.