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From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Passing NULLs to printf
Message-ID: <846@haddock.ISC.COM>
Date: Fri, 31-Jul-87 19:48:25 EDT
Article-I.D.: haddock.846
Posted: Fri Jul 31 19:48:25 1987
Date-Received: Sun, 2-Aug-87 04:49:53 EDT
References: <1407@cullvax.UUCP>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 16

In article <1407@cullvax.UUCP> drw@cullvax.UUCP (Dale Worley) writes:
>But, suppose we write:
>	printf("%.0s", (char *)NULL)
>This should print zero characters out of the string, and so won't
>actually reference any character through the null pointer.

I seem to remember noticing once that one implementation of strncpy would test
for a terminating NUL *before* testing the counter, thus when no NUL was
present it would fetch an extra byte.  Completely harmless, unless you
happened to be at the end of readable memory!

It would be nice if this were guaranteed not to happen (in printf as well as
in the strnXXX family).  In particular I agree it should be legal to grab zero
characters from a NULL pointer, e.g. the result of [ANSI] malloc(0).

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint