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From: drw@cullvax.UUCP (Dale Worley)
Newsgroups: comp.lang.c
Subject: Passing NULLs to printf
Message-ID: <1417@cullvax.UUCP>
Date: Fri, 31-Jul-87 10:11:54 EDT
Article-I.D.: cullvax.1417
Posted: Fri Jul 31 10:11:54 1987
Date-Received: Sat, 1-Aug-87 21:49:05 EDT
Organization: Cullinet Software, Westwood, MA, USA
Lines: 28

gwyn@brl-smoke.ARPA (Doug Gwyn ) writes:
| In article <1407@cullvax.UUCP> drw@cullvax.UUCP (Dale Worley) writes:
| >	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.  Presumably
| >this is valid ANSI C!
| 
| No, why should it be?  The printf() implementation may very well
| always inspect the argument string to find its null terminator,
| for example to determine its length before converting it.

Eh?  Well, certainly, if you do printf("%.100s", ...), you want it to
work if the pointer doesn't point to a block of memory with a null
byte in it?  This is useful if you have a "string" stored in
pointer/length format: printf("%.*s", len, ptr).

Although I think that a careful reading of the ANSI document (p. 117,
l. 26: "s format code: The argument shall be a pointer to a string."
p. 84, l. 7: "A string is an array of characters terminated by a null
character.") shows that I'm wrong.  But this use of %s is useful and
probably works in all implementations, and should be allowed.

Dale

-- 
Dale Worley	Cullinet Software		ARPA: cullvax!drw@eddie.mit.edu
UUCP: ...!seismo!harvard!mit-eddie!cullvax!drw
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