Document that passing NULL to %s prints "(null)".

lib/libc/stdio/printf.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: printf.3,v 1.38 2003/09/08 17:54:32 wiz Exp $
+.\"	$NetBSD: printf.3,v 1.39 2005/06/21 18:43:17 christos Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -33,7 +33,7 @@
 .\"
 .\"     @(#)printf.3	8.1 (Berkeley) 6/4/93
 .\"
-.Dd May 11, 2003
+.Dd June 21, 2005
 .Dt PRINTF 3
 .Os
 .Sh NAME
@@ -813,6 +813,17 @@ If you use positional arguments you must ensure that all parameters, up to the
 last positionally specified parameter, are used in the format string.
 This allows for the format string to be parsed for this information.
 Failure to do this will mean your code is non-portable and liable to fail.
+.Pp
+In this implementation, passing a
+.Dv NULL
+.Vt char *
+argument to the
+.Cm %s
+format specifier will output
+.Em "(null)"
+instead of crashing.
+Programs that depend on this behavior are non-portable and may crash
+on other systems or in the future.
 .Sh BUGS
 The conversion formats
 .Cm \&%D ,