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To: man-jp@jp.FreeBSD.org
From: kumagai@attbi.com (Norihiro Kumagai)
In-reply-to: Your message of "Sat, 22 Dec 2001 17:39:00 JST."
             <20011222173900P.a-gota@bokutou.jp>
Date: Sat, 22 Dec 2001 01:22:07 -0800
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X-Distribute: distribute version 2.1 (Alpha) patchlevel 24e+011218
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Subject: [man-jp 3880] Re: NUL
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$B7'C+$G$9!#(B

In Message <20011222173900P.a-gota@bokutou.jp>,
  Akihiko GOTANDA <a-gota@bokutou.jp> writes:
> > $B!{(B NULL $B$O=hM}7O$K$h$C$F$O(B 0 $B$G$J$$$+$b$7$l$J$$(B

$B@53N$K$O!"!V(BNULL $B$O$I$N=hM}7O$G$bDj?t<0(B 0 $B$G$"$k$,!"$=$NI=8=$O(B all bit
zero $B$H$O8B$i$J$$!#!W(B

> > $B!{(B 0 $B$O=hM}7O$K$+$+$o$i$:(B(?)$B%3%s%Q%$%i$,FCJL07$$$9$kCM$G$"$k(B

$B@53N$K$O!"!VDj?t$N(B 0 $B$,%]%$%s%?$rMW5a$9$k>l=j$K=P$F$/$l$P=hM}7O$K4X$o(B
$B$i$:%3%s%Q%$%i$,FCJL07$$$9$k!#!W(B

> > $B!{(B if (p == NULL)
> >    $B$h$j$O(B
> >    if (p == (char *)0)
> >    $B$NJ}$,NI$$(B
> > $B$H$+8@$C$F$$$k?M$b5o$k$h$&$K;W$&$N$G$9$,!"$3$l$C$F$I$&$J$s$G$7$g$&(B?

p $B$,(B (char *) $B$G$J$$$H$-$O!"(Bp == (char *)0 $B$O8m$j(B(undefined behavior)$B!#(B
p $B$,$I$N7?$N%]%$%s%?$G$b(B p == NULL $B$O@5$7$$!#(B
$B$N$G!"!V$3$l$C$F$h$/$J$$$G$9!#!W(B

> $B$3$l$O!"(B
> 
> (1) OS $B$K$h$C$F$O(B null pointer $B$,(B 0 $B$G$J$$>l9g$,$"$k(B
>     $B!J3N$+(B OS/2 $B$J$s$+$O<B:]$=$&$G$J$+$C$?$h$&$J!E!E!K(B

(1) OS $B$K$h$C$F$O(B null pointer $B$,(B all bit zero $B$G$J$$>l9g$,$"$k(B
$B$,@5$7$$!#(B

> (2) $B$J$N$G!"$=$N(B platform $B$r(B target $B$K$7$?=hM}7O$G$O(B NULL $B$,(B 0 $B$G$O$J(B
>     $B$$(B

$B$3$l$O0c$&!#(BC $B8@8l$G$"$k8B$j!"(BNULL $B$ODj?t<0(B 0 $B$G$9!#(B
NULL $B$N:G$b$"$j$=$&$JDj5A$O(B

#define NULL 0

$B$G$9!#$G!"(B($B!V(Bnull pointer $B$,(B 0 $B$G$J$$!W(BOS $B$G(B)$B%]%$%s%?9=J8$GDj?t(B 0 $B$r8+(B
$B$?;~$K!"%3%s%Q%$%i$O(B all bit zero $B$G$J$$2?$i$+$NDj?t$r@8@.$7$^$9!#(B

> $B$G!"!V(BNULL $B$,(B 0 $B$G$"$k=hM}7O$G$O!"EvA3(B 0 $B$rFCJL07$$$9$k!W$N$G!"$=$&$G(B
> $B$J$$=hM}7O$G$OJL$NCM$rFCJL07$$$9$k$O$:!J!a(B $BMW$9$k$K!"!V(BNULL$B!W$rFCJL07(B
> $B$$$7$?$$Lu$@$+$i!K$J$N$G!"!V(B0 $B$O=hM}7O$K4X$o$i$:1>!9!W$H$$$&$N$O8m$j$G(B
> $B$7$g$&!#(B

$B$3$l$O$A$c$$$^$9!#!V(BNULL $B$,(B all bit zero $B$G$"$k=hM}7O$G$"$m$&$,$=$&$G(B
$B$J$$=hM}7O$G$"$m$&$,!"Dj?t(B 0 $B$O=hM}7O$K4X$o$i$:FCJL07$$(B(== $B%]%$%s%?9=(B
$BJ8$G%J%k%]%$%s%?$H$7$F07$o$l$k(B)$B$5$l$^$9!W(B

$B7k6I!"!V(Bnull pointer $B$,(B 0 $B$G$"$k(B/$B$J$$!W$H$$$&I=8=$O$"$$$^$$$G$9!#$3$3(B
$B$N(B 0 $B$,!"!V%]%$%s%?$NCM$r(B16$B?J%@%s%W$7$?;~$NCM!W$J$N$+!"!V%=!<%9%3!<%I(B
$B>e$G$NI=8=!W$J$N$+$,$O$C$-$j$7$J$$$+$i$G$9!#$=$7$F!"(BC $B8@8l$G$N%J%k%]%$(B
$B%s%?$NDj5A$O!"$3$NN>35G0$r;H$C$F@bL@$5$l$^$9!#(B

--
$B7'C+(B $BE5Bg(B
