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To: man-jp@jp.FreeBSD.org
From: kumagai@attbi.com (Norihiro Kumagai)
In-reply-to: Your message of "Sun, 23 Dec 2001 00:40:31 JST."
             <200112221540.fBMFeVK71474@fifthluna.nokubi.or.jp>
Date: Sat, 22 Dec 2001 10:17:51 -0800
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$B7'C+$G$9!#(B

$B$3$NJU$NOC$K$D$$$F$O!"(B"C FAQ" $B$,;H$($^$9!#$^$k$4$H(B1$B>O$r$3$NLdBj$K=<$F(B
$B$F!"CzG+$K2r@b$7$F$^$9!#;d$b$3$$$D$GJY6/$7$^$7$?!#(B

http://lagendra.s.kanazawa-u.ac.jp/ogurisu/manuals/c/C-faq/index.html

In Message <200112221540.fBMFeVK71474@fifthluna.nokubi.or.jp>,
  NOKUBI Hirotaka <nokubi@ff.iij4u.or.jp> writes:
> >> > $B!{(B if (p == NULL)
> >> >    $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$$$G$9!#!W(B
> 
> $B$O$7$g$C$F=q$$$F$7$^$$$^$7$?$,!"$b$A$m$s(B p $B$N7?$K9g$o$;$F(B 0 $B$r(B
> $B%-%c%9%H$9$k$N$,NI$$$H8@$C$F$$$?$H;W$$$^$9!#>e5-Nc$O(B p $B$,(B char * $B$G(B
> $B$"$k$H$$$&A0Ds$G=q$$$F$$$^$7$?!#$3$N>l9g$ONI$$(B?

$BNI$$$G$9!#$?$@$7!"(BANSI C $B$N@$3&$G$O!"(B(char *) $B$X$N%-%c%9%H$OITMW$G$9!#(B

$B%3%s%Q%$%i$,%=!<%9%3!<%I$r$J$a$F$$$k$H$-$K!"(Bp == 0 $B$H$$$&%]%$%s%?$NHf(B
$B3S<0$r8+$D$1$^$9$H!"$3$N(B 0 $B$O%J%k%]%$%s%?Dj?t$H$_$J$5$l!"(B($B$=$N(BOS/$B%3%s(B
$B%Q%$%i$4$H$K7h$^$C$F$$$k(B)char * $B7?%J%k%]%$%s%?$NCM$r@8@.$9$k%3!<%I!"(B
char * $B7?JQ?t(B p $B$NFbMF$HHf3S$9$k%3!<%I$,@8@.$5$l$^$9!#(B

ANSI C $B$N>l9g!"(B($BM#0l$NNc30$r=|$-(B) 0 $B$NAj<j@h$N7?$O7h$^$C$F$$$k$N$G!"(B0 
$B$rFCDj$N7?$K%-%c%9%H$9$k$h$&$K%W%m%0%i%`$r=q$/$3$H$OITMW$G$9!#(B

$B$G!"M#0l$NNc30$H8@$&$N$O!"2DJQ8D0z?t4X?t$N8F$S=P$7$G$9!#2DJQ8D0z?t4X?t(B
$B$N8F$S=P$7$G$O!"8D!9$N4X?t0z?t$N7?$,7h$^$C$F$$$^$;$s!#Nc$($P!"(Bexecl $B$J(B
$B$s$+$N:G=*0z?t$N%J%k%]%$%s%?$O$A$c$s$H%-%c%9%H$7$F$d$kI,MW$,$"$j$^$9!#(B
execl $B$N%W%m%H%?%$%W@k8@$O!"(B

int execl (const char *path, const char *arg, ...);

$B$G$9$+$i!"Bh(B3$B0z?t0J8e$N7?$O%3%s%Q%$%i$bCN$j$h$&$,$"$j$^$;$s!#$G$9$+$i(B 
0 $B$r8+$F$b%J%k%]%$%s%?$r@8@.$9$k5$NO$NM/$-$h$&$b$"$j$^$;$s!#$3$N>l9g!"(B
$BNc$($P!"(B

execl ("/bin/sh", "sh", "-c", "ls -l", 0);

$B$G$O$^$:$/$F!"(B

execl ("/bin/sh", "sh", "-c", "ls -l", (char *)0);

$B$H$7$F$d$kI,MW$,$"$j$^$9!#(B

$B$^$!!"(BBSD $B$N@$3&$G@8$-$F$$$k$H!":#$G$bHs(B ANSI C $B$N%=!<%9%3!<%I$r?($i$M(B
$B$P$J$i$J$$$+$b$7$l$^$;$s!#$=$&$$$&>l9g!"$b$7(B gcc -traditional $B$d(B pcc 
$B$,!V%=!<%9%3!<%I$G(B 0 $B$r8+$D$1$?$iL5>r7o$K(B all bit zero $B$N(B int $B$NCM$r@8(B
$B@.$9$k!W$N$@$H$7$?$i!"(Bp == (char *)0 $B$H=q$$$F$d$k$3$H$O0UL#$,$"$j$^$9!#(B

gcc -traditional, pcc $B$,<B:]$K$I$&$$$&5sF0$r<($9$+$O$h$/CN$j$^$;$s!#$3(B
$B$$$D$i$,(B ANSI C $BIw$KF0$$$F$/$l$k$J$i!"<B:]$N$H$3$m$O%-%c%9%HITMW$+$b$7(B
$B$l$^$;$s$,!#(B

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