Date: Sun, 28 Jan 2001 18:22:05 -0700 From: Greg Skafte <skafte+freebsd-chat@trollkarl.net> To: freebsd-chat@freebsd.org Subject: Re: C Puzzle Message-ID: <20010128182205.A98336@trollkarl.skafte.org> In-Reply-To: <20010129013145.A4834@crow.dom2ip.de>; from tmoestl@gmx.net on Mon, Jan 29, 2001 at 01:31:45AM %2B0100 References: <20010128161353.C98223@trollkarl.skafte.org> <20010129013145.A4834@crow.dom2ip.de>
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I know its ugly ... its an example of what not to do ....
but I forgot to check the precedence of ?: .... I also
knew that they were syntactically incorrect.
thanks G
Quoting Thomas Moestl (tmoestl@gmx.net)
On Subject: Re: C Puzzle
Date: Mon, Jan 29, 2001 at 01:31:45AM +0100
> On Sun, Jan 28, 2001 at 04:13:53PM -0700, Greg Skafte wrote:
> > doesn't work :
> >
> > char* fn_mtrim __P((char*));
> > char* fn_mtrim (s)
> > char* s ;{
> > short i=0;
> > char *buffer= (char *) calloc (256,sizeof(char));
> > while (*s){
> > ( *s == ' ') ? s*++ : buffer[i++] = *s++ ;
> > };
> > return buffer;
> > }
> >
> > works :
> >
> > char* fn_mtrim __P((char*));
> > char* fn_mtrim (s)
> > char* s ;{
> > short i=0;
> > char *buffer= (char *) calloc (256,sizeof(char));
> > while (*s){
> > ( *s != ' ') ? buffer[i++] = s*++ : *s++ ;
> > };
> > return buffer;
> > }
> >
> > Why does the first one not work and the second one work ....
> Precedence tells us:
> ( *s == ' ') ? *s++ : buffer[i++] = *s++ ;
> is equivalent to
> (( *s == ' ') ? *s++ : buffer[i++]) = *s++ ;
> (notice the outer brackets). I guess you mean *s++ when you write s*++.
> If you try this with string literal as argument (fn_mtrim("foo bar")),
> the string will get written into, and this may even segfault using gcc.
> Otherwise, the result will be wrong anyway, because s gets incremented
> before it is tested against ' ' (this is not really well-defined), and
> then incremented again when *s == ' ' and the value is assigned to *s++.
>
> - thomas
>
> P.S.: this is really ugly ;-)
>
>
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Email: skafte@trollkarl.net ICQ: 93234105
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