Date: Mon, 31 Jan 2005 17:31:17 +0100 From: Ulrich Spoerlein <q@uni.de> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: arch@freebsd.org Subject: Re: c99/c++ localised variable definition Message-ID: <20050131163117.GE828@galgenberg.net> In-Reply-To: <90392.1107174969@critter.freebsd.dk> References: <20050131122609.GA83556@gurney.reilly.home> <90392.1107174969@critter.freebsd.dk>
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On Mon, 31.01.2005 at 13:36:09 +0100, Poul-Henning Kamp wrote:
> >If you carelessly c++-ify a loop like:
> >
> > for (int i = 0; i < N; i++)
> > {
> > if (some_condition(i)) break;
> > }
> > do_something_with(i); /* use finishing index */
> >
> >you can miss the fact that the value of i is used outside of the
> >loop. The newly created scope for "i" shadows the presumably
> >pre-existing definition of i at the top of the function, which
> >is what do_something_with() gets to see.
>
> I would _really_ hope we have the compiler warning about this
> already ?
Doesn't look so:
#include <stdlib.h>
#include <stdio.h>
int
main(int argc, char **argv) {
int N = 42;
int i;
for (int i = 0; i < N; i++)
if (i == 23)
break;
printf("%d\n", i); /* use finishing index */
return (0);
}
% cc -Wall -std=c99 test.c && ./a.out
1
% icc -Wall -std=c99 test.c && ./a.out
test.c(12): remark #592: variable "i" is used before its value is set
printf("%d\n", i); /* use finishing index */
^
0
But the ICC warning is bogus too, if you happen to set i before, the
warning disappears.
Ulrich Spoerlein
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Ok, which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn."
didn't you understand?
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