Date: Mon, 31 Jan 2005 16:58:17 +0000 From: Paul Richards <paul@originative.co.uk> To: Ulrich Spoerlein <q@uni.de> Cc: arch@freebsd.org Subject: Re: c99/c++ localised variable definition Message-ID: <20050131165817.GV61409@myrddin.originative.co.uk> In-Reply-To: <20050131163117.GE828@galgenberg.net> References: <20050131122609.GA83556@gurney.reilly.home> <90392.1107174969@critter.freebsd.dk> <20050131163117.GE828@galgenberg.net>
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On Mon, Jan 31, 2005 at 05:31:17PM +0100, Ulrich Spoerlein wrote:
> 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
gcc should be throwing an uninitialised warning here.
> % 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.
icc looks correct to me since the i being printed out is the one
in the outer scope which is unitialised.
--
Paul Richards
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