Date: Thu, 7 Aug 2008 11:00:03 -0500 (CDT) From: "Sean C. Farley" <scf@FreeBSD.org> To: Gabor Kovesdan <gabor@kovesdan.org> Cc: fjoe@FreeBSD.org, hackers@FreeBSD.org Subject: Re: strange issue reading /dev/null Message-ID: <alpine.BSF.1.10.0808071058020.1056@thor.farley.org> In-Reply-To: <489B0ACD.80008@kovesdan.org> References: <489B0ACD.80008@kovesdan.org>
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On Thu, 7 Aug 2008, Gabor Kovesdan wrote:
> Hello,
>
> I'm wondering why fgetc() returns 0xff if called with /dev/null:
>
> #include <stdio.h>
> #include <stdlib.h>
>
> int
> main(void)
> {
> int c;
> FILE *f;
>
> f = fopen("/dev/null", "r");
>
> if (c != EOF)
> printf("%c\n", fgetc(f));
> }
>
>> gcc foo.c
>> ./a.out
> ÿ
>
> This causes a bug in BSD grep as /dev/null is not distinguished from
> ordinary files in the code, thus I was expecting it just returned EOF,
> but in reality this is not the case. How such cases should be handled?
You are testing c which has not been set. It works OK if you set c then
do the test:
+ c = fgetc(f);
if (c != EOF)
- printf("%c\n", fgetc(f));
+ printf("%c\n", c);
Sean
--
scf@FreeBSD.org
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