Date: Tue, 10 Mar 2009 18:26:34 -0400 From: James Bailie <jimmy@mammothcheese.ca> To: freebsd-hackers@freebsd.org Subject: Re: fgetc doubts Message-ID: <49B6E91A.4040604@mammothcheese.ca> In-Reply-To: <49B6DC95.9070607@FreeBSD.org> References: <49B6DC95.9070607@FreeBSD.org>
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fgetc() returns an int so that EOF may be distinguished from valid return values. Valid values are 8-bit values. EOF is a 32-bit value. EOF is a 32-bit two's-complement -1 (0xffffffff), and -1 input is 8-bit two's-complement -1 (0xff). When fgetc() casts this to an int, it becomes 0x000000ff, or 255, and thus the two values may be distinguished from each other. I haven't looked at your code, but you are probably comparing EOF with the value returned by fgetc() after it has been cast to a char. EOF is getting cast to a char implicitly in the comparison, so the comparison becomes a comparison between 0xff and 0xff. You need to test the int returned by fgetc() for EOF before assigning it to a char. Gábor Kövesdán wrote: > Hello, > > I have a problem when reading files with fgetc when a 0xff character > comes. In my code the reading stops at that point as if EOF had been > reached, but that's not actually the case. > The code is here: > http://p4web.freebsd.org/@md=d&cd=//&c=Nsd@//depot/projects/soc2008/gabor_textproc/grep/file.c?ac=64&rev1=40 > > And the problem occurs in grep_fgetln() when the buffers is being filled > in: > for (; i < bufsiz && !grep_feof(f); i++) > binbuf[i] = grep_fgetc(f); > > Thanks in advance, > -- James Bailie <jimmy@mammothcheese.ca> http://www.mammothcheese.ca
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