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From: lm@snafu.Sun.COM (Larry McVoy)
Newsgroups: comp.unix.wizards
Subject: Re: question on lseek behavior
Keywords: weirdo Unix system call behavior
Message-ID: <138435@sun.Eng.Sun.COM>
Date: 5 Jul 90 23:22:30 GMT
References: <1416@software.software.org>
Sender: news@sun.Eng.Sun.COM
Reply-To: lm@sun.UUCP (Larry McVoy)
Distribution: usa
Organization: Sun Microsystems, Mountain View
Lines: 24

In article <1416@software.software.org> marshall@software.org (Eric Marshall) writes:
>
>	I was trying to use lseek to rewind to the beginning
>of input (a file), but I ran into difficulties.  When I run
>the program below, it outputs the file missing the first 3 characters,
>as if the lseek didn't do anything, then it outputs the entire
>file.  Could someone please explain why this occurs.  I eventually
>found the rewind(3S) call, and it works fine.  I am running
>on SunOS 4.1.

You are using stdio routines which buffer.  You bypassed those routines
when you issued the lseek() call; rewind is built on top of lseek and
looks something like:

rewind(f)
	FILE *f;
{
	lseek(f->_fd, 0, 0);
	f->_chars_in_buf = 0;
}

This is a common problem; many test suites make the same mistake.
---
Larry McVoy, Sun Microsystems     (415) 336-7627       ...!sun!lm or lm@sun.com