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From: kucharsk@uts.amdahl.com (William Kucharski)
Newsgroups: comp.unix.wizards,comp.sources.wanted
Subject: Re: ftruncate(2) for System V.3.2 needed
Message-ID: <02KJ02SJ3cms01@amdahl.uts.amdahl.com>
Date: 7 Jul 89 22:10:57 GMT
References: <1132@ssp15.idca.tds.philips.nl>
Reply-To: kucharsk@amdahl.uts.amdahl.com (William Kucharski)
Organization: Amdahl Coup, UTS Products Hen House
Lines: 71

In article <1132@ssp15.idca.tds.philips.nl> jos@idca.tds.PHILIPS.nl (Jos Vos) writes:
 >I need the ftruncate(2) function from BSD4.3 UNIX on System V.3.2.
 >For non-BSD-manual-owners, here's the description of ftruncate(2)...

I can see that this one is going to make it into the "frequently asked
question" section...

========[Cut Here]========

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

int
ftruncate(fd, length)
int     fd;     /* file descriptor */
off_t   length; /* length to set file to */
{
        extern  long    lseek();

        struct  flock   fl;
        struct  stat    filebuf;

        if (fstat(fd, &filebuf) < 0)
                return(-1);

        if (filebuf.st_size < length) {
                /* extend file length */

                if ((lseek(fd, (length - 1), SEEK_SET)) < 0)
                        return(-1);

                /* write a "0" byte */

                if ((write(fd, "", 1)) != 1)
                        return(-1);
        } else {
                /* truncate length */

                fl.l_whence = 0;
                fl.l_len = 0;
                fl.l_start = length;
                fl.l_type = F_WRLCK;    /* write lock on file space */

                /*
                 * This relies on the UNDOCUMENTED F_FREESP argument to
                 * fcntl(2), which truncates the file so that it ends at the
                 * position indicated by fl.l_start.
                 *
                 * Will minor miracles never cease?
                 */

		if (fcntl(fd, F_FREESP, &fl) < 0)
			return(-1);

        }

        return(0);
}

-- 
					William Kucharski

ARPA: kucharsk@uts.amdahl.com
UUCP: ...!{ames,decwrl,sun,uunet}!amdahl!kucharsk

Disclaimer:  The opinions expressed above are my own, and may not agree with
	     those of any other sentient being, not to mention those of my 
	     employer.  So there.