Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sources.redhat.com/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com
X-Authentication-Warning:	localhost.localdomain: ronald owned process doing -bs
Date:	Thu, 26 Jun 2003 14:34:10 +0200 (CEST)
From:	Ronald Landheer-Cieslak <ronald AT landheer DOT com>
X-X-Sender:	ronald AT localhost DOT localdomain
To:	Brian Dessent <brian AT dessent DOT net>
cc:	"Cygwin AT Cygwin DOT Com" <cygwin AT cygwin DOT com>
Subject:	Re: _pread() _pwrite
In-Reply-To:	<3EFAC669.30325C05@dessent.net>
Message-ID:	<Pine.LNX.4.44.0306261433430.2545-100000@localhost.localdomain>
MIME-Version:	1.0

Ah, yes, "the file offset is not changed".. I forgot about that..
Thanks for correcting me :)

rlc

On Thu, 26 Jun 2003, Brian Dessent wrote:

> Ronald Landheer-Cieslak wrote:
> > 
> > pread and pwrite are not in Cygwin (or at least are not exported by
> > cygwin1.dll). They are hardly the most portable functions in the world. I
> > suggest you write a wrapper. Something like:
> > 
> > <UNTESTED CODE>
> > ssize_t pread(int fd, void *buf, size_t count, off_t offset)
> > {
> >         if (lseek(fd, offset, SEEK_SET) == (off_t)-1)
> >         {
> >                 return(-1);
> >         }
> >         return(read(fd, buf, count));
> > }
> > 
> > and
> > ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset)
> > {
> >         if (lseek(fd, offset, SEEK_SET) == (off_t)-1)
> >         {
> >                 return(-1);
> >         }
> >         return(write(fd, buf, count));
> > }
> > </UNTESTED CODE>
> 
> You'll want to save the original file position and restore it after the
> operation, e.g.
> 
> ssize_t
> pread(int fd, void *p, size_t n, off_t off)
> {
>         off_t ooff;
>         int oerrno;
> 
>         if ((ooff  = lseek(fd, off, SEEK_SET)) == -1)
>                 return -1;
> 
>         n = read(fd, p, n);
> 
>         oerrno = errno;
>         lseek(fd, ooff, SEEK_SET);
>         errno = oerrno;
> 
>         return n;
> }
> 
> ssize_t
> pwrite(int fd, const void *p, size_t n, off_t off)
> {
>         off_t ooff;
>         int oerrno;
> 
>         if ((ooff  = lseek(fd, off, SEEK_SET)) == -1)
>                 return -1;
> 
>         n = write(fd, p, n);
> 
>         oerrno = errno;
>         lseek(fd, ooff, SEEK_SET);
>         errno = oerrno;
> 
>         return n;
> }
> 
> --
> Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
> Problem reports:       http://cygwin.com/problems.html
> Documentation:         http://cygwin.com/docs.html
> FAQ:                   http://cygwin.com/faq/
> 


--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/

- Raw text -