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.\" Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\" and (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" License.
.\" Modified Sat Jul 24 18:34:44 1993 by Rik Faith (faith@cs.unc.edu)
.\" Merged readv.[23], 2002-10-17, aeb
.\" 2007-04-30 mtk, A fairly major rewrite to fix errors and
.\"     add more details.
.\"
.\" 1996-04-12 Tom Bjorkholm <tomb@mydata.se>
.\"            First version written
.\" Modified Tue Oct 22 17:41:07 1996 by Eric S. Raymond <esr@thyrsus.com>
.\"
.\" Japanese Version Copyright (c) 1997-1999 HANATAKA Shinya
.\"         all rights reserved.
.\" Translated 1997-02-23, HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\" Updated 1999-04-03, HANATAKA Shinya
.\" Updated 2003-01-14, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2005-10-07, Akihiro MOTOKI
.\" Updated 2007-06-01, Akihiro MOTOKI, LDP v2.50
.\"
.\"WORD:	vector			٥ (vector)
.\"WORD:	file descriptor		եǥץ
.\"WORD:	buffer			Хåե
.\"
.TH READV 2  2002-10-17 "Linux" "Linux Programmer's Manual"
.SH ̾
readv, writev \- ʣΥХåեؤɤ߽񤭤Ԥʤ
.SH 
.nf
.B #include <sys/uio.h>
.sp
.BI "ssize_t readv(int " fd ", const struct iovec *" iov ", int " iovcnt );
.sp
.BI "ssize_t writev(int " fd ", const struct iovec *" iov ", int " iovcnt );
.fi
.SH 
.BR readv ()
ؿϡեǥץ
.I fd
˴Ϣդ줿ե뤫顢
.I iovcnt
ĤΥХåեʬΥǡɤ߹ߡ
.I iov
ǻꤵ줿Хåե˳Ǽ
("scatter input";֤Фޤϡ)
.PP
.BR writev ()
ؿϡ
.I iov
ǻꤵ줿Хåե
.I iovcnt
ĤΥХåեʬΥǡФ
եǥץ
.I fd
˴Ϣդ줿ե˽񤭹
("gather output";֤ϡ)
.PP
ݥ
.I iov

.I iovec
¤ΤؤΥݥ󥿤Ǥ롣
.I iovec
¤Τ
.I <sys/uio.h>
ǰʲΤ褦Ƥ:
.PP
.br
.in +4n
.nf
struct iovec {
    void  *iov_base;    /* Starting address */
    size_t iov_len;     /* Number of bytes to transfer */
};
.fi
.in
.PP
.BR readv ()
ؿϡʣΥХåե˥ǡɤ߹
.BR read (2)
ƱͤưԤ
.PP
.BR writev ()
ؿϡʣΥХåեΥǡ񤭽Фʳ
.BR write (2)
ƱͤưԤ
.PP
Хåեνǽ롣ϡ
.BR readv ()

.IR iov [0]
˰դˤʤޤǥǡͤƤ顢
.IR iov [0]
ʤɤ˿ʤळȤ̣
(ǡʬʤϡ
.I iov
ؤХåեΤդˤʤʤ)
Ʊͤˡ
.BR writev ()

.IR iov [0]
Ƥ񤭽ФƤ
.IR iov [1]
ʤɤ˿ʤࡣ
.PP
.BR readv ()

.BR writev ()
ˤǡž atomic ˹Ԥ롣Ĥޤꡢ
.BR writev ()
ˤǡ񤭹ߤϰĤΥ֥åȤƹԤ졢¾Υץ
write ˤ񤭹ߤȺ礦ȤϤʤ
(㳰˴ؤƤ
.BR pipe (7)
򻲾ȤΤ)Ʊͤˡ
.BR readv ()
ϥե뤫Ϣ³ǡ֥åɤ߽ФȤݾڤ졢
Ʊե뵭 (file description;
.BR open (2)
) 򻲾Ȥեǥץ¾Υåɤץ
¹Ԥ read αƶ뤳ȤϤʤ
.SH ֤
硢
.BR readv ()
ؿɤ߹Хȿ֤
.BR writev ()
ؿϽ񤭹Хȿ֤
顼ξ \-1 ֤\fIerrno\fP Ŭڤꤹ롣
.SH 顼
.BR read (2)

.BR write (2)
Ʊ顼Ƥ롣
˰ʲΥ顼Ƥ:
.TP
.B EINVAL
.I iov_len
ιפ
.I ssize_t
ϰϤ򥪡Сե⤷ϡ
٥ \fIiovcnt\fP  0 꾮Ĥ줿ͤ礭ä
.SH 
4.4BSD
.RB ( readv ()

.BR writev ()
ؿ 4.2BSD Ǻǽ˸줿)POSIX.1-2001
Linux libc5 Ǥ \fIiovcnt\fP ηȤ \fIsize_t\fP 
δؿ֤ͤȤ \fIint\fP ѤƤ
.\" readv/writev ƥॳ Linux 1.3.40 ϥХ餱Ǥä
.\" ( release.libc ˽񤫤Ƥ)
.SH 
.SS "Linux Ǥ"
POSIX.1-2001 Ǥϡ
.I iov
ϤȤǤǿ˾¤ߤǧƤ롣
ϡ
.I <limits.h>

.B IOV_MAX
뤳Ȥ䡢¹Ի
.I sysconf(_SC_IOV_MAX)
֤ͷͳǡξ¤򹭹𤹤뤳ȤǤ롣
Linux ǤϡλȤߤˤ깭𤵤¤ 1024 Ǥꡢ
ͤϥͥǤξ¤ΤΤǤ롣
ǡglibc ΥåѡؿϡδؿǸƤФ륫ͥ롦
ƥॳ뤬ξ¤ĶᤷƼԤȤ򸡽Фȡ
ɲäư򤹤롣
.BR readv ()
ξ硢åѡؿ
.I iov
ǻꤵ줿ƤǤǼǤ礭ΰХåեơ
.BR read (2)
ƤӽФݤˤΥХåեϤ
ΥХåեΥǡ
.I iov
γǤ
.I iov_base
եɤꤹ˥ԡƤ顢
ΥХåե롣
.BR writev ()
Υåѡؿ⡢Ʊ褦˰ХåեȤä
.BR write (2)
ƤӽФ
.SH Х
.BR readv ()

.BR writev ()
Τ褦ʥեǥץФԤؿȡ
ɸϥ饤֥δؿ򤴤ޤˤƸƤ֤ΤϤᤷʤ
ɤʷ̤ˤʤ뤫Ƥ餺
餯ߤ̤ʤ
.SH 
ʲΥץ륳ɤ
.BR writev ()
λˡ򼨤ΤǤ롣

.in +4n
.nf
char *str0 = "hello ";
char *str1 = "world\\n";
struct iovec iov[2];
ssize_t nwritten;

iov[0].iov_base = str0;
iov[0].iov_len = strlen(str0);
iov[1].iov_base = str1;
iov[1].iov_len = strlen(str1);

nwritten = writev(STDOUT_FILENO, iov, 2);
.fi
.in
.SH Ϣ
.BR read (2),
.BR write (2)