.\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
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.\" Modified Sat Jul 24 18:34:44 1993 by Rik Faith (faith@cs.unc.edu)
.TH READV 3  "April 25, 1993" "GNU" "Linux Programmer's Manual"
.SH NAME
readv, writev \- read or write data into multiple buffers
.SH SYNOPSIS
.nf
.B #include <sys/uio.h>
.sp
.BI "int readv(int " filedes ", const struct iovec *" vector ","
.BI "          size_t " count ");"
.sp
.BI "int writev(int " filedes ", const struct iovec *" vector ","
.BI "          size_t " count ");"
.fi
.SH DESCRIPTION
The
.B readv()
function reads
.I count
blocks from the file associated with the file descriptor
.I filedes
into the multiple buffers described by
.IR vector .
.PP
The
.B writev()
function writes at most
.I count
blocks described by
.I vector
to the file associated with the file descriptor
.IR filedes .
.PP
The pointer
.I vector
points to a
.B struct iovec
defined in
.B <sys/uio.h>
as
.PP
.br
.nf
.in 10
struct iovec {
.in 14
void *iov_base;   /* Starting address */
size_t iov_len;   /* Number of bytes */
.in 10
};
.fi
.PP
Buffers are processed in the order
.IR "vector[0]" ", " vector[1] ", ... " "vector[count]" .
.PP
The
.B readv()
function works just like
.BR read (2)
except that multiple buffers are filled.
.PP
The
.B writev()
function works just like
.BR write (2)
except that multiple buffers are written out.
.PP
.SH "RETURN VALUES"
The
.B readv()
function returns the number of bytes or \-1 on error; the
.B writev()
function returns the number of bytes written.
.SH "ERRORS"
The
.B readv()
and 
.B writev()
functions can fail and set
.I errno
to the following values:
.TP
.B EBADF
.I fd
is not a valid file descriptor.
.TP
.B EINVAL
.I fd
is unsuitable for reading (for
.BR readv() )
or writing (for
.BR writev() ).
.TP
.B EFAULT
.I buf
is outside the processes' address space.
.TP
.B EAGAIN
Non-blocking I/O had been selected in the 
.B open()
call, and reading or writing could not be done immediately.
.TP
.B EINTR
Reading or writing was interrupted before any data was transferred.
.SH "CONFORMING TO"
unknown
.SH "BUGS"
It is not advisable to mix calls to functions like
.BR readv() " or " writev() ,
which operate on file descriptors, with the functions from the stdio
library; the results will be undefined and probably not what you want.
.SH "SEE ALSO"
.BR read "(2), " write (2)