'\" et
.TH READV "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
readv
\(em read a vector
.SH SYNOPSIS
.LP
.nf
#include <sys/uio.h>
.P
ssize_t readv(int \fIfildes\fP, const struct iovec *\fIiov\fP, int \fIiovcnt\fP);
.fi
.SH DESCRIPTION
The
\fIreadv\fR()
function shall be equivalent to
\fIread\fR(),
except as described below. The
\fIreadv\fR()
function shall place the input data into the
.IR iovcnt
buffers specified by the members of the
.IR iov
array:
.IR iov [0],
.IR iov [1],
\&.\|.\|.,
.IR iov [\c
.IR iovcnt \-1].
The
.IR iovcnt
argument is valid if greater than 0 and less than or equal to
{IOV_MAX}.
.P
Each
.IR iovec
entry specifies the base address and length of an area
in memory where data should be placed. The
\fIreadv\fR()
function shall always fill an area completely before proceeding
to the next.
.P
Upon successful completion,
\fIreadv\fR()
shall mark for update the last data access timestamp of the file.
.SH "RETURN VALUE"
Refer to
.IR "\fIread\fR\^(\|)".
.SH ERRORS
Refer to
.IR "\fIread\fR\^(\|)".
.P
In addition, the
\fIreadv\fR()
function shall fail if:
.TP
.BR EINVAL
The sum of the
.IR iov_len
values in the
.IR iov
array overflowed an
.BR ssize_t .
.P
The
\fIreadv\fR()
function may fail if:
.TP
.BR EINVAL
The
.IR iovcnt
argument was less than or equal to 0, or greater than
{IOV_MAX}.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Reading Data into an Array"
.P
The following example reads data from the file associated with the file
descriptor
.IR fd
into the buffers specified by members of the
.IR iov
array.
.sp
.RS 4
.nf

#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
\&...
ssize_t bytes_read;
int fd;
char buf0[20];
char buf1[30];
char buf2[40];
int iovcnt;
struct iovec iov[3];
.P
iov[0].iov_base = buf0;
iov[0].iov_len = sizeof(buf0);
iov[1].iov_base = buf1;
iov[1].iov_len = sizeof(buf1);
iov[2].iov_base = buf2;
iov[2].iov_len = sizeof(buf2);
\&...
iovcnt = sizeof(iov) / sizeof(struct iovec);
.P
bytes_read = readv(fd, iov, iovcnt);
\&...
.fi
.P
.RE
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
Refer to
.IR "\fIread\fR\^(\|)".
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIread\fR\^(\|)",
.IR "\fIwritev\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<sys_uio.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .