READV
Section: POSIX Programmer's Manual (3P)
Updated: 2013
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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.
NAME
readv
--- read a vector
SYNOPSIS
#include <sys/uio.h>
ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);
DESCRIPTION
The
readv()
function shall be equivalent to
read(),
except as described below. The
readv()
function shall place the input data into the
iovcnt
buffers specified by the members of the
iov
array:
iov[0],
iov[1],
...,
iov[
iovcnt-1].
The
iovcnt
argument is valid if greater than 0 and less than or equal to
{IOV_MAX}.
Each
iovec
entry specifies the base address and length of an area
in memory where data should be placed. The
readv()
function shall always fill an area completely before proceeding
to the next.
Upon successful completion,
readv()
shall mark for update the last data access timestamp of the file.
RETURN VALUE
Refer to
read().
ERRORS
Refer to
read().
In addition, the
readv()
function shall fail if:
- EINVAL
-
The sum of the
iov_len
values in the
iov
array overflowed an
ssize_t.
The
readv()
function may fail if:
- EINVAL
-
The
iovcnt
argument was less than or equal to 0, or greater than
{IOV_MAX}.
The following sections are informative.
EXAMPLES
Reading Data into an Array
The following example reads data from the file associated with the file
descriptor
fd
into the buffers specified by members of the
iov
array.
-
#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];
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);
bytes_read = readv(fd, iov, iovcnt);
...
APPLICATION USAGE
None.
RATIONALE
Refer to
read().
FUTURE DIRECTIONS
None.
SEE ALSO
read(),
writev()
The Base Definitions volume of POSIX.1-2008,
<sys_uio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Reading Data into an Array
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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