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READV
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
Return to Main Contents
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
st_atime field 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
IEEE Std 1003.1-2001, <sys/uio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
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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