readv(3p)
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 .