man readv () - read a vector

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 .