NAME
write, writev - write output

SYNOPSIS
cc = write(d, buf, nbytes)
int cc, d;
const void *buf;
size_t nbytes;

#include <sys/types.h>
#include <sys/uio.h>

cc = writev(d, iov, iovcnt)
int cc, d;
struct iovec *iov;
int iovcnt;

DESCRIPTION
Write attempts to write nbytes of data to the object referenced by
the descriptor d from the buffer pointed to by buf. Writev
performs the same action, but gathers the output data from the
iovcnt buffers specified by the members of the iov array: iov[0],
iov[1], ..., iov[iovcnt-1].

For writev, the iovec structure is defined as

struct iovec {
caddr_t iov_base;
int iov_len;
};

Each iovec entry specifies the base address and length of an area
in memory from which data should be written. Writev will always
write a complete area before proceeding to the next.

On objects capable of seeking, the write starts at a position given
by the pointer associated with d, see lseek(2). Upon return from
write, the pointer is incremented by the number of bytes actually
written.

Objects that are not capable of seeking always write from the
current position. The value of the pointer associated with such an
object is undefined.

If the real user is not the super-user, then write clears the set-
user-id bit on a file. This prevents penetration of system
security by a user who "captures" a writable set-user-id file owned
by the super-user.

When using non-blocking I/O on objects such as sockets that are
subject to flow control, write and writev may write fewer bytes
than requested; the return value must be noted, and the remainder
of the operation should be retried when possible.

RETURN VALUE
Upon successful completion the number of bytes actually written is
returned. Otherwise a -1 is returned and the global variable errno
is set to indicate the error.

ERRORS
Write and writev will fail and the file pointer will remain
unchanged if one or more of the following are true:

[EBADF] D is not a valid descriptor open for writing.

[EPIPE] An attempt is made to write to a pipe that is not
open for reading by any process.

[EPIPE] An attempt is made to write to a socket of type
SOCK_STREAM that is not connected to a peer socket.

[EFBIG] An attempt was made to write a file that exceeds the
process’s file size limit or the maximum file size.

[EFAULT] Part of iov or data to be written to the file points
outside the process’s allocated address space.

[EINVAL] The pointer associated with d was negative.

[ENOSPC] There is no free space remaining on the file system
containing the file.

[EDQUOT] The user’s quota of disk blocks on the file system
containing the file has been exhausted.

[EIO] An I/O error occurred while reading from or writing
to the file system.

[EWOULDBLOCK] The file was marked for non-blocking I/O, and no
data could be written immediately.

In addition, writev may return one of the following errors:

[EINVAL] Iovcnt was less than or equal to 0, or greater than
16.

[EINVAL] One of the iov_len values in the iov array was
negative.

[EINVAL] The sum of the iov_len values in the iov array
overflowed a 32-bit integer.

SEE ALSO
fcntl(2), lseek(2), open(2), pipe(2), select(2)