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BSD 2.11 - man page for writev (bsd section 2)

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WRITE(2)										 WRITE(2)

NAME
       write, writev - write output

SYNOPSIS
       cc = write(d, buf, nbytes)
       int cc, d;
       char *buf;
       unsigned short 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;
		   u_short   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 associ-
       ated with d, see lseek(2).  Upon return from write, the pointer is incremented by the num-
       ber 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]       The sum of the iov_len values in the iov array overflowed a short.

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

4th Berkeley Distribution		  August 1, 1987				 WRITE(2)
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