WRITE(2)	    UNIX Programmer's Manual		 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 refer-
     enced 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 posi-
     tion 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


Printed 11/26/99	 August 1, 1987                         1


WRITE(2)	    UNIX Programmer's Manual		 WRITE(2)


     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.


Printed 11/26/99	 August 1, 1987                         2


WRITE(2)	    UNIX Programmer's Manual		 WRITE(2)


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


Printed 11/26/99	 August 1, 1987                         3


 
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