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
     _W_r_i_t_e attempts to write _n_b_y_t_e_s of data to the object refer-
     enced by the descriptor _d from the buffer pointed to by _b_u_f.
     _W_r_i_t_e_v performs the same action, but gathers the output data
     from the _i_o_v_c_n_t buffers specified by the members of the _i_o_v
     array: iov[0], iov[1], ..., iov[iovcnt-1].

     For _w_r_i_t_e_v, the _i_o_v_e_c structure is defined as

	  struct iovec {
	       caddr_t	 iov_base;
	       u_short	 iov_len;
	  };

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

     On objects capable of seeking, the _w_r_i_t_e starts at a posi-
     tion given by the pointer associated with _d, see _l_s_e_e_k(2).
     Upon return from _w_r_i_t_e, 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 _w_r_i_t_e 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, _w_r_i_t_e and _w_r_i_t_e_v may write



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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 _e_r_r_n_o is set to indicate the error.

ERRORS
     _W_r_i_t_e and _w_r_i_t_e_v 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 _i_o_v 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, _w_r_i_t_e_v may return one of the following errors:

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

     [EINVAL]	    The sum of the _i_o_v__l_e_n values in the _i_o_v
		    array overflowed a short.



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



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





















































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