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OpenDarwin 7.2.1 - man page for writev (opendarwin section 2)

WRITE(2)			     BSD System Calls Manual				 WRITE(2)

     write, writev, pwrite -- write output

     Standard C Library (libc, -lc)

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

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

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

     pwrite(int d, const void *buf, size_t nbytes, off_t offset);

     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].  Pwrite() performs the same function, but writes to the specified position in
     the file without modifying the file pointer.

     For writev(), the iovec structure is defined as:

	   struct iovec {
		   char   *iov_base;  /* Base address. */
		   size_t iov_len;    /* Length. */

     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

     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 which were 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.

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

     Write(), writev(), and pwrite() will fail and the file pointer will remain unchanged if:

     [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

     [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.

     [EINTR]		A signal interrupted the write before it could be completed.

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

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

     [EDESTADDRREQ]	The destination is no longer available when writing to a UNIX domain
			datagram socket on which connect(2) had been used to set a destination

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

     [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 inte-

     [ENOBUFS]		The mbuf pool has been completely exhausted when writing to a socket.

     The pwrite() call may also return the following errors:

     [EINVAL]		The specified file offset is invalid.

     [ESPIPE]		The file descriptor is associated with a pipe, socket, or FIFO.

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

     The write() function call is expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1'').  The
     writev() and pwrite() functions are expected to conform to X/Open Portability Guide Issue 4,
     Version 2 (``XPG4.2'').

     The pwrite() function call appeared in AT&T System V Release 4 UNIX.  The writev() function
     call appeared in 4.2BSD.  A write() function call appeared in Version 6 AT&T UNIX.

BSD					  April 2, 1994 				      BSD

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