writev(2)                           CLIX                           writev(2)



  NAME

    writev - Writes output from scattered locations

  LIBRARY

    Berkeley Software Distribution Library (libbsd.a)

  SYNOPSIS

    #include <sys/types.h>

    #include <sys/uio.h>

    int writev(
      int s ,
      struct iovec *iov ,
      int iovcnt );

  PARAMETERS

    s        Represents a socket descriptor.

    iov      Points to an array of buffers containing the data to be written.

    iovcnt   Specifies the number of buffers pointed to by iov.

  DESCRIPTION

    The writev() function attempts to write data to the object referenced by
    the descriptor s.  The output data is gathered from the iovcnt buffers
    specified by the members of the iov array:  iov[0], iov[1], ... ,
    iov[iovcnt-1].

    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.  The writev() function will
    always write a complete area before proceeding to the next.

    When using nonblocking I/O, writev() may write fewer bytes than requested;
    the return value must be noted and the remainder of the operation should
    be retried when possible.

  EXAMPLES




  2/94 - Intergraph Corporation                                              1

  writev(2)                           CLIX                           writev(2)



    To write data to socket sd:

    if (writev(sd, iov, iovcnt) == -1)
         perror("Writev failed");


  CAUTIONS

    The writev() function does not work on regular files; it is usable only
    with sockets.

  RETURN VALUES

    Upon successful completion, the number of bytes written is returned.
    Otherwise, a value of -1 is returned and errno is set to indicate the
    error.

  ERRORS

    The writev() function fails if one or more of the following is true:

    [EBADF]
           The descriptor is not valid.

    [ENOTSOCK]
           The descriptor references a file, not a socket.

    [EWOULDBLOCK]
           The socket is marked nonblocking and the requested operation would
           block.

    [EINTR]
           A signal was caught during the writev() function.

    [EFAULT]
           An invalid user space address was specified.

    [EPIPE]
           The socket was disconnected or shutdown for writing.

    [EINVAL]
           The maximum number of scatter gather locations was exceeded.

    [ENOTCONN]
           An attempt was made to send data on a stream socket that is not
           connected.

    [EDESTADDRREQ]
           An attempt was maded to send data on a datagram socket without a
           destination address.




  2                                              Intergraph Corporation - 2/94

  writev(2)                           CLIX                           writev(2)



    [EISCONN]
           An attempt was made to perform a sendto() on a connected socket.

  RELATED INFORMATION

    Functions:  fcntl(2), recv(2), writev(2), select(2), getsockopt(2),
    socket(2)















































  2/94 - Intergraph Corporation                                              3