WRITE(2)                COMMAND REFERENCE                WRITE(2)



NAME
     write, writev - write on a file

SYNOPSIS
     cc = write(fd, buf, nbytes)
     int cc;
     int fd;
     char *buf;
     int nbytes;

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

     cc = writev(fd, iov, iovcnt)
     int cc;
     int fd;
     struct iovec *iov;
     int iovcnt;

DESCRIPTION
     The write call attempts to write nbytes of data to the
     object referenced by the descriptor fd from the buffer
     pointed to by buf; writev performs the same action, but
     gathers the output data from iovcnt buffers specified by the
     members of the iovec array: iov[0], iov[1], ...,
     iov[iovcnt-1].

     The writev call is not supported for raw devices (for
     example, raw disks, terminals) nor is it supported for a
     file located on a remote host; both write and writev return
     the number of bytes written in cc.

     For writev, the iovec structure is defined in <sys/uio.h>
     as:



          struct iovec {
               caddr_t   iov_base;
               int  iov_len;
          };


     Each iovec entry specifies the base address and length of an
     area in memory where data is gathered.

     On objects capable of seeking, the write starts at a
     position given by the pointer associated with fd, see
     lseek(2).  Upon return from write, the pointer is
     incremented by the number of bytes actually written.





Printed 5/12/88                                                 1

WRITE(2)                COMMAND REFERENCE                WRITE(2)



     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 superuser, 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 superuser.

DIAGNOSTICS
     Calls write and writev fail and the file pointer remains
     unchanged if one or more of the following are true:

     [EBADF]      Fd 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.

     [EIO]        An I/O error occurred while reading from or
                  writing to the file system.

     [EPIPE]      An attempt is made to write to a socket of type
                  SOCK_STREAM which is not connected to a peer
                  socket.

     [EFBIG]      An attempt is 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.

     [EMSGSIZE]   Fd is a socket, and the message sent on it was
                  larger than the internal message buffer.

     [ENOTCONN]   Fd is a socket which is not connected.

     [EDESTADDREQ]
                  Fd is a socket, and a required address was
                  omitted from the write request on the socket.

     [EWOULDBLOCK]
                  Fd is in non-blocking mode, and the write would
                  cause a process block.

     [ENOBUFS]    Fd is a socket, and the system lacks sufficient
                  buffer space to do the write.

     In addition, writev fails if one or more of the following
     are true:




Printed 5/12/88                                                 2

WRITE(2)                COMMAND REFERENCE                WRITE(2)



     [EINVAL]     One of the iov_len values in the iov array is
                  negative.

     [EINVAL]     The sum of the iov_len values in the iov array
                  overflows a 32 bit integer.

     [EINVAL]     Iovcnt is less than or equal to 0, or greater
                  than 16.

     [ENXIO]      A writev call was attempted on an unsupported
                  raw device.

RETURN VALUE
     Upon successful completion the number of bytes written is
     returned in cc. Otherwise a -1 is returned and errno is set
     to indicate the error.

SEE ALSO
     lseek(2), open(2), pipe(2), and read(2).




































Printed 5/12/88                                                 3

%%index%%
na:264,83;
sy:347,1899;
de:2246,1731;4313,449;
di:4762,2166;7264,500;
rv:7764,294;
se:8058,200;
%%index%%000000000129