4.3BSD - /usr/man/cat2/write.0

WRITE(2)                                                              WRITE(2)


NAME
       write, writev - write output

SYNOPSIS
       cc = write(d, buf, nbytes)
       int cc, d;
       char *buf;
       int 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 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 speci‐
       fied  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;
                   int  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 position 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 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 con‐
                      taining the file.

       [EDQUOT]       The  user’s quota of disk blocks on the file system con‐
                      taining 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]       One of the iov_len values in the iov array was negative.

       [EINVAL]       The sum of the iov_len values in  the  iov  array  over‐
                      flowed a 32-bit integer.

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


4th Berkeley Distribution        May 14, 1986                         WRITE(2)