WRITE(2)                             BSD                              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 specified 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.

     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.

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' file size limit or the maximum file size.

     [EFAULT]        Part of iov or data to be written to the file points
                     outside the process' 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.

     [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 overflowed
                     a 32-bit integer.

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

DIAGNOSTICS
     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.

NOTES
     In other implementations, if the real user is not the super-user, then
     write clears the set-user-id bit on a file.  Under other implementations,
     write and writev fail if the following is true:

     [EDQUOT]        The user's quota of disk blocks on the file system
                     containing the file has been exhausted.