Writes into a given position within a file without changing the
    file pointer.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <unistd.h>

      ssize_t pwrite  (int file_desc, const void *buffer, size_t
                      nbytes, off_t offset);

1 - Arguments

 file_desc

    A file descriptor that refers to a file currently opened for
    writing or updating.

 buffer

    The address of contiguous storage from which the output data is
    taken.

 nbytes

    The maximum number of bytes involved in the write operation.

 offset

    The offset for the desired position inside the file.

2 - Description

    The pwrite function performs the same action as write, except
    that it writes into a given position in the file without changing
    the file pointer. The first three arguments to pwrite are the
    same as for write, with the addition of a fourth argument offset
    for the desired position inside the file.

3 - Return Values

    n                  The number of bytes written.
    -1                 Upon failure, the file pointer remains
                       unchanged and pwrite sets errno to one of
                       the following values:

                       o  EINVAL - The offset argument is invalid.
                          The value is negative.

                       o  ESPIPE - fildes is associated with a pipe
                          or FIFO.