directory

    A pointer to the pathname of the directory where you want to
    create a file.

 prefix

    A pointer to an initial character sequence of the filename. The
    prefix argument can be null, or it can point to a string of up
    to five characters used as the first characters of the temporary
    filename.

  . . .

    An optional argument that can be either 1 or 0. If you specify 1,
    tempnam returns the file specification in OpenVMS format. If you
    specify 0, tempnam returns the file specification in UNIX style
    format.