sds_id	IN:	Data set identifier returned by SDcreate or SDselect
	fill_value	OUT:	Buffer for the returned fill value

	Purpose	Reads the fill value of a data set, if the value has been set.
	Return value	Returns SUCCEED (or 0) if a fill value is retrieved and FAIL (or -1) otherwise, including when the fill value is not set.
	Description	SDgetfillvalue reads the fill value which has been set for the data set specified by the parameter sds_id. It is assumed that the data type of the fill value is the same as that of the data set.
		Note that there are two FORTRAN-77 versions of this routine: sfgfill and sfgcfill. The sfgfill routine reads numeric fill value data and sfgcfill reads character fill value data.

	FORTRAN	integer function sfgfill(sds_id, fill_value)
		integer sds_id
		<valid numeric data type> fill_value
		integer function sfgcfill(sds_id, fill_value)
		integer sds_id
		character*(*) fill_value