file_id	IN:	File identifier returned by Hopen
	label_buf	OUT:	The buffer allocated to hold the label
	buf_len	IN:	Size of the buffer allocated to hold the label
	isfirst	IN:	Determines the file label to be retrieved

	Purpose	Reads a file label from a file.
	Return value	Returns the length of the file description if successful and FAIL (or -1) otherwise.
	Description	If isfirst is 0, DFANgetfid gets the next file label from the file. If isfirst is 1, DFANgetfid gets the first file label in the file. If buf_len is not large enough, the label is truncated to buf_len-1 characters in the buffer label_buf.
		Valid values of isfirst are: 1 to read the first label, 0 to read the next label

	FORTRAN	integer function dagfid(file_id, label_buf, buf_len, isfirst)
		integer file_id, buf_len, isfirst
		character*(*) label_buf