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)