The H5A_OPEN_IDX function opens an existing attribute by the index of that attribute within an HDF5 file.
Result = H5A_OPEN_IDX(Loc_id, Index)
Returns an integer representing the attribute's identifier number.
An integer representing the identifier of the group, dataset, or named datatype containing the attribute within.
An integer representing the zero-based index of the attribute to be accessed.
H5A_OPEN_NAME, H5A_GET_NUM_ATTRS, H5A_GET_NAME, H5A_CLOSE