構造格子のセルで定義された倍精度実数の属性を読み込む。
call cg_iric_read_grid_real_cell(fid, label, values, ier)
ier = cg_iRIC_Read_Grid_Real_Cell(fid, label, values);
values = cg_iRIC_Read_Grid_Real_Cell(fid, label)