public static str COMVariant2Str(COMVariant _cv, int _decimals = 0, int _characters = 0, int _separator1 = 0, int _separator2 = 0)
{
    switch (_cv.variantType())
    {

        case (COMVariantType::VT_BSTR): return _cv.bStr();
        case (COMVariantType::VT_R4): return num2str(_cv.float(),_characters,_decimals,_separator1,_separator2);
        case (COMVariantType::VT_R8): return num2str(_cv.double(),_characters,_decimals,_separator1,_separator2);
        case (COMVariantType::VT_DECIMAL): return num2str(_cv.decimal(),_characters,_decimals,_separator1,_separator2);
        case (COMVariantType::VT_DATE): return date2str(_cv.date(),123,2,1,2,1,4);
        case (COMVariantType::VT_EMPTY): return '';

        default: throw error(strfmt('@SYS26908', _cv.variantType()));
    }
    return '';
}

how to use example :
YourClass::COMVariant2Str(cells.item(row,17).value());