Can't read file data twice using QAxObject

Question

I read excel file using QAxBase and QAxObject.

I got global variable QAxObject* db_workbook; where I store pointer to some workbook(don't know why it called like that, but whatever) in excel. I need it because of throught it I need to get excel file data in few functions, not just only one.

When readExcelFile method executes fine, in test_function() an exception

appears at this line sheet_N = db_workbook->querySubObject("Worksheets(int)", 1);

Why does it happens and how to fix it?

Code part is here

//
QAxObject* db_workbook;

//for read what we need to
void importdb_module::readExcelFile(QAxObject* excel, QString& file_path){

    if(initExcel(excel)){

        QAxObject* workbooks = excel->querySubObject("WorkBooks");
        workbooks->dynamicCall("Open (const QString&)", file_path);
        QAxObject* workbook = excel->querySubObject("ActiveWorkBook");
        db_workbook = workbook;//global ptr points same adress now
        QAxObject* worksheets = workbook->querySubObject("WorkSheets");

        //test getting sheet num 1 name
        QAxObject* sheet_hh = workbook->querySubObject("Worksheets(int)", 1);

        QString sheet_name = sheet_hh->property("Name").toString();

        qDebug()<<sheet_name<<"TEST!";//here everything works fine
    }
}

void importdb_module::test_function(){
    QAxObject* sheet_N;
    //ERROR IS HERE!
    sheet_N = db_workbook->querySubObject("Worksheets(int)", 1);

    QString sheet_name = sheet_N->property("Name").toString();

    qDebug()<<sheet_name;
}


//executes on button click
void importdb_module::testExlOp(QString &_path){
    QAxObject* excel;
    QStringList spreadsheet_list; //get spreadsheet list when opening file
    QString path = _path;//gonna use GUI choose

    if(initExcel(excel)){
        if (readExcelFile(excel, path)){
            //
            test_function();
            excel->dynamicCall("Quit(void)");
            }else{
            //error output
            QMessageBox::information(0, "", "Error");
        }
    }


    delete excel;
}

Thank you!

Answer 1

Probably you have a dangling pointer. Use QPointer<QAxObject> instead of a naked pointer. It will reset itself to null when the instance of QAxObject gets destructed.

Generally speaking, in this day and age, you're not supposed to be using naked pointers for anything that's not implicitly owned by something else. This means that for QObjects that have parents you don't need to do use smart pointers (although it doesn't hurt any). Generally speaking, smart pointers don't hurt. Use them.