memory leak - where?

[Tomasz]

Hello!

I've got my simple application, but it causes memory leak. I think one of this three functions is a problem:

bool MainWindow::pobierzKomunikaty()
{
    bool ok;
    QTextStream out(stdout);
    QString zapytanie;
    QSqlRecord rec;
    QSqlQueryModel queryModel;
 
    QFont font;
    font.setPointSize(7);
 
    odczytanoOstatnieKomunikaty=0;
 
    ok = bdb.open();
 
    if (ok)
    {
        out << endl << "Otworzylem baze!" << endl ;
    } else {
        out << "Nie udalo sie otworzyc bazy!" << endl;
    }
 
    queryModel.setQuery("SELECT * FROM server_notifications WHERE complete='0'", bdb); //LIMIT 1
 
    liczbaWiadomosci = queryModel.rowCount();
 
    bdb.close();
 
    out << "Mamy: " << liczbaWiadomosci << " wiadomosci!" << endl;
 
 
    for(int i=0 ; i<liczbaWiadomosci; i++)
    {
        rec = queryModel.record(i);
 
 
        out << rec.value(1).toString() << ": ";
        out << rec.value(2).toString() << endl;
 
        QMessageBox *msgBox=new QMessageBox;
 
        if(rec.value(1).toString()=="warning") msgBox->setIcon(QMessageBox::Warning);
        else if (rec.value(1).toString()=="info") msgBox->setIcon(QMessageBox::Information);
        else if (rec.value(1).toString()=="error") msgBox->setIcon(QMessageBox::Critical);
 
        msgBox->setFont(font);
 
        msgBox->setWindowTitle(rec.value(1).toString());
        msgBox->setText(rec.value(2).toString());
 
        QSpacerItem* horizontalSpacer = new QSpacerItem(240, 290, QSizePolicy::Minimum, QSizePolicy::Minimum);
        QGridLayout* layout = (QGridLayout*)msgBox->layout();
        layout->addItem(horizontalSpacer, layout->rowCount(), 0, 1, layout->columnCount());
 
        msgBox->move(0,0);
        msgBox->exec();
 
        delete msgBox;
 
        ok = bdb.open();
 
        zapytanie.clear();
        zapytanie="update server_notifications set complete='1'";
        zapytanie.append(" where id='");
        zapytanie.append(QString::number(rec.value(0).toInt()));
        zapytanie.append("'");
 
        QSqlQuery *query=new QSqlQuery;
 
        query->clear();
        query->prepare(zapytanie);
        ok = query->exec();
 
        bdb.close();
 
        delete query;
    }
 
    odczytanoOstatnieKomunikaty=1;
 
    return ok;
}
 
bool MainWindow::wyswietlKomunikaty()
{
    if(odczytanoOstatnieKomunikaty==0)
    {
 
    } else
    {
        pobierzKomunikaty();
        odczytajNotificationInterval();
        timer->start(notificationInterval);
    }
 
    return 1;
}
 
bool MainWindow::odczytajNotificationInterval()
{
    bool ok;
    QTextStream out(stdout);
    QSqlRecord rec;
    QSqlQueryModel queryModel;
 
    ok = bdb.open();
 
    if (ok)
    {
        out << endl << "Otworzylem baze!" << endl ;
    } else {
        out << "Nie udalo sie otworzyc bazy!" << endl;
    }
 
    queryModel.setQuery("SELECT * FROM config WHERE name='qt-notification-interval'", bdb);
 
    rec = queryModel.record(0);
    notificationInterval = (rec.value(1).toInt())*1000;
 
    out << "Notification interval: " << notificationInterval << " ms" << endl;
 
    bdb.close();
 
    return ok;
}

bool MainWindow::pobierzKomunikaty()
{
    bool ok;
    QTextStream out(stdout);
    QString zapytanie;
    QSqlRecord rec;
    QSqlQueryModel queryModel;

    QFont font;
    font.setPointSize(7);

    odczytanoOstatnieKomunikaty=0;

    ok = bdb.open();

    if (ok)
    {
        out << endl << "Otworzylem baze!" << endl ;
    } else {
        out << "Nie udalo sie otworzyc bazy!" << endl;
    }

    queryModel.setQuery("SELECT * FROM server_notifications WHERE complete='0'", bdb); //LIMIT 1

    liczbaWiadomosci = queryModel.rowCount();

    bdb.close();

    out << "Mamy: " << liczbaWiadomosci << " wiadomosci!" << endl;


    for(int i=0 ; i<liczbaWiadomosci; i++)
    {
        rec = queryModel.record(i);


        out << rec.value(1).toString() << ": ";
        out << rec.value(2).toString() << endl;

        QMessageBox *msgBox=new QMessageBox;

        if(rec.value(1).toString()=="warning") msgBox->setIcon(QMessageBox::Warning);
        else if (rec.value(1).toString()=="info") msgBox->setIcon(QMessageBox::Information);
        else if (rec.value(1).toString()=="error") msgBox->setIcon(QMessageBox::Critical);

        msgBox->setFont(font);

        msgBox->setWindowTitle(rec.value(1).toString());
        msgBox->setText(rec.value(2).toString());

        QSpacerItem* horizontalSpacer = new QSpacerItem(240, 290, QSizePolicy::Minimum, QSizePolicy::Minimum);
        QGridLayout* layout = (QGridLayout*)msgBox->layout();
        layout->addItem(horizontalSpacer, layout->rowCount(), 0, 1, layout->columnCount());

        msgBox->move(0,0);
        msgBox->exec();

        delete msgBox;

        ok = bdb.open();

        zapytanie.clear();
        zapytanie="update server_notifications set complete='1'";
        zapytanie.append(" where id='");
        zapytanie.append(QString::number(rec.value(0).toInt()));
        zapytanie.append("'");

        QSqlQuery *query=new QSqlQuery;

        query->clear();
        query->prepare(zapytanie);
        ok = query->exec();

        bdb.close();

        delete query;
    }

    odczytanoOstatnieKomunikaty=1;

    return ok;
}

bool MainWindow::wyswietlKomunikaty()
{
    if(odczytanoOstatnieKomunikaty==0)
    {

    } else
    {
        pobierzKomunikaty();
        odczytajNotificationInterval();
        timer->start(notificationInterval);
    }

    return 1;
}

bool MainWindow::odczytajNotificationInterval()
{
    bool ok;
    QTextStream out(stdout);
    QSqlRecord rec;
    QSqlQueryModel queryModel;

    ok = bdb.open();

    if (ok)
    {
        out << endl << "Otworzylem baze!" << endl ;
    } else {
        out << "Nie udalo sie otworzyc bazy!" << endl;
    }

    queryModel.setQuery("SELECT * FROM config WHERE name='qt-notification-interval'", bdb);

    rec = queryModel.record(0);
    notificationInterval = (rec.value(1).toInt())*1000;

    out << "Notification interval: " << notificationInterval << " ms" << endl;

    bdb.close();

    return ok;
}

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Maybe someone can tell me where?

thanks in advance
best regards
Tomasz

[wysota]

There is no memory leak here. But you are needlessly creating objects on heap and not on the stack (like the QSqlQuery object).

[Tomasz]

So I should create all the objects one time in my *.h file as a private objects?
One question to my code - after exiting each function all the objects are being deleted from memory?

And one more piece of code from beginning:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    setWindowFlags(Qt::CustomizeWindowHint|Qt::FramelessWindowHint);
 
    databaseName="/mybase";
    bdb = QSqlDatabase::addDatabase("QSQLITE");
    bdb.setDatabaseName(databaseName);
 
    connect(ui->pomiaryButton, SIGNAL(clicked()), this, SLOT(uruchomPomiary()));
    connect(ui->sterowanieButton, SIGNAL(clicked()), this, SLOT(uruchomSterowanie()));
    connect(ui->klimaButton, SIGNAL(clicked()), this, SLOT(uruchomKlima()));
    connect(ui->konfiguracjaButton, SIGNAL(clicked()), this, SLOT(uruchomKonfiguracja()));
 
    odczytanoOstatnieKomunikaty=0;
 
    odczytajNotificationInterval();
 
    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(wyswietlKomunikaty()));
    timer->start(notificationInterval);
 
    this->show();
 
    pobierzKomunikaty();
}

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    setWindowFlags(Qt::CustomizeWindowHint|Qt::FramelessWindowHint);

    databaseName="/mybase";
    bdb = QSqlDatabase::addDatabase("QSQLITE");
    bdb.setDatabaseName(databaseName);

    connect(ui->pomiaryButton, SIGNAL(clicked()), this, SLOT(uruchomPomiary()));
    connect(ui->sterowanieButton, SIGNAL(clicked()), this, SLOT(uruchomSterowanie()));
    connect(ui->klimaButton, SIGNAL(clicked()), this, SLOT(uruchomKlima()));
    connect(ui->konfiguracjaButton, SIGNAL(clicked()), this, SLOT(uruchomKonfiguracja()));

    odczytanoOstatnieKomunikaty=0;

    odczytajNotificationInterval();

    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(wyswietlKomunikaty()));
    timer->start(notificationInterval);

    this->show();

    pobierzKomunikaty();
}

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Now it's the whole code. Maybe somewhere here is memory leak? I'm thinking about memory leak because each time I check how many resources programs needs (by 'ps' in linux console) my application take more resources.

thanks in advance
best regards
Tomasz

[wysota]

So I should create all the objects one time in my *.h file as a private objects?

No. If you have an "int" variable somewhere in your code do you create it as:

int x;

int x;

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or

int *x = new int;

int *x = new int;

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?

Are any of those "private obejcts"?

One question to my code - after exiting each function all the objects are being deleted from memory?

The ones that are created on the stack are deleted automatically as the stack unwinds, the ones created in dynamic memory (heap) have to be released manually (unless they are parented QObjects, I'm sure you know the drill...).

Maybe somewhere here is memory leak?

If you don't have a corresponding "removeDatabase" to each "addDatabase" I suspect there could be a memory leak. I'm not sure if Qt releases the old connection when it detects a new one with the same name (but you surely get warning messages to the console if you are trying to reuse name of an active db connection).

[Tomasz]

I create my "private" variables as:

int x;

int x;

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But what about this objects in functions - all of them are created on heap or stack? I need to remove them?

thanks in advance
best regards
Tomasz

[wysota]

I create my "private" variables as:

int x;

int x;

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What about others? Have you ever (anywhere) created an int using the "new" operator?

[Tomasz]

The only thing created with "new" is timer:

private:
    Ui::MainWindow *ui;
    QString databaseName;
    int liczbaWiadomosci;
    QTimer *timer;
    int odczytanoOstatnieKomunikaty;
    int notificationInterval;
    QSqlDatabase bdb;

private:
    Ui::MainWindow *ui;
    QString databaseName;
    int liczbaWiadomosci;
    QTimer *timer;
    int odczytanoOstatnieKomunikaty;
    int notificationInterval;
    QSqlDatabase bdb;

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So I don't need to remove variables that I have in my function manually? Because I never did that in "pure" C/C++. As I remember I only need to remove things created with "new" operator.

thanks in advance
best regards
Tomasz

[wysota]

The only thing created with "new" is timer:

Look at the first snippet you provided and examine that. Especially the QSqlQuery instance.

[Tomasz]

Yes, You're right, but after using it I'm deleting it, right?

thanks in advance
best regards
Tomasz

[wysota]

Yes, You're right, but after using it I'm deleting it, right?

Yes, but there is no point in creating it on the heap (using the "new" operator) and having to worry about deleting it afterwards. Simply create the query and the message box on the stack and the compiler will take care of deleting them for you.

[Tomasz]

So, reassuming. Now If I don't change anything (later I will take care about what You said) there is no reason to worry about memory leak in this code above?

thanks in advance
best regards
Tomasz