closing database connection

[bart.hollis]

I have a function in my program that creates or opens a SqLite database:

QSqlError createDb()
{
    QSqlDatabase db;
    db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("tracker.db");
    db.open();
    return db.lastError();
}

It works fine.
In the function I call to quit the program is a call to this function:

/QSqlError closeDb()
{
    QSqlDatabase db;
    db = QSqlDatabase::database();

// debug text:
    if ( db.isOpen() )
        std::cout << "the database is:  open" << std::endl;
    else
        std::cout << "the database is:  Closed" << std::endl;

    db.close();

// debug text.
    if ( db.isOpen() )
        std::cout << "the database is:  open" << std::endl;
    else
        std::cout << "the database is:  Closed" << std::endl;

    db.removeDatabase( QSqlDatabase::defaultConnection );
    return db.lastError();
}

It also seems to work, based on the debug couts in place.

In various functions in the program, I create a QSqlQuery, but these are created within the function and should, as I understand it, go away or become non-existant when the function ends.

When I run the program, and close it, after the debug messages showing the database is closed, I get an error message stating :

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.

I read that message to mean that the database is closed but that I still have a connection to it somewhere. Further, there are some querys hanging around and that means memory leaks!

Looking at the docs for QSqlQuery, I see QSqlQuery::clear() with the statement that I should rarely if ever need it. I see ~QSqlQuery() which causes a crash. I see QSqlQuery::finish() which there's normally no need to call it.

So, what do I do? ( Read that as what do I not understand? )

[Christian Ehrlicher]

You have to make sure that no QSqlQuery exits using this connection when you want to close it to avoid this warning. Or just ignore it :)

[bart.hollis]

But if a query is created within a function, does it not cease to exist when the function returns?

[Christian Ehrlicher]

Yes but there must be an open QSqlQuery anywhere - at least this is what the warning tells you.
/edit: maybe a QSqlQuery as member value somewhere?

[aha_1980]

@bart.hollis said in closing database connection:

But if a query is created within a function, does it not cease to exist when the function returns?

if you create the query as a stack variable, the it is destroyed when the surrounding scope is leaved.

if you create the query as heap variable (with new) then it exists until delete or program end.

[bart.hollis]

I Found it!

In the closeDB function I wrote, I called the line:

QSqlDatabase db = QSqlDatabase::database();

And then closed it. This obviously created an instance of the connection which was left dangling when I removed it. The new function reads as follows:

// >>>>>>>>>>>>>>>>  Close the database when quitting  <<<<<<<<<<<<<<<<<<<<<
void closeDb()
{
    {
        QSqlDatabase db = QSqlDatabase::database();
        db.close();
    }
    QSqlDatabase::removeDatabase( QSqlDatabase::defaultConnection );
    return;
}

This has eliminated the warning.

Thanks all for your assistance.