• You will need the Qt SQL plugin corresponding to the type given to QSqlDatabase::addDatabase
• If you don't have the required SQL plugin, Qt will warn you that it can't find the requested driver
• If you don't have the required SQL plugin you will have to compile them from the Qt source

QTimer can also be used to request a function to run as soon as the event loop has processed all the other pending events. To do this, use an interval of 0 ms.

// option 1: Set the interval to 0 explicitly.
QTimer *timer = new QTimer;
timer->setInterval( 0 );
timer->start();

// option 2: Passing 0 with the start call will set the interval as well.
QTimer *timer = new QTimer;
timer->start( 0 );

// option 3: use QTimer::singleShot with interval 0
QTimer::singleShot(0, [](){
    // do something
});

Qt provides its own template container classes. They are all implicitly shared. They provide two kinds of iterators (Java style and STL style.)

Qt sequential containers include: QVector, QList, QLinkedList, QStack, QQueue.

Qt associative containers include: QMap, QMultiMap, QHash, QMultiHash, QSet.

QObject class is the base class for all Qt objects.

STL style iterators on Qt Container can have some negative side effect due to the implicit-sharing. It is advised to avoid copying a Qt container while you have iterators active on them.

QVector<int> a,b; //2 vectors
a.resize(1000); 
b = a; // b and a now point to the same memory internally

auto iter = a.begin(); //iter also points to the same memory a and b do
a[4] = 1; //a creates a new copy and points to different memory.
//Warning 1: b and iter point sill to the same even if iter was "a.begin()"

b.clear(); //delete b-memory
//Warning 2: iter only holds a pointer to the memory but does not increase ref-count. 
//           so now the memory iter points to is invalid. UB!

Qt Multimedia is a module providing handling of multimedia (audio, video) and also camera and radio functionality.

However, the supported files of QMediaPlayer depends on the platform. Indeed, on windows, QMediaPlayer uses DirectShow, on Linux, it uses GStreamer. So depending on the platform some files may work on Linux but not on Windows or the opposite.

The QDialog class is the base class of dialog windows. A dialog window is a top-level window mostly used for short-term tasks and brief communications with the user. QDialogs may be modal or modeless.

Note that QDialog (and any other widget that has type Qt::Dialog) uses the parent widget slightly differently from other classes in Qt. A dialog is always a top-level widget, but if it has a parent, its default location is centered on top of the parent's top-level widget (if it is not top-level itself). It will also share the parent's taskbar entry.

A modal dialog is a dialog that blocks input to other visible windows in the same application. Dialogs that are used to request a file name from the user or that are used to set application preferences are usually modal. Dialogs can be application modal (the default) or window modal.

The most common way to display a modal dialog is to call its exec() function. When the user closes the dialog, exec() will provide a useful return value.

A modeless dialog is a dialog that operates independently of other windows in the same application. Modeless dialogs are displayed using show(), which returns control to the caller immediately.