Widgets Tutorial

Writing a main Function

Many of the GUI examples in Qt follow the pattern of having a main.cpp file containing code to initialize the application, and a number of other source and header files containing the application logic and custom GUI components.

A typical main() function, written in main.cpp, looks like this:

 #include <QtGui>

 // Include header files for application components.
 // ...

 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);

     // Set up and show widgets.
     // ...

     return app.exec();
 }

We first construct a QApplication object which is configured using any arguments passed in from the command line. After any widgets have been created and shown, we call QApplication::exec() to start Qt's event loop. Control passes to Qt until this function returns, at which point we return the value we obtain from this function.

In each part of this tutorial, we provide an example that is written entirely within a main() function. In more sophisticated examples, the code to set up widgets and layouts is written in other parts of the example. For example, the GUI for a main window may be set up in the constructor of a QMainWindow subclass.

The Widgets examples are a good place to look for more complex and complete examples and applications.