About Qt

• Qt is a library of C++ GUI application development software. Its purpose is to provide everything needed to develop the user interface portion of applications. It does this primarily in the form of a collection of C++ classes. The Norwegian company Troll Tech ( http://www.trolltech.com http://www.trolltech.com ) first introduced Qt as a commercial product in 1995.
• The set of Qt classes is quite robust. The Qt classes include everything from basic window controls, drag and drop, and internationalization to network programming.
• The QObject Class; All but about a dozen of the Qt classes inherit from the base class QObject. This means that virtually every class in the Qt library contains the same basic set of methods. The constructor for this class can optionally accept the address of a parent object, and a character string that assigns the object a name:

  QObject(QObject *parent = 0, const char *name = 0);
  

• The MOC Compiler; One feature used by developers is the Meta Object Compiler (also called the MOC compiler).
  • The MOC compiler reads your source code and generates special C++ source files for you to compile and link along with your application.
  • These special files contain the code necessary for one object to emit a ``signal'' that is received by a ``slot'' in one or more other objects. This is the method used to asynchronously transmit information from one object to another within an application.
  • The MOC compiler is triggered by the presence of the Q_OBJECT macro within a class definition to determine whether to generate code, and what code is generated.
  • The resulting source code can be either compiled separately and linked, or simply included in your code with the #include directive.
  • Using the MOC compiler not only activates the signals and slots, but also generates code that enables some special methods that are defined in every Qt class (and thus, by inheritance, in every object in your program). These special methods are defined in the QtObject class.