The Qt Core Module

Qt 4 is a library consisting of smaller libraries, or modules. The most popular ones are

• core including QObject, QThread, QFile, and so forth
• gui all classes derived from QWidget, and some related classes
• xml for parsing and serializing XML
• sql for communicating with SQL databases
• net for communicating data between hosts on specific protocols (http, tcp, udp)

Except for core, modules need to be "enabled" in qmake project files in order to be used. For example:

QT += xml # to use the xml module
QT += gui # to use QWidgets
QT += sql # to use SQL module

The following section will introduce some of the core library classes.