QCoreApplication Class

The event loop is started with a call to exec(). Long-running operations can call processEvents() to keep the application responsive.

In general, we recommend that you create a QCoreApplication, QGuiApplication or a QApplication object in your main() function as early as possible. exec() will not return until the event loop exits; e.g., when quit() is called.

Several static convenience functions are also provided. The QCoreApplication object is available from instance(). Events can be sent with sendEvent() or posted to an event queue with postEvent(). Pending events can be removed with removePostedEvents() or dispatched with sendPostedEvents().

The class provides a quit() slot and an aboutToQuit() signal.

An application has an applicationDirPath() and an applicationFilePath(). Library paths (see QLibrary) can be retrieved with libraryPaths() and manipulated by setLibraryPaths(), addLibraryPath(), and removeLibraryPath().

Translation files can be added or removed using installTranslator() and removeTranslator(). Application strings can be translated using translate(). The QObject::tr() function is implemented in terms of translate().

The command line arguments which are passed to QCoreApplication's constructor should be accessed using the arguments() function.

For more advanced command line option handling, create a QCommandLineParser.

On Unix/Linux Qt is configured to use the system locale settings by default. This can cause a conflict when using POSIX functions, for instance, when converting between data types such as floats and strings, since the notation may differ between locales. To get around this problem, call the POSIX function setlocale(LC_NUMERIC,"C") right after initializing QApplication, QGuiApplication or QCoreApplication to reset the locale that is used for number formatting to "C"-locale.

See also QGuiApplication, QAbstractEventDispatcher, QEventLoop, Semaphores Example, Wait Conditions Example

This property holds the name of this application

The value is used by the QSettings class when it is constructed using the empty constructor. This saves having to repeat this information each time a QSettings object is created.

If not set, the application name defaults to the executable name (since 5.0).

Access functions:

• applicationName()

• void setApplicationName(const &application)

Notifier signal:

• void applicationNameChanged()

See Also▲

This property holds the version of this application

If not set, the application version defaults to a platform-specific value determined from the main application executable or package (since Qt 5.9):

On other platforms, the default is the empty string.

Access functions:

• applicationVersion()

• void setApplicationVersion(const &version)

Notifier signal:

• void applicationVersionChanged()

See Also▲

This property holds the Internet domain of the organization that wrote this application

The value is used by the QSettings class when it is constructed using the empty constructor. This saves having to repeat this information each time a QSettings object is created.

On Mac, QSettings uses organizationDomain() as the organization if it's not an empty string; otherwise it uses organizationName(). On all other platforms, QSettings uses organizationName() as the organization.

Access functions:

• organizationDomain()

• void setOrganizationDomain(const &orgDomain)

Notifier signal:

• void organizationDomainChanged()

See Also▲

This property holds the name of the organization that wrote this application

The value is used by the QSettings class when it is constructed using the empty constructor. This saves having to repeat this information each time a QSettings object is created.

On Mac, QSettings uses organizationDomain() as the organization if it's not an empty string; otherwise it uses organizationName(). On all other platforms, QSettings uses organizationName() as the organization.

Access functions:

• organizationName()

• void setOrganizationName(const &orgName)

Notifier signal:

• void organizationNameChanged()

See Also▲

This property holds whether the use of the QEventLoopLocker feature can cause the application to quit.

The default is true.

Access functions:

• bool isQuitLockEnabled()

• void setQuitLockEnabled(bool enabled)

See Also▲

Constructs a Qt core application. Core applications are applications without a graphical user interface. Such applications are used at the console or as server processes.

The argc and argv arguments are processed by the application, and made available in a more convenient form by the arguments() function.

Destroys the QCoreApplication object.

This signal is emitted when the application is about to quit the main event loop, e.g. when the event loop level drops to zero. This may happen either after a call to quit() from inside the application or when the user shuts down the entire desktop session.

The signal is particularly useful if your application has to do some last-second cleanup. Note that no user interaction is possible in this state.

See Also▲

Prepends path to the beginning of the library path list, ensuring that it is searched for libraries first. If path is empty or already in the path list, the path list is not changed.

The default path list consists of one or two entries. The first is the installation directory for plugins, which is INSTALL/plugins, where INSTALL is the directory where Qt was installed. The second is the application's own directory (not the current directory), but only after the QCoreApplication object is instantiated.

The library paths are reset to the default when an instance of QCoreApplication is destructed.

See Also▲

Returns the directory that contains the application executable.

For example, if you have installed Qt in the C:\Qt directory, and you run the regexp example, this function will return "C:/Qt/examples/tools/regexp".

On macOS and iOS this will point to the directory actually containing the executable, which may be inside an application bundle (if the application is bundled).

See Also▲

Returns the file path of the application executable.

For example, if you have installed Qt in the /usr/local/qt directory, and you run the regexp example, this function will return "/usr/local/qt/examples/tools/regexp/regexp".

See Also▲

Returns the current process ID for the application.

Returns the list of command-line arguments.

Usually arguments().at(0) is the program name, arguments().at(1) is the first argument, and arguments().last() is the last argument. See the note below about Windows.

Calling this function is slow - you should store the result in a variable when parsing the command line.

On Windows, the list is built from the argc and argv parameters only if modified argv/argc parameters are passed to the constructor. In that case, encoding problems might occur.

Otherwise, the arguments() are constructed from the return value of GetCommandLine(). As a result of this, the string given by arguments().at(0) might not be the program name on Windows, depending on how the application was started.

See Also▲

Returns true if the application objects are being destroyed; otherwise returns false.

See Also▲

Reimplements: QObject::event(QEvent *e).

Returns a pointer to the event dispatcher object for the main thread. If no event dispatcher exists for the thread, this function returns nullptr.

See Also▲