Topic Commands

A topic command tells QDoc which source code element is being documented. Some topic commands allow you to create documentation pages that aren't tied to any underlying source code element.

When QDoc processes a QDoc comment, it tries to connect the comment to an element in the source code by first looking for a topic command that names the source code element. If there is no topic command, QDoc tries to connect the comment to the source code element that immediately follows the comment. If it can't do either of these and if there is no topic command that indicates the comment does not have an underlying source code element (e.g. \page), then the comment is discarded.

The name of the entity being documented is usually the only argument for a topic command. Use the complete name. Sometimes there can be a second parameter in the argument. See e.g. \page.

\enum QComboBox::InsertPolicy

The \fn command is a special case. For the \fn command, use the function's signature including the class qualifier.

\fn void QGraphicsWidget::setWindowFlags(Qt::WindowFlags wFlags)

A topic command can appear anywhere in a comment but must stand alone on its own line. It is good practice is to let the topic command be the first line of the comment. If the argument spans several lines, make sure that each line (except the last one) is ended with a backslash. Moreover, QDoc counts parentheses, which means that if it encounters a '(' it considers everything until the closing ')' as its argument.

If a topic command is repeated with different arguments, the same documentation will appear for both the units.

/*!
    \fn void PreviewWindow::setWindowFlags()
    \fn void ControllerWindow::setWindowFlags()

    Sets the widgets flags using the QWidget::setWindowFlags()
    function.

    Then runs through the available window flags, creating a text
    that contains the names of the flags that matches the flags
    parameter, displaying the text in the widgets text editor.
*/

The PreviewWindow::setWindowFlags() and ControllerWindow::setWindowFlags() functions will get the same documentation.

Nomenclature for files generated by topic commands

For many topic commands, such as \page, QDoc generates a file when processing the documentation.

QDoc normalizes the name of each file before writing it to disk. The following operations are performed:

• All sequences of non alphanumeric characters are replaced with a hyphen, '-'.
• All uppercase letters are replaced with their lowercase equivalent.
• All trailing hyphens are removed.

For example, the following command generates a file named this-generates-a-file-and-writes-it-to-disk.html:

\page this_generates_a_file_(and_writes_it_to_DISK)-.html

As the example shows, the name that is given to the file in the command might differ from the name of the actual file that is written to disk.

Prefixes and Suffixes for generated files

When QDoc generates a file, it may add a prefix, a suffix, or both, depending on the element that the file will document.

The table below shows what those prefixes and suffixes are for various elements.

\class

The \class command is for documenting a C++ class, a C/C++ struct, or a union. The argument is the complete, qualified name of the class. The command tells QDoc that a class is part of the public API, and lets you enter a detailed description.

/*!
    \class QMap::iterator
    \inmodule QtCore

    \brief The QMap::iterator class provides an STL-style
    non-const iterator for QMap and QMultiMap.

    QMap features both \l{STL-style iterators} and
    \l{Java-style iterators}. The STL-style iterators ...
*/

The HTML documentation for the named class is written to a .html file named from the class name, in lower case, and with the double colon qualifiers replaced with '-'. For example, the documentation for the QMap::iterator class is written to qmap-iterator.html.

The file contains the class description from the \class comment, plus the documentation generated from QDoc comments for all the class members: a list of the class's types, properties, functions, signals, and slots.

In addition to the detailed description of the class, the \class comment typically contains an \inmodule command, as well as a \brief description. Here is a very simple example:

/*!
    \class PreviewWindow
    \inmodule CustomWidgets
    \brief The PreviewWindow class is a custom widget.
           displaying the names of its currently set
           window flags in a read-only text editor.

    \ingroup miscellaneous

    The PreviewWindow class inherits QWidget. The widget
    displays the names of its window flags set with the \l
    {function} {setWindowFlags()} function. It is also
    provided with a QPushButton that closes the window.

    ...

    \sa QWidget
*/

The way QDoc renders this \class depends on your style.css file.

\enum

The \enum command is for documenting a C++ enum type. The argument is the full name of the enum type.

The enum values are documented in the \enum comment using the \value command. If an enum value is not documented with \value, QDoc emits a warning. These warnings can be avoided using the \omitvalue command to tell QDoc that an enum value should not be documented. The enum documentation will be included on the class reference page, header file page, or namespace page where the enum type is defined. For example, consider the enum type Corner in the Qt namespace:

enum Corner {
    TopLeftCorner = 0x00000,
    TopRightCorner = 0x00001,
    BottomLeftCorner = 0x00002,
    BottomRightCorner = 0x00003
#if defined(QT3_SUPPORT) && !defined(Q_MOC_RUN)
    ,TopLeft = TopLeftCorner,
    TopRight = TopRightCorner,
    BottomLeft = BottomLeftCorner,
    BottomRight = BottomRightCorner
#endif
};

This enum can be cocumented this way:

/*!
    \enum Qt::Corner

    This enum type specifies a corner in a rectangle:

    \value TopLeftCorner
           The top-left corner of the rectangle.
    \value TopRightCorner
           The top-right corner of the rectangle.
    \value BottomLeftCorner
           The bottom-left corner of the rectangle.
    \value BottomRightCorner
           The bottom-right corner of the rectangle.

    \omitvalue TopLeft
    \omitvalue TopRight
    \omitvalue BottomLeft
    \omitvalue BottomRight
               Bottom-right (omitted; not documented).
*/

Note the inclusion of the namespace qualifier.

See also \value and \omitvalue.

\example

The \example command is for documenting an example. The argument is the example's path relative to one of the paths listed in the exampledirs variable in the QDoc configuration file.

The documentation page will be output to modulename-path-to-example.html. QDoc will add a list of all the example's source and images files at the end of the page, unless \noautolist command is used or the configuration variable url.examples is defined for the project.

For example, if exampledirs contains $QTDIR/examples/widgets/imageviewer, then

/*!
    \example widgets/imageviewer
    \title ImageViewer Example
    \subtitle

    The example shows how to combine QLabel and QScrollArea
    to display an image.

    ...
*/

See also: \noautolist, url.examples, \meta

\externalpage

The \externalpage command assigns a title to an external URL.

/*!
    \externalpage http://doc.qt.io/
    \title Qt Documentation Site
*/

This allows you to include a link to the external page in your documentation this way:

/*!
    At the \l {Qt Documentation Site} you can find the latest
    documentation for Qt, Qt Creator, the Qt SDK and much more.
*/

To achieve the same result without using the \externalpage command, you would have to hard-code the address into your documentation:

/*!
    At the \l {http://doc.qt.io/}{Qt Documentation Site}
    you can find the latest documentation for Qt, Qt Creator, the Qt SDK
    and much more.
*/

The \externalpage command makes it easier to maintain the documentation. If the address changes, you only need to change the argument of the \externalpage command.

\fn (function)

The \fn command is for documenting a function. The argument is the function's signature, including its template parameters (if any), return type, const-ness, and list of formal arguments with types. If the named function doesn't exist, QDoc emits a warning.

Since QDoc version 6.0, the \fn command can be used for documenting class members that are not explicitly declared in the header, but are implicitly generated by the compiler; default constructor and destructor, copy constructor and move-copy constructor, assignment operator, and move-assignment operator.

When documenting an hidden friend, it is required to prepend the enclosing class name to the function name. For example, for:

class Foo {
   ...
   friend bool operator==(const Foo&, const Foo&) { ... }
   ...
}

The command should be written as "\fn Foo::operator==(const Foo&, const Foo&)" and not as the free function "\fn operator==(const Foo&, const Foo&)".

Failure to do so will have QDoc complaining about being unable to resolve the function.

/*!
    \fn bool QToolBar::isAreaAllowed(Qt::ToolBarArea area) const

    Returns \c true if this toolbar is dockable in the given
    \a area; otherwise returns \c false.
*/

See also \overload.

\group

The \group command creates a separate page that lists the classes, pages, or other entities belonging to a named group. The argument is the group name.

A class is included in a group by using the \ingroup command. Overview pages can also be related to a group using the same command, but the list of overview pages must be requested explicitly using the \generatelist command (see example below).

The \group command is typically followed by a \title command and a short introduction to the group. The HTML page for the group is written to an .html file named <lower-case-group-name>.html.

Each entity in the group is listed as a link (using page title or class name), followed by a decription from the \brief command in the entity's documentation.

/*!
    \group io
    \title Input/Output and Networking
*/

QDoc generates a group page io.html.

Note that overview pages related to the group must be listed explicitly using the \generatelist command with the related argument.

/*!
    \group architecture

    \title Architecture

    These documents describe aspects of Qt's architecture
    and design, including overviews of core Qt features and
    technologies.

    \generatelist{related}
*/

See also \ingroup, \annotatedlist, \generatelist, and \noautolist.

\headerfile

The \headerfile command is for documenting the global functions, types and macros that are declared in a header file, but not in a namespace. The argument is the name of the header file. The HTML page is written to a .html file constructed from the header file argument.

The documentation for a function, type, or macro that is declared in the header file being documented, is included in the header file page using the \relates command.

If the argument doesn't exist as a header file, the \headerfile command creates a documentation page for the header file anyway.

/*!
   \headerfile <QtAlgorithms>

   \title Generic Algorithms

   \brief The <QtAlgorithms> header file provides
    generic template-based algorithms.

   Qt provides a number of global template functions in \c
   <QtAlgorithms> that work on containers and perform
   well-know algorithms.
*/

QDoc generates a header file page, qtalgorithms.html.

See also \inheaderfile.

\macro

The \macro command is for documenting a C++ macro. The argument is the macro in one of three styles: function-like macros like Q_ASSERT(), declaration-style macros like Q_PROPERTY(), and macros without parentheses like Q_OBJECT.

The \macro comment must contain a \relates command that attaches the macro comment to a class, header file, or namespace. Otherwise, the documentation will be lost.

\module

The \module creates a page that lists the classes belonging to the module specified by the command's argument. A class included in the module by including the \inmodule command in the \class comment.

The \module command is typically followed by a \title and a \brief command. Each class is listed as a link to the class reference page followed by the text from the class's \brief command. For example:

/*!
    \module QtNetwork

    \title Qt Network Module

    \brief Contains classes for writing TCP/IP clients and servers.

    The network module provides classes to make network
    programming easier and portable. It offers both
    high-level classes such as QNetworkAccessManager that
    implements application-level protocols, and
    lower-level classes such as QTcpSocket, QTcpServer, and
    QUdpSocket.
*/

The \noautolist command can be used here to omit the automatically generated list of classes at the end.

See also \inmodule

\namespace

The \namespace command is for documenting the contents of the C++ namespace named as its argument. The reference page QDoc generates for a namespace is similar to the reference page it generates for a C++ class.

/*!
    \namespace Qt

    \brief Contains miscellaneous identifiers used throughout the Qt library.
*/

Note that in C++, a particular namespace can be used in more than one module, but when C++ elements from different modules are declared in the same namespace, the namespace itself must be documented in one module only. For example, namespace Qt in the example above contains types and functions from both QtCore and QtGui, but it is documented with the \namespace command only in QtCore.

\page

The \page command is for creating a stand-alone documentation page.

The \page command expects a single argument that represents the name of the file where QDoc should store the page.

The page title is set using the \title command.

/*!
   \page aboutqt.html

   \title About Qt

   Qt is a C++ toolkit for cross-platform GUI
   application development. Qt provides single-source
   portability across Microsoft Windows, macOS, Linux,
   and all major commercial Unix variants.

   Qt provides application developers with all the
   functionality needed to build applications with
   state-of-the-art graphical user interfaces. Qt is fully
   object-oriented, easily extensible, and allows true
   component programming.

   ...
*/

QDoc renders this page in aboutqt.html.

\property

The \property command is for documenting a Qt property. The argument is the full property name.

A property is defined using the Q_PROPERTY() macro. The macro takes as arguments the property's name and its set, reset and get functions.

Q_PROPERTY(QString state READ state WRITE setState)

The set, reset and get functions don't need to be documented, documenting the property is sufficient. QDoc will generate a list of the access function that will appear in the property documentation which in turn will be located in the documentation of the class that defines the property.

The \property command comment typically includes a \brief command. For properties the \brief command's argument is a sentence fragment that will be included in a one line description of the property. The command follows the same rules for the description as the \variable command.

/*!
    \property QPushButton::flat
    \brief Whether the border is disabled.

    This property's default is false.
*/

\qmlattachedproperty

The \qmlattachedproperty command is for documenting a QML property that will be attached to some QML type. See Attached Properties. The argument is the rest of the line. It must start with the property type, followed by the QML type name where the property is declared, the :: qualifier, and finally the property name.

For example, to document a boolean QML attached property named isCurrentItem for the ListView type:

/*!
    \qmlattachedproperty bool ListView::isCurrentItem

    This attached property is \c true if this delegate is the current
    item; otherwise false.

    It is attached to each instance of the delegate.

    This property may be used to adjust the appearance of the current
    item, for example:

    \snippet doc/src/snippets/declarative/listview/listview.qml isCurrentItem
*/

QDoc includes this attached property on the QML reference page for the ListView type.

\qmlattachedsignal

The \qmlattachedsignal command is for documenting an attachable signal. The \qmlattachedsignal command is used just like the \qmlsignal command.

The argument is the rest of the line. It should be the name of the QML type where the signal is declared, the :: qualifier, and finally the signal name. For example, a QML attached signal named add() in the GridView element is documented like this:

/*!
    \qmlattachedsignal GridView::add()
    This attached signal is emitted immediately after an item is added to the view.
*/

QDoc includes this documentation on the QML reference page for the GridView element.

\qmlvaluetype

The \qmlvaluetype command is for documenting a value type for QML. The command takes a type name as its only argument.

\qmlvaluetype is functionally identical to the \qmltype command. The only difference is that the type will be titled (and grouped) as a QML value type.

\qmlclass

This command is deprecated. Use \qmltype instead.

\qmlmethod

The \qmlmethod command is for documenting a QML method. The argument is the complete method signature, including return type and parameter names and types.

/*!
    \qmlmethod void TextInput::select(int start, int end)

    Causes the text from \a start to \a end to be selected.

    If either start or end is out of range, the selection is not changed.

    After having called this, selectionStart will become the lesser, and
    selectionEnd the greater (regardless of the order passed to this method).

   \sa selectionStart, selectionEnd
*/

QDoc includes this documentation on the element reference page for the TextInput element.

\qmltype

The \qmltype command is for documenting a QML type. The command has one argument, which is the name of the QML type.

If the QML type is instantiated by a C++ class, that class must be specified using the \instantiates context command.

The \inqmlmodule command documents the QML module the type belongs to. The argument passed to this command must match with a documented \qmlmodule page.

/*!
    \qmltype Transform
    \instantiates QGraphicsTransform
    \inqmlmodule QtQuick

    \brief Provides a way to build advanced transformations on Items.

    The Transform element is a base type which cannot be
    instantiated directly.
*/

Here, the \qmltype comment includes \instantiates to specify that a Transform is instantiated by the C++ class QGraphicsTransform. A \qmltype comment should always include a \since command, because all QML types are new. It should also include a \brief description. If a QML type is a member of a QML type group, the \qmltype comment should include one or more \ingroup commands.

\qmlproperty

The \qmlproperty command is for documenting a QML property. The argument is the rest of the line. The argument text should be the property type, followed by the QML type name, the :: qualifier, and finally the property name. If we have a QML property named x in QML type Translate, and the property has type real, the \qmlproperty for it would look like this:

/*!
    \qmlproperty real Translate::x

    The translation along the X axis.
*/

QDoc includes this QML property on the QML reference page for the Translate type.

If the QML property is of enumeration type, or it holds a bit-wise combination of flags, the \value command can be used to document the acceptable values.

QDoc accepts also a fully qualified property name, including the QML module identifier:

\qmlproperty bool QtQuick.Controls::Button::highlighted

If specified, the module identifier (above, QtQuick.Controls) must match with value passed to \inqmlmodule command in the associated \qmltype documentation. If the name of the QML type the property belongs to is unique across all types in the documentation project, the module identifier can be omitted.

\qmlsignal

The \qmlsignal command is for documenting a QML signal. The argument is the rest of the line. The arguments should be: the QML type where the signal is declared, the :: qualifier, and finally the signal name. If we have a QML signal named clicked(), the documentation for it would look like this:

/*!
    \qmlsignal MouseArea::clicked(MouseEvent mouse)

    This signal is emitted when there is a click. A click is defined as a
    press followed by a release, both inside the MouseArea.
*/

QDoc includes this documentation on the QML reference page for the MouseArea type.

\qmlmodule

Use the \qmlmodule command to create a QML module page. A QML module page is a collection of QML types or any related material. The command takes an optional <VERSION> number argument, and is similar to the group-command.

A QML type is associated with a module by adding the \inqmlmodule command to the comment-block that documents the type. You can link to any member of a QML module using the module name and two colons (::) prefix.

/*!
    A link to the TabWidget of the UI Component is \l {UIComponent::TabWidget}.
*/

QDoc generates a page for the module that lists all the members of the module.

/*!
    \qmlmodule ClickableComponents

    This is a list of the Clickable Components set. A Clickable component
    responds to a \c clicked() event.
*/

\inqmlmodule

A QML type is marked as being available under a specific QML module import by inserting the \inqmlmodule command in a \qmltype topic. The command takes the module (import) name, without a version number, as the only argument.

The QML module name must match with a QML module documented with the (\qmlmodule command).

/*!
    \qmltype ClickableButton
    \inqmlmodule ClickableComponents

    A clickable button that responds to the \c click() event.
*/

QDoc outputs a row Import statement: import <qmlmodule> in a table at the top of the QML type reference page.

When linking to QML types, the QML module identifier may appear in the link target. For example:

\l {ClickableComponents::}{ClickableButton}

Links to the type reference page, with ClickableButton as the link text.

\instantiates

The \instantiates command is used in the QML type comment of an elemental QML type to specify the name of the C++ class that instantiates the QML type.

If the QML type is not instantiated by a C++ class, this command is not used.

/*!
    \qmltype Transform
    \instantiates QGraphicsTransform
    \inqmlmodule QtQuick

    \brief Provides a way to build advanced transformations on Items.

    The Transform element is a base type which cannot be
    instantiated directly.
*/

Here, the \qmltype comment includes \instantiates to specify that a Transform is instantiated by the C++ class QGraphicsTransform.

\typealias

The \typealias command is similar to \typedef, but specific to documenting a C++ type alias:

class Foo
{
public:
    using ptr = void*;
// ...
}

This can be documented as

/*!
    \typealias Foo::ptr
*/

The \typealias command was introduced in QDoc 5.15.

See also \typedef.

\typedef

The \typedef command is for documenting a C++ typedef. The argument is the name of the typedef. The documentation for the typedef will be included in the reference documentation for the class, namespace, or header file in which the typedef is declared. To relate the \typedef to a class, namespace, or header file, the \typedef comment must contain a \relates command.

/*!
    \typedef QObjectList
    \relates QObject

    Synonym for QList<QObject>.
*/

Other typedefs are located on the reference page for the class that defines them.

/*!
    \typedef QList::Iterator

    Qt-style synonym for QList::iterator.
*/

See also \typealias.

\variable

The \variable command is for documenting a class member variable or a constant. The argument is the variable or constant name. The \variable command comment includes a \brief command. QDoc generates the documentation based on the text from \brief command.

The documentation will be located in the in the associated class, header file, or namespace documentation.

In case of a member variable:

/*!
    \variable QStyleOption::palette
    \brief The palette that should be used when painting
           the control
*/

You can also document constants with the \variable command. For example, suppose you have the Type and UserType constants in the QTreeWidgetItem class:

enum { Type = 0, UserType = 1000 };

For these, the \variable command can be used this way:

/*!
    \variable QTreeWidgetItem::Type

    The default type for tree widget items.

    \sa UserType, type()
*/

/*!
    \variable QTreeWidgetItem::UserType

    The minimum value for custom types. Values below
    UserType are reserved by Qt.

    \sa Type, type()
*/