QMqttTopicFilter Class

The QMqttTopicFilter class represents a MQTT topic filter. More...

Header: #include <QMqttTopicFilter>
qmake: QT += mqtt

Note: All functions in this class are reentrant.

Public Types

enum MatchOption { NoMatchOption, WildcardsDontMatchDollarTopicMatchOption }
flags MatchOptions

Public Functions

QMqttTopicFilter(const QMqttTopicFilter &filter)
QMqttTopicFilter(const QLatin1String &filter)
QMqttTopicFilter(const QString &filter = QString())
QMqttTopicFilter &operator=(const QMqttTopicFilter &filter)
QString filter() const
bool isValid() const
bool match(const QMqttTopicName &name, QMqttTopicFilter::MatchOptions matchOptions = NoMatchOption) const
void setFilter(const QString &filter)
QString sharedSubscriptionName() const
void swap(QMqttTopicFilter &other)
QDataStream &operator<<(QDataStream &out, const QMqttTopicFilter &filter)
QDataStream &operator>>(QDataStream &in, QMqttTopicFilter &filter)

Detailed Description

QMqttTopicFilter is a thin wrapper around a QString providing an expressive data type for MQTT topic filters. Beside the benefits of having a strong type preventing unintended misuse, QMqttTopicFilter provides convenient functions related to topic filters like isValid() or match().

For example, the following code would fail to compile and prevent a possible unintended and meaningless matching of two filters, especially if the variable names were less expressive:

QMqttTopicFilter globalFilter{"foo/#"};
QMqttTopicFilter specificFilter{"foo/bar"};
if (globalFilter.match(specificFilter)) {

The usability, however, is not affected since the following snippet compiles and runs as expected:

QMqttTopicFilter globalFilter{"foo/#"};
if (globalFilter.match("foo/bar")) {

See also QMqttTopicName.

Member Type Documentation

enum QMqttTopicFilter::MatchOption
flags QMqttTopicFilter::MatchOptions

This enum value holds the matching options for the topic filter.

QMqttTopicFilter::NoMatchOption0x0000No match options are set.
QMqttTopicFilter::WildcardsDontMatchDollarTopicMatchOption0x0001A wildcard at the filter's beginning does not match a topic name that starts with the dollar sign ($).

The MatchOptions type is a typedef for QFlags<MatchOption>. It stores an OR combination of MatchOption values.

Member Function Documentation

QMqttTopicFilter::QMqttTopicFilter(const QMqttTopicFilter &filter)

Creates a new MQTT topic filter as a copy of filter.

QMqttTopicFilter::QMqttTopicFilter(const QLatin1String &filter)

Creates a new MQTT topic filter with the specified filter.

QMqttTopicFilter::QMqttTopicFilter(const QString &filter = QString())

Creates a new MQTT topic filter with the specified filter.

QMqttTopicFilter &QMqttTopicFilter::operator=(const QMqttTopicFilter &filter)

Assigns the MQTT topic filter filter to this object, and returns a reference to the copy.


Destroys the QMqttTopicFilter object.

QString QMqttTopicFilter::filter() const

Returns the topic filter.

See also setFilter().

bool QMqttTopicFilter::isValid() const

Returns true if the topic filter is valid according to the MQTT standard section 4.7, or false otherwise.

bool QMqttTopicFilter::match(const QMqttTopicName &name, QMqttTopicFilter::MatchOptions matchOptions = NoMatchOption) const

Returns true if the topic filter matches the topic name name honoring the given matchOptions, or false otherwise.

void QMqttTopicFilter::setFilter(const QString &filter)

Sets the topic filter to filter.

See also filter().

[since 5.12] QString QMqttTopicFilter::sharedSubscriptionName() const

Returns the name of a share if the topic filter has been specified as a shared subscription. The format of shared subscriptions is defined as $share/sharename/topicfilter.

This function was introduced in Qt 5.12.

void QMqttTopicFilter::swap(QMqttTopicFilter &other)

Swaps the MQTT topic filter other with this MQTT topic filter. This operation is very fast and never fails.

Related Non-Members

QDataStream &operator<<(QDataStream &out, const QMqttTopicFilter &filter)

Writes the topic filter filter to the stream out and returns a reference to the stream.

See also Format of the QDataStream operators.

QDataStream &operator>>(QDataStream &in, QMqttTopicFilter &filter)

Reads a topic filter into filter from the stream in and returns a reference to the stream.

See also Format of the QDataStream operators.

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