QMqttMessage Class | Qt MQTT 6.4.1

- Qt 6.4
- Qt MQTT
- C++ Classes
- QMqttMessage
- Qt 6.4.1 Reference Documentation

# QMqttMessage Class

The QMqttMessage class provides information about a message received from a message broker based on a subscription. More...

Header: | #include <QMqttMessage>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Mqtt) target_link_libraries(mytarget PRIVATE Qt6::Mqtt)
qmake: | QT += mqtt

- List of all members, including inherited members

## Properties

duplicate : const bool id : const quint16 payload : const QByteArray | qos : const quint8 retain : const bool topic : const QMqttTopicName

## Public Functions

| QMqttMessage(const QMqttMessage &other)
| QMqttMessage()
QMqttMessage & | operator=(const QMqttMessage &other)
bool | duplicate() const
quint16 | id() const
const QByteArray & | payload() const
QMqttPublishProperties | publishProperties() const
quint8 | qos() const
bool | retain() const
QMqttTopicName | topic() const
bool | operator!=(const QMqttMessage &other) const
bool | operator==(const QMqttMessage &other) const

## Detailed Description

An MQTT message is created inside the module and returned via the QMqttSubscription::messageReceived() signal.

## Property Documentation

### `[read-only]` duplicate : const bool

This property holds whether the message is a duplicate.

Duplicate messages indicate that the message has been sent earlier, but it has not been confirmed yet. Hence, the broker assumes that it needs to resend to verify the transport of the message itself. Duplicate messages can only occur if the QoS level is one or two.

Access functions:

bool | duplicate() const

### `[read-only]` id : const quint16

This property holds the ID of the message.

IDs are used for messages with a QoS level above zero.

Access functions:

quint16 | id() const

### `[read-only]` payload : const QByteArray

This property holds the payload of a message.

Access functions:

const QByteArray & | payload() const

### `[read-only]` qos : const quint8

This property holds the QoS level of a message.

Access functions:

quint8 | qos() const

### `[read-only]` retain : const bool

This property holds whether the message has been retained.

A retained message is kept on the broker for future clients to subscribe. Consequently, a retained message has been created previously and is not a live update. A broker can store only one retained message per topic.

Access functions:

bool | retain() const

### `[read-only]` topic : const QMqttTopicName

This property holds the topic of a message.

In case a wildcard has been used for a subscription, describes the topic matching this subscription. This property never contains wildcards.

Access functions:

QMqttTopicName | topic() const

## Member Function Documentation

### QMqttMessage::QMqttMessage(const QMqttMessage &other)

Constructs a new MQTT message that is a copy of other.

### QMqttMessage::QMqttMessage()

Creates a new MQTT message.

### QMqttMessage &QMqttMessage::operator=(const QMqttMessage &other)

Makes this object a copy of other and returns the new value of this object.

### `[since 5.12]` QMqttPublishProperties QMqttMessage::publishProperties() const

Returns the publish properties received as part of the message.

Note: This function only specifies the properties when a publish message is received. Messages with a QoS value of 1 or 2 can contain additional properties when a message is released. Those can be obtained by the QMqttClient::messageStatusChanged signal.

Note: This function will only provide valid data when the client specifies QMqttClient::MQTT_5_0 as QMqttClient::ProtocolVersion.

This function was introduced in Qt 5.12.

### bool QMqttMessage::operator!=(const QMqttMessage &other) const

Returns `true` if the message and other are not equal, otherwise returns `false`.

### bool QMqttMessage::operator==(const QMqttMessage &other) const

Returns `true` if the message and other are equal, otherwise returns `false`.