QT MQTT 3.1 vs 5.0

lukutis222

Hello. I would like to understand about QT MQTT module support for mqtt 5.0.

I have managed to sucesfully build simpleclient example:
https://doc.qt.io/qt-6/qtmqtt-simpleclient-example.html

and I do not fully understand whether it is MQTT 3.1 or MQTT 5.0.

From what I understand, the MQTT 5.0 is not backwards compatible with MQTT 3.1 hence if my server is running MQTT 5.0 and QT uses MQTT 3.1, I wont be able to communicate with it, is that correct?

SGaist

You have the QtMqttClient protocolVersion property for that if required.

SGaist

Hi,

Based on the index page, both are supported.

lukutis222

@SGaist

I have noticed that too which is a little bit confusing.

Since 5.0 is not backwards compatible, I cant really find a way on how to configure which MQTT version I want to use in QT. I would expect that I would need to manually choose whether I want to use 3.1 vs 5.0

SGaist

You have the QtMqttClient protocolVersion property for that if required.

lukutis222

@SGaist
You are right.. I missed that completely.

    m_client = new QMqttClient(this);
    m_client->setHostname(ui->lineEditHost->text());
    m_client->setPort(ui->spinBoxPort->value());
    m_client->setProtocolVersion(QMqttClient::MQTT_5_0);

Thank you very much for quick help