MQTT中回调有什么用？

Question

I am trying to implement a weather monitoring system using Arduino and MQTT protocol. While trying to understand the code behind this, I have come across a function:

void callback(char* topic, byte* payload, unsigned int length) {
}

So, my question is, what exactly is this function used for in MQTT? If someone explains to me or links a tutorial that will be useful. Thanks in advance!

Answer 1

This function is called by the underlying MQTT library when a new message is received from the broker (for a topic you have subscribed to).

It is up to you to fill in the detail of how you want to process the message.