callback

[openstep]

Could you show an example callback?
I have like this but not working.
Also could you please explain the difference between this (MQTTPubSubClient.h) and the PubSubClient.h ?
Thx

part of code in setup()

    // subscribe callback which is called when every packet has come
    mqtt.subscribe([](const String& topic, const String& payload, const size_t size) {
        Serial.println("mqtt received: " + topic + " - " + payload);
    });

void callback(char *topic, byte *payload, unsigned int length) {
    Serial.print("Message arrived in topic: ");
    Serial.println(topic);
    Serial.print("Message:");
    String message; //csaba
    for (int i = 0; i < length; i++) {
        message += (char) payload[i]; 
        Serial.print((char) payload[i]);
    }

}

[hideakitai]

A Callback for every packet should be this form:

void my_callback(const String& topic, const String& payload, const size_t size);
// or
void my_callback(const char* topic, const char* payload, const size_t size);