Adafruit is open, safely ... and shipping all orders at this time! Read more!
0

MQTT Publish topic path variable
Moderators: adafruit_support_bill, adafruit

Forum rules
If you're posting code, please make sure your code does not include your Adafruit IO Active Key or WiFi network credentials.
Please be positive and constructive with your questions and comments.

MQTT Publish topic path variable

by davieswa123 on Mon Jul 08, 2019 5:30 am

Hello;

Is there a way to create a topic path to include a variable? It seems to only accept fixed #define values.

// Notice MQTT paths for Adafruit AIO follow the form: <username>/feeds/<feedname>
Adafruit_MQTT_Publish pubmessage = Adafruit_MQTT_Publish(&mqtt, MQTT_TOPIC_Variable "Gateway/"NodeID);

Any help or an example much appreciated.

W

davieswa123
 
Posts: 2
Joined: Sat Jan 20, 2018 11:58 pm

Re: MQTT Publish topic path variable

by brubell on Mon Jul 08, 2019 10:20 am

The function signature for the Publish method follows the format:

Code: Select all | TOGGLE FULL SIZE
bool Adafruit_MQTT::publish(const char *topic, uint8_t *data, uint16_t bLen, uint8_t qos) {
via https://github.com/adafruit/Adafruit_MQ ... T.cpp#L304

Since topic is a const char, it is immutable and therefore not able to be changed or set to a variable.

brubell
 
Posts: 877
Joined: Fri Jul 17, 2015 10:33 pm

Please be positive and constructive with your questions and comments.