publish fails when including retained parameter about pubsubclient

[knolleary]

Hi,

this is what you want:

 client.publish(topic, (uint8_t*)msg, 50, true);

There are so many data types and ways the client gets used, providing every combination of every type and argument wouldn't be manageable. That said, it seems reasonable to want to have a publish(string,string,boolean) function that does what you want without having to worry about the length field - I'll add one next time I'm updating the client.

[TotallyInformation]

Huzzah! Thanks Nick, told you my C was rubbish. I hate it with a vengence but at least it works when you can figure it out unlike NODEMCU/LUA which I was fighting every step of the way and gave up when I got an out of memory error on a simple program.

You've also answered my next question which was why my LWT message wasn't getting the retained flag - true not 1!

[TotallyInformation]

Hmm, always too complex!

      IPAddress myAddr = WiFi.localIP();
      snprintf (myIP, 16, "%s.%s.%s.%s", myAddr[0],myAddr[1],myAddr[2],myAddr[3]);
      client.publish(topic, (uint8_t*)myIP, 50, true);

is what finally worked. It publishes the IP address when the device connects to the broker. The LWT changes the same topic to "Offline".

[knolleary]

Have just released v2.3 that introduces a publish(topic,payload,retained) function.

[TotallyInformation]

Ha ha! Cheers, I'll grab it shortly.

[knolleary]

If you do stick with what you've got there, you'll want to use strlen(myIP) rather than 50 - as it won't be a 50 character string.

[Gendiaaa]

If you do stick with what you've got there, you'll want to use strlen(myIP) rather than 50 - as it won't be a 50 character string.

hello Mr Knolleary

i was not able to publish to topic using a retain flag and Qos as this function shows
boolean publish_P(const char* topic, const uint8_t * payload, unsigned int plength, uint8_t qos, boolean retained);
i follow the same same and got this error
C:\Users\gendi\OneDrive\Documents\Arduino\DosingEsp32working in edit\DosingEsp32working in edit.ino:1415:70: error: no matching function for call to 'PubSubClient::publish(char [60], uint8_t*, unsigned int&, int, bool)'
client.publish(buf_topic,(uint8_t*) msg , arrSize, MQTTpubQos, true);
^
In file included from C:\Users\gendi\OneDrive\Documents\Arduino\DosingEsp32working in edit\DosingEsp32working in edit.ino:10:
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:151:12: note: candidate: 'boolean PubSubClient::publish(const char*, const char*)'
boolean publish(const char* topic, const char* payload);
^~~~~~~
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:151:12: note: candidate expects 2 arguments, 5 provided
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:152:12: note: candidate: 'boolean PubSubClient::publish(const char*, const char*, boolean)'
boolean publish(const char* topic, const char* payload, boolean retained);
^~~~~~~
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:152:12: note: candidate expects 3 arguments, 5 provided
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:153:12: note: candidate: 'boolean PubSubClient::publish(const char*, const uint8_t*, unsigned int)'
boolean publish(const char* topic, const uint8_t * payload, unsigned int plength);
^~~~~~~
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:153:12: note: candidate expects 3 arguments, 5 provided
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:154:12: note: candidate: 'boolean PubSubClient::publish(const char*, const uint8_t*, unsigned int, boolean)'
boolean publish(const char* topic, const uint8_t * payload, unsigned int plength, boolean retained);
^~~~~~~
c:\Users\gendi\OneDrive\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:154:12: note: candidate expects 4 arguments, 5 provided

exit status 1

Compilation error: no matching function for call to 'PubSubClient::publish(char [60], uint8_t*, unsigned int&, int, bool)'

any advice to how to publish Qos2 with retain flag set , i am using V2.8