mqttsubscribe

Subscribe to a topic.

Attention: Valid only with Altair Communication Extension.

Syntax

[mid,status,messageinfo] = mqttsubscribe(clientid, topic, qos)

Inputs

clientid
client id, an output of mqttclient.
Type: string
topic
topic to be subscribe.
Type: string
qos
the requested Quality of Service for this subscription, valid options are 0,1,2.
Type: scalar
qos = 0:
This level guarantees a best-effort delivery. There is no guarantee of delivery. The recipient does not acknowledge receipt of the message and the message is not stored and re-transmitted by the sender.
qos = 1:
This level guarantees that a message is delivered at least one time to the receiver. The sender stores the message until it gets a PUBACK packet from the receiver that acknowledges receipt of the message. It is possible for a message to be sent or delivered multiple times.
qos = 2:
This level guarantees that each message is received only once by the intended recipients. It is the safest and slowest quality of service level.

Outputs

mid
message id of publish command.
Type: scalar
status
status return codes.
Type: scalar
messageinfo
description of publish status flag
Type: string
status = 0:
on success.
status = 1:
out of memory condition occurred.
status = 3:
input parameters were invalid.
status = 4:
client isn’t connected to a broker.
status = 18:
topic is not valid UTF-8.
status = 25:
resulting packet is larger than supported by the broker.

Examples

subscribe to a given topic 
cld = mqttclient('test.mosquitto.org','port',1883);
[mid, rc, Mqttmessageinfo] = mqttsubscribe(cld, 'topic100',2)
mid = 1
rc = 0
Mqttmessageinfo = success
subscribe to a topic with on_subscribe callback 
function test_subscribecallback(clientid, mid, grant_qos)
		printf('Subscribe callback is triggered successfully\n');
		printf('message id: %s\n', num2str(mid));
		printf('grant_qos: %s\n', num2str(grant_qos));
end
cld = mqttclient('test.mosquitto.org','port',1883,'on_subscribe','test_subscribecallback');
[mid, rc, Mqttmessageinfo] = mqttsubscribe(cld, 'topic100',2)
mid = 1
rc = 0
Mqttmessageinfo = success
Subscribe callback is triggered successfully
message id: 1
grant_qos: 1