Paho MQTT C Client Library
Asynchronous subscription example
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#define ADDRESS "tcp://localhost:1883"
#define CLIENTID "ExampleClientSub"
#define TOPIC "MQTT Examples"
#define PAYLOAD "Hello World!"
#define QOS 1
#define TIMEOUT 10000L
volatile MQTTClient_deliveryToken deliveredtoken;
void delivered(void *context, MQTTClient_deliveryToken dt)
printf("Message with token value %d delivery confirmed\n", dt);
deliveredtoken = dt;
int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message)
int i;
char* payloadptr;
printf("Message arrived\n");
printf(" topic: %s\n", topicName);
printf(" message: ");
payloadptr = message->payload;
for(i=0; i<message->payloadlen; i++)
return 1;
void connlost(void *context, char *cause)
printf("\nConnection lost\n");
printf(" cause: %s\n", cause);
int main(int argc, char* argv[])
MQTTClient client;
int rc;
int ch;
MQTTClient_create(&client, ADDRESS, CLIENTID,
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
printf("Failed to connect, return code %d\n", rc);
printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
"Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
MQTTClient_subscribe(client, TOPIC, QOS);
ch = getchar();
} while(ch!='Q' && ch != 'q');
MQTTClient_disconnect(client, 10000);
return rc;