Paho MQTT C Client Library: Asynchronous subscription example

| Paho MQTT C Client Library

Asynchronous subscription example
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#define ADDRESS "tcp://mqtt.eclipseprojects.io: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)
{
printf("Message arrived\n");
printf(" topic: %s\n", topicName);
printf(" message: %.*s\n", message->payloadlen, (char*)message->payload);
MQTTClient_freeMessage(&message);
MQTTClient_free(topicName);
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;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
int rc;
if ((rc = MQTTClient_create(&client, ADDRESS, CLIENTID,
MQTTCLIENT_PERSISTENCE_NONE, NULL)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to create client, return code %d\n", rc);
rc = EXIT_FAILURE;
goto exit;
}
if ((rc = MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to set callbacks, return code %d\n", rc);
rc = EXIT_FAILURE;
goto destroy_exit;
}
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to connect, return code %d\n", rc);
rc = EXIT_FAILURE;
goto destroy_exit;
}
printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
"Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
if ((rc = MQTTClient_subscribe(client, TOPIC, QOS)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to subscribe, return code %d\n", rc);
rc = EXIT_FAILURE;
}
else
{
int ch;
do
{
ch = getchar();
} while (ch!='Q' && ch != 'q');
if ((rc = MQTTClient_unsubscribe(client, TOPIC)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to unsubscribe, return code %d\n", rc);
rc = EXIT_FAILURE;
}
}
if ((rc = MQTTClient_disconnect(client, 10000)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to disconnect, return code %d\n", rc);
rc = EXIT_FAILURE;
}
destroy_exit:
MQTTClient_destroy(&client);
exit:
return rc;
}
MQTTClient.h
MQTTClient_disconnect
int MQTTClient_disconnect(MQTTClient handle, int timeout)
MQTTClient_free
void MQTTClient_free(void *ptr)
MQTTClient_deliveryToken
int MQTTClient_deliveryToken
Definition: MQTTClient.h:262
MQTTClient
void * MQTTClient
Definition: MQTTClient.h:251
MQTTClient_create
int MQTTClient_create(MQTTClient *handle, const char *serverURI, const char *clientId, int persistence_type, void *persistence_context)
MQTTClient_subscribe
int MQTTClient_subscribe(MQTTClient handle, const char *topic, int qos)
MQTTClient_unsubscribe
int MQTTClient_unsubscribe(MQTTClient handle, const char *topic)
MQTTClient_connect
int MQTTClient_connect(MQTTClient handle, MQTTClient_connectOptions *options)
MQTTClient_setCallbacks
int MQTTClient_setCallbacks(MQTTClient handle, void *context, MQTTClient_connectionLost *cl, MQTTClient_messageArrived *ma, MQTTClient_deliveryComplete *dc)
MQTTClient_freeMessage
void MQTTClient_freeMessage(MQTTClient_message **msg)
MQTTCLIENT_SUCCESS
#define MQTTCLIENT_SUCCESS
Definition: MQTTClient.h:132
MQTTClient_destroy
void MQTTClient_destroy(MQTTClient *handle)
MQTTClient_connectOptions_initializer
#define MQTTClient_connectOptions_initializer
Definition: MQTTClient.h:982
MQTTCLIENT_PERSISTENCE_NONE
#define MQTTCLIENT_PERSISTENCE_NONE
Definition: MQTTClientPersistence.h:74
MQTTClient_connectOptions
Definition: MQTTClient.h:825
MQTTClient_connectOptions::cleansession
int cleansession
Definition: MQTTClient.h:870
MQTTClient_connectOptions::keepAliveInterval
int keepAliveInterval
Definition: MQTTClient.h:848
MQTTClient_message
Definition: MQTTClient.h:272
MQTTClient_message::payload
void * payload
Definition: MQTTClient.h:281
MQTTClient_message::payloadlen
int payloadlen
Definition: MQTTClient.h:279