.TH "subscribe" 3 "Sat Aug 16 2025 14:15:23" "Paho Asynchronous MQTT C Client Library" \" -*- nroff -*-
.ad l
.nh
.SH NAME
subscribe \- Subscription example 
.PP

.PP
.nf
#include <stdio\&.h>
#include <stdlib\&.h>
#include <string\&.h>
#include "MQTTAsync\&.h"

#if !defined(_WIN32)
#include <unistd\&.h>
#else
#include <windows\&.h>
#endif

#if defined(_WRS_KERNEL)
#include <OsWrapper\&.h>
#endif

#define ADDRESS     "tcp://test\&.mosquitto\&.org:1883"
#define CLIENTID    "ExampleClientSub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

int disc_finished = 0;
int subscribed = 0;
int finished = 0;

void connlost(void *context, char *cause)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
        int rc;

        printf("\\nConnection lost\\n");
        if (cause)
                printf("     cause: %s\\n", cause);

        printf("Reconnecting\\n");
        conn_opts\&.keepAliveInterval = 20;
        conn_opts\&.cleansession = 1;
        if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start connect, return code %d\\n", rc);
                finished = 1;
        }
}


int msgarrvd(void *context, char *topicName, int topicLen, MQTTAsync_message *message)
{
    printf("Message arrived\\n");
    printf("     topic: %s\\n", topicName);
    printf("   message: %\&.*s\\n", message\->payloadlen, (char*)message\->payload);
    MQTTAsync_freeMessage(&message);
    MQTTAsync_free(topicName);
    return 1;
}

void onDisconnectFailure(void* context, MQTTAsync_failureData* response)
{
        printf("Disconnect failed, rc %d\\n", response\->code);
        disc_finished = 1;
}

void onDisconnect(void* context, MQTTAsync_successData* response)
{
        printf("Successful disconnection\\n");
        disc_finished = 1;
}

void onSubscribe(void* context, MQTTAsync_successData* response)
{
        printf("Subscribe succeeded\\n");
        subscribed = 1;
}

void onSubscribeFailure(void* context, MQTTAsync_failureData* response)
{
        printf("Subscribe failed, rc %d\\n", response\->code);
        finished = 1;
}


void onConnectFailure(void* context, MQTTAsync_failureData* response)
{
        printf("Connect failed, rc %d\\n", response\->code);
        finished = 1;
}


void onConnect(void* context, MQTTAsync_successData* response)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
        int rc;

        printf("Successful connection\\n");

        printf("Subscribing to topic %s\\nfor client %s using QoS%d\\n\\n"
           "Press Q<Enter> to quit\\n\\n", TOPIC, CLIENTID, QOS);
        opts\&.onSuccess = onSubscribe;
        opts\&.onFailure = onSubscribeFailure;
        opts\&.context = client;
        if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start subscribe, return code %d\\n", rc);
                finished = 1;
        }
}


int main(int argc, char* argv[])
{
        MQTTAsync client;
        MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
        MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
        int rc;
        int ch;

        if ((rc = MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL))
                        != MQTTASYNC_SUCCESS)
        {
                printf("Failed to create client, return code %d\\n", rc);
                rc = EXIT_FAILURE;
                goto exit;
        }

        if ((rc = MQTTAsync_setCallbacks(client, client, connlost, msgarrvd, NULL)) != MQTTASYNC_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;
        conn_opts\&.onSuccess = onConnect;
        conn_opts\&.onFailure = onConnectFailure;
        conn_opts\&.context = client;
        if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start connect, return code %d\\n", rc);
                rc = EXIT_FAILURE;
                goto destroy_exit;
        }

        while (!subscribed && !finished)
                #if defined(_WIN32)
                        Sleep(100);
                #else
                        usleep(10000L);
                #endif

        if (finished)
                goto exit;

        do
        {
                ch = getchar();
        } while (ch!='Q' && ch != 'q');

        disc_opts\&.onSuccess = onDisconnect;
        disc_opts\&.onFailure = onDisconnectFailure;
        if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start disconnect, return code %d\\n", rc);
                rc = EXIT_FAILURE;
                goto destroy_exit;
        }
        while (!disc_finished)
        {
                #if defined(_WIN32)
                        Sleep(100);
                #else
                        usleep(10000L);
                #endif
        }

destroy_exit:
        MQTTAsync_destroy(&client);
exit:
        return rc;
}

.fi
.PP