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subscribe ā Subscription example
#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://mqtt.eclipse.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("0onnection lost0); if (cause) printf(" cause: %s0, cause); printf("Reconnecting0); conn_opts.keepAliveInterval = 20; conn_opts.cleansession = 1; if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS) { printf("Failed to start connect, return code %d0, rc); finished = 1; } } int msgarrvd(void *context, char *topicName, int topicLen, MQTTAsync_message *message) { printf("Message arrived0); printf(" topic: %s0, topicName); printf(" message: %.*s0, message->payloadlen, (char*)message->payload); MQTTAsync_freeMessage(&message); MQTTAsync_free(topicName); return 1; } void onDisconnectFailure(void* context, MQTTAsync_failureData* response) { printf("Disconnect failed, rc %d0, response->code); disc_finished = 1; } void onDisconnect(void* context, MQTTAsync_successData* response) { printf("Successful disconnection0); disc_finished = 1; } void onSubscribe(void* context, MQTTAsync_successData* response) { printf("Subscribe succeeded0); subscribed = 1; } void onSubscribeFailure(void* context, MQTTAsync_failureData* response) { printf("Subscribe failed, rc %d0, response->code); finished = 1; } void onConnectFailure(void* context, MQTTAsync_failureData* response) { printf("Connect failed, rc %d0, 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 connection0); printf("Subscribing to topic %s0or client %s using QoS%d0n" "Press Q<Enter> to quit0n", 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 %d0, 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 %d0, rc); rc = EXIT_FAILURE; goto exit; } if ((rc = MQTTAsync_setCallbacks(client, client, connlost, msgarrvd, NULL)) != MQTTASYNC_SUCCESS) { printf("Failed to set callbacks, return code %d0, 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 %d0, 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 %d0, 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; }
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Tue Sep 14 2021 Paho Asynchronous MQTT C Client Library