Connect via C SDK

Eclipse Paho C and Eclipse Paho Embedded C are all client libraries in C language (MQTT C Client) under the Eclipse Paho project, and are full-featured MQTT clients written in ANSI C.

Eclipse Paho Embedded C can be used on the desktop operating system, but mainly for embedded environments such as mbed, Arduino and FreeRTOS .

The client has synchronous/asynchronous APIs, which start with MQTTClient and MQTTAsync:

• The synchronous API is designed to be simpler and more useful and some calls will be blocked until the operation is completed, which is easier for programming;
• There is only one calling block API-waitForCompletion in the asynchronous API, which is notified through the callback, and is more suitable for the non-main thread environment.

Paho C Usage example

For detailed descriptions of the comparison, download, and usage of the two MQTT client libraries related to the C language, please move to the project homepage to view. This example contains the complete code of the Paho C in C language connecting to the EMQX, sending and receiving messages:

#include "stdio.h" #include "stdlib.h" #include "string.h"  #include "MQTTClient.h"  #define ADDRESS "tcp://broker.emqx.io:1883" #define CLIENTID "emqx_test" #define TOPIC "testtopic/1" #define PAYLOAD "Hello World!" #define QOS 1 #define TIMEOUT 10000L  int main(int argc, char* argv[]) {  MQTTClient client;  MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;  MQTTClient_message pubmsg = MQTTClient_message_initializer;  MQTTClient_deliveryToken token;  int rc;   MQTTClient_create(&client, ADDRESS, CLIENTID,  MQTTCLIENT_PERSISTENCE_NONE, NULL);    // MQTT Connection parameters  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);  exit(-1);  }    // Publish message  pubmsg.payload = PAYLOAD;  pubmsg.payloadlen = strlen(PAYLOAD);  pubmsg.qos = QOS;  pubmsg.retained = 0;  MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);  printf("Waiting for up to %d seconds for publication of %s\n"  "on topic %s for client with ClientID: %s\n",  (int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID);  rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);  printf("Message with delivery token %d delivered\n", token);    // Disconnect  MQTTClient_disconnect(client, 10000);  MQTTClient_destroy(&client);  return rc; }

Paho C MQTT 5.0 support

Paho C has fully supported MQTT 5.0 Currently.