MQTT C Client library

Eclipse Paho CMQTT C Client Library - 图1 (opens new window) and Eclipse Paho Embedded CMQTT C Client Library - 图2 (opens new window) 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 mbedMQTT C Client Library - 图3 (opens new window), ArduinoMQTT C Client Library - 图4 (opens new window) and FreeRTOSMQTT C Client Library - 图5 (opens new window) .

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 Broker, sending and receiving messages:

  1. #include "stdio.h"
  2. #include "stdlib.h"
  3. #include "string.h"
  5. #include "MQTTClient.h"
  7. #define ADDRESS     "tcp://broker.emqx.io:1883"
  8. #define CLIENTID    "emqx_test"
  9. #define TOPIC       "testtopic/1"
  10. #define PAYLOAD     "Hello World!"
  11. #define QOS         1
  12. #define TIMEOUT     10000L
  14. int main(int argc, char* argv[])
  15. {
  16.     MQTTClient client;
  17.     MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
  18.     MQTTClient_message pubmsg = MQTTClient_message_initializer;
  19.     MQTTClient_deliveryToken token;
  20.     int rc;
  22.     MQTTClient_create(&client, ADDRESS, CLIENTID,
  23.         MQTTCLIENT_PERSISTENCE_NONE, NULL);
  25.     // MQTT Connection parameters
  26.     conn_opts.keepAliveInterval = 20;
  27.     conn_opts.cleansession = 1;
  29.     if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
  30.     {
  31.         printf("Failed to connect, return code %d\n", rc);
  32.         exit(-1);
  33.     }
  35.     // Publish message
  36.     pubmsg.payload = PAYLOAD;
  37.     pubmsg.payloadlen = strlen(PAYLOAD);
  38.     pubmsg.qos = QOS;
  39.     pubmsg.retained = 0;
  40.     MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
  41.     printf("Waiting for up to %d seconds for publication of %s\n"
  42.             "on topic %s for client with ClientID: %s\n",
  43.             (int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID);
  44.     rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
  45.     printf("Message with delivery token %d delivered\n", token);
  47.     // Disconnect
  48.     MQTTClient_disconnect(client, 10000);
  49.     MQTTClient_destroy(&client);
  50.     return rc;
  51. }

Paho C MQTT 5.0 support

Paho C has fully supported MQTT 5.0 Currently.