Mqtt Raspberry PI C ++

Question

I would like to make raspberry pi a publisher only by using MQTT protocol. So far I have installed mosquitto library in my raspberry pi following this:

http://www.instructables.com/id/Installing-MQTT-BrokerMosquitto-on-Raspberry-Pi/

I will only have to publish int values from it. What I want to ask you guys is how will use mosquitto in my c++ program so I can achieve my goal mentioned above? (give me some guidance, links to where I can find something useful.)

Answer 1

You could do it easier by Python (especially when you are using Raspberry Pi). This tutorial is good to start with (you may need Google translate because it's in Vietnamese).

Basically, Raspberry Pi will be MQTT server and also MQTT client and it will Subscribe your Topic . Your PC will be the second MQTT client and will Publish the Topic .

Answer 2

with assumption that you've already installed mosquitto library. You can call the mqtt class as,

try {

    class myMqtt *qr2sp;
    //int rc;
    mosqpp::lib_init();

    qr2sp = new myMqtt ("qr2sp", "pcktatDoor", "192.168.178.100", 1883);

    while (1){

        /// call camera [qrcam()], read QR and send to publish()
        qr2sp->send_msg(qr2sp->qrcam().c_str());

        rc = qr2sp->loop();

        if (rc){
            qr2sp->reconnect();
}

and can declare the myMqtt class as,

class myMqtt : public mosqpp::mosquittopp
{
  private:
   const char * host;
   const char * id;
   const char * topic;
   int      port;
   int      keepalive;

   void on_connect(int rc);
   void on_disconnect();
   void on_publish(int mid);

  public:
   myMqtt(const char *id, const char * _topic, const char *host, int port);
   ~myMqtt();
   bool send_msg(const char *message);
   std::string qrcam();

};

I wrote a little application with openCV and Mqtt using C++ - here [https]://github[.]com/meAbab/qrMqtt

Probably will help you to understand