title: mosquittopp: publish message to broker
body: <p>I'm using cpp wrapper for mosquitto under linux.<br>
  After initializing:  </p>
  
  <pre><code>this-&gt;keepalive = 60;   
  this-&gt;id = id;
  this-&gt;port = port;
  this-&gt;host = host;
  this-&gt;topic = topic;
  mosquittopp::log_init(MOSQ_LOG_ALL, MOSQ_LOG_STDOUT);
  const int result = connect(host, port, keepalive);
  </code></pre>
  
  <p>how can I publish my custom message? </p>
  
  <p>I'm using publish method defined by wrapper in this way: </p>
  
  <pre><code>int publish(uint16_t *mid, const char *topic, uint32_t payloadlen=0, const uint8_t *payload=NULL, int qos=0, bool retain=false);
  </code></pre>
  
  <p>So I can call in this way:  </p>
  
  <pre><code>publish(NULL, topic, strlen(message));
  </code></pre>
  
  <p>but.. where I can specify the real "message"?</p>