Arduino MQTT 发布到主题问题

Question

I am trying to get my ESP8266 to publish to a topic with its mac address as a sub to differentiate between many devices, However when I create a Topic string with the mac in it the client.publish(Topic, String) breaks... I am getting this error

error: no matching function for call to 'PubSubClient::publish(<unresolved overloaded function type>, const char*)'
   if (client.publish(Topic.c_str, msg.c_str())){
                                              ^

void loop() {
      val = ( 100.00 - ( (analogRead(analogPin)/1023.00) * 100.00 ) );  // read the input pin
     // Serial.println(val);   
      client.loop();
      //client.publish("esp/test" val);
      String mac = WiFi.macAddress();

      String Topic = String("esp/test/moisture/" + mac);

      String msg = String("{Moisture:") + String(val) + String(", mac:") + String(mac) + String("}");
      if (client.publish(Topic.c_str, msg.c_str())){
          Serial.println("Message Sent!");
         // Serial.println(msg);
          Serial.println(msg.c_str());
      delay(10000);
    }
}

Answer 1

You're missing parentheses for the function call in the first argument to client.publish() . The line currently reads:

if (client.publish(Topic.c_str, msg.c_str())){

It should read

if (client.publish(Topic.c_str(), msg.c_str())){