void loop() {//主循环      String msg = "";//用于存放       reconnect();//确保连上服务器，否则一直等待。       client.loop();//MUC接收数据的主循环函数。       client.setServer(mqtt_server, port);//端口号       client.setCallback(callback); //用于接收服务器接收的数据                   while (Serial.available() > 0)          {            msg += char(Serial.read());            delay(2);        }        int msglen = msg.length();        if (msglen > 0)        {            Serial.println(msg);            char msgArr[msglen+1];            msg.toCharArray(msgArr,msglen + 1);            client.publish(topic_name,msgArr);        }

      Serial.println("wake up MCP9808.... "); // wake up MCP9808 - power consumption ~200 mikro Ampere      tempsensor.wake();   // wake up, ready to read! // Read and print out the temperature, also shows the resolution mode used for reading.      Serial.print("Resolution in mode: ");      Serial.println (tempsensor.getResolution());      float c = tempsensor.readTempC();      Serial.print("Temp: ");       Serial.print(c, 4); Serial.print("*C\t");       delay(20000);      Serial.println("Shutdown MCP9808.... ");      tempsensor.shutdown_wake(1); // shutdown MSP9808 - power consumption ~0.1 mikro Ampere, stops temperature sampling      Serial.println("");      delay(200);      char temp[25];      dtostrf(c,3,3,temp);       client.publish("register",MAC_char_STA);      client.publish(MAC_char_STA, temp);      Serial.println(MAC_char_STA);//      ESP.deepSleep(20e6);    }