use override declaration

src/ebusd/datahandler.h

@@ -152,7 +152,7 @@ class DataSink : virtual public DataHandler {
   virtual void notifyUpdate(Message* message);
 
   // @copydoc
-  virtual bool isDataSink() { return true; }
+  virtual bool isDataSink() override { return true; }
 
 
  protected:
@@ -182,7 +182,7 @@ class DataSource : virtual public DataHandler {
   virtual ~DataSource() {}
 
   // @copydoc
-  virtual bool isDataSource() { return true; }
+  virtual bool isDataSource() override { return true; }
 
 
  protected:

src/ebusd/mqtthandler.h

@@ -71,7 +71,7 @@ class MqttHandler : public DataSink, public DataSource, public Thread {
   virtual ~MqttHandler();
 
   // @copydoc
-  virtual void start();
+  virtual void start() override;
 
   /**
    * Notify the handler of a received MQTT message.
@@ -83,7 +83,7 @@ class MqttHandler : public DataSink, public DataSource, public Thread {
 
  protected:
   // @copydoc
-  virtual void run();
+  virtual void run() override;
 
 
  private: