Sketch with multiple classes (.h and .cpp) - how to interconnect classes

Question

I wanted to move most functionality of my sketch into different classes, to keep things better organized. One class worked just fine, but when I had to use multiple classes and pass information between then things stopped working.

I have two classes, my main Remote class, and my RemoteDisplay class. The main class takes care of fx, measuring battery voltage and I want to display this through the RemoteDisplay class. To do so I initiate the Display class with a pointer to the Remote class, so I can access the voltage function. This, however, doesn't work, even though I forward declare the Remote class in the Display class.

Remote.ino

#include "Remote.h"

Remote Remote;

void setup() {
  Serial.begin(9600);
}

void loop() {
  Remote.display.showBattery();
}

Remote.h

#include "RemoteDisplay.h"
class Remote
{

public: 

  RemoteDisplay display;

  Remote( void );

  float voltage;

};

Remote.cpp

#include "Remote.h"

Remote::Remote(void)
{
  display.initiate(this);
}

RemoteDisplay.h

class Remote;

class RemoteDisplay
{

public:

  RemoteDisplay(void);

  void initiate( Remote * _pointer );

  void showBattery( void );

private:

  /* Reference to the remote class */
  Remote * pointer;
};

RemoteDisplay.cpp

#include "RemoteDisplay.h"

void RemoteDisplay::initiate( Remote * _pointer )
{
  pointer = _pointer;
}

void RemoteDisplay::showBattery( void )
{
  Serial.println( pointer->voltage );
}

I get the errors:

error: invalid use of incomplete type 'class Remote'
showBattery( pointer->voltage() );

note: forward declaration of 'class Remote'
class Remote;

Why is it so? Any help is much appreciated.

Answer 1

In RemoteDisplay.cc you are using Remote in the Initiate method.

Also, since you use the voltage property, you need to include "Remote.h" within (as first line normally) in RemoteDisplay.cpp.

Also it is advised to use within every header file the following pattern (example for RemoteDisplay.h):

#ifndef REMOTE_DISPLAY_H
#define REMOTE_DISPLAY_H
...
...
#endif // REMOTE_DISPLAY_H

This prevents problems that two include header files forever include each other.