C++ - Where to code a member function for an inherited object.

Question

Hello!

I have a few classes (heat, gas, contact, pressure) inheriting from a main one (sensor).

I have a need to store them in a vector<Sensor *> (part of the specification).

At some point in time, I need to call a function that indiscriminately stores those Sensor *. (also part of the specification, not open for discussion)

Something like this:

for(size_t i = 0; i < Sensors.size(); ++i)
    Sensors[i]->storeSensor(os) //os is an ofstream kind of object, passed onwards by reference

Where and how shall storeSensor be defined?

Is there any simple way to do this or will I need to disregard the specification? Mind you, I'm a beginner!

Thanks for your time!

Answer 1

storeSensor should be declared virtual in Sensor (and any other class that may be further inherited). This will make sure that the call

Sensors[i]->storeSensor(os);

will pick up the correct method.

You only need to redeclare storeSensor in any class that has a different implementation for that method than the base class.

Answer 2

You need to make it a pure virtual function, which you then implement in each of the derived classes. The implementation can be pretty simple:

class sensor {
   ....
   virtual void storeSensor( ostream & os ) = 0;
};

class heat : public sensor {
   ....
  void storeSensor( ostream & os ) {
     os << * this;
  }

};

class light : public sensor {
   ....
  void storeSensor( ostream & os ) {
     os << * this;
  }

};

This assumes you have defined a suitable operator<< for each of your classes. If not, you need to write the specific sensors member variables explicitly. And that is the easy bit - the difficulty starts when you want to read the sensors back in again :-)

Answer 3

If StoreSensor is the same functionality for all types of sensors, define it in the base class as virtual, and be done with it.

If its differs depending on each type of sensor, and it is guaranteed to differ for all sensors, then define it as pure virtual in the base class, and override it in the derived sensor classes.

If it can differ, but is not guaranteed to, follow step 1, and then override in the derived classes when needed.

Answer 4

If all the subclasses use storeSensor() and it always takes the same parameter, you can just declare it in the parent class Sensor. Then store the pointer as a ofstream pointer in the parent Sensor class.

I really don't see why it needs to be virtual if it is always the same.