Inheritance and protected variables not working(C++).

Question

I have a class called that has protected data:

class Sensors {
public:   
/* other code here  */
   
    uint16_t getType()const { return type; } // accessors defined
    float getValue()const { return value; }
    bool getValid()const { return valid; }

protected:
    uint16_t type=0;
    float    value=0;
    bool     valid=false; 
};

class RoomControllers:public Sensors  
{
public:
   
    RoomControllers(); // constructor
    void printStates() const;
    void setTemperatureTarget();
    

private:
    float   targetTemperature=19.0; // default initialisation 
    bool    currentlyHeating{false};
    float   targetHumidity=50;
    bool    currentlyHumidifying{false}; 
    std::array<Sensors, 5> sensors; // C-style array replaced by C++ array
};

void RoomControllers::printStates() const
{
    uint16_t validSensorCount = 0;

    cout << "Sensors:" << endl;
    cout << "--------" << endl;

    // For each sensor, print its Type and Value
    for (uint16_t count = 0; count < MAX_NUM_SENSORS; count++) {
        if (sensors[count].valid) {                     // the problem is here
            validSensorCount++;

Error says 

error: ‘bool Sensors::valid’ is protected within this context

Please provide advice on how to access the valid variable without using a getter function.

Answer 1

Inheritance works fine. The problem is that you are not trying to access a protected member of the base class of your RoomController instance. Rather, you're trying to access a protected member of a Sensors class that has no relation (regarding inheritance) to your instance where you're trying to access it.

In other wolds inheritance only allows you to access member of the base class of your instance, not other instances of the same class.

Comments

what is the way around this problem?

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"Please provide advice on how to access the valid variable without using a getter function."

I'm afraid you need a getter function for this. :(

bool Sensors::IsValid() const { return valid; }

An alternative solution is to use friend functions/classes.

friend class RoomControllers;

Note: I tried to use a friend function, but it seems to be quite difficult as the friend would be a derived class at the same time.

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thanks man, interesting problem tho.