Protected Class Members

For example, we can create objects that allow the outside world to see our character's health, but not change it:

1class Character {
2public:
3  int GetHealth() { return mHealth; }
4
5private:
6  int mHealth { 100 };
7};

An interesting problem arises when we're using inheritance in this context. Specifically, code in a derived class also can't access any inherited private members.

Below, we have a new class that inherits from Character, but this code also can't access the private mHealth variable:

1class Character {
2public:
3  int GetHealth() { return mHealth; }
4
5private:
6  int mHealth { 100 };
7};
8
9class Healer : public Character {
10public:
11  void Heal(int Amount) { mHealth += Amount; }
12};

1error: 'Character::mHealth': cannot access private
2member declared in class 'Character'

Fortunately, we have an access level between public and private that solves this problem. This access level is called protected.

protected members cannot be accessed by functions that exist outside our class hierarchy, but they can still be accessed by code in child classes.

Below, we've changed mHealth to be protected rather than private:

1#include <iostream>
2using namespace std;
3
4class Character {
5public:
6  int GetHealth(){ return mHealth; }
7
8protected:
9  int mHealth{100};
10};
11
12class Healer : public Character {
13public:
14  void Heal(int Amount){ mHealth += Amount; }
15};
16
17int main(){
18  Healer Player;
19  cout << "Health: " << Player.GetHealth();
20
21  Player.Heal(50);
22  cout << "\nHealth: " << Player.GetHealth();
23}

1Health: 100
2Health: 150

We've now covered the three access levels we have in C++:

• private members are only accessible within the same class they are defined
• protected members are accessible within the same class, and any sub-class
• public members are accessible from anywhere