C++ Access Specifiers

What are access specifiers?

In C++ there are three access specifiers: public, private, and protected. You write them inside a class followed by a colon, and every member declared after them takes on that access level until another specifier appears. Think of them as labels that group your members into different levels of visibility.

• public: members can be reached from anywhere the object is visible, including from outside the class.
• private: members can only be reached from inside the class itself (its own methods).
• protected: like private, but also reachable from classes that inherit from this class.

#include <iostream>
using namespace std;

class Car {
  public:
    string brand;   // accessible from anywhere
    int speed;
};

int main() {
  Car myCar;
  myCar.brand = "Toyota";  // works: brand is public
  myCar.speed = 120;
  cout << myCar.brand << " at " << myCar.speed << " km/h";
  return 0;
}

#include <iostream>
using namespace std;

class BankAccount {
  private:
    double balance;   // hidden from outside code

  public:
    void setBalance(double amount) {
      balance = amount;   // allowed: same class
    }
    double getBalance() {
      return balance;
    }
};

int main() {
  BankAccount acc;
  acc.setBalance(500.0);       // works through a public method
  // acc.balance = 999;        // ERROR: balance is private
  cout << acc.getBalance();    // prints 500
  return 0;
}

In the example above, balance cannot be changed directly from main(). The only way in is through the public methods setBalance() and getBalance(). This lets the class stay in control of its own data, which is exactly the point of access specifiers.