What is the difference between protected and private class?

The key difference between protected and private members in a class lies in their accessibility. Private members are the most restrictive, while protected members offer a degree of accessibility to derived classes.

Access Modifiers: Private vs. Protected

Here's a breakdown of the differences, summarized in a table for clarity:

Feature	Private	Protected
Accessibility	Only accessible within the same class.	Accessible within the same class and derived classes.
Scope	Limited to the immediate class.	Extends to child classes (inheritance).
Use Case	Internal implementation details, encapsulation.	Allowing controlled access for inheritance.

In-Depth Explanation

• Private:

  • Private members (variables, methods, etc.) are exclusively accessible from within the class where they are declared.
  • No other class, not even a derived class (child class through inheritance), can directly access private members.
  • This provides the strongest level of encapsulation, hiding internal implementation details from the outside world.
  • According to the reference: Only code declared in the same class or struct can access this member.

• Protected:

  • Protected members are accessible from within the same class and any class derived from that class (i.e., child classes).
  • This allows derived classes to inherit and utilize certain members of the parent class, while still restricting access from unrelated classes.
  • Protected access is a balance between complete encapsulation (like private) and complete openness (like public).
  • The reference states: Only code in the same class or in a derived class can access this type or member.

Examples

Consider the following simplified C++ example:

class Base {
private:
  int privateVar; // Only accessible within Base

protected:
  int protectedVar; // Accessible within Base and Derived

public:
  void baseFunction() {
    privateVar = 1;    // OK
    protectedVar = 2;  // OK
  }
};

class Derived : public Base {
public:
  void derivedFunction() {
    // privateVar = 3; // Error!  Cannot access private member of Base
    protectedVar = 4; // OK
  }
};

int main() {
  Base baseObj;
  Derived derivedObj;

  // baseObj.privateVar = 5;   // Error!  Cannot access private member
  // baseObj.protectedVar = 6; // Error! Cannot access protected member outside the class hierarchy
  // derivedObj.protectedVar = 7; //Error!  Cannot access protected member outside the class hierarchy
  return 0;
}

In this example:

• privateVar can only be accessed within the Base class. Attempts to access it from Derived or main() result in compilation errors.
• protectedVar can be accessed within Base and Derived, but not directly from main().
• It is important to note that you also cannot access the protected member using derivedObj from main() because you are trying to access the variable from outside the class and derived class.

Practical Insights and Solutions

• Use private for internal data and methods that should never be accessed directly from outside the class.
• Use protected when you want to allow derived classes to access and potentially modify certain members, while still preventing direct access from other parts of the program. This is useful for implementing inheritance-based functionality.
• Careful consideration of access modifiers is crucial for maintaining code integrity, preventing unintended modifications, and ensuring proper encapsulation in object-oriented programming.