Access control in inheritance in C++ - Step-by-Step Execution

Concept Flow - Access control in inheritance

Base class members

↓

Inheritance type?

↓

Derived class access

Shows how base class members' access changes in derived class depending on inheritance type.

Execution Sample

C++

class Base {
public:
  int x;
protected:
  int y;
private:
  int z;
};

class Derived : public Base {
  void func() {
    x = 1; y = 2; // z not accessible
  }
};

Defines base class with different access levels and derived class accessing members under public inheritance.

Execution Table

Step	Code Line	Member Access	Access Allowed?	Reason
1	class Base { public: int x; }	x	Public	Accessible everywhere
2	class Base { protected: int y; }	y	Protected	Accessible in Base and derived classes
3	class Base { private: int z; }	z	Private	Accessible only in Base
4	class Derived : public Base	Inheritance type	Public	Public inheritance keeps access levels
5	Derived::func() { x = 1; }	x	Accessible	x is public in Base and remains public
6	Derived::func() { y = 2; }	y	Accessible	y is protected in Base and remains protected
7	Derived::func() { z = 3; }	z	Not accessible	z is private in Base, not inherited
8	class Derived : protected Base	Inheritance type	Protected	Public and protected become protected
9	Derived::func() { x = 1; }	x	Accessible	x becomes protected in Derived
10	Derived::func() { y = 2; }	y	Accessible	y remains protected
11	Derived::func() { z = 3; }	z	Not accessible	z is private in Base, not inherited
12	class Derived : private Base	Inheritance type	Private	Public and protected become private
13	Derived::func() { x = 1; }	x	Accessible	x becomes private in Derived
14	Derived::func() { y = 2; }	y	Accessible	y becomes private in Derived
15	Derived::func() { z = 3; }	z	Not accessible	z is private in Base, not inherited
16	Outside Derived: obj.x	x	Depends on inheritance	Public inheritance: accessible; protected/private: not accessible
17	Outside Derived: obj.y	y	Not accessible	Protected and private members not accessible outside
18	Outside Derived: obj.z	z	Not accessible	Private member never accessible outside Base
19	End of example	-	-	Demonstrates access control changes in inheritance

💡 All private members of Base are not accessible in Derived or outside; access levels of public/protected members depend on inheritance type.

Variable Tracker

Member	Base Access	Public Inheritance	Protected Inheritance	Private Inheritance
x	public	public	protected	private
y	protected	protected	protected	private
z	private	not inherited	not inherited	not inherited

Key Moments - 3 Insights

Why can't Derived class access private member z of Base?

Private members are only accessible inside their own class. Execution table rows 3, 7, 11, and 15 show z is never accessible in Derived.

How does inheritance type affect access to public member x in Derived?

Public inheritance keeps x public (row 5), protected inheritance makes x protected (row 9), private inheritance makes x private (row 13). See variable_tracker for summary.

Can code outside Derived access protected member y?

No, protected members are not accessible outside the class or its derived classes. Execution table row 17 shows outside access denied.

Visual Quiz - 3 Questions

Look at the execution table row 5. What is the access level of member x inside Derived under public inheritance?

A Private

B Protected

C Public

D Not accessible

💡 Hint

Check row 5 in execution_table where x is assigned inside Derived under public inheritance.

At which step does the code show that private member z is not accessible in Derived?

A Step 5

B Step 7

C Step 9

D Step 13

💡 Hint

Look for 'z not accessible' in execution_table rows 7, 11, or 15.

If Derived inherits Base privately, what is the access level of member y inside Derived?

A Private

B Protected

C Public

D Not accessible

💡 Hint

See variable_tracker row for y and column 'Private Inheritance'.

Concept Snapshot

Access control in inheritance:
- Base class members: public, protected, private
- Public inheritance: public->public, protected->protected
- Protected inheritance: public->protected, protected->protected
- Private inheritance: public->private, protected->private
- Private members never inherited
- Outside access depends on final access level

Full Transcript

This visual execution trace shows how access control works in C++ inheritance. The base class has members with public, protected, and private access. Depending on the inheritance type (public, protected, or private), the access level of inherited members changes in the derived class. Private members are never inherited and cannot be accessed in the derived class. Public inheritance keeps public members public and protected members protected. Protected inheritance changes public members to protected. Private inheritance changes public and protected members to private. Outside the derived class, only public members are accessible. The execution table traces each step of member access and inheritance type, while the variable tracker summarizes access changes. Key moments clarify common confusions about private member access and inheritance effects. The quiz tests understanding of access levels at different steps. This helps beginners see exactly how access control changes with inheritance in C++.