Base Classes and Derived Classes (Single and Multi-Level Inheritance)

Intermediate13 min read•Updated: 2026-10-22

🧬 Base Classes and Derived Classes (Inheritance)

Introduction

Inheritance allows you to create new classes (derived/subclasses) that inherit attributes and behaviors from existing classes (base/superclasses). This embodies the "is-a" relationship (e.g., a Developer is a StaffMember).

🏛️ Public Inheritance Syntax

In C++, access specifiers during inheritance govern how base members appear in the derived class:

1#include <iostream>
2#include <string>
3 
4// Base Class
5class StaffMember {
6protected:
7    std::string m_name;
8    int m_employeeId;
9    double m_baseSalary;
10 
11public:
12    StaffMember(const std::string& name, int id, double salary)
13        : m_name(name), m_employeeId(id), m_baseSalary(salary) {}
14 
15    void displayBaseInfo() const {
16        std::cout << "Staff: " << m_name << " (ID: " << m_employeeId << ") - Base Pay: ₹" << m_baseSalary << "\n";
17    }
18};
19 
20// Derived Class (Single Inheritance)
21class Instructor : public StaffMember {
22private:
23    std::string m_specializationSubject;
24 
25public:
26    // Constructor delegates initialization to Base Class constructor:
27    Instructor(const std::string& name, int id, double salary, const std::string& subject)
28        : StaffMember(name, id, salary), m_specializationSubject(subject) {}
29 
30    void conductLecture() const {
31        std::cout << "Instructor " << m_name << " is teaching " << m_specializationSubject << "\n";
32    }
33};
34 
35// Derived Class (Multi-Level Inheritance: StaffMember -> Instructor -> HeadInstructor)
36class HeadInstructor : public Instructor {
37private:
38    int m_batchSupervisionCount;
39 
40public:
41    HeadInstructor(const std::string& name, int id, double salary, const std::string& subject, int batches)
42        : Instructor(name, id, salary, subject), m_batchSupervisionCount(batches) {}
43 
44    void reviewCurriculum() const {
45        std::cout << "Head Instructor " << m_name << " is reviewing " << m_batchSupervisionCount << " active batches.\n";
46    }
47};
48 
49int main() {
50    HeadInstructor hod("Er. Sumit Sharma", 1001, 85000.0, "C++ & Systems Architecture", 8);
51    hod.displayBaseInfo(); // Inherited from StaffMember
52    hod.conductLecture();  // Inherited from Instructor
53    hod.reviewCurriculum(); // Defined in HeadInstructor
54    return 0;
55}

🔒 Types of Inheritance

class Derived : public Base: Public stays public; protected stays protected (Standard OOP "is-a").
class Derived : protected Base: Public becomes protected; protected stays protected.
class Derived : private Base: All inherited members become private ("implemented in terms of").

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Constructor and Destructor Call Order in Inheritance

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Related Lessons

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Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions	Constructor and Destructor Call Order in Inheritance

Practice Quiz

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🏛️ Public Inheritance Syntax

In C++, access specifiers during inheritance govern how base members appear in the derived class:

1#include <iostream>
2#include <string>
3 
4// Base Class
5class StaffMember {
6protected:
7    std::string m_name;
8    int m_employeeId;
9    double m_baseSalary;
10 
11public:
12    StaffMember(const std::string& name, int id, double salary)
13        : m_name(name), m_employeeId(id), m_baseSalary(salary) {}
14 
15    void displayBaseInfo() const {
16        std::cout << "Staff: " << m_name << " (ID: " << m_employeeId << ") - Base Pay: ₹" << m_baseSalary << "\n";
17    }
18};
19 
20// Derived Class (Single Inheritance)
21class Instructor : public StaffMember {
22private:
23    std::string m_specializationSubject;
24 
25public:
26    // Constructor delegates initialization to Base Class constructor:
27    Instructor(const std::string& name, int id, double salary, const std::string& subject)
28        : StaffMember(name, id, salary), m_specializationSubject(subject) {}
29 
30    void conductLecture() const {
31        std::cout << "Instructor " << m_name << " is teaching " << m_specializationSubject << "\n";
32    }
33};
34 
35// Derived Class (Multi-Level Inheritance: StaffMember -> Instructor -> HeadInstructor)
36class HeadInstructor : public Instructor {
37private:
38    int m_batchSupervisionCount;
39 
40public:
41    HeadInstructor(const std::string& name, int id, double salary, const std::string& subject, int batches)
42        : Instructor(name, id, salary, subject), m_batchSupervisionCount(batches) {}
43 
44    void reviewCurriculum() const {
45        std::cout << "Head Instructor " << m_name << " is reviewing " << m_batchSupervisionCount << " active batches.\n";
46    }
47};
48 
49int main() {
50    HeadInstructor hod("Er. Sumit Sharma", 1001, 85000.0, "C++ & Systems Architecture", 8);
51    hod.displayBaseInfo(); // Inherited from StaffMember
52    hod.conductLecture();  // Inherited from Instructor
53    hod.reviewCurriculum(); // Defined in HeadInstructor
54    return 0;
55}

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Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Constructor and Destructor Call Order in Inheritance