C++ Multilevel Inheritance

Inheritance in a chain

Imagine three classes stacked on top of each other. Class C inherits from class B, and class B inherits from class A. This means C has its own members, plus everything from B, plus everything from A. Each link in the chain passes its members further down.

#include <iostream>
using namespace std;

class Animal {                 // top level
  public:
    void breathe() { cout << "Breathing...\n"; }
};

class Mammal : public Animal { // middle level
  public:
    void feedMilk() { cout << "Feeding milk...\n"; }
};

class Dog : public Mammal {    // bottom level
  public:
    void bark() { cout << "Woof!\n"; }
};

int main() {
  Dog d;
  d.breathe();   // from Animal
  d.feedMilk();  // from Mammal
  d.bark();      // from Dog
  return 0;
}

The object d can call all three methods even though they were defined in three different classes. That is multilevel inheritance in action: the behavior accumulates as you move down the chain.

• Each derived class can add new members while keeping the inherited ones.
• The most-derived class has access to members from every ancestor above it.
• The chain can be as long as you like, though very deep chains get hard to follow.

#include <iostream>
using namespace std;

class A {
  public:
    A() { cout << "A constructor\n"; }
};

class B : public A {
  public:
    B() { cout << "B constructor\n"; }
};

class C : public B {
  public:
    C() { cout << "C constructor\n"; }
};

int main() {
  C obj;   // prints A, then B, then C
  return 0;
}

Multilevel inheritance is great for modeling natural hierarchies, but keep it reasonable. If a chain grows too deep, it can become confusing to track where each member came from.