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What is Inheritance / how is it implemented in C++ (1)
OO in C++ - beyond the basics example from a Well House Consultants training course
More on OO in C++ - beyond the basics [link]

This example is described in the following article(s):
   • C++ - a complete example with polymorphism, and how to split it into project files - [link]

Source code: first_inheritance.cpp Module: C233
using namespace std;

/*

This is a complete example!
        - A base class "Animal"
        - subclass "Human"
        - subclass "Pet"

We set up an array of four Animals in a test program (2
humans and 2 pets) and then we loop thought them, reporting
the age (which is implemented ONCE in the base class because
it's common code) and the name (which is implemented in each
subclass, because it differs between humans and pets)

Compile and load line:

g++ -o first_i first_inheritance.cpp

Take a deep breath. It's unusual to do this in one file. It
would normally be in ... 7
        3 files of headers, one for each class
        3 files of source, one for each class
        and the test program (a.k.a. the application)
You would compile each of the four sources separately, pulling
in the correct headers via #includes, and you would use #ifndefs
to avoid duplicate loading. That will be our next example.

*/


#include <iostream>

// Define the API to the classes
// -----------------------------

// Common things in "animal"

/* Note the "virtual" declaration which says that every
animal has a name, but it will be handled differently
depending on the type of animal. (The {} pair is VITAL!) */


class Animal {
        public:
                Animal(int age);
                int getAge();
                virtual char *getName() {};
        protected:
                int age;
};

// Specifics in "human" and "pet"

class Human : public Animal {
        public:
                Human(char *forename, char *surname, int age);
                char *getName();
        protected:
                char *forename;
                char *surname;
};

class Pet : public Animal {
        public:
                Pet(char *name, int age, char *breed, int weight);
                char *getName();
        protected:
                char *name;

};

// Define the classes themselves
// -----------------------------

Animal::Animal(int age) {
        this->age = age;
        }

int Animal::getAge() {
        return this->age;
        }

// Note that the Human constructor calls the Animal constructor ...

Human::Human(char *forename, char *surname, int age) : Animal (age){
        this->forename = forename;
        this->surname = surname;
        }

Pet::Pet(char *name, int age, char *breed, int weight): Animal (age) {
        this->name = name;
        }

char *Human::getName() {
        // Should really concat strings but this is an inheritance
        // demo and not a string one!
        return "Mrs Smith";
        }

char *Pet::getName() {
        return this->name;
        }

// Main test program
// -----------------

int main () {

        // Set up object pointer array for the underlying base class

        Animal * Ourhouse [4];
        int k;

        // Set up objects that are animals within that array
        // even if they are specialised types of animal

        Ourhouse[0] = new Human("Lisa","Ellis",21);
        Ourhouse[1] = new Human("Graham","Ellis",55);
        Ourhouse[2] = new Pet("Gypsy",4,"Dog",30);
        Ourhouse[3] = new Pet("Charlie",13,"Cat",3);

        // Loop through the animals and get their names, even
        // through that will be done differenly for pets and humans

        for (k=0; k<4; k++) {
                char * Name = Ourhouse[k]->getName();
                int years = Ourhouse[k]->getAge();
                cout << "Living there ... " << Name
                        << " aged " << years << endl;
                }

        return 0;
        }

/* Sample Output

wizard:cpp graham$ ./first_i
Living there ... Mrs Smith aged 21
Living there ... Mrs Smith aged 55
Living there ... Gypsy aged 4
Living there ... Charlie aged 13
wizard:cpp graham$

*/

Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in C and C++
 * C++ for C Programmers
 * C and C++ Programming
 * Learning to program in C and C++
 * C and C++ Programming
Also available on on site courses for larger groups

Books covering this topic
Yes. We have over 700 books in our library. Books covering C and C++ are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

Other Examples
This example comes from our "OO in C++ - beyond the basics" training module. You'll find a description of the topic and some other closely related examples on the "OO in C++ - beyond the basics" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
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