{"id":226,"date":"2020-09-01T10:33:30","date_gmt":"2020-09-01T10:33:30","guid":{"rendered":"https:\/\/www.kindsonthegenius.com\/cplusplus\/?p=226"},"modified":"2020-09-01T10:33:30","modified_gmt":"2020-09-01T10:33:30","slug":"c-oop-inheritance","status":"publish","type":"post","link":"https:\/\/kindsonthegenius.com\/cplusplus\/c-oop-inheritance\/","title":{"rendered":"C++ OOP – Inheritance"},"content":{"rendered":"

In the previous lesson we covered the Constructors<\/a>. In this lesson, we would examine yet another OOP concept: Inheritance<\/em><\/strong>. The following topics will be addressed:<\/p>\n

    \n
  1. Overview of C++ Inheritance<\/a><\/li>\n
  2. Access Specifiers<\/a><\/li>\n
  3. Inheritance Access Modes<\/a><\/li>\n<\/ol>\n

     <\/p>\n

    1. Overview of C++ Inheritance<\/strong><\/h4>\n

    As mentioned, inheritance is a key feature of OOP. It is a feature that allows to create a new class based on an existing class. And clearly, this aligns with the DRY(don’t repeat yourself) principle.<\/p>\n

    In writing a new class, the new class can derive functionalities, such as data members from existing class. Therefore the new class is called a derived class<\/strong> while the existing class is called a base class<\/strong>. Other terms care parent class<\/strong> and child class<\/strong>. It could also be superclass and subclass<\/strong>.<\/p>\n

    Inheritance implements is-a relationship as shown in the figure.<\/p>\n

    \"Inheritance<\/a><\/p>\n

    Let’s take an example:<\/p>\n

    \/\/ Base class<\/span>\r\nclass<\/span> Vehicle<\/span> {\r\n  public:<\/span>\r\n    string make =<\/span> \"Toyota\"<\/span>;\r\n    void<\/span> honk<\/span>() {\r\n      cout <<<\/span> \"Poom poom! <\/span>\\n<\/span>\"<\/span> ;\r\n    }\r\n};\r\n\r\n\/\/ Derived class of Vehicle<\/span>\r\nclass<\/span> Car<\/span>:<\/span> public<\/span> Vehicle {\r\n  public:<\/span>\r\n    string model =<\/span> \"Corolla\"<\/span>;\r\n};\r\n\r\nint<\/span> main<\/span>() {\r\n  Car car1;\r\n  car1.honk();\r\n  cout <<<\/span> car1.make +<\/span> \" \"<\/span> +<\/span> car1.model;\r\n  return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
    Here, the Car<\/strong> <\/em>class derives from the Vehicle<\/em> <\/strong>class. Since car derives from Vehicle, the member of Vehicle are accessible to Car<\/strong><\/em>.<\/p>\n
    One thing you should observe is the use of the keyword public while inheriting Car from Vehicle.<\/p>\n
    class<\/span> Car<\/span>:<\/span> public<\/span> Vehicle {\r\n   ...\r\n};\r\n<\/pre>\n
    The public keyword here is an access specifier<\/strong><\/em> and defines the access mode<\/strong><\/em> of the inheritance. We’ll now talk about access specifiers. Then we move on to access modes.<\/p>\n
     <\/p>\n
    2. Access Specifiers<\/strong><\/h4>\n
    By now, you have seen from previous examples that members of a class can be public. They can also be private or protected. These are called access specifiers. They specify how members of a class can be accessed. For example, the public members<\/strong> can be accessed from outside the class. The three access modifiers for class members are explained below.<\/p>\n
      \n
    • public<\/strong> – members are accessible from outside of the class<\/li>\n
    • private<\/strong> – members are not visible from outside the class<\/li>\n
    • protected<\/strong> – members are accessible from outside the class only by derived classes.<\/li>\n<\/ul>\n
      The program below illustrates this. There are 3 error I’ve indicated. Check to understand the reason behind each error<\/p>\n
      #include <iostream><\/span>\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\n\/\/ declare a class, shape<\/span>\r\nclass<\/span>  Shape<\/span> {\r\n\r\n  private:<\/span>\r\n       double<\/span> height =<\/span> 12.3<\/span>;\r\n\r\n  public:<\/span>\r\n       double<\/span> width =<\/span> 9.2<\/span>;\r\n\r\n  protected:<\/span>\r\n       double<\/span> length =<\/span> 34.02<\/span>;\r\n\r\n};\r\n\r\n\/\/ create a derived class cube<\/span>\r\nclass<\/span> Circle<\/span>:<\/span> Shape {\r\n\r\npublic:<\/span>\r\n\tvoid<\/span> getValues(){\r\n\r\n\t\theight =<\/span> 89.2<\/span>; \/\/3. Error: private member<\/span>\r\n\r\n\t\tlength =<\/span> 23.3<\/span>; \/\/Ok: derived class<\/span>\r\n\t}\r\n};\r\n\r\n\r\nint<\/span> main<\/span>() {\r\n\r\n\tShape shape1;\r\n\r\n\tshape1.height =<\/span> 9.3<\/span>; \/\/1. Error: private member<\/span>\r\n\r\n\tshape1.length =<\/span> 10.2<\/span>; \/\/2. Error: protected member<\/span>\r\n\r\n\tshape1.width =<\/span> 34.08<\/span>; \/\/OK: public member<\/span>\r\n\r\n    return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
       <\/p>\n
      3. Inheritance Access Mode(public, private, protected)<\/strong><\/h4>\n
      The access mode(also called types of inheritance) defines the ways classes can be derived. In order words, how much of the parents functionalities are inherited by the child. Let’s see.<\/p>\n
        \n
      • public<\/strong>: if a child class is derived using the public mode, then the members of the base class are inherited exactly as they are<\/li>\n
      • private<\/strong>:if a child class is derived with the private mode, then the members of the base class now become private members of the derived class.<\/li>\n
      • protected<\/strong>:in this case, public members of the base class become protected members of the derived class.<\/li>\n
      • default:<\/strong> when you don’t specify and access mode, then it’s automatically public.<\/li>\n<\/ul>\n
        In subsequent lessons, we’ll cover other aspects of inheritance including: multiple inheritance and function overloading.<\/p>\n","protected":false},"excerpt":{"rendered":"
        In the previous lesson we covered the Constructors. In this lesson, we would examine yet another OOP concept: Inheritance. 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