{"id":224,"date":"2020-08-31T17:46:49","date_gmt":"2020-08-31T17:46:49","guid":{"rendered":"https:\/\/www.kindsonthegenius.com\/cplusplus\/?p=224"},"modified":"2020-08-31T17:46:49","modified_gmt":"2020-08-31T17:46:49","slug":"c-oop-constructors","status":"publish","type":"post","link":"https:\/\/www.kindsonthegenius.com\/cplusplus\/c-oop-constructors\/","title":{"rendered":"C++ OOP – Constructors"},"content":{"rendered":"

In this lesson, we will cover Constructors and Copy Constructors in C++ under the following topics:<\/p>\n

    \n
  1. What is a Constructor?<\/a><\/li>\n
  2. Parameterized Constructors<\/a><\/li>\n
  3. Copy Constructor<\/a><\/li>\n<\/ol>\n

     <\/p>\n

    1. What is a Constructor?<\/strong><\/h4>\n

    A constructor in C++ is special\u00a0 member function of a class that is automatically called whenever a new object is created.<\/p>\n

    A constructor has the following properties:<\/p>\n

      \n
    • the same name as the class<\/li>\n
    • does not have a return type<\/li>\n<\/ul>\n

      Default constructor:<\/strong> C++ provides a default constructor. This is a constructor that accepts no parameters. For example<\/p>\n

      class<\/span>  Circle<\/span>{\r\n   public:<\/span>\r\n\r\n    \/\/ create a constructor<\/span>\r\n    Circle() {\r\n        \/\/ code<\/span>\r\n    }\r\n};\r\n<\/pre>\n
      Here, the function Circle() is a constructor of the class Circle. The program below show the use of default constructor<\/p>\n
      \/\/ Program to demonstrate default constructor<\/span>\r\n#include <iostream><\/span>\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\n\/\/ declare a class, circle<\/span>\r\nclass<\/span>  Circle<\/span> {\r\n\r\n  private:<\/span>\r\n       double<\/span> radius;\r\n\r\n   public:<\/span>\r\n    \/\/ create a constructor<\/span>\r\n    Circle() {\r\n\r\n        \/\/ initialize private variables<\/span>\r\n        radius =<\/span> 7.5<\/span>;\r\n\r\n        cout <<<\/span> \"Creating a circle.\"<\/span> <<<\/span> endl;\r\n        cout <<<\/span> \"Radius = \"<\/span> <<<\/span> radius <<<\/span> endl;\r\n    }\r\n};\r\n\r\nint<\/span> main<\/span>() {\r\n\r\n    \/\/ create an object<\/span>\r\n    Circle circle;\r\n\r\n    return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
      The output is:<\/p>\n
      Creating a circle.\r\nRadius = 7.5\r\n<\/pre>\n
      However, not that if we fail to provide a default constructor, C++ compiler will provide one implicitly.<\/p>\n
       <\/p>\n
      2. Parameterized Constructor<\/strong><\/h4>\n
      A constructor that accepts parameters is called a parameterized constructor. This is the preferred approach to initializing data members.<\/p>\n
      The program below illustrates parameterized constructor;<\/p>\n
      #include <iostream><\/span>\r\n#include <math.h>       <\/span>\/* pow *\/<\/span>\r\n\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\n\/\/ declare a class, circle<\/span>\r\nclass<\/span>  Cylinder<\/span> {\r\n\r\n  private:<\/span>\r\n       double<\/span> radius;\r\n       double<\/span> height;\r\n\r\n   public:<\/span>\r\n    \/\/ create a parameterized constructor<\/span>\r\n    Cylinder(double<\/span> r, double<\/span> h) {\r\n    \t\/\/ Initialise the member variables<\/span>\r\n    \tradius =<\/span> r;\r\n    \theight =<\/span> h;\r\n    }\r\n\r\n    double<\/span> calculateVolume(){\r\n    \treturn<\/span> 22<\/span>\/<\/span>7<\/span> *<\/span> pow(radius,2<\/span>) *<\/span> height;\r\n    }\r\n};\r\n\r\nint<\/span> main<\/span>() {\r\n\r\n    \/\/ create a cylinder with parameters<\/span>\r\n    Cylinder cylinder1(10.2<\/span>, 5.3<\/span>);\r\n    Cylinder cylinder2(20.5<\/span>, 2.5<\/span>);\r\n\r\n    cout <<<\/span>\"Volume 1: \"<\/span> <<<\/span> cylinder1.calculateVolume() <<<\/span>endl;\r\n    cout <<<\/span>\"Volume 2: \"<\/span> <<<\/span> cylinder2.calculateVolume() <<<\/span>endl;\r\n\r\n    return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
      Output of the program<\/p>\n
      Volume 1: 1654.24\r\nVolume 2: 3151.88\r\n<\/pre>\n
      Here we created a parameterized constructor Cylinder() with two parameters: radius and height. The values of these parameters are use to initialized the member variables when the Cylinder is instantiated.<\/p>\n
       <\/p>\n
      3. Copy Constructor<\/strong><\/h4>\n
      This is a constructor that instantiates an object by copying data from an existing object of the same class.<\/p>\n
      A copy constructor\u00a0 is used for the following:<\/p>\n
        \n
      • Initialize on object from another object<\/li>\n
      • copy an object to pass as an argument to a function<\/li>\n
      • copy an object to return from a function<\/li>\n<\/ul>\n
        Similar to normal constructor, if we don’t define a copy constructor, then the C++ compiler will define one implicitly.<\/p>\n
        A copy constructor for\u00a0 our cylinder object is given below:<\/p>\n
        \/\/ copy constructor with a Cylinder object as parameter<\/span>\r\nCylinder(Cylinder &<\/span>obj) {\r\n    \/\/ initialize private variables<\/span>\r\n    radius =<\/span> obj.radius;\r\n    height =<\/span> obj.height;\r\n}\r\n<\/pre>\n
        Notice in the code that the parameter to the copy constructor has the address of an object of the Cylinder class.<\/p>\n
        Final note<\/strong>: Although a constructor is used to initialize an object, they can also be used to perform certain operations when an object is created.<\/p>\n","protected":false},"excerpt":{"rendered":"
        In this lesson, we will cover Constructors and Copy Constructors in C++ under the following topics: What is a Constructor? Parameterized Constructors Copy Constructor   … <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2,35],"tags":[37],"class_list":["post-224","post","type-post","status-publish","format-standard","hentry","category-c-tutorials","category-oop","tag-constructors"],"_links":{"self":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts\/224","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/comments?post=224"}],"version-history":[{"count":1,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts\/224\/revisions"}],"predecessor-version":[{"id":225,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts\/224\/revisions\/225"}],"wp:attachment":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/media?parent=224"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/categories?post=224"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/tags?post=224"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}