Skip to main content

Introduction to Constructor and Destructor functions of a Class

Constructor and Destructor functions are Member Functions of a class having some special property.

Constructor function gets invoked when an object of a class is constructed (declared) and destructor function gets invoked when the object is destructed (goes out of scope).

Use of Constructor and Destructor function of a class

  • Constructor function is used to initialize member variables to pre-defined values as soon as an object of a class is declared.

  • Constructor function having parameters is used to initialize the data members to the values passed values, upon declaration.

  • Generally, the destructor function is needed only when constructor has allocated dynamic memory.

Defining Constructor and Destructor functions

The example below illustrates how constructor and destructor functions are defined:

  class myclass
  {
   private:
   int number;

   public:
   myclass()//constructor
   {
    number=10;
   }

   ~myclass()//destructor
   {
  //nothing needed
   }
  }; 

A few points to note:

  • Both of the functions have the same name as that of the class, destructor function having (~) before its name.

  • Both constructor and destructor functions should not be preceded by any data type (not even void).

  • These functions do not (and cannot) return any values.

  • We can have only the constructor function in a class without destructor function or vice-versa.

  • Constructor function can take arguments but destructors cannot.

  • Constructor function can be overloaded as usual functions.

Example 1: Using constructor function to initialize data members to pre-defined values

  //Example Program in C++
  #include<iostream.h>

  class myclass
  {
   private:
   int a;
   int b;

   public:
   myclass()
   {
   //here constructor function is used to
   //initialize data members to pre-def
   //values
   a=10;
   b=10;
   }

   int add(void)
   {
    return a+b;
   }
  };

  void main(void)
  {
   myclass a;

   cout<<a.add();
  }

Example 2: Using constructor function to initialize data members to values passed as arguments

  //Example Program in C++
  #include<iostream.h>

  class myclass
  {
   private:
   int a;
   int b;

   public:
   myclass(int i, int j)
   {
    a=i;
    b=j;
   }

   int add(void)
   {
    return a+b;
   }
  };

  void main(void)
  {
   //notice how the object of the class
   //has been declared
   //it can be thought as
   // myclass a;
   // a=myclass(10,20)
   myclass a(10,20);

   cout<<a.add();
  }

Notice that there is no destructor function in both the examples, just because we don’t need them.

I will discuss destructor functions in detail in the coming articles.

So, keep checking!

Related Articles:

Popular posts from this blog

Fix For Toshiba Satellite "RTC Battery is Low" Error (with Pictures)

RTC Battery is Low Error on a Toshiba Satellite laptop "RTC Battery is Low..." An error message flashing while you try to boot your laptop is enough to panic many people. But worry not! "RTC Battery" stands for Real-Time Clock battery which almost all laptops and PCs have on their motherboard to power the clock and sometimes to also keep the CMOS settings from getting erased while the system is switched off.  It is not uncommon for these batteries to last for years before requiring a replacement as the clock consumes very less power. And contrary to what some people tell you - they are not rechargeable or getting charged while your computer or laptop is running. In this article, we'll learn everything about RTC batteries and how to fix the error on your Toshiba Satellite laptop. What is an RTC Battery? RTC or CMOS batteries are small coin-shaped lithium batteries with a 3-volts output. Most laptops use

The Best Way(s) to Comment out PHP/HTML Code

PHP supports various styles of comments. Please check the following example: <?php // Single line comment code (); # Single line Comment code2 (); /* Multi Line comment code(); The code inside doesn't run */ // /* This doesn NOT start a multi-line comment block /* Multi line comment block The following line still ends the multi-line comment block //*/ The " # " comment style, though, is rarely used. Do note, in the example, that anything (even a multi-block comment /* ) after a " // " or " # " is a comment, and /* */ around any single-line comment overrides it. This information will come in handy when we learn about some neat tricks next. Comment out PHP Code Blocks Check the following code <?php //* Toggle line if ( 1 ) {      // } else {      // } //*/ //* Toggle line if ( 2 ) {      // } else {      // } //*/ Now see how easy it is to toggle a part of PHP code by just removing or adding a single " / " from th

Designing a Simple Order Form Application in PHP

Ok guys, for this post we’re going to create a simple yet complete order form page. Order forms are used on many sites to take customers order online. Order forms should have the capability to take orders from visitors regarding what items they want to purchase and store the information for further processing. For this post’s example, we are going to create an order form for a Book Seller. The form will be designed to take order of five different items (books). Our order form application should be able to take order of five different items in any separate quantities tht user wants, it should also ask for shipping address and name of the customer. It should then store the information provided in a file along with the date and time order was placed. The application should also be able to take any number of orders and store them all linearly for further human processing. For this, we need a front end of a HTML form to which the user would interact a