Skip to main content

Introduction to Virtual Functions

Virtual functions are special member functions of a class which may be re-defined in the derived classes. It is used to give specific meaning to the base class member function with respect to the derive class.

Virtual functions can be thought of as a function name reserved in the bas class which may be re-defined in the derived classes as per the need so that every derived class has the same function that performs specific (as redefined in the derived class) action.

Let’s now have a look at a simple program to show virtual functions inaction:


  // Virtual functions
  #include <iostream.h>

  // base class
  class base
  {
  public:
    // precede the function name
    // with the 'virtual' keyword
    // to make it a virtual function
    virtual void func()
    {
      cout<<"Base's func()\n";
    }
  };

  // derived class
  class derived:public base
  {
  public:
    // redefinition of the 
    // function
    void func()
    {
      cout<<"Derived's func()\n";
    }
  };

  // main
  void main()
  {
    base b;
    derived d;

    // notice that both are calling
    // the same function but different
    // functions gets called as per
    // the class to which the object
    // belongs to
    b.func();
    d.func();
  }

OUTPUT:

  Base's func()
  Derived's func()

The redefinition of the virtual function in the derived class is known as overriding


As you can see there is nothing confusing, the virtual function is a general member function and is defined as such, only difference being that it’s preceded by the virtual keyword that gives it the special property.

NOTE: By redefining a virtual function, all its previous meaning (as was defined in the base class) is lost.

As in the example program the base class defines the virtual function to print “Base's func()” and the derived class overrides it to print “Derived's func()”. So when we call the overridden function it only prints what was defined in the redefinition hence the original meaning of the function is lost.

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

How to Remove Bullet Points in CSS

This will be a short guide on how to remove bullet points from ordered/unordered lists with CSS, you only need two lines of CSS for this. The first removes the actual bullet points and the second one removes the space to the left, as evident from the following video: We'll also be doing some bullet beautification in the last section if that's what you are looking to do. How to Remove Bullet Points in HTML/CSS Now that we know what CSS properties actually accomplish what we want let's see how we can implement this in our HTML code. Using Inline "style" Tag (The quick and dirty way) As the title suggests, this is the quickest way to remove bullet points in which you wouldn't have to edit any CSS files (for example, for Blogger or WordPress). This method would be useful for a one-off case - just add the following " style " attribute to the list you want to remove the bullet points from: <h1>Ordered List</h1> <ol  style="list-styl