Solved

virtual function?

Posted on 1998-11-15
2
187 Views
Last Modified: 2013-11-15
for a project that I am developing, a friend told me to use 'pure virtual' functions in my classes. I am a beginner to C++ and hace no clue what she meant.
this project is due on Tuesday, so please answer fast!
0
Comment
Question by:dito
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
2 Comments
 
LVL 8

Accepted Solution

by:
MaDdUCK earned 960 total points
ID: 1177905
answer pending...
0
 
LVL 8

Expert Comment

by:MaDdUCK
ID: 1177906
A member function declaration that turns a normal class into an abstract class (i.e., an ABC). You normally only implement it in a derived class.

Some member functions exist in concept; they don't have any reasonable definition. E.g., suppose I asked you to draw a Shape at location (x,y) that has size 7. You'd ask me "what kind of shape should I draw?" (circles, squares, hexagons, etc, are drawn differently). In C++, we must indicate the existence of the draw() member function (so users can call it when they have a Shape* or a Shape&), but we recognize it can (logically) be defined only in subclasses:

    class Shape {
    public:
      virtual void draw() const = 0;  // = 0 means it is "pure virtual"
      // ...
    };

This pure virtual function makes Shape an ABC. If you want, you can think of the "= 0;" syntax as if the code were at the NULL pointer. Thus Shape promises a service to its users, yet Shape isn't able to provide any code to fulfill that promise. This forces any actual object created from a [concrete] class derived from Shape to have the indicated member function, even though the base class doesn't have enough information to actually define it yet.

Note that it is possible to provide a definition for a pure virtual function, but this usually confuses novices and is best avoided until later.

hope this helps,
MaDdUCK

0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Workplace bullying has increased with the use of email and social media. Retain evidence of this with email archiving to protect your employees.
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.

734 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question