• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
monkeyboi

Multi inheritance and pure virtual

4 posts in this topic

Hi I have some question about multi inheritance see the code snippet below


class Window{
public:
	virtual void drawBorder() = 0;
	virtual void prompt() =0;
};

class BorderedWindow:public virtual Window{
public:
	void drawBorder(){}
};

class WindowWithMenu : public virtual Window{
public:
	void prompt(){}
};

class CustomWindow : public BorderedWindow, public WindowWithMenu{
public:
	void draw(){drawBorder(); prompt();}
};

 

My questions are

  1. why does derived class not have to implement all pure virtual functions declared in base class? Because it is virtual inheritance?
  2. Is :public virtual Window different from :virtual public Window?
0

Share this post


Link to post
Share on other sites
1. That has nothing to do with virtual inheritance. Its to leave the possibility open that programmers make a class hierarchy with more than 2 steps where they continuously add common functionality first and later more specialized. If you try to make a BorderedWindow or WindowWithMenu you will see the compiler guards against this because its an abstract class like Window.
2. Should be the same if it both compiles.

Btw., you should always add a virtual destructor to any baseclass with a virtual method to prevent errors when you only have a pointer or reference to a baseclass which you initialized with an object of the derived class. Edited by wintertime
1

Share this post


Link to post
Share on other sites
In this case BorderedWindow::drawBorder() dominates WindowWithMenu::drawBorder() in CustomWindow and likewise WindowWithMenu::prompt() dominates BorderedWindow::prompt(). Since the dominant member functions are all non-pure virtual the CustomWindow is non-abstract.

Btw., you should always add a virtual destructor to any baseclass with a virtual method to prevent errors when you only have a pointer or reference to a baseclass which you initialized with an object of the derived class.

Note that this isn't necessary in C++11 anymore, as it makes the destructor implicitly virtual if a class has any virtual functions.
0

Share this post


Link to post
Share on other sites

In this case BorderedWindow::drawBorder() dominates WindowWithMenu::drawBorder() in CustomWindow and likewise WindowWithMenu::prompt() dominates BorderedWindow::prompt(). Since the dominant member functions are all non-pure virtual the CustomWindow is non-abstract.

Btw., you should always add a virtual destructor to any baseclass with a virtual method to prevent errors when you only have a pointer or reference to a baseclass which you initialized with an object of the derived class.

Note that this isn't necessary in C++11 anymore, as it makes the destructor implicitly virtual if a class has any virtual functions.
I can't find anything to back that up, and Visual Studio 2012 does not do it.

At the very least, it seems like a dangerous assumption, and could actually be wrong.
0

Share this post


Link to post
Share on other sites

1. That has nothing to do with virtual inheritance. Its to leave the possibility open that programmers make a class hierarchy with more than 2 steps where they continuously add common functionality first and later more specialized. If you try to make a BorderedWindow or WindowWithMenu you will see the compiler guards against this because its an abstract class like Window.
2. Should be the same if it both compiles.

Btw., you should always add a virtual destructor to any baseclass with a virtual method to prevent errors when you only have a pointer or reference to a baseclass which you initialized with an object of the derived class.

ok so for pure virtual functions, you dont necessarily have to implement the pure function in the NEXT level derived class. As long as in the hierarchy, derived class(that could be instantiated) has implemented all pure virtual functions from his "higher level base classes" no matter how many levels it derives?

 

That code was just for demostrating the problem. Thanks for heads up tho. 

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0