• 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
Youbar

Confused by Pointers (Beginner's Script):

6 posts in this topic

[CODE]// more pointers
#include <iostream>
using namespace std;
int main ()
{
int firstvalue = 5, secondvalue = 15;
int * p1, * p2;
p1 = &firstvalue; // p1 = address of firstvalue
p2 = &secondvalue; // p2 = address of secondvalue
*p1 = 10; // value pointed by p1 = 10
*p2 = *p1; // value pointed by p2 = value pointed by p1
p1 = p2; // p1 = p2 (value of pointer is copied)
*p1 = 20; // value pointed by p1 = 20

cout << "firstvalue is " << firstvalue << endl;
cout << "secondvalue is " << secondvalue << endl;
return 0;
}[/CODE]

I understand all but this line of the script, which I don't see any reason for:
[CODE]p1 = p2; // p1 = p2 (value of pointer is copied)[/CODE]

I can see that it says it was copied, but I thought that already happened in the line above that?
[CODE]*p2 = *p1; // value pointed by p2 = value pointed by p1[/CODE] Edited by Youbar
0

Share this post


Link to post
Share on other sites
What is it you find confusing about the two lines? One assigns pointers, the other assigns the values pointed to by the pointers. The line [i]p1=p2[/i] simply means that the two pointers point to the same address, while [i]*p2=*p1[/i] assigns the values pointed to by the two pointers.
1

Share this post


Link to post
Share on other sites
If there's no views it just means that nobody has looked yet.

Traffic varies.

Breathe deeply. [img]http://public.gamedev.net//public/style_emoticons/default/tongue.png[/img]
0

Share this post


Link to post
Share on other sites
A pointer contains the address of something, in the line above the asterisk "dereferences" the pointer (meaning it goes to the location the pointer is pointing to).
The first line says "pointer1 now points to the same thing as pointer2",
the second line says "the thing that pointer1 is pointing to is now the same as the thing that pointer2 is pointing to".
* and & can be a bit confusing for beginners because sometimes it depends on the context. For me it helps to put it into a phrase in this manner.
0

Share this post


Link to post
Share on other sites
The purpose might become clearer when additional output is used:
[code]
// more pointers

#include <string>
#include <iostream>


using namespace std;

void print(string description, int value1, int value2, int *pointer1, int *pointer2) {
cout << description << ": " << endl;
cout << " first value is " << value1 << endl;
cout << " second value is " << value2 << endl;
cout << " first pointer is at " << pointer1 << " with value " << *pointer1 << endl;
cout << " second pointer is at " << pointer2 << " with value " << *pointer2 << endl;
cout << endl;
}


int main()
{
int firstvalue = 5;
int secondvalue = 15;

int * p1 = &firstvalue;
int * p2 = &secondvalue;

print("Initial values", firstvalue, secondvalue, p1, p2);


// value pointed by p1 = 10
*p1 = 10;
print("After setting *p1 to 10", firstvalue, secondvalue, p1, p2);

// value pointed by p2 = value pointed by p1
*p2 = *p1;
print("After settings *p2 to *p1", firstvalue, secondvalue, p1, p2);

// p1 = p2 (value of pointer is copied)
p1 = p2;
print("After pointing p1 to p2", firstvalue, secondvalue, p1, p2);

// value pointed by p1 = 20
*p1 = 20;
print("After setting *p1 to 20", firstvalue, secondvalue, p1, p2);

return 0;
}
[/code]

On my system, this produces:
[code]
Initial values:
first value is 5
second value is 15
first pointer is at 0x7fffe8171510 with value 5
second pointer is at 0x7fffe8171514 with value 15


After setting *p1 to 10:
first value is 10
second value is 15
first pointer is at 0x7fffe8171510 with value 10
second pointer is at 0x7fffe8171514 with value 15

After settings *p2 to *p1:
first value is 10
second value is 10
first pointer is at 0x7fffe8171510 with value 10
second pointer is at 0x7fffe8171514 with value 10


After pointing p1 to p2:
first value is 10
second value is 10
first pointer is at 0x7fffe8171514 with value 10
second pointer is at 0x7fffe8171514 with value 10

After setting *p1 to 20:
first value is 10
second value is 20
first pointer is at 0x7fffe8171514 with value 20
second pointer is at 0x7fffe8171514 with value 20
[/code]

As you can see, after that line the two pointers point at the same location, and dereferencing them yields the same value. Edited by rip-off
1

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