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Simple class question

Started by jrmiller84 Sep 8, 2005 at 4:03 PM 4 replies 800+ views

Original Post

Sep 8, 2005 at 4:03 PM

Hey everyone, I have a pretty simple question whose answer I cant seem to find anywhere. Is there a way to determine if an instance of a class exists? Basically I have an array of classes that amount to blocks, when the ball collides with the blocks, they need to disappear. Now, I know the easy way out would be to just set a bool value that states that it has not been hit and once it's hit, set it to true and then don't render that block, but I'm looking for something a little more elegant so I don't waste resources. I've tried a few different things with no luck. Any help would be great. Thanks everyone.

SiCrane

Mod

473

SiCrane

Sep 8, 2005 at 4:08 PM

In what programming language?

jrmiller84

Author

jrmiller84

Sep 8, 2005 at 4:08 PM

I guess that would be helpful, sorry haha, C++

MidoriKid

Sep 8, 2005 at 4:32 PM

I would use a linked list to hold the blocks. When the ball hits one simply remove it. Check out stl::list.

edit: Untested example

#include <list>#include "Block.hpp"#include "Ball.hpp"int main() {    stl::list<Block> blocks;    Ball myBall(30,50);    // add blocks to the list here    blocks.push_back(Block(25,25));    blocks.push_back(Block(50,25));    // main loop    while (!gameOver) {        // check every block to see if it touches the ball        for(stl::list<Block>::iterator b = blocks.begin(); b != blocks.end(); b++) {           if (myBall.collides(b)) {               b = blocks.erase(b);           }        }    }}

Horatius83

Sep 8, 2005 at 4:51 PM

You could use a linked list, or if you want to access it like an array you could create a vector (or array, whatever) of pointers, then allocate them individually, when the ball hits that block you deallocate it (the block, not the ball) and set to null, thus you are freeing up memory and you are able to determine if the instance exists or not.

Edit: Of course if you don't want to use dynamic memory, you could use bitwise freakiness or bitvectors, you'd still have boolean values, but they'd only be 1bit, you'd be suprised how much information you can cram into 32bits.

streamer

Sep 8, 2005 at 5:14 PM

for determining if an instance if class exist, you can use Singletone class.
Basicly this class looks like:

class Singleton
{
public:
static Singleton * instance ();

protected:
Singleton ();

private:
static Singleton * m_pInstance;
};

Singleton * Singleton :: m_pInstance = 0L;

Singleton * Singleton :: instance ()
{
return ((m_pInstance ? m_pInstance
: (m_pInstance = new Singleton)));
}

now you can check with instance call if there is instance of something, and if not it will be created...
To get more sophisticated source code just do some google search..

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