dynamic array in class help

PTBmilo · 03-08-2003, 12:15 AM

Hi all. I have written a program for the LIFE game. I would like to make it possible for the user to change the world size, but am having some trouble making it work from within a class. I'm pretty sure that the problem is in this code:

Maybe somebody can see what I'm doing wrong?

Code:

class lifeBoard
{
public:
        void setEnv(int RCOUNT, int CCOUNT);
        typedef int* IntPoint;
private:        
        IntPoint *board;
        IntPoint *neighborCount;
}

void lifeBoard::setEnv(int RCOUNT, int CCOUNT)
{
        board=new IntPoint[RCOUNT];
        neighborCount=new IntPoint[RCOUNT];
        for(int row=0;row<RCOUNT;row++)
        {
                board[row]=new int[CCOUNT];
                neighborCount[row]=new int[CCOUNT];
        }
}

Dark_Helmet · 03-08-2003, 12:32 AM

I'll keep looking at the code some more, but I don't see anything immediately.

I do have a suggestion though. Is there any particular reason you want an array of arrays of ints? Why not do this:

Code:

class lifeBoard
{
public:
        void setEnv(int RCOUNT, int CCOUNT);
        // typedef int* IntPoint;
private:        
        int *board;
        int *neighborCount;
}

void lifeBoard::setEnv(int RCOUNT, int CCOUNT)
{
        board=new int[RCOUNT * CCOUNT];
        neighborCount=new int[RCOUNT * CCOUNT];
        // Initialization here for good measure...
        for(int index=0; index<(RCOUNT * CCOUNT); index++)
        {
                board[index]=0;
                neighborCount[index]=0;
        }
}

From that point on, you just need to be consistent in handling your rows and columns. As in row 2, column 4 (assuming 0 base) could be identified in one of two ways:
1) board[2*RCOUNT + 4]
2) board[2 + 4*CCOUNT]

The fewer nested pointers the better...

PTBmilo · 03-08-2003, 01:23 PM

Thanks for looking at the code. It was helpfull knowing that I needed to look elsewhere for the error. I found it this morning.... I needed CCOUNT and RCOUNT in later calculations, so I threw them in the class and all was O.K.:
(relevant code

Code:

class lifeBoard
{
public:

        int RCOUNT;
        int CCOUNT;
        void setEnv(int RCOUNT, int CCOUNT);
        void output();
        typedef int* IntPoint;
private:
        IntPoint *board;
        IntPoint *neighborCount;
};

void lifeBoard::setEnv(int RCOUNT, int CCOUNT)
{
        this->RCOUNT=RCOUNT;
        this->CCOUNT=CCOUNT;
        board=new IntPoint[RCOUNT];
        neighborCount=new IntPoint[RCOUNT];
        for(int row=0;row<RCOUNT;row++)
        {
                board[row]=new int[CCOUNT];
                neighborCount[row]=new int[CCOUNT];
        }
}

void lifeBoard::setCleanBoard()
{
        for(int row=0;row<RCOUNT;row++)
        {  
                for(int colum=0;colum<CCOUNT;colum++)
                {
                        board[row][colum]=0;
                        neighborCount[row][colum]=0;
                }
        }       
}

At least, this is how I got it to work, I don't know if it's the 'accepted' way of doing it (I'm curious about the "this->"... should I use a different method?)

Your suggestion about the array is interesting. I am going to play around with that.

Thanks again.

Dark_Helmet · 03-08-2003, 03:56 PM

Whichever version you understand better is the better way to go. You have enough to deal with in developing new code rather than trying to decipher some obscure way of making data structures.

I would suggest changing the variable names for RCOUNT and CCOUNT; either in the class itself or the setEnv() method. Personally, for those types of methods, I usually name them "new_<var name>". Like new_RCOUNT and new_CCOUNT. That way, you could simply say "RCOUNT = new_RCOUNT" and "CCOUNT = new_CCOUNT". That would also get rid of the "this->" references and it should be completely clear what's going on to anybody looking at the code.

Again, what you're comfortable with and understand is the most important thing. What you showed in your last post should work fine. Just remember to free/delete your board and neighborCount pointers in your class destructor... otherwise you'll have a big, fat memory leak...

PTBmilo · 03-08-2003, 06:26 PM

Thank you. I had it all working for a while, then I decided to include a 'resetEnv' member. Something wasn't working and now I'm way off on a tangent. Suppose I have this:

Code:

class lifeBoard
{
public:
        typedef int* IntPoint;
private:
        struct environment
        {
                int RCOUNT;
                int CCOUNT;
                IntPoint *board;
                IntPoint *neighborCount;
        };

        environment* world;
};

Then have a default constructor with, say:

Code:

lifeBoard::lifeBoard(int newRCOUNT,int newCCOUNT)
{
        setEnv(newRCOUNT,newCCOUNT);
}

void lifeBoard::setEnv(int newRCOUNT, int newCCOUNT)
{
        world=new environment;

        world->RCOUNT=newRCOUNT;
        world->CCOUNT=newCCOUNT;
        world->board=new IntPoint[newRCOUNT];
        world->neighborCount=new IntPoint[newRCOUNT];
        for(int row=0;row<newRCOUNT;row++)
        {
                world->board[row]=new int[newCCOUNT];
                world->neighborCount[row]=new int[newCCOUNT];
        }
        setCleanBoard();
}

If I ever want to reference *world.RCOUNT, I use this:

Code:

void lifeBoard::resetEnv(int newRCOUNT, int newCCOUNT)
{
        for(int row=0, row<(world->RCOUNT),row++)
        {
                delete [] world->board[row];
                delete [] world->neighborCount[row];
        }

        delete [] world->board;
        delete [] world->neighborCount;

        setEnv(newRCOUNT,newCCOUNT);
}

But the compiler spits out this:

Code:

/home/milo/ENG_38/dev [222]> g++ lifeClass-point.cpp
lifeClass-point.cpp: In method `void lifeBoard::resetEnv(int, int)':
lifeClass-point.cpp:59: parse error before `)'
lifeClass-point.cpp:62: void value not ignored as it ought to be
lifeClass-point.cpp:63: parse error before `}'

This is the first function after the class dec, and I'm sure it'd continue on the next one if I moved it.

I know that this is a total overkill for the problem, I am just trying to learn the tools (understand pointers?)

Can you see where I'm going wrong?

rmartine · 03-08-2003, 07:27 PM

When you see a parse error you should start looking for "syntax-type" errors before where the compiler tells you the error is.

From looking at the resetEnv function you have

for(int row=0, row<(world->RCOUNT),row++)

I think you want semicolons instead of commas in that for loop.

My 2 cents. BTW I like your new way of making the lifeboard class. It was easier for me to understand.

Again my 2 cents.

PTBmilo · 03-09-2003, 02:35 AM

Quote:

Originally posted by rmartine

I think you want semicolons instead of commas in that for loop.

boy do I feel silly

That was it man. Thank you very much.