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(Axter) Your 2D Array Code

I'm trying to access a member function of a 2D array class I created with your header file, and while trying to write the data in it out to a file using member functions, the first one [0][0] wrote out just fine, but the second one [1][0] freaked out. What's going on with this?
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SonicX_BlueBlur
Asked:
SonicX_BlueBlur
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2 Solutions
 
rstaveleyCommented:
[He's going to ask you to post some code.]
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SonicX_BlueBlurAuthor Commented:
(Okay!)

This code uses the 2D array:
for (int Y = 0; Y < bHeight; Y++)
{
      for (int X = 0; X < bWidth; X++)
      {
            BoardTile[X][Y]->WriteData(boardFile);
      }
}
BoardTile is the 2D array. bWidth and bHeight are int; they hold the width and height for the array.

This goes to:
void BoardData::WriteData(FILE *boardFile)
{
      fwrite(&Color1, sizeof(int), 1, boardFile);
      fwrite(&Color2, sizeof(int), 1, boardFile);
      fwrite(&CharNum, sizeof(int), 1, boardFile);
      fwrite(&Param1, sizeof(int), 1, boardFile);
      fwrite(&Param2, sizeof(int), 1, boardFile);
}

BoardTile is of BoardData. All these member variables of BoardData are int. [0][0] works fine, but [1][0] messes up the program.
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SonicX_BlueBlurAuthor Commented:
Oh, by the way, BoardTile is a pointer to the templated linked list. It's inside another class (which is a templated linke list), and gets dynamically created when the class is constructed.
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rstaveleyCommented:
> BoardTile is a pointer to the templated linked list

I'm only familiar with Axter's 2D array, which was suggested by your title. In my experience, it's not common practice to use indexing in linked lists... and 2D indexing looks particularly tricky. If you are talking about a dynamic_2d_array<BoardData*>  (as in a http://axter.com/code/dynamic_2d_array.h), can you show us the code in which you populate the array?
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SonicX_BlueBlurAuthor Commented:
It is Axter's code. In the class containing this array is:

(public:) dynamic_2d_array<BoardData> *BoardTile;

The constructor for the top class:
BoardInfo::BoardInfo(char *nBoardName, int nWidth, int nHeight)
{
      BoardName = new char[strlen(nBoardName) + 1];
      strcpy(BoardName, nBoardName);
      bWidth = nWidth;
      bHeight = nHeight;

      BoardTile = new dynamic_2d_array<BoardData> (bWidth, bHeight);
}

(+20 pts)
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rstaveleyCommented:
Since it is dynamic_2d_array<BoardData> rather than dynamic_2d_array<BoardData*>, I think you want to change...

    BoardTile[X][Y]->WriteData(boardFile);

...to...

    BoardTile[X][Y].WriteData(boardFile);

...but the sun is over the yard arm and I'm not at my most reliable right now %-}
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SonicX_BlueBlurAuthor Commented:
Thing is, this:
dynamic_2d_array<BoardData> *BoardTile;
makes BoardTile a pointer, so I have to use ->. However, I see how you're declaring it... Should it be BoardData* in there instead of just BoardData? I'll try it.
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SonicX_BlueBlurAuthor Commented:
No, that doesn't work. If I type:
dynamic_2d_array<BoardData*> *BoardTile;
the program won't compile anymore.
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AxterCommented:
The problem is that you're using a pointer instead of a static variable.

If you want to correctly access the operator[] functions, you need to dereference the pointer.
Example:
dynamic_2d_array<BoardData> *BoardTile = new dynamic_2d_array<BoardData> (bWidth, bHeight);

//Use ( ) to dereference variable
(*BoardTile)[1][0] = somevalue;

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AxterCommented:
You could also call the operators explicitly via following method:
BoardTile->operator[](1)[0] = somevalue;

The main problem is that you're using a pointer.  You would run into this problem when ever you try to access the operator[] from an object via a pointer.
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AxterCommented:
I recommend that you make BoardTile member variable a static variable instead of a pointer.

You can still initialize it via initialize list.
BoardInfo::BoardInfo(char *nBoardName, int nWidth, int nHeight)
:BoardTile(nWidth, nHeight)
{
     BoardName = new char[strlen(nBoardName) + 1];
     strcpy(BoardName, nBoardName);
     bWidth = nWidth;
     bHeight = nHeight;
}

Notice the FULL colon on the initialize list line.
With the above example BoardTile is of the following type:
dynamic_2d_array<BoardData> BoardTile;
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SonicX_BlueBlurAuthor Commented:
Ah. Well, thanks. The second method didn't work; the first and third did. I decided to go with the third.
rstaveley: You tried. You get points too :)
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AxterCommented:
>>I decided to go with the third.

IMHO, that's the better choice.
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