Creating A Multidimentional Array Of Classes

[davidthefat]

I feel like a total noob asking this, but I was unsuccessful with making a 2d array of classes. I would get runtime errors, but not compiler errors. I tracked down the error using a debugger to a initialization of a 2d array of classes using pointers. I will post the code as soon as I can get my hands on it (its on a school computer)

[K-Bal]

Without code there is not much to say. You could use std::vector though:

Code: Select all

std::vector< std::vector< xyz > > myDynamic2dArray;

[Ginto8]

Without code there is not much to say. You could use std::vector though:

Code: Select all

std::vector< std::vector< xyz > > myDynamic2dArray;

Unless you NEED it to be dynamic, you don't want to use vectors. And even if you need it to be dynamic, you only want to use vectors if they have a significant advantage over simple dynamic arrays.

As for the OP's problem, without more informationt there isn't anything to do. To quote Sherlock Holmes, "One should never theorize until he has data."

[K-Bal]

Unless you NEED it to be dynamic, you don't want to use vectors. And even if you need it to be dynamic, you only want to use vectors if they have a significant advantage over simple dynamic arrays.

There are many ways to do it. I like it for it's simplicity and would never use it in high performance programs.

[davidthefat]

Code: Select all

//Image.cpp

#include "Image.h"

Image::Image(int H, int W)
{
    Height = H;
    Width = W;
    **Points = *new Location[Height];  //This is the problem
    for(int c = 0; c < H; c ++)
    {
        *Points[c] = *new Location[Width];
    }
    for(int h = 0; h < H; h ++)
    {
        for(int w = 0; w < W; w ++)
        {
            Points[h][w].setLocation(*new Location((float)w / 3 , (float)h / 3, 0));
        }
    }
}

Image::~Image()
{
    //dtor
}

float Image::getX(int H, int W)
{
    return Points[H][W].getX();
}
float Image::getY(int H, int W)
{
    return Points[H][W].getY();
}
float Image::getZ(int H, int W)
{
    return Points[H][W].getZ();
}
int Image::getHeight()
{
    return Height;
}
int Image::getWidth()
{
    return Width;
}

Code: Select all

//Image.h

#include "Location.h"

class Image
{
public:
    Image(int H, int W);
    virtual ~Image();
    float getX(int H, int W);
    float getY(int H, int W);
    float getZ(int H, int W);
    int getHeight();
    int getWidth();
protected:
private:
    Location **Points;
    int Height;
    int Width;
};

[Falco Girgis]

You reeeeeaally might want to have a look here:
http://www.codeproject.com/KB/cpp/arrayDinamic.aspx

Sorry to be a cheap ass, but I've answered this question about 3 times this month in C and C++.

Code: Select all

Points[h][w].setLocation(*new Location((float)w / 3 , (float)h / 3, 0));

THAT is a very bad idea. I'm pretty sure this is memory leak city, unless you are explicitly freeing the new locations when they're done being used. I'm fairly certain that you just want to instantiate the temporary variable on the stack.

ALWAYS beware of instantiating temporary variables on the stack--unless whatever is receiving them is also deleting them, you are losing your reference to the pointer and can never free it.

[Bakkon]

Code: Select all

**Points = *new Location[Height];  //This is the problem

No shit, it's a problem. The syntax is entirely wrong.

Code: Select all

Location*** Points = new Location**[COLS];

for(int i = 0; i < COLS; i++)
     Points[i] = new Location*[ROWS];

for(int y = 0; y < COLS; y++)
     for(int x = 0; x < ROWS; x++)
          Points[x][y] = new Location(params);

for(int y = 0; y < COLS; y++)
     for(int x = 0; x < ROWS; x++)
          delete Points[x][y];

for(int i = 0; i < COLS; i++)
     delete [] Points[i];

delete [] Points;

[K-Bal]

ALWAYS beware of instantiating temporary variables on the stack--unless whatever is receiving them is also deleting them, you are losing your reference to the pointer and can never free it.

You wanted to say heap

[Falco Girgis]

ALWAYS beware of instantiating temporary variables on the stack--unless whatever is receiving them is also deleting them, you are losing your reference to the pointer and can never free it.

You wanted to say heap

Ah, shit. You're right.

[davidthefat]

Code: Select all

**Points = *new Location[Height];  //This is the problem

No shit, it's a problem. The syntax is entirely wrong.

Code: Select all

Location*** Points = new Location**[COLS];

for(int i = 0; i < COLS; i++)
     Points[i] = new Location*[ROWS];

for(int y = 0; y < COLS; y++)
     for(int x = 0; x < ROWS; x++)
          Points[x][y] = new Location(params);

for(int y = 0; y < COLS; y++)
     for(int x = 0; x < ROWS; x++)
          delete Points[x][y];

for(int i = 0; i < COLS; i++)
     delete [] Points[i];

delete [] Points;

Unfortunately, that has the same error... IDK what to do... Its due on Wednesday and I still have to get the socket connection working too...