pointers to 3D arrays C++

Question

C++: I have a problem with pointers to 3D arrays - I'm writing a basic game with 2D arrays, each 2D array is a separate level and these levels are grouped into a 3D array called map.

How can I point to each 'level' of my game? My streamlined code:

#include<iostream>
using namespace std;

#define LEVEL  2
#define HEIGHT 3
#define WIDTH  3

bool map[LEVEL][HEIGHT][WIDTH] = { {{1, 0, 1},   
                                    {1, 0, 1},   
                                    {0, 0, 1}},

                                   {{1, 1, 0},   
                                    {0, 0, 0},   
                                    {1, 0, 1}} };
int main()
{
  // ideally this points to level#1, then increments to level#2 
  bool *ptrMap;

  for(int i=0; i<HEIGHT; i++)
  {
     for(int j=0; j<WIDTH; j++)
       cout << map[1][i][j];       // [*ptrMap][i][j] ?
     cout << endl;
  }
return 0;    
}

Combination of a struct with a one dim array is easier to understand. — masoud, Aug 16 '13 at 22:38

score 0 · Answer 1 · answered Aug 16 '13 at 22:48

0

bool (*ptrMap)[HEIGHT][WIDTH] = &map[level];
bool (&refMap)[HEIGHT][WIDTH] = map[level];

cout << (*ptrMap)[y][x];
cout << refMap[y][x];

answered Aug 16 '13 at 22:48

Jarod42

203,559
14
181
302

1

No explanation? If the OP is confused about his code he sure as hell ain't gonna understand this. – Tyler Jandreau Aug 16 '13 at 23:53

score 0 · Accepted Answer · answered Aug 17 '13 at 05:46

0

Assign,

bool *ptrmap= &map[0][0][0];// gives you level 0
cout<<*ptrmap; //outputs the first element, level 0
cout<<*(ptrmap+9);// outputs first element, level 1

If you do not want a linear increment of pointers,

i.e. map[0][0][0] as *ptrmap & map[1][0][0] as *(ptrmap + 9)

, I suggest you use pointer of pointers to create the matrix (ex. bool ***ptrmap) and then create a temporary pointer to dereference it.

answered Aug 17 '13 at 05:46

Stephen Jacob

889
1
15
33

Multidimensional arrays should never be casted to pointers: http://stackoverflow.com/questions/2895433/casting-char-to-char-causes-segfault – Manu343726 Aug 17 '13 at 10:24
But I believe this is not casting, it is simply assigning the address of the array to the pointer – Stephen Jacob Aug 17 '13 at 10:47
Read the answer of the link. The problem is with the memory layout of a static array, and a dynamic array (Array of arrays), is not the same. – Manu343726 Aug 17 '13 at 11:03
I am sorry but I don't understand, what's that got to do with my answer to this question, I guess I have not understood your point. Is it something to do with this answer or is it something to do with c++ per se? I am a relative newbie to c++. – Stephen Jacob Aug 17 '13 at 12:28

pointers to 3D arrays C++

2 Answers2

Linked