Run-time error allocating 3-D array

This is a discussion on Run-time error allocating 3-D array within the C++ Programming forums, part of the General Programming Boards category; I posted this message earlier in the C forum, and was told this is a C++ problem so I am ...

  1. #1
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    Run-time error allocating 3-D array

    I posted this message earlier in the C forum, and was told this is a C++ problem so I am posting it here. I hope I am not offending anybody with a cross-post.

    Following some literature I was able write the code below to dynamically allocate a two dimensional array. I made the attempt to extrapolate the code for a three dimensional array. The code below for the 3-D array compiles, but gives me a fatal run-time error. Since the 3-D array is not used anywhere in the code (I am just setting it up for now), the run-time error must come from the algorithm I am using to allocate. Evidently, I don't fully understand what is going on. I appreciate any help I can get.

    Thanks, Jeff


    Code:
    /*******TWO DIMENSIONAL ARRAY*******/
    int nx,ny;
    struct GRID
    {
    	float	x1;
    	float	y1;
    	float	x2;
    	float	y2;
    };
    GRID **grid2, *grid1;
    
    nx = 8;
    ny = 4;
    grid1 = new GRID[nx*ny];
    grid2 = new GRID * [nx];
    for (i=0; i<nx; i++)
    	grid2[i] = &(grid1[i*ny]);  // Sets up a 2-D array with dimension grid[8][4]
    
    /*******THREE DIMENSIONAL ARRAY*******/
    int ndt,nx,ny;
    struct CELL
    {
    	float	height;
    	int	col;
    };
    CELL ***cell3,**cell2, *cell1;
    
    ndt = 100;
    nx = 8;
    ny = 4;
    cell1 = new CELL[ndt*nx*ny];
    cell2 = new CELL * [ndt*nx];
    cell3 = new CELL ** [ndt];
    for (t=0; t<ndt; t++)
    	cell2[t] = &(cell1[(t*nx)]);
    for (t=0; t<ndt; t++)
    	for (i=0; i<nx; i++)
    		cell3[t][i] = &(cell2[(t*nx)][(i*ny)]);  // Sets up a 3-D array with dimension cell[100][8][4]

  2. #2
    Super Moderator VirtualAce's Avatar
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    Read: 3D array=bad.

  3. #3
    and the hat of wrongness Salem's Avatar
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    Try this
    Code:
    #include <iostream>
    #include <iomanip>
    using namespace std;
    
    /* make int a[max_x][max_y][max_z] */
    int ***make3d ( int max_x, int max_y, int max_z ) {
      int ***px = new int**[max_x];
      int  **py = new int* [max_x * max_y];
      int   *pz = new int  [max_x * max_y * max_z];
      int rx, ry, rz;
    
      for ( rx = 0 ; rx < max_x ; rx++ ) {
        px[rx] = py;
        py += max_y;
        for ( ry = 0 ; ry < max_y ; ry++ ) {
          px[rx][ry] = pz;
          pz += max_z;
          for ( rz = 0 ; rz < max_z ; rz++ ) {
            px[rx][ry][rz] = rx + ry + rz;
          }
        }
      }
    
      return px;
    }
    
    void show ( int ***a, int max_x, int max_y, int max_z ) {
      int rx, ry, rz;
      for ( rx = 0 ; rx < max_x ; rx++ ) {
        for ( ry = 0 ; ry < max_y ; ry++ ) {
          for ( rz = 0 ; rz < max_z ; rz++ ) {
            cout << setw(4) << a[rx][ry][rz];
          }
          cout << endl;
        }
        cout << "--" << endl;
      }
    }
    
    void free3d ( int ***a ) {
      delete [] a[0][0];
      delete [] a[0];
      delete [] a;
    }
    
    int main ( ) {
      int ***a = make3d ( 2, 3, 4 );
      show ( a, 2, 3, 4 );
      free3d ( a );
      return 0;
    }
    If this is C++, consider using say vectors.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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