在 C 中动态分配一个 3D 矩阵

Question

So I've got a 2D Array which I am creating like this:

int** init_grid(int cell_grid_size) {
    // matrix variables
    int *memory_grid;
    int **matrix;
    int i;
    int j;

    // memory for matrix
    memory_grid = malloc(cell_grid_size * cell_grid_size * sizeof(int));
    matrix = malloc(cell_grid_size * sizeof(int *));

    // fill matrix with rows
    for(i = 0; i < cell_grid_size; i++) {
        matrix[i] = &memory_grid[i*cell_grid_size];
    }

    // return fresh matrix
    return matrix;
}

As you can see it's initialising a matrix of integers. However, I'd like to to initialize a matrix of integer arrays of size 2 (ie a 3D Matrix) but I can't quite seem to get my head around how to add the next dimension.

Any help would be greatly appreciated.

Answer 1

For an int *** pointing to an array of pointers of type int ** . Each pointing to an int * . Each int * pointer to an array of int .

Allocation checks for NULL omitted for brevity.

int*** init_grid(size_t xsize, size_t ysize, size_t zsize) {
  int ***matrix = malloc(sizeof matrix[0] * xsize);

  for (x = 0; x < xsize; x++) {
    matrix[x] = malloc(sizeof matrix[x][0] * ysize);
    for (y = 0; y < ysize; y++) {
      matrix[x][y] = malloc(sizeof matrix[x][y][0] * zsize);
      // or to zero-out the `int` data
      matrix[x][y] = calloc(zsize, sizeof matrix[x][y][0]);
    }
  }
  return matrix;
}

Use size_t for array indexing and sizing.

To free:

void free_grid(int ***matrix, size_t xsize, size_t ysize) {
  if (matrix) {
    for (x = 0; x < xsize; x++) {
      if (matrix[x]) {
        for (y = 0; y < ysize; y++) {
          free(matrix[x][y])
        }
      }
      free(matrix[x]);
    }
    free(matrix);
  }
}

Answer 2

void grid_init(int* matrix, unsigned int xsize, unsigned int ysize, unsigned int unsigned int zsize)
{
    unsigned int matrix_size;

    // flatten matrix size in Byte
    matrix_size = xsize*ysize*zsize*sizeof(int);

    matrix = (int*)malloc(matrix_size);
    memset(matrix, 0, sizeof(matrix_size);
}

Once matrix is built, you can loop through it using that loop:

void grid_fill(int* matrix, int value, unsigned int xsize, unsigned int ysize, unsigned int zsize)
{
 int i,j,k;

 for(k=0; k<zsize; k++)
 {
     for(i=0; i<ysize; i++)
     {
         for(j=0; j<xsize; j++)
         {
              matrix[j+i*xsize+k*ysize*xsize] = value;
         }
     }
  }
}