Multi-Dimensional Arrays

  
// 2D array allocation

#include <stdlib.h>
#include <stdio.h>


/*-------------------------------------------------------------------------------------

  FUNCTION		: array_int_2D(int nrows, int ncols)

  PURPOSE		: Template for allocating arrays. Could be used for any 2D array.

  RETURN     	: Start address of array

  PARAMS     	: nrows  - number of rows
				: ncols  - number of columns

--------------------------------------------------------------------------------------*/
int **array_int_2D(int nrows, int ncols)
{
	int i, j;

	// allocate the memory for rows
	int **arr = malloc(nrows * sizeof(int *));

	if(!arr) return 0;

	printf("Pointers to Rows allocated: %p\n", arr);

	// allocate the rows i.e. number of columns/row
	for(i = 0; i < nrows; i++){

		arr[i] = malloc(ncols * sizeof(int));

		if (!arr[i]){
			for (int k=0; k<(i-1); k++)
				free(arr[k]);  // release memory for all previously allocated
			free(arr);
		    return 0;
		}

		printf("Row %2d allocated: %p\n", i, arr[i]);
	}

	// fill in some values
	for (i=0; i < nrows; i++)
		for (j=0; j < ncols; j++)
			arr[i][j] = (i+1) * (j+1); // rows

	return arr;
}

/*-------------------------------------------------------------------------------------

  FUNCTION		: array_free_2D(int ***arr, int nrows, int ncols)

  PURPOSE		: Free memory allocated for 2D array.

  RETURN     	: NONE

  PARAMS     	: arr    - pointer to 2D array
				: nrows  - number of rows
				: ncols  - number of columns

--------------------------------------------------------------------------------------*/
void array_free_2D(int ***arr, int nrows, int ncols)
{
	int **array = *arr;		// dereference pointer to array


	if (array){
		for( int i = 0; i < nrows; i++){
			free(array[i]);
			printf("Row %2d de-allocated: %p\n", i, array[i]);
		}
		free(array);
		printf("Pointers to Rows de-allocated: %p\n", array);
		*arr = 0;
	}

}

int main (void)
{
	int i, j;
	int nrows = 24;
	int ncols = 8;
	int **matric;

	matric = array_int_2D(nrows, ncols);

	printf("\n------------------------------------------------------------------------------\n");

	printf("Dumping array contents\n");

	printf("\n------------------------------------------------------------------------------\n");

	if (matric){

		printf("Column |");
		for (i=0; i < ncols; i++)
			printf("\t%3d",i);

		printf("\n------------------------------------------------------------------------------\n");

		for (i=0; i < nrows; i++) {

			printf("Row %2d |", i);

			for (j=0; j < ncols; j++)
				printf("\t%3d", matric[i][j]);

			printf("\n");
		}
	}else{
		printf("No mem");
	}

	printf("\n------------------------------------------------------------------------------\n");

	// release the memory

	printf("Address of array before free %p\n", matric);
	array_free_2D(&matric, nrows, ncols);
	printf("Address of array after free %p\n", matric);
	return 0;
}