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Laroche

Multi-Dimensional Arrays

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How do you allocate multi-dimensional arrays and how do you clean them up? I can''t seem to find it in my c++ reference for some reason.

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Here''s how you do it in C, YMMV


  
// 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;
}

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