Assigning values to 3d array in C

Question

I have 2 arrays as follows -

int **data; 
int ***count;

After running some analysis, I want make the following assignment-

count[i][j][k] = data[i][j];

However, I keep getting Segmentation fault which I think is related to some pointer assignment issues - Can anyone suggest how I can make this assignment?

Typical values of - data[i][j] = 0/1/2.

Definition of ZALLOC:

#define ZALLOC(item,n,type)      if ((item = (type *)calloc((n),sizeof(type))) == NULL)    fatalx("Unable to allocate %d unit(s) for item\n",n)

// memory assignment
int **data; 
int nrow, ncol; 

ZALLOC(data, ncol, int *);

for (index = 0; index < ncol; index++)
{
    ZALLOC(data[index], nrow, int);
}

int g=0, index1=0, index2=2;
data[index1][index2] = g;


int ***count;
int dim1 = 100, dim2 = 1, dim3=2;
ZALLOC(count, dim1, int **);

for (i = 0; i < dim1; i++)
{
ZALLOC(count[i], dim2, int *);
for (j = 0; j < dim2; j++)
{
ZALLOC(count[i][j], dim3, int);
}
}

// Initialize
for (i = 0; i < dim1; i++)
{
    for (j = 0; j < dim2; j++)
{
    for (k = 0; k < dim3; k++)
    {
        count[i][j][k] = 0;
    }
}
}
// Assignment
count[0][1][2] = data[1][2];

Those aren't arrays; they're pointers. How are you initializing them? — melpomene
– melpomene, Commented Feb 25, 2013 at 3:52
The problem lies in either your initializations or in the indices. — asheeshr
– asheeshr, Commented Feb 25, 2013 at 3:57
No this is not homework.The way I am initializing it as follows -for(i = 0; i < 10; i++) — user19758
– user19758, Commented Feb 25, 2013 at 3:57
@user19758 That only sets i to 10. It doesn't initialize data or count. — melpomene
– melpomene, Commented Feb 25, 2013 at 4:02

Jonathan Leffler · Accepted Answer · 2013-02-25 05:56:20Z

Your organization of the allocations is a bit odd. If you have 3 dimensions (lets call them levels, rows, and columns), you would normally allocate space to hold the levels, and then for each level you would allocate the space for the rows within the level, and then finally you would allocate the space for the columns within the row.

Your code seems to start in the middle (rows); then does some work at levels; and finally at the columns.

This code is a complete rewrite of yours, but it works without crashing. I've not yet validated it with valgrind; I need to upgrade the version on this machine.

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

#define ZALLOC(item, n, type) if ((item = (type *)calloc((n), sizeof(type))) == NULL) \
                                  fatalx("Unable to allocate %d unit(s) for item\n", n)

static void fatalx(const char *str, size_t n)
{
    fprintf(stderr, "%s: %zu\n", str, n);
    exit(1);
}

static int ***alloc_3d(int levels, int rows, int cols)
{
    int count = 0;
    int ***array_3d;
    ZALLOC(array_3d, levels, int **);
    for (int i = 0; i < levels; i++)
    {
        int **data;
        ZALLOC(data, rows, int *);
        array_3d[i] = data;
        for (int j = 0; j < rows; j++)
        {
            int *entries;
            ZALLOC(entries, cols, int);
            array_3d[i][j] = entries;
            for (int k = 0; k < cols; k++)
            {
                array_3d[i][j][k] = count++;
            }
        }
    }
    return array_3d;
}

static void print_3d(int ***a3d, int levels, int rows, int cols)
{
    for (int i = 0; i < levels; i++)
    {
        printf("%d:\n", i);
        for (int j = 0; j < rows; j++)
        {
            printf("   %d:  ", j);
            for (int k = 0; k < cols; k++)
                printf(" %3d", a3d[i][j][k]);
            putchar('\n');
        }
    }
}

static void free_3d(int ***a3d, int levels, int rows)
{
    for (int i = 0; i < levels; i++)
    {
        for (int j = 0; j < rows; j++)
            free(a3d[i][j]);
        free(a3d[i]);
    }
    free(a3d);
}

int main(void)
{
    int d1 = 3;
    int d2 = 5;
    int d3 = 7;
    int ***a3d = alloc_3d(d1, d2, d3);

    print_3d(a3d, d1, d2, d3);
    free_3d(a3d, d1, d2);

    return(0);
}

Output:

0:
   0:     0   1   2   3   4   5   6
   1:     7   8   9  10  11  12  13
   2:    14  15  16  17  18  19  20
   3:    21  22  23  24  25  26  27
   4:    28  29  30  31  32  33  34
1:
   0:    35  36  37  38  39  40  41
   1:    42  43  44  45  46  47  48
   2:    49  50  51  52  53  54  55
   3:    56  57  58  59  60  61  62
   4:    63  64  65  66  67  68  69
2:
   0:    70  71  72  73  74  75  76
   1:    77  78  79  80  81  82  83
   2:    84  85  86  87  88  89  90
   3:    91  92  93  94  95  96  97
   4:    98  99 100 101 102 103 104

Dear Jonathan, Thank you very much for your response. This was exactly the problem - after correcting the assignment, I found that the code works properly. Thanks again!!
Now checked over with valgrind; no problems (memory accesses or leaks) visible.

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