Calloc for an array of array with negative index in C

Question

I have an array of array with negative index. It is an array which has real dimensions [dim_y + 40][dim_x + 40] but the user uses the array like it has dimensions [dim_y][dim_x]. First i had global and already defined the dimensions dim_x, dim_y, so i had this

int map_boundaries[dim_y + 40][dim_x + 40];
int (*map)[dim_x+40] = (int(*)[dim_x+40])&map_boundaries[20][20];

It worked fine. Now i need the dimensions dim_y and dim_x to be variable, and with this i mean that i want the array 'map' to not have fixed size but dynamic, i need to read the dim_y, dim_x from a user and the array 'map' to be global, so i have

int **map_boundaries;

and i use calloc in main()

map_boundaries = (int **)calloc(dim_y + 40,sizeof(int*)); 
for(i = 0; i < dim_y + 40; i++){
    map_boundaries[i] = (int *)calloc(dim_x + 40,sizeof(int));
}

, but i don't know how to declare the second line

For better understanding of the boundaries thing i did what is posted in the 2nd comment here: http://everything2.com/title/Negative+array+indexing

I assume you mean you "need the dimensions to be variable" *per-top-level-dimension*. I.e. `map_boundaries[0]` will point to an array that may be a *different* dimension than `map_boundaries[1]`, etc. If that isn't what you meant, perhaps clarify your question (and include your `calloc` line, which you seem to have left out for no particular reason). — WhozCraig, Oct 14 '14 at 00:05
yeah, we got that. Again, do you mean `dim_x` needs to be able to vary **per row**? It makes a difference. As you have it now you're using VLA declarations which is fine for any *given* `dim_x` and `dim_y` that will fit in your automatic variable allowable space, but won't work if you want, say, the first row to have 3 elements, the second to have 5, etc. *Is that what you need* ? — WhozCraig, Oct 14 '14 at 00:10
@WhozCraig no, i just need to get two values from a user, a dim_x and a dim_y, like i have a normal double array, for example dim_y = 10, dim_x = 15. So every row has the same number of columns — user3143155, Oct 14 '14 at 00:14
C99 supports VLA, so after you get them from the user, you can declare them using your old fashion. it is called variable length array. — CS Pei, Oct 14 '14 at 00:15
@JohnSmith , thanx for your answer, could you plz post this line how it should be? — user3143155, Oct 14 '14 at 00:18
Then your question is somewhat unclear. What does "negative indexes" have to do with any of this? Sry if its seems redundant, but you may clearly see your problem; we don't. What is the actual *problem*? (i.e. what does the "negative indexes" have to do with *any* of this. — WhozCraig, Oct 14 '14 at 00:18
`int map_boundaries[dim_y + 40][dim_x + 40]; int (*map)[dim_x+40] = (int(*)[dim_x+40])&map_boundaries[20][20];` — CS Pei, Oct 14 '14 at 00:19
@WhozCraig I build a simulation, my map has dimensions dim_y and dim_x, but i need to have some additional boundaries just for me, the user don't need them. So i have additional space that i only see. That is the reason of negative index. But i just need this to declare it with variable dim_x and dim_y instead of being static — user3143155, Oct 14 '14 at 00:22
@JohnSmith i can't do this i need the variable 'map' to be global — user3143155, Oct 14 '14 at 00:24
What is the range of valid indexes that you require? From your general description, it looks as if you want to be able to use `map[x][y]` with `x` in the range `-20 .. x_dim+20` and with `y` in the range `-20 .. y_dim + 20`. Is that correct? And you need `x_dim` and `y_dim` to be selectable at run time, not compile time constants, but the offsets (-20, +20) are fixed at compile time. — Jonathan Leffler, Oct 14 '14 at 01:16
@JonathanLeffler yes the offsets are fixed. For example map[0][0] is map_boundaries[20][20]. For the user the range of row lets say, is (0, dim_y), but for me is (-20, dim_y + 20). I want the offsets (-20, 20) to be fixed whatever the dim_y, dim_x will be. Till now i defined dim_y and dim_x, but now i just need the user to define them at run time. — user3143155, Oct 14 '14 at 01:31
'Tis doable, but tricky. I'm still not completely clear on what the 'user' (programmer) sees vs what 'you' (library provider?) see. I need to read the code and comments to get the variable names straight. If I'm interpreting your last comment correctly, ... oh, it changed and came into line with what I was expecting. Phew! — Jonathan Leffler, Oct 14 '14 at 01:32
@JonathanLeffler lets say the array is a square. So we have a big square and a small one in it. I (the one who writes the code) see the big one, and the user sees just the small one which is in the big. The boundaries are just for me — user3143155, Oct 14 '14 at 01:38

score 0 · Answer 1 · answered Oct 14 '14 at 01:42

I would allocate a single array:

int* storage = calloc((dim_x + 40) * (dim_y + 40), sizeof(int));

Then I'd return it to the user in an opaque struct like this:

struct map {
  int* storage;
  size_t dim_x;
  size_t dim_y;
};

Then I would define an indexing function for the user:

int* get_cell(struct map* m, x, y) {
  return &m->storage[(x + 20) + (m->dim_x + 40) * (y + 20)];
}

And perhaps to get an entire row if the user wants to read/write multiple elements in one row:

int* get_row(struct map* m, y) {
  return get_cell(m, 0, y);
}

size_t get_row_size(struct map* m) {
  return m->dim_x;
}

Since you want the dimensions to be determined at runtime, you will need to do runtime index calculations in any case.

score 0 · Answer 2 · edited May 23 '17 at 11:49

Here's my version of the code. The int **map value is what both user and library use to access the data. The Matrix structure encapsulates all the information about the array, including a member that is use to initialize map. The code sets up the sizes, allocates and initializes the structure, then initializes the array, then uses it as a user would, and as the library would. Finally, the allocated memory is freed.

In practice, you'd probably want to split this up into a number of separate functions.

Source: `2da.c`:

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include "stderr.h"

typedef struct Matrix
{
    int  *map_base;
    int **map_rows;
    int   x_dim;
    int   y_dim;
    int   extra;
    int **map;
} Matrix;

int main(void)
{
    Matrix m;
    int x_dim = 8;
    int y_dim = 6;
    int extra = 5;

    /* Allocation */
    m.extra = extra;
    m.x_dim = x_dim;
    m.y_dim = y_dim;
    int x_cells = x_dim + 2 * extra;
    int y_cells = y_dim + 2 * extra;
    m.map_base = calloc(x_cells * y_cells, sizeof(**m.map));
    if (m.map_base == 0)
        err_syserr("Failed to allocate %zu bytes memory\n",
                   x_cells * y_cells * sizeof(**m.map));
    m.map_rows = calloc(x_cells, sizeof(*m.map));
    if (m.map_rows == 0)
        err_syserr("Failed to allocate %zu bytes memory\n",
                   x_cells * sizeof(*m.map));
    //printf("Map base: 0x%.8" PRIXPTR "\n", (uintptr_t)m.map_base);
    //printf("Map rows: 0x%.8" PRIXPTR "\n", (uintptr_t)m.map_rows);
    for (int i = 0; i < x_cells; i++)
    {
        m.map_rows[i] = &m.map_base[i * y_cells + extra];
        //printf("Row[%2d]   0x%.8" PRIXPTR "\n", i, (uintptr_t)m.map_rows[i]);
    }
    m.map = &m.map_rows[extra];

    int **map = m.map;
    //printf("Map:      0x%.8" PRIXPTR "\n", (uintptr_t)map);

    /* Initialization */
    int x_min = -extra;
    int y_min = -extra;
    int x_max = x_dim + extra;
    int y_max = y_dim + extra;
    printf("Initialization:\n");
    for (int i = x_min; i < x_max; i++)
    {
        for (int j = y_min; j < y_max; j++)
        {
            map[i][j] = i * 100 + j;
            //printf("[%2d,%2d] = %4d\n", i, j, map[i][j]);
        }
    }

    printf("User view:\n");
    for (int i = 0; i < x_dim; i++)
    {
        for (int j = 0; j < y_dim; j++)
            printf("[%2d,%2d] = %4d\n", i, j, map[i][j]);
    }

    printf("Library view:\n");
    for (int i = x_min; i < x_max; i++)
    {
        for (int j = y_min; j < y_max; j++)
            printf("[%2d,%2d] = %4d\n", i, j, map[i][j]);
    }

    /* Deallocation */
    free(m.map_base);
    free(m.map_rows);

    return 0;
}

Example output

When run under valgrind 3.10.0 on Mac OS X 10.9.5 with GCC 4.9.1, I got the following output. The "stderr.h" header is in $HOME/inc and declares err_syserr(), while libjl.a is in $HOME/lib/64 and provides the implementation for err_syserr(), a function that reports the given error message and the error identified by errno and exits. I'm too lazy to write the code in this program this time around. (Search for '[c] user:15168 err_syserr' in SO to find Protect a shared memory segment with semaphore does not work, which has essentially equivalent code. I didn't call err_setarg0() in the code in this answer.)

$ gcc -O3 -g -I/Users/jleffler/inc -std=c11 -Wall -Wextra -Wmissing-prototypes \
>     -Wstrict-prototypes -Wold-style-definition -Werror 2da.c -o 2da \
>     -L/Users/jleffler/lib/64 -ljl
$ valgrind ./2da
==26293== Memcheck, a memory error detector
==26293== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==26293== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==26293== Command: 2da
==26293== 
Initialization:
User view:
[ 0, 0] =    0
[ 0, 1] =    1
[ 0, 2] =    2
[ 0, 3] =    3
[ 0, 4] =    4
[ 0, 5] =    5
[ 1, 0] =  100
[ 1, 1] =  101
[ 1, 2] =  102
[ 1, 3] =  103
[ 1, 4] =  104
[ 1, 5] =  105
[ 2, 0] =  200
[ 2, 1] =  201
[ 2, 2] =  202
[ 2, 3] =  203
[ 2, 4] =  204
[ 2, 5] =  205
[ 3, 0] =  300
[ 3, 1] =  301
[ 3, 2] =  302
[ 3, 3] =  303
[ 3, 4] =  304
[ 3, 5] =  305
[ 4, 0] =  400
[ 4, 1] =  401
[ 4, 2] =  402
[ 4, 3] =  403
[ 4, 4] =  404
[ 4, 5] =  405
[ 5, 0] =  500
[ 5, 1] =  501
[ 5, 2] =  502
[ 5, 3] =  503
[ 5, 4] =  504
[ 5, 5] =  505
[ 6, 0] =  600
[ 6, 1] =  601
[ 6, 2] =  602
[ 6, 3] =  603
[ 6, 4] =  604
[ 6, 5] =  605
[ 7, 0] =  700
[ 7, 1] =  701
[ 7, 2] =  702
[ 7, 3] =  703
[ 7, 4] =  704
[ 7, 5] =  705
Library view:
[-5,-5] = -505
[-5,-4] = -504
[-5,-3] = -503
[-5,-2] = -502
[-5,-1] = -501
[-5, 0] = -500
[-5, 1] = -499
[-5, 2] = -498
[-5, 3] = -497
[-5, 4] = -496
[-5, 5] = -495
[-5, 6] = -494
[-5, 7] = -493
[-5, 8] = -492
[-5, 9] = -491
[-5,10] = -490
[-4,-5] = -405
[-4,-4] = -404
[-4,-3] = -403
[-4,-2] = -402
[-4,-1] = -401
[-4, 0] = -400
[-4, 1] = -399
[-4, 2] = -398
[-4, 3] = -397
[-4, 4] = -396
[-4, 5] = -395
[-4, 6] = -394
[-4, 7] = -393
[-4, 8] = -392
[-4, 9] = -391
[-4,10] = -390
[-3,-5] = -305
[-3,-4] = -304
[-3,-3] = -303
[-3,-2] = -302
[-3,-1] = -301
[-3, 0] = -300
[-3, 1] = -299
[-3, 2] = -298
[-3, 3] = -297
[-3, 4] = -296
[-3, 5] = -295
[-3, 6] = -294
[-3, 7] = -293
[-3, 8] = -292
[-3, 9] = -291
[-3,10] = -290
[-2,-5] = -205
[-2,-4] = -204
[-2,-3] = -203
[-2,-2] = -202
[-2,-1] = -201
[-2, 0] = -200
[-2, 1] = -199
[-2, 2] = -198
[-2, 3] = -197
[-2, 4] = -196
[-2, 5] = -195
[-2, 6] = -194
[-2, 7] = -193
[-2, 8] = -192
[-2, 9] = -191
[-2,10] = -190
[-1,-5] = -105
[-1,-4] = -104
[-1,-3] = -103
[-1,-2] = -102
[-1,-1] = -101
[-1, 0] = -100
[-1, 1] =  -99
[-1, 2] =  -98
[-1, 3] =  -97
[-1, 4] =  -96
[-1, 5] =  -95
[-1, 6] =  -94
[-1, 7] =  -93
[-1, 8] =  -92
[-1, 9] =  -91
[-1,10] =  -90
[ 0,-5] =   -5
[ 0,-4] =   -4
[ 0,-3] =   -3
[ 0,-2] =   -2
[ 0,-1] =   -1
[ 0, 0] =    0
[ 0, 1] =    1
[ 0, 2] =    2
[ 0, 3] =    3
[ 0, 4] =    4
[ 0, 5] =    5
[ 0, 6] =    6
[ 0, 7] =    7
[ 0, 8] =    8
[ 0, 9] =    9
[ 0,10] =   10
[ 1,-5] =   95
[ 1,-4] =   96
[ 1,-3] =   97
[ 1,-2] =   98
[ 1,-1] =   99
[ 1, 0] =  100
[ 1, 1] =  101
[ 1, 2] =  102
[ 1, 3] =  103
[ 1, 4] =  104
[ 1, 5] =  105
[ 1, 6] =  106
[ 1, 7] =  107
[ 1, 8] =  108
[ 1, 9] =  109
[ 1,10] =  110
[ 2,-5] =  195
[ 2,-4] =  196
[ 2,-3] =  197
[ 2,-2] =  198
[ 2,-1] =  199
[ 2, 0] =  200
[ 2, 1] =  201
[ 2, 2] =  202
[ 2, 3] =  203
[ 2, 4] =  204
[ 2, 5] =  205
[ 2, 6] =  206
[ 2, 7] =  207
[ 2, 8] =  208
[ 2, 9] =  209
[ 2,10] =  210
[ 3,-5] =  295
[ 3,-4] =  296
[ 3,-3] =  297
[ 3,-2] =  298
[ 3,-1] =  299
[ 3, 0] =  300
[ 3, 1] =  301
[ 3, 2] =  302
[ 3, 3] =  303
[ 3, 4] =  304
[ 3, 5] =  305
[ 3, 6] =  306
[ 3, 7] =  307
[ 3, 8] =  308
[ 3, 9] =  309
[ 3,10] =  310
[ 4,-5] =  395
[ 4,-4] =  396
[ 4,-3] =  397
[ 4,-2] =  398
[ 4,-1] =  399
[ 4, 0] =  400
[ 4, 1] =  401
[ 4, 2] =  402
[ 4, 3] =  403
[ 4, 4] =  404
[ 4, 5] =  405
[ 4, 6] =  406
[ 4, 7] =  407
[ 4, 8] =  408
[ 4, 9] =  409
[ 4,10] =  410
[ 5,-5] =  495
[ 5,-4] =  496
[ 5,-3] =  497
[ 5,-2] =  498
[ 5,-1] =  499
[ 5, 0] =  500
[ 5, 1] =  501
[ 5, 2] =  502
[ 5, 3] =  503
[ 5, 4] =  504
[ 5, 5] =  505
[ 5, 6] =  506
[ 5, 7] =  507
[ 5, 8] =  508
[ 5, 9] =  509
[ 5,10] =  510
[ 6,-5] =  595
[ 6,-4] =  596
[ 6,-3] =  597
[ 6,-2] =  598
[ 6,-1] =  599
[ 6, 0] =  600
[ 6, 1] =  601
[ 6, 2] =  602
[ 6, 3] =  603
[ 6, 4] =  604
[ 6, 5] =  605
[ 6, 6] =  606
[ 6, 7] =  607
[ 6, 8] =  608
[ 6, 9] =  609
[ 6,10] =  610
[ 7,-5] =  695
[ 7,-4] =  696
[ 7,-3] =  697
[ 7,-2] =  698
[ 7,-1] =  699
[ 7, 0] =  700
[ 7, 1] =  701
[ 7, 2] =  702
[ 7, 3] =  703
[ 7, 4] =  704
[ 7, 5] =  705
[ 7, 6] =  706
[ 7, 7] =  707
[ 7, 8] =  708
[ 7, 9] =  709
[ 7,10] =  710
[ 8,-5] =  795
[ 8,-4] =  796
[ 8,-3] =  797
[ 8,-2] =  798
[ 8,-1] =  799
[ 8, 0] =  800
[ 8, 1] =  801
[ 8, 2] =  802
[ 8, 3] =  803
[ 8, 4] =  804
[ 8, 5] =  805
[ 8, 6] =  806
[ 8, 7] =  807
[ 8, 8] =  808
[ 8, 9] =  809
[ 8,10] =  810
[ 9,-5] =  895
[ 9,-4] =  896
[ 9,-3] =  897
[ 9,-2] =  898
[ 9,-1] =  899
[ 9, 0] =  900
[ 9, 1] =  901
[ 9, 2] =  902
[ 9, 3] =  903
[ 9, 4] =  904
[ 9, 5] =  905
[ 9, 6] =  906
[ 9, 7] =  907
[ 9, 8] =  908
[ 9, 9] =  909
[ 9,10] =  910
[10,-5] =  995
[10,-4] =  996
[10,-3] =  997
[10,-2] =  998
[10,-1] =  999
[10, 0] = 1000
[10, 1] = 1001
[10, 2] = 1002
[10, 3] = 1003
[10, 4] = 1004
[10, 5] = 1005
[10, 6] = 1006
[10, 7] = 1007
[10, 8] = 1008
[10, 9] = 1009
[10,10] = 1010
[11,-5] = 1095
[11,-4] = 1096
[11,-3] = 1097
[11,-2] = 1098
[11,-1] = 1099
[11, 0] = 1100
[11, 1] = 1101
[11, 2] = 1102
[11, 3] = 1103
[11, 4] = 1104
[11, 5] = 1105
[11, 6] = 1106
[11, 7] = 1107
[11, 8] = 1108
[11, 9] = 1109
[11,10] = 1110
[12,-5] = 1195
[12,-4] = 1196
[12,-3] = 1197
[12,-2] = 1198
[12,-1] = 1199
[12, 0] = 1200
[12, 1] = 1201
[12, 2] = 1202
[12, 3] = 1203
[12, 4] = 1204
[12, 5] = 1205
[12, 6] = 1206
[12, 7] = 1207
[12, 8] = 1208
[12, 9] = 1209
[12,10] = 1210
==26293== 
==26293== HEAP SUMMARY:
==26293==     in use at exit: 29,341 bytes in 374 blocks
==26293==   total heap usage: 452 allocs, 78 frees, 36,581 bytes allocated
==26293== 
==26293== LEAK SUMMARY:
==26293==    definitely lost: 0 bytes in 0 blocks
==26293==    indirectly lost: 0 bytes in 0 blocks
==26293==      possibly lost: 0 bytes in 0 blocks
==26293==    still reachable: 4,096 bytes in 1 blocks
==26293==         suppressed: 25,245 bytes in 373 blocks
==26293== Rerun with --leak-check=full to see details of leaked memory
==26293== 
==26293== For counts of detected and suppressed errors, rerun with: -v
==26293== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$

The 'still reachable' block is the buffer for stdout; if I included fclose(stdout); before returning from main(), it would go. The Mac OS X runtime library allocates a lot of memory too, but that usage is identified in the suppressed information.

Comment and response

I do the whole initiallization as you see in 2 lines. But it is not the initialization that's the problem; the problem is that in every frame the values of map are changed. So I need just a 'map' which points directly to 'boundaries map'. map[0][0] is boundaries_map[20][20] and so on. I tried to declare global **map and then write my second line into the main but I get an error about cast. (*map)[dim_x+40] this is a **map isn't it?

I'm not sure I completely understand what you're after, which is one reason this response has taken a long time.

You cannot have global variables that are VLAs; they can only be allocated in functions, either on the stack as local variables or on the heap via malloc() et al. The original code I showed allows you to define an array via a global variable, a double pointer, that can be accessed from any code that can read the double pointer.

The code below could be considered an exercise in constructing VLAs. It uses malloc() to create a VLA, recording where it was created in a pointer to a VLA. This can be passed to a function just like a stack-based VLA can be passed. The code compiles cleanly under GCC 4.9.1 on Mac OS X 10.9.5:

$ gcc -g -O3 -std=c99 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Werror \
>     2dv.c -o 2dv

It runs cleanly and leak-free according to valgrind.

Source: `2dv.c`:

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

static void dump_vla_1(int x_size, int y_size, int vla[x_size][y_size]);
static void dump_vla_2(int x_min, int y_min, int x_size, int y_size,
                       int vla[x_size][y_size]);
static void dump_vla_3(int x_min, int x_max, int y_min, int y_max,
                       int x_size, int y_size, int vla[x_size][y_size]);

int main(void)
{
    int extra = 3;
    int x_base = 5;
    int y_base = 4;
    int x_size = x_base + 2 * extra;
    int y_size = y_base + 2 * extra;

    int (*vla)[x_size][y_size] = calloc(x_size * y_size, sizeof(int));

    for (int i = 0; i < x_size; i++)
        for (int j = 0; j < y_size; j++)
            (*vla)[i][j] = (i + 1) * 100 + (j + 1);

    for (int i = 0; i < x_size; i++)
    {
        for (int j = 0; j < y_size; j++)
            printf(" %4d", (*vla)[i][j]);
        putchar('\n');
    }

    dump_vla_1(x_size, y_size, *vla);
    dump_vla_2(0, 0, x_size, y_size, *vla);

    /* Harsh cast! */
    int (*vla_2)[x_size][y_size] = (int (*)[x_size][y_size])&(*vla)[extra][extra];

    dump_vla_2(-extra, -extra, x_size, y_size, *vla_2);

    dump_vla_3(-extra, x_size - extra, -extra, y_size - extra, x_size, y_size, *vla_2);
    dump_vla_3(0, x_base, 0, y_base, x_size, y_size, *vla_2);

    free(vla);
    return 0;
}

static void dump_vla_1(int x_size, int y_size, int vla[x_size][y_size])
{
    printf("Matrix %dx%d\n", x_size, y_size);
    for (int i = 0; i < x_size; i++)
    {
        for (int j = 0; j < y_size; j++)
            printf(" %4d", vla[i][j]);
        putchar('\n');
    }
}

static void dump_vla_2(int x_min, int y_min, int x_size, int y_size,
                       int vla[x_size][y_size])
{
    printf("Matrix %dx%d (%d..%d, %d..%d)\n",
           x_size, y_size, x_min, x_min + x_size - 1, y_min, y_min + y_size - 1);
    for (int i = x_min; i < x_min + x_size; i++)
    {
        for (int j = y_min; j < y_min + y_size; j++)
            printf(" %4d", vla[i][j]);
        putchar('\n');
    }
}

static void dump_vla_3(int x_min, int x_max, int y_min, int y_max,
                       int x_size, int y_size, int vla[x_size][y_size])
{
    printf("Matrix %dx%d (%d..%d, %d..%d)\n",
           x_size, y_size, x_min, x_max, y_min, y_max);
    for (int i = x_min; i < x_max; i++)
    {
        for (int j = y_min; j < y_max; j++)
            printf(" %4d", vla[i][j]);
        putchar('\n');
    }
}

Note the use of *vla and *vla_2 to pass the VLA to the functions. Since the vla and vla_2 variables are pointers to a VLA, *vla is the VLA which the functions expect.

Output:

  101  102  103  104  105  106  107  108  109  110
  201  202  203  204  205  206  207  208  209  210
  301  302  303  304  305  306  307  308  309  310
  401  402  403  404  405  406  407  408  409  410
  501  502  503  504  505  506  507  508  509  510
  601  602  603  604  605  606  607  608  609  610
  701  702  703  704  705  706  707  708  709  710
  801  802  803  804  805  806  807  808  809  810
  901  902  903  904  905  906  907  908  909  910
 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010
 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110
Matrix 11x10
  101  102  103  104  105  106  107  108  109  110
  201  202  203  204  205  206  207  208  209  210
  301  302  303  304  305  306  307  308  309  310
  401  402  403  404  405  406  407  408  409  410
  501  502  503  504  505  506  507  508  509  510
  601  602  603  604  605  606  607  608  609  610
  701  702  703  704  705  706  707  708  709  710
  801  802  803  804  805  806  807  808  809  810
  901  902  903  904  905  906  907  908  909  910
 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010
 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110
Matrix 11x10 (0..10, 0..9)
  101  102  103  104  105  106  107  108  109  110
  201  202  203  204  205  206  207  208  209  210
  301  302  303  304  305  306  307  308  309  310
  401  402  403  404  405  406  407  408  409  410
  501  502  503  504  505  506  507  508  509  510
  601  602  603  604  605  606  607  608  609  610
  701  702  703  704  705  706  707  708  709  710
  801  802  803  804  805  806  807  808  809  810
  901  902  903  904  905  906  907  908  909  910
 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010
 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110
Matrix 11x10 (-3..7, -3..6)
  101  102  103  104  105  106  107  108  109  110
  201  202  203  204  205  206  207  208  209  210
  301  302  303  304  305  306  307  308  309  310
  401  402  403  404  405  406  407  408  409  410
  501  502  503  504  505  506  507  508  509  510
  601  602  603  604  605  606  607  608  609  610
  701  702  703  704  705  706  707  708  709  710
  801  802  803  804  805  806  807  808  809  810
  901  902  903  904  905  906  907  908  909  910
 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010
 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110
Matrix 11x10 (-3..8, -3..7)
  101  102  103  104  105  106  107  108  109  110
  201  202  203  204  205  206  207  208  209  210
  301  302  303  304  305  306  307  308  309  310
  401  402  403  404  405  406  407  408  409  410
  501  502  503  504  505  506  507  508  509  510
  601  602  603  604  605  606  607  608  609  610
  701  702  703  704  705  706  707  708  709  710
  801  802  803  804  805  806  807  808  809  810
  901  902  903  904  905  906  907  908  909  910
 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010
 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110
Matrix 11x10 (0..5, 0..4)
  404  405  406  407
  504  505  506  507
  604  605  606  607
  704  705  706  707
  804  805  806  807

Thank you for your answer, but my simulator makes heavy usage already of the gpu, i do the whole initiallization as you see in 2 lines. But it is not the initiallization the problem, the problem is that in every frame the values of map are changed. So i need just a 'map' which points directly to 'boundaries map'. map[0][0] is boundaries_map[20][20] and so on. i tried to declare global **map and then write my second line into the main but i get an error about cast. (*map)[dim_x+40] this is a **map isn't it? — user3143155, Oct 14 '14 at 09:53

Calloc for an array of array with negative index in C

2 Answers2

Source: `2da.c`:

Example output

Comment and response

Source: `2dv.c`:

Linked

Calloc for an array of array with negative index in C

2 Answers2

Source: 2da.c:

Example output

Comment and response

Source: 2dv.c:

Linked

Source: `2da.c`:

Source: `2dv.c`: