2D array becoming "deallocaded"

Hello. I'm having trouble with a structure that points to a dynamically allocated 2D array. For some reason, after I allocate the array, it becomes "deallocated" in the middle of the program.

I have a pointer to a structure which has a pointer to a 2D array. The full program gives a bus error, which happens when I try to access a cell in the structure's array. I've removed a bunch of the code that actually does stuff for this post. I can still see though where the problem is coming from through the debugger (I just have no clue why it's there!)

The main program:

Code:

---

int main()
{
        Map *map_p = map_create_p(10, 10);
       
        Creature *player_p = creature_create_p();
       
        printf("This is just busywork.\n");
       
        return 0;
}

---

This is the problem structure:

Code:

---

struct map
{
        unsigned int maxRows;
        unsigned int maxCols;
       
        char **tiles_p; // A 2D array
};

typedef struct map Map;

---

How I create a Map structure:

Code:

---

Map *map_create_p(unsigned int maxRows, unsigned int maxCols)
{
        int r, c;
        Map *map_p;
       
        map_p = malloc(sizeof(map_p));
       
        map_p->maxRows = maxRows;
        map_p->maxCols = maxCols;
       
        map_p->tiles_p = calloc(maxRows, sizeof(map_p->tiles_p));
       
        for (r = 0; r < maxRows; r++)
        {
                map_p->tiles_p[r] = calloc(maxCols, sizeof(map_p->tiles[r]));
               
                for (c = 0; c < maxCols; c++)
                {
                        map_p->tiles_p[r][c] = '.';
                }
        }
       
        return map_p;
}

---

When I first create a Map structure, I can access the elements of its tiles_p array fine. But after a few lines I can't access them anymore.

This is what running it through gdb is like (with spaces added for emphasis):

Code:

---

(gdb) br 13
Breakpoint 1 at 0x109e4: file main.c, line 13.
(gdb) r
Starting program: /users/cs/macdona2/other/tehrogue/tehrogue

Breakpoint 1, main () at main.c:13
13              Map *map_p = map_create_p(10, 10);
(gdb) print map_p
$1 = (Map *) 0x0
(gdb) n
15              Creature *player_p = creature_create_p();
(gdb) print map_p
$2 = (Map *) 0x210e0

(gdb) print map_p->tiles_p[0][0]
$3 = 46 '.'          // *** Everything is fine. ***

(gdb) print player_p
$4 = (Creature *) 0x0
(gdb) n
23              printf("This is just busywork.\n");

(gdb) print map_p->tiles_p[0][0]
Cannot access memory at address 0x2151000 // *** How did this happen?! ***

(gdb)

---

The strange thing is that this only happens when I create the Creature structure. If I comment that line out the array in the Map structure stays fine.

Here's the Creature structure by the way:

Code:

---

struct creature
{
        unsigned int row;
        unsigned int col;
       
        Map *map_p;
       
        char symbol;
};

typedef struct creature Creature;

---

And here is how I create a Creature structure:

Code:

---

Creature *creature_create_p()
{
        Creature *cp = malloc(sizeof(cp));
       
        cp->row = 0;
        cp-col = 0;
       
        cp->map_p = NULL;
       
        return cp;
}

---

If someone can help me figure this out I'd really appreciate it.

Thanks.

Use the idiom

Code:

---

p = malloc(sizeof *p);

---

instead of

Code:

---

p = malloc(sizeof p);

---

(And copy and paste to avoid miscellaneous unrelated typos.)

Thank you. That seemed to fix everything.

I should probably go read the FAQs now.