Thread: 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.

Thank you. That seemed to fix everything.

I should probably go read the FAQs now.