Question

OS: Windows 7, Compiler: GCC 3.2.3 (MinGW)

I have created those three data structures in C:

#define MAP_NAME_LEN    30
#define MAP_W           25
#define MAP_H           19
#define WORLD_W         32
#define WORLD_H         32

typedef unsigned char byte;

typedef struct Tile
{
    byte type;
    byte character;
    byte fgColor;
    byte bgColor;
};

typedef struct Map
{
    char name[MAP_NAME_LEN];
    Tile overlay[MAP_H][MAP_W];
    Tile underlay[MAP_H][MAP_W];
};

typedef struct World
{
    Map area[WORLD_H][WORLD_W];
};

When I try to create individual instances of Tile and/or Map, it’s ok, no problem at all, everything works. But then if I try to create a World, like…

int main()
{
    World world;
}

…the program simply crashes (Windows 7 says that the program has crashed and is looking for a solution, etc). Do you guys have any idea why does that happen?

Thanks!

Answer 1

Depending on the values of MAP_NAME_LEN, MAP_H, MAP_W, WORLD_H, and WORLD_W, you may have created a MASSIVE structure on the stack. Don’t do that. The stack is relatively small, and generally cannot handle allocations of more than a few megabytes total (and often can only handle a few dozen kilobytes of allocation at a time). Given your constant values, you’re likely to be running up against these limits – your World structure is nearly 4MB large, way too big to reasonably put on the stack.

So, instead, allocate it on the heap with malloc, or as a global or file-local static variable:

World world;

int main()
{
    /* ... */
}

or

int main()
{
    World *world = malloc(sizeof(*world));
    /* ... */
    free(world);
}