How can i malloc a char **

Question

I have to code a battleship game for school so i'm trying to generate the map on which the players are going to place their boats, i have a segfault but i don't see why.

Here's my code :

Main :

int main(int ac, char **av)
{
    map_data map_data;
    print_map(map_gen(map_data));
    return(0);
}

Struct :

typedef struct map_data {
    int lines;
    int letters;
    int width;
    int height;
}map_data;

Map generation :

char **map_gen(map_data map_data)
{
    map_data.lines = 0;
    map_data.width = 18;
    map_data.height = 10;
    map_data.letters = 65;
    char **map = malloc(sizeof((char)18 * 10));

    for (int s = 0; s <= map_data.height ; s++) {
        for (int c = 0; c <= map_data.width; c++) {
            map_fill(map, map_data, s, c);
        }
    }
    return (map);
}

Filling of the char **map :

void char_fill(char **map, char ch, int s, int c)
{
        map[s][c] = ch;
}

void map_fill(char **map, map_data map_data, int s, int c)
{
    if (c == 1)
        char_fill(map, '|', s, c);
    if (s == 1)
        char_fill(map, '-', s, c);
    if (c == map_data.width)
        char_fill(map, '\n', s, c);
    map_fill2(map, map_data, s, c);
}

int map_fill2(char **map, map_data map_data, int s, int c)
{
    if (s == 0 && c == 0)
        char_fill(map, ' ', s, c);
    if (s == 1 && c == 1)
        char_fill(map, '+', s, c);
    if (c > 1 && c % 2 == 0)
        char_fill(map, '.', s, c);
    if (s > 1 && c % 2 == 1)
        char_fill(map, ' ', s, c);
    if (s == 10 && c == 18)
        char_fill(map, '\0', s, c);
    if (s > 1 && c == 0) {
        char_fill(map, my_int_to_char(map_data.lines), 0, 0);
        map_data.lines = map_data.lines + 1;
    }
    if (!map[s][c]) {
        my_putstr("error filling the map, please try again.");
        return (EXIT_FAILURE);
    }
}

Print :

void print_map(char **map)
{
    int h = 0;
    int w = 0;

    while (map[h][w] != '\0') {
        while (map[h][w] != '\n') {
            my_putchar(map[h][w]);
            w = w + 1;
        }
        h = h + 1;
    }
}

Am i doing something wrong ? Any tips on how to improve my code ?

Thanks

Answer 1

1. you do not need a pointer to pointer only 2D array for it.
2. Use the correct types.
3. Wrap the data into your structure. Do noy use separate data structures without need
4. Indexes in C atart from 0.

typedef struct map_data {
    size_t lines;
    size_t letters;
    size_t width;
    size_t height;
    char map[];
}map_data;

int map_fill2(map_data *map, size_t s, size_t c);


void char_fill(map_data *map, char ch, size_t s, size_t c)
{
    char (*cmap)[map -> width] = (char (*)[map -> width])map -> map;
    cmap[s][c] = ch;
}

void map_fill(map_data *map, size_t s, size_t c)
{
    if (c == 0)
        char_fill(map, '|', s, c);
    if (s == 0)
        char_fill(map, '-', s, c);
    if (c == map -> width - 1)
        char_fill(map, '\n', s, c);
    map_fill2(map, s, c);
}

int map_fill2(map_data *map, size_t s, size_t c)
{
    char (*cmap)[map -> width] = (char (*)[map -> width])map -> map;
    if (s == 0 && c == 0)
        char_fill(map, ' ', s, c);
    if (s == 1 && c == 1)
        char_fill(map, '+', s, c);
    if (c > 1 && c % 2 == 0)
        char_fill(map, '.', s, c);
    if (s > 1 && c % 2 == 1)
        char_fill(map, ' ', s, c);
    if (s == 10 && c == 18)
        char_fill(map, '\0', s, c);
    if (s > 1 && c == 0) {
        char_fill(map, my_int_to_char(map -> lines), 0, 0);
        map -> lines += 1;
    }
    if (!cmap[s][c]) {
        puts("error filling the map, please try again.");
        return (EXIT_FAILURE);
    }
    return 0;
}

map_data *map_gen(size_t lines, size_t letters, size_t width, size_t height)
{
    map_data *map = malloc(sizeof(*map) + width * height * sizeof(map -> map[0]));

    if(map)
    {
        map -> width = width;
        map -> lines = lines;
        map -> letters = letters;
        map -> height = height;
        for (size_t s = 0; s < height ; s++) 
        {
            for (size_t c = 0; c < width; c++) 
            {
                map_fill(map, s, c);
            }
        }
    }
    return (map);
}

Answer 2

At least this issue:

sizeof((char)18 * 10) is the sizeof an int, likely 4.

Allocate to the size of the referenced object times the number needed.

// char **map = malloc(sizeof((char)18 * 10));
char **map = malloc(sizeof *map * map_data.height);

Then allocate for each row

// Note <, not <=
for (int row = 0; row < map_data.height; row++) {
    map[row] = malloc(sizeof *(map[row]) * map_data.width);
    for (int col = 0; col < map_data.width; col++) {
        map_fill(map, map_data, row, col);
    }
}

Robust code would also check for allocation failures.