Segmentation error due to the use of a char ** - c

Question

I have to program a function that browses a map that I have previously stored in a char **. At each char I have to check if the 8 characters that surround it and check if on these 9 there are at least 2 that correspond to '#', so I created a struct *matrix that is supposed to check this.
I am only allowed to use the following functions/system calls: malloc, free, exit, (f)open, (f)close, (f)read, (f)write, getline, ioctl, usleep, sigaction, signal, stat, lstat, fstat
The problem is that despite the fact that I check if the array exists, the program returns a segmentation fault.
Here are the 2 functions that concern the matrix structure:
matrix_t *create_matrix(char **map, size_t y, size_t x)
{
matrix_t *out = malloc(sizeof(matrix_t));
if (!out) {
my_perr("[ERROR] Memory's allocation failure\n");
}
out->nbr = 0;
set_mat_nbr(out, map, y - 1, x);
set_mat_nbr(out, map, y, x);
set_mat_nbr(out, map, y + 1, x);
return out;
}
void set_mat_nbr(matrix_t *matrix, char **map, long y, long x)
{
if (y != 0 && map[y] != NULL && x != 0 && map[y][x - 1] == '#') {
matrix->nbr++;
}
if (y != 0 && map[y] != NULL && map[y][x] == '#') {
matrix->nbr++;
}
if (y != 0 && map[y] != NULL && map[y][x + 1] == '#') {
matrix->nbr++;
}
}
And here is the calling function (This one is not finished yet and only checks the top border for the moment) :
void check_border(char **map)
{
size_t y = 0, x = 0;
matrix_t *matrix = NULL;
while (map[0][x] != '\0') {
matrix = create_matrix(map, 0, x);
if (matrix->nbr < 2) {
my_perr("[ERROR] Corrupted border\n");
}
free(matrix);
x++;
}
}
According to valgrind, the segfault is triggered on the 3 if() of set_mat_nbr().
Do you know what is wrong with my code?

Answer 1

Thank you all, I have corrected the problem and everything works now. Here is the new code:
void set_mat_nbr(matrix_t *matrix, char **map, size_t y, size_t x)
{
if (x == 0) {
(map[y][x] == '#') ? matrix->nbr++ : 0;
(map[y][x + 1] == '#') ? matrix->nbr++ : 0;
} else if (map[y][x] == '\0') {
(map[y][x - 1] == '#') ? matrix->nbr++ : 0;
(map[y][x] == '#') ? matrix->nbr++ : 0;
} else {
(map[y][x - 1] == '#') ? matrix->nbr++ : 0;
(map[y][x] == '#') ? matrix->nbr++ : 0;
(map[y][x + 1] == '#') ? matrix->nbr++ : 0;
}
}
And :
matrix_t *create_matrix(char **map, size_t y, size_t x)
{
matrix_t *out = malloc(sizeof(matrix_t));
if (!out)
my_perr("[ERROR] Memory's allocation failure\n");
out->nbr = 0;
if (y == 0) {
if (!map[y + 1]) {
set_mat_nbr(out, map, y, x);
} else {
set_mat_nbr(out, map, y, x);
set_mat_nbr(out, map, y + 1, x);
}
} else if (!map[y + 1]) {
set_mat_nbr(out, map, y, x);
set_mat_nbr(out, map, y - 1, x);
} else {
set_mat_nbr(out, map, y - 1, x);
set_mat_nbr(out, map, y, x);
set_mat_nbr(out, map, y + 1, x);
}
return out;
}