array of pointers to bit arrays - c

Question

I want to make an array of pointers to bit arrays. I make this func2 to test the pointers, but I get a seg fault when I try to acess an elemeny of the bit array outside the function. What am I doing wrong?
int func2(int i, int* bit_array){
int j;
for(j = 0; j< i; j++)
bit_array[j] = malloc(sizeof(int) * i);
for(j = 0; j< i; j++)
bit_array[j] = 0;
return 1;
}
int main(){
int** bit_root;
bit_root = malloc(sizeof(int *) * 5);
func2(5, bit_root);
int n;
for(n = 0; n < 5; n++)
printf("%d ", bit_root[0][n]); //error
printf("\n");
return 0;
}

Answer 1

You are sending the array incorrect to the function func2. func2 need to be:
int func2(int i, int** bit_array){
int j,k;
for(j = 0; j< i; j++)
bit_array[j] = malloc(sizeof(int) * i);
for(j = 0; j< i; j++)
for(k = 0; k< i; k++)
bit_array[j][k] = 0;
return 1;
}
int main(){
int** bit_root;
bit_root = malloc(sizeof(int *) * 5);
func2(5, bit_root);
int n;
for(n = 0; n < 5; n++)
printf("%d ", bit_root[0][n]); //error
printf("\n");
return 0;
}

Answer 2

In the lines below you allocate memory for array of int for each element of bit_array and assign pointers to int arrays to bit_array elements:
for(j = 0; j< i; j++)
bit_array[j] = malloc(sizeof(int) * i);
But here you assign zeroes to bit_array elements. Thus you rewrite pointers to zero as if you didn't allocate memore at all:
for(j = 0; j< i; j++)
bit_array[j] = 0;
To fix it replace the this last block this a following code:
int k;
for(j = 0; j< i; j++)
for(k = 0; k < i; k++)
bit_array[j][k] = 0;
Here in the first loop you iterate through the array of pointers to int arrays (bit_array[j]) and in the inner loop you iterate through the array of ints (bit_array[j][k]). These changes requires changing of func2 definition - second parameter must be pointer to pointer to int instead of just a pointer. It helps you to get rid from warnings of compiler.
To see what is going on clearly you can use following code:
int k, *int_array = NULL;
for(j = 0; j< i; j++)
{
int_array = bit_array[j]; // get the pointer to int array
for(k = 0; k < i; k++)
int_array[k] = 0; // assign values to int array
}
And don't forget to free all these memory for both inner arrays and bit_array.