Unable to access struct data using arrow notation when pointer

Question

I have created an array of structs and I am getting a BAD_ACCESS error. When I switch everything to dot notation it works fine, why is this?

Struct

typedef struct data{
    int num;
}data;

Main

int main(void){
  // This works
  data data[4];
  data[0].num = 10;
  printf("Number is = %d\n", data[0].num);

  // This does not work
  data *data[4];
  data[0]->num = 10;
  printf("Number is = %d\n", data[0]->num);

Answer 1

// This does not work
data *data[4];
data[0]->num = 10;
printf("Number is = %d\n", data[0]->num);

Since data is an array of four pointers, data[0] is the first of those four pointers. But what does it point to? Since you haven't done something like data[0] = malloc(sizeof(struct data)); , it points to nothing in particular -- uninitialized garbage. It's not surprising that trying to write to what the pointer points to causes a bad access error.

Before you dereference a pointer, you need to make the pointer actually point to something.