C dereference an integer pointer in a structure

Question

I am having a problem correctly dereferencing a pointer to an integer that resides in an array of structures. The relevant parts of the code are:

typedef struct hf_register_info {
  int                   *p_id;  /**< written to by register() function */
  header_field_info     hfinfo; /**< the field info to be registered */
} hf_register_info;
.
.
hf_register_info hf[MAX_HF_COUNT];
.
.
*(hf[i].p_id) = -1;

The final line of code above causes an exception. How do I correctly deference p_id?

Thanks and regards...Paul

Answer 1

You need to initialize your pointers. You pointers in your structs aren't pointing to anything at the moment you initialize your array.

So for every struct in your array you want to dereference your pointer and assign a value to, you'll need to allocate space in your memory first.

hf_register_info hf[MAX_HF_COUNT];

// some code here

hf[i].p_id = malloc(sizeof(int)); // or unsigned long or whatever
*(hf[i].p_id) = -1;