Accessing address of struct element via pointer-to-pointer

Question

Lets say I have a structure :

struct ABC 
{
   char a;
   char b;
   char c;
}

I can declare a pointer to a pointer to the above structure as :

struct ABC** abc

Now abc is a pointer pointing to the structure pointer *abc and *abc is a structure pointer pointing to the structure abc. Thus; sizeof(**abc) will be 4, sizeof(*abc) will also be 4 and sizeof(abc) will be 3 (considering pointers are 4 bytes in size and characters are 1 byte in size).

My question is this:

How to declare a character pointer that points to the member variable c using abc that was declared above ?

Answer 1

sizeof(**abc) will be 4, sizeof(*abc) will also be 4 and sizeof(abc) will be 3 

I think that should be, assuming no padding of the structure,

sizeof(**abc) will be 3, sizeof(*abc) will also be 4 and sizeof(abc) will be 4
                     ^^^                                                    ^^^  
                      Change here                                           change here

To get a pointer to member variable c do

&(*abc)->c

Note the paranthesis around *abc. The reason for this is that -> has a higher precedence than * and so you need to make sure the first dereference (to go from pointer-to-pointer to pointer) happens first.

Or you can do

&(**abc).c

Same reason for the parenthesis... need to make sure you've dereferenced (twice) before applying the member-selection-via-object-name ..

Answer 2

Provided all of your pointers are valid, so that you can dereference them, you can do it like this:

char* a_ptr = &((*abc)->a);
or 
char* b_ptr = &((**abc).b);