Difference Between *list and **list

Question

If I have a struct:

typedef struct A
{
   char c[100];
}A;

Then I create a

sizeOfA = 5000;
A *list = (A*) malloc(sizeOfA * sizeof(A));

Is list[i] a pointer to a struct?

Or if I want a pointer to the struct, should I do

A **list = (A**) malloc (sizeOfA * sizeof(A*);

[EDIT]

Now let's say I created the list using A *list (which I did already). How would I create 5000 pointers and make them point to the elements on the list?

p0 -> list[0]
p1 -> list[1]
..
..
p[n] -> list[n]

After going back and forth a few times I noticed that for sorting the pointers help a lot.

To be fair I will post the edit above as a separate question.

Answer 1

A *list = (A*) malloc(sizeOfA * sizeof(A));
Is list[i] a pointer to a struct?

No -- list is a pointer to an address in the heap, which is the start of a memory chunk that has size sizeOfA * sizeof(A). list[i] is the same thing as *(list + i), which is a dereference that will give you an actual A.

However..

A **list = (A**) malloc (sizeOfA * sizeof(A*);
Is list[i] a pointer to a struct?

Yup.

Answer 2

After this statement:

A *list = (A*) malloc(sizeOfA * sizeof(A));

list is a pointer to the starting location of a memory block that can hold sizeOfA elements of type struct A. Thus, *list is of type struct A, and similarly, list[i] is of type struct A, not pointer to struct A (that would be list+i).

If you want list[i] to be a pointer to struct A, then your second piece of code would be the correct one, since you're allocating a memory location with enough space to hold sizeOfA pointers to struct A. Note that you are only allocating space to hold pointers, not actual struct A instances. Attempting to read list[i]->c will result in undefined behavior.