Question

I have the following Structs

struct node{
    int value;
    struct node *next;
    struct node *prev;
};

And I think that the size must be greater than sizeof(integer).

But it’s confusing how to calculate the whole size of this struct.

So how to caculate the size?

I mean I want to calculate it manually by hand, not by computer…

Answer 1

Generally, size of structure is addition of size of each member field. But compiler may add some extra bytes for padding/align members appropriately.

So in your case,

sizeof(struct node) = sizeof(int) + sizeof(struct node *) + sizeof(struct node *)
                 12 = 4 + 4 + 4  (on 32-bit)
                 20 = 4 + 8 + 8  (on 64-bit)

This is general guideline may differ depending upon compiler/platform you choose.