What's the difference between these two Structs when making Linked Lists?

Question

Just having confusion what is the difference between the two structs. What does the order do to alter the definition? Thanks.

// 1 
struct list
{
    struct list* next;
    unsigned long val;
};

// 2
struct list
{
    unsigned long val;
    struct list* next;
};

Generically, changing the order of members can add or remove padding for the purposes of [memory alignment](https://stackoverflow.com/q/4306186/1707353) but if you adhere to accessing members in a standard way, then you shouldn't be too concerned about the order of members. — Jeff Holt, Apr 09 '21 at 02:31
They are equivalent. Depending on the size of the elements on your platform there could be a difference in position or presence of padding but they are still equivalent. — Retired Ninja, Apr 09 '21 at 02:31
**1** The second is neater in documenting when vertically drawing a list: last field `next` pointing to the next `struct list` below. **2** The first has a pointer field at the 0 offset of the struct. Some processor might have a more optimal instruction for that. **3** The only difference concerns padding of the fields. Pointer and long must be different length and there must be padding. Which is unlikely here. — Joop Eggen, Apr 09 '21 at 02:33
I'd put the link _first_--it's easy to find. This might be more obvious with a more complex linked list element (e.g.) `struct list { struct list *next; unsigned long val; long arrcount; int *arrbase; int param[1000]; };` — Craig Estey, Apr 09 '21 at 03:05

score 1 · Answer 1 · answered Apr 09 '21 at 02:31

1

Functionally, these two structs will work the same way. They might not be the same size though due to padding.

answered Apr 09 '21 at 02:31

dbush

1 Answers1