CODEWITHSUNDEEP
cpointersstructtypedefdoubly-linked-list
TheAlPaca02
TheAlPaca02

Reputation: 523

Unclear variables in a struct - Doubly linked list

I'm analysing this bit of code on which I am to build a doubly linked list:

struct dplist_node {
  dplist_node_t * prev, * next;
  element_t element;
};

struct dplist {                     
  dplist_node_t * head;
  // more fields will be added later
};

In an included header file I found the following lines:

typedef int element_t;
typedef struct dplist dplist_t;
typedef struct dplist_node dplist_node_t;

What I gather from this is that dplist_node_t is a typedef of the struct dplist_node but there are still pointers defined to dplist_node_t (and thus dplist_node) in both structs.

I find all of this very confusing and can't seem to unravel what is an element of which struct or what pointer is pointing where. Can anyone help me understand?

Upvotes: 1

Views: 54

Answers (1)

Jabberwocky
Jabberwocky

Reputation: 50911

Actually this equivalent declaration is easier to understand:

struct dplist_node {
  struct dplist_node * prev, * next;
  element_t element;
};

struct dplist {                     
  struct dplist_node * head;
  // more fields will be added later
};

the typedef adds only confusion in this case.

With:

typedef struct dplist dplist_t;

you can write dplist_t instead of struct dplist, or dplist_t* instead of struct dplist*.

Illustration

struct dplist_node {
  struct dplist_node * prev, * next;
  element_t element;
};

Here it is clear that prev and next are pointers to the struct dplist_node itself.

Original declaration:

struct dplist_node {
  dplist_node_t * prev, * next;
  element_t element;
};

when we see this, we dont know what dplist_node_t is unless we look into the header file where dplist_node_t is defined as being the equivalent of struct dplist. So IMO it's less clear.

Upvotes: 1

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