How to use a struct in C?

Question

This is code for a linked list in the C programming language.

#include <stdio.h>    /* For printf */
#include <stdlib.h>   /* For malloc */

typedef struct node {
    int data;
    struct node *next; /* Pointer to next element in list */
} LLIST;

LLIST *list_add(LLIST **p, int i);
void list_remove(LLIST **p);
LLIST **list_search(LLIST **n, int i);
void list_print(LLIST *n);

The code is not completed, but I think it's enough for my question. Here at the end of struct node "LLIST" is used, and it's also used as a return type in the prototyping of the function list_add. What is going on?

Answer 1

That's a typedef. It's actually doing two things at once. First, it defines a structure:

struct node {
    int data;
    struct node *next;
}

And then does a typedef:

typedef struct node LLIST;

That means LLIST is a type, just like int or FILE or char, that is a shorthand for struct node, your linked-list node structure. It's not necessary - you could replace LLIST with struct node in all of those spots - but it makes it a bit easier to read, and helps hide the implementation from pesky end-users.

Answer 2

LLIST is just another type name for the struct that has been created. In general, the following format will create a type "NAME" that is a "struct x":

typedef struct x { ... } NAME;