Error when defining a struct - c

Question

I am attempting to write a simple linked list just for practice and to jog my memory a little bit, but I have ran into trouble. I am pretty inexperienced in C, and I don't understand why this isn't working. I am trying to define a Node and a LinkedList struct, but every time I try to compile I get an error saying Node is an unknown type. I'm sure I am missing something, but I can't figure this out. Thanks all!
This is my ll.h file
1 #ifndef ll_h
2 #define ll_h
3
4 #include <stdio.h>
5
6 typedef struct {
7 void *data;
8 Node *next;
9 Node *prev;
10 } Node;
11
12
13 typedef struct {
14 Node *first;
15 Node *last;
16 int size;
17 } LinkedList;
18
19
20 void *getData(LinkedList list, int index);
21 int getSize(LinkedList list);
22 void *deleteNode(LinkedList, int index);
23 void add(LinkedList list, void *data);
24 void freeList(LinkedList list);
25
26 #endif
Errors I am receiveing
cc -Wall -g -c -o ll.o ll.c
In file included from ll.c:3:0:
ll.h:8:5: error: unknown type name ‘Node’
ll.h:9:5: error: unknown type name ‘Node’
ll.c: In function ‘getData’:
ll.c:8:18: error: expected expression before ‘LinkedList’
ll.c:12:7: warning: assignment from incompatible pointer type [enabled by default]
ll.c: In function ‘getSize’:
ll.c:21:12: error: expected expression before ‘LinkedList’
ll.c: In function ‘deleteNode’:
ll.c:26:18: error: expected expression before ‘LinkedList’
ll.c:32:7: warning: assignment from incompatible pointer type [enabled by default]
ll.c:37:12: error: request for member ‘next’ in something not a structure or union
ll.c:38:12: warning: assignment from incompatible pointer type [enabled by default]
ll.c:40:12: error: request for member ‘next’ in something not a structure or union
ll.c: In function ‘add’:
ll.c:52:16: warning: assignment from incompatible pointer type [enabled by default]
ll.c:54:21: warning: assignment from incompatible pointer type [enabled by default]
ll.c: In function ‘freeList’:
ll.c:61:18: error: expected expression before ‘LinkedList’
ll.c:62:18: warning: initialization from incompatible pointer type [enabled by default]
ll.c:65:7: warning: assignment from incompatible pointer type [enabled by default]
ll.c:67:7: warning: assignment from incompatible pointer type [enabled by default]
ll.c:62:11: warning: variable ‘next’ set but not used [-Wunused-but-set-variable]
ll.c:60:9: warning: unused variable ‘i’ [-Wunused-variable]
ll.c: In function ‘main’:
ll.c:85:6: error: ‘LinkedList’ has no member named ‘add’
ll.c:91:10: warning: dereferencing ‘void *’ pointer [enabled by default]
ll.c:91:10: error: void value not ignored as it ought to be
ll.c: In function ‘getSize’:
ll.c:22:1: warning: control reaches end of non-void function [-Wreturn-type]
make: *** [ll.o] Error 1

Answer 1

Use this:
typedef struct Node{
void *data;
struct Node *next; // note here
struct Node *prev;
} Node;

Answer 2

You either need forward declaration, or you need to drop the typedef. You can also use typedef with having the Node twice.
Forward declaration
typedef struct Node Node; // Necessary in C, harmless (but non-idiomatic) in C++
typedef struct {
void *data;
Node *next;
Node *prev;
} Node;
No typedef (Will only work in C++, not C)
struct Node {
void *data;
Node *next;
Node *prev;
};
Using typedef with tag
Works in C and C++, but non-idiomatic for C++.
typedef struct Node {
void *data;
struct Node *next;
struct Node *prev;
} Node;

Answer 3

Posting an Answer for the next reader brought here by Google searching:error: void value not ignored as it ought to be
Remember when trying to implement pseudo-code that function pointers get initialized with the name of the function without any parenthesis. Rookie mistake? Maybe, but I'm not exactly rookie (taught C/C++ Labs at university in mid 90s) and it got me. Had I typed it and not cut-n-pasted, I probably would have caught the error, as I know not to create that code...
Example with declarations supplied for completeness:
// Static menu manager
#define MAX_SELECTIONS 4
#define MAX_PROMPT_LEN 20
typedef struct _selection {
char prompt[MAX_PROMPT_LEN];
void(*function) ( void );
int fn_arg;
} SELECTION ;
typedef struct _menu {
int id;
int num_selections;
SELECTION selection[MAX_SELECTIONS];
} MENU;
enum _menu_ids { MAIN_MENU, DEPOSIT_MENU, WITHDRAWL_MENU, BALANCE_MENU };
enum _menu_keys { DEPOSIT, WITHDRAWL, BALANCE, CHECKING, SAVINGS };
Wrong:
// WRONG
static MENU menu[] = {
{ MAIN_MENU, 4,
{"Perform A Deposit", goto_menu(), DEPOSIT_MENU},
{"Perform a Withdrawl", goto_menu(), WITHDRAWL_MENU },
{"Get Balance", goto_menu(), BALANCE_MENU },
{"Hide Menu", menu_hide(), 0}
}
}
Correct:
// Correct
static MENU menu[] = {
{ MAIN_MENU, 4, {
{"Perform A Deposit", goto_menu, DEPOSIT_MENU},
{"Perform a Withdrawl", goto_menu, WITHDRAWL_MENU },
{"Get Balance", goto_menu, BALANCE_MENU },
{"Hide Menu", menu_hide, 0} }
}
}
Particularly observant readers might notice the additional braces required to initialize the struct's array's members were missing in the pseudo-code. The gcc compiler was kind enough to provide a useful error:MENU: improper number of initializers.