C: dereferencing pointer to incomplete type singly linked list

Question

list.h

#ifndef LIST_H
#define LIST_H

/* Function prototypes */
struct nodeStruct* List_createNode(int item);
#endif

list.c

#include <stdio.h>
#include <stdlib.h>

struct nodeStruct {
    int item;
    struct nodeStruct *next;
};
struct nodeStruct* List_createNode(int item) {
    struct nodeStruct *node = malloc(sizeof(struct nodeStruct));
    if (node == NULL) {return NULL;}
    node->item = item;
    node->next = NULL;
    return node;
}

Main.c:

#include "list.h"
#include <assert.h>
#include <sys/types.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

struct nodeStruct *one = List_createNode(1);
while(one != NULL) {
    printf("%d", one->item); //error
    one= one->next; //error
}

Error: error: dereferencing pointer to incomplete type printf("%d", one->item); The error is at one->item, I have tried several combinations to dereference, but does not seem to work. What's the right approach?

Updated:

list.h

#ifndef LIST_H
#define LIST_H

    struct nodeStruct {
    int item;
    struct nodeStruct *next;
};
/* Function prototypes */
struct nodeStruct* List_createNode(int item);
#endif

Now the error is, invalid application of ‘sizeof’ to incomplete type ‘struct nodeStruct’ struct nodeStruct *node = malloc(sizeof(struct nodeStruct)); From my list.c file.

Did you include the definition of struct nodeStruct in the main .c file? Also, you probably want to remove the * in one = *one->next;. Oh, and modifying one may leak memory. — EOF
So the definition of struct nodeStruct is, in fact, not available to main(). Put the definition of struct nodeStruct into list.h. Hint: It's currently in list.c. — EOF
...And now you also need to #include "list.h" in list.c. — EOF
Actually, where's your int main() function? It's not in the main.c you've posted — EOF

R Sahu R Sahu · Accepted Answer · 2015-01-26T01:33:33

I can think of couple of ways:

Put the definition of struct in a header file and #include the header file in main.c.

Add couple of functions

int getNodeItem(struct nodeStruct* node)
{
   return node->item;
}

struct nodeStruct* getNextNode(struct nodeStruct* node)
{
   return node->next;
}

and call the functions from main.

while (one != NULL) {
   printf("%d", getNodeItem(one));
   one = getNextNode(one);
}

C: dereferencing pointer to incomplete type singly linked list

2 Answers