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user1369975
user1369975

Reputation: 420

C Error Dereferencing pointer to incomplete type

I made this code,following the functions given in the book "Fundamental Of Data Structures in C",I made the following code for implementing a simple linked list,but I don't seem to get where I am wrong,as the book code is supposed to be correct:

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

typedef struct node *listpointer;

typedef struct        {

int data;
listpointer link;
}  node;

void print(listpointer first)
 {
while  (first)      {
           printf("%d\n",first->data);
           first=first->link;
}
 }

void addAtFront(listpointer *first,int n)
{
listpointer t=*first,temp;
temp=malloc(sizeof(node));
int i=1;
while (i <= n)  {
                t=t->link;
                i++;
}
if(*first)  {
       temp->link=t->link;
        temp->data=90; 
       t->link=temp;
}
else 
{
      *first=temp;
        temp->link=NULL;
}
}       


listpointer createList( )
{
listpointer first,second;
if(first=malloc(sizeof(node)))  {
           first->data=67;
           if(second=malloc(sizeof(node)))  {
         second->data=65;
         first->link=second;
         second->link=NULL;
           }
}
return first;
  }





    main( )
   {
listpointer first=createList( );
addAtFront(&first,2);
print(first);
   }

Upvotes: 2

Views: 4213

Answers (3)

Ady
Ady

Reputation: 1

Why I was getting this error was because I had not included the header file which contained the structure definition.

Upvotes: 0

Carl Norum
Carl Norum

Reputation: 224944

You have this typedef:

typedef struct node *listpointer;

But you didn't ever define struct node. You have this definition of an anonymous struct typedefed to node, though:

typedef struct {
    int data;
    listpointer link;
} node;

Probably you meant:

typedef struct node {
    int data;
    listpointer link;
} node;

Upvotes: 6

Daniel Fischer
Daniel Fischer

Reputation: 183888

You define the struct without a tag,

typedef struct node *listpointer;

typedef struct        {

int data;
listpointer link;
}  node;

so the struct node that a listpointer is supposed to point to remains an incomplete type.

You should give the struct a tag,

typedef struct node { ...

then listpointer points to a complete object type.

Upvotes: 5

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