Thread: 0 being inserted at start of linked-list

Hi all -

I'm poking around with doing a few Haskell-like functions for linked-lists. Take, drop and so on.

I've done the code below. The problem is that it mysteriously inserts a 0 at the start of the list, and I have no idea why. So - hopefully someone can help out here.

Code:

  

#include <stdio.h>
#include <stdlib.h> 
#include <stddef.h> 
#include <string.h>
#include <ctype.h> 
#include <malloc.h> 


/*  List functions.  */  

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


/* Function to add data to end of a list  */ 
struct node *list_append(struct node *n, int data)
{  
   
   /* A pointer to iterate along the list */ 
   struct node *ptr = NULL; 
   
   /* Now, create a new node using the data. */ 
   struct node *newnode = NULL; 
   newnode = malloc(sizeof(struct node));  
   
   newnode->data = data; 
   newnode->next = NULL;   
  
  /* Is our existing list null? */ 
  /* If so, our "list" is just the newly-created node. */ 
   if(n == NULL) 
     {  
        n = newnode;         
     }             
           
   else 
     {         
         for( ptr = n; ptr->next != NULL; ptr = ptr->next ) 
           { 
             /* Iterate through the list until we find the last node */   
           }         
      
       /* Add the new node to the end of the list. */ 
       /* In other words: the last ptr->next WAS null, but it is */ 
       /* now pointing to newnode. */  
       ptr->next = newnode;       
     }     
       
  return n;                 
       
}  /* End of list_append  */  

    
    
/* Free the list memory. */ 
void free_list(struct node *n) 
{ 
  /* We create TWO pointers. */ 
  /* ptr is used to iterate through the list. */ 
  /* tmp (which points to the same place) is used to */ 
  /* actually free the memory. */    
   struct node *ptr, *tmp = NULL;        
          
  /* Check that the list is non-null. */   
   if(n != NULL) 
     {  
                          
         for( ptr = n; ptr->next != NULL; ptr = ptr->next ) 
           { 
             /* Iterate through the list */   
              printf( "Freeing %d\n",  (ptr->data) );  
              tmp = ptr;              
              free(tmp);                   
           }         
      
       /* Free the last element of the list */ 
       /* (where ptr->next IS null). */        
        printf( "Freeing %d\n",  (ptr->data) ); 
        free(ptr);      
     }         
}     
               

void print_list(struct node *n)
{ 
   /* A pointer for iterating. */ 
   struct node *ptr = NULL;  
    
   /* Iterate along the list.  */ 
    for( ptr = n; ptr->next != NULL; ptr = ptr->next )    
       { 
          printf( "mylist->data = %d\n",  (ptr->data) );               
       }         
    
    /* For the last nore (where ->next IS NULL), we need to print */ 
    /* it outside the loop. */ 
    printf( "mylist->data = %d\n",  (ptr->data) ); 
  
}


struct node *take(struct node *n, int i)
{ 
   struct node *ret = NULL;   
   ret = malloc(sizeof(struct node));    
   
    /* A pointer for iterating. */ 
   struct node *ptr = NULL;  
       
   int j=0;      
        
   for( ptr = n; ( ptr->next != NULL && j < i ); ptr = ptr->next )         
   {                
      list_append(ret, ptr->data) ;   
      /* memcpy( (int *)ret->data, (int *)ptr->data, sizeof( (int *)ptr->data) );  */ 
      j++;
   }
    
 return ret;

} 
 

int main() 
{

struct node *mynode = NULL; 

mynode = list_append(mynode, 23) ; 
mynode = list_append(mynode, 45) ; 
mynode = list_append(mynode, 71) ; 
mynode = list_append(mynode, 248) ; 
mynode = list_append(mynode, 18) ; 

struct node *mynode2 = NULL; 
mynode2 = take(mynode, 3); 

print_list(mynode); 

puts("Now the new list \n");  
print_list(mynode2);  
 
free_list(mynode);     
free_list(mynode2);         

return 0; 

}

Many thanks in advance for your help!
Bye for now -
- latte123