Problem with a linked list

Question

I have a problem with this small program. It added some value to list. If I uncomment //printf("%d",first->val); the program gives error. Everything seems to be ok ;(

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

 typedef struct element {
   struct element *next;
   int val;
 } el_listy;

el_listy *first = 0;


void add_to_list(el_listy *lista, int value)
{

 if(lista == 0)
    {
        lista = malloc (sizeof(el_listy));
        lista->val = value;
        lista->next = 0;
        printf("added as first \n");
    }
        else
        { printf("added as fsecond  \n");
    el_listy *wsk = lista,*tmp;

                while(wsk->next != 0) wsk = wsk->next;

                tmp = malloc (sizeof(el_listy));
                tmp->val = value;
                tmp->next = 0;  

                wsk->next = tmp;                    
        }
}

 int main ()
 {
         add_to_list(first,2);
            add_to_list(first,4);
            //printf("%d",*first->val);
            system("pause");
   return 0;
 }

MByD · Accepted Answer · 2011-03-25 22:20:22Z

4

first->val is just like (*first).val, you can't use them both. also, as missingno said, add_to_list never changes first you should pass it's address as argument, not the pointer itself, meaningadd_to_list(&first,4); (and change the implementation of add_to_list as well)

answered Mar 25, 2011 at 22:20

MByD

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hugomg · Accepted Answer · 2011-03-25 22:19:10Z

2

Your program never changes the value of first. It remains a null pointer and thus gives an error when dereferenced.

answered Mar 25, 2011 at 22:19

hugomg

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geekosaur · Accepted Answer · 2011-03-25 22:17:37Z

1

-> already follows a pointer, so the * tries to treat first as pointer to pointer to el_listy. You might find cdecl helpful.

answered Mar 25, 2011 at 22:17

geekosaur

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Bo Persson · Accepted Answer · 2011-03-25 22:19:59Z

1

You should use either (*first).val or first->val. Otherwise you get the wrong level of indirection.

answered Mar 25, 2011 at 22:19

Bo Persson

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iCoder · Accepted Answer · 2011-03-25 22:26:43Z

0

Yes, it's a simple mistake.

fitsr won't change after *add_to_list()* function is called.

You should define function like this:

add_to_list(El_list **lista, ...)

answered Mar 25, 2011 at 22:26

iCoder

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