How to initialize a Linked List with a struct with many variables

Question

I still have troubles with the relations between the linked lists and the structures.

See, my objectif is to create a list where each node contains 2 characters strings. So, I tried something like this : first, I create a structure that represent an element with my 2 char ; second, a control structure for my list, thath will point at the beginning of my list. Which, in my .h, gives something like this :

typedef struct s_def { char *first_word; char *second_word; struct s-def *next; }  t_def

typedef struct s_type { t_def *first; } t_list;

Next, I try to initialize my list. I make a function that work like this :

t_list *list;
t_def *words;

list = malloc(sizeof(*list));
words = malloc(sizeof(*words));
if (list == 0 || words == 0)
   return (NULL);
words = NULL;
words->next = NULL;
list->first = words;

return (list);

Precision : I try to make an empty list for now, so that the user can add some elements later.

And that's where it block : when I run the program, it gives the typical Segmentation Fault. But it don't see what's wrong with what I made ! I put some write in my function to retrace the process : the malloc are working ok, as well as the words = NULL, but then the segment fault seems to run at the line

words->next = NULL;

What do I make wrong ? Why can't I give a NULL value at the next of my words ?

Answer 1

You first initialize the word pointer with allocated memory

words = malloc(sizeof(*words));

Then 3 lines down you set that pointer to NULL again, creating a memory leak

words = NULL;

And then you try to dereference the pointer that you just set to NULL:

words->next = NULL;

So, just remove the words = NULL;