Question

I am trying to figure out why my program crashes right when calling ll_print. [[this is a pretty simple and straight forward question i am not sure of what to add really to fill up the explanation gap]]

    struct ll{
          struct ll* next;
          int n;
        } ll;

   void ll_print(struct ll *l){
      while (l) {
        printf("%d ", l->n);
        l=l->next;
      }
    }

    void ll_fill(struct ll *l, int n){
      struct ll *temp= NULL;
       while (n>0){
        l= (struct ll*)malloc(sizeof(struct ll));
        l->n=n;
        l->next= temp;
        temp=l;
        n--;
      }
     }

    int main(void){
      int i=0;
      struct ll *l;                                                                                                                                          
      ll_fill(l, 10);
      ll_print(l);  /** causing a segmntation fault **/                                                                                                                                                                 
    }

Answer 1

This happens because l pointer is never initialized. It seems that you expect ll_fill to initialize it, but you are wrong – it is being passed by value (read – by copy), and whatever you assign to l in ll_fill function does not assign a value to l declared inside main. To achieve what you want, pass l by pointer (you will have pointer to pointer). Alternatively, make it a return value of ll_fill and do l = ll_fill(l, 10);. Also, get yourself a debugger – it will help you a great deal.