CSC161 2010F, Class 56: Discussion of Exam 3

Overview:
* The final.
* Some thoughts on exam 3.
* Final comments.

Admin:
* It is neither national pipe cleaner day nor national chenille stem day.  
  Nonetheless, we are celebrating.
* Our final exam is next Wednesday at 9 a.m. in this room.
  * Three hours
* You should have received tentative grades.  Let me know if you did not.
* It's computer science education week, and Mattel has released Computer
  Engineer Barbie!
* Do you want Aditi to run a review session?

The Final

* Four questions
* You will have limited computer access
  * You will answer questions on the computer, using code I provide
  * Steps: Copy tarball, untar tarball, work, tar, email back to Sam
  * You will be able to use any shell commands, including man 
  * NO WEB ACCESS
  * NO ACCESS TO OUR EXAMPLES DIRECTORY
    (Please do not make a massive copy of it before the exam.)
  * You can access your old homework
  * You can access any EBoards (if you know where they are)
    I'll tell you where they are.
* One "fix this code" question
* At least one problem quite similar to a previous exam problem
* I will provide unit tests where appropriate

Exam 3

* General issues
  * Way too many memory leaks.
    char *str = malloc (128);
    str = strdup(target);
  * Carelessness in the amount of memory you allocate.  Goal: Make
    str a copy of target.
    char *str = malloc (strlen (target) * sizeof (char));
    strcpy (str, target);
    * This allocated one character too few
    char *str = malloc (sizeof (target))
    strcpy (str, target);
    * sizeof does not give the length of a string; sizeof indicates, for
      a variable or type, how much memory that variable or type requires.
      target holds a pointer to a char, so it requires FOUR BYTES
  * Forgets to allocate memory
    char *stuff[12]; // An array of 12 strings
    for (i = 0; i < 12; i++)
      strcpy (stuff[i], whatever);

Problem 1

* See sample code

Problem 4

* Inserting into lists
  * Lots of inefficiencies
    node1 = find_before (lst, target);
    node2 = find (lst, target);
    * node2 = node1->next would be much more efficient
  * Some code that makes me unhappy
    node1 = lst->head;
    while (strcmp (node1->data, target) != 0)
      node1 = node1->next;  
    * Yes, it violates the preconditions, but segfaults are not a good 
      way to indicate that.

Problem 6

struct string_list *
slist_transform (struct string_list *list, void (*fun)(char *str))
{
  struct node *n = list->head;
  while (n != NULL);
    {
      (*fun)(n->data);
      n = n->next;
    }
  return list;
}

Problem 7