Arraylist in C not working

Question

I am currently writing a program to implement an arraylist (or dynamic array) in C. Hmm... I think I have 70 - 80% done with it, however, I found a serious problem with my c

Answer 1

As others have noted, the problem is in the arraylist_add() function, which needs to dynamically allocate memory. This problem is actually perfectly suited for realloc(), which will expand the dynamically allocated array (meaning you don't have to do the copying loop):

void arraylist_add(struct arraylist *list, value_type value) {
  int size = arraylist_get_size(*list);
  value_type *new_data;

  new_data = realloc(list->data, (size + 1) * sizeof new_data[0]);

  if (new_data)
  {
      new_data[size] = value;
      arraylist_set_data_collection(list, new_data);
      ++list->size;
  }
}

This will even work for the first allocation, since realloc() works like malloc() if you pass it a NULL.

PS:

To make the implementation more efficient, you shouldn't expand the array by one entry each time - instead, keep track of the number of allocated blocks separately from the number of entries.