Thread: Freeing memory from dynamically allocated array of linked lists

Hi folks,
Having some frustrating issues trying to free memory from a dynamically allocated array of pointers to linked lists. I think the problem is in how I initialize the pointers to NULL. Is there a more elegant way to have the program recognize that the list is empty so it knows to create a head node for the linked list in the function 'add_end_stub_to_array'?

I ran the code through Valgrind and it says that memory is definitely lost from this array. Any help would be greatly appreciated.
Thanks!

This is the structure definition.

Code:

struct stub_edge {
      int loc_id;
      int anim_type;
      int mkt;
      struct stub_edge *next_node;
  };

Here is the code snippet from main allocating and deallocating memory to the array.

Code:

struct stub_edge **stub_list = (struct stub_edge **)malloc( sizeof(struct stub_edge *) * 12);
for (i = 0; i < 12; i++)
   {
     stub_list[i] = (struct stub_edge *)malloc(sizeof(struct stub_edge));
     stub_list[i] = NULL;
   }
   
stub_list = add_end_stub_to_array(end_stubs, stub_list);
destroy_end_stub_array(stub_list);

Here the function for adding nodes to the lists by reading through a dynamically allocated 2D array. (The end_stubs array is ordered by month and each linked list represents events occuring within the month).

Code:

struct stub_edge **add_end_stub_to_array(int **end_stubs, struct stub_edge **list)
{
   long int i = 0;
   int mon = 0;
 
   struct stub_edge *current_node1;
   struct stub_edge *new_node1;
    
   int break1 = 0;
   while(i < num_edges && break1 == 0 && mon < 12)
     {  
         current_node1 = list[mon];
         if(current_node1 == NULL && end_stubs[i][1] == mon)
            {
               current_node1 = (struct stub_edge*)malloc(sizeof( struct stub_edge ));           
               current_node1 -> loc_id = end_stubs[i][0];
               current_node1 -> anim_type = end_stubs[i][2];
               current_node1 -> mkt = end_stubs[i][5];
               current_node1 -> next_node = NULL;          
               i = i + 1;
               list[mon] = current_node1;
            }
         while( end_stubs[i][1] == mon && break1 == 0 )
            {
               new_node1 = (struct stub_edge*)malloc(sizeof( struct stub_edge ));           
               new_node1 -> loc_id = end_stubs[i][0];
               new_node1 -> anim_type = end_stubs[i][2];
               new_node1 -> mkt = end_stubs[i][5];
               new_node1 -> next_node = NULL;

               current_node1 -> next_node = new_node1;
               current_node1 = new_node1;
               i = i + 1;
               if(i == num_edges)
                  {
                     break1 = 1;
                     i = 0;
                  }
            }           
         mon = mon + 1;
     }
 
 return(list);             
}

Here is the function for freeing memory from the list.

Code:

void destroy_end_stub_array(struct stub_edge **list)
{   
   if(list != NULL)
     {  
        int mon = 0;  
        struct stub_edge *current_node1;
        struct stub_edge *new_node1;

        for(mon = 0; mon < 12; mon++)
          {
             current_node1 = list[mon];
             while(current_node1 != NULL)
                {
                  new_node1 = current_node1 -> next_node;
                  free(current_node1);
                  current_node1 = new_node1;
                } 
             free(list[mon]);
          }
    }